Minimum alveolar sevoflurane concentrations required for insertion of the cuffed oropharyngeal airway and the laryngeal mask airway: a comparative study

Both the cuffed oropharyngeal airway and the laryngeal mask airway share a similar property of being less stimulating to the upper airway than the tracheal tube. This study was conducted to compare sevoflurane concentrations required for insertion of the cuffed oropharyngeal airway and the laryngeal mask airway in elderly and young adult patients. Forty-one elderly (65-90 years) and 34 young adult (18-50 years) patients, scheduled for elective surgery during spontaneous breathing anaesthesia were randomly assigned to either the cuffed oropharyngeal airway or the laryngeal mask airway group. After a predetermined end-tidal concentration of sevoflurane had been established and maintained for at least 20 min, insertion of the device was attempted without neuromuscular relaxants or other adjuvants. Each concentration at which insertion of the device was attempted was predetermined by modification of Dixon's up-and-down method with 0.5% as the step size. Sevoflurane MACCOPA [mean 1.17 (SD 0.38)%, 0.77-1.56% (95% CI)] was significantly less than MACLMA [2.00 (0.52)%, 1.45-2.55%, p < 0.05] for elderly patients. Similarly, sevoflurane MACCOPA [1.33 (0.38)%, 0.94-1.73%] was significantly less than MACLMA [2.00 (0.42)%, 1.56-2.44%, p < 0.05] for young adult patients. There were no significant differences in either MACCOPA or MACLMA between the elderly and the young adult patients. We conclude that the insertion of the cuffed oropharyngeal airway can be accomplished at a lower sevoflurane concentration, and hence, is less stimulating to the upper airway than that of the laryngeal mask airway.     

Physiological dead space/tidal volume ratio during face mask, laryngeal mask, and cuffed oropharyngeal airway spontaneous ventilation

Objective: To compare the physiological dead space/tidal volume ratio and arterial to end-tidal carbon dioxide tension (ETCO₂) difference during spontaneous ventilation through a face mask, a laryngeal mask (LMA), or a cuffed oropharyngeal airway.

Design: Prospective, randomized, cross-over study.

Setting: Inpatient anesthesia at a university department of orthopedic surgery.

Patients: 20 ASA physical status I and II patients, without respiratory disease, who underwent ankle and foot surgery.

Interventions: After a peripheral nerve block was performed, propofol anesthesia was induced and then maintained with a continuous intravenous (IV) infusion (4 to 6 mg/kg/h). A face mask, a cuffed oropharyngeal airway, or an LMA were placed in each patient in a random sequence. After 15 minutes of spontaneous breathing through each of the airways, ventilatory variables, as well as arterial, end-tidal, and mixed expired CO₂ partial pressure, were measured, and physiological dead space/tidal volume ratio was calculated.

Measurements and Main Results: Expired minute volume and respiratory rate (RR) were lower with LMA (5.6 ± 1.2 L/min and 18 ± 3 breaths/min) and the cuffed oropharyngeal airway (5.7 ± 1 L/minand 18 ± 3 breaths/min) than the face mask (7.1 ± 0.9 L/min and 21 ± 3 breaths/min) (p = 0.0002 and p = 0.013, respectively). Physiological dead space/tidal volume ratio and arterial to end tidal CO₂ tension difference were similar with the cuffed oropharyngeal airway (3 ± 0.4 mmHg and 4.4 ± 1.4 mmHg) and LMA (3 ± 0.6 mmHg and 3.7 ± 1 mmHg) and lower than with the face mask (4 ± 0.5 mmHg and 6.7 ± 2 mmHg) (p = 0.0001 and p = 0.001, respectively).

Conclusion: Because of the increased dead space/tidal volume ratio, breathing through a face mask required higher RR and expired minute volume than either the cuffed oropharyngeal airway or LMA, which, in contrast, showed similar effects on the quality of ventilation in spontaneously breathing anesthetized patients.     

