T. Asai

Jaw thrusting as a clinical test to assess the adequate depth of anaesthesia for insertion of the laryngeal mask.

We have studied the efficacy of the loss of response to jaw thrust as a clinical test to assess adequate depth of anaesthesia for insertion of the laryngeal mask in 60 patients. After induction of anaesthesia with propofol (infused using a syringe driver), the patients were randomly allocated to one of two groups. In one group, insertion of the laryngeal mask was attempted immediately after the loss of verbal contact and in the other group, after the loss of motor response to a jaw thrust. Conditions for insertion of the laryngeal mask were assessed. The mean dose of propofol required to obtain loss of verbal contact was 1.94 mg. kg−1 (SD 0.39, 95% confidence intervals (CI) 1.79–2.08 mg. kg−1) and that for the loss of response to jaw thrust was 2.55mg. kg−1 (SD 0.46, 95% CI 2.38–2.72 mg. kg−1). When depth of anaesthesia was assessed using jaw thrusting, it was always possible to insert the mask and the conditions were optimal in 87% (95% CI 72–95%) of patients. Neither coughing nor gagging occurred. In contrast, conditions were almost always less than optimal when insertion was attempted after the loss of verbal contact. Conditions were significantly better when jaw thrust was used as a clinical test compared with loss of verbal contact (p = 0.001). No marked haemodynamic depression occurred in any patient. Thus, jaw thrust is a reliable clinical test to assess the adequate depth of anaesthesia for uncomplicated insertion of the laryngeal mask after induction of anaesthesia with propofol.

Intra-ocular pressure changes in patients with glaucoma.: Comparison between the laryngeal mask airway and tracheal tube

We performed a randomised prospective study in 20 patients with glaucoma to examine the effects of tracheal intubation and laryngeal mask insertion on intra‐ocular pressure, mean arterial blood pressure and heart rate. After induction of anaesthesia with propofol, intra‐ocular pressure decreased significantly below baseline values in both the laryngeal mask and tracheal tube groups. After insertion of the laryngeal mask, intra‐ocular pressure remained significantly below baseline values in all patients. In contrast, tracheal intubation was associated with a significant increase in intra‐ocular pressure to above baseline values in three out of eight patients. Insertion of the laryngeal mask had minimal effects on mean arterial blood pressure and heart rate, whereas tracheal intubation significantly increased both factors relative to pre‐intubation values.

Insertion methods of the laryngeal mask airway. A survey of current practice in Wales.

Summary The efficacy of the laryngeal mask is widely accepted, but there is a lack of consensus on the best insertion method and on the use of the mask, for certain surgical procedures. We sent a questionnaire to all anaesthetists in Wales to discover the frequency of use of the laryngeal mask and the preferred insertion method. The questionnaire also enquired about the use of the laryngeal mask during anaesthesia for laparoscopic clip sterilisation. Replies were received from 125 consultants (89% of those circulated) and 122 non-consultants (69%). The insertion method described in the manufacturers instruction manual was preferred by 30% of consultants and 34% of the others. The next most popular option was insertion of the mask with the cuff partially inflated. Twenty-three per cent of consultants and 34% of non-consultants were prepared to use the laryngeal mask during anaesthesia for laparoscopic clip sterilisation. Although the insertion technique described in the instruction manual is the most widely employed, a large number of alternative methods are frequently used.The efficacy of the laryngeal mask is widely accepted, but there is a lack of consensus on the best insertion method and on the use of the mask, for certain surgical procedures. We sent a questionnaire to all anaesthetists in Wales to discover the frequency of use of the laryngeal mask and the preferred insertion method. The questionnaire also enquired about the use of the laryngeal mask during anaesthesia for laparoscopic clip sterilisation. Replies were received from 125 consultants (89% of those circulated) and 122 non‐consultants (69%). The insertion method described in the manufacturers instruction manual was preferred by 30% of consultants and 34% of the others. The next most popular option was insertion of the mask with the cuff partially inflated. Twenty‐three per cent of consultants and 34% of non‐consultants were prepared to use the laryngeal mask during anaesthesia for laparoscopic clip sterilisation. Although the insertion technique described in the instruction manual is the most widely employed, a large number of alternative methods are frequently used.

