Endotracheal tube cuff inflation pressure varieties and response to education among anesthetists

ABSTRACT Background This study aimed to evaluate endotracheal tube (ETT) cuff inflation pressure (CIP) applied by anesthetists as well as the effect of an interview and feedback on their CIP accuracy. Methods This single-blind, controlled trial involved two series of CIP measurements in intubated patients before and after an interview and feedback of the participating anesthetists who were asked to inflate the cuffs for all intubated patients as per their clinical judgment. The cuff pressures were measured using a manometer and accordingly adjusted to 25 cm H2O by the researchers. For each anesthetist, 3 measurements were recorded, and the mean pressure values were calculated for each setting. The anesthetists were initially blinded, then they were informed about the pressure values and the adjustments. The primary outcome was the anesthetists’ accuracy regarding ETT inflation following the feedback. The secondary outcomes were pressure values in senior and junior anesthetists as well as in scheduled and emergency operations. Results The study enrolled 28 anesthetists; six registrars or senior registrars and 22 residents. Interview and feedback significantly lowered the mean pressure applied by the anesthetists. The cuff inflation pressure decreased from 33.8 ± 1.95 to 30.8 ± 3.24 and from 32.9 ± 2.38 to 29.9 ± 3.44 for emergency and scheduled surgeries, respectively. Furthermore, the frequency of safe CIP increased significantly for both emergency and scheduled surgeries. However, the senior staff showed no significant increase in safety CIP. Conclusion Anesthetists improved their accuracy of CIP after educational feedback. ETT cuff pressures should be routinely measured in intubated patients under general anesthesia.


Introduction
Maintenance of adequate pressure in the endotracheal tube (ETT) cuff is an important part of the management of the artificial airway. The cuff is inflated to seal the airway and to deliver mechanical ventilation [1]. A cuff pressure between 20 and 30 cm H 2 O is recommended to provide an adequate seal, ensure delivery of the prescribed mechanical ventilation tidal volume, reduce the risk for aspiration of secretions that accumulate above the cuff, and avoid compromising tracheal perfusion [2,3]. However, ETT cuff pressure varies and may be out of range. A minimal pressure of 20 cm H 2 O is recommended to prevent aspiration and ventilatorassociated pneumonia [4,5]. Overinflation is associated with damage of tracheal mucosa by compromising capillary perfusion, which leads to significant adverse effects [6]. For long times, without any evidence-based data, it has been believed that well-trained anesthetists can determine proper ETT cuff pressures. Anesthetists can detect appropriate inflation pressure and avoid overinflating the ETT cuff by palpating the ETT pilot balloon. It is the most common technique of ETT cuff pressure assessment in clinical settings. However, several studies suggest that this approach is unreliable [7][8][9][10]. It is supposed that experienced anesthesia staff may improve the safety of the palpation technique; however, earlier studies noticed a negative role of experience and recommended using a manometer [11]. Measurement of ETT cuff pressure by a monometer could reduce the rate of complications, but this is not widely available, especially in resource-limited settings and in emergency situations [12]. Hence, educational programs to increase awareness of anesthetists about overinflation risks may improve recent clinical practice.
The aim of this study was to assess the ETT cuff inflation pressure applied by anesthetists and to evaluate the effect of an interview and feedback on their accuracy during cuff inflation.

Ethical considerations
The study was carried out following approval by the Ethics Committee of Suez Canal University Hospital. The work described has been carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans. Written informed consents were obtained from the study participants after an explanation of the purpose and technique of the study. All data were kept confidential.

Study design, setting, and date
This single-blind, controlled trial was conducted at the Suez Canal University Hospital, Egypt from May 2017 through August 2017.

Eligibility criteria
The study recruited 37 anesthetists providing anesthesia for both emergency and scheduled surgeries at the Suez Canal University Hospital. Of those, 21 were residents (R1, R2, and R3) and 16 were registrars and senior registrars.

