Pharmacodynamics of intravenous frusemide bolus in critically ill patients

Objective: To assess the physiological, biochemical and haemodynamic response to a single intravenous (IV) dose of frusemide in critically patients. Design, setting and patients: A prospective observational study of 21 critically ill patients in a tertiary intensive care unit in Australia. Interventions: We collected information on urine output (UO), fluid balance, serum and urinary electrolyte levels, serum biochemical levels and haemodynamics. We compared data from the 6-hour period before administration of a single IV bolus of frusemide 40 mg with data from the 6-hour period after administration. Results: We studied 21 patients (12 of whom were women) with a median age of 73 years (interquartile range [IQR], 64-80 years). The IV bolus induced a > 1000 mL increase in UO in six patients (28.6%); a 500-1000 mL increase in six patients (28.6%) and a < 500 mL increase in nine patients (42.8%). The median difference in UO before and after frusemide was 590 mL (IQR, 290-1111 mL). The 6-hour fluid balance became negative in 15 patients (71.4%) and positive in six patients (28.6%), with a median change of 595 mL (IQR, 880 to 98 mL). Frusemide significantly increased urinary sodium, potassium and chloride losses and decreased blood chloride levels. There were no detectable changes in haemodynamics. On linear regression analysis, sodium excretion and UO correlated with higher mean arterial pressure (MAP) and age, and with lower albumin and creatinine levels. Conclusions: In a cohort of critically ill patients without chronic renal impairment, frusemide increased UO and urinary sodium, potassium and chloride losses, and induced hypochloraemia and metabolic alkalosis. However, its diuretic effects were extremely variable and were modified by age, MAP and creatinine and albumin levels.