The effects of Pressure-Controlled Volume-Guaranteed ventilation (PCV-VG) on Postoperative Pulmonary Complications (PPCs) of oral and maxillofacial patients undergoing free flap reconstruction: a randomized controlled trial

Abstract

Background

To analyze the effects of pressure-controlled volume-guaranteed ventilation (PCV-VG) and volume-controlled ventilation (VCV) on postoperative pulmonary complications (PPCs) after oral and maxillofacial surgery with free flap reconstruction.

Methods

This was a prospective, randomized, controlled trial comparing two intraoperative ventilation strategies. Two hundred and forty patients who underwent oral and maxillofacial surgery with free flap reconstruction were randomly allocated to either VCV group (n = 120) or the PCV-VG group (n = 120). After induction of anesthesia, for both modes of ventilation, the target tidal volume (VT) was 6 mL/kg and the respiratory rate was adjusted to avoid hypercarbia. The primary outcome was a composite of postoperative pulmonary complications within the first seven postoperative days. The peak and mean inspiratory pressures and dynamic compliance were recorded at T1(the time after the patients entered the operation room), T2 (the time of skin incision), T3 (the time when anastomosing blood vessels), T4 (the time of closure of the incision). And oxygenation index (OI) and arterial partial pressure of oxygen (PaO₂) / fraction of inspiration oxygen (FiO₂) were calculated and recorded at T1 and T4.

Results

The two groups had similar characteristics at baseline. 26.7% patients in PCV-VG group, and 34.2% patients in VCV group experienced PPCs within the first 7 days after surgery (P = 0.051). In the first 7 days after surgery, the PCV-VG group had a better postoperative survival probability, but without significant statistical differences (Log-rank test, P = 0.056). But in tracheotomy patients, PCV-VG group had a lower incidence of PPCs (P < 0.05). In addition, the PCV-VG group had a shorter length of stay in hospital after surgery (9 days vs. 10 days, P = 0.041). Furthermore, PCV-VG group had significantly lower peak inspiratory pressure and greater dynamic compliance than VCV group (P < 0.05). At the same time, OI and PaO₂/FiO₂ were better in PCV-VG group (P < 0.05).

Conclusions

For patients undergoing oral and maxillofacial surgery with free flap reconstruction who were at intermediate or high risk of developing PPCs, PCV-VG could shorten the length of stay in hospital and showed a trend toward being superior to VCV in its ability to provide ventilation with lower peak inspiratory pressure, greater dynamic compliance, and better oxygenation. Meanwhile, in tracheotomy patients, the PCV-VG group had a lower incidence of PPCs.

Trial registration

Chinese Clinical Trial Registry, www.chictr.org.cn, number: ChiCTR2200060865; Registered on June 12, 2022.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12893-025-03318-5.

Background

Postoperative pulmonary complications (PPCs) are a category of hospital-acquired respiratory events that occur within the first week following major surgeries. They are recognized as a major cause of morbidity and mortality for patients [1, 2]. Among the non-cardiothoracic surgeries that are most likely to interfere with respiratory function and are strongly linked to PPCs, head and neck surgery takes the third place [3], with an incidence of PPCs ranging from 18.8% to 47% [4–9]. Oral and maxillofacial surgery constitutes a distinct surgical sub-specialty of head and neck surgery, and is regarded as an intermediate and high-risk procedure for PPCs, particularly in the context of radical oral and maxillofacial cancer surgery involving free flap reconstruction or microvascular free tissue transfer [8, 9]. This assertion was further substantiated by our prior clinical trials [10, 11]. The following three reasons have been identified as the primary causes of the high incidence of PPCs in patients undergoing free flap reconstruction in oral and maxillofacial surgery. Firstly, in oral and maxillofacial surgery, due to the proximity of the patient’s surgical site to the respiratory system, the postoperative airway function is more or less affected [12]; Secondly, the surgical areas include the oral and maxillofacial and free flap areas, and free flap reconstruction is also required, resulting in long surgical time and mechanical ventilation times (mostly more than three hours), which may lead to ventilation-induced lung injury (VILI) [13]; Third, during harvest of the free fibular or forearm flap, a tourniquet is applied to the donor limb to establish a bloodless surgical field and minimize bleeding, which may lead to tourniquet-associated limb ischemia reperfusion injury, further leading to secondary lung injury [14]. Consequently, it is imperative and urgent to prevent and reduce the occurrence of PPCs in such kind of patients, which is also the original intention of this study.

To date, there has been a paucity of high-quality evidence to support the efficacy of any interventions to prevent PPCs [1]. However, mechanical ventilation under general anesthesia has been found to play an important role in the development of PPCs [15–17]. Previously, our team studied the anesthesia regimen (propofol vs. sevoflurane) [11] and specific anesthetics (dexmedetomidine) [10] on the effects of PPCs of patients undergoing oral and maxillofacial surgery with free flap reconstruction, but further research is required. In light of the aforementioned reasons, namely of the high incidence of pulmonary complications following oral and maxillofacial surgery, the present study focuses on VILI, with the aim of studying the effects of different modes of ventilation on PPCs.

The conventional ventilation modes encompass pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV), each with its own set of advantages and limitations [15, 18]. VCV has the capacity to ensure the supply of tidal volume and to completely replace spontaneous breathing. However, VCV has been observed to result in elevated high peak inspiratory pressure during surgical procedures, which can potentially lead to lung injury. Conversely, PCV maintains airway pressure within the predefined pressure range. However, PCV can lead to tidal volume instability, which cannot guarantee minute ventilation, and requires constant adjustment of parameters by anesthesiologists [18–22]. A novel ventilation mode, termed pressure-controlled ventilation-volume guaranteed (PCV-VG), offers a dual-control mode of ventilation and an alternative to PCV or VCV, and has recently been adopted in clinical practice. PCV-VG represents a novel ventilation mode that integrates the merits of both VCV and PCV, leveraging the respective advantages of these modes to align mechanical ventilation closely with human lung physiology. This approach aims to improve oxygenation through pressure control to minimize potential airway injury while ensuring adequate tidal volume. It thereby addresses the key challenges inherent in conventional modes: unpredictable pressure fluctuations with VCV and variable tidal volumes with PCV [18, 19, 22–27]. Most previous studies on PCV-VG have focused on general surgery, laparoscopic procedures, or thoracic surgeries where patient demographics and risks differ significantly [22–27]. Our study targets a specialized population in head and neck surgery, which involves distinct challenges such as altered airway anatomy, higher rates of tracheotomy, and increased susceptibility to PPCs due to surgical site proximity to the respiratory system, which has not been extensively explored before [12–14, 28].

The present study was conducted with the objective of investigating the differential impact of PCV-VG and VCV on the incidence of PPCs following oral and maxillofacial surgery involving free flap reconstruction. We hypothesized that PCV-VG’s pressure-limiting properties would reduce barotrauma and improve dynamic compliance, thereby lowering PPC incidence compared to VCV.

Methods

Study design

This prospective, randomized, comparative clinical trial was conducted at the Department of Anesthesiology, Peking University Hospital of Stomatology, a tertiary level academic hospital in Beijing, China. Ethical approval was obtained from Peking University Hospital of Stomatology Biomedical Ethics Committee (No: PKUSSIRB-202270001) on 14 December 2021. The trial was registered with the Chinese Clinical Trials Registry, www.chictr.org.cn (No: ChiCTR2200060865) on 12 June 2022. This manuscript report adhered to CONSORT guidelines.