The cuffed oropharyngeal airway vs. the laryngeal mask airway: a randomised cross-over study of oropharyngeal leak pressure and fibreoptic view in paralysed patients

We conducted a randomised cross-over study of 20 patients to test the hypothesis that oropharyngeal leak pressure and the fibreoptic view differ between the cuffed oropharyngeal airway and laryngeal mask airway in paralysed patients. We also tested the design premise that inflation of the cuffed oropharyngeal airway cuff elevates the epiglottis from the posterior pharyngeal wall. Both airways were inserted into each patient in random order. Oropharyngeal leak pressure and fibreoptic view were documented at zero volume and after each additional 10 ml up to the maximum recommended volume for each device. The laryngeal mask had a higher maximum (23 vs. 16 cmH2O, p = 0.03), minimum (9 vs. 2 cmH2O, p < 0.02) and overall (17 vs. 9 cmH2O, p < 0.001) oropharyngeal leak pressure compared with the cuffed oropharyngeal airway. The glottic inlet was visible more frequently with the laryngeal mask (96 vs. 39%, p < 0.0001). There was no elevation of the epiglottis from the posterior pharyngeal wall with the cuffed oropharyngeal airway. We conclude that the laryngeal mask forms a more effective seal and provides a better fibreoptic view of the glottic inlet than the cuffed oropharyngeal airway in paralysed patients. Inflation of the cuffed oropharyngeal airway cuff does not cause elevation of the epiglottis.     

The pressor response and laryngeal mask insertion

The pressor response associated with laryngoscopy and tracheal intubation may be harmful to certain patients. The laryngeal mask airway avoids the need for laryngoscopy and allows positive pressure ventilation of the lungs in appropriate patients. This study compared the pressor response of tracheal intubation with that of mask insertion in two groups of 24 and 23 healthy patients respectively. All patients were anaesthetised with thiopentone, nitrous oxide, enflurane and paralysed with atracurium. We have shown a similar, but attenuated pattern of response associated with mask insertion in comparison with laryngoscopy and intubation; significant differences between the groups were evident in arterial diastolic blood pressure immediately after insertion and again 2 minutes later. Use of the laryngeal mask may therefore offer some limited advantages over tracheal intubation in the anaesthetic management of patients where the avoidance of the pressor response is of particular concern.     

A comparison of four methods for assessing oropharyngeal leak pressure with the laryngeal mask airway (LMA) in paediatric patients

BACKGROUND: This study compares four tests for assessing oropharyngeal leak pressure with the laryngeal mask airway (LMA). We tested the hypothesis that the oropharyngeal leak pressure and interobserver reliability differs between tests. METHODS: Eighty paralysed anaesthetized paediatric patients (weight 10-30 kg) were studied with the intracuff pressure set at 60 cmH2O. Four different oropharyngeal leak pressure tests were performed in random order on each patient by two observers blinded to each other's measurements. Test 1 involved detection of an audible noise. Test 2 involved detection of endtidal CO2 in the oral cavity. Test 3 involved observation of the aneroid manometer dial as the pressure increased and noting the airway pressure at which the dial reaches stability. Test 4 involved detection of an audible noise by neck stethoscopy. RESULTS: The mean oropharyngeal leak pressure was 12.5 cmH2O and was similar between tests. The intraclass correlation coefficient was 0.99 for all tests and was classed as excellent. CONCLUSIONS: We conclude that all four tests provide accurate and reliable information about oropharyngeal leak pressure in children.     

The laryngeal mask airway

A new form of airway has recently been described, which is introduced blindly into the hypopharynx to form a seal around the larynx, so permitting spontaneous or positive pressure ventilation without penetration of the larynx or oesophagus. The further development of this new airway is described and the results of 18 months' clinical experience are presented. The airway was used successfully in 118 patients, 17 of whom received controlled ventilation of their lungs. It was used in place of the facemask in routine anaesthesia, and was of particular value in ophthalmic, dental and ear, nose and throat procedures and where difficulties with the airway were expected. The incidence of sore throat and other problems was low. Experience of more than 500 cases suggests that the laryngeal mask airway may have a valuable r?le to play in all types of inhalational anaesthesia, while its proven value in some cases of difficult intubation indicates that it may contribute significantly to the safety of general anaesthesia.     

