Doxapram and the neuromuscular junction.
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Biomedical subjects
Publications and source records attributed to S A Feldman.
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A subparalytic dose (0.015 mg/kg) of vecuronium bromide was administered to matched pairs of patients undergoing routine dental surgery under enflurane-nitrous oxide/oxygen anesthesia either as a rapid bolus injection or as a slow infusion over 5 min. It was demonstrated that bolus injection produced peak plasma levels of drug considerably greater than those following slow infusion. Time to maximum block was more rapid following bolus (368 +/- 84 [SD] sec) than by infusion (615 +/- 88 sec), but the maximum block produced, either demonstrated by the reduction in amplitude of T1 from control or the T1:T4 ratio on the integrated electromyogram (Datex IEMG), was similar in each group irrespective of rate of injection, T1 and T4 referring to the first and last twitch in a train of four series.
Vecuronium was administered to patients in doses of 100, 150, 200 and 250 micrograms/kg and the duration of action recorded by noting the time to recovery of the first twitch in a train-of-four to 10% of the control twitch. The recovery times ranged from a mean of 28.4 minutes (100 micrograms/kg) to 72.4 minutes (250 micrograms/kg). It is suggested that for operations of medium to long duration the use of a large initial bolus dose of vecuronium is a technique with advantages over the use of an infusion or frequent incremental doses.
A blind trial, comparing time of onset of satisfactory conditions for tracheal intubation with atracurium 0.6 mg/kg, vecuronium 0.1 mg/kg and pancuronium 0.1 mg/kg is described. Intubation was attempted at 30-second intervals in 60 patients, randomly allocated to receive one of the above muscle relaxants. Patients receiving atracurium 0.6 mg/kg could be intubated from 30 to 120 seconds. Patients receiving either vecuronium 0.1 mg/kg or pancuronium 0.1 mg/kg were able to be intubated between 60 and 240 seconds. The results showed a statistically significant earlier onset of satisfactory intubating conditions with atracurium than with vecuronium or pancuronium in these doses but no difference between vecuronium and pancuronium.
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The case of tracheal intubation using two doses of the new steroid neuromuscular blocking compound ORG NC45 (Norcuron) 0.1 and 0.15 mg/kg was compared with a standard dose of pancuronium 0.1 mg/kg at 60, 90 and 120 seconds. The results did not reveal any statistically significant benefit of the new drug within 2 minutes of administration over the control.
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Neostigmine failed to modify the development of neuromuscular block in the presence of a high local concentration of tubocurarine. Only when the concentration of tubocurarine was reduced, and a suitable concentration gradient established between the receptor area and the plasma, did neostigmine increase the rate of recovery from the action of non-depolarizing neuromuscular blocking agents.
To establish whether the plasma concentration of pancuronium reflects magnitude of neuromuscular blockade, the authors determined times of recovery from neuromuscular blockade and associated plasma concentrations following equipotent doses of pancuronium using three methods of pancuronium administration: the isolated-arm technique in conscious volunteers (n = 4), and the bolus intravenous injection (n = 7) and continuous-infusion methods (n = 3) in anesthetized patients. Although maximum depressions of twitch tension were similar (85 +/- 11,91 +/- 6, and 92 +/- 4 per cent, respectively) with the three techniques, times to recovery from neuromuscular blockade differed significantly, being 10 +/- 2 min with the isolated-arm technique, 23 +/- 7 min with the bolus-injection technique, and 46 +/- 5 min with the continuous-infusion method. The plasma concentration of pancuronium necessary for neuromuscular blockade was least with the isolated-arm technique and greatest with continuous infusion. At 25 and 75 per cent recovery, mean plasma concentrations were 0.07 +/- 0.01 and 0.04 +/- 0.01 microgram/ml in the isolated arm; 0.13 +/- 0.04 and 0.09 +/- 0.02 microgram/ml after bolus injection, and 0.20 +/- 0.04 and 0.11 microgram/ml during continuous infusion, respectively. It is concluded that the relationship between plasma concentration of pancuronium and magnitude of neuromuscular blockade depends on the method of pancuronium administration.
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The effect of changes in muscle blood flow on the rate of recovery from neuromuscular block produced by pancuronium was investigated in dogs, and were shown to be independent variables. The significance of this finding in relation to recent work on blood concentrations of the drug and on the pharmacodynamics of the drug is discussed.
The interaction of halothane and pancuronium is demonstrated in the dog tibialis anterior-sciatic nerve preparation. The results show a dose related effect of halothane on the recovery index and the 50% recovery times. These results are compared to other reports and possible mechanisms are discussed.
A 42-year-old male was hemodialyzed for 2 years with excellent control of calcium-phosphate metabolism. He received a cadaveric renal transplant but experienced a prolonged episode of acute tubular necrosis during which he could not tolerate phosphate-binding antacids. His calcium X phosphate product became markedly elevated for 20 days. Following a brief period of function, the homograft was removed on the 45th post-transplant day after severe rejection and subsequent infection. Chest X-ray was normal. Six days after graft nephrectomy, he became acutely dyspneic and markedly hypoxemic. Diffuse, flocculent pulmonary infiltrates appeared on the chest film. The patient expired 1 day later. At postmortem examination, there was severe, diffuse pulmonary alveolar calcification demonstrated by chemical and histologic examination. Although unlikely, the prolonged post-transplant period characterized by elevated calcium X phosphate product may have played a pathogenetic role. Calciphylaxis may have occurred, with hyperparathyroidism as the sensitizing agent and any of several drugs acting as challenger.