Anaesthesia and Intensive Care

A double-blind comparison of some analgesic and gastrointestinal effects of nalbuphine and pethidine was performed in 28 women undergoing laparoscopic sterilisation. The opioid was given as an initial loading dose prior to the induction of general anaesthesia and further doses were given on demand in the postoperative period to achieve and maintain adequate pain relief. Gastric emptying in the immediate postoperative period was also assessed in each patient by measuring the rate of absorption of orally administered paracetamol. Nalbuphine was equally effective as pethidine as a postoperative analgesic, but may have been a less effective supplement to anaesthesia in the doses used in this study. Gastric emptying was profoundly depressed in all patients irrespective of which analgesic was used.

A new approach to the lateral cutaneous nerve of thigh is described. It depends on locating the depth of the canal through which the nerve passes immediately medial to the anterior superior iliac spine. Anatomical dissections show that it lies deep to the attachments of external oblique aponeurosis, the internal oblique muscle, and a deep fascial layer. Two district ‘pops’ or loss of resistance can be identified during insertion of a short-bevelled needle. Location of the canal by the technique described has been confirmed radiographically.

Volume and pH of gastric contents were measured after anaesthetic induction in 99 in-patients undergoing general and vascular surgery scheduled for either morning (50) or afternoon (49) lists. Significantly fewer patients in the morning group had pH values below 2.5. The mean pH value of the morning group was significantly higher than that of the afternoon group. There was a positive correlation between duration of fast and pH (the longer the more alkaline) for the groups combined. No significant relationship could be shown for any factor with volume.

Plasma levels of bupivacaine were measured following lumbar epidural administration of 3 mg/kg of 0.5% plain solution in sixteen children. The peak levels were generally between 1.0 and 2 μg/ml, the highest being 2.9 μg/ml. No manifestations of toxicity were observed. There was a significant positive correlation between peak plasma levels and increasing age.

Eight mongrel puppies were studied at intervals of a few weeks. Lignocaine 4mg/kg was infused over 60 seconds. Frequent samples were taken over 30 minutes for plasma lignocaine assay. Initially the concentrations were significantly higher in the oldest group (178–191 days) but after 10 minutes the youngest group (3–16 days) had significantly higher levels than the other groups.

Pharmacokinetic data derived included the rate constants k₂₁, k₁₂ (drug movement between two compartments), k₁₀ (elimination from the central compartment), and the volume of distribution (V_β). The elimination rate constant k₁₀ was significantly lower in Group 1 (3–16 days) than all other groups and Group 2 (37–57 days) was lower than Group 4 (178–191 days). The calculated β half-life was significantly longer in the youngest group than the others. There was no significant difference in the volume of distribution between these age groups — up to 6 months.

A mathematical model correlating the spread of analgesia to the dose of local anaesthetic and to age or body weight was found analysing the data of 763 caudal blocks in children from age one day to twelve years. Two graphs have been plotted: (1) spread of analgesia, dose, age and (2) spread of analgesia, dose, weight.

Both age and weight can be used as predictors to determine the desired level of analgesia, but weight is more useful in very young patients while age is a better guide in older children.

Single doses (0.3 MAC) of thiopentone or fentanyl did not affect the serum liver enzyme concentrations (SGPT, SGOT) in the rat. 0.3 MAC of fentanyl but not of thiopentone given for six consecutive days led to significantly higher SGPT levels (P<0.01) versus the control group. Rats that received repeated injections of thiopentone or fentanyl had significantly higher SGPT levels versus the groups that received one injection (P<0.05 and P<0.01 respectively). Rats that had repeated injections of thiopentone showed a significantly higher SGOT versus the groups that had one injection of thiopentone, fentanyl or normal saline (P<0.01, P<0.05 and P<0.05 respectively).

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 ½ 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.

The observed effect of midazolam on anxiety is equivocal in part because previous studies have not ruled out pre-treatment differences in anxiety scores between patients who received midazolam and those who did not (controls). This study re-examines the anxiolytic effect of premedication with intramuscular midazolam using a sample size calculated to be of sufficient size to rule out population differences as a variable affecting treatment results. In the midazolam group (n = 49) anxiety scores were determined prior to administration of midazolam 0.07 mg/kg intramuscularly, and again 60 minutes later. In the control group (n = 47) anxiety scores were determined prior to intramuscular injection of a similar volume of matching placebo (midazolam vehicle), and again 60 minutes later. No differences in anxiety scores between groups either before treatments or 60 minutes after treatments were observed. Within both groups, anxiety scores at 60 minutes were no different from pre-treatment scores. In this study midazolam did not produce a statistically significant decrease in pre-operative anxiety scores at 60 minutes following intramuscular administration.

Hypertension after cardiac surgery is common and requires accurate control by carefully regulated infusions of drugs such as sodium nitroprusside. A microprocessor-based controller has been designed to close the loop between the blood pressure response and the infusion rate of a hypotensive drug. This system has been refined by computer simulation of the blood pressure response to sodium nitroprusside and by experience gained in using the controller in eleven patients in the early recovery period after cardiac surgery. The controller was able automatically to maintain blood pressure within 10% of a specified value. Provision of sophisticated safety features in automatic drug infusion controllers is essential for patient protection.

A series of modifications designed to increase the suitability of the quadrupole mass spectrometer for multipatient gas monitoring in the operating suite are presented and evaluated. The adaptations include a pressure-stabilised long capillary inlet system and computer control of the quadrupole filter together with tuning, calibration and subsequent multitheatre analysis and display of clinical information. A pilot study of three months clinical monitoring provided documentation of contributions towards the safety and effectiveness of anaesthesia. These included indication of equipment malfunction, and fluctuations in gas exchange associated with inappropriate ventilation, haemodynamic instability and variations in body temperature. Limited accuracy for carbon dioxide and a low signal-to-noise ratio together with rapid ageing of electron multipliers were identified as problems still only partially solved.

Thirteen commercially available ventilator monitoring alarms supplied by the distributors were evaluated. It was decided that devices with no power failure precautions or unprotected variable controls could not be recommended for general use. By these criteria only two devices could be recommended for general use as ventilator alarms and a further three as disconnect alarms; in each instance these recommendations are subject to certain reservations and suggested modifications. A ventilator alarm should be regularly serviced and checked before use and should be not used by anyone unfamiliar with the applications or limitations of that particular device.

This paper was commissioned to cover the beginning of anaesthesia: the transition from surgical operations with pain to those without. It reviews some previous pre-anaesthetic histories (Part I): it focuses upon attitudes to pain; and it seeks evidence from the one hundred years before the discovery of anaesthesia. Finally (Part II) it outlines the introduction of nitrous oxide and of ether anaesthesia.