Open versus closed suctioning on lung volume and oxygenation in ARDS patients with PEEP 5–10 cmH2O: A randomized controlled trial

Haotian Gao; Yidie Ying; Jun Yang

doi:10.1371/journal.pone.0351172

. 2026 Sep 30;21(9):e0351172. doi: 10.1371/journal.pone.0351172

Open versus closed suctioning on lung volume and oxygenation in ARDS patients with PEEP 5–10 cmH₂O: A randomized controlled trial

Haotian Gao ¹, Yidie Ying ², Jun Yang ^3,^*

Editor: Vincenzo Lionetti⁴

PMCID: PMC13626340 PMID: 42814700

Abstract

Objective

To compare the effects of open suctioning (OS) versus closed suctioning (CS) on lung volume and oxygenation in acute respiratory distress syndrome (ARDS) patients receiving mechanical ventilation with positive end-expiratory pressure (PEEP) of 5–10 cmH₂O.

Methods

This single-center, prospective randomized controlled trial enrolled 60 ARDS patients, who were randomly assigned to OS (n = 30) or CS (n = 30). All patients received lung-protective ventilation with volume-controlled mode. SpO₂ was recorded before suctioning and at 1, 10, 20, and 30 minutes post-suctioning. Arterial blood gas analysis was performed at 30 minutes to calculate the oxygenation index (PaO₂/FiO₂). Changes in end-expiratory lung impedance (ΔEELI) were monitored using electrical impedance tomography (EIT) for the whole lung and four regions of interest (ROI). Secondary outcomes included extubation and survival, analyzed using Kaplan-Meier curves and Cox regression.

Results

The absolute values of global ΔEELI were significantly lower in the CS group than in the OS group at 1 minute (−0.54 ± 0.18 vs. −2.32 ± 1.34, P < .001) and 10 minutes (−0.31 ± 0.25 vs. −1.14 ± 0.80, P < .001) after suctioning, indicating that CS better preserved lung volume. However, lung volume recovered more rapidly in the OS group, returning to baseline by 20 minutes, whereas recovery in the CS group was not achieved until 30 minutes. Regional analysis showed that the protective effect of CS was primarily observed in non-dependent regions (ROI 1–3), with no significant difference in the gravity-dependent ROI 4 (P = .430). SpO₂ was significantly lower in the OS group than in the CS group at 1 minute post-suctioning (98.07 ± 1.26% vs. 99.03 ± 0.93%, P = .007), and returned to baseline by 20 minutes in the OS group versus 10 minutes in the CS group. No significant difference in oxygenation index was observed at 30 minutes (P = .329). Secondary outcomes, including extubation and survival, did not differ significantly between the two groups (all P > .050). No adverse events were recorded.

Conclusions

In ARDS patients receiving PEEP 5–10 cmH₂O, CS reduces lung volume loss during suctioning and better preserves early oxygenation, but results in slower post-suctioning lung volume recovery compared with OS. These findings reveal a physiologically important trade-off between the two methods, though their clinical relevance warrants further investigation in larger, outcome-focused trials.

Introduction

Mechanical ventilation is a cornerstone in the management of acute respiratory distress syndrome (ARDS), and endotracheal suctioning (ES) is critical for maintaining airway patency. The two widely used methods, open suctioning (OS) and closed suctioning (CS), differ in their impact on the breathing circuit and patient physiology—OS requires disconnection from the ventilator, while CS maintains circuit integrity.

ARDS is characterized by high mortality and complex pathophysiology involving alveolar-capillary barrier disruption, alveolar collapse, and V/Q mismatch [1–5]. Current guidelines [6] recommend lung-protective ventilation with low tidal volume, plateau pressure limitation, and appropriate positive end-expiratory pressure (PEEP) to recruit collapsed alveoli and minimize ventilator-induced lung injury (VILI). In this context, any PEEP disruption during suctioning may directly translate into lung volume loss. OS, by requiring ventilator disconnection, inevitably leads to PEEP loss, alveolar collapse, and reduced lung volume [7–9]. In contrast, CS, by maintaining circuit integrity, is theoretically expected to better preserve lung volume and oxygenation [7–10].

However, conflicting findings exist. A study by Heinze et al. [11] demonstrated that regardless of whether CS or OS was used, functional residual capacity decreased after suctioning and remained at reduced levels for up to 20 minutes. Conversely, a study by Corley et al. [8] reported that lung volume recovery was slower following CS compared with OS. These contradictory results suggest that the choice of suctioning technique may be influenced by multiple factors, including the patient’s baseline condition, disease severity, and PEEP level, warranting further investigation.

Notably, electrical impedance tomography (EIT) is a non-invasive, radiation-free imaging technique that enables assessment of changes in end-expiratory lung volume (EELV) by monitoring variations in end-expiratory lung impedance (EELI). This provides a new tool for real-time, bedside quantification of the impact of suctioning on lung volume [12,13].

Current guidelines and studies [7,14] primarily address patients receiving high PEEP (≥10 cmH₂O), recommending CS in this setting. However, epidemiological data [1] indicate that approximately 50% of mechanically ventilated ARDS patients receive PEEP levels below 10 cmH₂O—representing a substantial proportion of the ARDS population. For this large patient subgroup, current clinical guidelines offer no clear recommendations, and the limited available evidence remains inconclusive [9,15,16]. Therefore, a dedicated comparison of the safety and efficacy of OS versus CS in this specific population is warranted.

This study focuses on patients with ARDS receiving PEEP levels between 5 and 10 cmH₂O. By comparing the effects of OS and CS on lung volume and oxygenation, we aim to evaluate the benefits of each suctioning method in this specific patient population and provide evidence to inform clinical practice.

Methods

1 Participants

This study was a single-center, prospective, randomized controlled trial. Patients admitted to the Intensive Care Unit of the Third Medical Center of Chinese Peoples Liberation Army General Hospital between June 1, 2025, and February 28, 2026, were screened for enrollment according to predefined inclusion and exclusion criteria. The study protocol was approved by the institutional ethics committee (No. KY2025−006) and was registered with the Chinese Clinical Trial Registry (registration No. ChiCTR2500105587).

1.1 Inclusion criteria.

(1) Patients receiving mechanical ventilation with a confirmed diagnosis of ARDS according to the Berlin Definition [17];
(2) PEEP level: 5 ≤ PEEP < 10 cmH₂O;
(3) Age between 18 and 85 years, with written informed consent obtained.

1.2 Exclusion criteria.

(1) PEEP ≥ 10 cmH₂O or < 5 cmH₂O;
(2) Age < 18 years or > 85 years;
(3) Pregnancy, presence of an implanted pacemaker, chest trauma or skin lesions precluding placement of the electrode belt, pneumothorax, or terminal illness.

2 Study protocol

2.1 Randomisation.

The random allocation sequence was generated by a physician who was not involved in clinical intervention or data collection. Using Microsoft Excel, the physician assigned a sequential number from 1 to 60 to each patient and generated a random number between 0 and 1 for each using the RAND function. Patients were then sorted in ascending order by the random numbers. The first 30 patients were allocated to the open suctioning (OS) group, and the remaining 30 to the closed suctioning (CS) group. The allocation sequence was concealed in sequentially numbered, opaque, sealed envelopes. Patients who met the eligibility criteria were enrolled and assigned according to the envelope sequence.

