Effect of pneumoperitoneum and Trendelenberg position on oropharyngeal sealing pressure of I-gel™ and ProSeal LMA™ in laparoscopic gynecological surgery: A randomized controlled trial.

BACKGROUND: A sustained and effective oropharyngeal sealing with supraglottic airway (SGA) is required to maintain the ventilation during laparoscopic gynecological surgery in the Trendelenburg position. This study was conducted with I-gel™ and ProSeal LMA™, two prototype SGA devices with a gastric access.
MATERIALS AND METHODS: We enrolled 60 American Society of Anesthesiologists physical status I and II patients and randomized to either I-gel or ProSeal LMA (PLMA) group. After induction of anesthesia using a standardized protocol, one of the SGA devices was inserted. The primary objective of this study was to compare the oropharyngeal leak (sealing) pressure of I-gel™ and ProSeal LMA™ after pneumoperitoneum and Trendelenberg position. The secondary objectives were to compare ease of insertion, cuff position as assessed by the fiberoptic view of the glottis, adequacy of ventilation and incidence of complication.
RESULTS: The baseline (before pneumoperitoneum) oropharyngeal leak pressure of I-gel was less than the PLMA (mean (standard deviation [SD]) 24 (4) vs. 29 (4) cmH2O, respectively; P < 0.001). After pneumoperitoneum, the leak airway pressure in I-gel group was significantly less than that of PLMA group (mean [SD] 27 (3) vs. 34.0 (4) cmH2O, respectively; P < 0.001). Peak airway pressure was increased after pneumoperitoneum compared to baseline in both the groups. However, end-tidal carbon dioxide was maintained within normal limits. The insertion parameters, fiberoptic view of the glottis, fiberoptic view of the drain tube, and complications were comparable between the groups.
CONCLUSION: Both I-gel and PLMA are effective for ventilation in gynecological laparoscopic surgeries. However, PLMA provides better sealing as compared to I-gel.

RCT Entities:   Population Interventions Outcomes

INTRODUCTION

Gynaecological laparoscopic surgeries are associated with a decrease in thoraco-pulmonary compliance due to pneumoperitoneum and the Trendelenburg position. Minute ventilation needs to be increased to compensate for this reduction in compliance in order to maintain end-tidal carbon dioxide (EtCO2) during pneumoperitoneum. This increase in minute ventilation can lead to increase in airway pressures in excess of 20 cmH2O. ProSeal laryngeal mask airway™ (ProSeal LMA), a supraglottic airway (SGA) with a drain tube, is effective in maintaining an airway seal up to 30 cmH2O and is widely used as an alternative to endotracheal intubation for the gynaecological laparoscopic surgeries[123] under controlled ventilation. The I-gel[4567] (Intersurgical Inc.,), a single use SGA with noninflatable cuff and drain tube is being used for airway management during anesthesia since last few years. The noninflatable cuff of I-gel is made of a soft gel-like medical grade thermoplastic elastomer. The device has a buccal cavity stabilizer, an integral bite block and an epiglottic rest with a protective ridge, which prevents down folding of epiglottis during insertion.[89] This study was designed to evaluate the effectiveness of I-gel as compared to ProSeal LMA (PLMA) in airway maintenance and controlled ventilation in gynecological laparoscopic surgeries. Our primary objective was to compare the oropharyngeal leak pressures between the two groups before pneumoperitoneum and 5 min after pneumoperitoneum with head down tilt. Secondary objective was to compare the insertion parameters, fiberoptic view of glottis, fiberoptic view of the drain tube, immediate intraoperative, and postoperative complications (like laryngospasm, blood staining of the SGA, and sore throat).

