The Endotracheal Tube (ETT) is a vital tool in airway management, categorized broadly into kink and non-kink variants. The non-kink ETT features an internal circular wire to prevent bending, which is commonly employed in surgeries involving the head and neck regions or positions prone to ETT bending. Conversely, the kink ETT lacks an internal wire and typically includes a cuff to prevent air leakage. Two cuff types are available high-pressure (low-volume) and low-pressure (high-volume). While high-pressure cuffs may lead to tracheal mucosa ischemia and are less suitable for prolonged surgeries, low-pressure cuffs may increase the risk of throat discomfort due to wider contact, aspiration, spontaneous extubation, and insertion difficulties [1, 2].
Regular monitoring of Endotracheal Tube (ETT) intracuff pressure is essential. The cuff should be inflated with the minimal volume necessary to prevent air leakage during positive pressure inspiration. The recommended cuff pressure range is between 20 to 30 cm H2O [3]. Excessive cuff pressure can cause the tracheal mucosa injury. Meanwhile, the cuff pressure below the ideal value results in airflow leakage in the positive pressure and aspiration vents. Therefore, cuff pressure outside the ideal value range (<20 cm H2O and >30 cm H2O) has the potential to harm patients [4].
The positioning of the ETT may alter with movements of the patient’s head and neck, potentially leading to shifts in ETT cuff pressure. These positional changes can occur due to alterations in the patient’s orientation, resulting in adjustments in ETT placement and variations in the surrounding anatomical structures’ configuration [5-7]. In their 2021 study, H.J. Kim et al. observed a cephalad shift in the ETT with lateral head-neck rotation, leading to increased intracuff pressure. This pressure elevation was more pronounced when the lateral head-neck rotation was towards the same side as the tube fixation, compared to rotation in the opposite direction. The precise cause of this pressure rise remains unclear, as factors influencing ETT intracuff pressure are still relatively limited. A study conducted in South Korea identified several potential factors contributing to changes in ETT intracuff pressure, including alterations in the neck position, neck anatomy, and increased intrathoracic pressure associated with the prone position.
Intracuff ETT pressure variations are not only evident between supine and lateral positions but also occur between supine and prone positions. D. Kim et al. [8] in their study obtained the results of intracuff ETT pressure in supine patients higher than intracuff ETT pressure at the prone position. Another study found that the intracuff ETT pressure of patients in the supine position was lower than in the prone position [9]. The findings of various studies investigating alterations in ETT intracuff pressure from supine to prone positions prompted the author to explore differences in intracuff pressure between supine and prone positions among patients intubated in the operating room. This study’s aim is to investigate the impact of supine and prone positioning changes on ETT pressure.
Patients and methods
This analytical experimental research aimed to assess the pressure differential in ETT cuffs between the supine and prone positions among patients intubated in the operating room. The study protocol received approval from the Health Research Ethical Committee of Dr. Saiful Anwar General Hospital (No. 400/057/K.3/102.7/2023). The target population comprised surgery patients undergoing general anesthesia via intubation at the Central Surgical Department.
The inclusion criteria included patients aged 18 to 64, patients with prone position surgery, height 150-180 cm, and willingness to follow research procedures. The exclusion criteria included patients with cervical abnormalities, with a history of chronic obstructive pulmonary disease, pregnant patients, morbid obese patients (BMI >40 kg/m2), and patients with possible difficult airway management.
The study sample was the eligible population that met the inclusion criteria and did not meet the exclusion criteria. Samples are taken by consecutive sampling, where each subject who meets the criteria for research inclusion is included in the study until a certain period of time so that the required number of subjects is met. The size of the subjects in this study was calculated based on the analytical research sample size formula for paired numerical data:
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N1=N2 - number of subjects; Zα - deviat baku alpha; Zβ - deviat baku beta; S - standard deviation of pressure in the ETT cuff neutral head-neck position established based on preliminary research; X1-X2 - minimum mean difference that is considered meaningful.
In previous research by A.W. Handayanto et. al [10], the number of samples used was 40. In this study the error rate of type I (value a) was set at 0.05 so that Za = 1.96 (two-way hypothesis). The error rate of type II (P value) is set at 0.1 which is the research power so that the Zp value = 1.28 is obtained. The combined standard deviation will be determined based on preliminary research and the minimum mean difference considered meaningful is 5. The minimum sample size required for preliminary research is 7 people. The minimum sample was 12 people. To anticipate the possibility of selected subjects dropping out, an additional 20% of the minimum sample size was carried out. So that the minimum number of samples is 15 people.
