The haemodynamic effects of bolus versus slower infusion of intravenous crystalloid in healthy volunteers

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This pilot study aimed to characterise the haemodynamic effect of 1L of IV normal saline (NS) administered as a rapid versus slow infusion on cardiac output (CO), heart rate (HR), systemic blood pressures, and carotid blood flow in six healthy volunteers.

Materials and methods:

Six healthy male volunteers aged 18–65 years were randomized to receive 1L NS given over 30 min or 120 min. On a subsequent study session the alternate fluid regimen was administered. Haemodynamic data was gathered using a non-invasive finger arterial pressure monitor (Nexfin®), echocardiography and carotid duplex sonography. Time to micturition and urine volume was also assessed.


Compared to baseline, rapid infusion of 1 L of saline over 30 min produced a fall in Nexfin®-measured CO by 0.62 L/min (p < 0.001), whereas there was a marginal but significant increase during infusion of 1L NS over 120 min of 0.02 L/min (p < 0.001). This effect was mirrored by changes in HR and blood pressure (BP) (p < 0.001). There were no significant changes in carotid blood flow, time to micturition, or urine volume produced.


Slower infusion of 1L NS in healthy male volunteers produced a greater increase in CO, HR and BP than rapid infusion.

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