1Department of Anesthesia, Chang Gung Memorial Hospital, 5 Fu-Hsin Street, Kuei-Shan Hsiang, 333 Taoyuan Hsien, Taiwan. 2University of Queensland and James Cook University, Department of Anaesthesia and Intensive Care, Cairns Base Hospital, The Esplanade, Cairns 4870, Australia*Corresponding author
Declaration of interest: Professor Brimacombe has intermittently received funds for research and lecturing overseas from Intavent Ltd, which manufactures both the devices used in this study. This study was not sponsored by Intavent Ltd.
LMA® is the property of Intavent Ltd.
Accepted for publication: January 17, 2002
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Abstract |
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Methods. Eighty anaesthetized, paralysed patients (ASA 12, aged 1880 yr) were randomly allocated for airway management with the PLMA or LMA. Ease of insertion and efficacy of seal were determined. Peak airway pressures were recorded immediately before and after carboperitoneum to 2.0 kPa. The inspired oxygen concentration and/or the ventilatory variable were adjusted according to a protocol to maintain SpO2 95% and E'CO2 <6.0 kPa. Oxygenation was considered suboptimal if SpO2 fell to 9490% and failed if SpO2 was <90%. Ventilation was considered suboptimal if E'CO2 was >6.07.3 kPa and failed if E'CO2 was >7.3 kPa.
Results. First-time insertion success rates were higher for the LMA (40/40 vs 33/40; P=0.02). Seven patients required two attempts with the PLMA. Oropharyngeal leak pressure was higher for the PLMA [29 (SD 6) vs 19 (4) cm H2O; P<0.001]. There was a similar, significant increase in peak airway pressure after carboperitoneum for both devices (P<0.001). Before carboperitoneum, oxygenation and ventilation were optimal in all patients in both groups. After carboperitoneum, oxygenation was optimal in all patients in both groups, but ventilation was suboptimal more frequently with the LMA (8 vs 0; P=0.01). In three of these eight patients, ventilation failed but was subsequently optimal with the PLMA.
Conclusion. The PLMA is a more effective ventilatory device for laparoscopic cholecystectomy than the LMA. We do not recommend the use of the LMA for laparoscopic cholecystectomy.
Br J Anaesth 2002; 88: 8247
Keywords: equipment, masks anaesthesia; surgery, laparoscopy; ventilation, positive end-expiratory pressure
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Introduction |
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Methods |
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A standard anaesthesia protocol was followed and routine monitoring applied. Anaesthesia was in the supine position with the patients head on a standard pillow 7 cm in height. Anaesthesia was induced with fentanyl 2 µg kg1 and thiopental 5 mg kg1. Maintenance was with 13% sevoflurane in 50% oxygen and air. Neuromuscular blockade was achieved with atracurium 0.5 mg kg1 and maintained with 0.15 mg kg1 boluses to maintain a train-of-four count of <1. The patients lungs were ventilated with a face mask until neuromuscular blockade was complete. Experienced LMA users (PLMA, >30 uses; LMA, >1000 uses) performed all the insertions and data were collected by independent observers. A size 4 PLMA or LMA was used for females and a size 5 PLMA or LMA was used for males. A clear, water-based gel was used for lubrication. The insertion technique for both devices was identical to the finger technique recommended for the LMA, and included neck flexion/head extension and full deflation of the cuff.9 A slight lateral approach was used if resistance was felt in the oropharynx. The introducer tool was not used with the PLMA because the operators had more experience with insertion using the finger technique. The PLMA or LMA was connected to a circle breathing system and the cuff inflated with air until an effective airway was established or the maximum recommended inflation volume reached (size 4, 30 ml; size 5, 40 ml). Fixation was by taping the tube over the chin. A rolled gauze swab was used as a bite block with the LMA. The number of insertion attempts to achieve effective ventilation was recorded. Effective ventilation was defined as a square-wave capnograph trace and normal thoracoabdominal movement. A failed insertion attempt was defined as removal of the device from the mouth. Three attempts were allowed before insertion was considered a failure.
Once an effective airway had been obtained, intracuff pressure was set at 60 cm H2O using a digital cuff pressure monitor, and the oropharyngeal leak pressure was determined by closing the expiratory valve of the circle system at a fixed gas flow of 3 litre min1 and noting the airway pressure (maximum allowed was 40 cm H2O) at which equilibrium was reached.10 The location of gas leak at oropharyngeal leak pressure was determined as: (i) mouth: audible sound of gas escaping from the mouth heard by listening with the ear close to the mouth; (ii) stomach: audible sound of gas escaping into the oesophagus heard by listening over the epigastrium; and (iii) drainage tube: bubbling of lubricant placed on the proximal end of the drainage tube. For the PLMA group, insertion of a gastric tube (size 4, 14-FG; size 5, 16-FG) was attempted if there was no gas leak from the drainage tube during positive pressure ventilation. Any changes in peak airway pressure during gastric tube placement were noted. Correct placement was confirmed by injection of air and epigastric stethoscopy. The number of insertion attempts was recorded. Suction was applied to the gastric tube and the presence or absence of any gastric contents was recorded. The gastric tube was then removed. Gastric tube placement was not attempted with the LMA.