MATERIALS AND METHODS

This study was conducted over a period of 2 years (between the years 2011 and 2013) after obtaining approval from Institute Ethics Committee. 60 American Society of Anaesthesiologists physical status I-II adult female patients scheduled for elective gynecological laparoscopic surgery were enrolled into the study after obtaining written informed consent. The presence of any significant lung disease, anticipated difficulty in intubation, increased the risk of aspiration, body mass index >35, gastroesophageal reflux, neuromuscular disease, pharyngeal dysfunction etc., are excluded from the study. All patients enrolled were premedicated with intravenous (i.v.) midazolam 2 mg, ranitidine 50 mg and metoclopramide 10 mg 15 min before surgery. Pulse oximetry, noninvasive blood pressure, electrocardiogram, EtCO2 and inhalational anesthetic agent concentration were monitored using Datex-Ohmeda S/5 multiparameter monitor. Fentanyl 2 µg/kg i.v. was given 3 min before induction of anesthesia. After preoxygenation, anesthesia was induced with propofol 2 mg/kg, and muscle relaxation was achieved with atracurium 0.5 mg/kg. Patients were mask ventilated for 3 min with 50% oxygen in 50% air and 1.5% isoflurane. The SGA devices were inserted by single, experienced anesthesiologist after ensuring adequate jaw relaxation with a minimal alveolar concentration of 1.2–1.5.

Then patients were randomized to either I-gel group (30 patients) or PLMA group (30 patients) by computer generated allocation. PLMA size was chosen according to the patient's body weight. PLMA was inserted using the index finger or the introducer tool as instructed in the manufacturer's manual. The dorsum of the cuff was lubricated with water soluble jelly. The cuff was inflated according to the size of PLMA. The size was chosen according to the patient body weight (<60 kg - size 3, ≥60 kg - size 4). The I-gel was inserted according to the manufacturer's recommendations. Appropriate placement of airway device was determined by chest expansion, auscultation of breath sounds, continuous square-wave capnogram, no oropharyngeal leak with peak airway pressures (PAWs) of 20 cmH2O and lack of gastric insufflation. The presence of gastric insufflation was determined by epigastric auscultation. If any one of the criteria for satisfactory ventilation was not met, I-gel or PLMA was manipulated in situ by using the first step of the Chandy's maneuver[10] (rotating the device in the sagittal plane until the least resistance to bag ventilation is achieved). Anesthesia was maintained with 1% isoflurane and 50% oxygen and air. Patient's lungs were mechanically ventilated by the anesthesia ventilator with a tidal volume of 10 ml/kg and respiratory rate of 12/min. Baseline parameters (PAW, leak airway pressure [LAW] and EtCO2) were measured and 30–45° Trendelenburg tilt was given as per surgeons request. Insufflation (pneumoperitoneum) was adjusted to an intra-abdominal pressure (IAP) of 12–15 mmHg. After 5 min of pneumoperitone-ium, PAWs and EtCO2 concentration values were noted. Before noting the airway parameters, cuff pressure was maintained at 60 cm of H2O for PLMA both at baseline and after pneumoperitoneum. The LAW (oropharyngeal sealing pressure) was determined by placing the patient in manual mode with APL valve closed with a fresh gas flow of 3 L/min (Datex-Ohmeda S/5 anesthesia delivery system). The pressure at which audible leak occurred was taken as LAW.[101112] The inter-observer reliability and accuracy of this measuring system have already been validated.[12] The differences between the LAW-PAW after pneumoperitoneum was also calculated, as described in previous studies.[813]

An easy insertion was defined as insertion of airway device in a single maneuver into the pharynx without resistance. A difficult insertion was one in which there was resistance to insertion or where more than one maneuver was required to seat the device within the pharynx. Ease of device insertion was graded subjectively (1 – Easy, 2 – Difficult). Insertion time was taken as the interval from picking up the airway device to the establishment of an effective airway. Three insertion attempts (1, 2, 3, failure) were allowed in both the groups before a failure of insertion was recorded. The trachea was intubated conventionally if the I-gel or PLMA could not achieve a satisfactory airway within three attempts at insertion. Placement of airway device was considered satisfactory if the expired tidal volume was more than 8 ml/kg with no noticeable air leak through the drain tube. Cuff positioning[12] of the airway device (as assessed by fiberoptic view of the glottis was determined objectively by passing a fiberoptic laryngoscope (diameter, 3.7 mm: Karl-Storz, Tuttlingen, Germany) through the airway channel to a position approximately 1 cm proximal to the end of the tube (mask aperture). Fiberoptic view of the glottis was scored using established Brimacombe scoring system[1213] (Score: 4 - Only vocal cords visible, 3 - vocal cords plus posterior epiglottis visible, 2 - Vocal cords plus anterior epiglottis visible, 1 - Vocal cords not seen). After satisfactory placement is confirmed, position of the drain tube was determined by passing insertion cord of fiberoptic scope down the drain tube to a position just proximal (about 1 cm) to the end of the tube. Fiberoptic view was classified as closed hypopharynx (mucosa blocking the end of the drain tube), open hypopharynx (short conical tube of mucosa visible from drain tube), open upper esophageal sphincter (clear view down the esophagus) and others (glottis, epiglottis, arytenoids). A well lubricated 60-cm long, 12-Fr gastric tube was inserted through the drain tube. Correct gastric tube placement was assessed by or detection of injected air by epigastric auscultation and/or aspiration of gastric content. The gastric tube was left in situ throughout the procedure. At the end of the procedure, neuromuscular blockade was antagonized, and the device was removed once patients became fully conscious. The patients were followed-up postoperatively for first 12 h for any airway device-related complications.

