ABSTRACT
Cold atmospheric plasma (CAP) therapy has emerged as a promising therapy for wound healing. This study aimed to evaluate the feasibility, safety and efficacy of adjunctive CAP therapy for early tracheostomy wound healing compared with standard wound care (SWC) alone. This single‐centre, parallel‐group pilot randomised controlled trial (1:1 allocation) enrolled critically ill patients undergoing tracheostomy. Patients received 1‐min CAP applications on postoperative days 1, 3 and 5 plus SWC or SWC alone. The primary endpoint was the percentage reduction in tracheostomy wound area through postoperative day 7, assessed by a blinded outcome assessor. Due to the nature of the intervention, blinding of participants and treating clinicians was not feasible; however, the outcome assessor was blinded to group allocation. Wound healing trajectories were analysed using linear mixed‐effects models adjusted for baseline wound area. Forty‐two patients were included (CAP, n = 21; SWC, n = 21), with comparable baseline characteristics. By postoperative day 7, wound area reduction was greater in the CAP group than in the SWC group (30.3% vs. 23.6%, p = 0.15). Estimated wound area decreased by 0.08 versus 0.06 cm2/day (95% CI 0.06–0.10 and 0.04–0.08, respectively; p = 0.17). No treatment‐related adverse events were observed. Adjunctive CAP therapy was feasible, safe and demonstrated a non‐significant trend towards improved early tracheostomy wound healing. These findings support further evaluation in larger, adequately powered trials.
Keywords: cold atmospheric plasma, critically ill patients, pilot randomised controlled trial, plasma medicine, tracheostomy wound
Key Points
This pilot randomised controlled trial evaluated adjunctive CAP therapy for early tracheostomy wound healing in critically ill patients.
CAP therapy was feasible and well tolerated, with no treatment‐related adverse events observed.
Wound‐area reduction was numerically greater with CAP plus standard wound care than with standard wound care alone, although the between‐group difference was not statistically significant.
Larger, adequately powered trials are needed to determine the efficacy of CAP therapy for tracheostomy wound healing.
1. Introduction
Tracheostomy is increasingly performed in critically ill patients requiring prolonged mechanical ventilation, with approximately 10% of mechanically ventilated patients in the United States undergoing the procedure [1, 2]. The tracheostomy stoma is considered a clean‐contaminated surgical wound that is continuously exposed to respiratory secretions and bacterial colonisation. Consequently, stoma infection has been reported in approximately 5%–6% of patients [3]. Current standard tracheostomy wound care consists of routine cleansing of the stoma and regular dressing changes [4]. However, these measures are primarily supportive, and no adjunctive intervention has been established to actively promote wound healing [5].
Critically ill patients experience impaired wound healing due to systemic inflammation, microcirculatory dysfunction and metabolic derangements, particularly in those with sepsis or septic shock. In addition, advanced age, comorbidities such as diabetes mellitus, malnutrition and corticosteroid exposure further compromise the complex, multi‐phase wound healing process, resulting in delayed epidermal regeneration and epithelialisation [6, 7].
Cold atmospheric plasma (CAP) is an emerging biomedical technology that generates reactive oxygen and nitrogen species (RONS) from ambient gases and liquids [8]. CAP has gained increasing interest for various therapeutic applications, with wound healing representing a particularly promising indication [9, 10]. The biological effects of CAP relevant to wound repair include antimicrobial and anti‐biofilm activity, as well as direct tissue‐modulating effects [8]. Experimental studies suggest that CAP‐generated RONS act as signalling molecules that stimulate cell proliferation, migration, angiogenesis and extracellular matrix remodelling while preserving host tissue integrity [8, 9, 10].
Despite promising findings supporting the use of CAP in chronic wounds [9, 10], emerging evidence from clinical studies suggests that CAP may also facilitate healing in acute and postoperative wounds [11, 12]. However, evidence regarding its application in tracheostomy wounds among critically ill patients remains limited. Given the high risk of delayed wound healing in this population, the antimicrobial and tissue‐regenerative properties of CAP, together with its non‐contact application that facilitates bedside wound care, make it a promising adjunctive therapy. Therefore, this pilot randomised controlled trial aimed to evaluate the feasibility and safety of adjunctive CAP therapy and to generate preliminary estimates of its efficacy for early tracheostomy wound healing compared with standard wound care (SWC) alone in critically ill patients.
