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* From the Departments of Anesthesia, and
Community Health Sciences, University of Calgary, Calgary, Alberta, Canada.
Address correspondence to: Dr. J. Roger Maltby, Department of Anesthesia, Foothills Medical Centre, 1403 - 29th Street NW, Calgary, Alberta T2N 2T9, Canada. Phone: 403-944-1667; Fax: 403-944-2425; E-mail: maltby{at}ucalgary.ca
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Abstract |
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Methods: We stratified 209 women, aged 
18 yr, ASA physical status I–III, by body mass index as non-obese (# 30 kg•m-2) or obese (> 30 kg•m-2) and randomized them to LMA-C/PLMA or ETT groups for airway management. Anesthesia was induced with propofol, fentanyl and succinylcholine or rocuronium. In the LMA-C/PLMA group we used a size 4 LMA-C in non-obese patients and size 4 or 5 PLMA in obese patients. In the ETT group we used a cuffed 7.0 mm ETT in all patients. Anesthesia was maintained with isoflurane in nitrous oxide and 30–50% oxygen, fentanyl and neuromuscular blockade with mechanical ventilation (tidal volume 10 mL•kg-1). The staff surgeon, blinded to the type of airway, scored stomach size on an ordinal scale 0–10 at initial insertion of the laparoscope and immediately before the conclusion of the surgical procedure.
Results: There were no crossovers and no statistically significant differences between LMA-C/PLMA and ETT groups for SpO2, PETCO2 or airway pressure before or during peritoneal insufflation in short (# 15 min) or long (> 15 min) periods of peritoneal inflation. Differences between groups with respect to stomach size changes during surgery were not statistically significant.
Conclusion: A correctly placed LMA-C or PLMA is as effective as an ETT for positive pressure ventilation without clinically important gastric distension in non-obese and obese patients.
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Introduction |
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The LMA-ProSealTM (PLMA; The Laryngeal Mask Company, Henley-on-Thames, UK)6 was designed to permit higher airway pressure than the LMA-C (approximately 20 cm water) without leak of anesthetic gases. Its cuff extends over the posterior surface of the bowl to push the mask anteriorly to sustain airway pressure > 30 mmHg. A second tube, parallel to the ventilation tube, passes through the bowl of the mask to the tip of the cuff where it opens at the upper esophageal sphincter. This drain tube separates the respiratory tract from the esophagus. It directs passively regurgitated gastric fluid away from the airway, and provides a conduit for blind passage of a gastric tube for aspiration of gas or liquid contents from the stomach. The PLMA is therefore more appropriate than the LMA-C for obese patients and those with pulmonary disease who require higher airway pressures for adequate ventilation, and for surgical procedures in which intraoperative gastric drainage is desirable and in patients with GER.
In this study, we compared ventilation measurements, change in stomach size and emergence outcomes for the LMA-C (non-obese patients) or PLMA (obese patients) with the ETT during gynecologic laparoscopy.
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Methods |
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18 yr, ASA physical status I–III, scheduled for elective gynecologic laparoscopy under general anesthesia were stratified by body mass index (BMI) as non-obese (BMI # 30 kg•m-2) or obese (BMI > 30 kg•m-2) and randomized to the appropriate LMA device (LMA-C for non-obese, PLMA for obese) or ETT using computer-generated tables of random numbers. The stratification ensured approximately equal distribution of non-obese and obese patients in each group. Patients with a history of GER or hiatus hernia were included, provided they were currently asymptomatic and had taken an H2 receptor blocker or proton pump inhibitor on the day of surgery. Patients fasted according to current Canadian Anesthesiologists’ Society Guidelines (minimum two hours after clear liquid, six hours after a light meal).7 No sedative premedication was given unless requested by the patient.
The four investigators had extensive experience over several years with the LMA-C and six months experience with the PLMA. Short cases (# 15 min peritoneal insufflation) were diagnostic or sterilization procedures and long cases (> 15 min peritoneal insufflation) were operative procedures. Criteria for crossover were: a) failure to place the randomly assigned airway device within three attempts; b) respiratory obstruction; c) persistent oropharyngeal leak with inadequate ventilation (PETCO2 39 mmHg before peritoneal insufflation, 45 mmHg during peritoneal insufflation); d) gastric distension interfering with surgical field.
