Pneumoperitoneum via CO2 insufflation is essential for laparoscopic surgery. Abdominal insufflation markedly increases respiratory system resistance, which returns to baseline immediately after abdominal deflation . However, increased endotracheal tube cuff pressure (Pcuff) resulting from pneumoperitoneum may raise the risk of postoperative complications such as cough, sore throat, hoarseness, and blood-streaked expectorations [2, 3]. Several factors affect endotracheal tube Pcuff during general anesthesia, including the use of nitrous oxide, changes in head and neck position, pneumoperitoneum, and the Trendelenburg position [1, 2, 4, 5, 6]. The current study evaluated endotracheal tube Pcuff changes and airway pressure (Pairway) changes during pneumoperitoneum for laparoscopic cholecystectomy in the “head up” position. Then, correlations between body mass index (BMI), pneumoperitoneum time, and Pcuff changes were investigated.
2 Patients and methods
2.1 Patient selection
The current study was approved by the relevant institutional review board and written informed consent was obtained from all patients. The patients included ranged from 20–70 years in age, were of American Society of Anesthesiologists physical status I and II, and were undergoing elective one-port laparoscopic cholecystectomy. Patients with a history of tracheostomy, abnormal airway anatomy, lung disease with impaired compliance, upper respiratory tract infection within the last 2 weeks and failure of first intubation, and bucking after intubation or during surgery were excluded. The protocol of this clinical trial was registered at the Clinical Information Service (available at http://cris.nih.go.kr, KCT 0002937). Patients were allocated to either a study group (BMI ≥ 25 kg/m2) or a control group (BMI < 25 kg/m2).
2.2 Anesthesia and endotracheal tube cuff pressure measurement
No premedication was given to any patients included in the study. On arrival to the operating room, standard monitoring with electrocardiography, pulse oximetry, noninvasive blood pressure, and bispectral index (BIS) was performed. Anesthesia was induced via propofol (1.5–2.0 mg/kg) and rocuronium (6–8 mg/kg). Endotracheal intubation was performed with a high-volume low-pressure cuffed oral endotracheal tube of appropriate size (male 7.5 mm ID and Female 7 mm ID) by an experienced anesthesiologist. After tracheal intubation, a manometer (Mallinckrodt pressure manometer; Mallinckrodt Covidien, Athlone, Ireland) was connected to the pilot balloon using a 3-way stopcock and the endotracheal tube cuff was inflated with air using a 10 mL syringe. The target pressure was 22 cmH2O. Air leakage around the endotracheal tube was monitored with a stethoscope. All measurements were taken during the inspiratory phase of positive pressure ventilation and performed by one anesthesiologist. Mechanical ventilation was controlled to maintain the end tidal carbon dioxide tension at 35 to 40 mmHg. Anesthesia was maintained using 50% oxygen in nitrous oxide mixture and desflurane. The inhalational desflurane concentration was adjusted to maintain systolic blood pressure within ± 20% of the pre-anesthetic value and maintain the BIS at 40–60. Body temperature (36–37°C) was maintained by forced air warming and controlled room temperature. All patients received abdominal CO2 insufflation with intra-abdominal pressure maintained at 12 mmHg prior to adopting a head-up position. Pcuff was monitored continuously until CO2 desufflation, and the change in Pcuff was defined as the difference between the pressure just before intra-abdominal CO2 insufflation and the pressure before CO2 desufflation. Airway pressure (Pairway) was also monitored, and change in Pairway was defined in the same manner. Body temperature was checked during surgery and pneumoperitoneum time was recorded. Sore throat was assessed at 1 and 24 hours after extubation. The grade of sore throat was evaluated using a numerical rating scale ranging from 0 (no discomfort) to 10 (most severe discomfort).
