Intracranial pressure increases during alfentanil-induced rigidity

Intracranial pressure (ICP) was measured during alfentanil-induced rigidity in rats. Ten rats had arterial, central venous (CVP), and subdural cannulae inserted under halothane anesthesia. The animals were mechanically ventilated to achieve normocarbia (PCO2 = 42 +/- 1 mmHg, mean +/- SE). Following instrumentation, halothane was discontinued and alfentanil (125 mu/kg) administered iv during emergence from halothane anesthesia. In the five rats that developed somatic rigidity, ICP and CVP increased significantly above baseline (delta ICP 7.5 +/- 1.0 mmHg, delta CVP 5.9 +/- 1.3 mmHg). These variables returned to baseline when rigidity was abolished with metocurine. In five rats that did not become rigid, ICP and CVP did not change following alfentanil. These observations suggest that rigidity should be prevented when alfentanil, and, presumably, other opiates, are used in the anesthetic management of patients with ICP problems.