August 1997

Nicardipine versus nitroprusside for controlled hypotension during spinal surgery in adolescents.
Hersey SL, O'Dell NE, Lowe S, Rasmussen G, Tobias JD, Desphande JK, Mencio G, Green N; Anesth Analg 1997;84:1239-44.
[ see abstract below ]

This is an interesting paper because it examines this group's experience with two techniques for induced hypotensive anesthesia. The authors prospectively compared sodium nitroprusside versus the calcium channel blocker nicardipine. Both groups were evenly matched for age, weight, and operative time.

Two differences were found:

1. blood loss was significantly greater in the nitroprusside group (1,298 � 264 vs 761 � 199 ml - p < 0.05);
   
   
2. the time to restoration of mean arterial blood pressure was longer in the nicardipine group (26.8 � 4.0 vs 7.3 � 1.1 min - p < 0.002).
   
   

The authors concluded that controlled hypotension could be easily achieved with nicardipine but that there is a slow return to baseline blood pressure and a reduction in blood loss. On the surface this sounds good, but the paper still leaves the reader with a few questions.

Since patients were not monitored with central venous catheters, and since the study was an open label design (the anesthesiologists knew the technique), how can we be certain that observer bias did not influence the transfusions administered? Had central venous pressure been monitored and patients transfused to the same objective endpoint, then perhaps we would have more confidence in this observation.

Another concern which was not commented upon was what effect if any does nicardipine induced hypotension have on spinal cord blood flow and the distribution of cerebrocortical blood flow? It is known that there are significant differences between cortical blood flow distribution when nitroprusside is compared to ganglionic blockade induced with trimethaphan.

Although these differences are of theoretic concern, one should not be too quick to jump into a new technique until important information is available; Hersey, et al are to be congratulated for starting the ball rolling. I would hope that they or other investigators examine both spinal cord and cerebral blood flow changes before generally advocating this technique.

The time it took for restoration of normal arterial blood pressure brings up an additional concern. Whenever major and massive blood loss is a possibility, easy reversibility of the hypotensive agent is an advantage; nicardipine would not appear to have this advantage and may in fact present a disadvantage. When this situation occurs, even nitroprusside can seem to take an inordinate period of time to wear off. I would hate to have to wait 25 minutes to return to normal in this circumstance.

Perhaps an acceptable middle ground would be to use lower doses of nicardipine and lower doses of nitroprusside combined. This would reduce the exposure to nitroprusside while at the same time minimizing the potential for adverse effects due to higher doses of single agents. I do not mean to be a therapeutic nihilist, but I am always concerned about reaching wide based conclusions based on a small number of patients.

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ABSTRACT