2.2 Participants and interventions.

Mechanically ventilated patients with ARDS who met the eligibility criteria were enrolled and assigned to receive either open or closed suctioning immediately after enrollment. A total of 60 patients were enrolled and randomly assigned to either the OS group (n = 30) or the CS group (n = 30). All patients received lung-protective ventilation, with volume-controlled mode, tidal volume (Vt) set at 4–8 ml/kg of predicted body weight (PBW), plateau pressure maintained below 30 cmH₂O, and PEEP titrated by two independent physicians blinded to the study using the ARDSnet low PEEP–FiO₂ table to determine FiO₂ and PEEP levels, targeting percutaneous oxygen saturation (SpO₂) ≥ 88%. Permissive hypercapnia was accepted as part of the ventilation strategy. Adequate sedation and analgesia were administered to all patients, with the Richmond Agitation-Sedation Scale (RASS) maintained between −4 and −5 and the Critical-Care Pain Observation Tool (CPOT) maintained at 0, so as to ensure the absence of any visible spontaneous breathing effort by the patient. No neuromuscular blocking agents were used during the study period. None of the enrolled patients had undergone fiberoptic bronchoscopy or prone positioning prior to enrollment, and none received these interventions during the study period; all patients were maintained in the supine position throughout the suctioning and observation protocol. Except for the suctioning method, all other treatments were identical between the two groups.

2.3 Suctioning procedure.

All suctioning procedures were performed through the patients’ orotracheal tubes by intensive care unit nurses who underwent standardized training, strictly following established suctioning protocols. Prior to suctioning, all patients received 100% oxygen for 60 seconds as pre-oxygenation. The suction pressure was set at −80 to −120 mmHg. The size of both open and closed suction catheters was selected according to the principle that the catheter outer diameter should not exceed one-half of the inner diameter of the artificial airway. Each suctioning pass lasted less than 15 seconds. Normal saline instillation was not routinely performed before suctioning; it was administered only when secretions were thick and viscous and conventional therapy was considered insufficient, in order to facilitate secretion clearance. No recruitment maneuvers were performed after suctioning.

2.4 Outcome measures and data collection.

Demographic characteristics, underlying diseases, Acute Physiology and Chronic Health Evaluation Ⅱ (APACHE Ⅱ) score, Sequential Organ Failure Assessment (SOFA) score, and etiology of ARDS were collected for each patient.

The following parameters were recorded before suctioning (ES-0) and at 1, 10, 20, and 30 minutes after suctioning (ES-1, ES-10, ES-20, ES-30): (1) Oxygenation: percutaneous oxygen saturation (SpO₂) was recorded, and arterial blood gas analysis was performed at ES-0 and ES-30 to calculate the oxygenation index (PaO₂/FiO₂); (2) Lung volume: Changes in end-expiratory lung impedance (ΔEELI) from baseline (ES-0) were continuously monitored using EIT with the Infivision ET1000 device (Hunan Huaruiboshi Medical Equipment Co., Ltd., Xiangtan, China). Global △EELI and regional △EELI for four regions of interest (ROI) were recorded at ES-1, ES-10, ES-20, and ES-30, denoted as △EELI (global) and △EELI (ROI 1–4), respectively. A positive △EELI value indicated an increase in end-expiratory lung volume, whereas a negative value indicated a decrease. In addition, secondary outcomes included successful extubation (no reintubation within 48 hours), mechanical ventilation survival time, and ICU survival time. These data were recorded for all enrolled patients.

Adverse events including desaturation (SpO₂ < 90%) and arrhythmia, which were systematically recorded during and within 30 minutes after each suctioning procedure.

3 Statistical analysis

The modified intention-to-treat (mITT) principle was applied in this study, whereby all randomized patients who received at least one study-specified suctioning procedure were included in the final statistical analysis. Statistical analysis was performed using GraphPad Prism 10.0 software and R 4.5.2. Continuous variables were expressed as mean ± standard deviation or median (interquartile range), and categorical variables were expressed as number (percentage). For baseline comparisons, continuous variables were analyzed using the independent samples t-test or Mann-Whitney U test, and categorical variables were analyzed using the chi-square test or Fisher’s exact test, as appropriate.

A two-way repeated measures analysis of variance was used to analyze the primary outcome measures, with time points (ES-0, ES-1, ES-10, ES-20, ES-30) as the within-subject factor and suctioning method (OS group, CS group) as the between-subject factor. In the presence of significant main effects, simple effects analysis was performed with Bonferroni correction. Comparisons of △EELI values against baseline were performed using one-sample t-tests (test value set to 0). To control for type I error, the significance level was adjusted using the Bonferroni method, with a P < .00625 considered statistically significant.

Kaplan–Meier curves with log-rank tests were used to compare mechanical ventilation survival and ICU survival between the two groups. Time on mechanical ventilation was defined as the interval from enrollment to successful extubation or death. Univariate Cox regression was performed to estimate the hazard ratio (HR) and 95% confidence interval (CI) for the effect of suctioning method on mortality. Extubation outcomes were compared using a Fine-Gray competing-risk model, with death treated as a competing event.

All tests were two-tailed, and a P < .050 was considered statistically significant. Bonferroni correction was applied for multiple comparisons.

Results

1 Baseline characteristics

From June 2025 to February 2026, a total of 62 patients with ARDS were admitted to the ICU of our hospital, of whom 60 met the inclusion criteria and were randomly assigned to the OS group (n = 30) or the CS group (n = 30), as shown in Fig 1. Among the enrolled patients, ARDS was caused by pulmonary factors (pulmonary infection) in 56 cases (bacterial infection in 52, viral infection in 3, fungal infection in 1) and by extrapulmonary factors (sepsis) in 4 cases.

Baseline characteristics of the two groups are presented in Table 1. The median (IQR) age of patients in the OS group was 75.00 (65.50, 80.25) years, compared with 69.50 (61.00, 78.25) years in the CS group. The APACHE II mean (SD) scores were 25.00 ± 3.35 and 23.97 ± 5.03, and the SOFA median (IQR) scores were 9.50 (7.00, 13.00) and 9.00 (6.00, 10.50), respectively. No statistically significant differences were observed in baseline characteristics between the two groups.

Table 1. Baseline characteristics of the patients.