Sample size was calculated based on a pilot study of 10 patients, with 5 patients each, in group I-gel and group PLMA. Airway sealing pressure difference of 30% between the groups with type 1 error of 0.05 and a power of 0.8 yielded a sample size of 30 in each group. Statistical analysis was performed using SPSS Version 18 (SPSS Inc., Chicago, IL, USA) and GraphPad InStat 3.0 for Windows (GraphPad Software, San Diego, CA, USA). Distribution of data was determined by Kolmogorov–Smirnov analysis. Descriptive statistics was performed on all demographic variables. Continuous variables were expressed as mean ± standard deviation and categorical variables as number %. Unpaired Student's t-test was used to compare continuous variables between the two groups. Paired t-test was used to compare continuous variables within groups, that is, before and after pneumoperitoneum. Mann–Whitney U-test was used for analysis of nonparametric data (e.g., fiberoptic score). P < 0.05 was considered statistically significant.

RESULTS

A total of 60 patients were enrolled for this study, and there were no dropouts [Figure 1]. Baseline demographic and surgical characteristics were comparable between the two groups [Table 1].

Figure 1

CONSORT figure representing enrolment data

Table 1

Demographic characteristics and insertion parameters

The three parameters, that is, LAW pressure, PAW pressure and the difference of the two (LAW-PAW, demonstrating efficacy of sealing) were measured both before and after pneumoperitoneum. The baseline (before pneumoperitoneum) [Table 2] EtCO2 and PAWs values were comparable between the two groups. The oropharyngeal leak pressure in the I-gel group was less than that of the PLMA group (24 ± 4 and 29 ± 4 in cmH2O respectively; P < 0.001). After pneumoperitoneum, the PAWs were comparable between the groups (22 ± 0.4 [in cmH2O] in I-gel group and 22 ± 0.7 [in cmH2O] in PLMA group), although there was an increase within the groups before and after pneumoperitoneum [Figure 2 and Graph 1]. The LAW after pneumoperitoneum in I-gel group was significantly less than that of PLMA group (27 ± 3 vs. 34 ± 4 cmH2O, respectively; P < 0.001) [Figure 3, Graph 2 and Table 2]. The efficacy of sealing (LAW-PAW) was better with PLMA compared to I-gel (12 ± 4 vs. 5 ± 3 cmH2O, respectively; P < 0.001) after pneumoperitoneum [Figure 4 and Graph 3 and Table 2]. EtCO2 values in the I-gel group were comparable to PLMA group both before and after pneumoperitoneum.

