The Effect of Body Position on Endotracheal Tube Cuff Pressure in Morbidly Obese Patients

Abstract

Background:

This study aims to ascertain whether different patient positions affect endotracheal tube cuff pressure in morbidly obese patients.

Materials and Methods:

There were 40 patients, who have body mass index (BMI) <30 kg/m² (Group I) and BMI >40 kg/m² (Group II), included in the study. All patients were intubated with a high-volume low-pressure endotracheal tube. All of the patients were kept in supine, 30° trendelenburg, and 30° reverse trendelenburg positions over a period of 5 min. During this period of time, these patients' endotracheal tube cuff pressures, hemodynamic, and ventilation parameters were measured.

Results and Discussion:

Peak airway pressure in Group II was statistically different from that in Group I in all of the three positions. The trendelenburg positions in both groups were statistically different from the supine positions, and the trendelenburg position in Group I was statistically different from the reverse trendelenburg position. A significant correlation was established between BMI (r = 0.454) and peak airway pressure (r = 0.492) in morbidly obese patients

Conclusion:

When morbidly obese patients are in the trendelenburg position under general anesthesia, endotracheal tube pressure is more affected by comparison with those with a normal BMI. For this reason, monitorization of tube cuff pressure is essential for morbidly obese patients in the trendelenburg position.

Introduction

By time, there has been an increase in patients who receive bariatric surgery because of morbid obesity. The maintenance of respiratory passage anatomy and functions of perioperative period is one of the most important issues for these patients, who may have many associate problems. Supine position, general anesthesia application, endotracheal intubation, anatomic effect of obesity, preference of especially laparoscopic surgery instead of open surgery, giving trendelenburg or reverse trendelenburg positions, and combined effects of these on intraabdominal and intrathoracic pressure may effect respiratory passage mechanics and functions.^1–6 During general anesthesia, endotracheal intubation may cause trauma and function loss for respiratory passage.⁷ To refrain from some respiratory passage complications of these patients, controlling and maintenance of endotracheal tube cuff pressures of desired levels may be beneficial.⁸ Since there are both morbid obesity's respiratory passage features and intubation-originated possible respiratory passage problems, this study aims to ascertain whether lying position and changes in endotracheal tube cuff pressures and constant monitorization are needed.

Material and Method

Research was planned as a prospective study. After Faculty Research Ethics Committee approval and patient confirmation obtained, 40 patients to whom general surgery was administered in operating theater were included into the study: 20 patients who were going to be operated for any reason with a body mass index (BMI) <30 kg/m² were assessed in Group I and 20 patients who were to undergo bariatric surgery with a BMI >40 kg/m² were assessed in Group II. Included patients were ASA I–III adults between 18 and 75 years old. Those who were pregnant, or needed urgent operation, or underwent respiratory passage surgeries, those whose endotracheal tube was tucked or obstructed and those who experienced laryngospasm or bronchospasm after intubation were not included in the research. This exclusion was made in order to not to influence the results by the surgical type. Planned study period of each patient was the period that was between the beginning of anesthesia induction and beginning of surgery.

All of the patients were taken to the operating room after their demographic data (age, weight, height, sex, and BMI) were recorded. Standard monitorizations (noninvasive arterial pressure, electrocardiography, and SpO₂) were carried out. Peripheral venous vascular access was established through 18–20 G branule. After a routine anesthesia method, standard induction (atropine 0.5 mg iv, propofol 2 mg/kg iv, remifentanil 1 μg/kg iv, and rocuronium 0.9 mg/kg) was provided to all patients; after muscle relaxation was confirmed through TOF-Guard monitorization, male patients were intubated by 7.5–8 mm (No: 7.5–8) inner diameter, female patients were intubated by 7–7.5 mm (No: 7–7.5) inner diameter high volume, low pressure endotracheal tube (ETT) administered as a routine. Tubes were placed with tips in 21–23 cm depth and their cuffs were inflated. Cuff pressures were adjusted as 25 cmH₂O by using cuff manometer (Microcuff Gmbh, Weinheim, Germany). Establishment of each of the two lungs' ventilation was confirmed by auscultation and ETT was detected.