After placement of the electrocardiogram, pulse oximeter, and non-invasive blood pressure monitor, preoxygenation was maintained until FEO2 was > 80%. Anesthesia was induced with 20 mg lidocaine, 2–2.5 mg•kg-1 propofol, 1–2 µg•kg-1 fentanyl, and 1.5 mg•kg-1 succinylcholine or # 0.75 mg•kg-1 rocuronium intravenously. Bag and mask ventilation was avoided between induction of anesthesia and insertion of the airway device.
Non-obese patients randomized to the LMA-C/PLMA group received a size 4 LMA-C, and obese patients a size 4 or 5 PLMA. The cuff was inflated with room air to the manufacturer’s recommended cuff pressure of 60 cm water before the anesthetic circuit was connected and the patient’s lungs ventilated. After observing bilateral chest movement, square PETCO2 waveform during manual ventilation, and silent epigastrium by stethoscope auscultation, we performed an airway pressure leak test. We set a continuous fresh gas flow (FGF) of 3 L•min-1 with the adjustable pressure-limiting valve closed and the circuit connected to the reservoir bag. The leak pressure was recorded when airway pressure reached a plateau, which was simultaneously marked by a clearly audible oropharyngeal leak around the LMA cuff. We then reverted to intermittent PPV with VT 10 mL•kg-1 and f 10•min-1. With the PLMA, we filled the proximal 3 cm of the drain tube with a water-soluble lubricant jelly; if a gas bubble rose through the jelly during inspiration, indicating a gas leak into the esophagus, we corrected the position of the PLMA and repeated the test until no bubble appeared.
In the ETT group, we inserted a 7.0-mm internal diameter tube in all patients and inflated the cuff until no leak was audible during manual ventilation. Each patient’s head and neck were covered with a towel to conceal the ETT or LMA before the surgeon entered the operating room. A gastric tube was not passed prophylactically in either group, but was permitted in individual patients if gastric distension interfered with the surgeon’s operative field.
We maintained anesthesia at 1.0–1.3 MAC with isoflurane and nitrous oxide in 30–50% oxygen with incremental doses of fentanyl. Neuromuscular blockade was maintained at # 1 twitch of a train-of-four for long cases. High initial FGF (6 L•min-1) was reduced to maintenance flows according to each investigator’s normal clinical practice. Trendelenburg tilt # 15° was provided at the gynecologist’s request. We recorded SpO2, FIO2, PETCO2, FGF, minute ventilation and peak airway pressure before insertion of the Veress needle for peritoneal insufflation to 15 mmHg, and immediately before peritoneal deflation at the end of the procedure. Each surgeon scored the size of the stomach on an ordinal scale of 0–10 (0 = empty stomach and 10 = distension of stomach that interfered with surgery) at initial insertion of the laparoscope and immediately before its removal at the end of the surgical procedure. Neuromuscular blockade was reversed and the airway device was removed in the operating room when the patient responded to verbal commands. Cough, laryngeal stridor or spasm and the need for airway intervention during emergence from anesthesia were recorded. Patients were still blinded to their randomization when the research nurse contacted them on the first postoperative day to identify anesthesia-related morbidity.
Data for respiratory variables and change in stomach size were analyzed according to short (# 15 min) or long (> 15 min) duration of peritoneal insufflation. Our primary respiratory variable was PETCO2. In our matched groups with predetermined ventilator settings, a statistically significant difference in PETCO2 would reflect a difference in clinical performance of the airway devices. We based our sample size on PETCO2 results obtained during a previous laparoscopic cholecystectomy study.8 If PETCO2 during peritoneal insufflation was 41 ± 5 mmHg in the LMA group and 36 ± 5 mmHg in the ETT group, then a two-sided test with 
= 0.05 would have power (1-ß) greater than 99% of detecting that difference with 40 patients in each group. It also had a 90% chance of detecting a difference if a clinically significant increase (
3 score) in stomach size occurred in 50% of patients in the LMA group and in 10% of patients in the ETT group.
The groups were compared using an independent group’s t test (for measured variables) and the Fisher exact test (for discrete variables). The Fisher exact test was used to assess changes in gastric distension after the scores were converted into three clinically relevant ranges: slight decrease (
1–2), no change or slight increase ( 0–2), marked increase ( 3–6). No adjustments were made for multiple comparisons. When P values were less than 5%, comparisons are noted in the tables.