The cuffed oropharyngeal airway for spontaneous ventilation anaesthesia. Clinical appraisal in 100 patients

The cuffed oropharyngeal airway is a modified Guedel airway with a distal inflatable cuff and a proximal connector for attachment to an anaesthesia circuit. The purpose of this study was to evaluate this device for spontaneous ventilation anaesthesia in 100 adult patients. Anaesthesia was induced with fentanyl and propofol and maintained with nitrous oxide and isoflurane in oxygen. The device was inserted when anaesthetic depth was judged to be adequate. Adverse airway events and interventions (i.e., manoeuvres performed in order to provide a clear airway) were analysed from video recordings and detailed notes. The position of the device was assessed fibreoptically during spontaneous ventilation. The device provided a clear airway in 98% of patients during manually assisted ventilation, in 100% during spontaneous ventilation and in 100% during emergence. However, 91% of patients required at least one airway intervention at some time. Jaw life was required for 33% of the time during manually assisted ventilation and 21% of the time during spontaneous ventilation. Most interventions occurred during the first 3 min of either manually assisted or spontaneous ventilation. The incidence of adverse airway events during manually assisted ventilation was 8%, during spontaneous ventilation was 5% and during emergence was 5%. Oxygen saturation briefly fell to between 87 and 89% on six occasions. On fibreoptic assessment, the vocal cords were visible in 29% of patients on fibreoptic assessment and the epiglottis was visible in 90%. Mild sore throat occurred in 4% of patient. We conclude that the cuffed oropharyngeal airway is suitable for spontaneous ventilation anaesthesia and has a low complication rate but that most patients require one or more interventions to provide a clear airway.     

The cardiovascular response to insertion of the intubating laryngeal mask airway

Sixty-one patients received a standardised anaesthetic and were randomly assigned to three groups: tracheal intubation via direct laryngoscopy, tracheal intubation via an intubating laryngeal mask airway with immediate removal of the device, and tracheal intubation via an intubating laryngeal mask airway with delayed removal. The cardiovascular response to intubation was of a similar magnitude in all groups, although delayed removal of the intubating laryngeal mask airway was associated with a second pressor response. Norepinephrine changed significantly over time following direct laryngoscopy and following immediate removal of the intubating laryngeal mask airway, but not after delayed removal. The findings of this study do not support using the intubating laryngeal mask instead of direct laryngoscopy purely to decrease the response to intubation.     

The use of the cuffed oropharyngeal airway in paediatric patients

BACKGROUND: The cuffed oropharyngeal airway (COPA) is a device which has already been demonstrated to be suitable for anaesthetized adult patients undergoing either spontaneous or mechanical ventilation. There are few reports on the use of the COPA in children. In this study, the authors assessed the COPA in paediatric patients undergoing minor surgery. METHODS: The same anaesthesiologist inserted the COPA in 40 consecutive paediatric patients, ASA I and II, aged 1.8-15.3 years. (7.4 +/- 3.9), after induction of anaesthesia with N2O/O2/sevoflurane. COPA size was chosen by measuring the distal tip of the device at the angle of the jaw with the COPA perpendicular to the patient's bed. The proper positioning of the COPA was assessed by observing thoracoabdominal movements, regular capnograph trace, the reservoir bag movements and SpO2 > 94% with a fraction of inspired oxygen of 0.5. Anaesthesia was maintained with 1 MAC halothane, sevoflurane, or isoflurane in N2O/O2 (50%) and the patients were spontaneously breathing. The stability of the COPA following changes in head, neck and body position was tested. We recorded the duration time for COPA insertion, the side-effects of placement of the COPA and during the intraoperative period, the number of attempts, the type of manipulation in order to provide an effective airway and postoperative symptoms, such as the presence of blood on the device, sore throat, neckache, jaw pain and PONV. RESULTS: Successful COPA insertion at the first attempt was 90% and at the second attempt in the remaining 10%. The most frequent airway manipulations were head tilt in 27.5% (obtained by a pillow under shoulders) and chin lift in 5%. No complications both at COPA placement nor during the intraoperative period were observed. On the basis of weight and age, the COPA size was no. 8 in 50%, no. 9 in 30%, no. 10 in 12.5%, and no. 11 in 7.5%. The COPA demonstrated stability after changes in head, neck and body position. Postoperative complications were the presence of blood stains in one case and PONV in six cases (15%). CONCLUSIONS: The COPA is an extratracheal airway device suitable in paediatric patients undergoing general anaesthesia with spontaneous ventilation for minor surgery and other painful procedures. This study shows that for paediatric patients: (i) complications seem to be rare; (ii) the COPA allows hands free anaesthesia; (iii) specific indication for the COPA could be obese patients with a small mouth; and (iv) COPA sizing can be easily established by the weight or age of the patients.     