Damage to the laryngeal mask by residual fluid in the cuff

It has been suggested that, in some situations, the cuff of the laryngeal mask should be filled with fluid. We speculated that this practice might damage the device during sterilisation in an autoclave. We studied whether injection of a small volume of water into the cuff of the laryngeal mask and subsequent sterilisation affected the integrity of the cuff. First, a pressure–volume relationship for each of 20 new masks was obtained by inflating the cuff with increasing volumes of air (5–45 ml). The masks were then randomly allocated into four groups (W0, W0.25, W0.5 or W1.0), 0, 0.25, 0.5 or 1.0 ml of water was injected into the cuff and the mask was then sterilised in an autoclave. After sterilisation, the shape of the cuff was examined and pressure–volume relationships were obtained again. The baseline intracuff pressures were similar in the four groups. After sterilisation, the pressure was significantly lower in groups W0.25, W0.5 and W1.0 than in group W0 (p < 0.05). Two masks in group W1.0 lost their integrity, resulting in herniation of and rupture of the cuff. We conclude that the cuff of the laryngeal mask should not be inflated with fluid unless the device is discarded afterwards.

Effects of magnesium sulphate on suxamethonium-induced complications during rapid-sequence induction of anaesthesia

Twenty patients were studied in a double‐blind manner to investigate whether magnesium sulphate, when given during a rapid‐sequence induction of anaesthesia, lessens the side effects caused by suxamethonium. Patients were randomly allocated to two groups; equal volumes of either magnesium sulphate (40 mg.kg‐1) or saline were given during rapid‐sequence induction of anaesthesia, after thiopentone but before the administration of suxamethonium (1.5 mg.kg‐1). The changes in the serum potassium concentration, the degree of muscle fasciculations and the presence of postoperative myalgia were recorded. The mean serum potassium concentration increased by 0.08 mmol.l‐1 in the magnesium group and by 0.1 mmol.l‐1 in the control group at 2 min after injection of suxamethonium; in neither group was there a significant increase from baseline values. The systolic blood pressure and heart rate increased in both groups after tracheal intubation. The incidence of fasciculations was significantly lower in the magnesium group. Magnesium did not clinically prolong muscle relaxation. There was no difference between the groups in the incidence of myalgia after surgery (one patient in each group). Since no significant increase in the serum potassium concentration was demonstrated, no assessment could be made of the effect of magnesium sulphate on the serum potassium concentration after administration of suxamethonium.

The laryngeal mask and patients with‘collapsible’airways

The manufacturing method from 1991 to the present has always included bonding the APL valve in place, so that the user cannot transpose it with the breathing bag. In this case, the error occurred during assembly of the anaesthetic system. The assembly method was consequently amended to make the joining of the elbow and T-piece components impossible, unless the valve and breathing bag were in the correct locations. This modification leaves us confident that this error will not be repeated. We would agree that this emphasises the importance of medical staff checking equipment before use, and routinely using capnography. However, making products safer by design is one of our foremost aims, and this incident will be further considered during the design review.

Kinking of a tracheal tube in the nasal cavity

and (c) which require active participation in the writing, but I feel that we should have a more ready way of recognising the originators of ideas put forward either in conversation or lectures. The ‘Notice to Contributors’ to Anaesthesia clearly discriminates against the spoken word; maybe a form of ‘Verbal Communication’ should be allowable? original ideas fertilised by discussion with others. A communication to a journal may put forward those thoughts and I may wish to recognise the vital part in the thinking played by my colleagues. Verbal communication is unacceptable as a reference and if these colleagues are to be recognised in a citation index as contributors in this field, I have to include them as co-authors, when what I really mean is co-thinkers. When doing this, I do of course pass the manuscript to them for comment and correction, so as to fdful criteria (b) Salisbury Hospital, Salisbury SP2 8BJ J.A. LACK

Inflation of the cuff of the laryngeal mask

The first day after surgery the patient had a sore throat, but didn’t complain to his doctor. On the 6th postoperative day his sore throat was so painful that swallowing and eating of solid food was impossible. Subsequently inspection of the oral cavity showed ulceration on the soft palate and the uvula (Fig. I). The condition was treated with chlorhexidine 0.05% mouth washes. The patient was discharged from hospital on the 7th postoperative day. On the 10th day the complaints had almost completely disappeared and eventually the ulcer healed without scarring. Laryngeal mask airways are now firmly established in anaesthetic practice. Oropharyngeal mucosal injury and uvular bruising have been reported [I, 21. However, extensive ulceration of the soft palate in patients with