Written informed consent was obtained from all participating patients or their next of kin or legal representative, who were required to understand the description of the study given by the recruiter. The primary objective of the study was to assess the superiority of the intervention. Eligible patients were recruited and randomly assigned to receive either PCV-VG or VCV.

Participants

From July 2022 to March 2023, patients were included if they (1) were scheduled to undergo oral and maxillofacial surgery with free flap reconstruction under general anesthesia, (2) were 18 years old or older, (3) had an intermediate to high risk of developing PPCs as assessed by the Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) score [29](cumulative ARISCAT risk score was 26 or greater). Patients were excluded if they met the following criteria: (1) body mass index of 35 or greater, (2) severe chest wall malformation, or acute exacerbation of chronic obstructive pulmonary disease (AECOPD), or uncontrolled asthma (asthma control test ≤ 18), or pulmonary artery stenosis, or pulmonary hypertension, (3) complex cardiac malformation, or congestive heart failure or known preoperative left ventricular ejection fraction less than 30%, (4) severe liver dysfunction (Child-Pugh class C) or severe renal dysfunction (requiring renal replacement therapy), (5) history of mental illness, (6) refusal to participate in the clinical trial. Enrolled patients were randomly assigned to two equal groups: VCV group and PCV-VG group (120 patients each). Random allocation was performed using sealed envelopes.

Randomization and blinding procedure

The randomization sequence was computer-generated by an independent biostatistician using SAS 9.2 (SAS Institute, Cary, NC), maintaining a 1:1 allocation ratio. Sequentially numbered, opaque envelopes contained the assignment results, ensuring concealment. During the trial period, eligible participants were randomly assigned to receive either PCV-VG or VCV based on this sequence.

All study personnel—including surgical teams, nursing staff, and postoperative evaluators—alongside enrolled patients, remained blinded to treatment assignments throughout the investigation. Attending anesthesiologists were not blinded to group allocation due to the need for real-time ventilator mode management, but postoperative outcome assessors remained blinded throughout the study. Emergency unmasking was permitted exclusively for attending anesthesiologists managing critical events (e.g., life-threatening adverse reactions, refractory hemodynamic instability, or rapid clinical deterioration), allowing protocol adjustments. All instances of unblinding were formally documented, while primary analyses adhered strictly to the intention-to-treat (ITT) principle.

Interventions

Eligible patients were randomly allocated to either the PCV-VG ventilation group or the conventional VCV ventilation group. Participants assigned to the.

PCV-VG cohort received the novel pressure-controlled volume-guaranteed ventilation mode, while those in the control cohort underwent traditional volume-controlled ventilation.

Mechanical ventilation parameters were systematically established to align with lung-protective strategies throughout the surgical procedures. Inspired oxygen concentration (FiO₂) was maintained within 40–60% to balance oxygenation efficacy against potential oxygen toxicity risks. Tidal volumes, calculated based on predicted body weight rather than actual mass to mitigate volutrauma, were precisely regulated between 6 and 8 mL/kg. This weight adjustment methodology accounted for anthropometric variations while ensuring consistent lung stress distribution across diverse somatotypes. A fixed positive end-expiratory pressure of 5 cm H₂O was uniformly applied to prevent alveolar collapse during expiration, thereby optimizing functional residual capacity without compromising hemodynamic stability.

Respiratory frequency underwent dynamic titration guided by continuous capnography, with real-time adjustments targeting end-tidal carbon dioxide (EtCO₂) values of 35–45 mmHg. This physiological parameter optimization served dual purposes: maintaining acid-base homeostasis through controlled CO₂ elimination while preventing cerebral vasoconstriction associated with hypocapnia. The ventilation management strategy reflected contemporary protective ventilation paradigms, particularly crucial during prolonged surgical durations exceeding three hours where cumulative mechanical stress could potentiate ventilator-induced lung injury. Notably, these parameters remained constant across both study arms except for the fundamental difference in ventilation mode delivery mechanisms, creating controlled comparison conditions for evaluating PCV-VG versus VCV performance.

Anesthesia methods and perioperative managements

Preoperative preparation and antimicrobial prophylaxis​

All enrolled patients received standardized perioperative management under a unified clinical pathway. Following national guidelines (2015), antimicrobial prophylaxis with intravenous cefuroxime (1.5 g) was administered 30 min preoperatively. A supplemental dose was repeated intraoperatively for procedures exceeding 4 h.

Standard monitoring and vascular access​

Standard monitoring comprised electrocardiography, non-invasive blood pressure, pulse oximetry, end-tidal carbon dioxide, and airway pressure. Neuromuscular function was assessed via train-of-four (TOF) ratio, and anesthetic depth was monitored using the Bispectral Index™ (BIS). Invasive arterial pressure monitoring was established via contralateral dorsalis pedis artery cannulation post-induction.

Anesthesia induction and maintenance protocol

General anesthesia was uniformly induced through nasotracheal intubation. Pharmacological induction employed sequential administration of midazolam (0.05 mg/kg), sufentanil (0.3 µg/kg), propofol (2 mg/kg), and rocuronium bromide (0.6 mg/kg). Maintenance therapy featured target-controlled infusion (TCI) of propofol (plasma concentration 2–6 µg/mL) and remifentanil (0.5–6.5 ng/mL), ​with or without​ sevoflurane inhalation. Intraoperative titration of anesthesia depth was guided by real-time BIS values (maintained at 40–60), surgical stimulus intensity, and hemodynamic parameters. Supplemental analgesia was provided through sufentanil boluses (0.1–0.5 µg/kg) based on nociceptive response, while neuromuscular blockade was sustained with intermittent rocuronium administration (10 mg boluses) guided by TOF monitoring.

Fluid management and transfusion strategy​

Perioperative fluid resuscitation was guided by institutional enhanced recovery protocols, utilizing crystalloid solutions (predominantly lactated Ringer’s injection) colloid supplementation with 6% hydroxyethyl starch 130/0.4 sodium infusion. Packed red blood cell transfusion thresholds were strictly implemented when hemoglobin concentrations fell below 7 g/dL, ensuring hemodynamic stability while minimizing transfusion-associated risks.

Emergence and postoperative care pathway

At the end of the surgery, patients either retained the endotracheal tube or underwent tracheotomy. The standardized tracheotomy procedures were performed following confirmation of adequate neuromuscular recovery, defined by train-of-four ratios exceeding 0.9. All patients were subsequently transferred to the postoperative care unit for specialized monitoring until 08:30 on postoperative day 1, after which they transitioned to general surgical wards under continuous surveillance.

Postoperative analgesia was administered via a standardized intravenous patient-controlled analgesia (PCA) protocol for 48 h, containing:

• • Sufentanil: 1.0–1.5 µg/kg total dose.

• • Tropisetron: 10 mg.

• • Respiratory therapy included:

  Tri-daily nebulization with ambroxol (60 mg) and hydrocortisone (4 mg).

  High-frequency chest wall oscillation therapy three times daily for 5 days.”

  Decannulation typically occurred on postoperative day 5 following comprehensive airway assessment by oral and maxillofacial surgeons, contingent upon satisfactory wound healing and respiratory function. Multimodal rehabilitation strategies included protocol-driven early mobilization initiated on day 4, anticoagulation regimens (5-day courses of either aspirin or low-molecular-weight heparin), and tailored nutritional support through combined enteral-parenteral approaches, all aligned with institutional enhanced recovery after surgery (ERAS) pathways.

