The contribution of fluid temperature to the effect of crystalloid fluid bolus therapy (FBT) in post-cardiac surgery patients is unknown. We evaluated the hemodynamic effects of FBT with fluid warmed to 40°C (warm FBT) versus room-temperature fluid.

In this single centre prospective before-and-after study, we evaluated the effects of 500 ml of warm versus room-temperature compound sodium lactate administered over <30 minutes, in 50 cardiac surgery patients admitted to ICU. We recorded hemodynamics continuous before and for 30 minutes after the first FBT. We defined CI responsiveness (CI-R) as an CI increase >15% of baseline immediately after FBT and effect dissipation if the CI returned to <5% of baseline and MAP responsiveness as >10% increase and dissipation as return to <3 mmHg of baseline.

Hypotension (56%) and low CI (40%) typically triggered FBT. Temperature decreased >0.3°C in 13 (52%) patients after room-temperature FBT versus 0 (0%) after warm FBT (p < 0.01). CI and MAP responsiveness was similar (16 [64%] versus 11 [44%], p = 0.15 and 15 [60%] versus 17 [68%], p = 0.77, respectively). Among CI responders, CI increased more with room-temperature FBT (+0.6 [IQR, 0.5–1.1] versus +0.5 [IQR, 0.4–0.6] L/min/m², p = 0.01). However, dissipation was more common after room-temperature versus warm FBT (9/16 [56%] versus 1/11 [9%], p = 0.02).

In postoperative cardiac surgery patients, warm FBT preserved core temperature and induced smaller but more sustained CI increases among responders. Fluid temperature appears to impact both core temperature and the duration of CI