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Results |
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). The median (range) airway pressure during the leak test with continuous airway pressure immediately after inflation of the LMA cuff was 20 (10–38) cm water for the LMA-C in non-obese patients, and 30 (14–50) cm water for the PLMA in obese patients. Even when gas leaked at a low airway pressure (< 20 cm water) during the leak test, adequate airway pressure without gas leak was achieved with intermittent PPV during the laparoscopic procedure. There were no crossovers from LMA-C/PLMA to ETT, and none from ETT to LMA-C/PLMA.
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). There was no correlation between BMI and SpO2, FIO2 or PETCO2. During maintenance of anesthesia, three of the four anesthesiologists reduced FGF to the minimum required to refill the ventilator reservoir bag (300–600 mL•min-1). The fourth anesthesiologist used 1–2 L•min-1, as was his usual practice.
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). In more than 90% of cases, the surgeon estimated that the change in stomach size was not clinically significant (score # 2). Greater increase (score 3) in stomach size in long cases was observed in 7/51 patients in the LMA- C/PLMA group and in 2/49 in the ETT group. This difference was not statistically significant and in no case did the size of the stomach interfere with surgery. The drain tube of the PLMA filled with gastric fluid in one patient, immediately before deflation of the pneumoperitoneum. There was no visual contamination of the anterior surface of the PLMA bowl or the pharyngeal wall, and respiration was not affected immediately or postoperatively.
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). Sore throat 24 hr postoperatively was more common with ETT than LMA-C/PLMA (28% vs 17%; P < 0.05). No patient reported numbness of the tongue or other morbidity attributable to the airway devices.
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Discussion |
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Measurement of PETCO2 may not be as accurate as blood gas analysis for assessing adequacy of pulmonary ventilation, particularly in obese patients and those in the Trendelenburg position. However, any error would apply equally to patients with LMA-C/PLMA or ETT. We were comparing the clinical efficacy of LMA-C/PLMA and ETT rather than seeking absolute scientific values. We do not believe that, for this type of clinical study, the potential morbidity of invasive monitoring is justified when capnography is the standard measurement used in clinical practice.
The LMA-C is considered safe and effective in moderate obesity, but is not recommended in the morbidly obese.9 Weight or BMI criteria may vary for each category and non-obesity and grades of obesity are a continuum. We chose 30 kg•m2 as the BMI above which we would use the PLMA instead of the LMA-C in the LMA-C/PLMA group.
Brimacombe and Brain10 initially included a "rule of 15" in guidelines for use of the LMA-C during laparoscopic surgery. These "rules" were Trendelenburg tilt < 15°, peritoneal insufflation < 15 cm water and duration of the procedure < 15 min. In our study, the head down tilt was # 15° and peritoneal insufflation pressure was preset at 15 mmHg. We did not limit the duration of peritoneal insufflation to 15 min because inadequate ventilation or gastric distension should be evident within 15 min of starting the laparoscopic procedure. If it does not occur within 15 min, it should not occur later, provided that anesthetic depth and muscular relaxation are adequate and the LMA-C/PLMA is not dislodged. Furthermore, we had previously shown that the LMA-C and ETT with PPV were equally effective during laparoscopic cholecystectomy in non-obese patients, when mean peritoneal insufflation time was 47 min.7
The PLMA permitted higher airway pressures without leak in all obese patients, satisfactory pulmonary ventilation without clinically significant gastric distension, and use of basal or near-basal FGF. Our inclusion of obese patients with a history of GER may be controversial. We ensured that they all took appropriate medication on the day of surgery to minimize gastric fluid volume and acidity. In addition, the PLMA drainage tube prevents passively regurgitated liquid from contaminating the airway,11–14 as happened in one patient in this study.
Gastric distension may occur when high airway pressure is employed to overcome a partially obstructed airway, or from inadvertent esophageal intubation.15–17 The surgeon may then perforate the distended stomach with the Veress needle or trochar. There were reports of at least 13 such gastric perforations before the danger of a distended stomach and the necessity of deflating it with a gastric tube (rather than manual compression) were fully recognized. The potential for gastric distension exists with all airway devices. If the LMA is malpositioned it may cause partial or complete respiratory obstruction and air will be forced into the stomach. If it is too small, the tip may enter the upper esophagus and allow gas to enter the stomach. Cases of marked gastric distension have been reported during PPV with the LMA-C18–20 and, when this occurs, both the cause and its effect must be treated.