Outcome measures

Follow-up protocol​

Trained research personnel (uninvolved in clinical care) conducted in-person assessments at 10:00 AM and 2:00 PM daily for seven postoperative days, supplemented by 30-day mortality verification via telephone interviews. All evaluators underwent standardized protocol training prior to study initiation.

Primary endpoint​

The primary endpoint was defined as the occurrence of PPCs within 7 days after surgery. PPCs encompassed: respiratory infection, respiratory failure, pleural effusion, atelectasis, pneumothorax, bronchospasm, aspiration pneumonitis, pulmonary edema.

The diagnostic framework for individual PPCs maintained rigorous alignment with validated criteria established in foundational clinical investigations [2]. Severity stratification employed the Clavien-Dindo classification system [30], wherein only complications reaching grade II or higher were incorporated into primary incidence calculations.

Diagnostic determinations emerged through multidisciplinary consensus among attending clinicians spanning anesthesiology, critical care, and pulmonology specialties. This diagnostic paradigm integrated longitudinal clinical assessments including comprehensive history reviews, serial physical examinations, continuous physiological monitoring data, biomarker profiles, and radiological evidence. Each confirmed PPC event triggered systematic documentation capturing both the temporal onset (precise initial diagnosis timestamp) and evidentiary foundations supporting the diagnosis – incorporating radiographic characteristics, microbiological confirmation where applicable, and clinically defining symptom complexes.

The adjudication process required concordance across at least two independent specialists, ensuring diagnostic validity while maintaining blinding to ventilation group allocation throughout endpoint assessment. This methodological approach guaranteed both criterion standardization across all participants and audit-ready documentation of diagnostic rationales, fulfilling CONSORT guidelines for endpoint validation in perioperative trials.

Secondary endpoints

Secondary endpoints comprised the following parameters:

1. ​Incidence of individual PPCs within the initial 7 postoperative days;

2. Time to first PPC diagnosis: Interval between surgery completion and initial PPC detection during the 7-day postoperative period;

3. Severity grading of PPCs: Assessed using the Clavien-Dindo classification system for postoperative complications;

4. PPCs frequency: Total count of confirmed PPCs occurring within postoperative 7 days;

5. ​Non-pulmonary complications: Defined as clinically significant extrapulmonary events requiring intervention within 7 days post-surgery;

6. Postoperative length of stay: Duration from postoperative day 1 to discharge date;

7. 30-day mortality: Causes and timing of deaths occurring within 30 postoperative days.

Sample size calculation and statistical analysis

This trial enrolled patients undergoing oral and maxillofacial free flap reconstruction who were stratified as intermediate-to-high risk for PPCs based on validated predictive models. Our prior investigations demonstrated a baseline PPCs incidence of approximately 32% in such patients receiving VCV with 5 cm H₂O PEEP [10, 11]. We hypothesized that PCV-VG ventilation would reduce PPCs occurrence by 50%. Using a two-sample proportion test with bilateral significance (α = 0.05, power = 80%), the expected incidence rates were: Experimental group (PCV-VG): Pt = 0.16; Control group (VCV): Pc = 0.32. Given a 1:1 allocation ratio, the calculated minimum sample size was 108 patients per group. Accounting for an estimated 10% attrition rate, we planned to enroll 120 participants per group, yielding a total target enrollment of 240 patients.

All statistical analyses were conducted using SPSS Statistics version 24.0 (IBM Corp., Armonk, NY), with a two-tailed significance threshold of P < 0.05. Primary efficacy assessments employed ITT analysis. A per-protocol (PP) analysis was conducted as a supplementary sensitivity analysis.

Continuous variables were expressed as mean ± standard deviation when normally distributed, analyzed via independent samples t-test; for continuous variables that did not meet the assumption of normality (assessed using the Shapiro-Wilk test), data are presented as median [interquartile range], and comparisons were made using the Mann-Whitney U test. Categorical variables were reported as frequencies (%) and compared using Chi-square or Fisher’s exact tests. Baseline characteristics including demographic profiles, medical histories, perioperative medications, and management protocols underwent descriptive statistical summarization.

For the primary endpoint (PPCs occurrence within 7 postoperative days), Chi-square testing generated relative risk (RR) estimates with 95% confidence intervals (CI), complemented by frequency distributions. Secondary endpoints employed distribution-appropriate comparative methods: parametric continuous variables used t-tests, non-parametric variables employed Mann-Whitney U tests, and categorical variables applied Chi-square/Fisher’s exact tests. Time-to-event data underwent Kaplan-Meier survival analysis with log-rank testing. Subgroup analyses, including for tracheotomy patients, were conducted post-hoc to explore potential effect modifiers. These analyses should be considered hypothesis-generating and interpreted with caution due to the increased risk of type I error.

In addition to frequentist analysis, we conducted a Bayesian re-analysis of the primary outcome (PPCs incidence) to estimate the probability of a true treatment effect. We used a skeptical prior distribution (normal distribution centered on a risk ratio of 1.0 with a standard deviation of 0.2), representing doubt about a large effect size, as recommended for clinical trials. The analysis was performed using R software (version 4.2.0) with the ‘bayesmeta’ package, generating posterior distributions and the probability that the risk ratio is less than 1 (i.e., PCV-VG reduces PPCs).

Results

Participant flow

The flow of participants through each stage of the trial, including enrollment, allocation, follow-up, and analysis, is presented. The CONSORT-compliant flowchart detailing screening, eligibility, randomization, and group allocation is provided in ​Figure 1. From July 2022 to March 2023, 342 patients were assessed for eligibility, and 102 were excluded (25 for being enrolled in other studies, 51 for ARISCAT score < 26, 23 for surgeries canceled, 13 for refusing to participate). The remaining 240 participants were randomized equally to PCV-VG (n = 120) and VCV (n = 120) groups. Complete data were available for 110 PCV-VG and 108 VCV patients in the per-protocol analysis, with 10 and 12 exclusions respectively due to protocol deviations or loss to follow-up. This transparent recruitment pathway demonstrated robust methodological integrity throughout the trial period.

Fig. 1.

Flow diagram of patients through trial

Baseline and preoperative characteristics

Baseline demographic and clinical parameters were compared between the two study groups to confirm successful randomization. As detailed in ​Table 1, the PCV-VG and VCV groups demonstrated excellent homogeneity, with no statistically significant differences in age, sex distribution, ARISCAT risk scores, comorbidities, or preoperative laboratory values (all P > 0.05). Median age was comparable (PCV-VG: 58 years [IQR 54–64] vs. VCV: 61 [IQR 55–66], P = 0.274), as was male predominance (63.8% vs. 66.3%, P = 0.592). ARISCAT risk scores (28.32 ± 4.83 vs. 28.36 ± 4.82, P = 0.486) and ASA classifications showed no significant differences. Comorbidity profiles including respiratory (10.0% vs. 10.0%, P = 0.831), cardiovascular (51.3% vs. 42.5%, P = 0.213), and endocrine disorders (15.0% vs. 17.5%, P = 0.415) were balanced. Preoperative laboratory values including hemoglobin (13.54 ± 2.03 vs. 13.72 ± 1.92 g/dL, P = 0.295) and oxygenation indices (PaO₂/FiO₂ 414 ± 107 vs. 409 ± 139 mmHg, P = 0.314) further confirmed group equivalence at baseline. This balance at baseline confirms that the groups were comparable prior to the intervention, allowing for a valid comparison of outcomes.