Higher airway seal does not imply adequate positioning of laryngeal mask airways in paediatric patients

BACKGROUND: It has been generally accepted that a higher airway seal pressure indicates adequate positioning of the laryngeal mask airway (LMA) in adult patients. The present study was undertaken to clarify whether a higher airway seal pressure correlates with an adequate positioning of the LMA in paediatric patients. METHODS: One hundred and eighty-one healthy children, aged 6-121 months, weighing 7.0-30.0 kg, managed with size 1.5-2.5 LMAs during elective surgery, were enrolled in this study. LMAs were inserted without using muscle relaxants, and patients breathed spontaneously during surgery. At the end of surgery, we documented oropharyngeal sealing pressure and fibreoptic aperture views of the LMA. We used a new fibreoptic score evaluating the anatomical relationship between LMA aperture and epiglottis: 1, the aperture view covered with anterior epiglottis completely, but the airway staying open; 2, anterior epiglottis seen for more than two-thirds of the aperture view in diameter; 3, anterior epiglottis seen for more than one-third, but less than two-thirds of the aperture view in diameter; and 4, anterior epiglottis seen for less than one-third of the aperture view in diameter. RESULTS: The oropharyngeal sealing pressures for each fibreoptic position, scores 1 to 4, were 17.0 +/- 6.4, 17.9 +/- 4.2, 20.1 +/- 7.3 and 17.1 +/- 6.1 cm H2O, respectively. There were no significant differences in sealing pressure between the four groups (P=NS). CONCLUSIONS: A higher airway seal is believed to be one of the clinical signs correlating with the correct position of an LMA. We found no relationship between oropharyngeal sealing pressure and LMA cuff position in paediatric patients.     

The laryngeal mask airway - anatomical and physiological implications

The laryngeal mask airway (LMA) is a relatively new general purpose airway which fills a niche between the face mask and tracheal tube, both in terms of anatomical location and degree of invasiveness. It sits in the hypopharynx at the interface between the gastrointestinal and respiratory tracts, where it forms a circumferential low pressure seal around the glottis. This has advantages in terms of gas flow through the upper airway and allows direct access to the glottis without loss of airway control. LMA insertion can be considered in the context of swallowing and combines the ability to insert blindly whilst avoiding collision with highly innervated anterior pharyngeal structures. This review deals briefly with the concepts behind LMA design and insertion, and focuses on the anatomical and physiological implications of the LMA with respect to the swallowing reflex, the oesophagus, the pharyngeal mucosa, pulmonary defences, pulmonary mechanics and the cardiovascular system. The possible role of the LMA as a monitor of anaesthetic depth and areas of future research are also discussed.     

Fentanyl decreases propofol requirement for laryngeal mask airway insertion

BACKGROUND: Since fentanyl is a potent depressant of the upper airway reflex, preadministration of fentanyl may facilitate insertion of the laryngeal mask airway (LMA) using propofol. Accordingly, we tested the hypothesis that fentanyl pretreatment would reduce the dose of propofol required for the LMA insertion. METHODS: Forty-one healthy patients without sedative premedication were randomly assigned to either fentanyl group, receiving fentanyl 2 microg kg-1 intravenously, or control group, receiving equal volumes of normal saline. Then, 3 ml of 2% lidocaine was given intravenously to alleviate pain associated with propofol administration. Thirty s after the fentanyl or saline injection, a predetermined dose of 1% propofol was given at a rate of 100 mg min-1. Insertion of the LMA was attempted 90 s after the completion of the propofol injection. The dose of propofol given to a particular patient was determined by the response of the preceding patient in that group to a higher or lower dose, using the up-and-down method. The first patient in each group received 2.5 mg kg-1 of propofol, while the step-size was 0.25 mg kg-1. Patients responses were assessed by a blinded observer. RESULTS: ED50 and ED95 of propofol requirements were significantly less in the fentanyl group (0.82, 1.17 mg kg-1, respectively) than those in the control group (2.39, 2.62 mg kg-1, P < 0.001). CONCLUSION: Our results indicate that preadministration of fentanyl 2 microg kg-1 decreases the propofol requirement for the LMA insertion.     

