Risk factor evaluation of cuff pressure of >30 cmH2O to stop air leakage during mechanical ventilation: A prospective observational study

Abstract

Aim

The commonly recommended endotracheal tube cuff pressure is 20–30 cmH₂O. However, some patients require a cuff pressure of >30 cmH₂O to prevent air leakage. The study aims to determine the risk factors that contribute to the endotracheal tube cuff pressure of >30 cmH₂O to prevent air leakage.

Design

A multi-centre prospective observational study.

Methods

Eligible patients undergoing mechanical ventilation in the intensive care unit of three hospitals between March 2020 and July 2022 were included. The endotracheal tube cuff pressure to prevent air leakage was determined using the minimal occlusive volume technique. The patient demographics and clinical information were collected.

Results

A total of 284 patients were included. Among these patients, 55 (19.37%) patients required a cuff pressure of >30 cmH₂O to prevent air leakage. The multivariate logistic regression results revealed that the surgical operation (odds ratio [OR]: 8.485, 95% confidence interval [CI]: 1.066–67.525, p = 0.043) was inversely associated with the endotracheal tube cuff pressure of >30 cmH₂O, while the oral intubation route (OR: 0.127, 95% CI: 0.022–0.750, p = 0.023) and cuff inner diameter minus tracheal area (OR: 0.949, 95% CI: 0.933–0.966, p < 0.001) were negatively associated with the endotracheal tube cuff pressure of >30 cmH₂O. Therefore, a significant number of patients require an endotracheal tube cuff pressure of ＞30 cmH₂O to prevent air leakage. Several factors, including the surgical operation, intubation route, and difference between the cuff inner diameter and tracheal area at the T3 vertebra, should be considered when determining the appropriate cuff pressure during mechanical ventilation.

INTRODUCTION

Endotracheal intubation is a common medical procedure to maintain adequate ventilation and oxygenation in patients under respiratory distress or anaesthesia (Dancy, 2021; Hung et al., 2021). Most endotracheal tubes have a cuff at the end to achieve a seal in the airway (Haas et al., 2014; Sanaie et al., 2019). The appropriate pressure in the cuff is essential for a successful mechanical ventilation. A low cuff pressure would result in aspiration and air leakage, while a high cuff pressure would cause tracheal injury (Gaspar et al., 2019; Spapen et al., 2020). Understanding the factors associated with cuff pressure could ensure a safe seal around the endotracheal tube.

Background

In general, an endotracheal tube cuff pressure of 20–30 cmH₂O is recommended to create an adequate seal between the tube and trachea (Ferreira et al., 2021; Saxena et al., 2022; Wang et al., 2021). However, several studies have revealed that a cuff pressure of >30 cmH₂O is required for some patients during mechanical ventilation (Nseir et al., 2009; Peters & Hoogerwerf, 2013; Rosero et al., 2018; Wu et al., 2021). The previous study conducted by the investigators revealed that several factors, including the type and diameter of the endotracheal tube, intubation method, peak inspiration pressure (PIP), and gender, are associated with air leakage in patients who require an endotracheal cuff pressure of >30 cmH₂O (Wu et al., 2023). However, additional studies with a large patient sample size are required to externally validate those study results.

Therefore, the present prospective observational study was conducted to further investigate the risk factors associated with high endotracheal tube cuff pressure (>30 cmH₂O) to prevent the air leakage in patients undergoing mechanical ventilation in three intensive care units (ICUs). The present study results were compared to the results of previous published reports, in order to provide adequate sealing for patients.

METHODS Study design and participant selection

The present multicentre prospective observational study was conducted in three ICUs of two tertiary hospitals in Nantong, China. These three ICUs were as follows: the cardiothoracic ICU and respiratory ICU at the Affiliated Hospital of Nantong University and the comprehensive ICU at the Affiliated Nantong Hospital 3 of Nantong Unversity. The study period was from March 2020 to July 2022. The study protocol was approved by the ethics committee of each hospital. All study participants provided a signed informed consent.