2. Materials and Methods
2.1. Study Design and Setting
This study was a single‐centre, parallel‐group pilot randomised controlled trial conducted in critically ill patients at a Maharaj Nakorn Chiang Mai Hospital, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand between November 2023 and March 2025. The trial was designed to evaluate the feasibility, safety and preliminary efficacy of adjunctive CAP therapy on early tracheostomy wound healing.
The study protocol was approved by the Research Ethics Committee of the Faculty of Medicine, Chiang Mai University (study code: MED‐2566‐0260, on 6 November 2023). This study was conducted in accordance with the Declaration of Helsinki and the International Council for Harmonization‐Good Clinical Practice (ICH‐GCP) guidelines. Written informed consent was obtained from all participants or their legally authorised representatives prior to enrollment.
The study was registered in the Thai Clinical Trial Registry (TCTR) under the identifier number TCTR20240423002 (https://www.thaiclinicaltrials.org/show/TCTR20240423002).
2.2. Participants
Adult patients aged ≥ 18 years who underwent surgical tracheostomy during their ICU stay and were expected to remain hospitalised for at least 7 postoperative days were screened for eligibility. Patients were excluded if informed consent could not be obtained from them or their legally authorised representative.
2.3. Randomisation, Allocation Concealment and Blinding
Eligible participants were randomised in a 1:1 ratio to receive either standard wound care alone (SWC group) or CAP therapy plus SWC (CAP group). Randomisation was performed using a computer‐generated random sequence, and allocation was concealed using sequentially numbered allocation. Treatment assignments were securely maintained and were accessible only to authorised personnel not involved in outcome assessment. Because of the nature of the intervention, participants and intervention operators were not blinded. The wound outcome assessor (LJ) was blinded to group allocation.
2.4. Standard Wound Care
All participants received tracheostomy SWC three times daily in accordance with institutional protocols. SWC included cleansing with sterile 0.9% sodium chloride solution, inspection for signs of infection or local complications and sterile dressing changes.
2.5. CAP Therapy
Participants allocated to the CAP group received adjunctive CAP therapy following SWC. CAP was delivered using a pulse‐controllable CAP jet device (NIGHINGALE device, InnoPlasCM Co. Ltd., Chiang Mai, Thailand), which generates RONS from ambient air (Figure S1). The device has been previously characterised as a low‐temperature atmospheric plasma jet operating at 2.52 kV and 2 kHz, generating multiple RONS, including nitric oxide, hydroxyl radicals, atomic oxygen, ozone and hydrogen peroxide, while maintaining a treatment temperature below 40°C. Detailed physicochemical characterisation of the CAP device has been reported elsewhere [9, 13]. CAP was applied at the third intensity level for 1 min per session on postoperative days 1, 3 and 5, with treatment duration controlled using the device's built‐in timer (Figure S2). The probe was positioned 1.0–2.0 cm from the wound surface, and no direct contact with the tissue occurred during application.
2.6. Data Collection
Collected data included baseline characteristics, primary diagnosis, indication for tracheostomy, laboratory investigations performed on the day of tracheostomy and severity of illness.
Wound area was measured on postoperative days 1, 3, 5 and 7, and was calculated in square centimetres using the elliptical formula based on maximal wound length (transverse axis) and width (vertical axis). Bacterial wound cultures were obtained on postoperative days 1 and 7.
2.7. Wound Assessment
Tracheostomy wound area was assessed using a standardised ruler‐based planimetric method. The maximal wound length and width were measured in centimetres using a sterile ruler placed on the wound surface, and wound area was calculated using the elliptical formula. To minimise inter‐observer variability, all wound area measurements were performed using the same technique at each time point by a single dedicated assessor who was blinded to the treatment allocation.
2.8. Outcomes
The primary outcome was early tracheostomy wound healing, assessed by the percentage reduction in wound area from baseline through postoperative day 7. Wound area reduction was selected as a clinically meaningful surrogate marker of early wound healing trajectory, rather than complete wound healing.
Secondary outcomes included the rate of wound area reduction (cm2/day) and an exploratory assessment of complete wound healing, defined as full epithelialisation of the skin surrounding the tracheostomy site when present during the study period. Additional secondary outcomes included the number of positive bacterial wound cultures. Adverse events, including local irritation, burning sensation, or other potential CAP‐related effects, were monitored and documented throughout the study period.
