Succinylcholine and Intracranial Pressure???A Cause for ???Pause???

Based on their study in cats, Cottrell et al. (1) conclude that succinylcholine may be contraindicated in neurosurgical anesthesia. We question this conclusion. One should always be careful in making inferences based on animal experiments. It is well-known that species differences exist and that animal data may not be applicable to humans. This issue is particularly relevant here because, as Cottrell et al. mention, succinylcholine does not increase intracranial pressure (ICP) in dogs (2,3). In addition, light anesthesia cannot be excluded as a factor in the increase in ICP in the cats studied by Cottrell et al. It is doubtful that 25 mgkg of pentobarbital would provide adequate anesthesia beyond 2 hr (4). Use of an epidural balloon to simulate a space-occupying lesion would also seem to be a more clinically relevant model than communicating hydrocephalus employed in this study. Cottrell et al. in their review of the human data on succinylcholine and ICP in humans, have omitted some important aspects of the papers they quote. For instance, in the paper by Marsh et al. (5) who studied the effect of succinylcholine infusion on ICP in eight patients, in only one patient did ICP increase more than 6 mm Hg and the authors concluded that succinylcholine is safe in neuroanesthesia. This is important, because in evaluating physiological parameters such as ICP, percentage changes are often not as meaningful as absolute changes; an increase in ICP from 23-27 mm Hg (17%) is, for example, physiologically more important than a change from 2-5 mm Hg (250%). McLeskey et al. (6) studied the influence of succinylcholine and pancuronium on ICP before, during, and after intubation in twelve patients. When quoting their findings, Cottrell and his associates omitted to mention that ICP decreased in all four patients who received thiopental and succinylcholine. In both groups, ICP increased to a variable extent during intubation. The greater mean increase with succinylcholine probably reflects the fact that only four subjects were studied and one had a very large increase. In addition, the relatively long delay between administration of succinylcholine and intubation (2 min) may also be a factor. Mean blood pressure increased 40 mm Hg on intubation in those patients given pancuronium. This could be disastrous in patients with intracranial vascular anomalies. Lewelt et al. (7) found in seven patients, that the increase in ICP associated with succinylcholine started during the fasciculations and reached the highest value during intubation. In 5 out of 24 patients given pancuronium, there was also a marked increase in ICP, primarily related to problems with intubation. Moreover, the duration between administration of barbiturate and intubation was considerably longer in the succinylcholine group. It is important to separate the effects of the drug from the effects of actions performed while the patient is under the influence of the drug. Summarizing the available evidence, we conclude that succinylcholine does not increase ICP in dogs; succinylcholine may increase ICP in cats; and the response of ICP to succinylcholine in humans is variable with ICP increasing during intubation in the nonor lightly anesthetized patient. In the absence of inadequate anesthesia and/or hypercapnia, the use of succinylcholine in neurosurgical anesthesia is compatible with safe practice.