The inclusion criteria were as follows: (1) patients who received mechanical ventilation with nasal or oral endotracheal intubation or tracheotomy cannula; (2) ≥18 years old; (3) normal vital signs with a urine volume of ≥2 mL/kg/h; and (4) patients with chest computed tomography (CT) scan results in the previous 3 months. The exclusion criteria were as follows: (1) massive pleural effusion; (2) pneumothorax; or (3) peak airway pressure of ≥45 cmH₂O during mechanical ventilation.

Materials

The following equipment and devices were used for the endotracheal intubation: reinforced endotracheal tubes (Smith Medical Devices Co., Ltd., Shanghai, China; Galanz Medical Equipment Co., Ltd., Jiangxi, China; Weili Medical Equipment Co., Ltd., Guangzhou, China), tracheotomy cannula (Weili Medical Equipment Co., Ltd., Guangzhou, China; Quan'an Medical Instrument Co., Ltd., Shanghai, China), cuff pressure gauges (Ranran Trade Co., Ltd., Hangzhou, China), retractable tubes with a 1.5-m suction loop (Intesec Medical Devices Co., Ltd., Changzhou, China), and stethoscopes (Hausheng Technology and Trade Co., Ltd., Beijing, China).

Endotracheal intubation

The anesthesiologists were responsible for the oral and nasal endotracheal intubation of all study participants. In general, the tube size ranges within 7.0–8.0 and 7.5–8.5 mm, for female and male patients, respectively, during oral endotracheal intubation, and 6.5–7.0 and 7.0–7.5 mm, for female and male patients, respectively, during nasal endotracheal intubation (WSE A, 2005; Xue, 2002). However, the anesthesiologists had the flexibility to select the size of the endotracheal tube, according to their experience and the clinical situation, since the present study is an observational study. Furthermore, the mode of mechanical ventilation was determined by the anesthesiologists.

Data collection

The patient demographics, height, weight, and surgical versus non-surgical causes were recorded. The ventilator settings, including the tidal volume, PIP, bladder temperature, and approaches of endotracheal intubation (oral or nasal), were documented. Information on the endotracheal tube included the inner diameter (ID) (3.0–9.0), and the cross-sectional cuff area of the tracheal catheter was = π × r² (Huang et al., 2022), with r = L/2. The cuff diameter (L) was obtained from the manufracturer's manual.

The patient airway cross-sectional area was calculated using the transverse image at the distal end of the tracheal catheter in the CT images. All calculations were performed in the hospital PACS system (Figure 1) (Farheen et al., 2022; Song, 2021; Wu et al., 2021).

FIGURE 1. Method for measuring the trachea area at the T3 level in the computed tomography image.

Minimum cuff pressure measurement

The lowest endotracheal cuff pressure to prevent air leakage was determined using the minimal occlusive volume technique within 24 h after tracheal catheter placement, as previously described (Park et al., 2020). Briefly, the patient was placed at the 30-degree semi-recumbent position. After suction to clean the airway and nasal cavity, the cuff was deflated to hear the air leakage and slowly re-inflated to obtain the minimum pressure to prevent air leakage. The air leakage was determined by the auscultation at the trachea using a stethoscope. The value displayed on the balloon pressure gauge (VBM, Germany) was the minimum cuff pressure to prevent air leakage. This measurement was separately performed by two anesthesiologists. The average of these two measurements was used for the analysis. The patients were assigned into two groups based on the minimum cuff pressure to prevent air leakage (≤30 cmH₂O group and >30 cmH₂O group).

Statistical analysis

The statistical analysis was performed using SPSS 20.0 (IBM, NY, USA). The figures were prepared using Prism 8 (GraphPad, CA, USA). The variables were compared between patients with an endotracheal cuff pressure of ≤30 or >30 cmH₂O by t-test for continuous variables and Chi-square test for categorical variables. Variables with a p-value of <0.05 were entered into the binary multivariate logistic regression analysis, in order to determine the risk factors for a cuff pressure of >30 cmH₂O. The odds ratios (ORs) and 95% confidence intervals (CIs) were calculated after considering the potential confounding variables. A p-value of <0.05 was considered statistically significant.