2.3 Statistical analysis
The sample size was calculated using power analysis (α = 0.05, power = 0.9) based on a previous study . Twenty-five patients were required in each group (N = 50), and a total of sixty patients were recruited to allow for an estimated dropout rate of 10%. SPSS v. 24.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analyses. Data are expressed as numbers or mean ± SD. The independent t-test was used for comparisons of age, height, weight, BMI, duration of anesthesia and surgery, changes in Pcuff and Pairway, and sore throat grade between the two groups at each time-point. Pearson’s correlations were calculated to assess relationships between change in Pcuff and BMI and pneumoperitoneum time for all patients. P < 0.05 was deemed to indicate statistical significance.
3.1 Demographic data
A total of 66 patients undergoing one-port laparoscopic cholecystectomy under general anesthesia were assessed for eligibility. Two declined to participate, thus a total of 64 patients were enrolled: 33 in the study group and 31 in the control group. One patient in each group was excluded due to bucking after intubation, and the surgery method was changed to open cholecystectomy in one patient in the study group. One patient in the study group was excluded due to hypothermia. Therefore, 30 patients in each group were included in the final analysis (Figure 1). Demographic and clinical characteristics of the patients are shown in Table 1. By virtue of the study design (i.e., the group allocation criterion), BMI and body weight differed significantly in the two groups.
3.2 Changes of Pcuff and Pairway
Pcuff increased to 5.3 ± 3.6 cmH2O in the study group and 5.7 ± 5.4 cmH2O in the control group from just before CO2 insufflation to prior desufflation. However, there was no significant difference between the two groups (Table 2). After CO2 desufflation, Pcuff decreased or remained stable in all but one patient in each group. The mean changes were 1.7 ± 1.9 cmH2O in the study group and 1.4 ± 1.6 cmH2O in the control group. Changes in Pairway were similar to changes in Pcuff, and there was no significant difference between the two groups (Table 2). After CO2 desufflation, Pairway either decreased or remained stable in all patients. The mean changes were 3.0 ± 2.0 cmH2O in the study group and 2.9 ± 1.8 cmH2O in the control group.
3.3 The correlation between body mass index, pneumoperitoneum time, and Pcuff changes
There was a significant correlation between the change in Pcuff and the duration of pneumoperitoneum (r = 0.309, p = 0.016) (Figure 2). BMI was not correlated with the change in Pcuff (r = 0.022, p = 0.867) (Figure 3). Sore throat score at 1 and 24 hours after extubation did not differ significantly between the two groups.
Based on international guidelines, Pcuff should be kept between 20 and 30 cm H2O using a manometer . The pressure within the inflated cuff is dynamic and can be altered by various clinical factors including the size and shape of the trachea, the use of N2O, head or neck position, body temperature, the use of specialized surgical instruments [1, 2, 4, 5, 6, 8], endotracheal suctioning, and coughing . However, no standard exists with regard to the frequency and method of Pcuff monitoring, and Pcuff measurement is not part of routine anesthesia monitoring. While inappropriately low Pcuff can induce ventilator leakage during mechanical ventilation and aspiration, excessive Pcuff can increase the risk of postoperative complications such as cough, sore throat, hoarseness, and blood-streaked expectorations [2, 3]. The impairment of tracheal mucosal blood flow is also an important factor in tracheal morbidity associated with intubation. Hence, it is recommended that cuff inflation pressure should not exceed 30 cmH2O .