In the operating room, after the patient is fitted with standard monitoring equipment, assured of an adequate and patented i.v. pathway, the patient is given preoxygenation, which is breathing using a 100% oxygen fraction. The patient receives general anesthesia according to the procedure. Patients receive standard general anesthesia with Fentanyl 2 mcg/kgBW, Propofol 1.5-2.5 mg/kgBW, and Atracurium 0.5 mg/kgBW. The Endotracheal Tube used is uniform, of the non-kinking brand Remedi®, with an inner diameter size of 6.5-7.5 mm, adjusted to the patient’s condition. After approximately 5 minutes of assisted controlled ventilation, a single intubation attempt was performed. Endotracheal intubation involves inserting the ETT into the patient’s trachea to mitigate upper airway obstruction and facilitate air entry into the lungs. For consistency, ETT insertion depths adhered to standards of 18 cm for women and 21 cm for men.
As soon as endotracheal intubation is successfully performed, the body is positioned supine. The cuff was inflated using the minimal occlusive volume technique. Checking the entry or absence of ETT into the trachea through auscultation and evaluation of ETCO2, then examined symmetrically right and left, then fixation on ETT at the corner of the right lip. After ETT is well fixed, cuff pressure measurement is performed at the supine position using a Portex® Cuff inflator at end-expiration of manual ventilation without removing the anesthesia circuit from ETT and conditions without PEEP. During measurement, patient oxygenation is maintained by passive oxygenation method using 100% oxygen fraction and 5 lpm oxygen flow.
Before changing the position of the patient’s head and neck, ventilation was carried out using 100% fraction oxygen for 3 minutes with the aim of providing preoxygenation before measurement. Then, the patient was positioned in the prone position (see Figure). Remeasured pressure inside the ETT cuff with a Portex® Cuff inflator during end-expiration from manual ventilation without removing the anesthesia circuit from ETT and conditions without PEEP. During measurement, patient oxygenation is maintained by passive oxygenation method using 100% oxygen fraction and 5 lpm oxygen flow. If the data has been recorded, the patient’s position is returned to the position according to the needs of the operation, a re-examination is carried out to determine whether the ETT is still at the correct depth, and then the ETT cuff is developed up to 25 cm H2O using a cuff inflator. If the surgery has been completed, the patient is awakened, and then extubation is performed. Post-extubation, a reevaluation of the patient’s condition is carried out. If stable, the patient is taken to the post-anesthesia recovery room for observation.
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The data was analyzed using a paired t-test. The Wilcoxon test is used if the paired t-test conditions are not met (the data are not normally distributed). The difference in measurement results between groups was tested with a level of significance a=0.05 and a confidence interval of 95%.
Results
A total of 21 male patients undergoing Prone Position surgery with an ETT internal diameter of 7.5 were selected based on predefined inclusion and exclusion criteria. The average age of the patients was 46±14.05 years, with weights ranging from 50 to 80 kg and an average height of 164.28±5.19 cm. According to the American Society of Anesthesiologists (ASA) physical status classification, 1 (4.8%) patient was classified as ASA 1, 8 (38.1%) patients as ASA 2, and 12 (57.1%) patients as ASA 3. The majority of patients underwent orthopedic surgery (90.5%), while one patient underwent plastic surgery (4.8%) and another patient underwent neurosurgery (4.8%) (table 1).
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The ETT pressure cuff pressure was significantly different in the supine body position, at 24.81±1.24 cm H2O, and increased to 26.38±1.28 cm H2O in the prone position (table 2).
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Changes in body position from supine to prone position result in a difference in intracuff pressure ETT. The lowest pressure difference of 1 cm H2O and the highest pressure difference of 2 cmH2O were obtained. The average pressure difference of a total of 21 research subjects after changing body position was 1.7±2.0 cm H2O (table 3).
