Convection warmers--not just hot air.

We sought to determine whether the forced air convection warmers (nine Bair Huggers, Augustine Medical, and one Warm Touch, Mallinkrodt Medical) used in our operating theatres could be a source of microbial pathogens. Agar plates were placed directly in the air stream of the warmers. Four of these grew potentially pathogenic organisms. When the warmers were set to blow through perforated blankets, no growth occurred. Three of the warmers were swabbed and sites of colonisation were found in their hoses. After fixing a microbial filter to the end of the hose, organisms were no longer detectable. We conclude that these warming devices are a potential source of nosocomial infection. They should only be used in conjunction with perforated blankets, should have their microbial filters changed regularly and their hoses sterilised. The inclusion of a microbial filter into the nozzle of the hose could be incorporated into the design of the warmer.

Total intravenous anesthesia using propofol and alfentanil for coronary artery bypass surgery.

Total intravenous anesthesia (TIVA) using alfentanil and propofol was used in 10 patients undergoing coronary artery bypass grafting. In an attempt to diminish unwanted side effects, lower doses were chosen than if either drug had been used alone. Anesthesia was induced with alfentanil, 75 micrograms/kg, followed by a sleep dose of propofol (mean dose 0.5 mg/kg). Maintenance in the precardiopulmonary bypass (CPB) period was achieved by infusions of propofol (6 mg/kg/h) and alfentanil (100 micrograms/kg/h). These were decreased by two thirds on commencement of CPB, and increased to half the initial rate on rewarming to 32 degrees C. Additional boluses of alfentanil were used to control breakthrough hypertension. The mean arterial pressure (MAP) and left ventricular stroke work index (LVSWI) fell significantly on induction. MAP but not LVSWI returned to baseline levels at skin incision. The cardiac index (CI) was maintained. A degree of myocardial depression was suggested by a fall in LVSWI despite maintaining preload, and by the failure of CI to increase in the presence of a reduced SVR. Anesthesia was satisfactory in all but one patient who developed breakthrough hypertension on sternotomy with transient ST segment depression, and awareness after CPB despite a plasma alfentanil concentration of 450 ng/mL. Mean time to wakening was 55 minutes. The study indicated that TIVA using propofol and alfentanil in the dosages described provides satisfactory basal anesthesia for coronary artery bypass surgery in patients with good left ventricular function, but requires additional pharmacologic manipulation, particularly with boluses of alfentanil, to control breakthrough hypertension.

The effect of dopamine on graft function in patients undergoing renal transplantation.

We studied the effect of a low-dose dopamine infusion on graft function in 60 patients undergoing transplantation with cadaveric kidneys in a prospective controlled trial. Recipients were allocated to either a control or a dopamine group, the latter receiving a 3 micrograms.kg-1 x min-1 infusion of dopamine starting intraoperatively. Evaluation of dopamine's effect was undertaken in two stages, namely, (i) initial graft function 1 wk after transplantation and (ii) graft survival at 3 mo. Initial graft function was determined by the ability of the transplanted kidney to reduce serum creatinine, and the development of acute tubular necrosis as confirmed by renal biopsy. Of the dopamine group 33.3% developed acute tubular necrosis compared to 23.3% of the control group. The second-stage evaluation was based on plasma creatinine levels and the requirement for dialysis within 3 mo of transplantation. 92.8% of the dopamine group and 76.9% of the control group had good graft function. No statistically significant difference between the two groups was found. The perioperative infusion of dopamine at 3 micrograms.kg-1 x min-1 was not shown to have any beneficial effect on the transplanted kidney in patients who do not have serious vascular disease, or who do not receive kidneys subjected to prolonged hypotension or prolonged preservation or anastomotic times.

Postoperative intensive care and the South African Society of Anaesthetists' patient category.

A group of 412 postoperative patients admitted to an intensive care unit of an academic hospital were evaluated in terms of their need for intensive care. The Acute Physiology and Chronic Health Evaluation score, the Therapeutic Intervention Scoring System (TISS) and the South African Society of Anaesthetists' (SASA) patient category were utilised to determine the level of care required by each patient. A further objective of the study was to determine if the SASA patient category, on its own, adequately described the need for intensive care in postoperative patients. Evaluation of the data indicated that, in terms of TISS, 66% of the patients required intensive care. These patients were distributed throughout all three SASA categories. Of the 137 patients who, according to TISS, did not require intensive care, 122 were SASA category 3 patients. However, of the total number of category 3 patients, just less than half required intensive care. In order to identify better those patients within a specific SASA category who require intensive care we suggest further subdivision of each category into groups A, B and C, according to the number of TISS points scored at 24 hours postoperation. In this way a retrospective audit using SASA categories would clearly identify those postoperative patients who required intensive care.

