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Biomedical subjects

R S Vaughan

Publications and source records attributed to R S Vaughan.

At least 19 recordsLinked to original sources
PubMed1996

Cricoid pressure applied after placement of the laryngeal mask prevents gastric insufflation but inhibits ventilation.

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.

Adolescent↗
PubMed1996

The use of bromothymol blue and sodium thiopentone to confirm tracheal intubation.

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.

Adult↗
PubMed1996

The use of a non-invasive method to measure intrapulmonary shunt during one-lung anaesthesia.

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.

Adult↗
PubMed1996

Simulated difficult intubation. Comparison of the gum elastic bougie and the stylet.

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.

Adult↗
PubMed1996

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 2.55 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.

Adult↗
PubMed1995

Cricoid pressure impedes placement of the laryngeal mask airway.

We have studied 22 patients to examine whether or not cricoid pressure affects ventilation of the lungs via the laryngeal mask and its correct positioning. In a randomized, crossover design, the laryngeal mask was inserted with or without cricoid pressure applied with a standardized force of 30 N using a cricoid yoke. A standardized pillow (6 cm in height) was placed under the patient's occiput, but the neck was not supported. Ventilation of the lungs via the laryngeal mask was adequate in all patients when no cricoid pressure was applied, but in only three of 22 patients when cricoid pressure was applied (P << 0.001; 95% confidence interval (CI) 0.72-1.0). The mask was positioned correctly in 18 patients when no pressure was applied, and in none after application of cricoid pressure (P << 0.001; 95% CI 0.66-0.98). We had planned to study, in an additional 20 patients, the effect of cricoid pressure without a pillow under the occiput; placement of the mask, however, was difficult even when cricoid pressure was not applied and there was a high incidence of bleeding from the oropharynx. We thus abandoned that part of the study after eight patients. In those eight patients, the success rate of ventilation via the laryngeal mask was lower when cricoid pressure was applied. We conclude that when sufficient force was applied, cricoid pressure, regardless of the method of application, did impede placement of the laryngeal mask.

Adult↗
PubMed1995

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.

Adolescent↗
PubMed1994

Cricoid pressure impedes placement of the laryngeal mask airway and subsequent tracheal intubation through the mask.

We have studied 40 patients to see if cricoid pressure affects the success rate of ventilation through, and the position of, the laryngeal mask and subsequent fiberscope-aided tracheal intubation. Adequate ventilation of the lungs was produced through the laryngeal mask in 19 of 20 patients in the control group, but in only 10 of 20 patients in the cricoid pressure group (P < 0.002). The laryngeal mask was positioned correctly in 16 patients in the control group, but in only two patients in the cricoid pressure group (P < 0.001). Tracheal intubation was accomplished in 19 patients in the control group, but in only three patients in the cricoid pressure group (P < 0.001). Release of cricoid pressure after placement of the laryngeal mask improved the view of the glottis, but tracheal intubation was still difficult because of laryngeal deviation. These results show that cricoid pressure impedes placement of the laryngeal mask and subsequent fiberscope-aided tracheal intubation.

Adult↗
PubMed1994

Teaching fibreoptic intubation. Effect of alfentanil on the haemodynamic response.

A technique for teaching fibreoptic orotracheal intubation in patients under general anaesthesia is described and evaluated. A standard general anaesthetic was administered to 60 patients presenting for elective gynaecological surgery. Patients were randomly assigned to receive either alfentanil 10 micrograms.kg-1 or a placebo, and to be intubated either by a consultant experienced in the use of the fibreoptic bronchoscope or by an inexperienced trainee under instruction. Heart rate, arterial pressure and oxygen saturation were monitored continuously. The time to achieve tracheal intubation in the trainee group was significantly prolonged (p < 0.001), but no patient developed arterial desaturation. The hypertensive response to fibreoptic intubation was suppressed in those patients who received alfentanil (p < 0.001). The increase in heart rate was not suppressed, but was attenuated when these patients were compared with those who had received the placebo (p < 0.001). Alfentanil 10 micrograms.kg-1 minimises the haemodynamic response when teaching fibreoptic orotracheal intubation under general anaesthesia.

Adolescent↗
PubMed1993

Endobronchial cuff pressures.

In 20 adult patients (18 male) who presented for thoracotomy, the trachea was intubated using Mallinckrodt disposable double-lumen tubes (18 large and two medium). The endobronchial cuff was inflated by a trained operating department assistant using an air-filled syringe. The volume of air and the initial endobronchial cuff pressure were measured. The minimum cuff pressure required to prevent respiratory gas leakage from the isolated lung was measured also and maintained using the Cardiff Cuff Controller. Mean initial cuff pressure was 69.3 (SEM 6.0) mm Hg, whereas the mean minimum cuff pressure was 29.5 (4.0) mm Hg (P < 0.0001). The results suggest that the method described of inflating the endobronchial cuff may lead to overinflation and subsequent excessive pressure on the endobronchial wall.

Bronchi↗
PubMed1993

The distance between the grille of the laryngeal mask airway and the vocal cords. Is conventional intubation through the laryngeal mask safe?

The distance between the grille of the laryngeal mask airway and the vocal cords was measured with a fibreoptic bronchoscope in 30 male and 30 female patients. The mean distance was 3.6 cm (SD 0.5 cm; range 2.5-4.7 cm) in males and 3.1 cm (SD 0.5 cm; range 2.0-4.2 cm) in females. These results suggest that the cuff of an uncut 6.0 mm tracheal tube would often lie between the vocal cords when the tube is fully inserted through a laryngeal mask airway. To avoid this complication, the tracheal tube must protrude more than 9.5 cm beyond the grille of the laryngeal mask airway. When either neck extension or flexion is required, the laryngeal mask airway should be removed as the margin of safety is small.

Adult↗
PubMed1993

Epidural catheters. Breaking and extraction forces.

The forces required to break and to remove catheters from epidural spaces were investigated. Provided the patient's back is fully flexed and a slow steady pull is applied to the epidural catheter, the extraction forces required at both thoracic and lumbar levels are well below the minimum force required to break the same catheters.

Analgesia, Epidural↗
PubMed1992

Effects of posture, phonation and observer on Mallampati classification.

We have studied the effects of phonation and posture on the Mallampati classification of view of the pharyngeal structures. Differences between observers were allowed for by the experimental design and log-linear modelling. Sixty-four patients were assessed on the ward, sitting upright, with and without phonation, by each of two observers. Another 64 patients were assessed without phonation, but both upright and supine, again by both observers. Phonation (the patient saying "Ah") produced a marked, systematic improvement of view; moving to the supine posture produced a small, systematic, non-significant worsening of the view. Differences between observers were non-systematic but substantial. About 25% of patients phonated spontaneously. It is recommended that anaesthetists make their own assessments of Mallampati classification, with the patient in either of the postures but always either with or without phonation, and thereby gradually "calibrate" their assessments against the degree of difficulty encountered in intubation.

Humans↗