Anesthesia maintenance of all patients who were included in the study was provided by O₂/air mixture (FiO₂ 0.4–0.5), sevofluran (end tidal 1–2%), and remifentanil 0.25–0.5 μg/kg/min infusion as a routine; ventilation parameters were adjusted as VT: 6–7 mL/ideal body weight, respiratory frequency: 12–16/min, and ETCO₂: 32–37 mmHg. Subsequently, measurement parameters were obtained like this. After the first stabilization while the patients were in supine straight horizontal position, first measurements were taken in the fifth minute. Later, the patients were put in the 30° trendelenburg position and in the fifth minute after being put in this position, second measurements were taken. Finally, the patients were put in the 30° reverse trendelenburg position and third measurements were taken in the fifth minute after repositioning. In each period, hemodynamia (arterial blood pressure, pulse rate, SpO₂, and ETCO₂) and ventilator parameters (tidal volume and peak airway pressure) were recorded at the same time with ETT cuff pressures.

Statistical method

For statistical assessment, SPSS 16.0 statistical software was used. Quantitative data was stated as mean standard deviation ± or median. For both groups, to compare the peak airway pressure and cuff pressures that were obtained in different periods (in patient positions), Friedman and Wilcoxon test was used. While comparing the groups, t-test was used on the data that provided parametric assumptions; but on the data that did not provide parametric assumptions, Mann–Whitney U test was used. The relationship between the parameters was assessed through Spearman correlation test. For statistical significance, p < 0.05 was accepted.

Results

Group I that consisted of patients with BMI <30 kg/m² and Group II that consisted of patients with BMI >40 kg/m² were significantly different in terms of body weight (Table 1).

Table 1.

Demographic Data

	Grup I	Grup II
Age (year)	49 ± 14	43 ± 10
BMI (kg/m²)	25 ± 3	47 ± 5^a
Weight (kg)	68 ± 9	126 ± 21^a
Height (cm)	165 ± 7	161 ± 13
Gender (M/F)	6/14	3/17

p < 0.05.

BMI, body mass index.

The effect of patient's lying position on ETT tube cuff is given in Table 2; effects on hemodynamic (pulse rate, systolic, diastolic, and average arterial pressure) and inspiratory parameters (tidal volume, ETCO₂, and peak airway pressure) are given in Table 3.

Table 2.

Changes in Variations of Cuff Pressure, According to the Position (cmH₂O)

	Group I	Group II
Supine	24.8 ± 0.6	25.3 ± 0.9
Trendelenburg	27 ± 1.2^a,b	31 ± 3.5^a–c
Reverse trendelenburg	24.5 ± 0.8	25 ± 1.5

p < 0.05: Difference according to supin position.

p < 0.05: Difference according to reverse trendelenburg position.

p < 0.05: Difference among the groups.

Table 3.

The Positions' Relationship Between Hemodynamic and Respiratory Parameters

	Groups	Supine	Trendelenburg	Reverse trendelenburg
HR	I	82 ± 15	82 ± 16	80 ± 11
	II	89 ± 18	89 ± 16	91 ± 11
SAP (mmHg)	I	112 ± 22	124 ± 35^a	108 ± 21^b
	II	109 ± 35	126 ± 24^a	111 ± 21^b
DAP (mmHg)	I	75 ± 12	70 ± 25^a	65 ± 19^b
	II	77 ± 17	69 ± 17^a	67 ± 19
MAP (mmHg)	I	87 ± 13	88 ± 27	80 ± 19^b
	II	88 ± 20	88 ± 17	82 ± 19^b
ETCO₂	I	34 ± 4	34 ± 3	34 ± 3
	II	36 ± 3	37 ± 3	36 ± 3
Tidal volume	I	438 ± 78	450 ± 75	437 ± 80
	II	469 ± 70	465 ± 75	461 ± 66
Peak airway pressure	I	15.6 ± 3.4	17.2 ± 3.9^a	15.4 ± 2.7
	II	23 ± 4^c	26.6 ± 3.7^a,c	22 ± 3.6^b,c

p < 0.05: Difference according to supin position.

p < 0.05: Difference according to trendelenburg position.

p < 0.05: Difference among the groups.

DAP, diastolic arterial pressure; HR, heart rate; MAP, mean arterial pressure; SAP, systolic blood pressure.