Effect of two different syringes on syringe driver function.

A laboratory investigation into the effect of two different syringes on the performance of a syringe driver was undertaken in order to assess accuracy of delivery, occlusion-alarm delay time and the effect of incorrectly coding the device for the syringe in use. Results indicated that accuracy of delivery was of the order of -1%/h for both syringe types at an infusion rate of 5 ml/h. Clinically and statistically significant differences in the occlusion-to-alarm time were found between syringes and between infusion rates. At 99.9 ml/h lag time was about 30 seconds for both syringes, whereas at 5 ml/h this was 667 seconds for one syringe and 903 seconds for the other. Incorrect coding of the driver for the syringe in use, resulted in a significant change in the accuracy of delivery at an infusion rate of 5 ml/h. Similarly, incorrect coding resulted in changes in the occlusion-alarm time. These results carry significant pharmacological implications for the clinical situation.

Rapid inhalational induction of anaesthesia with isoflurane or halothane in humidified oxygen.

This study was designed to determine the relative speeds of induction and complication rates using either halothane or isoflurane for rapid inhalational induction of anaesthesia. Forty ASA physical status 1 and 2, unpremedicated patients presenting for day-care dental surgery received a rapid inhalational induction (RII) with either halothane 3.5% or isoflurane 5% in humidified oxygen. The carrier gas was humidified in order to limit airway irritation caused by the pungency of the volatile agents. Isoflurane produced a faster induction than halothane-121(50) (SD) sec vs 176(36) sec (P less than 0.01). Complication rates during induction (coughing, secretions, excessive movement and abandoned inductions) were similar for the two groups. The majority of patients in both the isoflurane group (17/20) and the halothane group (14/20) found the technique of RII to be acceptable. The incidences of headache, nausea and vomiting were low and not significantly different for the two groups. Isoflurane 5% in humidified oxygen is as acceptable for RII as halothane 3.5% and has a similar complication rate. Isoflurane may be used for RII in cases where it is deemed necessary to avoid halothane, or when a more rapid inhalational induction is required than is possible with halothane. The technique of RII with either agent in unpremedicated patients is well suited to day-care anesthesia.

Rapid inhalation induction with isoflurane in humidified carrier gas.

This study was designed to determine if rapid inhalation induction of anaesthesia (RII) with 5% isoflurane (4.5 MAC equivalent) in oxygen offers any advantage in terms of complication rate, speed of induction and patient acceptance in comparison with a previously described technique of RII using 2% isoflurane in nitrous oxide and oxygen. Forty ASA I and II unpremedicated patients were allocated randomly to receive RII with either 5% isoflurane in oxygen or 2% isoflurane and nitrous oxide in oxygen. The carrier gas was humidified in order to limit airway irritation associated with the use of isoflurane for inhalation induction. In this study the observed difference in mean induction time (7 s) between the two groups was neither clinically nor statistically significant. The groups were similar also with regard to complication rate and patient acceptance.

Self-tuning, microprocessor-based closed-loop control of atracurium-induced neuromuscular blockade.

A self-tuning, closed-loop computerized system was used to maintain atracurium-induced neuromuscular blockade in patients undergoing routine lower abdominal gynaecological surgery. The controller is based on a unique algorithm which utilizes a bi-exponential model wherein two of the variables are estimated on-line. This enables the system to optimize the sizes of subsequent bolus doses according to patient sensitivity. In this study an initial bolus of 0.3 mg kg-1 was given in a trade-off aimed at achieving earlier intubating conditions rather than taking control of relaxation ab initio and obtaining the pre-programmed setpoint of 15% single twitch response (STR) without overshoot. This was successful in all of the 11 patients studied, the mean time from injecting the bolus to intubation being 2.47 (SD 0.95) min and the drug maintenance requirement being 0.34 (0.07) mg kg-1 h-1. This provided a mean value of 10.26% STR with minimal oscillation about the setpoint (average standard deviation = 4.31 (2.53)) for up to 147 min.

Endotoxaemia in exhausted runners after a long-distance race.