	Open suctioning (OS)	Closed suctioning (CS)
Age (years)	75.00(65.50, 80.25)	69.50(61.00, 78.25)
Male (n, %)	22(73.33)	20(66.67)
BMI (kg/m²)	23.58(19.53, 26.31)	22.55(21.39, 24.83)
Pulmonary etiology (n, %)	27(90.00)	29(96.67)
Medical history
Hypertension (n, %)	17(56.67)	19(63.33)
Diabetes mellitus (n, %)	9(30.00)	10(33.33)
Coronary heart disease (n, %)	9(30.00)	8(26.67)
Pulmonary disease (n, %)	3(10.00)	4(13.33)
Smoking history (n, %)	11(36.67)	9(30.00)
APACHE Ⅱ score	25.00 ± 3.35	23.97 ± 5.03
SOFA score	9.50(7.00, 13.00)	9.00(6.00, 10.50)
PEEP (cmH₂O)	6.00(5.00, 7.00)	7.00(5.00, 8.00)
HR (beats/min)	92.20 ± 13.86	88.27 ± 17.68
SBP (mmHg)	128.63 ± 28.22	128.60 ± 23.17
DBP (mmHg)	74.27 ± 16.32	74.43 ± 18.34
CVP (cmH₂O)	11.23 ± 1.91	11.40 ± 1.98
Pplat (cmH₂O)	22.93 ± 2.80	23.83 ± 3.32
Pmean (cmH₂O)	12.75 ± 2.64	13.56 ± 3.21
Cst (ml/cmH₂O)	22.50 ± 4.58	21.73 ± 3.98
SpO₂ (%)	99.33 ± 0.92	99.50 ± 0.68
PaO₂/FiO₂ (mmHg)	191.38 ± 37.69	196.06 ± 44.73
FiO₂ (%)	0.55(0.50, 0.60)	0.50(0.50, 0.60)
PaCO₂ (mmHg)	39.07 ± 6.80	38.40 ± 7.23
Vt (ml)	371.20 ± 45.83	370.83 ± 45.04

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Abbreviations: HR, heart rate; SBP, systolic blood pressure; DBP, diastolic blood pressure; CVP, central venous pressure; Pplat, plateau pressure; Pmean, mean airway pressure; Cst, static compliance; Vt, tidal volume

2 Primary outcomes

2.1 △EELI (global).

Repeated measures analysis of variance for △EELI (global) revealed significant interaction effect (F (1.47, 85.12) = 44.24, P < .001), time effect (F (1.47, 85.12) = 105.29, P < .001), and group effect (F (1, 58) = 30.23, P < .001).

Further between-group comparisons showed that compared with the CS group, the OS group exhibited a greater decrease in EELI at 1 minute (−2.32 ± 1.34) and 10 minutes (−1.14 ± 0.80) after suctioning (P < .001), as shown in Table 2 and Fig 2.

Table 2. Intergroup comparison of △EELI (global) post-suctioning.

	ES-1	ES-10	ES-20	ES-30
OS	−2.32 ± 1.34	−1.14 ± 0.80	−0.35 ± 0.66	0.13 ± 0.43
CS	−0.54 ± 0.18	−0.31 ± 0.25	−0.16 ± 0.22	−0.01 ± 0.19
P	<.001	<.001	.610	.690
95%CI	(−2.44, −1.13)	(−1.24, −0.43)	(−0.52, −0.15)	(−0.11, 0.35)

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Regarding the recovery of EELI after suctioning, the mean △EELI values at the four time points were compared against zero for each group, as values closer to zero indicate a return to baseline. The results demonstrated that EELI recovery was faster in the OS group than in the CS group. In the OS group, EELI returned to baseline by 20 minutes after suctioning (P = .007), whereas in the CS group, recovery was not achieved until 30 minutes after suctioning (P = .790), as shown in Table 3.

Table 3. Post‑suctioning △EELI (global) versus baseline.

Group(time point)	95%CI	t(df)	P
OS(ES-1)	(−2.82, −1.82)	9.48(29.00)	<.000
OS(ES-10)	(−1.44, −0.84)	7.79(29.00)	<.001
OS(ES-20)	(−0.59, −0.10)	2.90(29.00)	.007
OS(ES-30)	(−0.03, 0.29)	1.62(29.00)	.115
CS(ES-1)	(−0.60, −0.47)	16.77(29.00)	<.001
CS(ES-10)	(−0.40, −0.21)	6.69(29.00)	<.001
CS(ES-20)	(−0.24, −0.08)	4.09(29.00)	<.001
CS(ES-30)	(−0.06, 0.08)	0.27(29.00)	.790

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Note: The significance threshold was set at P < .00625 after Bonferroni correction.

2.2 △EELI (ROI 1).

Analysis of △EELI in ROI 1 revealed significant interaction effect (F (1.51, 87.44) = 42.80, P < .001), group effect (F (1, 58) = 31.85, P < .001), and time effect (F (1.51, 87.44) = 101.15, P < .001).

Compared with the CS group, the OS group exhibited a greater decrease in EELI at 1 minute (−0.83 ± 0.49 vs. −0.17 ± 0.10) and 10 minutes (−0.49 ± 0.38 vs. −0.09 ± 0.07) after suctioning (P < .001), as shown in Fig 3A. EELI returned to baseline by 20 minutes after suctioning in both the OS and CS groups (P = .007 and P = .020, respectively).

Fig 3A (left) and Fig 3B (right) represent △EELI for ROI 1 and ROI 2, respectively.

2.3 △EELI (ROI 2).

Analysis of △EELI in ROI 2 revealed significant interaction effect (F (1.63, 94.54) = 24.84, P < .001), group effect (F (1, 58) = 12.99, P < .001), and time effect (F (1.63, 94.54) = 70.29, P < .001).

Between-group comparisons showed that compared with the CS group, the OS group showed a greater decrease in EELI at 1 minute (−0.99 ± 0.70 vs. −0.24 ± 0.09, P < .001) and 10 minutes (−0.49 ± 0.60 vs. −0.13 ± 0.13, P < .010) after suctioning, as shown in Fig 3B. Regarding recovery, EELI returned to baseline by 20 minutes after suctioning in the OS group (P = .080), whereas recovery in the CS group was not achieved until 30 minutes (P = .220).

2.4 △EELI (ROI 3).

Analysis of changes in EELI in ROI 3, a gravity-dependent region, revealed significant interaction effect (F (1.42, 82.61) = 16.18, P < .001), group effect (F (1, 58) = 7.64, P = .008), and time effect (F (1.42, 82.61) = 28.75, P < .001).

Compared with the CS group, the OS group exhibited a greater decrease in EELI at 1 minute after suctioning (−0.43 ± 0.38 vs. −0.10 ± 0.06, P < .001). No statistically significant differences were observed between the two groups at 10, 20, or 30 minutes after suctioning, as shown in Fig 4A. Regarding recovery, EELI returned to baseline by 20 minutes after suctioning in both the OS and CS groups (P = .670 and P = .080, respectively).

Fig 4A (left) and Fig 4B (right) represent △EELI for ROI 3 and ROI 4, respectively.

2.5 △EELI (ROI 4).

Analysis of changes in EELI in ROI 4, a gravity-dependent region, revealed significant interaction effect (F (1.92, 111.38) = 4.91, P = .010) and time effect (F (1.92, 111.38) = 8.80, P < .001), whereas the group effect was not significant (F (1, 58) = 0.63, P = .430).

Between-group comparisons showed no statistically significant differences in the magnitude of EELI decrease at any time point between the two groups, as shown in Fig 4B. Further analysis of changes within each group revealed that EELI in the OS group did not change significantly from baseline at any time point (P > .050), whereas EELI in the CS group decreased after suctioning and returned to baseline by 20 minutes (P = .009).

2.6 Percutaneous oxygen saturation.

Analysis of SpO₂ in the two groups revealed a significant interaction effect (F (1.95, 113.20) = 15.01, P < .001), a non-significant group effect (F (1, 58) = 2.22, P = .140), and a significant time effect (F (1.95, 113.20) = 63.04, P < .001).