The laryngeal mask airway

A prototype size 3 laryngeal mask was used in 100 patients by 18 anaesthetists with no previous experience of its use. A clear and unobstructed airway was obtained in 98% of patients, without requiring support of the jaw, thus leaving the anaesthetists' hands entirely free. The patency of the airway did not deteriorate during the course of the anaesthetic. In 10 patients there was obstruction of the airway at the first attempt to place it without the introducer and this obstruction appeared to be as a result of downfolding of the epiglottis. Subsequent attempts at passage were successful in all 10 patients. The seal between the mask and the larynx was adequate for artificial ventilation of the patients, but the mean leak pressure was 1.7 kPa.     

The laryngeal mask airway

The laryngeal mask airway is an important addition to the anaesthetist's armamentarium, but its use is not without the possibility for misfortune. We encountered an unusual and potentially serious complication. A patient's epiglottis became trapped between the pliable grates in the mask portion of the laryngeal mask and partially obstructed his airway. Should this problem occur and remain unnoticed, in addition to the problem of airway obstruction during the anaesthetic, the oedematous epiglottis could be severely injured upon removal of the laryngeal mask. This, in turn, could result in airway obstruction requiring emergency treatment.     

Pollution with nitrous oxide using laryngeal mask or face mask

BACKGROUND: As environmental pollution by nitrous oxide may influence the health of the personnel working in operating theatres, the incidence and magnitude of nitrous oxide (N2O) leakage, when using a face mask or a laryngeal mask airway (LMA) for controlled ventilation, were studied in 34 patients scheduled for elective cystoscopy. METHODS: A semi-closed gas delivery ventilation system with active scavenging was used. The N2O concentrations were measured every 8 s at a position 30 cm above the patient's mouth with a N2O gas monitor (GD 200, Simrad Optronics). RESULTS: When using a face mask, the leakage of N2O resulted in a N2O concentration of 157 (85-332) p.p.m. (parts per million) (median concentration and 25% and 75% percentiles). With the LMA, a lower median concentration of N2O of 60 (28-126) p.p.m. was found (P=0.04). With the face mask, a concentration above 100 p.p.m. was found during 51% of the exposure time compared to 24% of the time in the LMA group. CONCLUSION: Environmental pollution was less with the LMA than the face mask, but under the conditions of the study both modes of airway management were associated with levels of N2O peak concentrations in the breathing zone of anaesthetists that are deemed to be excessively high by the Danish National Institute for Occupational Safety.     

The laryngeal mask airway in paediatric anaesthesia

Forty-eight children, aged between 2 and 10 years, admitted as day cases for otological surgery were allocated at random into two groups. The first group was anaesthetised using a standard facemask, and the second with a laryngeal mask airway. The laryngeal airway produced a satisfactory airway in all children, and was inserted on the first attempt in 67% of patients. Hypoxia was significantly less frequent in the laryngeal airway group (p less than 0.05), and there were significantly fewer interruptions to surgery than in the facemask group (p less than 0.001). Patient safety, operating and anaesthetic conditions were all considered superior in the laryngeal airway group.     

Bilateral recurrent laryngeal nerve neuropraxia following laryngeal mask insertion: a rare cause of serious upper airway morbidity

We report the case of a 4-year-old boy who developed bilateral recurrent laryngeal nerve neuropraxia following a routine anaesthetic with a laryngeal mask airway. The possible mechanisms of injury and the ways that this rare but critical complication might be avoided are discussed.     

Complications following use of the laryngeal mask airway in children

Anaesthetic records from 507 children anaesthetized using the laryngeal mask airway (LMA) breathing spontaneously were analysed. Failure to insert the LMA occurred in 10 (2.0%) children and there were difficulties with insertion in 36 (7.1%) children. There was a total of 81 (16%) children with complications in the recovery period. Most of these were not clinically significant. Twenty-three children showed evidence of trauma to the pharynx or larynx. This study demonstrates that the LMA is a safe and effective tool for use in paediatric anaesthesia. However, the incidence of trauma may be higher than expected and attempts should be made to minimize this with a gentle technique and adequate depth of anaesthesia.