Thoracic electrical bioimpedance: a non-invasive measure of cardiac output for porcine research.

A comparison of two techniques for measuring cardiac output, thermodilution (TD) and thoracic electrical bioimpedance (TEB), was undertaken in a porcine model. Eight anaesthetized large white pigs were studied. A total of 436 paired measurements were performed over a range of cardiac outputs from 1.7 to 15.1 l/min as measured by thermodilution. The Pearson product moment correlation coefficient was r = 0.963 with P < 0.001. Analysis by Bland and Altman statistics revealed a mean difference (bias) of -0.02 l/min and the limits of agreement were +/- 1.6 l/min, similar to figures found in human comparative studies. These results confirm that thoracic electrical bioimpedance is a valid method of measuring cardiac output in pigs. It has significant advantages compared to thermodilution, in particular it is cheap, simple to use, non-invasive and provides continuous data.

Validation of thoracic electrical bioimpedance as a porcine research tool.

We have compared the accuracy of two methods of measuring cardiac output, thoracic electrical bioimpedance (TEB) and thermodilution (TD), in pigs. We studied four anaesthetized pigs, producing 145 paired cardiac output values over a range of TD cardiac outputs of 2.6-12.6 litre min-1. TEB cardiac output was less than that measured by TD, by a constant factor throughout the observed range of values, because of differences in porcine thoracic shape. The Pearson product moment correlation coefficient suggested a good correlation (r = 0.984, P < 0.001). More importantly, analysis by the Bland and Altman statistical method suggested a high level of agreement, with 95% confidence intervals of +/- 1.0 litre min-1. These results suggest that TEB can be used as a satisfactory method to measure cardiac output in porcine models.

Prediction of postoperative nausea and vomiting using a logistic regression model.

In a previous study, logistic regression analysis was used to determine the association of independent fixed patient factors with the incidence of postoperative nausea and vomiting (PONV). Female sex, previous history of PONV, use of postoperative opioids, previous history of motion sickness and an interaction between male sex and previous history of PONV were combined in an equation from which risk of PONV could be estimated. The present study was designed to test this equation in a group of patients with wide selection criteria. Data on 400 patients were collected in relation to pre-, per- and postoperative factors which may influence the incidence of PONV. The equation was used to predict PONV, and actual outcome was compared with that predicted. The overall incidence of PONV was 36%. The equation predicted an overall probability of PONV of 27.4%. If the model was used to define individual patients as predicted to have or not to have PONV, it was correct only 71% of the time. However, there was good agreement between the actual incidences of PONV and those predicted among the 16 risk groups created by the model.

The use of the Hayek Oscillator during microlaryngeal surgery.

An extremely mounted cuirass ventilator, the Hayek Oscillator, was used on 41 patients undergoing surgery to the larynx without the use of tracheal tube. Gas exchange and cardiovascular parameters remained satisfactory during the use of this technique, which offers a significant advance over existing tubeless methods of anaesthesia.

Awake oral fibreoptic intubation for caesarean section.

A 35-week pregnant patient with ankylosing spondylitis and a known previous failed intubation required an elective caesarean section for intrauterine growth retardation. Regional anaesthesia was prevented by extensive spinal fusion. The anaesthetic management involved an awake oral fibreoptic intubation followed by induction and maintenance of general anaesthesia allowing delivery of a live infant without harm to the mother.

Intubating conditions following 1R CIS, 1'R CIS atracurium (51W89). A comparison with atracurium.

51W89 besylate, a new intermediate acting non-depolarising muscle relaxant, consisting of a single stereo-isomer of the commercial preparation of atracurium has been assessed in respect of intubating conditions during nitrous oxide-propofol-isoflurane anaesthesia. Intubating conditions at 2 min were acceptable in 67% of patients following a dose of 0.1 mg.kg-1 and in 90% of patients following a dose of 0.15 mg.kg-1. Intubating conditions at 1.5 min were acceptable in 76% of patients following a dose of 0.2 mg.kg-1. In comparison, intubating conditions at 2 min were acceptable in 95% of patients following 0.5 mg.kg-1 of atracurium. The intubating conditions at 2 min following a dose of 0.1 mg.kg-1 51W89 besylate were significantly worse than the other three groups (p < 0.05); however, there was no significant differences between the scores in the other three groups. There was no clinical evidence of histamine release in the groups receiving 51W89 besylate compared to two out of the 19 patients who had cutaneous flushing following the administration of atracurium. Our results suggest that 51W89 besylate provides acceptable intubating conditions at 2 min following a dose of 0.15 mg.kg-1 and may prove to be an acceptable alternative to atracurium if studies in progress confirm its greater cardiovascular stability and reduced propensity to release histamine than its parent compound.

Use of the Hayek oscillator in a case of failed fibreoptic intubation.

We describe the management of a patient with predicted difficult tracheal intubation after failed awake fibreoptic intubation. Anaesthesia was induced with propofol and ventilation controlled by means of the Hayek oscillator, a high frequency cuirass ventilator, without tracheal intubation. The patient underwent uneventful laser debulking of his massive pharyngeal tumour to establish a clear airway.

Reducing the incidence of postoperative nausea and vomiting.

In the first part of this article (Vol 53(7) 1995, p.327), the physiology of vomiting and the factors known to influence postoperative nausea and vomiting (PONV) were summarised. In this second part the therapeutic options available to reduce the incidence of PONV are reviewed.

Physiology of postoperative nausea and vomiting.

Postoperative nausea and vomiting remains a common cause of morbidity. This is a complex reflex involving multiple inputs via diverse receptor pathways which are integrated in the brainstem emetic centre. Factors related to the patient, the surgery, the anaesthetic and the recovery period are known to influence an individual's risk of vomiting.