Biomedical subjects
Publications and source records attributed to C McLoughlin.
PRESENTATION: An elderly man had recurrent hospital admissions with falls. OUTCOME: Acetylcholine receptor antibodies and single-fibre electromyogram were useful in the diagnosis of myasthenia gravis. Treatment prevented further hospital admissions.
We describe the case of a pregnant woman, 35 weeks' gestation, with primary pulmonary hypertension and coarctation of the aorta requiring emergency Caesarean section under general anaesthesia. The patient had a pulmonary artery catheter inserted before operation which revealed pulmonary artery pressures in excess of 80/40 mm Hg. These were lowered using an infusion of glyceryl trinitrate. After delivery of the baby and administration of oxytocin, pulmonary artery pressures were more difficult to control. An infusion of prostacyclin was substituted which stabilized pulmonary pressures. After operation, she was transferred to the intensive care unit where prostacyclin was administered by an "aerosolized" route. Her trachea was extubated after 48 h and she made an uneventful recovery.
We have examined postoperative muscle pain and early increases in serum concentrations of myoglobin after administration of suxamethonium to see if these changes were dependent on the dose of drug. Thirty ASA I and II adult patients undergoing day-case surgery received a standard anaesthetic technique, including one of three doses of suxamethonium: 0.5, 1.5 or 3.0 mg kg-1. The incidence of postoperative myalgia and the severity of fasciculations were greater after suxamethonium 1.5 mg kg-1 than after a dose of 0.5 or 3.0 mg kg-1. Serum concentrations of myoglobin increased in a dose-dependent manner. Intubating conditions were significantly better with suxamethonium 1.5 or 3.0 mg kg-1 than with 0.5 mg kg-1. Changes in serum concentrations of calcium and potassium were small and similar in the three groups. We conclude that a dose of 3.0 mg kg-1 of suxamethonium provided a better combination of intubating conditions and minimal postoperative myalgia than the two lower doses.
The pharmacology of 3-desacetylvecuronium, the principal metabolite of vecuronium, was investigated. We studied 12 healthy volunteers, each on two occasions. First they received 3-desacetylvecuronium alone and then, on a later occasion, vecuronium. Six subjects received a large dose of each drug (pharmacokinetic study), the remaining six received a small dose (pharmacodynamic study). Drug concentrations in plasma and urine were measured using capillary gas chromatography. Neuromuscular block was assessed by measuring force of contraction of the adductor pollicis. Drug plasma concentration vs. time and neuromuscular effect data were analyzed by nonlinear mixed-effects modeling. 3-Desacetylvecuronium, compared with vecuronium (median, range in parentheses), had a smaller plasma clearance, 3.51 (2.11-6.57) vs. 5.39 (5.04-7.19) ml.kg-1.min-1; a larger steady-state distribution volume, 254 (215-410) vs. 152 (111-170) ml.kg-1; a longer terminal elimination half-life 116 (44-672) vs. 34 (25-61) min and a longer mean residence time, 67 (42-145) vs. 26 (18-32) min (P < .05). Renal clearances of 3-desacetylvecuronium and vecuronium were 0.85 (0.15-1.24) and 0.58 (0.16-0.66) ml.kg-1.min-1, respectively (P < .05). Conversion to 3-desacetylvecuronium accounted for 12% of vecuronium's clearance. Concentrations of 3-desacetylvecuronium and vecuronium that produced 50% neuromuscular block were 123 (109-154) and 102 (71-123) ng.ml-1, respectively (P < .05). 3-Desacetylvecuronium is a potent neuromuscular blocking drug and may be responsible for episodes of prolonged paralysis after long-term administration of vecuronium to patients in intensive care units.
The incidence of muscle pains and changes in serum concentrations of potassium, calcium and creatine kinase following suxamethonium were investigated after no pretreatment or pretreatment with intravenous tubocurarine 0.05 mg.kg-1, intravenous chlorpromazine 0.1 mg.kg-1, alphatocopherol (vitamin E) 600 mg in three divided doses orally, aspirin 600 mg orally or intravenous calcium chloride 5 mg.kg-1 in groups of 20 patients each. The incidence of myalgia was reduced significantly by tubocurarine, chlorpromazine and alphatocopherol. However, the increase in creatine kinase was attenuated only in the groups of patients who received tubocurarine and chlorpromazine. The changes in serum potassium and calcium concentrations were within acceptable limits. The intubating conditions were not as good in the patients who received tubocurarine as in the other groups. Effectiveness of chlorpromazine in preventing both the myalgia and the biochemical changes suggests the involvement of phospholipases in the pathogenesis of suxamethonium-induced muscle damage.
Muscle damage induced by suxamethonium, and the influence of halothane on it, has been examined by measuring the efflux of creatine kinase (CK) in the biventer cervicis muscle of the chick. Whereas halothane and suxamethonium alone did not increase the enzyme efflux significantly, the combination of the two was associated with significant increase in the concentration of CK in the bathing medium by 59-157%. The increase in CK was prevented by adding chlorpromazine 100 mumol litre-1 to the medium, suggesting the involvement of phospholipases in the pathogenesis of suxamethonium-induced muscle damage.
The efficacy of five different techniques of pre-oxygenation before a modified rapid intubation sequence was assessed, using oxygen saturation measurement, in patients aged over 65 years. Twenty patients in each group were pre-oxygenated using four deep breaths or normal tidal breathing for 1, 2, 3, or 4 minutes. The acceptable period of apnoea was defined as the time taken to desaturate to 93%. The mean times (SD) taken to reach this end-point were 3.7 (1.6), 4.1 (1.2), 5.4 (1.7), 5.4 (1.4) and 5.2 (1.7) minutes respectively. The apnoea times with 2, 3 and 4 minutes pre-oxygenation were not significantly different from each other but were significantly longer than after four deep breaths and 1 minute. It is concluded that a pre-oxygenation period of at least 2 minutes should be employed in the elderly before a rapid sequence induction.
Sixty unpremedicated patients presenting for day-care arthroscopy surgery were allocated randomly to receive diclofenac 1 mg kg-1 i.m., fentanyl 1 microgram kg-1 i.v. or no analgesic during the course of anaesthesia. Patients receiving fentanyl had slightly, although not significantly prolonged recovery times. Patients receiving diclofenac had significantly improved postoperative visual analogue pain scores compared with patients receiving placebo medication (P less than 0.05). With fentanyl, pain scores were reduced also, but the effect was not statistically significant. Both fentanyl and diclofenac produced significant reduction in postoperative analgesic requirements (P less than 0.05). We conclude that diclofenac 1 mg kg-1 i.m. was an effective analgesic for arthroscopic procedures on the knee and is a useful alternative to opioids for day-care patients.
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Eighty-four fit, unpremedicated patients who presented for routine surgery and received a standard anaesthetic technique were allocated randomly to three equal groups. Group 1 received tubocurarine 0.05 mg/kg before induction of anaesthesia. Group 2 received soluble aspirin 600 mg orally one hour before surgery, while Group 3 received no pretreatment. Aspirin prophylaxis produced a significant reduction in the incidence of subsequent suxamethonium-induced myalgia and the improvement was similar to that achieved with tubocurarine pretreatment. Pre-operative oral administration of aspirin effectively reduces muscle pains and avoids many of the complications associated with pretreatment with non-depolarising agents.
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