Table 1.

Baseline patient demographic and preoperative Characteristics (ITT analysis)

	PCV-VG group (n = 120)	VCV group (n = 120)	P value
Age, year	58(54, 64)	61(55, 66)	0.274
Sex			0.592
Male	77(63.8)	80(66.3)
Female	43(36.3)	40(33.8)
High, cm	168.0(160.0,171.5)	166.00(160.0,172.0)	0.832
Weight, kg	60.50(55.0,69.5)	62.00(57.5,71.0)	0.284
BMI a, kg/m2	23.79(20.35,25596)	23.04(21.48,25.78)	0.905
Education year, year	9(8,16)	9(4,16)	0.226
Tobacco use	47(39.1%)	44(36.4%)	0.845
Alcohol use b	37(30.9%)	32(26.4%)	0.504
ARISCAT score c			0.312
Intermediate risk	115(95.5)	118(98.2)
High risk	5(4.5)	2(1.8)
Mean (SD)	28.32 ± 4.83	28.36 ± 4.82	0.486
ASA physical status classification d			0.838
1	24(20.0%)	25(20.9%)
2	92(76.4%)	95(79.1%)
3	4(3.6%)	0(0%)
NYHA heart failure class e			0.615
I	71(59.1%)	76(63.6%)
II	49(40.9%)	44(36.4%)
Comorbidity
Respiratory system disease	12(10.0%)	12(10.0%)	0.831
COPD	5(3.8%)	6(5.0%)	0.173
Asthma	3(2.5%)	2(1.3%)	0.316
Chronic bronchitis	3(2.5%)	6(5.0%)	0.484
Tuberculosis history	2(1.3%)	3(2.5%)	0.765
Lung infection within the last month	0(0.0%)	0(0.0%)	> 0.999
Cardiovascular system diseases	62(51.3%)	51(42.5%)	0.213
Hypertension	41(33.8%)	36(30.0%)	0.611
Coronary artery disease	12(10.0%)	6(5.0%)	0.230
Arrhythmia	9(7.5%)	9(7.5%)	> 0.999
Endocrine system diseases	18(15%)	21(17.5%)	0.415
Diabetes	14(11.3%)	18(15.0%)	0.483
Thyroid Diseases	5(3.8%)	3(2.5%)	0.635
Central Nervous System Diseases	17(13.8%)	15(12.5%)	0.678
TIA	3(2.5%)	5(3.8%)	0.701
Ischemic stroke	12(10.0%)	11(8.8%)	0.605
Hemorrhagic stroke	2(1.3%)	0(0.0%)	0.897
Other	8(6.3%)	9(7.5%)	0.817
Liver dysfunction	5(3.8%)	5(3.8%)	> 0.999
Renal dysfunction	3(2.5%)	5(3.8%)	0.701
Age-adjusted Charlson Comorbidity Index (aCCI)	5(4,6)	5(4,5)	0.435
Preoperative laboratory tests
Alb, g/L	39.99 ± 5.12	40.01 ± 4.56	0.813
Hb, g/L	13.54 ± 2.03	13.72 ± 1.92	0.295
Scr, µmol/L	86.93 ± 21.91	91.78 ± 28.90	0.091
Glu, mmol/L	5.98 ± 1.89	5.7 ± 1.43	0.085
Alt, umol/L	14.99(11.48,26.43)	15.97(12.01,27.01)	0.786
Na+, mmol/L	140.11 ± 2.91	140.83 ± 2.52	0.096
K+, mmol/L	3.98 ± 0.42	4.01 ± 0.39	0.227
Coagulation abnormality	3(3.8%)	4(5.0%)	0.321
Preoperative SpO2			0.978
≥96	100(83.6%)	103(85.5%)
91–95	18(15.0%)	16(13.6%)
≤90	2(1.3%)	1(1.0%)
Preoperative anemia(Hb ≤ 10 g/dl)	14(11.3%)	8(6.3%)	0.263
Preoperative lung-related investigations
Abnormal preoperative chest radiograph	6(5.0%)	12(10.0%)	0.230
Preoperative pulmonary function tests	54(45.0%)	71(58.8%)	0.214
Abnormal pulmonary function tests	57(47.2%)	61(51.1%)	0.389
Hypoventilation	37(30.6%)	43(36.2%)	0.402
Diffusion hypofunction	20(16.7%)	18(14.9%)	0.786
Arterial blood gas analysis	32(26.3%)	38(31.3%)	0.836
PH	7.42 ± 0.03	7.42 ± 0.04	0.627
PaO2, mmHg	86.34 ± 28.65	88.21 ± 30.14	0.426
PaCO2, mmHg	37.98 ± 4.22	38.23 ± 4.51	0.284
PaO2/FiO2, mmHg	414 ± 107	409 ± 139	0.314
SaO2, %	95.36 ± 2.0	95.51 ± 1.99	0.296
Malignant tumor	104(86.4%)	105(87.3%)	0.924

Data are presented as median (interquartile range), mean ± SD, or n (%);P-values derived from Mann-Whitney U test

Abbreviations: IQR interquartile range, BMI body mass index, ARISCAT Assess Respiratory Risk in Surgical Patients in Catalonia, ASA American Society of Anesthesiology, NYHA New York Heart Association, SpO₂ oxygen saturation as measured by pulse oximetry, Hb Hemoglobin, COPD chronic obstructive pulmonary disease

^a Calculated as weight in kilograms divided by height in meters squared

^b Defined as more than 2 drinks per day during the past 2 weeks

^c Score range is from 0 to 123; higher scores indicate a higher risk of postoperative pulmonary complications. Patients with scores of 26 to 44 are considered at intermediate risk; those with scores more than 44 are considered at high risk

^d Score range is from 1 to 6 and includes a classification for normal health as 1; mild systemic disease, 2; severe systemic disease, 3; severe systemic disease that is a constant threat to life,4. patients with scores of 5 or 6 were excluded

^e Score range is from I to IV; higher scores indicate a higher extent of heart failure. Patients without limitation of their ordinary physical activity are classified NYHA class I; those with slight limitation of their activity are classified as NYHA class II. Patients with scores of III or IV were excluded

Intraoperative parameters and hemodynamics

Surgical and anesthetic management was standardized across groups (Table 2). Flap distribution (P = 0.827), operative duration (median 318 vs. 320 min, P = 0.683), and limb ischemia time (58 vs. 59 min, P = 0.622) showed no significant differences. Tracheotomy rates were nearly identical (54.2% vs. 53.3%, P = 0.635). Medication administration including opioids (sufentanil 30[20–40] vs. 30[25–45] µg, P = 0.083) and fluids (crystalloids 1700[1700–2200] vs. 1700[1600–2200] ml, P = 0.947) demonstrated comparable intraoperative management protocols.

Table 2.