Procedure
The current study recorded two settings of ETT cuff pressure measurements in the intubated patients. The enrolled anesthetists were asked to inflate the ETT cuffs for all intubated anesthetized patients as per their clinical judgment. The cuff pressures were measured using a special aneroid manometer (VBM Medizintechnik, GmbH) and accordingly adjusted to 25 cm H 2 O by the researchers. For each anesthetist, 3 measurements were recorded, and the mean pressure values were calculated for both settings. The safety of the applied pressure was judged proper for pressure readings less than 30 cm H 2 O. For the initial 2 months, all anesthetists were blinded to the pressure values and the adjustments; then, they were informed about their mean ETT cuff inflating pressure during the surgeries and the performed adjustments. For the following two months, cuff pressure was measured, recorded, and accordingly adjusted by the researchers. All anesthetists were informed about their pressure values and the required adjustments.

Data collection
The researchers randomly selected days of work to gather data from operating theatre for both routine and emergency surgeries. On the 2 nd , 4 th , 7 th , 9 th , 11 th , 15 th , 16 th , 21 st , 22 nd , and 23 rd of May 2017 the researchers visited the operating theatre and collected data from the participating physicians. On these days, 29 anesthetists (22 residents and 7 registrars or senior registrars) completed their 3 rounds by giving general anesthesia for 3 different patients. No one inflates the ETT cuff below 25 cm H 2 O. The researchers estimated the mean of three readings for every participating anesthetist. After 2 months the researchers made an interview with the study participants and told each anesthetist about his or her results. The researchers asked them again to judge the ETT inflation pressure to be 25 cm H 2 O or around and be ready for the second round of the study. On the 6 th , 9 th , 10 th , 11 th , 12 th , 13 th , 16 th , 17 th , and 20 th of July 2017 the researchers again collected data from the participating physicians during anesthetizing their patients. On these days, 28 anesthetists completed their 3 rounds by giving general anesthesia for 3 different patients (22 residents and 6 registrars or senior registrars), and one senior anesthetist had no results.

Outcomes
The primary outcome was to assess the anesthetists' accuracy in inflating the cuffs of ETTs used to maintain the airway of generally anesthetized patients following the researchers' feedback. The secondary outcomes were to compare pressure values between senior and junior anesthetists and between scheduled and emergency operations.

Statistical analysis
Statistical analysis was performed using the Statistical Package for Social Sciences (IBM SPSS Statistics) for Windows, version 26 (IBM Corp., Armonk, N.Y., USA). For quantitative data, the Shapiro-Wilk test for normality was performed. Normally distributed data were summarized as mean ± standard deviation (SD), and groups were compared using paired t-test. Qualitative data were summarized as frequencies, and associations were tested using Pearson's Chi-square test. A p-value <0.05 was chosen to interpret the significance of statistical tests.

Results
The study enrolled 6 senior and 22 junior anesthetists with a mean age of 25.32 ± 2.91 years ( Table 1). The ETT cuff pressure values after the intervention were significantly lower than before the intervention. Concerning emergency surgeries, the mean cuff pressure decreased from 33.8 ± 1.95 to 30.8 ± 3.24 cm H 2 O (P = 0.000), while at scheduled surgeries the pressure decreased from 32.9 ± 2.38 to 29.9 ± 3.44 cm H 2 O (P = 0.001) ( Table 2). Before the intervention, only one anesthetist inflated the ETT cuff to the recommended safe limit (below 30 cm H 2 O), while most (96.4%) anesthetists inflated the cuffs above this limit. After the intervention, a significant (P = 0.000) elevation in awareness about safe pressure limits was noticed ( Table 3). The frequency of safe inflation pressure significantly increased in emergency surgeries from 0% to 38.5% (P = 0.000) ( Table 4) and from 7.7% to 42.3% in scheduled operations (P = 0.004) (  Table 6). After the intervention, seniors showed no significant difference (P = 0.079) in safety pressure limits of cuff inflation, meanwhile, 36.4% of junior staff significantly (P = 0.002) improved their performance and applied ETT cuff pressure below the safety limit after the intervention (Table 7).

