Biomedical subjects
Publications and source records attributed to R S Vaughan.
Acute cardiac herniation after radical pneumonectomy is extremely rare and is associated with an immediate mortality greater than 50%. We report a patient in whom cardiac herniation produced no signs or symptoms. The heart was returned to its correct position and the pericardial defect was repaired.
A breathing system filter can remain connected to a laryngeal mask airway during recovery from anaesthesia. The Luer-lock monitoring port on the filter could be used for the delivery of supplementary oxygen. The efficacy of this technique was assessed in vitro by comparing the performance of two filters with four other devices, including a T-piece with a 40% oxygen injector. The minimum inspired oxygen fraction and pressure drop were measured over a range of ventilatory conditions and oxygen flows. The minimum inspired oxygen fraction measured with the remaining devices was greater than with the T-piece at an oxygen flow of 10 l.min-1. The pressure drop was greater with the breathing system filters than with the T-piece. A potential advantage in using filters is that no additional equipment is required. However, if using the filters as oxygen supplementation devices, there is only one port open to the atmosphere in the system and inadvertent obstruction of this port could cause barotrauma. It must be remembered that the nonstandard use of such equipment contravenes the recently introduced Medical Device Directive regulations.
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Sixty patients were randomly allocated to one of three groups and the incidences of respiratory complications which occurred during emergence from anaesthesia were compared under the following three circumstances: tracheal extubation after the patient had regained consciousness (awake group); tracheal extubation while the patient was still anaesthetised (anaesthetised group); and the use of the laryngeal mask during emergence from anaesthesia (mask group). In the mask group, the laryngeal mask was inserted under deep anaesthesia before tracheal extubation and the lungs were ventilated through the laryngeal mask after tracheal extubation. In the awake group, straining (bucking) occurred in 18 patients and desaturation (arterial oxygen haemoglobin saturation < 95%) in two patients. In the anaesthetised group, airway obstruction occurred in 17 patients and desaturation in one of these patients. In the mask group, ventilation through the laryngeal mask was temporarily difficult immediately after tracheal extubation in one patient and coughing occurred before removal of the mask in three patients. No respiratory complications occurred in two patients in the awake group, three patients in the anaesthetised group and 16 patients in the mask group. The incidence of respiratory complications during recovery from anaesthesia was significantly lower in the mask group than in the other two groups (pooled) (p << 0.001). Therefore, the use of the laryngeal mask after tracheal extubation decreases the incidence of respiratory complications during recovery from anaesthesia.
We studied the efficacy of the cuffed oropharyngeal airway in 100 patients. Insertion of the airway after induction of anaesthesia with propofol was easy in 95 of 100 patients, moderately difficult in four patients and failed in one patient. Complications, such as coughing, gagging or body movement, occurred during induction and insertion in 15 patients. Insertion of the airway was not associated with tachycardia or hypertension. Manual ventilation through the airway was easy in less than 30% of patients immediately after insertion. Manual ventilation became easier after adjusting the position of the patient's head, neck or jaw. During spontaneous breathing, adjustment of the head, neck or jaw was required in 30% of patients. Complete airway obstruction occurred in one patient after insertion of the device and in two patients during maintenance of anaesthesia. The airway was left in place during emergence from anaesthesia in the remaining 97 patients. No complications occurred in 91 patients and coughing occurred in the remaining six patients before or during removal of the airway. No regurgitation, vomiting or laryngospasm occurred in any patient at any time. Therefore, the cuffed oropharyngeal airway has a potential use in anaesthetised patients who are breathing spontaneously.
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We conducted a prospective survey on the incidence of respiratory complications associated with tracheal intubation and extubation in 1005 patients who underwent elective general anaesthesia over a 4-month period. During induction of anaesthesia, respiratory complications occurred in 46 patients (4.6%; 95% confidence limits (CL): 3.3, 5.9%). The common complications were coughing (1.5%) and difficult ventilation through a facemask (1.4%). Tracheal intubation was difficult in eight patients (0.8%). Complications occurred immediately after tracheal extubation in 127 patients (12.6%; 95% CL: 10.6, 14.7) and in the recovery room in 95 patients (9.5%; 95% CL: 7.6, 11.3%). The common complications immediately after extubation were coughing (6.6%) and oxygen desaturation (SaO2 < 90%) (2.4%), and in the recovery room, airway obstruction (3.8%) and coughing (3.1%). The incidence of complications was significantly higher immediately after tracheal extubation than during induction of anaesthesia (P << 0.001). Even when all incidents of coughing that occurred after tracheal extubation were disregarded as a complication, the overall incidence was still higher immediately after extubation (7.4%) than during induction of anaesthesia (P < 0.01). We conclude that the incidence of respiratory complications associated with tracheal extubation may be higher than that during tracheal intubation.
We have investigated the effects of clonidine on gastric emptying of liquids in 30 patients. In a double-blind, randomized design, clonidine 150 micrograms, morphine 10 mg or saline in 1 ml was given i.m. One hour later, the patient drank a paracetamol solution (1.5 g in 50 ml water). Venous blood samples were obtained every 15 min for 90 min thereafter. Plasma paracetamol concentrations were measured using high-pressure liquid chromatography and the area under the concentration-time curve was calculated. The degree of sedation and complications were recorded. The area under the curve for 0-60 min was significantly smaller in the morphine group than in the saline group (P = 0.002; 95% confidence interval (CI) for difference -1237 to -502 micrograms min ml-1), whereas it was greater in the clonidine group compared with the saline group, although this was not significant (95% CI for difference -423 to 1264 micrograms min ml-1). Arterial pressure was significantly lower in the clonidine group compared with the saline group. Both clonidine and morphine appeared to cause mild sedation. We conclude that clonidine 150 micrograms i.m. does not delay gastric emptying of liquids in a similar manner to morphine.
