The standard method for estimating cyanide liberated from sodium nitroprusside (SNP) has been colorimetric. Using a cyanide ion-selective electrode technique, it was found that SNP remained unchanged in the presence of whole blood, plasma and washed erythrocytes, no cyanide being detected. Previously reported releases of cyanide from SNP in vivo and in vitro are probably inaccurate. Values obtained could have arisen not from reaction with blood, but from photo-decomposition during the lengthy analysis required by the colorimetric method or during infusion, if the solution was left uncovered. Because of the supposed cyanide hazard, low doses of SNP have been recommended; it may now be possible to revise these.
SummaryFort)' patients were chosen at random to receive halothane or isoflurane anuesthesia during craniotomy and a comparison i f the po.stoperutive hjpertcnsive response nus made using a microcomputer-bused clo.sed-loop urteriul pressure control sysrern with .soilium tritroprusside to control and U S S~S S arterial pressure during the first 6 postoperative hours. A desired turget sj~stolic pressure nus chosen ,fiw iwch patient und the,frequency o f hypertension, sodium nitroprusside requirements and quulity of urterid pressure control were conipured between the two groups. Thirty-$ve patients required sodium nitroprusside. The halothane group required u niediun dose of 1-5.2 mg (range 0-72) compared to 3.4 mg (range 0-87) in the isoflurane group. This di#erencc i s not stutistically significant. Quolit)! of arterial pressure control IVUS .satisfiictorj> in both groups. In conclusion, urreriul hypertension occurs jrequentlj~ j0llowing intracranial surgery and is uninfluenced by the choice of halothune or isr~fluriine intra-operati~iel~~. This i~l o~e i l -l~~p urtcvYnl pressure conrrol system ,functioned s.f;lj, and c@ctiveIv in this i~~t~s t . Key words Anuestherii~s. ~~o l t r t i l~~;halothane, isofluranc. Blood pressurc; hypertension. Equipment; computers.Arterial hypertension often occurs in the tirst few hours after intracranial surgery and is undesirable when autorcgulation of cerebral blood flow is dcrangcd and cerebral blood flow is pressure dependant [I]. This hypertension may also lead to a reduction in brain compliance and increase the ratc and spread of cercbral oedema [2]. In addition. hypertensive surges in the early postoperativc period may be associated with reactive intracranial blceding.This arterial hypertcnsion can be trcatcd with short acting vasodilators such as sodium nitroprusside (SNP). I t has bccn shown that closcd-loop computer-controlled administration of SNP can provide better control o f artcrial pressurc than that achieved with manual administration from nursing staff [3-51. A computer-control system can record cardiovascular information on disc, and supply detailed and unbiased data.It has been suggested that patients who received isotliirane during intracranial surgcry have a better arterial prcssure protilc in the early postoperative period than those who receive halothane. The aim of this study was to evaluate the incidencc and severity of arterial hypertension following intracranial surgcry and to dctcrminc if there was any difference between patients anaesthctised with either halothane or isoflurane during craniotomy using a closcdloop computer-controlled SNP infusion as an unbiased asscssor. MethodsWe studied 40 patients, aged 18 to 70 ycars and weighing 45 to 100 kg, who underwent intracranial surgery. lnformcd consent was obtained from the patient or next of kin before operation. and hospital ethics comniittcc approval was also obtained. Patients with sevcrc hepatic or rcnal discasc and thosc with any contraindication to SNP were not studied.All patients were prcmedicat...
Sodium nitroprusside is a valuable vasodilator, but its use has been curtailed because of numerous reports that, in the presence of blood, nitroprusside decomposes with release of toxic cyanide. We have examined the release of cyanide in terms of the known chemistry of nitroprusside and suggest that photochemical decomposition of nitroprusside and (or) its metabolism in vivo invalidates the analytical procedure used by previous workers. We also present evidence for the stability of nitroprusside in blood, based on 13C nuclear magnetic resonance studies.
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