The patients lungs were initially ventilated with a tidal volume of 8 ml kg1, a respiratory rate of 12 b.p.m. and an inspiratory:expiratory ratio of 1:2. Fresh gas flow was 1.5 litre min1. Peak airway pressures were recorded immediately before and after carboperitoneum to 2 kPa in the supine position. The inspired oxygen concentration and/or the ventilatory variables were monitored continuously and adjusted according to a protocol to maintain SpO2 95% and E'CO2<6.0 kPa. If SpO2 fell below 97%, FIO2 was increased to 0.8, then to 1.0, and then the tidal volume was increased to 12 ml kg1. If the E'CO2 increased above 5.6 kPa, the respiratory rate was first increased to 14 b.p.m., then 16 b.p.m., and then the tidal volume increased to 12 ml kg1. A period of 3 min was allowed between adjustments. Oxygenation was considered suboptimal if SpO2 fell to 9490% and failed if SpO2 <90%. Ventilation was considered suboptimal if E'CO2 >6.07.3 kPa or failed if E'CO2 >7.3 kPa. If oxygenation or ventilation failed during the procedure, the surgeon released the gas from the abdominal cavity, the patient was preoxygenated and the alternative device was inserted. If oxygenation or ventilation failed with the alternative device, the surgeon released the gas from the abdominal cavity, the patient was preoxygenated and the trachea intubated using a laryngoscope. Any episodes of gastric insufflation detected through the laparoscope by the surgeon were documented. The PLMA or LMA was removed at the end of surgery when the patient was able to open their mouth to command. Any blood detected on the device upon removal and the duration of anaesthesia were recorded. The oxygen saturation was recorded in the postanaesthesia care unit, 1020 min after removal of the PLMA or LMA, the patient receiving oxygen at 4 litre min1 via a Hudson-like face mask. Any adverse events (regurgitation, aspiration, bronchospasm, laryngospasm, coughing, retching, gagging, hiccup) were documented.
Sample size was based upon a projected difference of 20% between the groups for frequency of suboptimal ventilation, a type I error of 0.05 and a power of 0.9. Parametric data were analysed with unpaired and paired t-tests. Non-parametric data were analysed with the 2 test. Data are mean (SD, range) or number of patients unless otherwise stated. Significance was taken as P<0.05.
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Results |
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Gastric tube placement was successful in all patients with the PLMA. There was no change in peak airway pressure during its placement. Fluid was detected in 31 out of 40 patients with the PLMA: 16 out of 40 had clear fluid, 14 out of 40 had bile-stained fluid and one out of 40 had semisolid fluid. Fluid detection was not attempted with the LMA.
There was a significant increase in peak airway pressure after carboperitoneum for both devices (Table 1). Before carboperitoneum, ventilation was optimal in all patients. After carboperitoneum, ventilation was suboptimal in eight patients with the LMA and none with the PLMA (P=0.01). Ventilation failed in three of these patients and was subsequently optimal with the PLMA (Table 1). No patient required tracheal intubation. There were no episodes of hypoxia, but gastric insufflation was identified in all three patients in whom use of the LMA was unsuccessful. In one patient (PLMA group), the laparoscopic procedure was converted to an open procedure because of surgical problems. Blood was detected more frequently with the PLMA at removal (6/40 vs 0/37; P=0.014). Postoperative oxygen saturation was similar [PLMA, 96.3 (1.9, 9399)%; LMA, 96.9 (1.8, 92100)%]. There were no other adverse events. Comparative data are summarized in Table 2.
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Discussion |
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We found that 78% of patients in the PLMA group had some residual gastric fluid and that in almost half of these the fluid was bile-stained or contained semisolid material. Interestingly, none of these patients had symptoms of reflux and were therefore not considered at risk of aspiration during induction. Unfortunately, we did not measure residual gastric volume or pH. However, one of the authors (JB) has measured the volume and pH of fluid in 23 patients undergoing laparoscopic cholecystectomy with the PLMA, and found that the mean (range) volume was 18 (059) ml and pH 3.5 (2.55.8). Brain and colleagues6 found that the average residual gastric volume in patients undergoing routine minor procedures with the PLMA was 15 ml. The extent to which residual gastric fluid increases the risk of regurgitation and aspiration is unknown. We consider that residual gastric fluid should be removed by routine insertion of a gastric tube, but there is always the possibility that this might trigger regurgitation.11
The use of LMA for laparoscopic cholecystectomy is not conventional, but has been practised in some centres since the mid-1990s.5 However, there are insufficient data demonstrating that the technique is safe and effective, despite recent positive findings.24 12 There have also been two reports of aspiration in patients undergoing open cholecystectomy with the LMA.13 14 Sidaras and Hunter,15 in a recent editorial, comment on the dangers of extrapolating the risk and mortality of aspiration with the LMA from small numbers of subjects.
Our experience with the LMA was much greater than with the PLMA. There is both short-term16 and long-term17 skill acquisition with the LMA, and this probably applies to the PLMA. It is likely that first-time insertion failure rates and the frequency of trauma would be reduced with increasing experience. We suggest that the PLMA is only used for laparoscopic cholecystectomy by experienced LMA users who have a high success rate with the PLMA (say >95%) and substantial experience with the PLMA for other laparoscopic procedures, such as sterilization and inguinal hernia repair. The ventilatory capability and position of the PLMA should be assessed carefully after insertion. The patient should be intubated if the ventilatory capability is considered inadequate for carboperitoneum and/or the PLMA is malpositioned.
We conclude that the PLMA is a more effective ventilatory device for laparoscopic cholecystectomy than the LMA. We do not recommend the use of the LMA for laparoscopic cholecystectomy.
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References |
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2
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15
Sidaras G, Hunter JM. Is it safe to artificially ventilate a paralysed patient through the laryngeal mask? The jury is still out. [Editorial]. Br J Anaesth 2001; 86: 74953
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