Further between-group comparisons showed that both groups experienced a significant decrease in oxygenation at 1 minute after suctioning, with SpO₂ being significantly lower in the OS group (98.07 ± 1.26%) than in the CS group (99.03 ± 0.93%, P = .007). SpO₂ returned to baseline by 10 minutes after suctioning in the CS group (P = .170), whereas recovery in the OS group was not achieved until 20 minutes (P = .640). The trend of SpO₂ changes before and after suctioning in the two groups is shown in Fig 5. In the OS group, oxygenation decreased immediately after suctioning and recovered more slowly.

Fig 5 — Time points 0, 1, 2, 3, and 4 indicate ES-0, ES-1, ES-10, ES-20, and ES-30, respectively.

2.7 Oxygenation index.

Analysis of the oxygenation index at 30 minutes after suctioning showed values of 188.1 ± 38.46 mmHg in the OS group and 199.6 ± 51.36 mmHg in the CS group, with no significant difference between the two groups (t (58) = 0.99, P = .329).

3 Secondary outcomes

Extubation rates did not differ significantly between the two groups (P = .270). Survival analyses were performed using hospital stay and duration of mechanical ventilation as the time-to-event variables. Median hospital survival was 17 days in the OS group and 20 days in the CS group (P = .230); univariate Cox regression gave a hazard ratio (HR) of 0.67 (95% CI (0.35, 1.29), P = .228) for CS versus OS. For mechanical ventilation survival, median times were 17 and 20 days, respectively (P = .210), with the same HR of 0.67 (95%CI (0.35, 1.29), P = .228). None of these differences reached statistical significance.

4 Adverse events

No adverse events were observed during the study period

Discussion

This randomized controlled trial in ARDS patients receiving PEEP 5–10 cmH₂O demonstrates that, compared with open suctioning (OS), closed suctioning (CS) better preserves lung volume immediately after suctioning, particularly in non-dependent regions, but lung volume recovery is slower. OS causes a more pronounced early decrease in oxygenation and a slower recovery. These findings reveal a physiologically important trade-off between the two methods that may inform clinical decision-making in this patient population.

1 Lung volume: preservation advantage of CS and delayed recovery

For patients with ARDS, appropriate levels of PEEP help maintain the patency of recruitable alveoli and prevent end-expiratory alveolar collapse [18,19]. When PEEP is suddenly discontinued, alveoli that depend on PEEP for patency rapidly collapse, resulting in a significant reduction in lung volume. Concurrently, negative pressure suctioning causes further lung volume loss, exacerbating alveolar collapse. In contrast, CS does not require disconnection from the ventilator during the suctioning procedure and thus maintains continuous PEEP, which theoretically better preserves lung volume [7–9].

EELI is an important parameter derived from EIT, and multiple studies have confirmed a strong linear correlation between EELI and EELV, allowing changes in EELI to represent changes in EELV [20–23]. In the present study, △EELI was used to quantify the impact of the two suctioning methods on lung volume. Consistent with the presumed advantage of CS, the absolute values of △EELI in the CS group were lower than those in the OS group at 1 minute (−0.54 ± 0.18 vs. −2.32 ± 1.34, P < .001) and 10 minutes (−0.31 ± 0.25 vs. −1.14 ± 0.80, P < .001) after suctioning. Further analysis of △EELI across the four ROI revealed that this lung volume protective effect was primarily observed in ROI 1, 2, and 3, with no significant difference between the two groups in the gravity-dependent ROI 4. This finding holds clinical relevance. In patients with ARDS, increased lung density due to inflammation results in inhomogeneous ventilation distribution along the gravity axis. In the supine position, increased lung density makes the dorsal region (i.e., the gravity-dependent region) more prone to alveolar collapse, and ventilated lung tissue is typically confined to the ventral region [24]. In this study, ROI 4 represented the most dorsal, gravity-dependent region, where alveolar recruitability is poorer and may be less sensitive to changes in lung volume induced by suctioning.

However, this presumed advantage of CS is challenged by the recovery pattern observed after suctioning. Although CS better preserved lung volume immediately after suctioning, the recovery of EELI was slower in the CS group than in the OS group. EELI returned to baseline by 20 minutes after suctioning in the OS group, whereas recovery in the CS group was not achieved until 30 minutes. This finding aligns with the study by Corley et al. [8], who conducted a crossover trial in 20 mechanically ventilated patients after cardiac surgery and similarly found that although CS reduced suction-induced lung volume loss, the recovery of lung volume after suctioning was slower compared with OS. Corley et al. further suggested that this delayed recovery of lung volume following CS may be even more pronounced in patients with ARDS.

The mechanism underlying the delayed recovery of end-expiratory lung volume after CS remains unclear, and the study by Corley et al. did not elucidate it. An in vitro study by El Masry et al. [25] evaluated the response of 11 ventilators to CS and demonstrated that ventilator response to CS varied significantly depending on the ventilation mode and parameter settings. The extent to which ventilator gas delivery is affected by suctioning is closely related to the ventilation mode and tidal volume settings. In the present study, ventilator settings were identical between the two groups, and we did not evaluate the effects of the two suctioning methods on lung volume under other ventilator modes. Given the heterogeneity in ventilator mode settings, suction pressure, and suction catheter size selection across previous studies, further research is needed to elucidate the mechanisms underlying the slower recovery of end-expiratory lung volume following CS. Notably, no adverse events such as desaturation were recorded following suctioning, and secondary clinical outcomes (extubation and survival) did not differ significantly between the two groups. Therefore, the slower recovery of lung volume observed after CS should not be interpreted as evidence of impaired clinical recovery or an increased risk of complications.

In this study, both groups experienced significant lung volume loss after suctioning. Therefore, our findings support the suggestion by Corley et al. [8] that regardless of the suctioning method used, lung recruitment maneuvers may be considered after suctioning to restore lost lung volume and minimize adverse effects such as alveolar collapse and atelectasis. However, lung recruitment maneuvers carry potential risks, including barotrauma, alveolar overdistension, and hemodynamic instability. Therefore, the decision to perform such maneuvers should be tailored to the clinical context, and these risks can be minimized by using strategies such as gradually increasing PEEP in pressure-controlled mode [26].

2 Oxygenation: early oxygenation stability with CS

The decrease in percutaneous oxygen saturation is associated with V/Q mismatch resulting from lung volume loss. OS causes loss of PEEP due to ventilator disconnection, leading to alveolar collapse. Some alveoli remain perfused but non-ventilated, resulting in intrapulmonary shunting and reduced oxygenation. CS, by maintaining continuity of the breathing circuit and preserving PEEP levels, better maintains lung volume stability, reduces intrapulmonary shunting, and thereby better preserves oxygenation. A study by Cereda et al. [9] found a significant decrease in percutaneous oxygen saturation after OS. The present study yielded similar results, with SpO₂ in the OS group decreasing significantly at 1 minute after suctioning (P < .001) and returning to baseline by 20 minutes, whereas SpO₂ in the CS group decreased only at 1 minute and returned to baseline by 10 minutes.

