Acute effect of diuretics on central hemodynamics in the early postoperative period

The effects on the central circulation of furosemide and mannitol in the second postoperative hour were studied in 2 groups of 8 patients, who had undergone upper abdominal surgery. Cardiac output [Q(T)] was measured with thermodilution technique. Systemic arterial (SBP), pulmonary arterial (PAP), right atrial (RAP) and pulmonary capillary wedge pressure (PCWP) were recorded. Pulmonary (PVR) and systemic vascular resistance (SVR) were calculated. Neuroleptic anesthesia was used. One hour after the termination of anesthesia central hemodynamics were assessed. Furosemide 1 mg/kg or mannitol 0.5 g/kg was then infused. Determinations of central circulation and Q(T) were then performed at 10, 30 and 50 min after the infusion. In the furosemide group RAP remained stable. Decreases were found in: Q(T) from 6.24 to 5.00 l/min (P < 0.001), SBP from 13.8 to 12.0 kPa (P < 0.05), PAP from 1.76 to 1.23 kPa (P < 0.01) and PCWP from 1.06 to 0.71 kPa (P < 0.01). Increases were found in SVR from 2.15 to 2.51 kPa x min x l^-1 (P < 0.05) and PVR from 0.12 to 0.15 (P < 0.05). In the mannitol group SBP, RAP and PVR remained stable. Increases were found in: Q(T) from 5.55 to 7.08 l/min (P < 0.001), PAP from 1.98 to 2.63 kPa (P < 0.01) and PCWP from 1.05 to 1.42 kPa (P < 0.05). SVR decreased from 2.17 to 1.93 kPa x min x l^-1 (P < 0.05). The effect of furosemide is probably due to a reduction in central blood volume and decreased filling pressure and Q(T); while mannitol increased preload and Q(T). These findings suggest that mannitol should be preferred to furosemide as a first hand diuretic in postoperative (posttraumatic) patients without known cardiovascular disease associated with increased preload.