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Canadian Journal of Anesthesia, Vol 25, 92-105, Copyright © 1978 by Canadian Anesthesiologists' Society

Nitroprusside, Its Metabolites and Red Cell Function

J. DU CAILAR 1, J. C. MATHIEU-DAUDE 2, J. DESCHODT 2, Y. LAMARCHE 3, and C. CASTEL 2

1 Département d'Anesthésie-Réanimation (Pr J. du Cailar, Hôpital Saint Eloi 34059 Montpellier Cedex) et Département de Biophysique Médicale (Pr Ch. Bnezech-Pr Llory) de la Faculté de Médecine Montpellier, France
2 Département d'Anesthésie-Réanimation (Pr J. du Cailar, Hôpital Saint Eloi 34059 Montpellier Cedex) et Département de Biophysique Médicale (Pr Ch. Bnezech-Pr Lory) de la Faculté de Médecne Montpellier, France
3 Département d'Anesthésie-Réanimation, Centre Hospitalier Universitaire, Sherbrooke, Qué., Canada

The effects on metabolism and red cell function of blood levels of thiocyanate (SCN-) and cyanide (CN-) were studied in 42 patients undergoing surgery under controlled hypotension (CH) induced by sodium nitroprusside (SNP).

The mean dosage of SNP administered was 21.38 mg (SD = 12). The durating of perfusion was 121 minutes (SD = 11). All operations were performed under neuroleptanalgesia without complications. No tachyphylaxis was encountered.

Under SNP a slight increase of blood SCN- (from 13.9 mg/1±1.1 to 23 mg/l ±2.6) was found. Blood levels of CN- are increased mostly in the red cell, the mean value being 0.300 mg/1 ±0.10 for whole blood after two hours of perfusion. This value decreased when perfusion was stopped. All blood samples were negative for methaemoglobin and cyanmethaemoglobin. Carbonic anhydrase activity was not modified, CN- toxicity levels for this enzyme being 50 times higher than those found during our study. 2,3-DPG levels did not vary. Blood gases, acid-base balance and Dav002 did not change significantly, although a slight increase in blood lactate was measured. As shown by this study, appreciable amounts of CN- are detected in blood during SNP perfusion while SCN- stays at relatively low levels. Fortunately most of the CN- released from SNP moves into the red cell and does not alter its functions at clinical concentrations. The low plasma concentration of CN- is not sufficient to cause important metabolic disturbances. However, dosages of SNP higher than those administered during this toxic levels. A toxicity study shows that, during a relatively short period of time, SNP dosage should not exceed 1.16 mg/kg or a maximum of 10 µg/kg/min fora period of two hours.






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Copyright © 1978 by the Canadian Anesthesiologists' Society.