However, it should be noted that these SpO₂ changes were observed in the context of a standardized pre-oxygenation protocol (100% FiO₂ for 60 seconds), which may have attenuated the magnitude of desaturation in both groups and contributed to the absence of any clinically significant hypoxemic events during the study period.

Notably, previous studies have reported inconsistent findings. For instance, Lee and Kim [16] observed lower baseline SpO₂ in CS patients prior to suctioning in a pressure-controlled ventilation setting, a difference that may reflect variations in baseline patient characteristics, ventilation mode, or pre-oxygenation protocols rather than the suctioning method per se. Such discrepancies highlight the influence of contextual factors—including PEEP level, ventilation mode, and pre-oxygenation practice—on the comparative effects of OS and CS, and underscore the need for standardized protocols in future research.

Taken together, these findings suggest that CS may offer an advantage over OS in mitigating early post-suctioning oxygenation decline under the conditions of this study. However, this advantage was transient and did not translate into a sustained difference in oxygenation at 30 minutes. Given that both groups maintained clinically acceptable SpO₂ levels throughout the observation period, the clinical significance of this early difference remains uncertain and warrants further investigation in larger, outcome-focused trials.

3 Study limitations

This study has several limitations. First, the sample size was relatively small, which may have limited the power to detect differences in secondary clinical outcomes such as extubation and survival rates; indeed, we observed no significant differences between the groups in these endpoints (all P > .050), consistent with previous reports. Second, due to the nature of the procedure, the suctioning operators and data collectors were not blinded, which may have introduced potential bias. Finally, although our study focused on physiological endpoints, the choice between OS and CS may also have implications for cost and environmental sustainability, which deserve attention in clinical practice. Future studies should incorporate larger, multicenter randomized controlled trials, along with imaging techniques such as chest CT and ultrasound, and include a more comprehensive assessment of clinical outcomes, including ventilator-associated pneumonia, atelectasis, and other pulmonary complications, so as to provide more robust evidence for clinical decision-making.

Conclusions

In ARDS patients receiving PEEP 5–10 cmH₂O, CS reduces lung volume loss during suctioning and better preserves early oxygenation, but results in slower post-suctioning lung volume recovery compared with OS. Therefore, the physiological trade-off between the two methods should be considered when selecting a suctioning strategy. There were no significant differences between the two groups in secondary clinical outcomes, including extubation and survival. Whether these physiological differences translate into clinically meaningful outcomes warrants further investigation.

Supporting information

S1 Table. The raw data.

(XLSX)

pone.0351172.s001.xlsx^{(30.3KB, xlsx)}

S1 File. CONSORT 2025 editable checklist.

(DOCX)

pone.0351172.s002.docx^{(31KB, docx)}

S2 File. Study Protocol.

(DOCX)

pone.0351172.s003.docx^{(21.4KB, docx)}

Acknowledgments

We acknowledge all the teachers who have generously shared their knowledge and offered helpful advice during the various stages of this work.

Data Availability

The minimal data set is available in the Supporting Information.

Funding Statement

The author(s) received no specific funding for this work.

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PLoS One. doi: 10.1371/journal.pone.0351172.r001

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available??>

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Interesting article looking at effectiveness for two suctionaning methods on lung volvume and oxygenation in patient with ARDS receicing PEEP levels

Some comments:

1) Can the authors follow the CONSORT 2025 reporting guidelines.

2) Statistical analysis section - define population for analysis

3) How was missing data handled?

4) Suggest to have a clear outcome section that combining this with data collection, and in the outcomes make clear which is primary and secondary outcomes.

5)Remove p-values from baseline table - as this is an RCT any difference observed would be due to randomness - not recommended to include comparisons in an individually randomised trial.

6) Table 1 - replace "OS" and "CS" with actual terms and further abbreviations in the table - either a footnote or stated in full in the table.

7) Sample size calculation is not reported - justification of chosen sample needs to be stated together with what the estimated clinical difference is.

8) If the primary comparisons is OS vs CS - what is the correction for and what was the primary timepoint?

9) Line 185 - reporting of age - state what the numbers in brackets are, i.e range /IQR, similar also for APACHEII. Line 187 suggest the sentence starts like "The APACHE II mean(SD) scores were......." "The mean (??) age of patients in OS...... "

10) The authors used a repeated measures ANOVA - why not use the mixed effect model?

11) To what extent was blinding observed - can this be stated. Also when was the SAP finalised and was analysis blinded?

Reviewer #2: Thank you to the Editor for the opportunity to review this manuscript. The topic is clinically important and deserves careful consideration, given the vulnerability of patients with acute respiratory distress syndrome (ARDS). Overall, the authors have designed and conducted an interesting randomized study using bedside electrical impedance tomography. However, several methodological, statistical, and reporting issues should be addressed before the conclusions can be considered fully supported.

Major comments

Introduction and study rationale

The Introduction is somewhat lengthy. After the general background on ARDS, suctioning methods, and EIT, the central rationale for studying patients receiving low PEEP is not sufficiently emphasized. The authors should more clearly explain why suctioning-related lung-volume changes may be particularly relevant at PEEP levels of 5 to <10 cmH2O, why this population is clinically important, and why it remains insufficiently studied compared with patients receiving higher PEEP.

Sample-size calculation

The manuscript does not report a sample-size or power calculation. Please specify the primary outcome used for the calculation, the anticipated effect size and variability, alpha level, power, expected drop-out rate, and the planned number of participants per group.

Timing of enrolment and study procedures

The authors should report the time from intubation, ARDS diagnosis, and ICU admission to study enrolment and to the suctioning procedure. It is unclear whether randomisation and the study intervention were performed immediately after inclusion or after a period of clinical stabilisation. This information is important because respiratory mechanics and recruitability may vary substantially during the course of ARDS.

Baseline ARDS severity and respiratory status

Please report ARDS severity according to the Berlin categories at enrolment and at the time of the study procedure. Baseline respiratory variables should be presented more comprehensively, including tidal volume indexed to predicted body weight, respiratory rate, FiO2, ventilatory mode, driving pressure, arterial pH, PaCO2, and duration of mechanical ventilation.

Prone positioning and patient position during EIT assessment

The manuscript should clarify whether patients had been managed in the prone position before enrolment, whether any were studied after a prone-positioning session, and whether all measurements were performed in the supine position. This is particularly relevant for the interpretation of regional EIT findings and the definition of dependent versus non-dependent regions.

Airway characteristics and secretion burden

It is not clear whether suctioning was performed through an orotracheal tube or a tracheostomy cannula. Please report the number of patients with pre-existing tracheostomy, tracheomalacia, airway abnormalities, or other relevant airway conditions. The authors should also clarify whether patients had undergone bronchoscopy before inclusion and whether airway patency or secretion burden was assessed before suctioning. If available, please report secretion volume, viscosity, or a standardized secretion score in both groups.

Standardisation of the suctioning procedure

Although the manuscript states that nurses followed standardized protocols, the actual suctioning procedure is insufficiently described. Please provide details regarding indications for suctioning, routine suctioning frequency per nursing shift, suction pressure, catheter size, catheter-to-tube diameter ratio, suction duration, number of passes, use of saline instillation, pre-oxygenation, ventilator disconnection technique in the OS group, and whether recruitment manoeuvres were allowed after suctioning.