2.9. Sample Size Calculation
As this study was a pilot study designed to assess feasibility and generate preliminary estimates of treatment effect, a formal power calculation for definitive efficacy was not the primary objective. Sample size estimation was informed by a previous study by Stratmann et al. [14], which reported differences in wound area reduction following CAP therapy in patients with chronic wounds.
Based on an estimated effect size derived from that study, a total of 42 participants (21 per group) were considered sufficient to provide preliminary comparative data, using 80% power and a two‐sided significance level of 0.05. Given the pilot nature of the trial, this calculation was used to guide sample size selection rather than to establish definitive efficacy. To account for potential attrition, a target enrollment of 50 participants was planned. The sample size was not intended to detect definitive efficacy differences but to inform the design of future adequately powered trials.
2.10. Statistical Analysis
Baseline continuous variables were presented as medians with interquartile ranges (IQRs), and categorical variables as frequencies and percentages. Between‐group comparisons of continuous variables were performed using the Mann–Whitney U test, and categorical variables were compared using Fisher's exact test.
The percentage reduction in wound area from baseline to postoperative day 7 was compared between groups using the Mann–Whitney U test in the modified intention‐to‐treat (mITT) population, defined as all randomised participants with available day 7 primary outcome data at postoperative day 7.
Wound healing trajectories over time were evaluated using a linear mixed‐effects model, accounting for repeated measurements and potential non‐linear healing patterns. Models were adjusted for baseline wound area measured on postoperative day 1 before the first study intervention.
The exploratory analysis of time to complete wound healing was analysed using a flexible parametric model (FPM) with a time‐varying covariate (TVC) to account for non‐proportional hazards.
Statistical significance was defined as a two‐sided p value < 0.05. All statistical analyses were performed using Stata software (version 18.0; StataCorp, College Station, TX, USA).
2.11. Disclosing the Use of Artificial Intelligence
ChatGPT was used as an AI‐assisted tool to improve language clarity, grammar and manuscript structure. All AI‐generated content was carefully reviewed and edited by the authors.
3. Results
3.1. Participants
A total of 44 participants were enrolled between November 2023 and March 2025, representing 88% (44/50) of the planned recruitment target. Following randomisation, one participant in the CAP group withdrew consent, and one participant in the SWC group died before completion of the primary outcome assessment. Consequently, 42 participants (21 per group) were included in the final analysis. The participant flow is summarised in Figure 1. Recruitment did not reach the target sample size because of the limited data collection period. Baseline demographic and clinical characteristics are summarised in Table 1 and were comparable between groups (all p > 0.05).
FIGURE 1.
CONSORT flow diagram.
TABLE 1.
Baseline characteristics of the participants.
| Demographics | Total (n = 42) | CAP (n = 21) | SWC (n = 21) |
|---|---|---|---|
| Age (years) | 74 (66, 84) | 74 (66, 84) | 73 (64, 84) |
| Female, n (%) | 23 (52) | 10 (45) | 13 (59) |
| Body weight (kg) | 50 (42, 57) | 49 (40, 55) | 54 (42, 58) |
| Height (cm) | 157 (150, 167) | 157 (150, 166) | 156.5 (153, 167) |
| Body mass index (kg/m2) | 20.2 (18.2, 22.0) | 19.8 (16.7, 22.0) | 20.3 (19.0, 21.2) |
| Underlying disease, n (%) | |||
| Hypertension | 21 (48) | 10 (45) | 11 (50) |
| Diabetes mellitus | 11 (25) | 3 (14) | 8 (36) |
