SummaryThe neuromuscular block of successive doses of suxamethonium I00 mg. monitored by electromyography. was investigated in a myasthenic patient (class IIB) , undergoing thymectomy. The results suggest that successive doses of suxamethonium in the myasthenic patient are followed by a progressive prolongation of the neuromuscular block. This may be attributed to rapid desensitisation of the myasthenic endplate receptors and the rapid development of phase II block, as evidenced by a progressive decrease of the T4/TI ratio.
Key wordsNeuromuscular relaxants; suxamethonium. Complications; myasthenia gravis.Payne and Holmdahl have shown, in man, that suxamethonium results in a progressively diminishing neuromuscular block when given repeatedly at short intervals [I]. This phenomenon of increasing resistance (tachyphylaxis) following successive doses of suxamethonium has been attributed to desensitisation of the motor endplate [2, 31.The myasthenic patient, because of the decreased number of functional endplate receptors, can manifest resistance to suxamethonium [4,5], and may develop rapid desensitisation of the endplate receptors following the administration of repeated doses. The present report investigates in a myasthenic patient undergoing thymectomy the neuromuscular response to successive doses of suxamethonium.
Case historyThe patient was a 25 year old woman, weighing 60 kg who had generalised myasthenia gravis (Osserman grade IIB) [6]. CT scan of the chest revealed a thymoma. The patient was treated medically for 7 months with oral pyridostigmine, prednisone and immuran before admission for thymectomy. The pyridostigmine treatment was discontinued 3 days before operation.On the morning of surgery, cholinesterase activity was estimated as 2.4 U.ml-' using spectrophotometry and proprionylthiocholine as a substrate [7]. The dibucaine number was 70.Neuromuscular transmission was monitored in the operating theatre by electromyography using a Datex Relaxograph (R) monitor. The ulnar nerve was stimulated supramaximally at the wrist every 20 s, and the resulting electromyographic response displayed. The monitor uses the train-of-four principle at a stimulus frequency of 2 Hz, and computes the ratio of the fourth to the first evoked response (T4/TI ratio), as well as the Tl/control ratio. The patient was premedicated with intramuscular atropine (0.6 mg) and pethidine (75 mg). Anaesthesia was induced with thiopentone 5 mg.kg-', and was maintained with nitrous oxide : oxygen (2 : 1) supplemented with intermittent doses of fentanyl. The electromyographic response was recorded. When a steady response was achieved, suxamethonium 100 mg was injected intravenously and the neuromuscular response was monitored. At maximal neuromuscular block, the trachea was intubated. Following recovery of neuromuscular transmission, the same dose of suxamethonium was administered, and this was repeated as required with train-of-four monitoring until the end of surgery. The degree of neuromuscular block achieved by the initial and successiv...
To determine whether alpha-stat or pH-stat strategy should be used, 20 patients undergoing coronary artery bypass grafting during moderate hypothermic hemodilutional cardiopulmonary bypass were studied. The carbon dioxide management during bypass was randomly done according to alpha-stat strategy in 10 patients (i.e., temperature-uncorrected PaCO2 was kept near 40 mm Hg and uncorrected pHa was kept at about 7.4) and according to pH-stat strategy in the other 10 patients (i.e., temperature-corrected PaCO2 was kept near 40 mm Hg and uncorrected pHa was kept at about 7.4). In both groups, when the central venous temperature was stable at 26.5 +/- 2.5 degrees C, the perfusion flow was altered sequentially from 2.4 to 1.8 and 1.2 L.min-1.m-2. The mixed venous oxyhemoglobin saturation at the different perfusion flows was monitored by the Oxy-Stat meter and was correlated with the corresponding mixed venous oxygen tension to construct an oxyhemoglobin dissociation curve. Also, the whole-body oxygen consumption at the different perfusion flows was computed. The whole-body oxygen consumption and the oxyhemoglobin dissociation were not significantly different between the alpha-stat and the pH-stat groups. In both groups, the dissociation curve is shifted to the left, but the oxygen consumption per unit time does not significantly change despite decreasing the perfusion flow from 2.4 to 1.2 L.min-1.m-2. The results suggest that oxygen delivery is not impaired during moderate hypothermic cardiopulmonary bypass independent of whether alpha-stat or pH-stat strategy is used.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.