Variation in the depth of the epidural space in successive pregnancies.

The epidural records of 151 patients who had received two effective lumbar epidurals during subsequent labours were studied. For each patient the depth of the epidural space from the skin was recorded at both insertions and the differences between the two measurements compared. Factors which are known to cause a variation in this value were excluded. The skin to epidural space depth was virtually unchanged in 72 (47.7%) of the repeat epidurals. In 18 cases (11.9%) however, the measured depth of the epidural space differed by more than 1.5 cm from one insertion to the next. Possible explanations for these differences are discussed.

The effect of cardiopulmonary bypass on cholinesterase activity.

Cholinesterase activity was determined in 18 patients who had undergone either hypothermic (n = 9) or normothermic (n = 9) cardiopulmonary bypass. The anaesthetic technique was standardised to avoid agents known to affect cholinesterase. Activity was determined in blood samples taken before the induction of anaesthesia, during cardiopulmonary bypass and for at least 7 days postoperatively. In six patients cholinesterase activity was also measured at 6 weeks postoperatively. All the patients were of normal cholinesterase genotype. In both groups cholinesterase activity fell by approximately 60% coinciding with the start of cardiopulmonary bypass, from a mean of 5976 to 2636 IU.l-1 in the hypothermic group, and from 5901 to 2615 IU.l-1 in the normothermic group (p < 0.001 in both instances) (normal range 4300-10,500 IU.l-1). Cholinesterase activity remained at this reduced level for at least 7 days postoperatively. By 6 weeks, activity had returned to within 7% of pre-induction values. There were no differences in cholinesterase activity between the hypothermic and normothermic groups at any of the sampling times.

An assessment of the Cerebrotrac 2500 for continuous monitoring of cerebral function in the intensive care unit.

Experience of the use of the Cerebrotrac 2500 EEG monitor in 17 patients subjected to artificial ventilation in an intensive care unit is reported; seven were receiving continuous sedation with morphine, midazolam and propofol singly or in combination and 10 received both sedation and the neuromuscular blocking agent, atracurium. The processed EEG patterns could not be precisely correlated with a standard clinical scoring system but were useful in determining the adequacy of sedation, particularly when a muscle relaxant was used. The monitor also shows considerable promise in the management of the paralysed patient with widespread convulsive activity in whom ischaemic brain damage may be occurring from epileptiform activity in the absence of any clinical manifestation. The ability to detect cerebral irritability or isolated epileptiform discharges using this apparatus is, however, questionable. The equipment was easy to use and robust; the running costs were 9.5p per hour.

Transplacental distribution of atracurium, laudanosine and monoquaternary alcohol during elective caesarean section.

Maternal venous (MV), umbilical venous (UV) and umbilical arterial (UA) blood samples were obtained for assay of atracurium, laudanosine and monoquaternary alcohol concentrations in 22 healthy patients undergoing elective Caesarean section under general anaesthesia. At delivery (at a mean time of 8.2 min after atracurium 0.3 mg kg-1), the mean UV concentrations were 103 ng ml-1 (range 44-189 ng ml-1) for atracurium, 26 ng ml-1 (range 6-60 ng ml-1) for laudanosine and 59 ng ml-1 (range 21-148 ng ml-1) for monoquaternary alcohol. The ratios of UV:MV, UA:MV and UA:UV blood concentrations were related positively to time since injection of atracurium for all three substances (P less than 0.01 in each instance). The UV:MV ratio at delivery was greatest for laudanosine: mean 19.4% (range 1-35%), compared with 7% (range 2-21%) for atracurium and 10% (range 0-15%) for monoquaternary alcohol. These low values confirm that, although atracurium crosses the placental barrier and its metabolites may be found in the fetus, the drug is safe to use during Caesarean section.

Clearance of atracurium and laudanosine in the urine and by continuous venovenous haemofiltration.

We have measured the steady state urinary clearances of atracurium, given by constant infusion, and laudanosine in eight patients undergoing artificial ventilation; all had normal renal function (mean creatinine clearance 81 ml min-1). Mean (SD) urinary clearance of atracurium was 0.55 (0.5) ml kg-1 min-1; that of laudanosine was 0.33 (0.2) ml kg-1 min-1. Simultaneous plasma clearances were 7.1 (1.4) ml kg-1 min-1 and 3.8 (1.5) ml kg-1 min-1, respectively. Notional haemofiltration clearances of the two substances were measured also in seven critically ill patients with renal and respiratory failure undergoing continuous venovenous haemofiltration. Mean (SD) clearances of atracurium and laudanosine in the haemofiltrate fluid were 0.11 (0.06) ml kg-1 min-1 and 0.09 (0.02) ml kg-1 min-1, respectively whilst plasma clearances were atracurium 6.7 (1.8) ml kg-1 min-1 and laudanosine 4.5 (1.8) ml kg-1 min-1. There were no significant differences between the plasma clearances of the drugs in the two groups, despite the difference in severity of sickness. Urinary clearance rates of atracurium and laudanosine were approximately 8 and 9% of that in the plasma, but the haemofiltration clearance of both substances was only 2%.

Haemodynamic effects and comparison of enoximone, dobutamine and dopamine following mitral valve surgery.

Mitral valve surgery may be complicated by a post-operative low output state requiring inotropic support, and a wide variety of factors may influence the choice of agents used to treat this condition. The authors have examined and compared the haemodynamic effects of the highly specific phosphodiesterase inhibitor enoximone, and the adrenergic agents dobutamine and dopamine in patients undergoing mitral valve surgery. Enoximone, 0.5 mg kg-1 bolus, followed by a continuous infusion of 5 micrograms kg-1 min-1, was compared against dobutamine, 7 micrograms kg-1 min-1, and dopamine, 5 micrograms kg-1 min-1, with the protocol allowing for an increase in the infusion rate by a factor of two if clinical and haemodynamic measurements indicated. All 25 patients receiving enoximone were successfully weaned from cardiopulmonary bypass at the first attempt, with significant increases in cardiac index and stroke index, combined with little or no change in heart rate or pulmonary artery pressures and a highly significant reduction in systemic vascular resistance, and a reduction in mean arterial pressure. Three of the 25 patients receiving dobutamine were withdrawn from the study because of inadequate haemodynamic response, while the remaining 22 patients demonstrated significant increases in heart rate, cardiac index and stroke index, with a reduction in systemic vascular resistance. Nine of the 25 patients receiving dopamine failed to respond adequately, while the remaining 16 demonstrated an increase in heart rate and cardiac index but with little change in stroke index and a modest reduction in systemic vascular resistance. Enoximone has been shown to be a highly effective first-line inotrope in patients following mitral valve surgery with significant advantages over dobutamine and dopamine.