Table 2

Airway and ventilatory parameters

Figure 2 and Graph 1

Effect of pneumoperitoneum on peak airway pressure

Figure 3 and Graph 2

Effect of pneumoperitoneum on leak airway pressure

Figure 4 and Graph 3

Effect of pneumoperitoneum on efficacy of sealing (leak airway pressure-peak airway pressure)

Both the groups were similar in terms of ease of insertion, number of attempts taken, time taken for insertion and ease of insertion of the gastric tube through the drain tube. The I-gel was inserted successfully in the first attempt in 27 cases (90%) and in second attempt in 3 (10%) cases, while PLMA was inserted successfully in the first attempt in all cases [Table 1]. Manipulations like jaw thrust were required in only 3 (10%) patients in the I-gel group and none in the PLMA group. Fiber-optic scores of the airway tube and drain tube were also comparable between the two groups [Table 3]. Good view of the glottis (score 3 and 4) was obtained in 13 (43%) cases in I-gel group and 11 cases (37%) in PLMA group. During the entire study and in 12 h of postoperative follow-up, no untoward airway sequelae were recorded in either of the groups.

Table 3

Fiber-optic scores

DISCUSSION

In our study, we found that both the I-gel and PLMA are easy to insert, with an equally successful insertion rate on the first attempt. Both airway devices had comparable oropharyngeal leak pressures and proved to be effective ventilatory devices for gynecological laparoscopic procedures. Gastric tubes were successfully inserted on the first attempt. The fiberoptic views of the airway and drain tube were not significantly different between the two groups. This is similar to the findings of earlier studies,[314] which evaluated the respiratory mechanics of PLMA with I-gel in laparoscopic cholecystectomy.

There was an increase in EtCO2 values in both groups at 5 min after pneumoperitoneum as expected with carbon dioxide insufflation;[1516] however it was not significantly different between the groups [Table 2].

Before pneumoperitoneum, the oropharyngeal leak pressure (baseline) in the I-gel group was 24 ± 4 (in cmH2O) which was less as compared to the PLMA group, 29 ± 4 (in cmH2O) and this was found to be statistically significant. This difference in leak pressure between the two devices is possibly attributed to the presence of inflatable cuff in PLMA which offers a tight seal than a cuffless device. These findings were comparable to other similar studies[15] (higher seal pressure for PLMA has been attributed to its deeper bowl, a bigger cuff with its dorsal and ventral components, the larger surface area and inflatable nature of the cuff in comparison to the cuffless I-gel.

After pneumoperitoneum, PAW in both groups was higher than the baseline value and this difference was statistically significant [Figure 2]. Because of pneumoperitoneum, the pulmonary compliance is reduced, and the resistance increased, leading to higher airway pressures.[1516] There was an increase in LAW in both devices after pneumoperitoneum. This finding could be attributed to the upward movement of the trachea due partly to an increase in IAP and partly to the Trendelenburg position. However, this proposed explanation needs further evaluation. It was also found that the LAW was statistically significantly different between the two groups and also within the groups both before and after pneumoperitoneum, with better seal provided by PLMA as compared to I-gel [Table 2]. EtCO2 was optimal in both groups before and after pneumoperitoneum.

A previous study,[16] indicate that the I-gel is a reasonable alternative to the PLMA for controlled ventilation during laparoscopic gynecological surgery; in that study they compared the LAW, PAW and platue pressure between the groups. In our study, we did not measure the platue pressure. However, we measured and compared the PAW, EtCO2 (as evidence for ventilation) and also the fiberoptic view of the glottis through the airway channel of both the devices.

Another previous study[17] has shown that PLMA was associated with increased rates of postoperative blood staining and sore throat compared with the I-gel, although such difference was not statistically significant. However, no case of blood staining or sore throat attributable to the I-gel or PLMA was found in the present study.

Our study has a few limitations. First, as most of the surgeries were of shorter duration, we were unable to measure the changes in sealing pressures over time, as could have been possible in more prolonged laparoscopic procedures. Second after pneumoperitoneum, we did not use the fiberoptic view of the glottis through the airway channel to assess the anatomical position of the I-gel and PLMA in relation to the vocal cords. However, a previous study has questioned[18] the value of fiberoptic position as a means of assessing the anatomic position. Third in our study we did not measure pressure-volume changes between the two devices.

CONCLUSION

Both I-gel and PLMA were effective for controlled ventilation in gynecological laparoscopic surgeries. However, the airway sealing pressure was better preserved with the PLMA after the creation of pneumoperitoneum with Trendelenburg position. Both the devices were comparable in terms of ease of insertion, time taken to insert, EtCO2, fiber-optic view of the glottis and airway adverse events.