The frequency of laparoscopic surgery is increasing. Pneumoperitoneum for laparoscopic surgery is essential and causes increased respiratory system resistance. However, respiratory system resistance reportedly returns to baseline immediately after abdominal deflation . The concern of the anesthesiologist is the change in Pcuff caused by pneumoperitoneum for surgery. Yildirim et al. reported that pneumoperitoneum by CO2 insufflation and the reverse Trendelenburg position caused Pcuff elevation and a higher incidence of sore throat after surgery . Yu et al. reported that a head-up position did not affect Pcuff . However, they investigated Pcuff during a short period just before and after abdominal insufflation and position change in laparoscopic surgery. Geng et al. observed increases in Pcuff and Pairway during pneumoperitoneum and with patients in the Trendelenburg position . They suggested that the increased Pairway during laparoscopic surgery would conduct and press part of the cuff, resulting in increased Pcuff. In the current study, the effect of the head-up position was difficult to assess because CO2 insufflation and the head-up position change were performed almost simultaneously. Gali et al. reported that peak inspiratory Pairway at 30 minutes after incision for robotically assisted hysterectomy with pneumoperitoneum and the steep Trendelenburg position increased in conjunction with increasing BMI . In the current study, which involved pneumoperitoneum and the head-up position, Pcuff and Pairway were monitored continuously until abdominal CO2 desufflation. Pcuff and Pairway were gradually increased during pneumoperitoneum regardless of BMI. Sore throat is a common postoperative complaint following endotracheal intubation . It has been suggested that over-inflation may increase the cuff-tracheal contact area and damage the tracheal mucosa . In the present study, there was no difference in sore throat between the two groups, and sore throat scores were lower than expected. Pcuff was very high when inflated by the anesthesiologist, according to his personal experience using the pilot balloon palpation method without the assistance of instrumentation. Liu et al. also reported that Pcuff estimated by palpation based on personal experience is often much higher than that measured, or what may be optimal . If a surgery is performed under an already high Pcuff and the pressure increases during pneumoperitoneum, there will be a greater risk of complications after a surgery. The lower than expected sore throat scores in this study were a result of initial adequate air inflation in accordance with manometer targeting of 22 cmH2O, and relatively short surgery time. It has been suggested that Pcuff should be measured regularly. Kako et al. suggested that fluctuations in Pcuff can be expected during prolonged surgical procedures and supports the need for continuous monitoring of Pcuff .
In the present study, the highest Pcuff was 48 cmH2O. Seven patients in the study group and eight in the control group had Pcuff that was > 30 cmH2O. However, there was no significant relationship between peak Pcuff and sore throat score. If the surgery time is extended and Pcuff is not monitored, an increase in intracuff pressure may compromise perfusion to the tracheal mucosa and cause patient discomfort . Nitrous-oxide anesthesia during laparoscopy also increases the cuff pressure and the incidence of postoperative sore throat. Thus, routine monitoring of cuff pressure is needed. 
Pcuff can also be reduced by several factors [8, 13]. In the supine position, during the induction of anesthesia, the loss of consciousness is associated with loss of the tonicity of the muscles around the neck. This may cause an initial decrease in Pcuff, and the continuous unconsciousness and paralysis over time may result in further reduction in Pcuff . In one study, Pcuff values were < 20 cmH2O in 30% of patients in intensive care unit, and patients who were less sedated with higher levels of consciousness had greater fluctuations in Pcuff . In the current study there were also initial decreases in Pcuff in five patients in the study group and six in the control group. However, there were no audible leakages. Because the change in Pcuff was defined as the difference in Pcuff between the pressure just prior intra-abdominal CO2 insufflation and the pressure before CO2 desufflation, initial Pcuff decreases did not affect the results.
The present study had some limitations. First, the mean BMI in the study group was lower than expected, although by design, there was a statistically significant difference in BMI between the two groups. Second, pneumoperitoneum time was relatively short. If BMI had differed more substantially in the two groups, and pneumoperitoneum time had been longer, different results may have been obtained.
The change in Pcuff was not affected by BMI, and it was significantly correlated with pneumoperitoneum time in laparoscopic cholecystectomy. Thus, we recommend regular measurement and adjustment of Pcuff in all patients during laparoscopic surgery with nitrous–oxide anesthesia.
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About the article
Published Online: 2019-05-30
Conflict of interestConflict of interest statement: Authors state no conflict of interest.
Citation Information: Open Medicine, Volume 14, Issue 1, Pages 431–436, ISSN (Online) 2391-5463, DOI: https://doi.org/10.1515/med-2019-0046.
© 2019 Youngsuk Kwon et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. BY-NC-ND 4.0