Ventilatory management and rationale for low PEEP

The authors state that all patients received lung-protective ventilation, but the protocol is not sufficiently described. Please clarify whether permissive hypercapnia was accepted, whether plateau pressure and driving pressure targets were standardized, and whether neuromuscular blockade was used. The rationale for selecting PEEP values between 5 and <10 cmH2O should be explained. In particular, please indicate whether PEEP was selected according to a standardized protocol, ARDSNet tables, clinician judgment, compliance, oxygenation, or transpulmonary-pressure measurements.

Co-interventions and assessment of lung morphology

Please describe relevant co-interventions and whether they were balanced between groups, including prone positioning, recruitment manoeuvres, bronchodilator therapy, inhaled pulmonary vasodilators, corticosteroids, and neuromuscular blocking agents. It would also be useful to state whether patients underwent chest CT or routine lung ultrasound and to report, where available, the degree of atelectasis, consolidation, and recruitability.

Clinical outcomes and length of stay

Even if the trial was not powered for clinical outcomes, the authors should report ICU length of stay, hospital length of stay, duration of mechanical ventilation, ventilator-associated pneumonia, reintubation or tracheostomy where applicable, and mortality. These variables would provide useful clinical context for the physiological findings.

Ethics and informed consent

The manuscript states that written informed consent was obtained, but it does not specify when consent was obtained, from whom it was obtained, or how consent was managed in deeply sedated patients without decision-making capacity. Please clarify whether consent was obtained from the patient, a legal representative, or through a deferred-consent procedure, and ensure that this is consistent with the ethics approval.

Discussion

The Discussion should be substantially reorganized. It should begin with a concise statement of the main findings, followed by a structured interpretation of each finding. The authors should then compare their results with previous studies of OS and CS, particularly studies conducted in patients receiving higher PEEP. The reasons why CS was associated with less immediate lung-volume loss but slower recovery should be discussed more clearly and cautiously. The current wording occasionally suggests clinical benefits or risks that were not directly measured in this study.

Environmental and economic considerations

In a sustainability perspective, it would be valuable to include at least a descriptive comparison of the costs and material waste associated with closed versus open suctioning. Even a brief discussion of device use, disposable materials, and potential waste generation would improve the clinical relevance of the manuscript. Once these issues have been adequately addressed, the conclusions should be revised to reflect the corrected analyses and the physiological, rather than clinical-outcome, nature of the findings. There are some typos in Table 3

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Reviewer #2: Yes: Raffaele Mandarano

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PLoS One. 2026 Sep 30;21(9):e0351172. doi: 10.1371/journal.pone.0351172.r002

Author response to Decision Letter 1

19 Aug 2026

Dear Editor and Reviewers,

We sincerely thank the Editor and the reviewers for their thorough and constructive evaluation of our manuscript. We greatly appreciate the time and effort invested in reviewing our work. We have carefully considered all comments and suggestions, and have revised the manuscript accordingly. Below we provide a point-by-point response to each comment. All changes in the revised manuscript have been highlighted in yellow for easy identification.

Responses to Academic Editor

We have carefully addressed all comments raised by both reviewers and we have also formatted the manuscript according to the journal's requirements. We have revised the data availability statement as requested, and the raw data have been added to the supporting information.

Responses to Reviewer #1

Comment 1: Can the authors follow the CONSORT 2025 reporting guidelines?

Response: We thank the reviewer for this suggestion. We have ensured that our manuscript adheres to the CONSORT 2025 reporting guidelines. The flow diagram has been included as Figure 1 (Page 10), and all CONSORT checklist items have been addressed throughout the manuscript. The trial registration number has been provided in the Methods section (Page 5).

Comment 2: Statistical analysis section - define population for analysis.

Response: We have clarified the analysis population in the Statistical analysis section. We now explicitly state that the modified intention-to-treat (mITT) principle was applied, whereby all randomized patients who received at least one study-specified suctioning procedure were included in the final statistical analysis. (Page 8, lines 169–171)

Comment 3: How was missing data handled?

Response: We thank the reviewer for this important question. In this study, there were no missing data for the primary outcome measures (ΔEELI and SpO2) or the secondary outcomes (extubation and survival), as all measurements were completed according to the protocol. For baseline characteristics, complete data were available for all enrolled patients.

Comment 4: Suggest to have a clear outcome section that combining this with data collection, and in the outcomes make clear which is primary and secondary outcomes.

Response: We have reorganized the “Outcome Measures and Data Collection” section to clearly distinguish primary and secondary outcomes (Page 8, lines 163–165), and the results are reported separately in the Results section (Page 11–15).

Comment 5: Remove p-values from baseline table - as this is an RCT any difference observed would be due to randomness - not recommended to include comparisons in an individually randomised trial.

Response: We agree with the reviewer's point. We have removed p-values from the baseline characteristics table in the revised manuscript (Table 1, Page 10–11).

Comment 6: Table 1 - replace "OS" and "CS" with actual terms and further abbreviations in the table - either a footnote or stated in full in the table.

Response: We have revised Table 1 to replace "OS" and "CS" with the full terms "Open suctioning (OS)" and "Closed suctioning (CS)" in the table header. All other abbreviations in the table have been defined in a footnote. (Table 1, Page 10–11).

Comment 7: Sample size calculation is not reported - justification of chosen sample needs to be stated together with what the estimated clinical difference is.

Response: We thank the reviewer for the valuable comment on sample size. The sample size was estimated based on the primary outcome—the change in end‑expiratory lung impedance (ΔEELI) at the end of suctioning. According to Yildirim et al. (2024), the mean ΔEELI values were −4415 ± 2363 in the open suctioning group and −2661 ± 1937 in the closed suctioning group. Assuming a two‑sided α = 0.05, power = 80%, and a 10% dropout rate, the calculation yielded 34 patients per group. Owing to the single‑center design, we ultimately enrolled 30 patients per group; however, no dropout occurred during the study, so the effective sample size (30 per group) was close to the target. We acknowledge that the relatively small sample size may have limited the power to detect differences in secondary outcomes, and we have clearly stated this as a limitation in the Discussion section of the revised manuscript (page 19–20, lines 403–406).

Comment 8: If the primary comparisons is OS vs CS - what is the correction for and what was the primary timepoint?

Response: Since we performed a total of eight comparisons of ΔEELI against a test value of 0 at the 1-, 10-, 20-, and 30-minute time points post-suctioning in the two groups, we applied Bonferroni correction to control for type I error.

Comment 9: Line 185 - reporting of age - state what the numbers in brackets are, i.e range/IQR, similar also for APACHE II. Line 187 suggest the sentence starts like "The APACHE II mean (SD) scores were......." "The mean (??) age of patients in OS......"

Response: We have revised the reporting of descriptive statistics in the Results section as suggested. For age and SOFA scores, we now clearly indicate that the numbers in parentheses represent the interquartile range (IQR). For APACHE II scores, we report mean ± SD. The sentences have been rephrased accordingly. (Page 10, lines 201–204)

Comment 10: The authors used a repeated measures ANOVA - why not use the mixed effect model?