| Malignancy | 8 (18) | 3 (14) | 5 (23) |
| Coronary heart disease | 7 (16) | 5 (23) | 2 (9) |
| Chronic kidney disease | 8 (18) | 3 (14) | 5 (23) |
| Adrenal insufficiency | 5 (12) | 2 (9) | 3 (14) |
| Malnutrition | 28 (64) | 14 (64) | 14 (64) |
| Diagnosis, n (%) | |||
| Acute respiratory failure | 44 (100) | 22 (100) | 22 (100) |
| Sepsis/septic shock | 32 (73) | 18 (82) | 14 (64) |
| Acute kidney injury | 24 (55) | 14 (64) | 10 (46) |
| Indication for tracheostomy, n (%) | |||
| Prolonged intubation | 43 (98) | 22 (100) | 21 (95) |
| Ventilator dependent | 12 (27) | 6 (27) | 6 (27) |
| Airway protection | 9 (20) | 5 (23) | 4 (18) |
| SOFA score | 3 (2, 5) | 3 (2, 5) | 4 (2, 5) |
| Vital signs | |||
| Systolic blood pressure (mmHg) | 131 (120, 144) | 131 (112, 140) | 131 (121, 146) |
| Respiratory rate (/min) | 17 (15, 21) | 18 (15, 22) | 17 (14, 20) |
| Glasgow Coma Scale | 15 (12, 15) | 15 (12, 15) | 14 (10, 15) |
| Laboratory investigations | |||
| Haematocrit (%) | 27.2 (25.6, 29.9) | 27.2 (26.2, 29.4) | 27.2 (24.5, 29.9) |
| White blood cell count (×103/mm3) | 9.9 (8.5, 13.8) | 9.5 (8.8, 11.1) | 10.8 (8.7, 14.1) |
| Lymphocyte count (×103/mm3) | 1.1 (0.7, 1.4) | 1.09 (0.7, 1.4) | 1.2 (0.7, 1.5) |
| Platelet count (×109/L) | 227 (143, 353) | 227 (119, 383) | 237 (159, 324) |
| Serum creatinine (mg/dL) | 1.03 (0.70, 1.95) | 1.06 (0.80, 1.42) | 1.01 (0.60, 3.20) |
| Serum albumin (g/dL) | 2.8 (2.6, 3.1) | 2.8 (2.4, 2.8) | 2.8 (2.4, 3.1) |
Note: Continuous data are expressed as median (IQR) and categorical variables as number (%).
Abbreviation: SOFA, Sequential Organ Failure Assessment.
3.2. Feasibility Outcomes
All participants allocated to the CAP group completed the three planned CAP treatment sessions. No treatment discontinuation, protocol deviations or treatment‐related adverse events were observed during the study. Serial clinical assessments of the tracheostomy wound before and after each CAP application revealed no clinically apparent tissue injury, clinically significant bleeding, stomal cellulitis or device‐related complications attributable to CAP therapy.
3.3. Primary Outcome
Wound area characteristics are summarised in Table 2. Baseline wound size was slightly larger in the CAP group than in the SWC group, although this difference was not statistically significant (1.41 cm2 [IQR 0.99, 1.77] vs. 1.18 cm2 [IQR 0.79, 1.60], p = 0.18).
TABLE 2.
Study outcomes.
| Outcomes | CAP (n = 21) | SWC (n = 21) | p |
|---|---|---|---|
| Tracheostomy wound area (cm2) | |||
| Postoperative day 1 | 1.41 (0.99, 1.77) | 1.18 (0.79, 1.60) | 0.18 |
| Postoperative day 3 | 1.30 (1.10, 1.65) | 1.10 (0.78, 1.32) | 0.13 |
| Postoperative day 5 | 1.04 (0.85, 1.43) | 0.94 (0.71, 1.34) | 0.45 |
| Postoperative day 7 | 0.94 (0.75, 1.12) | 0.79 (0.71, 1.23) | 0.55 |
| Primary outcome | |||
| Percentage reduction in wound area (%) | 30.3 (19.2, 43.4) | 23.6 (13.6, 31.3) | 0.15 |
| Secondary outcome | |||
| Rate of wound area reduction (cm2/day) a | 0.08 (0.06, 0.10) | 0.06 (0.04, 0.08) | 0.17 |
| Time to complete wound healing (day) | 15 (11, 21) | 16 (13, 19) | 0.71 b |
| Number of organisms isolated from wound culture | |||
| Postoperative day 1 | 2 (1, 3) | 1 (0, 2) | 0.13 b |
| Postoperative day 7 | 2 (1, 2) | 1 (0, 2) | 0.27 b |
Note: Continuous data are expressed as median (IQR).
Estimated from the adjusted linear mixed‐effects model and presented as the estimated slope (95% confidence intervals).
Analyses were performed using the 40 and 35 available cases, respectively.
From postoperative day 1 through postoperative day 7, the percentage reduction in wound area was numerically greater in the CAP group than in the SWC group (30.3% [IQR 19.2, 43.4] vs. 23.6% [IQR 13.6, 31.3]). The Hodges–Lehmann median between‐group difference was 7.2% (95% CI −3.4 to 16.8; p = 0.15).