RESULTS Characteristics of the study participants

A total of 457 patients, who underwent mechanical ventilation during the study period, were screened. Among these patients, 284 patients were included and analysed. Among these 284 patients, 55 (19.37%) patients required an endotracheal tube cuff pressure of >30 cmH₂O to prevent air leakage. There were 210, 31, and 43 patients in the cardiothoracic ICU of the Affiliated Hospital of Nantong University, respiratory ICU of the Affiliated Hospital of Nantong University, and ICU of Affiliated Nantong Hospital, respectively.

Comparisons between patients with an endotracheal cuff pressure of ≤30 or >30 cmH₂O

As shown in Table 1, the gender, age, height, body mass index, surgical operation, intubation route, and cuff inner diameter minus tracheal area T₃ differed between the two groups (p < 0.05).

TABLE 1 Comparison of patients with endotracheal cuff pressure of ≤30 and >30 cmH₂O.

Variables	≤30 cmH2O (n = 229)	>30 cmH2O (n = 55)	x2/t	p
Gender (M/F)	157/72	52/3	15.41	<0.001
Age (year)	63.91 ± 14.17	70.51 ± 12.16	3.18	0.002
Weight (kg)	65.14 ± 11.51	63.45 ± 10.63	0.99	0.325
Height (cm)	166.0 ± 7.19	169.1 ± 6.07	2.95	0.004
Body mass index (kg/m2)	23.62 ± 3.70	22.16 ± 3.24	2.70	0.008
Temperature (°C)	37.46 ± 0.85	37.48 ± 0.93	0.11	0.915
Surgical operation (Y/N)	187/42	34/21	10.11	<0.001
Oral intubation route (Y/N)	216/13	43/12	18.70	<0.001
PIP (cmH2O)	20.64 ± 4.14	21.82 ± 5.67	1.76	0.080
Tidal volume (mL)	561.7 ± 100.20	545.6 ± 88.41	1.10	0.274
Cuff inner diameter minus tracheal area T3	−12.29 ± 113.0	212.30 ± 85.96	16.30	<0.001

Note: All continuous data were presented as mean ± standard deviation.

Abbreviation: PIP, peak inspiratory pressure.

Multivariate analysis of risk factors associated with an endotracheal cuff pressure of >30 cmH₂O

As shown in Table 2, the surgical operation, intubation route, and cuff inner diameter minus tracheal area T₃ were statistically associated with the endotracheal cuff pressure of >30 cmH₂O during mechanical ventilation. The larger cuff inner diameter minus tracheal area value corresponded to the lower minimum cuff pressure to prevent air leakage in the oral intubation group.

TABLE 2 Multivariate logistic regression analysis of independent risk factors for endotracheal cuff pressure of >30 cmH₂O.

Variables	B	SE	Wald	OR	95% CI	p	p
Constant	11.833	10.332	1.312	137,667.575		0.252	0.281
Surgical operation	2.138	1.058	4.082	8.485	1.066–67.525	0.043	0.009
Oral intubation route	−2.064	0.906	5.190	0.127	0.022–0.750	0.023
Cuff inner diameter minus tracheal area T3	−0.052	0.009	34.029	0.949	0.933–0.966	<0.001	0.000

Abbreviations: CI, confidence interval; OR, odds ratio.

Surgical operation

The minimum cuff pressure to prevent air leakage was further compared between the surgical vs. non-surgical group. As shown in Figure 2, the cuff pressure was significantly lower in the surgical group, when compared to the non-surgical group (22.42 ± 17.72 vs. 34.62 ± 23.43 cmH₂O).

FIGURE 2. Comparison of minimum cuff pressures to prevent air leakage between the surgical versus non-surgical group.

