1Royal United Hospital, Combe Park, Bath BA1 3NG, UK. 2Royal Berkshire Hospital, Reading, Berkshire RG1 5AN, UK. 3Wycombe Hospital, High Wycombe, Buckinghamshire HP11 2TT, UK. 4Kings College Hospital, Denmark Hill, London SE5 9SR, UK. 5Oxford Radcliffe Hospital Trust, Oxford OX3 9DU, UK. 6Frenchay Hospital, Bristol BS16 1LE, UK*Corresponding author
Declaration of interest. T.M. Cook received an honorarium for addressing staff of the company of Intavent Orthofix.
Accepted for publication: November 30, 2001
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Abstract |
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Methods. The ProSeal and classic laryngeal mask airways were compared in 180 patients in a randomized crossover study. Patients were anaesthetized without neuromuscular blocking drugs.
Results. The ProSeal took more time and more attempts to insert successfully than the classic laryngeal mask airway. Insertion was successful on the first attempt in 81% of cases with the ProSeal and 90% with the classic laryngeal mask airway. The ProSeal required more air to achieve an intracuff pressure of 60 cm H2O (6 ml more for size 4 and 12 ml more for size 5). Laryngeal seal pressure was better with the ProSeal than the classic laryngeal mask airway. Median seal pressure was 29 cm H2O with the ProSeal and 18 cm H2O with the classic laryngeal mask airway. Laryngeal seal pressure was greater than 20 cm H2O in 87% of patients with the ProSeal and 41% with the classic laryngeal mask airway. Laryngeal seal pressure was greater than 40 cm H2O in 21% of patients with the ProSeal and in none of the patients with the classic laryngeal mask. Once placed, the ProSeal remained a stable and effective airway. Gastric tube insertion through the drain tube was attempted in 147 cases and was successful in 135 (92%).
Conclusion. The ProSeal is more difficult to insert than the classic laryngeal mask airway but allows positive pressure ventilation more reliably than the classic laryngeal mask airway.
Br J Anaesth 2002; 88: 52733
Keywords: equipment, airway; equipment, masks anaesthesia; larynx
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Introduction |
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Method |
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Premedication with oral temazepam 1020 mg was used when indicated. Anaesthesia was induced with propofol and fentanyl 12 µg kg1 and maintained with either propofol infusion or a volatile anaesthetic in nitrous oxide and oxygen. Standard anaesthetic monitoring was used. The size of device to be used was decided by the individual investigator. Both devices were deflated fully before insertion. The ProSeal was inserted with either the ProSeal introducer tool or the index finger, as described in the manufacturers product literature. The classic laryngeal mask was inserted with the standard technique [3]. A maximum of three attempts were allowed with each device. After insertion, the cuff was inflated with air to a pressure of 60 cm H2O. A blob of lubrication gel was placed over the proximal opening of the ProSeal drain tube. Positive pressure ventilation was started at a tidal volume of 8 ml kg1. Adequacy of ventilation was assessed by chest movement, the capnograph signal and the presence or absence of an audible leak. With the ProSeal, the drain tube was also observed for displacement of the gel. Seal pressure was measured by stopping ventilation, occluding the spill valve with a fresh flow rate of 5 litre min1 until airway pressure reached a steady value (seal pressure). The airway pressure was not allowed to exceed 40 cm H2O. Seal pressure was observed and recorded by someone other than the investigator, to reduce observer bias. After measurement of seal pressure, intermittent positive pressure ventilation was restarted. The airway tube and drain tube were examined with a flexible fibreoptic scope. The view from the bulb of either device was graded in a standardized manner (Table 1). A single attempt was made to pass a gastric tube through the drain tube of the ProSeal. Placement of the gastric tube in the stomach was confirmed by aspiration of gastric contents or by auscultation over the stomach as air was syringed into the tube. The cuff was then deflated and the volume of air recorded. This completed the evaluation of the first device used, and it was removed. The same procedure was then followed for the other device. The second device was then used for the duration of the surgical procedure. At the end of the surgical procedure, anaesthesia was discontinued and the device was removed as the patients reflexes returned, in accordance with the manufacturers recommendations.2 3 A checklist of complications relating to insertion, maintenance and removal was completed after use of each device.