The Portex introducer for the laryngeal mask airway was designed as an aid to successful insertion, acting as an idealised 'artificial hard palate' to guide the tip of the laryngeal mask into the correct position. A number of authors have investigated laryngeal mask insertion by unskilled personnel in certain situations, one example being nurses during in-hospital cardiopulmonary resuscitation. We investigated whether the introducer had any effect on the incidence of first-time successful LMA placement by unskilled personnel. These were nonanaesthetist doctors, randomly assigned to have one attempt at LMA insertion in an anaesthetised patient, with and without the introducer. In 44 patients with the LMA being inserted according to the manufacturer's instructions, there was a 68% success rate (14 failures). In 45 patients with the LMA being inserted with the aid of a Portex introducer, there was a 96% success rate (two failures). This was a highly significant improvement (p < 0.001).
We randomly allocated 60 patients with normal airways into three groups to compare the ease of fibrescope-aided tracheal intubation using 8.0-mm internal diameter (group F8) and 6.0-mm (group F6) reinforced tracheal tubes and to evaluate the efficacy of the laryngeal mask as an aid for fibreoptic tracheal intubation (group L). In group F8 tracheal intubation was optimal in 2 of 20 patients and in two patients in whom intubation over the fibrescope was difficult the attempts resulted in inadvertent oesophageal intubation. In group F6 intubation was always successful and significantly easier than in group F8 (p < 0.005; 95% confidence interval for the difference in the proportion of the optimal intubation grade: 20-70%). In group L tracheal intubation was optimal in 18 of 20 patients and easier than in group F6 (p = 0.014; 95% confidence interval for difference: 10-60%). In both groups F6 and L tracheal intubation was completed within less than about 1 min. We conclude that conventional fibrescope-aided tracheal intubation with a 6.0-mm tracheal tube is easier than with an 8.0-mm tube and that the laryngeal mask facilitates fibrescope-aided tracheal intubation.
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We studied 50 patients, in a blind, crossover study, to assess if cricoid pressure applied after placement of the laryngeal mask prevented gastric insufflation without affecting ventilation. After induction of anaesthesia and neuromuscular block, a laryngeal mask was inserted and confirmed to be placed correctly. The lungs were ventilated with a maximum inflation pressure of 15 cm H2O. In the first 25 patients, expiratory volumes were measured with and without cricoid pressure (30 N). On both occasions, a free hand was placed under the patient's neck. In the next 25 patients, the effect of cricoid pressure on ventilation without support of the neck was also studied. The effect of cricoid pressure with support of the neck on gastric insufflation was then assessed using a stethoscope in all 50 patients, while the lungs were ventilated with a maximum inflation pressure of 30 cm H2O. At the end of the study, the position of the mask was re-assessed. Cricoid pressure significantly decreased mean expiratory volume (P << 0.001). This inhibitory effect was significantly greater when the pressure was applied without support of the neck (P << 0.001). Cricoid pressure significantly reduced the incidence of gastric insufflation (12 patients vs one patient; P << 0.001; 95% CI for difference 10.5-33.5%). In no patient was the mask dislodged after these procedures. Thus, although cricoid pressure applied after insertion of the laryngeal mask prevented gastric insufflation, it also decreased ventilation. The inhibitory effect of cricoid pressure on ventilation without support of the neck was greater than cricoid pressure with support of the neck.
The possibility of using chemical changes to confirm correct tracheal tube placement was investigated with a view to their use in developing countries where more sophisticated methods are unavailable. The effect of bubbling expired gases through a 10% solution of bromothymol blue and a 0.25% solution of thiopentone led to chemical changes producing, in the case of bromothymol blue, a colour change and in that of thiopentone, precipitation, probably due to a change in pH caused by carbon dioxide. We also discovered that the time to precipitation of the thiopentone could be greatly reduced if it was mixed with a precise quantity of lignocaine. These simple end points can reliably confirm the correct placement of a tracheal tube at least as rapidly as the correct use of capnography.
The Non Invasive Virtual Shunt computer program has previously been described and validated. The system has subsequently been developed to give a real time, continuous trace of virtual shunt. A portable computer connected to routine monitoring equipment displays a plot of virtual shunt updated every 10 s. A practical use of this device in the clinical setting of one-lung anaesthesia is described. The equipment was used to monitor shunt before, during and after surgery in three patients. In one case, a displaced double lumen bronchial tube was detected before there was any other indication of the problem.
A randomised study was carried out to compare the efficacy of the gum elastic bougie and the stylet in a simulated difficult intubation. A laryngoscopic assessment, as described by Cormack and Lehane, was made in 100 patients. A Grade 3 view was then simulated. In the Bougie First Group (50 patients) two attempts were made to pass a gum elastic bougie and a tracheal tube into the trachea. If these first two attempts were not successful, two further attempts at intubation were allowed with a stylet placed in the tracheal tube. In the Stylet First Group (50 patients) the order was reversed. After two attempts the tube was correctly placed in the trachea in 96% of cases in the Bougie First Group compared to only 66% of cases in the Stylet First Group (p < 0.001). We recommend that a gum elastic bougie should be readily available and that anaesthetists should use it in preference to a stylet whenever a good view of the glottis is not immediately available.
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 2.55 mg.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.