The extent to which plasma endotoxin concentrations increased was measured in 89 randomly selected exhausted runners who required admission to the medical tent for treatment in the 1986 Comrades Marathon (89,4 km). Eighty-one per cent had concentrations above the upper limit of 0,1 ng/ml ('endotoxaemic'), including 2% above 1 ng/ml (the reported lethal level in humans), and only 19% had normal levels. There was a negative correlation between plasma endotoxin and plasma anti-endotoxin IgG concentration (P less than 0,025). Those runners completing the race in less than 8 hours had a significantly lower average endotoxin value than those taking longer than 8 hours (P less than 0,025). Also 80,6% of runners (58/72) with high plasma endotoxin values reported nausea, vomiting and/or diarrhoea, compared with 17,7% (3/17; P less than 0,001) with low endotoxin values. Elevated plasma endotoxin concentrations of 32 randomly selected endotoxaemic runners had returned to normal 1-3 weeks later, and most of them (25/32) had increased anti-endotoxin IgG concentrations (P less than 0,02). Fifty-nine runners randomly selected in a short run (21,1 km) 3 weeks after the 89,4 km run completed the race without problems and none showed any increase in endotoxin levels. Further studies in this field are warranted, especially the measurement of endotoxin and anti-endotoxin values from commencement of training to full fitness. It is possible that these measurements may prove useful as predictors of an athlete's or combat soldier's performance.

The effects of calcium channel blocking drugs on halothane initiation of malignant hyperthermia in MHS swine and on the established syndrome.

We have investigated in malignant hyperthermia susceptible swine in vivo the effects on halothane initiation of the MH syndrome and on the established syndrome of five calcium channel blocking drugs--nifedipine, nisoldipine, diltiazem, verapamil and flunarazine. Nifedipine alone caused attenuation of halothane-initiated malignant hyperthermia to the extent of blocking onset of the syndrome in 29% of animals for the 60 minute period of exposure. In the face of the established malignant hyperthermia syndrome, all the drugs tested were therapeutically completely ineffective.

Halothane decreases albumin and transferrin synthesis: studies in the isolated, perfused rat liver and in the intact rat.

Isolated perfused rat livers exposed to 1.5% halothane (equivalent to 1.35 MAC) in O2/CO2 or to O2/CO2 alone produced urea, as well as albumin and transferrin (both measured by immunodiffusion), at constant rates during a 4.25-h perfusion. Urea production did not differ in the two treatment groups, but halothane depressed albumin and transferrin synthesis 43% and 45%, respectively. Intact rats were also exposed to halothane, after which albumin synthesis was measured by the (14C)carbonate technique. The minimum halothane concentration required to insure sufficient relaxation for ventilation was selected and ranged from 1.0 to 1.5%. Measurements were made in control rats not exposed to halothane (group I) and in halothane exposed rats immediately after 1 h of anesthesia (group II), 24 h after the start of 1 h of anesthesia (group III), and immediately after 1/2 h of anesthesia preceded by a 1-h exposure 24 h earlier (group IV). Single exposures to halothane (groups II and III) resulted in a decrease in albumin synthesis immediately or 24 h later that did not differ significantly from controls (group I). However, halothane given twice to rats at 24-h intervals (group IV) reduced their mean albumin synthesis rate to half that of controls. The early onset and constancy of halothane depression of export protein synthesis by isolated, perfused livers may reflect a response to halothane itself, rather than an effect resulting from the accumulation of halothane metabolites. Similarly, reduction of albumin synthesis in intact rats immediately after a second halothane exposure may indicate a response to halothane, rather than to halothane metabolites.

Acute calcium homeostasis in MHS swine.

To elucidate a pathogenesis for the reduction in bone calcium content observed in MHS individuals, we studied the acute calcium homeostasis of MHS swine. This was achieved by the serial measurement, with a calcium selective electrode, of calcium transients in Landrace MHS (five) and control Landrace/large white cross MH negative (five) swine following IV bolus injection of calcium gluconate 0.1 mmol X kg-1--a dose which induced an acute 45 per cent increase in plasma ionised calcium. Experimental animals were anaesthetised with ketamine 10 mg X kg-1 IM, thiopentone (intermittent divided doses) 15-25 mg X kg-1 (total) IV and N2O/O2 (FIO2 0.3) by IPPV to maintain a normal blood gas, acid/base state. The plasma ionised calcium decay curve observed in MHS swine did not differ from that of control normal swine. Further it was noted that the induced acute rise in plasma ionised calcium failed to trigger the MH syndrome in any MHS swine. It is concluded that the mechanisms of acute calcium homeostasis in MHS swine are normal. An explanation for the reduction in bone calcium content observed in MHS individuals must be sought, therefore, through study of the slow long-term component of the calcium regulatory process. In addition, the conventional strictures placed on the use, in MHS patients, of calcium gluconate are called in question.