Intraoperative Characteristics (ITT analysis)

	PCV-VG group (n = 120)	VCV group (n = 120)	P value
Flap type			0.827
Forearm	27(22.5%)	26(21.7%)
Fibula	36(30%)	37(30.8%)
Thigh	28(23.3%)	29(24.2%)
Ilium	16(13.3%)	15(12.5%)
Groin	11(9.17%)	12(10%)
Other	2(1.67%)	1(0.8%)
Cervical lymph node dissection			0.917
No	25(20.9%)	24(19.7%)
Unilateral	69(57.1%)	68(56.9%)
Bilateral	26(22.0%)	28(23.4%)
Duration of surgery, min a	318(257, 390)	320(261, 392)	0.683
Duration of anesthesia, min b	359(301, 437)	361(299, 441)	0.823
Duration of limb ischemia time, min c	58(52, 72)	59(51, 69)	0.622
At the PACU			0.635
Tracheotomy	65(54.2%)	64(53.3%)
With tracheal tube	55(45.8%)	56(46.7%)
Intraoperative medication
Sufentanil, µg	30(20, 40)	30(25, 45)	0.083
Propofol, mg	2400(2050, 2510)	2500(2000, 2700)	0.092
Remifentanil, µg	2550(2300, 3200)	2625(1700, 3000)	0.365
Dexmedetomidine, µg	86(68, 180)	87(65, 181)	0.362
Dexamethasone	69(86.3%)	64(80.0%)	0.367
Atropine	1(1.3%)	1(1.3%)	> 0.999
Penehyclidine	56(70.0%)	58(72.5%)	0.724
Crystalloids, ml	1700 (1700, 2200)	1700 (1600, 2200)	0.947
Colloids, ml	500 (500, 500)	500 (500, 500)	0.149
Blood transfusion, ml	0(0.0%)	0(0.0%)	0.896
Estimated blood loss during surgery, ml	300(200, 400)	300(200, 350)	0.508
Urine output, ml	675(400, 900)	500(350, 700)	0.066
Total intraoperative infusion, ml	1450(1000, 1900)	1450(1075, 1875)	0.895

Data are presented as median (interquartile range), or n (%)

Abbreviations: PACU post anesthesia care unit

P-values derived from Mann-Whitney U test

^a Calculated as the time between skin incision and closure of the incision

^b Calculated as the time from the start of induction to the patient leaving the operating room

^c Calculated as the time from the beginning of inflation to the end of exhalation of the tourniquet in the limb

Intraoperative hemodynamics remained stable and comparable at all measured timepoints (Table 3). Heart rates (e.g., T3: 66[60–72] vs. 69[61–75]/min, P = 0.657) and mean arterial pressures (e.g., T4: 84[79–89] vs. 86[80–89] mmHg, P = 0.785) showed no statistically significant variations, confirming that ventilation modes did not differentially impact cardiovascular function during surgery.

Table 3.

Intraoperative hemodynamics (ITT analysis)

	PCV-VG group(n = 120)	VCV group(n = 120)	P value
Heart rate,/min
T1	65(60, 70)	69(65, 74)	0.123
T2	60(57, 65)	61(58, 66)	0.786
T3	66(60, 72)	69(61, 75)	0.657
T4	62(56, 68)	65(60, 70)	0.569
Mean arterial pressure, mmHg
T1	85(80, 91)	89(82, 93)	0.149
T2	82(78, 86)	86(80, 90)	0.235
T3	84(80, 89)	85(80, 90)	0.334
T4	84(79, 89)	86(80, 89)	0.785

Data are presented as median (interquartile range)

P-values derived from Mann-Whitney U test

Ventilation mechanics​ and gas exchange

PCV-VG demonstrated superior respiratory mechanics throughout the procedure (Table 4). Peak inspiratory pressures were significantly lower at closure (T4: 18.21 ± 1.87 vs. 22.65 ± 3.89 cm H₂O, P < 0.001) (Fig. 2), while dynamic compliance was substantially higher during vascular anastomosis (T3: 58.21 ± 2.43 vs. 51.35 ± 1.73 mL/cm H₂O, P < 0.001) (Fig. 3). These findings substantiate the mechanistic advantage of PCV-VG in providing lung-protective ventilation with lower driving pressures and improved lung distensibility.

Table 4.

Intraoperative ventilation parameters (ITT analysis)

	Group	T1 a	T2 b	T3 c	T4 d
Peak pressure, cm H2O	PCV-VG	16.25 ± 1.38	16.31 ± 1.27	17.32 ± 2.51	18.21 ± 1.87
	VCV	16.32 ± 1.36	16.45 ± 1.31	18.45 ± 3.24	22.65 ± 3.89
Platform pressure, cm H2O	PCV-VG	10.23 ± 1.39	10.20 ± 2.32	12.98 ± 1.45	13.10 ± 2.34
	VCV	10.20 ± 1.10	10.23 ± 0.95	15.23 ± 2.31	16.34 ± 1.62
Dynamic compliance, ml/cm H2O	PCV-VG	62.32 ± 0.97	61.33 ± 1.32	58.21 ± 2.43	51.32 ± 1.93
	VCV	61.99 ± 1.32	60.23 ± 1.72	51.35 ± 1.73	40.38 ± 2.31
Exhaled tidal volume, ml	PCV-VG	480.2 ± 23.4	481.1 ± 25.1	481.0 ± 21.2	480.8 ± 19.5
	VCV	480.4 ± 24.1	480.2 ± 30.1	481.1 ± 29.1	481.0 ± 10.4
Respiratory rate,/min	PCV-VG	12.21 ± 0.82	12.34 ± 0.91	13.02 ± 0.76	14.01 ± 0.93
	VCV	12.34 ± 0.73	12.21 ± 0.56	13.06 ± 0.98	14.32 ± 0.91
End-expiratory carbon dioxide, mmHg	PCV-VG	32.23 ± 2.51	34.24 ± 2.91	39.21 ± 4.01	40.82 ± 3.01
	VCV	32.45 ± 3.14	33.27 ± 3.31	38.91 ± 4.10	40.29 ± 3.81

Data are presented as mean ± SD

^a the time after the patients entered the operation room

^b the time of skin incision

^c the time when anastomosing blood vessels

^d the time of closure of the incision

Fig. 2.

Comparison of peak pressure in two groups

Fig. 3.

Comparison of dynamic compliance in two groups

Oxygenation efficiency significantly favored PCV-VG by the end of surgery (Table 5). At closure (T4), Oxygenation Index was more favorable (2.14 ± 0.34 vs. 3.17 ± 0.45, P < 0.001) (Fig. 4), and PaO₂/FiO₂ ratio was markedly higher (488 ± 108 vs. 402 ± 99 mmHg, P < 0.001) (Fig. 5). These differences emerged during the procedure, with comparable values at baseline (T1), indicating progressive benefits under PCV-VG ventilation during prolonged surgery. The superior gas exchange observed with PCV-VG indicates enhanced oxygenation efficiency, likely due to improved alveolar recruitment and ventilation-perfusion matching.

Table 5.

Intraoperative gas exchange (ITT analysis)

	Group	T1 a	T4 b
PH	PCV-VG	7.41 ± 0.02	7.36 ± 0.01
	VCV	7.39 ± 0.01	7.35 ± 0.02
PaO2, mmHg	PCV-VG	123.34 ± 28.65	203.32 ± 30.14
	VCV	122.67 ± 42.19	192.22 ± 29.82
PaCO2, mmHg	PCV-VG	31.28 ± 2.11	38.78 ± 3.21
	VCV	31.45 ± 2.20	45.24 ± 3.54
OI	PCV-VG	1.68 ± 0.24	2.14 ± 0.34
	VCV	1.64 ± 0.23	3.17 ± 0.45
PaO2/FiO2	PCV-VG	414 ± 107	488 ± 108
	VCV	413 ± 139	402 ± 99
SaO2	PCV-VG	97.37 ± 2.01	99.23 ± 0.30
	VCV	97.54 ± 1.99	99.21 ± 0.59

Data are presented as mean ± SD

^a the time after the patients entered the operation room

^b the time of closure of the incision

Fig. 4.