Routes of intubation

The minimum cuff pressure was significantly lower in the oral intubation group, when compared to the non-oral intubation group (Figure 3).

FIGURE 3. Comparison of minimum cuff pressures to prevent air leakage between the oral intubation and the non-oral intubation group.

Cuff diameter provided by different manufacturers

The cuff diameters of the endotracheal tubes significantly varied. The same cuff size provided by different manufactures can have different cuff diameters (Figure 4).

FIGURE 4. The cuff diameters of the endotracheal tubes significantly varied, even with the same size label provided by different manufacturers.

DISCUSSION

The present multi-centre prospective observational study revealed that the surgical operation, cuff diameter, nasal intubation, and tracheal area T3 can affect the tube pressure to achieve adequate sealing in patients undergoing mechanical ventilation. The present study results had similarities and differences, when compared to the previous study results reported by the investigators.

During mechanical ventilation, a small tube size can cause air leakage in the airway, while a large tube size can lead to tube folding in the airway (Jinqiu et al., 2020). Both situations can lead to poor airway sealing, increasing the risk of oropharyngeal and gastrointestinal reflux aspiration into the airway, and subsequent ventilator-associated pneumonia. Although the recommended cuff pressure is 20–30 cmH₂O (Bowton, 2022; Nseir & Gaudet, 2021; Totonchi et al., 2015), air leakage during endotracheal intubation has been frequently reported in clinic (Satya Prakash et al., 2022). In the present study, a significant number of patients (55 patients, 19.37%) required a cuff pressure of >30 cmH₂O to achieve adequate sealing, which was higher than that reported by the previous study of the investigators (14.5%) (Wu et al., 2023).

One of the major findings of the present study was the correlation between the tracheal area T3 and requirement of a cuff pressure of >30 cmH₂O for adequate sealing. This was not reported in the previous study conducted by the invetigators (Wu et al., 2023). Several previous literatures have measured the trachea diameter in CT images, and suggested that the transverse diameter of the subglottic area and diameter of the cricoid cartilage can be measured to facilitate the selection of the appropriate size of endotracheal tube (Jugpal et al., 2015; Stagnaro et al., 2017; Wu et al., 2021). Other previous studies have revealed that the trachea size can vary, depending on the gender, age, height, and body mass index (Cao et al., 2021; Chan et al., 2020; Ritchie-McLean et al., 2018). In the present study, the tracheal area at the T3 level was measured, as shown in the CT images. The results revealed that the tracheal area at the T3 level was associated with the requirement of a cuff pressure of >30 cmH₂O for adequate sealing. A large tracheal area at the T3 level correlated with a large size larynx, which can easily lead to leakage during mechanical ventilation. The present study suggests that clinicians should know the cuff diameter, and review the previous CT images, when available, in order to determine the tracheal area at the T3 level, and ensure adequate sealing after endotracheal intubation.

The present analyses revealed that the cuff pressure requirement in the surgical operation group was significantly lower, when compared to the non-surgical operation group. This result was not reported in the previous study conducted by the investigators (Wu et al., 2023). Laryngeal oedema might be one of the reasons for the decrease in incidence of leakage. Clinical studies have revealed that intubation can cause laryngeal edema or vocal cord injury (Shinohara et al., 2020). These patients might receive a large amount of colloid or infusion during the surgical operation, resulting in laryngeal oedema (Shinohara et al., 2020), and this facilitates the sealing of the tube in the laryngeal area. On the other hand, non-surgical patients with advanced age commonly had chronic lung disease, such as chronic obstructive pulmonary disease. Studies have reported that the tracheal area of these patients was bigger, when compared to that of patients with other conditions (Aljathlany et al., 2021; Wani et al., 2016). All of these can contribute to the requirement of low cuff pressure in surgical patients vs. non-surgical patients in the present study.

The present study revealed that different intubation routes have different likelihoods for a cuff pressure of >30 cmH₂O for adequate sealing. Furthermore, nasal endotracheal intubation is associated with an increased risk of requiring a cuff pressure of >30 cmH₂O, which was consistent with the previous study results of the investigators (Wu et al., 2023).

