The effects of bupivacaine on the umbilical circulation and placental gas exchange in the fetal lamb.

Seven chronically catheterized fetal sheep at 125-140 days gestation were studied in 12 experiments to determine the direct effects of the local anesthetic bupivacaine (infused intravenously to the fetus) on the umbilical circulation and placental gas exchange. Electrocortical activity, umbilical blood flow, heart rate, and umbilical arterial and venous pressures were continuously monitored in experiments comprising a baseline period, a drug infusion period and a recovery period, each of 2 hr duration. Samples of umbilical arterial and venous blood were taken for blood gas analysis, and for bupivacaine assay using high pressure liquid chromatography technique. Fetal plasma bupivacaine levels were 1.3 +/- 0.3 microgram/ml (mean +/- SEM) between 60-120 min of infusion. Heart rate and umbilical blood flow decreased significantly to 89 and 94% of control, respectively, (P less than 0.05) during the infusion and returned to control levels by 2 hr afterwards. Mean umbilical arterial and venous pressures were not significantly altered, and no significant rise in umbilical vascular resistance occurred. No changes occurred in umbilical arterial or venous pH, PO2, or PCO2. In summary, bupivacaine reversibly depressed fetal heart rate and umbilical blood flow without detrimental changes in fetal blood gas or acid-base status.

Problems with automating anaesthetic records.

A truly automated recording system is one which measures the parameters selected and requires nothing more than attaching the monitors to the patient. It should be capable of being easily and rapidly started when appropriate. The user should then be able to enter quantitative and qualitative information about drug and fluid therapy in a manner which is less distracting than the present long-hand method. A system is described which has gone a considerable way towards achieving good automated physiological monitoring. The system has not resolved the problems of data entry which must be overcome before such equipment is made available for general use. The problems of automation which we encountered are presented and some possible solutions considered.

An investigation of the effectiveness of bupivacaine applied to the abdominal wall and fallopian tubes in reducing pain after laparoscopic tubal ligation.

Sixty women having laparoscopic sterilisation performed under general anaesthesia were randomly allocated to one of two groups. Intraoperatively, one group had bupivacaine applied topically to the fallopian tubes and injected into the skin wounds, while the other group received no local anaesthetic. A double-blind investigation utilising a visual analogue scale failed to demonstrate a statistically significant difference in postoperative pain between the two groups. In both groups there was a significant reduction in mean pain scores between 1/2 and 7 hours, but there was no further reduction between 7 hours and 17 hours. At 7 hours, only 10% of patients scored their pain as 3 or greater (out of a possible 10). It is concluded that the use of bupivacaine as described is not a useful adjuvant to general anaesthesia and that the low incidence of even moderate pain at 7 hours confirms the view that these patients are suitable for management in the day-stay unit.

Implications for vigilance of a method for evaluating patterns of change in heart rate during anaesthesia.

Instantaneous heart rate was recorded in five patients and analysed for change in rate using the criterion of percentage variation either side of the starting rate with resetting throughout the anaesthetic each time the permitted variation was exceeded. The number of occasions on which change occurred was counted, the patterns of change were analysed and the effect of two sampling methods (six-second sample and six-second average) on these patterns was compared. A large number of patients (131) was investigated using the six-second sampling method and the number of changes and patterns of change were evaluated. It is suggested that the six-second sampling technique, combined with the 10 or 15% variation, may be useful for the evaluation of vigilance, and has implications for the design of monitoring apparatus in the future.

One year's evaluation of a system of on-line computerisation of anaesthetic records using a computer bureau.

A system for the on-line computerisation of anaesthetic records using a computer bureau is described. The requirements of the system are a keyboard and video display unit appropriately linked to the bureau's computer. The system was cheap and easy to install. It required no programming expertise from department members. Disadvantages included the need to change between two screens for data entry, a delay of over 8 months before satisfactory reports materialised for individuals or the department, congestion at peak times for data entry, excessive time spent on data entry, reluctance of the bureau to alter the format of the screens once they had been generated. The cost of the system is felt to be justified by the information provided for both accreditation requirements and for department management.

Factors affecting an anaesthetist's work: some findings on vigilance and performance.