Gastric inflation may also occur with the PLMA, despite its gastric drainage tube.21 If the tip of the PLMA turns back on itself during insertion, this may not be recognized unless the anesthesiologist also tries to pass a #14 or #16 gastric tube through the drainage tube and finds this impossible. We did not use this additional test because we had not encountered this problem when we prepared our protocol. In a previous study of PLMA vs ETT during laparoscopic cholecystectomy,22 a #14 gastric tube passed easily through the drainage tube into the stomach in all patients in whom initial tests indicated correct placement. In the present study, laparoscopic assessment of stomach size by our gynecologist colleagues, who were blinded to the airway device being used, enabled us to avoid the use of surrogate auditory markers to detect gas leakage into the stomach.23,24 In no patient did change in stomach size interfere with the surgical field.
The PLMA broadens the application of supraglottic devices to include clinical situations for which the LMA-C is not recommended. Keller et al. confirmed its ventilatory efficacy in 60 morbidly obese patients.25 Oropharyngeal leak pressure was 32 ± 4 cm water and PPV without leaks was possible in 57/60 patients. There was no gastric leak, no air leak into the drain tube and no PETCO2 > 45 mmHg in any patient. They then replaced the PLMA with an ETT for surgery in 58/60 patients. In the remaining two patients, intubation was impossible. The PLMA was reinserted and the surgery was completed uneventfully.
Our study was too small to determine the safety of the LMA-C/PLMA with respect to pulmonary aspiration. Nevertheless, the best available evidence indicates that the incidence in similar elective surgical patient populations is approximately 1 in 5–12,000.4,26 The PLMA drain tube allows passively regurgitated gastric contents to be vented without soiling of the patient’s airway.12–14 This suggests that the PLMA may be safer than the LMA-C in patients with untreated GER. However, Brimacombe and Keller demonstrated in fresh cadavers that a correctly placed LMA-C prevented passage of saline from the esophagus into the pharynx until the fluid pressure reached 39 cm water.27 Resting intragastric pressure in healthy subjects is 12.1 (± SE 0.82) cm water,28 and does not rise until intragastric volume reaches 1000–1500 mL.29 The LMA-C may therefore prevent passively regurgitated fluid from reaching the pharynx, whereas the PLMA allows its safe, visible drainage. Whether the PLMA drain tube is equally effective when gastric contents are vomited with a pressure > 60 cm30 is not yet known. A clinical trial to demonstrate a 50% reduction in the frequency of clinically significant aspiration for the PLMA vs LMA-C would require approximately 1.3 million patients in each group.13
We conclude that the LMA-C and ETT in non-obese patients provide adequate pulmonary ventilation as assessed by PETCO2 without gastric distension during gynecologic laparoscopic examination or surgery. Since laparoscopic surgery provides the most severe test for efficacy of supraglottic airway devices, the LMA-C should be effective during PPV in other types of surgery in non-obese patients. The PLMA and ETT appeared to be equally effective in obese patients, but larger numbers of obese patients are required to confirm this. The higher airway pressure afforded by the PLMA, and its separation of alimentary and respiratory tracts, represent significant advances for airway management.
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Acknowledgments |
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Revision received October 14, 2002. Accepted for publication June 10, 2002.
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References |
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2 Maltby JR, Loken RG, Watson NC. The laryngeal mask airway: clinical appraisal in 250 patients. Can J Anaesth 1990; 37: 509–13.
3 Joris JL. Anesthesia for laparoscopic sugery. In: Miller RD (Ed.). Anesthesia, 5th ed., vol 2. Philadelphia: Churchill Livingstone: 2000: 2003–23.
4 Verghese C, Brimacombe JR. Survey of laryngeal mask airway usage in 11,910 patients: safety and efficacy for conventional and nonconventional usage. Anesth Analg 1996; 82: 129–33.[Abstract]
5 Simpson RB, Russell D. Anaesthesia for daycase gynaecological laparoscopy: a survey of clinical practice in the United Kingdom. Anaesthesia 1999; 54: 72–6.[Medline]
6 Brain AIJ, Verghese C, Strube PJ. The LMA ‘Pro-Seal’ – a laryngeal mask with an oesophageal vent. Br J Anaesth 2000; 84: 650–4.