Response: We thank the reviewer for this question. We chose repeated measures ANOVA because our data were complete (no missing values) and the study design was balanced, with equal group sizes and the same set of time points for all participants. Under these conditions, repeated measures ANOVA is appropriate and widely accepted in the literature.

Comment 11: To what extent was blinding observed - can this be stated. Also when was the SAP finalised and was analysis blinded?

Response: We acknowledge that, due to the nature of the suctioning procedure, blinding of the suctioning operators and data collectors was not feasible, and we have discussed this as a limitation in the revised manuscript. However, the physicians responsible for PEEP titration were blinded to group allocation. The statistical analysis plan was finalized before data analysis commenced, although the analysis itself was not performed in a blinded manner.

Responses to Reviewer #2

Comment 1 (Introduction and study rationale): The Introduction is somewhat lengthy. After the general background on ARDS, suctioning methods, and EIT, the central rationale for studying patients receiving low PEEP is not sufficiently emphasized. The authors should more clearly explain why suctioning-related lung-volume changes may be particularly relevant at PEEP levels of 5 to <10 cmH2O, why this population is clinically important, and why it remains insufficiently studied compared with patients receiving higher PEEP.

Response: We thank the reviewer for this important suggestion. We have revised the Introduction to more clearly and concisely emphasize the rationale for focusing on the PEEP 5–10 cmH2O population. We have added explicit statements highlighting that approximately 50% of mechanically ventilated ARDS patients receive PEEP below 10 cmH2O, that current guidelines offer no clear recommendations for this substantial group, and that the limited available evidence remains inconclusive. (Page 3–4)

Comment 2 (Sample-size calculation): The manuscript does not report a sample-size or power calculation. Please specify the primary outcome used for the calculation, the anticipated effect size and variability, alpha level, power, expected drop-out rate, and the planned number of participants per group.

Comment 3 (Timing of enrolment and study procedures): The authors should report the time from intubation, ARDS diagnosis, and ICU admission to study enrolment and to the suctioning procedure. It is unclear whether randomisation and the study intervention were performed immediately after inclusion or after a period of clinical stabilisation. This information is important because respiratory mechanics and recruitability may vary substantially during the course of ARDS.

Response: We thank the reviewer for the comment. In this study, patients were randomized and enrolled immediately after meeting the inclusion and exclusion criteria following endotracheal intubation, and subsequently received the corresponding suctioning intervention; we have revised the manuscript to clarify this (Page 6, lines 122–123). However, we acknowledge that the time from ARDS diagnosis to enrollment was not recorded.

Comment 4 (Baseline ARDS severity and respiratory status): Please report ARDS severity according to the Berlin categories at enrolment and at the time of the study procedure. Baseline respiratory variables should be presented more comprehensively, including tidal volume indexed to predicted body weight, respiratory rate, FiO2, ventilatory mode, driving pressure, arterial pH, PaCO2, and duration of mechanical ventilation.

Response: We thank the reviewer for this valuable suggestion. We have expanded Table 1 to include additional baseline respiratory variables, including FiO2, PaCO2, and tidal volume (Vt). The ventilatory mode (volume-controlled) has been described in the Methods section (Page 6, line 125). ARDS severity is reflected in Table 1 by the oxygenation index (PaO2/FiO2). We acknowledge that respiratory rate, driving pressure, arterial pH, and other variables were not recorded in this study.

Comment 5 (Prone positioning and patient position during EIT assessment): The manuscript should clarify whether patients had been managed in the prone position before enrolment, whether any were studied after a prone-positioning session, and whether all measurements were performed in the supine position. This is particularly relevant for the interpretation of regional EIT findings and the definition of dependent versus non-dependent regions.

Response: We appreciate the reviewer's careful attention to this methodological detail. We have now clarified that none of the enrolled patients had undergone prone positioning prior to enrollment, and none received prone positioning during the study period. All measurements were performed with patients in the supine position. This information has been added to the Methods section. (Page 7, lines 135–137)

Comment 6 (Airway characteristics and secretion burden): It is not clear whether suctioning was performed through an orotracheal tube or a tracheostomy cannula. Please report the number of patients with pre-existing tracheostomy, tracheomalacia, airway abnormalities, or other relevant airway conditions. The authors should also clarify whether patients had undergone bronchoscopy before inclusion and whether airway patency or secretion burden was assessed before suctioning. If available, please report secretion volume, viscosity, or a standardized secretion score in both groups.

Response: In response to the reviewer's comment, we have clarified that all suctioning procedures were performed through the patients' orotracheal tubes. None of the enrolled patients had preexisting tracheostomy, tracheomalacia, or other relevant airway abnormalities, and none had undergone fiberoptic bronchoscopy prior to enrollment. (Page 7, lines 134–136; lines 140–141) Regarding secretion assessment, we have added that normal saline instillation was not performed on a routine basis; it was administered only when secretions were thick and viscous and, in the assessment of the attending nurse, conventional therapy was considered insufficient to facilitate secretion clearance. (Page 7, lines 146–149) We acknowledge, however, that a standardized secretion score was not recorded prior to suctioning in this study.

Comment 7 (Standardisation of the suctioning procedure): Although the manuscript states that nurses followed standardized protocols, the actual suctioning procedure is insufficiently described. Please provide details regarding indications for suctioning, routine suctioning frequency per nursing shift, suction pressure, catheter size, catheter-to-tube diameter ratio, suction duration, number of passes, use of saline instillation, pre-oxygenation, ventilator disconnection technique in the OS group, and whether recruitment maneuvers were allowed after suctioning.

Response: We have substantially expanded the description of the suctioning procedure in the Methods section. We now provide details on: pre-oxygenation (100% FiO2 for 60 seconds), suction pressure (−80 to −120 mmHg), catheter size selection (outer diameter not exceeding one-half of the inner diameter of the artificial airway), suction duration (less than 15 seconds per pass), saline instillation (not routinely performed; only for thick secretions), and that no recruitment maneuvers were performed after suctioning. Regarding the ventilator disconnection technique in the OS group, suctioning was performed after disconnecting the patient from the ventilator circuit. (Page 7, lines 139–149)

Comment 8 (Ventilatory management and rationale for low PEEP): The authors state that all patients received lung-protective ventilation, but the protocol is not sufficiently described. Please clarify whether permissive hypercapnia was accepted, whether plateau pressure and driving pressure targets were standardized, and whether neuromuscular blockade was used. The rationale for selecting PEEP values between 5 and <10 cmH2O should be explained. In particular, please indicate whether PEEP was selected according to a standardized protocol, ARDSNet tables, clinician judgment, compliance, oxygenation, or transpulmonary-pressure measurements.

Response: We have expanded the description of ventilatory management. We now clarify that: (1) permissive hypercapnia was accepted as part of the ventilation strategy; (2) plateau pressure was maintained below 30 cmH2O; (3) no neuromuscular blocking agents were used; (4) PEEP was titrated by two independent physicians blinded to the study using the ARDSnet low PEEP-FiO2 table to determine FiO2 and PEEP levels, targeting SpO₂ ≥ 88%. The rationale for selecting PEEP 5–10 cmH2O is that this range represents a substantial proportion of ARDS patients for whom current guidelines offer no clear recommendations. (Page 6, lines 125–134; Page 4, lines 81–87)

Comment 9 (Co-interventions and assessment of lung morphology): Please describe relevant co-interventions and whether they were balanced between groups, including prone positioning, recruitment manoeuvres, bronchodilator therapy, inhaled pulmonary vasodilators, corticosteroids, and neuromuscular blocking agents. It would also be useful to state whether patients underwent chest CT or routine lung ultrasound and to report, where available, the degree of atelectasis, consolidation, and recruitability.