ETT cuff pressures that were measured 5 min after the first stabilization were similar as planned (p > 0.05). However, the trendelenburg position caused significant increase in ETT cuff pressure (p < 0.05). The increase in cuff pressure was found significantly higher in the morbid obese group during the trendelenburg position (Group 1: 27 ± 1.2 – Group 2: 31 ± 3.5) than in the other group (p < 0.05). In the reverse trendelenburg position, ETT cuff pressures declined to supine position rates (p > 0.05) and the rates were found similar between the groups (p > 0.05).

In both groups, pulse rate was not affected by position changes. In both groups, an increase was detected in systolic and diastolic arterial pressures in the trendelenburg position in comparison with supine position (p > 0.05); in the reverse trendelenburg position a decrease was detected (p < 0.05). Average arterial pressure declined significantly in both groups in the reverse trendelenburg position only in comparison with trendelenburg position (p < 0.05) (Table 3).

Tidal volume and ETCO₂ rates were not affected by position changes (p > 0.05). Peak airway pressure was found more significantly higher in the morbid obesity group than in the other group, both in starting supine position and in other positions (P < 0.05). Although in both groups peak airway pressure increased at the same time with trendelenburg position, this increase was found significantly higher in the morbid obese group than in the other group (Table 3).

When the relationship between hemodynamic and inspiratory parameters with ETT cuff pressures in the trendelenburg position was assessed in the morbid obesity group BMI (r = 0.454, p = 0.02), a significant positive relationship between peak airway pressures (r = 0.492, p = 0.02) and end-tidal carbon dioxide with ETT cuff pressure was detected. (Table 4).

Table 4.

The Relationship Between Trendelenburg Positon's Cuff Pressure and the Variables (p)

	Group I	Group II
BMI	0.21	0.01 (r = 0.454)
Weight	0.44	0.66
Ideal body weight	0.18	0.3
Height	0.67	0.93
Peak airway pressure	0.93	0.02 (r = 0.492)
SAP	0.16	0.23
DAP	0.9	0.16
MAP	0.11	0.12
HR	0.4	0.4
ETCO₂	0.7	0.03 (r = 0.512)
SpO₂	0.3	0.2

Discussion

Our study has shown that morbid obese patients during the operation especially when they are put in the trendelenburg position, ETT cuff pressures increase significantly around 5.7 cmH₂O. The patients who were not morbid obese were studied in the same conditions and no significant increase was detected. Another main finding of our study is the significant increase of endotracheal tube cuff pressure and peak airway pressure in the trendelenburg position in both groups of patients, and the clarity of this significant increase in morbid obese patients than the patients who are not obese. In this study, a significant relationship between BMI and peak airway pressure in the trendelenburg position with ETT cuff pressure has also been presented. In the reverse trendelenburg position in both groups, no specific difference in cuff pressure and peak airway pressure was observed in comparison with supine position.

In morbid obese patients, airway resistance increase has been observed because of the fact that airway dynamics are affected because of fat deposit on pharyngeal structures, change in upper airway structure, short and thick neck structure, and also because of restrictive respiration pattern that was originated from diaphragm, which is under pressure, and chest wall mass.^6,9–12 This increase is higher in supine lying position.¹¹ For this reason, generally a lying position, in which back is raised, is recommended because it decreases the problems already mentioned.³

Today, there is no other study that evaluates ETT cuff pressures of obese patients in terms of their lying position. However, there are studies that relate ETT cuff pressures to head and neck positions, airway pressures, and complications in patients who have normal body weights.^13–15

It is stated that minimum cuff pressure that will not leak and that will be used to block aspiration is 25 cmH₂O.¹⁶ It is also suggested that cuff pressure should not exceed 30 cmH₂O in order not to disrupt mucosal perfusion.⁷

It is stated that there is a relationship between tube cuff pressure and head–neck positions as well.¹⁷ Patients', whose cuff pressures were adjusted as 40.8 cmH₂O in neutral position, average cuff pressures were found high as 51.7 while their heads were in anteflexion, 43.5 cmH₂O while in extension and 47.6 cmH₂O while in rotation to both sides. In a study that evaluated changes in positions and changes in ETT cuff pressures of patients to whom mechanical ventilation was applied, it was concluded that there were important changes in ETT cuff pressure in left–right decubitus and supine position changes.¹⁸ Again in intensive care patients, through 16 types of head, neck, and patients changes, an important rate of increase in ETT cuff pressure was revealed.¹⁹ 40.6 percent of these patients, cuff pressure in any position was found above the rate of 30 cmH₂O.