The screening of atracurium in MHS swine.

The potential role of atracurium besylate as a trigger or attenuator of the malignant hyperthermia syndrome was tested in six MHS Landrace swine. Animals were tested for susceptibility and then exposed to atracurium given as an i.v. bolus both alone and concomitantly with 2% halothane. In no instance could the syndrome be triggered by atracurium nor did it convincingly attenuate the syndrome when triggered by halothane.

Self-administered intravenous analgesia during labour. A comparison between pentazocine and pethidine.

Pentazocine or pethidine was administered to healthy parturients up to the time of delivery using a self-demand (self-administration on demand) intravenous apparatus, the Cardiff Palliator. Good analgesia was obtained with both drugs. The patients receiving pethidine exhibited side-effects (nausea, vomiting and drowsiness), whereas there were no side-effects among those receiving pentazocine. Apgar and neurobehavioural scores of the babies of mothers in both groups were the same and did not differ from those of a third group of babies, the mothers of whom had received 4-hourly intramuscular pethidine on demand according to the usual hospital routine. The self-administration technique proved a safe and effective means of providing analgesia during labour and delivery, with pentazocine having a decided advantage over pethidine because of its lack of side-effects.

Calcium supplementation during cardiopulmonary bypass in paediatric surgery.

This paper reports on the monitoring of plasma ionized calcium (Ca++) levels in children undergoing cardiopulmonary bypass (CPB) for open-heart surgery. The pump was primed with blood treated with either heparin or citrate-phosphate-dextrose (CPD). In certain cases calcium supplementation was used. In all cases a sudden drop in Ca++ levels took place at the start of CPB, followed by a slow recovery. In the patients who received heparinized blood the drop was slight (14%) and recovery fast (10 minutes), but in those who received CPD the drop was excessive (58%) and recovery was still incomplete after 1 hour despite supplementation with 0,5 g calcium gluconate per unit of whole blood. Different supplementation regimens were tried and the optimum was achieved by using 1 g calcium gluconate per unit of whole blood. This limited the drop in the Ca++ level to 42%, and recovery to prebypass levels took place within 45 minutes.

Total intravenous anaesthesia using low-dose ketamine infusion for caesarean section. A comparison with a standard inhalation anaesthetic technique.

Anaesthesia was induced in 65 parturients undergoing elective caesarean section with thiopentone 3,5 mg/kg and suxamethonium 1,5 mg/kg intravenously. For anaesthetic maintenance patients were randomly divided into two groups. Patients in group A were ventilated with 50% nitrous oxide in oxygen, supplemented with 0,6-0,8% enflurane and 50 mg pethidine given intravenously after delivery. Group B patients were ventilated with 50% oxygen in nitrogen and received a continuous intravenous infusion of ketamine (70 micrograms/kg/min), with 5 mg diazepam intravenously following delivery. All patients received intravenous alcuronium 0,2 mg/kg. Inspired oxygen concentration (0,5) and end-tidal carbon dioxide tensions (4,0-5,0 kPa), were standardized. Despite a high incidence of predelivery hypotension in group A but not in group B, the fetal acid-base status, materno-placento-fetal exchange and immediate clinical state of the neonates were comparable. Neonatal neurobehavioural assessment scores assessed 2-4 hours after birth favoured the inhalation technique, but this difference disappeared at 24 hours. A higher incidence of factual recall in group B (14,3% v. 7,4%), frequently painful (10,7% v. 0%), the reporting of unpleasant dreams and a lack of significant postoperative analgesia makes the ketamine infusion technique unsatisfactory.

Lignocaine kinetics during cardiopulmonary bypass. Optimum dosage and the effects of haemodilution.

Lignocaine was administered to patients undergoing cardiopulmonary bypass at 28-29 degrees C in bolus doses of 1.5, 2.5 and 3.5 mg kg-1. Plasma concentrations greater than 1.5 micrograms ml-1 were found briefly and inconsistently in patients receiving the usually recommended dose (1.5 mg kg-1), but reliably for 14 min in those receiving 2.5 mg kg-1. The 3.5 mg kg-1 dose produced statistically and clinically significant decreases in mean arterial pressure. Examination of calculated kinetic parameters showed a two-fold decrease in T1/2 alpha, two-fold increases in T1/2 beta and Vss and unaltered ClP and VP when compared with those of unanaesthetized, normothermic patients. The alteration in pharmacokinetics may be attributed largely to decreased binding to albumin following haemodilution.