Response: We have clarified that none of the enrolled patients received prone positioning, fiberoptic bronchoscopy, or neuromuscular blocking agents during the study period. All other treatments were identical between the two groups except for the suctioning method. Regarding lung morphology assessment, we did not perform routine chest CT or lung ultrasound as part of this study protocol; this has been acknowledged as a limitation and a direction for future research. (Page 7, lines 133–138; Page 20, lines 410–414)

Comment 10 (Clinical outcomes and length of stay): Even if the trial was not powered for clinical outcomes, the authors should report ICU length of stay, hospital length of stay, duration of mechanical ventilation, ventilator-associated pneumonia, reintubation or tracheostomy where applicable, and mortality.

Response: We have reported the available secondary clinical outcomes in the "Secondary Outcomes" section, including extubation rates, hospital survival, and mechanical ventilation survival. ventilator-associated pneumonia data were not systematically collected as part of this study protocol; we have noted this as a direction for future research. (Page 15, lines 299–306; Page 20, lines 410–414)

Comment 11 (Ethics and informed consent): The manuscript states that written informed consent was obtained, but it does not specify when consent was obtained, from whom it was obtained, or how consent was managed in deeply sedated patients without decision-making capacity. Please clarify whether consent was obtained from the patient, a legal representative, or through a deferred-consent procedure, and ensure that this is consistent with the ethics approval.

Response: Written informed consent was obtained from the patient's legal representative (next of kin) for all enrolled patients, as all patients were deeply sedated and lacked decision-making capacity at the time of enrollment. This is consistent with the ethics approval (No. KY2025-006).

Comment 12 (Discussion): The Discussion should be substantially reorganized. It should begin with a concise statement of the main findings, followed by a structured interpretation of each finding. The authors should then compare their results with previous studies of OS and CS, particularly studies conducted in patients receiving higher PEEP. The reasons why CS was associated with less immediate lung-volume loss but slower recovery should be discussed more clearly and cautiously. The current wording occasionally suggests clinical benefits or risks that were not directly measured in this study.

Response: We have substantially reorganized and revised the Discussion according to the reviewer's suggestion. Specifically: (1) The Discussion now begins with a concise summary of the principal findings. (2) The Discussion has been structured into clear subsections: "Lung volume: preservation advantage of CS and delayed recovery" and "Oxygenation: early oxygenation stability with CS." (3) We have compared our results with those of previous studies, including studies conducted in patients receiving higher PEEP (Yildirim et al.) and the study by Corley et al., acknowledging both consistencies and discrepancies. (4) The mechanism underlying the slower recovery of lung volume after CS has been discussed more cautiously, with explicit recognition that this is a physiological observation rather than an indicator of clinical harm. In addition, we have removed wording that could be interpreted as claiming clinical benefits not directly measured in this study. (Pages 15–20)

Comment 13 (Environmental and economic considerations): In a sustainability perspective, it would be valuable to include at least a descriptive comparison of the costs and material waste associated with closed versus open suctioning. Even a brief discussion of device use, disposable materials, and potential waste generation would improve the clinical relevance of the manuscript. Once these issues have been adequately addressed, the conclusions should be revised to reflect the corrected analyses and the physiological, rather than clinical-outcome, nature of the findings. There are some typos in Table 3.

Response: We thank the reviewer for the valuable comments. We have added environmental and sustainability considerations to the Discussion and revised the Conclusions to better reflect the physiological nature of our findings. We are also grateful for the correction of an extra minus sign in Table 3, which has now been fixed.

We sincerely hope that the revised manuscript now meets the standards for publication in PLOS One. We are grateful again to the editor and reviewers for their time and efforts.

Yours sincerely,

Jun Yang

Attachment

Submitted filename: Response to Reviewers.docx

pone.0351172.s005.docx^{(124.2KB, docx)}

PLoS One. doi: 10.1371/journal.pone.0351172.r003

Decision Letter 1

Vincenzo Lionetti

15 Sep 2026

Open versus Closed Suctioning on Lung Volume and Oxygenation in ARDS Patients with PEEP 5–10 cmH2O: A Randomized Controlled Trial

PONE-D-26-16870R1

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PLoS One. doi: 10.1371/journal.pone.0351172.r004

Acceptance letter

Vincenzo Lionetti

PONE-D-26-16870R1

PLOS One

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Supplementary Materials

S1 Table. The raw data.

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S1 File. CONSORT 2025 editable checklist.

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pone.0351172.s002.docx^{(31KB, docx)}

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pone.0351172.s003.docx^{(21.4KB, docx)}

Attachment

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Data Availability Statement

The minimal data set is available in the Supporting Information.

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PERMALINK

Open versus closed suctioning on lung volume and oxygenation in ARDS patients with PEEP 5–10 cmH2O: A randomized controlled trial

Haotian Gao

Yidie Ying

Jun Yang

Roles

Abstract

Objective

Methods

Results

Conclusions

Introduction

Methods

1 Participants

1.1 Inclusion criteria.

1.2 Exclusion criteria.

2 Study protocol

2.1 Randomisation.

2.2 Participants and interventions.

2.3 Suctioning procedure.

2.4 Outcome measures and data collection.

3 Statistical analysis

Results

1 Baseline characteristics

Fig 1. Guidelines Flow Diagram.

Table 1. Baseline characteristics of the patients.

2 Primary outcomes

2.1 △EELI (global).

Table 2. Intergroup comparison of △EELI (global) post-suctioning.

Fig 2. Comparison of △EELI (global) between groups.

Table 3. Post‑suctioning △EELI (global) versus baseline.

2.2 △EELI (ROI 1).

Fig 3. Comparison of △EELI in the non-dependent region between groups.

2.3 △EELI (ROI 2).

2.4 △EELI (ROI 3).

Fig 4. Comparison of △EELI in the gravity-dependent region between groups.

2.5 △EELI (ROI 4).

2.6 Percutaneous oxygen saturation.

Fig 5. SpO2 before and after suctioning.

2.7 Oxygenation index.

3 Secondary outcomes

4 Adverse events

Discussion

1 Lung volume: preservation advantage of CS and delayed recovery

2 Oxygenation: early oxygenation stability with CS

3 Study limitations

Conclusions

Supporting information

Acknowledgments

Data Availability

Funding Statement

References

Decision Letter 0

Vincenzo Lionetti

Roles

Author response to Decision Letter 1

Decision Letter 1

Vincenzo Lionetti

Roles

Acceptance letter

Vincenzo Lionetti

Roles

Associated Data

Supplementary Materials

Data Availability Statement

ACTIONS

PERMALINK

RESOURCES

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Links to NCBI Databases

Open versus closed suctioning on lung volume and oxygenation in ARDS patients with PEEP 5–10 cmH₂O: A randomized controlled trial

Fig 5. SpO₂ before and after suctioning.