Discussion
During the study, 21 patients were enrolled. All samples were male, and all study samples obtained a median age of 46 years, with an age range of 18-65 years. The mean ETT intracuff pressure was increased from a supine to a prone position. This study supports the previous research study conducted by E. Choi et al [9]. Intracuff pressure may affected by several causes, such as the type of ETT used and the inflation technique. Both studies use the minimal occlusive volume technique. The minimum occlusive methods work by filling a certain amount of air volume into the cuff so that there is no more leakage of breath sounds in the end-inspiratory phase when given positive pressure ventilation [5]. In our study, the mean intracuff ETT pressure in the prone position was 26.38±1.28 cm H2O. This contrasts with the findings of E. Choi et al. [9] who reported an average intracuff ETT pressure of 28.0±1.9 cm H2O in the prone position. Our study utilized the cuff filling method with the minimum occlusive volume technique, resulting in variable intracuff pressures in the supine position. In contrast, E. Choi et al. [9] employed the cuff inflator method to standardize intracuff pressure at 22 cm H2O in a neutral head-neck position.
The mean ETT intracuff pressure in our study while prone was 26.38±1.28 cm H2O, consistent with the findings of E. Choi et al. (2017), who reported an average intracuff pressure of 28.0 ± 1.9 cm H2O in the prone position. These results fall within the normal range of 20-30 cm H2O. Prolonged intracuff pressures exceeding this range (>30 cm H2O) can induce hypoperfusion of the tracheal mucosa, potentially leading to mucosal damage, ulceration, necrosis, perichondritis, and subsequent chondritis. Chronic ulcer healing may result in tracheal stenosis due to fibrotic tissue formation. Elevated intracuff pressure beyond 30 cm H2O has been associated with ischemic tracheal events, ETT obstruction, and tracheal wall damage. Animal and human studies have demonstrated that intracuff pressures exceeding 30 cm H2O can induce decreased blood flow to the tracheal mucosa within as little as 25 minutes [9].
A significant difference in ETT intracuff pressure between the supine and prone positions has been observed in various studies [5, 7]. This phenomenon is likely attributed to head and neck position changes, potentially leading to a cephalad shift of the ETT. Such a shift may position the ETT cuff adjacent to anatomical structures with limited compliance, such as the cricoid cartilage. According to Boyle’s law, which states that at a constant temperature, the pressure and volume of a gas are inversely proportional, a decrease in the volume of gas in a closed space will result in an increase in pressure. Consequently, compression of the ETT cuff volume due to surrounding airway structures post-cephalad shift following a positional change could lead to elevated intracuff pressure. Our study’s findings align with those of E. Choi et al. [9] and D. Kim et al [8]. Both concluded a significant difference in pressure between the two positions.
Our study showed a significant increase in intracuff ETT pressure (p<0.001) from the supine position to the prone position, which was 1.58 cm H2O. The increase in ETT intracuff pressure in our study was almost the same as E. Choi et al.’s study [9]. Different results were obtained from other studies conducted in India and Korea. The intracuff ETT pressure of female patients in the neutral supine position (25.2 cm H2O) was higher than in the neutral prone position (24.8 cm H2O). The intracuff ETT pressure of male patients in the neutral supine position (24.8 cm H2O) was lower than in the neutral prone position (25.1 cm H2O) [11]. What underlies these differences is the difference in the sex of the sample used. In male patients, intracuff ETT pressure increases in the prone position compared to the supine one. This is consistent with our study, where our patients were all male and had intracuff ETT pressure in the prone position, which increased higher than the supply position. The difference in results between men and women in the study is unknown.
After examining the difference in ETT intracuff pressure between the supine position and the prone position in intubated patients, it can be concluded that there is a significant difference in ETT intracuff pressure between the supine position and prone position in intubated patients. From all study samples, no patients exceeded the safe level of intracuff ETT pressure (>30 cm H2O) after a change in position. In addition, the minimum occlusive volume technique used to develop the ETT cuff can generate ETT intracuff pressure at a safe range (20-30 cm H2O). Based on these things, we recommend closely monitoring intracuff pressure during anesthesia maintenance in surgery with a change in a supine position to prone so that complications from intracuff pressure changes can be prevented. The use of the cuff inflator tool as a gold standard in carrying out the ETT cuff development procedure. ETT cuff development techniques with minimum occlusive volume techniques are used as an alternative in carrying out non-kinking type ETT cuff development procedures with high volume-low pressure cuff types if the cuff inflator tool is unavailable.
Conclusion
ETT intracuff pressure was significantly higher after the position change from the supine position to the prone position.