Preoperative beta-blockade for patients undergoing craniotomy: a comparison between propranolol and atenolol.

This study was undertaken to establish if beta-blocking drugs given orally before surgery could reduce the pressor responses to laryngeal instrumentation and tracheal intubation in neurosurgical patients. Forty-two neurosurgical patients undergoing craniotomy were randomized into three groups. Groups 1 and 2 received atenolol (100 mg) and propranolol (80 mg) respectively. Group 3 were controls and given no beta-blockers. A standard anaesthetic technique was used and blood pressure and heart rate were measured continuously from induction of anaesthesia until five minutes after tracheal intubation. There were increases in both heart rate and systolic blood pressure in all three groups but the rises in the treated groups were significantly less than in the control group (P less than 0.01). There were no significant differences in the haemodynamic responses between the propranolol and atenolol treated patients.

Monophasic action potential recordings in response to graded hyperkalemia in dogs.

Recent interest in sudden cardiac death during exercise in normal healthy people has highlighted the possible role of swings of extracellular potassium in arrhythmogenesis in conditions other than ischemia. Regional differences in action potential duration and conduction may be important. We have recorded monophasic action potentials (MAPs) from the endocardium and epicardium in nine open-chest dogs during graded intravenous infusion of potassium up to a plasma level of 9 mM. The animals were anesthetized with alpha-chloralose and urethan. Continuous, online arterial potassium monitoring was employed. MAP duration showed a biphasic response with initial shortening up to 7 mM, which tended to be more obvious on the epicardium. Regional activation time was measured as the difference between the onset of depolarization of the endocardial and epicardial MAP. Regional activation time also showed a biphasic response with initial shortening and subsequent delay. The QRS width of the scalar lead II electrocardiogram also showed biphasic changes, and the T wave amplitude progressively decreased. Our results suggest that regional differences in repolarization time may develop in the nonischemic myocardium in response to increased extracellular potassium levels mainly as a result of local changes in regional activation time rather than as a result of a direct effect on action potential duration.

The effects of beta blockade on dopamine and dobutamine induced hypokalaemia in dogs.

The effect of beta 1 and beta 2 blockade on dopamine and dobutamine induced hypokalaemia was investigated in dogs. Arterial plasma potassium was continuously monitored using a potassium-sensitive electrode sited in the abdominal aorta. Dopamine and dobutamine were infused at 15 micrograms kg-1 min-1 into animals pre-treated with atenolol (0.5 mg kg-1) or ICI 118551 (0.5 mg kg-1) and the potassium changes compared to those seen in control animals. The inotrope infusions caused a small and transient rise in plasma potassium (p less than 0.05) followed by a more profound hypokalaemia (p less than 0.05) sustained for the duration of the infusion. The potassium falls in the control animals were similar to those in the beta 1 and beta 2 blockade groups. The results suggest that beta 2 receptor stimulation cannot alone be responsible for dopamine and dobutamine induced hypokalaemia and a multiple receptor activation is postulated.

Continuous multi-channel intravascular monitoring of the effects of dopamine and dobutamine on plasma potassium in dogs.

The effects of dopamine and dobutamine on plasma potassium were investigated in dogs using continuous, multi-channel, intravascular ion-selective potassium electrodes situated in the aorta and abdominal and thoracic inferior vena cavae. Doses of 10 and 30 micrograms kg-1 min-1 of each drug were used, and the effects on potassium compared with isoprenaline 0.07 and 0.2 microgram kg-1 min-1. Both the drugs caused a biphasic pattern of potassium change consisting of an initial small rise in the potassium level, followed by a sustained period of hypokalaemia. The changes were greater with the higher dose of each drug compared with the lower dose, but there were no significant differences between the drugs. Comparison of the potassium changes between the three vascular sites studied suggested that the rise in potassium may be a result of release of the ion from the liver, and that the liver may also be the principle site of potassium uptake during the hypokalaemic phase.

Simultaneous endocardial and epicardial monophasic action potential recordings during brief periods of coronary artery ligation in the dog: influence of adrenaline, beta blockade and alpha blockade.

Local differences in the time course of recovery of excitability during the early phase of myocardial ischaemia are important in the genesis of arrhythmias. Catecholamines are known to encourage the formation of arrhythmias and adrenergic blockade is a recognised therapeutic regime. The purpose of this study was to compare the effect of short periods of coronary artery ligation on endocardial and epicardial repolarisation time, to assess any disparity between the two surfaces, and investigate the influence of catecholamines and adrenergic blockade. Simultaneous left ventricular endocardial and epicardial monophasic action potentials (MAPs) were recorded during short periods of left anterior descending coronary artery (LAD) ligation in 9 open chested dogs. Recordings were made during two 90 s periods of LAD ligation. Two further ligations were made during infusion of adrenaline (1 microgram.kg-1.min-1). Subsequently ligations were made after beta blockade with propranolol (0.25 mg.kg-1) and then in the presence of a combination of alpha blockade (phentolamine, 0.15 mg.kg-1) and beta blockade. MAP duration was measured at 90% repolarisation. LAD ligation produced a marked shortening of MAP duration epicardially with only minimal shortening endocardially, which resulted in a highly significant difference between the repolarisation times on the two surfaces. The disparity between surfaces tended to be augmented by adrenaline and was significantly minimised by either beta blockade alone or in combination with alpha blockade. Our results show rapid development of substantial regional differences in repolarisation time between endocardium and epicardium in response to "ischaemia".(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cardiopulmonary bypass on circulating concentrations of leucocyte elastase and free radical activity.

Circulating concentrations of leucocyte elastase and free radical activity were measured in 11 adults undergoing cardiopulmonary bypass. In all patients the bypass procedure was associated with pronounced changes in plasma elastase concentrations, and peak enzyme concentrations correlated closely with the duration of bypass (r = 0.91, p less than 0.001). Serial measurement of octadeca-9, 11-dienoic acid, a non-peroxide marker of free radical activity, showed significant changes only in the plasma free fatty acid fraction, suggesting a direct relation to the action of heparin rather than to the bypass procedure as such. These studies support the hypothesis that neutrophil activation plays a central role in the organ dysfunction that may complicate cardiopulmonary bypass and suggest that elastase release rather than free radical generation may be the appropriate marker of the event.

Continuous display of plasma potassium during cardiac surgery.

We have evaluated the use of an intravascular ion-selective electrode for continuous plasma potassium monitoring in patients during and after cardiac surgery. Potassium estimations from the indwelling electrode provided a rapid and sensitive, but only moderately reliable, indicator of potassium as confirmed by blood samples. Several significant changes in the plasma potassium were found to occur in the period studied and using this continuous monitor, the precise time course of these changes was recorded.

Continuous clinical monitoring with ion-selective electrodes. A feasible or desirable objective?

Ion-selective electrodes have been developed for the continuous monitoring of blood cations and pH. The background to this development, technical requirements for these systems and possible advantages and disadvantages of their use are discussed.

Meptazinol--a cause of respiratory depression in general anaesthesia.

The respiratory effects of meptazinol 1 mg kg-1 have been compared with those of pethidine 0.5 mg kg-1 and 1 mg kg-1 in a double-blind trial in 30 patients undergoing arthroscopic meniscectomy under general anaesthesia. Respiratory depression was seen in all treatment groups. Pethidine 1 mg kg-1 produced respiratory depression which was greater than that produced by meptazinol 1 mg kg-1. The least depressant respiratory effects were seen in the group receiving pethidine 0.5 mg kg-1. We submit that the measurement of tidal volume enhances the assessment of the respiratory effects of analgesic drugs during anaesthesia.