3.4. Secondary Outcomes
For the secondary outcome, based on the linear mixed‐effects model adjusted for baseline wound area measured on postoperative day 1 before the assigned intervention, wound area decreased by an estimated 0.08 cm2/day (95% CI 0.06–0.10) in the CAP group and 0.06 cm2/day (95% CI 0.04–0.08) in the SWC group. The adjusted between‐group difference was 0.02 cm2/day (95% CI −0.01 to 0.04, p = 0.17), indicating a numerically greater reduction in the CAP group, although the difference did not reach statistical significance (Figure 2).
FIGURE 2.
Changes in tracheostomy wound area. Data are presented as median; error bars indicate the IQR.
For the exploratory outcome of time to complete wound healing, the median healing time was shorter in the CAP group than in the SWC group (15 days [IQR 11–21] and 16 days [IQR 13–19], respectively). The Hodges–Lehmann median between‐group difference was 1 day (95% CI −3 to 5, p = 0.71) (Table 2).
Kaplan–Meier curves for the exploratory outcome of time to complete wound healing, stratified by treatment group, are shown in Figure 3. The log‐rank test showed no significant difference between groups (p = 0.90). The hazard ratio (HR) estimated from the Cox proportional hazards model was 1.04 (95% CI 0.55–1.96, p = 0.90). However, the proportional hazards assumption was violated, as demonstrated by the smoothed hazard and log–log plots (Figure S3A,B). Therefore, the estimated HR should be interpreted with caution and should not be considered to represent a constant treatment effect over time.
FIGURE 3.
Kaplan–Meier curves for time to complete wound healing according to treatment group. Solid maroon lines indicate KM estimates, and dashed navy lines indicate model‐based estimates from the FPM with time‐varying treatment effect. CAP, cold atmospheric plasma; FPM, flexible parametric model; KM, Kaplan–Meier.
To account for non‐proportional hazards, a FPM with a TVC was applied. The resulting time‐dependent HR suggested a higher probability of wound healing in the CAP group during the early postoperative period, with the treatment effect gradually diminishing over time and approaching unity at approximately postoperative day 14 (Figure 4A). Differences in the RMST over time were illustrated in Figure 4B. Additionally, RMST differences at prespecified time horizons are reported in Table 3.
FIGURE 4.
Treatment effect of CAP therapy compared with SWC, illustrated by (A) time‐dependent HR and (B) difference in RMST as a function of time. CAP, cold atmospheric plasma; HR, hazard ratio; RMST, restricted mean survival time.
TABLE 3.
Restricted mean survival time differences at prespecified time horizons.
| Time (days) | Adjunctive CAP therapy | Standard wound care | RMST difference (95% CI) | p | ||
|---|---|---|---|---|---|---|
| Number at risk | RMST (95% CI) | Number at risk | RMST (95% CI) | |||
| 7 | 29 | 6.99 (6.92–7.03) | 20 | 7.00 (6.96–7.01) | −0.12 (−0.06 to 0.03) | 0.48 |
| 14 | 10 | 12.27 (11.24–13.30) | 14 | 12.84 (12.06–13.62) | −0.57 (−1.83 to 0.69) | 0.38 |
| 21 | 5 | 14.79 (12.66–16.74) | 3 | 15.66 (13.81–17.52) | −0.96 (−3.63 to 1.70) | 0.48 |
There were no significant between‐group differences in the median number of organisms isolated from tracheostomy wound cultures on postoperative day 1 (p = 0.13, 40 cases) or postoperative day 7 (p = 0.26, 35 cases), as shown in Table 2.
Within‐group analyses were performed using the 35 paired cases with wound culture results available on both postoperative day 1 and postoperative day 7. No significant change in the median number of organisms was observed over time in either the CAP group (p = 0.30) or the SWC group (p = 0.09) (Figure S4).
4. Discussion
This single‐centre, parallel‐group pilot randomised controlled trial evaluated the feasibility, safety, and preliminary efficacy of adjunctive CAP therapy combined with SWC for enhancing tracheostomy wound healing in critically ill patients. Although adjunctive CAP therapy resulted in a numerically greater reduction in wound area by postoperative day 7 compared with SWC alone (30.3% vs. 23.6%), the between‐group difference did not reach statistical significance.
Exploratory analyses also suggested a slightly faster rate of wound area reduction in the CAP group compared with the SWC group (0.08 vs. 0.06 cm2/day) and a modestly shorter time to complete wound healing in the CAP group, with a median healing time of 15 days (IQR 11, 21) versus 16 days (IQR 13, 19). However, neither difference reached statistical significance. These results suggest a potential early benefit of CAP while underscoring the challenges of demonstrating efficacy in a complex ICU population within a short observation period.