Comparison of oxygenation index in two groups

Fig. 5.

Comparison of PaO₂/FiO₂ ratio in two groups

Postoperative course

Recovery parameters remained similar between groups (Table 6). PACU stay duration (855[675–970] vs. 923[730–1020] minutes, P = 0.073) and tracheotomy tube duration (5 [5, 6] vs. 5 [5, 6] days, P = 0.551) showed no significant differences. Pain scores at surgical sites and sleep patterns across postoperative days 1–3 were statistically comparable (all P > 0.05), indicating equivalent postoperative comfort and recovery trajectories.

Table 6.

Postoperative characteristics (ITT analysis)

	PCV-VG group (n = 120)	VCV group (n = 120)	P value
Length of stay in PACU, min	855(675, 970)	923 (730, 1020)	0.073
Time with tracheal tube, h	15.2(10.0, 22.5)	15.5(9.8, 23.1)	0.675
Time with tracheotomy tube, d	5(5,6)	5(5,6)	0.551
Total infusion, ml
The operation day	1860(1491,2325)	1997(1585,2345)	0.702
The first day after surgery	890(270,1807)	1010(310,1708)	0.742
The second day after surgery	890(50,1015)	825(58,1588)	0.717
NRS for oral and maxillofacial area pain
The first day after surgery	1(0,2)	1(0,2)	0.872
The second day after surgery	1(0,2)	1(0,2)	0.546
The third day after surgery	1(0,2)	1(0,2)	0.346
NRS for flap area
The first day after surgery	2(0,3)	2(0,4)	0.783
The second day after surgery	1(0,2)	1.5(0,2)	0.642
The third day after surgery	1(0,2)	1(0,2)	0.764
Sleep time, h
The first day after surgery	5.0(5.0, 7.0)	4.9(3.3, 7.0)	0.875
The second day after surgery	5.0(4.3, 6.0)	5.0(4.0, 6.0)	0.520
The third day after surgery	5.5(4.1, 6.5)	5.5(4.0, 6.4)	0.657

Data are presented as median (interquartile range)

Abbreviations: PACU post anesthesia care unit, NRS numeric rating scale

P-values derived from Mann-Whitney U test

Primary and secondary outcomes

Primary endpoint interpretation​

The incidence of postoperative pulmonary complications (PPCs) within 7 days demonstrated a non-significant trend toward reduction in the PCV-VG group compared to conventional VCV ventilation. In the ITT analysis, 26.7% (32/120) of PCV-VG patients experienced PPCs versus 34.2% (41/120) in the VCV group (relative risk [RR] = 0.78, 95% CI: 0.53–1.15, P = 0.051). This 7.5% absolute risk reduction approached but did not reach statistical significance and aligned with our pre-trial hypothesis of PCV-VG’s lung-protective benefits. The per-protocol analysis reinforced this trend with 28.2% (31/110) incidence in PCV-VG versus 36.1% (39/108) in VCV (RR = 0.61, 95% CI: 0.53–1.31, P = 0.050)（See Supplementary Material). The consistent direction of effect across analytical methods suggests biological plausibility despite borderline statistical significance in the primary analysis. (Table 7) ​.

Table 7.

Primary and secondary outcomes of PCV-VG group and VCV group (ITT analysis)

	PCV-VG group(n = 120)	VCV group(n = 120)	RR(95% CI)	P value
Primary outcome
Overall incidence of PPCs(ITT analysis)	32(26.7%)	41(34.2%)	0.56(0.35 ~ 1.22)	0.051
Secondary outcomes
Incidence of each PPC
Respiratory infection	12(10.0%)	13(10.8%)	0.64(0.41 ~ 4.16)	0.823
Respiratory failure	8(6.7%)	10(8.3%)	0.41(0.13 ~ 1.60)	0.182
Pleural effusion	0(0%)	3(2.4%)		0.172
Atelectasis	11(9.2%)	12(10.0%)	0.31(0.42 ~ 1.57)	0.289
Pneumothorax	0(0%)	0(0%)		> 0.999
Bronchospasm	0(0%)	1(1.3%)		0.316
Aspiration pneumonitis	0(0%)	0(0%)		> 0.999
Pulmonary edema	1(1.2%)	2(1.7%)	0.49(0.06 ~ 3.41)	0.661
he time to first diagnosis of PPCs, n day after surgery a	4(2, 5)	3(2, 5)		0.731
Severity of PPCs				0.897
II	29(24.2%)	36(30.0%)
III a	1(0.8%)	1(0.8%)
III b	0(0.0%)	0(0.0%)
IV a	2(1.7%)	3(2.5%)
IV b	0(0.0%)	1(0.8%)
V	0(0.0%)	0(0.0%)
The number of PPCs b
0	88(73.3%)	79(65.8%)	1.28(0.27 ~ 2.23)	0.792
1	27(22.5%)	33(27.5%)	0.48(0.36 ~ 1.03)	0.213
2	5(4.2%)	8(6.7%)	0.61(0.31 ~ 2.48)	0.411
Tracheotomy subgroup PPCs			0.38(0.36 ~ 0.84)	0.032
Tracheotomy subgroup(n = 65 in the PCV-VG group and n = 64 in the VCV group, total n = 129)	20/65(30.8%)	29/64(45.3%)
Endotracheal intubation subgroup(n = 55 in the PCV-VG group and n = 56 in the VCV group, total n = 111)	8/55(14.5%)	5/56(8.9%)
Postoperative extrapulmonary complications c	19(15.8%)	28(23.3%)	0.68(0.05 ~ 2.14)	0.341
Central nervous system	2(1.7%)	6(5.0%)	0.33(0.03 ~ 1.45)	0.215
Stroke	0(0.0%)	0(0.0%)		> 0.999
TIA	1(0.8%)	2(1.7%)	0.50(0.06 ~ 2.45)	0.452
Delirium	1(0.8%)	4(3.3%)	0.25(0.03 ~ 2.19)	0.173
Circulatory system	6(5.0%)	7(5.8%)	0.86(0.33 ~ 4.19)	0.744
Acute myocardial infarction	0(0.0%)	1(0.8%)		0.943
Circulatory insufficiency	1(0.8%)	1(0.8%)	1.00(0.06 ~ 15.71)	> 0.999
Anemic d	3(2.5%)	2(1.7%)	1.50(0.26 ~ 8.74)	0.650
New-onset arrhythmia	2(1.7%)	3(2.5%)	0.67(0.13 ~ 2.39)	0.871
Surgical complications
Second operation e	4(3.3%)	6(5.0%)	0.67(0.20 ~ 2.27)	0.514
Infection-related complications	4(3.3%)	7(5.8%)	0.57(0.04 ~ 1.45)	0.467
Extra-pulmonary infection	2(1.7%)	4(3.3%)	0.50(0.09 ~ 2.65)	0.405
Sepsis	2(1.7%)	3(2.5%)	0.67(0.11 ~ 2.10)	0.576
Other complications	3(2.5%)	2(1.7%)	1.50(0.23 ~ 3.19)	0.421
Postoperative hospital stays, days	9(8, 11)	10(9, 11)		0.041
All-cause mortality 30 days after surgery	0(0.0%)	0(0.0%)		> 0.999

Data are presented as median (interquartile range), or n (%)

Abbreviations: PPCs postoperative pulmonary complications

P-values derived from Mann-Whitney U test

^a Indicated the time from end of surgery to first diagnosis of PPCs within 7 days after surgery

^b Indicated the number of diagnosed individual PPCs within 7 days after surgery

^c Defined as complications other than PPCs that occur during operation and within 7 days after surgery, and require therapeutic intervention

^d Defined as hemoglobin less than 9 g/dL

^e Included hematoma or vascular crisis exploration within 7 days after surgery

Bayesian re-analysis of the primary outcome supported the trend observed in frequentist analysis. The posterior distribution indicated a 96.3% probability that PCV-VG reduces PPCs (risk ratio < 1), with a median risk ratio of 0.78 (95% credible interval: 0.56 to 1.05). This suggests a high probability of a true treatment effect, consistent with the 22% relative risk reduction observed.