The present analysis revealed that the endotracheal tubes provided by different manufacturers significantly vary. Furthermore, tubes with the same labelled tube size have different cuff diameters. A vary small tracheotomy cannula cuff size might be the reason for the high incidence of air leakage in patients with tracheotomy. Therefore, the investigators considered that it is necessary to create a standard criterion for the selection of endotracheal tubes with a tube size that matches the cuff diameter across different manufacturers.

The present study results revealed a negative relationship between the minimum cuff pressure to seal the airway and the cuff inner diameter minus tracheal area value. A smaller difference between the cuff inner diameter and tracheal area at the T₃ vertebra can lead to a higher risk of airway leakage. During mechanical ventilation, the endotracheal tube cuff and patient airway can present with the following three situations: (1) if the endotracheal tube cuff is significantly larger than the area of the airway, the cuff would not be fully inflated, and the cuff wall may have wrinkles that would allow for the leakage of oral and nasal secretions into the lower airway; (2) if the cuff is slightly larger than the airway, the cuff can be fully inflated to seal the airway with no excessive tension, and the pressure inside the cuff would be similar to the pressure of the cuff wall pressed on the airway mucosa; (3) if the endotracheal tube cuff is significantly smaller than the airway, the cuff would not be able to adequately seal the airway even when fully inflated, and the high pressure inside the cuff might not be the pressure of the cuff wall pressed on the airway mucosa. Therefore, the ideal size of the endotracheal cuff should be slightly larger than the size of the patient airway, providing adeqeuate sealing, and a pressure inside the cuff similar to the pressure pressed on the airway mucosa from the cuff wall. When selecting the appropriate endotracheal tube, the medical staff should consider the cuff inner diameter minus tracheal area value through CT imaging technology, in order to provide adequate sealing, and avoid injury to the mucosa.

STRENGTHS AND LIMITATIONS

The strengths of the present study include its multi-centre design and the relatively large sample size. The present study had several limitations. First, the multi-centre study was performed in three ICUs. However, these three ICUs were located in two local hospitals. This could limit the generalizability of the present study for patients with different ethnic backgrounds. Second, merely patients older than 18 years old were included. Therefore, these results are not applicable to infants and young children. Finally, the patients were not followed up to determine the clinical outcomes. Future studies would address these issues.

CONCLUSION

A significant number of patients require an endotracheal tube cuff pressure of >30 cmH₂O to prevent air leakage during mechanical ventilation. Clinicians should consider factors, such as the surgical operation, intubation route, and cuff inner diameter minus tracheal area T₃, in order to determine the appropriate cuff pressure for patients undergoing mechanical ventilation.

AUTHOR CONTRIBUTIONS

H-LW and Y-HW: patient recruitment, data collection, and manuscript draft; J-HS: data analysis and study design; Y-HX and LD: patient recruitment, data collection, and informed consent process; H-WS, J-HS, Y-PZ, and W-QS: study design, patient recruitment, and manuscript proofreading.

ACKNOWLEDGEMENTS

We would like to thank our colleagues at the Cardiothoracic Intensive Care Unit and Respiratory Medical Care Unit of the Affiliated Hospital of Nantong University, and the Comprehensive Intensive Care Unit of Nantong Third People's Hospital for their important contributions.

FUNDING INFORMATION

The study was supported by the Postgraduate Research & Practice Innovation Program of Jiangsu, China (2021, SJCX21_1479) and the Scientific Research Fund of Health Commission in Nantong City (2021006, MS2023072).

CONFLICT OF INTEREST STATEMENT

The authors have no conflicts of interest to declare.

DATA AVAILABILITY STATEMENT

The data are available upon reasonable request to the corresponding author.

ETHICS STATEMENT

The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the ethics committee of The Affiliated Hospital of Nantong University and Nantong Third People's Hospital (NO.: 2021-K062-01), and an informed consent was obtained from all individual participants.