Although the observed between‐group differences were modest and did not reach statistical significance, they may still represent a clinically relevant signal for adjunctive CAP therapy. However, because no minimal clinically important difference was prespecified and this pilot study was not powered to evaluate efficacy, the clinical significance of these findings remains uncertain and should be confirmed in larger, adequately powered trials.
Critically ill patients are uniquely vulnerable to impaired wound healing due to systemic inflammation, sepsis, malnutrition, and altered skin barrier function [6, 7]. Koskela et al. demonstrated that ICU patients with sepsis exhibit increased susceptibility to skin injury and delayed epithelial repair, likely mediated by dysregulated transepidermal water loss, impaired macrophage activity, and altered keratinocyte proliferation and migration [7]. In routine clinical practice at our institution, delayed tracheostomy wound healing is sometimes observed, supporting the clinical relevance of investigating adjunctive therapies in this setting.
CAP therapy has gained increasing attention as a wound‐healing modality due to its ability to generate RONS that exert antimicrobial, anti‐biofilm, and tissue‐modulating effects [8]. Experimental data suggest that controlled RONS exposure can stimulate angiogenesis, fibroblast activity, keratinocyte migration, and extracellular matrix deposition, processes essential for wound repair. Thana et al. developed a pulse‐controllable cold air plasma jet capable of generating RONS from ambient air while preserving host cell integrity and reducing bacterial proliferation [9]. This same device was used in the present study, providing translational continuity between bench and bedside applications.
Preclinical evidence further supports the biological plausibility of CAP therapy for enhancing wound healing. In an in vivo rat pressure‐ulcer model, Chatraie et al. demonstrated significantly increased epithelialisation, collagen synthesis, and angiogenesis following non‐thermal plasma exposure compared with controls [10]. These mechanistic observations are consistent with the early trend towards greater wound area reduction observed in our CAP‐treated patients, despite the lack of statistical significance.
Clinical evidence for the efficacy of CAP has primarily been derived from studies of chronic wounds. Early clinical studies supported the safety and potential efficacy of CAP in chronic wounds, venous leg ulcers, and pressure ulcers, demonstrating reduced bacterial burden and improved wound healing without treatment‐related adverse effects [15, 16, 17]. More recently, Stratmann et al. conducted a randomised, placebo‐controlled trial in patients with diabetic foot ulcers and demonstrated significantly improved healing outcomes following eight CAP applications over 14 days, including greater wound area reduction (remaining wound area: 30.5% vs. 55.2%, p = 0.03), enhanced epithelialisation, and a shorter time to clinically relevant wound reduction, without any reported treatment‐related adverse effects [14]. Collectively, these studies suggest that repeated CAP applications are safe and may enhance wound healing across different chronic wound types.
Emerging evidence also supports the application of CAP in acute surgical wounds. Heinlin et al. demonstrated that a single 2‐min argon‐based CAP treatment significantly improved healing of split‐thickness skin graft donor sites, with enhanced re‐epithelialisation, fewer fibrin deposits and blood crusts, and no relevant treatment‐related adverse effects [11]. More recently, Werra et al. reported that a single intraoperative CAP application significantly reduced the need for surgical revision due to inguinal wound healing disorders following peripheral arterial reconstruction in high‐risk patients [18]. These findings suggest that CAP may also promote healing in acute postoperative wounds, although the treatment protocols, wound characteristics, and clinical settings differ substantially from those of the present study.
These findings are directionally consistent with the numerically greater wound area reduction observed in our study. However, the treatment effect was more modest than that reported in previous clinical studies. This difference may be explained by variations in wound characteristics and treatment protocols. Compared with the chronic wounds and relatively clean surgical wounds evaluated in previous studies, tracheostomy wounds are continuously exposed to airway secretions, saliva, sputum and repetitive mechanical irritation, creating a more challenging healing environment. In addition, our study employed only three CAP applications within the first five postoperative days, which may have limited the treatment effect.
To the best of our knowledge, the literature on adjunctive therapies targeting early tracheostomy wound healing in critically ill patients is limited, whereas healing timelines have been commonly reported after tracheostomy decannulation. Christiansen et al. reported substantial variability in healing duration following tracheostomy decannulation, with some wounds requiring more than 3 weeks to achieve complete epithelialisation [19]. This observation suggests that tracheostomy wounds may require longer healing periods, which should be considered in the design of future trials.