Endotracheal tube cuff pressure and some airway complications are associated. Child patients in whom outpatient surgery was carried out, relationship between ETT cuff pressure and postoperative throat ache was studied, and it is stated that the incidence of throat ache was higher in patients especially whose cuff pressures were more than 30 cmH₂O.²⁰ Throat ache incidence in this study was found 4% in patients whose cuff pressures were between 11 and 20 cmH₂O; 20% in those whose cuff pressures were between 21 and 30 cmH₂O; 68% in those whose cuff pressures were between 31 and 40 cmH₂O; and 98% in those whose cuff pressures were more than 40 cmH₂O. It is concluded that a cuff pressure rate, which especially reaches 30 cmH₂O, may be clinically important in terms of postoperative complications.

In a study carried out in patients who underwent a laparoscopic cholecystectomy in head up position and in those who underwent a colon surgery in head down position, it is observed that with head down position, ETT cuff pressures increase around 6 cmH₂O. In this study, no relationship could be shown between BMI and abdominal pressure.²¹ In a study carried out on 40 patients who underwent laparoscopic gynecologic surgery (BMI 25.2 ± 4.1 kg/m²) and 30 patients who underwent gynecologic surgery by laparotomy (BMI 24.1 ± 3.9 kg/m²), it was stated that the trendelenburg position and pneumoperitoneum could be related to ETT cuff pressure and that cuff pressure increase showed significant positive correlation with peak airway pressure.⁵ Again in a study carried out on patients to whom laparoscopic chole- cystectomy and inguinal hernia repair were administered, it was observed that pneumoperitoneum significantly increased cuff pressure; however, it was also observed that after pneumoperitoneum in the reverse trendelenburg position caused a significant decrease in cuff pressure in comparison with ETT balloon position in supine position.

In our study, however, in our group with BMI lower than 30 kg/m², in the trendelenburg position, peak airway pressure and ETT cuff pressure increase are around 1.6 and 2.2 cmH₂O, respectively. This is statistically significant but this is not a clinically significant increase. In our morbid obese group, these increases were detected to be more dramatic and significant as being around 3.6 and 5.7 cmH₂O. A study that shows trendelenburg position and pneumoperitoneum could increase tube cuff pressure in morbid obese patients does not exist. As seen in results of our study, body position changes in patients with normal body structure effect cuff pressure within normal limits. However, in morbid obese patients, in the trendelenburg position, cuff pressure may rise above the desired limits. Nevertheless, surprisingly enough, this increase was not excessive. Although in the beginning of our study in supine position ETT cuff pressure was adjusted as 25 cmH₂O, in 60% of the morbid obese patients, ETT cuff pressure of 30 cmH₂O and above was reached when patients were put in the trendelenburg position. In the reverse trendelenburg position, there was no change in ETT cuff pressure, which could be considered as significant in both groups of patients. Our study presents positive significant relationship between BMI and peak airway pressure and ETT cuff pressure. Thus, when morbid obese patients are put in the trendelenburg position, in the case of an increase of both parameters, it is possible to predict that ETT cuff pressure has increased.

Common conclusion of studies that have been carried out so far is that ETT cuff pressure should be kept between 20 and 30 cmH₂O. When pressure exceeds 30 cmH₂O, deterioration of blood's building up on trachea mucosa was related to morbidity as mentioned before. A factor that limits our study is that no postoperative period morbidity evaluation was aimed. Therefore, in the patients, whose pressures increased more than 30 cmH₂O, the pressures decreased less than 30 cmH₂O by the end of the study.

To conclude, in our study in the trendelenburg position, in both groups, there is an increase in ETT tube cuff pressure, but this increase is significantly higher in the morbid obese patient group. The data clearly demonstrate a correlation between increased airway pressures and increased cuff pressures. We believe that in such patients, monitorization of endotracheal tube cuff pressure is necessary. However, to determine whether an increase in endotracheal tube cuff pressure causes serious complications, other studies covering more patients are needed.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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