When choosing a neuromuscular blocker for intubation, oneshould take into account how long the procedure will be, how long the patient is expected to remainintubatedintherecoveryroomorintensivecareunit,andthepatient's underlying physiologic status. The presence of underlying organ dysfunction, particularly hepatic and renal systems, can affect the metabolism and excretion of these drugs and lead to a longer half-life and duration of action.
In patients with hepatic failure, depending on the nondepolarizing neuromuscular blocker used, the initial dose required may be larger due to an increase in the volume of distribution but the amount used to redose will be lower due to a reduction in plasma clearance. Pancuronium is metabolized to a limited degree by the liver and its effects will be moderately prolonged in liver failure. Vecuronium is excreted by the biliary system but its duration of action is modestly prolonged by liver failure when used in standard doses. Similarly, rocuronium's duration of action is modestly prolonged in severe liver disease. Cisatracurium is a good choice is liver failure because its metabolismandeliminationareindependent ofliverdysfunction.However,do not limit yourself to cisatracurium when choosing a neuromuscular blocker (NMB) for patients with liver failure. Cisatracurium's duration of action may be least affected by liver failure but takes 2 minutes to provide good intubation conditions, which is longer than rocuronium, so consider both the onset and duration of action when choosing a nondepolarizing NMB.
When choosing a NMB for patients with chronic renal failure, one must consider when the last dialysis was performed to ascertain volume status. In addition, a serum potassium level, preferably within the past 24 hours, is an essential laboratory value to determine prior to surgery to determine if anesthesia can be safely induced and if succinylcholine is an option during intubation. An intubation dose of succinylcholine will raise the serum potassium by 0.5 mEq/L. Other electrolyte abnormalities are also important. For example, magnesium prolongs the duration of nondepolarizing NMB by competing with calcium at the prejunctional sites. Although some studies have shown it can reduce the onset of action of pancuronium, magnesium is not used in standard practice as an adjunct to NMB. Pancuronium's long duration of action will increase in patients with renal failure, because pancuronium is primarily excreted by the kidneys. Vecuronium's duration of action will also be prolonged; however, it depends only secondarily on renal excretion, which makes it an acceptable choice but a rarely used alternative. Rocuronium is eliminated slightly by the kidneys, so its duration of action will not be significantly prolonged by renal dysfunction. Of the nondepolarizing NMB, cisatracurium will provide the most predictable neuromuscular blockadebecause its metabolism is least dependentonrenal function. In fact, cisatracurium undergoes degradation in the plasma by organ-independent Hoffman elimination. However, as in patients with liver dysfunction, if a rapid sequence intubation is required, succinylcholine or rocuronium are more appropriate choices.
The studies on the affect of acid–base balance and NMB have primarily investigated pancuronium and vecuronium because these are some of the oldest and most widely established nondepolarizing NMBs. Acidemia prolongs the duration of a nondepolarizing NMB, whereas alkalemia will shorten it. Some explanations include the effect of pH on the binding of vecuronium on acetylcholine receptors, the effect of intracellular Ca2+on the neuromuscular junction, and the effect of pH on blood flow to the muscle. For practical purposes, however, the intubation and maintenance doses will remain the same.
When in doubt, before redosing a NMB, monitor the neuromuscular function with a peripheral nerve stimulator. Common sites to test include the ulnar nerve and the facial nerve. If there are no twitches on the Train- of-four, do not redose. Also, if you suspect that the NMB is lasting longer than predicted, be sure that the patient is receiving adequate sedation and analgesia to cover the period of neuromuscular blockade.
Fawcett WJ, Haxby EJ, Male DA. Magnesium: physiology and pharmacology. Br J Anaesth.
1999;83:302–320.
Khuenl-Brady KS, Pomaroli A, Pühringer F, et al. The use of rocuronium (ORG 9426) in
patients with chronic renal failure. Anaesthesia. 1993;48(10):873–875.
MorganGE,MikhailMS,MurrayMJ,etal.ClinicalAnesthesiology.3rded.NewYork:McGraw-
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98–101.
Review other book chapters online related to Selective IgA Deficiency:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Avoiding Common Pediatric Errors Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7489-6 
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