1Department of Anaesthesia, University of Cape Town, Groote Schuur Hospital, Observatory,Cape Town 7925, South Africa*Corresponding author
Declaration of interest. The authors wish to thank Chris Goslin of Olympus (SA). N.R.E. received funding from Marland Medical South Africa. Marland Medical South Africa also funded the salary of a research assistant and provided the masks. AstraZeneca (South Africa) provided the propofol used in this study.
Accepted for publication: November 27, 2000
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Abstract |
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Methods. We studied the ability of the PLMA to isolate the airway in 103 anaesthetized adults who were breathing spontaneously or given neuromuscular blocking agents, by filling the hypopharynx with methylene blue-dyed saline introduced down the drainage tube once the mask was in place. At the beginning and end of the procedure, a fibre-optic bronchoscope was passed down the airway tube to observe any dyed saline in the bowl of the mask.
Results. The PLMA was positioned correctly in all successful attempts (102 out of 103 attempts) and was able to isolate the glottis from fluid in the hypopharynx in all patients initially. Leakage of saline into the bowl of the mask occurred in two patients in whom displacement of the mask was caused by upper airway events during the procedure. In the remaining 100 patients, the glottis was isolated successfully for the duration of the procedure.
Conclusions. The PLMA can be positioned reliably. It can isolate the airway from fluid in the hypopharynx.
Br J Anaesth 2002; 88: 5847
Keywords: equipment, masks anaesthesia; larynx, bronchoscopy fibreoptic; complications, aspiration; complications, regurgitation
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Introduction |
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Methods and results |
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A fibre-optic bronchoscope (Olympus BF 240) was introduced down the airway to a position 1 cm proximal to the end of the tube. If the view showed that the mask was rotated or distorted without surrounding the glottis, the test was halted and the reason noted. Normal saline dyed with methylene blue was prepared by adding methylene blue 20 mg to normal saline 1 litre. The dyed saline was previously found to be easily visible through the bronchoscope when present within the bowl of the PLMA. The dyed saline was introduced down the drainage tube until the hypopharynx was filled and a column of saline flowed back up the drainage tube to form a meniscus outside the patients mouth at the level of the lips. In vitro testing found that the volume of methylene blue required to fill the drainage tube until the meniscus reached the level corresponding to the patients lips was 7 ml in a size 4 PLMA and 10 ml in a size 5 PLMA; the height of this column was found to be 12 cm above the tip of the mask. The presence or absence of a leak into the bowl of the mask was noted via the bronchoscope. If a leak was present, the process was halted, the saline suctioned from the tube and the case noted as a failure. The fluid in the hypopharynx and column of blue saline was then left in the drainage tube for the duration of the procedure, the meniscus being maintained by adding further amounts of methylene blue saline if necessary. The total amount of methylene blue saline used was recorded. In the event of any change in respiratory measurements combined with a drop in the level of the meniscus, airway endoscopy was repeated to see if a leak had occurred within the mask. If so, the saline was suctioned out and a failure noted. Otherwise, at the end of the procedure the bronchoscope was reintroduced and the bowl of the mask reinspected for any signs of leaked blue saline. The bronchoscope was then removed and the saline aspirated from the drainage tube.
The details of anaesthesia are shown in Table 1. Placement of the PLMA was unsuccessful in one patient.
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Comment |
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In all but one case, the volume of dyed saline injected into the drainage tube was greater than the volume of the tube, indicating that the saline must have entered the hypopharynx. We presume that in the one case in which a smaller volume was injected an airlock must have occurred within the tube.
This study has shown that the properly positioned PLMA can isolate the airway from fluid contained within the hypopharynx in paralysed and non-paralysed patients, even when that fluid is present for a considerable period of time and the patient is in a variety of positions, including head-down. This study did not mimic the act of passive regurgitation, as the fluid did not travel up the oesophagus. However, the pressure attained in the drainage tube, and therefore, presumably, within the hypopharynx during this study (12 cm H2O) is greater than that normally associated with passive regurgitation, but less than the described maximum pressures of 30 cm H2O.3 The study by Brimacombe and colleagues in cadavers4 showed that, when the drainage tube was closed, the PLMA successfully protected the airway from fluid injected up the oesophagus until pressures of 6368 cm H2O had been achieved. If the drainage tube was left open, no leaks occurred.
It is therefore reasonable to conclude that the PLMA is likely to provide better protection of the airway from passive regurgitation than either no airway protection device or the classic laryngeal mask airway.
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References |
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2 Evans NR, Gardner SV, James MFM et al. The ProSeal laryngeal mask: results of a descriptive trial with experience of 300 cases. Br J Anaesth 2002; 88: 0000
3 Holloway RH, Hongo M, Berger K, McCallum RW. Gastric distension: a mechanism for postprandial gastroesophageal reflux. Gastroenterology 1985; 89: 77984[ISI][Medline]
4
Keller C, Brimacombe J, Kleinsasser A, Loeckinger A. Does the ProSeal laryngeal mask airway prevent aspiration of regurgitated fluid? Anesth Analg 2000; 91: 101720