Secondary outcomes analysis​

Composition of PPCs

Respiratory infections constituted the most frequent complication (10.0% PCV-VG vs. 10.8% VCV, P = 0.823), followed by atelectasis (9.2% vs. 10.0%, P = 0.289). The VCV group demonstrated higher rates of pleural effusions (0% vs. 2.4%, P = 0.172) and respiratory failure (6.7% vs. 8.3%, P = 0.182), though these differences did not reach statistical significance. Importantly, no cases of pneumothorax or aspiration pneumonitis occurred in either group. (Table 7)

Severity and burden

When assessing complication severity using Clavien-Dindo classification, fewer PCV-VG patients experienced Grade II complications requiring pharmacological intervention (24.2% vs. 30.0%). The proportion of patients with multiple concurrent PPCs was lower in the PCV-VG group (4.2% vs. 6.7% for ≥ 2 complications, P = 0.411), indicating reduced cumulative morbidity. The median time to first PPC diagnosis was comparable (4 vs. 3 days, P = 0731), suggesting PCV-VG’s benefit lies in prevention rather than delayed onset. (Table 7)

Time-to-event and hospitalization impact

The temporal progression of complication risk was further elucidated through Kaplan-Meier analysis (Fig. 6), revealing a clinically protective effect of PCV-VG beginning at postoperative day 3, though without significant difference (Log-rank test, P = 0.056).

Fig. 6.

Comparative Probability of Remaining Free from Postoperative Pulmonary Complications (PPCs) over Time. Kaplan-Meier analysis demonstrating the probability of PPCs-free survival among patients receiving PCV-VG (blue line) versus conventional VCV ventilation (red line) during the first 7 postoperative days

A statistically significant reduction in postoperative hospitalization duration was observed (median 9 days [IQR 8–11] vs. 10 days [9–11], P = 0.041). This one-day difference represents a 10% reduction in hospital stay as detailed in Fig. 7, translating to substantial resource savings while maintaining patient safety, as evidenced by comparable 30-day mortality (0% in both groups). (Table 7)

Fig. 7.

Comparison of Length of Stay in Hospital in two groups. Box-plot analysis demonstrates significantly shorter hospitalization for PCV-VG recipients (median 9 days [IQR 8–11]) versus VCV (median 10 days [9–11]), *P = 0.041. This 10% reduction in median stay translates to clinically meaningful resource savings

Extrapulmonary complications

Rates of non-pulmonary complications were balanced between groups, including neurological events (2.5% vs. 7.5%, = 0.215), cardiovascular issues (7.5% vs. 8.8%, = 0.744), and surgical complications requiring reoperation (5.0% vs. 7.5%, = 0.514). (Table 7)

Subgroup analyses

Stratification by airway management approach revealed differential ventilation efficacy. In a post-hoc subgroup analysis of patients who underwent tracheotomy (n = 65 in the PCV-VG group and n = 64 in the VCV group, total n = 129), the incidence of PPCs was 30.8% (20/65) in the PCV-VG group versus 45.3% (29/64) in the VCV group (P = 0.032, Chi-square test). This represents a 16.0% absolute risk reduction and a 35% relative risk reduction in this subgroup (Table 7，Fig. 8), correlating with intraoperative respiratory mechanics advantages.​In contrast, no significant differences were observed in all-patient cohorts (32.0% vs. 41.0%) or intubation subgroups (14.5% vs. 8.9%). This subgroup-specific benefit aligns with PCV-VG’s pressure-limiting properties mitigating barotrauma risks in surgically altered airways.

Fig. 8.

Differential Incidence of Postoperative Pulmonary Complications (PPCs) by Ventilation Mode and postoperaitive airway management approach. Incidence of Postoperative Pulmonary Complications (PPCs) stratified by ventilation mode and postoperaitive airway management approach. Black bars: PCV-VG group; gray bars: VCV group. Asterisk denotes statistically significant difference in tracheotomy patients (P < 0.05)

Discussion

This randomized controlled trial demonstrated that PCV-VG mode provided significant physiological advantages over VCV in patients undergoing complex oral and maxillofacial surgery with free flap reconstruction. While the primary outcome of overall PPCs reduction showed a strong trend without reaching conventional statistical significance (26.7% vs. 34.2%, P = 0.051), we observed clinically important improvements in several key areas: significantly better intraoperative respiratory mechanics with lower peak inspiratory pressures and improved dynamic compliance, superior oxygenation parameters, a statistically significant reduction in hospital length of stay (9 vs. 10 days, P = 0.041), and most notably, a substantial reduction in PPCs incidence among tracheotomy patients (30.8% vs. 45.3%, P = 0.032).

Although the primary outcome yielded a P-value of 0.051, the observed 7.5% absolute risk reduction (22% Relative Risk Reduction) warrants clinical consideration. In the context of perioperative interventions, an Absolute Risk Reduction of this magnitude is substantively important. This suggests that our findings, while not meeting traditional statistical thresholds, may still reflect a clinically meaningful protective effect of PCV-VG, particularly given the high-risk population studied. In addition, as supported by Bayesian analysis (96.3% probability of benefit), the trend toward PPCs reduction with PCV-VG, though not statistically significant in frequentist terms, may still reflect a clinically meaningful effect.

Our findings align with emerging evidence supporting PCV-VG in various surgical populations. For instance, studies in laparoscopic and thoracic surgeries have reported similar reductions in peak airway pressures and improvements in compliance with PCV-VG compared to VCV [13, 18, 22, 23, 25, 28]. However, the effect size in our study (22% relative risk reduction in PPCs) is notably larger than that observed in general abdominal surgery cohorts, where meta-analyses typically report absolute risk reductions of 5–8% [17]. This discrepancy may be attributed to the unique vulnerabilities of head and neck surgery patients, who experience direct airway manipulation, prolonged mechanical ventilation, and increased risk of aspiration due to surgical site proximity to the respiratory system [8–14]. In such contexts, PCV-VG’s ability to deliver stable tidal volumes with minimal pressure swings may be particularly beneficial in mitigating ventilator-induced lung injury (VILI) and atelectasis. Lower peak pressures with PCV-VG likely mitigated barotrauma, while stable tidal volumes prevented volutrauma—synergistically reducing VILI risk [13, 17]. This is especially critical in prolonged surgeries (> 3 h), where cumulative mechanical stress exacerbates pulmonary vulnerability [20]. On the other hand, the 13% higher PaO₂/FiO₂ ratio in PCV-VG group in our study further confirmed enhanced oxygenation efficiency of PCV-VG, likely due to improved alveolar recruitment and ventilation-perfusion matching [23, 26].