Discussion
This study investigated the effect of an interview and feedback on Suez Canal University anesthetists regarding ETT inflation pressure during both emergency and scheduled surgeries. The ETT cuff pressure after the intervention was significantly lower than its value before the intervention, which was associated with increased safety of ETT cuff inflation. This finding is in agreement with Seyed Siamdoust et al. [13] who found that safety of inflation pressure was significantly elevated among anesthetists after an educational intervention. Additionally, Sole et al. [14] reported that an educational intervention was substantially effective in maintaining cuff pressure within the optimum range. Endotracheal tube cuff pressure measurement is affected by various factors including the cuff diameter, thickness, compliance, shape, filling material (air or water in certain surgeries), and head and neck position [15,16]. Several factors may influence the tone of the pilot balloon and consequently the reliability of the palpation technique, such as the tube type, geometry of the cuff, and the filling material [8,10]. Using a manometer could underestimate the measured ETT cuff pressure. When the external balloon is attached to the pressure gauge, air leakage occurs due to internal gauge space and pressure equalization [17].
Comparable results were reported by earlier studies [12,18], where most of the participating anesthetists underestimated the cuff inflation pressure. Seegobin and van Hasselt [6] showed evidence of obstruction to the tracheal mucosal blood flow at a lateral wall pressure above 30 cm H 2 O (22 mm Hg) with total occlusion of the flow over the tracheal rings and posterior tracheal wall at a pressure of 50 cm H 2 O (37 mm Hg). Capillary perfusion pressure has been recorded as ranging between 22 and 32 mm Hg, and the upper limit is uncertain. Hence, careful attention to the inflation technique and the intracuff pressure is important.      The current study showed that in emergency surgeries no anesthetist inflated the cuff within the safe pressure limit. After the intervention, in both scheduled and emergency surgeries, the safety of the inflation pressure was significantly increased. Similarly, Hoffman et al. [19] reported that emergency physicians were unable to inflate the ETT cuffs to safe pressures or estimate the cuff pressures by palpation. This could be attributed to the rare usage of manometers for cuff pressure measurements and the lack of sufficient time during emergencies. In contrast, a study conducted at the intensive care units reported that anesthesia providers used manometers frequently as they were oriented about the hazards of ETT cuff pressure in critical care patients [9].
Before the intervention, the ETT cuffs were overinflated (above 30 cm H 2 O) by all senior and junior anesthetists. After the intervention, anesthesia staff improved their skills and accuracy in adjusting the cuff inflation within a safe range (20-30 cm H 2 O). Nevertheless, the practice of senior staff did not show significant improvement. This was in accordance with Sayed Siamdoust et al. [13] and Wujtewicz et al. [20] who reported that the length of experience did not improve the anesthetists' skills for inflating the ETT cuff to a safe pressure. This could be explained considering the high self-confidence of the senior anesthetists that might be a barrier toward learning despite the value of the experience for safe anesthetists' clinical practice. The absence of manometer usage to measure the cuff inflation pressures could be another reason [21,22].
The differences between studies regarding the impact of the length of experience should be evaluated seeing that most anesthesia courses and curricula lack sufficient skills training. Therefore, it is crucial to implement educational programs for junior and senior anesthetists regarding the use of manometers in cuff pressure evaluation and limiting the palpation technique that is usually practiced by seniors. The use of a measurement device should be the standard practice for cuff inflation. Manometers are considered a safe measurement method during scheduled operations and can also be used in emergency conditions once the patients are stabilized [23,24].
The current study enrolled a small number of anesthetists. Further research is needed including a larger number of anesthetists from various health institutions with the identification of variables that may influence the cuff pressure, such as the ETT type and duration of intubation. Recognizing these variables may assist in maintaining the cuff pressure within an optimal range.

Conclusions
Interview and feedback to anesthetists were effective in lowering the ETT cuff inflation pressure to safer levels. The length of experience did not improve the anesthetists' accuracy for safe cuff inflation. The ETT cuff pressure should be routinely measured in patients scheduled for any surgical maneuver under general anesthesia with endotracheal intubation.

Disclosure statement
No potential conflict of interest was reported by the author(s).