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Results |
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Two ProSeals failed during sterilization. The cuffs developed leaks where the posterior cuff was bonded to the stem of the device.
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Discussion |
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This study was done without the use of neuromuscular blocking drugs. Two sizes of device, 4 and 5, were used. We demonstrated that the median seal pressure with the ProSeal is 12 cm H2O greater than with the classic laryngeal mask airway. Two smaller studies of seal pressure in paralysed patients used a size 4 ProSeal only. In one study of 30 patients, the difference in seal pressure was 14 cm H2O,1 while in the second study, with 60 patients, the difference was 1012 cm H2O.4 Our results underestimate the true difference, as in 21% of cases the seal pressure achieved with the ProSeal exceeded the upper limit we set.
A limitation of the study is that anaesthetic technique was not standardized. However, all patients received the same anaesthetic with the exception of the use of propofol or isoflurane for maintenance of anaesthesia. ProSeal placement in patients who received volatile anaesthesia took 7 s longer than in those maintained with total intravenous anaesthesia, but the number of insertion attempts, failure rate and the number of complications did not differ significantly.
All investigators took longer to insert the ProSeal than the classic laryngeal mask airway but the absolute time difference was of negligible clinical importance. Investigators required more attempts to insert the ProSeal successfully. Complications were more frequent with the ProSeal but were minor and without sequelae. There was general agreement that the device is more difficult to place than the classic laryngeal mask airway. This applied whether the introducer tool or a finger was used for insertion. We found no clinically important differences in insertion characteristics whether or not the introducer was used. Previous work in paralysed patients has shown greater success with insertion when the introducer is used5 but we did not find this. Insertion may be more difficult because the device is larger and bulkier than the classic laryngeal mask airway and more mouth opening is needed. During insertion of the ProSeal, there were more complications (including movement, coughing, breath-holding and laryngospasm) than with the classic laryngeal mask. A greater depth of anaesthesia may be needed for insertion of the ProSeal than the classic laryngeal mask airway, but this was not studied specifically. When deflated, the semirigid distal end of the drain tube forms the leading edge of the ProSeal, which is more rigid than the leading edge of the classic laryngeal mask airway. These factors may contribute to difficult insertion and minor trauma. All investigators were experienced anaesthetists and had inserted a minimum of five ProSeals before starting the trial. Despite this, several investigators needed fewer insertion attempts in the second half of the study than in the first. Whether this indicates that there is a long learning curve is unclear.
All study centres performed equally well, with one exception. In one centre, where fewer than 10% of all cases were studied, the use of the ProSeal (and the classic laryngeal mask airway) was considerably less successful than at the other four centres. Both failures with the ProSeal occurred at this centre and, in comparison with results from the other centres, both the ProSeal and the classic laryngeal mask airway were more frequently poorly placed. Seal pressures were significantly lower at this centre with both the ProSeal and the classic laryngeal mask airway. For both devices, the volume of air used for inflation was greater than at the other centres. Careful examination of these outlying results did not reveal an explanation. Minor differences in cuff inflation volume do not explain the findings.
The cuffs for all devices were inflated to a predetermined pressure (rather than a volume). The ProSeal cuff has a larger volume than that of the classic laryngeal mask airway in vitro.1 Despite the larger static cuff volume, the difference in volume required to reach target pressure was small. Small increases in the volume of air caused marked increases in intra-cuff pressure. This might be explained by the ProSeal adapting more closely to the shape of the pharynx and larynx,1 which might account for the improved seal pressure and low compliance during further inflation.
Two ProSeals failed in similar fashion. Manufacture of the back cuff is technically demanding. Unlike the cuff of the classic laryngeal mask airway, the ProSeal cuff cannot be made as a single piece of silicone. Silicone joins may lead to device weakness and scrupulous deflation of the device is necessary before sterilization. We did not encounter any device failures after adopting this precaution.
The drain tube appeared to be placed optimally in all but one case. Gastric tube insertion was remarkably easy in the majority of cases. On occasions when insertion was not possible, the drain tube appeared to have kinked in the posterior pharynx.
