Thiocyanate Accumulation in Critically Ill Patients Receiving Nitroprusside Infusions.

PURPOSE

This study evaluated thiocyanate concentrations and factors associated with thiocyanate accumulation in intensive care unit patients receiving nitroprusside with and without sodium thiosulfate coadministration.

MATERIALS AND METHODS

This retrospective study evaluated critically ill adults who received nitroprusside infusions and had at least one thiocyanate concentration. Patients with thiocyanate accumulation (concentrations ≥30 µg/mL) were compared to patients without accumulation. Factors associated with accumulation were determined by Spearman correlation and multivariate regression.

RESULTS

Thiocyanate concentrations (n = 192) were obtained from 87 patients. Fourteen of the 87 (16%) patients experienced thiocyanate accumulation with a mean (SD) thiocyanate concentration of 44 ± 11 µg/mL. Patients with accumulation had received greater cumulative nitroprusside doses (28 vs 8.2 mg/kg, P < .01), greater cumulative sodium thiosulfate doses (16.8 vs 10.1 mg/kg, P < .01), and longer infusion durations (10.9 vs 6.0 days, P < .01), compared to patients without accumulation. Sodium thiosulfate coadministration resulted in greater thiocyanate concentrations (22.8 ± 16.7 vs 16.8 ± 14.9 μg/mL, P = .01), despite utilization of lower cumulative nitroprusside doses (10.2 vs 14.6 mg/kg, P = .03). Cumulative nitroprusside dose ( r .44, P < .001) and cumulative sodium thiosulfate dose ( r .32, P < .001) demonstrated a significant correlation with measured thiocyanate concentrations. Thiocyanate accumulation was independently associated with cumulative nitroprusside dose in mg/kg (regression coefficient 0.75, 95% CI 0.63-0.89; P < .01). No clinically significant adverse effects of cyanide or thiocyanate toxicity were observed.

CONCLUSIONS

Cumulative nitroprusside dose was independently associated with thiocyanate accumulation. Despite elevated thiocyanate levels in 16% of patients, there was no clinical evidence of cyanide or thiocyanate toxicity. Routine monitoring of thiocyanate concentrations appears most warranted in patients receiving higher cumulative doses of nitroprusside.