Interestingly, clinical studies have shown mixed results regarding the effect of CAP on bacterial burden. While several studies have reported significant reductions in bacterial burden following CAP therapy [15, 16, 17], others, including Stratmann et al. [14] and the present study, found no significant reduction in bacterial burden compared with the control group. These inconsistent findings suggest that the antimicrobial effects of CAP may be highly context‐dependent and influenced by factors such as wound moisture, biofilm architecture, and ongoing microbial contamination.
4.1. Strengths
This study has several notable strengths. To our knowledge, it is the first randomised controlled trial to evaluate CAP therapy for tracheostomy wound healing in critically ill patients. Unlike prior CAP studies focused on chronic wounds, this trial addresses a novel clinically relevant surgical wound context in the ICU. The use of a pulse‐controllable, ambient‐air CAP device enhances feasibility and translational potential while demonstrating a favourable safety profile. In addition, the randomised design, standardised wound care protocol, and blinded outcome assessment strengthen the internal validity of the findings.
4.2. Limitations
Several limitations should be acknowledged. First, the sample size was informed by effect estimates derived from chronic wounds, which may not accurately reflect the expected treatment effect in acute tracheostomy wounds, resulting in limited statistical power. Second, the 7‐day primary follow‐up period may not have been sufficient to fully capture CAP effects on tracheostomy wound healing trajectories, which often extend beyond 2 weeks. This relatively short follow‐up was based on the initial clinical assumption that tracheostomy wounds might behave similarly to uncomplicated surgical wounds, in which measurable improvement is often observed within the first postoperative week. Third, the anatomical complexity and secretion‐rich environment of the tracheostomy wound may have reduced effective plasma delivery to the target tissue. Fourth, although blinded outcome assessment was implemented, complete blinding was not feasible due to the nature of the intervention. Finally, participant recruitment did not reach the planned target of 50 participants due to practical constraints related to the study period. Nevertheless, the prespecified minimum sample size for this pilot study was achieved.
5. Conclusions
Adjunctive CAP therapy demonstrated a favourable, though non‐significant, trend towards enhanced early tracheostomy wound healing and a modestly faster healing rate compared with SWC alone in critically ill patients. CAP therapy was safe and well tolerated throughout the study. These pilot findings support the feasibility and safety of CAP as an adjunctive therapy and provide preliminary estimates of efficacy to inform the design of larger, adequately powered randomised controlled trials.
Funding
This study was supported by the Faculty of Medicine, Chiang Mai University, Thailand (grant number 35‐67). The funder had no specific role in the conceptualisation, study design, data collection, data analysis, decision to publish, or preparation of the manuscript.
Ethics Statement
The study protocol was approved by the Research Ethics Committee of the Faculty of Medicine, Chiang Mai University (study code: MED‐2566‐0260, on 6 November 2023). This study was conducted in accordance with the Declaration of Helsinki and the International Council for Harmonization‐Good Clinical Practice (ICH‐GCP) guidelines. Written informed consent was obtained from all participants or their legally authorised representatives prior to enrollment.
Consent
The authors confirm that this manuscript represents original work and has not been published previously, nor is it under consideration for publication elsewhere. All authors have reviewed and approved the final version of the manuscript. The study was conducted in accordance with relevant ethical standards and institutional guidelines, and the clinical trial was approved by the institutional ethics committee and registered in the Thai Clinical Trial Registry. The authors accept full responsibility for the accuracy and integrity of the work.
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
Figure S1: Cold atmospheric plasma device and its probe.
Figure S2: Study protocol.
Figure S3: (A) Smoothed hazard estimation and (B) log–log plot of survival.
Figure S4: Number of organisms from tracheostomy wound culture on postoperative day 1 and 7.
Acknowledgements
We would like to thank the Plasma and Beam Physics Research Facility, Faculty of Science, Chiang Mai University, Chiang Mai, Thailand, and its spin‐off company, InnoPlasCM Co. Ltd., for providing the CAP device used in this study.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Figure S1: Cold atmospheric plasma device and its probe.
Figure S2: Study protocol.
Figure S3: (A) Smoothed hazard estimation and (B) log–log plot of survival.
Figure S4: Number of organisms from tracheostomy wound culture on postoperative day 1 and 7.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.