Use of a laryngeal mask airway for positive pressure ventilation is not new but is regarded by some as controversial. The ProSeal provides a more reliable airway than the classic laryngeal mask airway for positive pressure ventilation. The lungs of most healthy patients can be ventilated if the seal pressure exceeds 20 cm H2O. In this study, the seal pressure was above this value in 87% of cases with the ProSeal and 41% with the classic laryngeal mask airway. If peak inflation pressure exceeds leak pressure, the likelihood of gastric insufflation is increased. In one study, leakage of inspired volume increased from 13% to 25% as peak pressure was increased from 15 to 30 cm H2O.4 Our results suggest that, if a classic laryngeal mask airway is selected for positive pressure ventilation, leakage will occur in more than half of the patients, but that leakage occurs in very few cases with the ProSeal.
The risk of aspiration with the classic laryngeal mask airway is probably low5 6 but remains controversial.7 8 The ProSeal drain tube allows easy passage of a gastric tube, which enables emptying of the stomach of gas or fluid. There is evidence from cadavers that the drain tube allows regurgitated fluid to bypass the larynx even when no gastric tube is in place.10 Further study is needed to show that the ProSeal will reduce the risk of aspiration of regurgitated matter. Use of the classic laryngeal mask airway is an accepted technique for gynaecological laparoscopy11 12 and is currently used by up to 60% of UK anaesthetists for this procedure.13 However, in the same study 89% of anaesthetists still intubated some patients and 35% intubated all patients. Seventeen per cent of laryngeal mask airway users expressed some concern with the technique. The classic laryngeal mask airway is used less widely for upper abdominal laparoscopic surgery, although several reports exist.14 15 Increased seal pressure and access to drain the stomach are distinct advantages of using the ProSeal for such procedures, but further evaluation is required.
Recent studies show that the classic laryngeal mask airway provides smooth and safe emergence from anaesthesia with less haemodynamic disturbance16 and fewer respiratory complications17 compared with emergence with a tracheal tube. For most patients and most operations, these considerations are not critical. However, patients emerging from anaesthesia for neurosurgery, cardiac surgery and open eye surgery benefit from a smooth recovery. The ProSeal may find a role during such procedures, either as the sole airway or as a secondary airway inserted at the end of surgery before lightening anaesthesia.
There are other potential roles for the ProSeal in the intensive care unit. The classic laryngeal mask airway has been used for short-term ventilatory support18 19 and for weaning from ventilation.20 The ProSeal drain tube would allow insertion of a gastric tube to prevent gastric distension and facilitate enteral feeding (although regurgitation cannot be ruled out). The classic laryngeal mask airway is often used for airway maintenance during percutaneous tracheostomy.21 22 These patients have typically poor lung compliance and the improved laryngeal seal provided by the ProSeal would enable better ventilation during the procedure.
The classic laryngeal mask airway is widely used as a rescue airway in failed intubation.23 In experienced hands, if lung compliance is reduced or the risk of aspiration is high, the ProSeal could allow more reliable positive pressure ventilation and the ability to drain the stomach, which might have become inflated during multiple attempts at bag-valve-mask ventilation.
Finally, the ProSeal has potential advantages over the classic laryngeal mask airway during cardiopulmonary resuscitation (CPR). The classic laryngeal mask airway is recommended for airway management during CPR in the current international guidelines.24 The incidence of regurgitation during CPR when a classic laryngeal mask airway is used as the first airway adjunct is of the order of 3.5%.25 This could be less with the ProSeal because the improved laryngeal seal should reduce the risk of gastric inflation and the drain tube provides an opportunity to empty the stomach. This supposition is entirely untested. Non-anaesthetists are able to place the classic laryngeal mask airway with considerable success26 but the ProSeal is less easy. Further work is needed to determine whether infrequent users and non-anaesthetists are able to place the ProSeal with the same degree of accuracy before it can be recommended for use in resuscitation.
There might be a temptation to consider the ProSeal as a universal substitute for the tracheal tube. However, on a minority of occasions placement does not allow positive pressure ventilation. Concern about regurgitation also remains and we have not studied this. We have not compared the relative safeties of the ProSeal and the classic laryngeal mask airway. Further data from large studies or widespread clinical use will be needed before these questions can be answered.
In summary, we have shown that the ProSeal provides improved seal pressure for positive pressure ventilation compared with the classic laryngeal mask airway. It also provides an excellent route for insertion of a gastric tube. These benefits are at the cost of slightly increased difficulty in insertion of the ProSeal.
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Acknowledgements |
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References |
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