This paper reviews factors which may influence the vigilance tasks of an anaesthetist during an anaesthetic. Vigilance tasks are found to be unlike any other automatic, repetitive or monotonous tasks. While many factors affect vigilance and may result in performance decrements during psychological testing, little of this work has been done on anaesthetists. We suggest, however, that there are many parallels between findings related to vigilance in general and the type of work done by anaesthetists. Implications of major factors are discussed, and recommendations for further study are proposed.

Carbon dioxide output in anaesthetised children.

Carbon dioxide output was measured in 278 children aged between 1 day and 16 years, who were anaesthetised with thiopentone and nitrous oxide and ventilated mechanically following the injection of a non-depolarising neuro-muscular blocking agent. It is suggested that the results obtained form a clinically useful guide to the carbon dioxide output of anaesthetised children.

Morphological effects of chronic tracheal ligation and drainage in the fetal lamb lung.

The relationship between lung liquid flow and fetal lung development has been studied at the cellular level using ultrastructural techniques. Continuous in utero tracheal ligation and drainage (over a period of 21-28 days) both result in malformations of the developing fetal lamb lung. Ligated lungs are larger, and drained lungs are smaller, than normal lungs at a similar gestational age. These changes are not merely due to altered lung liquid volume, but actual tissue growth thas been affected. Future alveolar wall thinning is enhanced in ligated lungs and inhibited in drained lungs, whilst the presence of differentiated alveolar type II cells (probably related to surfactant production) is decreased in ligated lungs and markedly enhanced in drained lungs. These results indicate the importance of fetal lung liquid in the regulation of pulmonary development in the fetus.

Tutor-student interaction in the operating theatre.

This paper examines the view that productive teaching in the operating theatre requires a recognition of the unique set of factors which may influence the process of communication. For tutor-student interaction to occur in a productive manner, the tutor's behaviour will need to be modified to suit the demands of the other tasks in which both tutor and student are involved. The particular value of recognizing the role of nonverbal behaviours during interaction is discussed, with the use of specific examples related to the positioning of the tutor and student, and their use of facial expression, the eyes and voice.

Teaching and learning in the operating theatre.

The anaesthetist's role during an anaesthetic is one of vigilance. Any interaction between tutor and student in this situation must be structured around the vigilance task. Teaching that recognizes this role may be educationally fruitful and may even improve vigilance. Teaching which disregards this function is less likely to result in learning and may interfere with patient care. Some of the types of teaching that are likely to be appropriate or inappropriate to different phases of an anaesthetic are indicated.

Diaphragmatic activity and lung liquid flow in the unanesthetized fetal sheep.

For some time it has been suggested that breathing movements are made "in utero" and recently measurements of tracheal pressure and lung liquid flow in chronic fetal preparations have led to the hypothesis that rapid changes in these parameters are the result of respiratory muscle activity. To test this hypothesis diaphragmatic electrical activity was measured in seven chronic unanesthetized fetal sheep preparations and correlated with lung liquid flow and tracheal pressure. Diaphragmatic activity led to a fall of tracheal pressure and movement of a small volume of lung liquid into the lung. After the activity ceased, tracheal pressure returned to normal and flow diminished to zero or was directed out of the lung. The breathing pattern was unassociated with the net movement of lung liquid out of the lung. A histogram of the interval between breaths revealed a changing pattern of activity throughout gestation. The pattern was significantly altered after premature delivery of one animal with a respiratory problem. These observations provide evidence that respiratory muscles are active "in utero" and that the pattern of activity changes throughout gestation.

Lung liquid production and composition in the "in utero" foetal lamb.

Experiments were carried out on foetal lambs in utero from 103 to 133 days' gestation, to measure the daily flow and solute composition of liquid from the foetal lung. The mean daily flow from foetuses with a tracheal fistula was 231 ml/day (9.6 ml/h), while the mean hourly flow in foetuses with a tracheal loop was 5.1 ml/h. The pattern of flow of lung liquid was intermittent and irregular, with short periods of rapid flow interspersed with longer periods of slow and no flow. The Na+, Ca2+, Mg2+, Cl- and urea concentrations showed no significant change with increasing gestational age, but the K+ concentration showed a significant rise. It is concluded that the lung of the foetal lamb behaves as an exocrine gland, secreting a substantial volume of liquid of a relatively constant composition.