7 Maltby JR, Beriault MT, Watson NC, Fick GH. Gastric distension and ventilation during laparoscopic cholecystectomy: LMA-Classic vs. tracheal intubation. Can J Anesth 2000; 47: 622–6.
8 Canadian Anesthesiologists’ Society. 2001 CAS guidelines to the practice of anesthesia. Can J Anesth 2001; 48 Supplement.
9 Brain AIJ. The Laryngeal Mask Airway (LMA) Instruction Manual. Intavent Res Limited, 1995: 31.
10 Brimacombe JR, Brain AIJ. The Laryngeal Mask Airway. A Review and Practical Guide. London: W.B. Saunders Company Ltd.; 1996: 164–6.
11 Stix MS, Rodriguez-Sallaberry FE, Cameron EM, Teague PD, O’Connor CJ Jr. Esophageal aspiration of air through the drain tube of the ProSealTM laryngeal mask. Anesth Analg 2001; 93: 1354–7.
12 Dalgleish DJ, Dolgner M. The ProSeal laryngeal mask airway (Letter). Anaesthesia 2001; 56: 1010.
13 Cook TM, Nolan JP. The ProSeal laryngeal mask airway (Letter). Anaesthesia 2002; 57: 288–9.
14 Evans NR, Llewellyn RL, Gardner SV, James MF. Aspiration prevented by the ProSealTM laryngeal mask airway: a case report. Can J Anesth 2002; 49: 413–6.
15 Whitford JHW, Gunstone AJ. Gastric perforation: a hazard of laparoscopy under general anaesthesia. Br J Anaesth 1972; 40: 97–9.
16 Reynolds RC, Pauca AL. Gastric perforation, an anesthesia-induced hazard in laparoscopy. Anesthesiology 1973; 38: 84–5.[Medline]
17 Endler GC, Moghissi KS. Gastric perforation during pelvic laparoscopy. Obstet Gynecol 1976; 47(Suppl): 40–2s.
18 Wittmann PH, Wittmann FW. Laryngeal mask and gastric dilatation (Letter). Anaesthesia 1991; 46: 1083.
19 Brimacombe JR, Brain AIJ, Berry AM, Verghese C, Ferson D. Gastric insufflation and the laryngeal mask (Letter). Anesth Analg 1998; 86: 914–5.
20 Maltby JR, Beriault MT. Abdominal distension during transurethral resection of a bladder tumour (Letter). Can J Anaesth 1998; 45: 1134.[Medline]
21 Brimacombe JR, Keller C, Berry A. Gastric insufflation with the ProSeal laryngeal mask. Anesth Analg 2001; 92: 1614–5.
22 Maltby JR, Beriault MT, Watson NC, Liepert D, Fick GH. The LMA-ProSealTM is an effective alternative to tracheal intubation for laparoscopic cholecystectomy. Can J Anesth 2002; 49: 857–62.
23 Ho-Tai LM, Devitt JH, Noel AG, O’Donnell, MP. Gas leak and gastric insufflation during controlled ventilation: face mask versus laryngeal mask airway. Can J Anaesth 1998; 45: 206–11.
24 Weiler N, Latorre F, Eberle B, Goedecke R, Heinrichs W. Respiratory mechanics, gastric insufflation pressure, and air leakage of the laryngeal mask airway. Anesth Analg 1997; 84: 1025–8.[Abstract]
25 Keller C, Brimacombe J, Kleinsasser A, Brimacombe L. The laryngeal mask airway ProSealTM as a temporary ventilatory device in grossly and morbidly obese patients before laryngoscopy-guided tracheal intubation. Anesth Analg 2002; 94: 737–40.
26 Warner MA, Warner ME, Weber JG. Clinical significance of pulmonary aspiration during the perioperative period. Anesthesiology 1993; 78: 56–62.[Medline]
27 Brimacombe J, Keller C. Water flow between the upper esophagus and pharynx for the LMA and COPA in fresh cadavers. Can J Anesth 1999; 46: 1064–6.
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30 Guyton AC, Hall JE. Textbook of Medical Physiology, 10th ed. Philadelphia: WB Saunders Company, 2000: 731.
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