The most compelling finding of our study was the significant protective effect of PCV-VG in tracheotomized patients (30.8% vs. 45.3% PPCs, P = 0.032). This subgroup-specific benefit can be explained by several mechanisms beyond the well-documented reduction in peak airway pressures. First, the decelerating flow pattern of PCV-VG may enhance secretion clearance by maintaining higher mean airway pressures without increasing peak pressures, thus reducing the risk of mucus plugging and postoperative pneumonia—a common issue in tracheotomy patients with impaired cough reflex [13]. Second, PCV-VG’s adaptive pressure control may better accommodate the altered airway anatomy during the operation, where changes in airway resistance and compliance require a ventilation mode that can respond dynamically to prevent hyperinflation or collapse. Finally, PCV-VG likely improves ventilation–perfusion matching by promoting more homogeneous gas distribution, which is crucial in patients with potential ventilation inequalities due to surgical manipulation or sedation effects [4, 6, 9, 10]. The post-hoc analysis of tracheotomy patients suggested a potential benefit of PCV-VG in reducing PPCs; however, this finding should be interpreted with caution as it was not pre-specified and may be subject to type I error. It generated a hypothesis for future randomized trials focused on this high-risk subgroup. But we still could infer that these mechanisms collectively contribute to the reduced PPCs incidence and shorter hospital stay observed in this subgroup. The 1-day reduction in postoperative hospitalization (9 vs. 10 days; P = 0.041) underscores PCV-VG’s economic and clinical value. Shorter stays reflect fewer complications and accelerated recovery, potentially reducing healthcare costs by ~ 15% based on institutional data [12]. Importantly, PCV-VG did not increase extrapulmonary complications or mortality, supporting its safety profile.

Innovation and Clinical Significance

Unique Population Focus: Our study enrolled patients with ARISCAT scores ≥ 26, indicating intermediate-to-high risk for PPCs, and focused on those undergoing free flap reconstruction—a procedure with prolonged mechanical ventilation times and unique physiological stresses (e.g., tourniquet-induced ischemia-reperfusion injury). This contrasts with most trials that include broader surgical populations.

Mechanistic Insights: We elaborated on the novel mechanistic insights, such as the role of PCV-VG in enhancing secretion clearance and adaptation to altered airway anatomy in tracheotomy patients, which emerged from our subgroup analysis. This goes beyond the usual focus on peak pressures and compliance, offering a deeper understanding of why PCV-VG might be beneficial in this specific context.

Clinical Implications: Our study provided the first evidence-based guidance on ventilation mode selection for oral and maxillofacial surgery, potentially influencing clinical guidelines and practice in a niche but high-risk area. For instance, the finding that PCV-VG reduces PPCs in tracheotomized patients (a subgroup with heightened vulnerability) could lead to tailored ventilation strategies that improve outcomes and reduce hospital stays.

In summary, our study innovates by demonstrating that PCV-VG ventilation offers some advantages in a high-risk, understudied population—oral and maxillofacial surgery patients undergoing free flap reconstruction. Unlike previous research, we show that PCV-VG’s benefits are particularly pronounced in tracheotomized patients, likely due to its ability to mitigate barotrauma and optimize gas exchange in surgically altered airways. This work fills a critical gap in the literature and provides a foundation for personalized ventilation strategies in complex head and neck surgeries.

While our study focused specifically on oral and maxillofacial surgery patients, the physiological advantages of PCV-VG observed in our trial—particularly its ability to maintain stable tidal volumes with lower peak pressures and improved dynamic compliance—suggest potential applications in other surgical specialties. For instance, in abdominal and laparoscopic surgeries requiring Trendelenburg positioning, PCV-VG may mitigate the effects of increased intra-abdominal pressure on respiratory mechanics, potentially reducing postoperative pulmonary complications [6, 18, 21, 22, 25]. Similarly, in thoracic surgeries requiring one-lung ventilation, PCV-VG’s ability to optimize oxygenation while minimizing barotrauma could prove particularly beneficial[23.26]. The mode’s adaptive pressure control may also offer advantages in obese patients undergoing various procedures, where altered respiratory mechanics increase susceptibility to ventilation-induced lung injury [21]. Future research should explore these potential applications across different surgical populations and settings.

Limitations and strengths

Our study has several limitations. First, it was conducted at a single center with a relatively small sample size, which may limit generalizability. Second, we focused on short-term outcomes; long-term effects of ventilation mode on pulmonary function remain unknown. Third, our study focused on intermediate-to-high-risk patients (ARISCAT ≥ 26), limiting generalizability to lower-risk populations. The borderline significance of the primary outcome (P = 0.051) may reflect insufficient power for subgroup interactions, though the tracheotomy-specific effect reached statistical significance. Future research should include larger multicenter RCTs to validate these findings, investigate the mechanisms underlying PCV-VG’s benefits (e.g., through biomarker analysis of lung injury), and explore the integration of PCV-VG with other protective strategies (e.g., driving pressure-guided ventilation) in diverse surgical populations.

Conclusion

For patients undergoing oral and maxillofacial free flap reconstruction, PCV-VG could improve intraoperative respiratory mechanics, enhances oxygenation, and showed a trend toward reducing PPCs incidence compared to conventional VCV. The 22% relative risk reduction in PPCs—particularly pronounced in tracheotomy recipients (35% reduction)—combined with shorter hospital stays, positions PCV-VG as a promising lung-protective strategy for this high-risk population.

Abbreviations

PPCs

Postoperative pulmonary complications

PCV-VG

Pressure-controlled volume-guaranteed ventilation

VCV

Volume-controlled ventilation

VT

Tidal volume

OI

Oxygenation index

PaO₂

Arterial partial pressure of oxygen

FiO₂

Fraction of inspiration oxygen

VILI

Ventilation-induced lung injury

ARISCAT

Assess Respiratory Risk in Surgical Patients in Catalonia

AECOPD

Acute exacerbation of chronic obstructive pulmonary disease

ITT

Intention-to-treat

EtCO₂

End-tidal carbon dioxide concentration

TOF

Train-of-Four

BIS

Bispectral Index

TCI

Target-controlled infusion

ERAS

Enhanced recovery after surgery

PP

Per-protocol

RR

Relative risk

CI

Confidence interval

NRS

Numeric rating scale

ASA

American Society of Anesthesiologists

IQR

Interquartile range

BMI

Body mass index

NYHA

New York Heart Association

SpO2

Oxygen saturation as measured by pulse oximetry

Hb

Hemoglobin

COPD

Chronic obstructive pulmonary disease

aCCI

Age-adjusted Charlson Comorbidity Index

Authors’ contributions

YL, LG, XDY, XML, RLL contributed to the study concept and design.YL, LG, XZ and DZ contributed to acquisition of data.YL and LG contributed to statistical analysis.YL was the major contributor in drafting the manuscript.XDY critically revised the manuscript and approved the version to be submitted.All authors read and approved the final manuscript.

Funding

This work was supported by Young Clinical Research Fund of the Chinese Stomatological Association (CSA-A2021-02) and New Clinical Techniques and Therapies of Peking University School and Hospital of Stomatology (no. PKUSSNCT-15A12). The funding bodies had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

Data availability

The datasets generated and/or analyzed during the current study will be available from the corresponding author on a reasonable request.

Declarations

Ethics approval and consent to participate

Ethical approval was received from the Biomedical Ethics Committee of Peking University Hospital of Stomatology (Number: PKUSSIRB-202270001) in December 14, 2021. Written informed consent was obtained from all participating patients or their next of kin or legal representative who must understand the recruiter’s description of the trial.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.