Abstract
Background & Objectives: The administration of crystalloid fluid therapy for resuscitation, to restore euvolaemia, and/or improve cardiac output (CO) is perhaps the most frequent therapeutic intervention in medicine. Several studies based on mathematical modelling of volume kinetics have suggested that the effect of a fixed volume of intravenous fluid varies considerably with baseline hydration state, rate of fluid infusion and the presence or absence of anaesthesia.[i],[ii],[iii] It has been demonstrated that the degree of plasma expansion produced by the same volume of IV crystalloid is greater with a lower rate of infusion, and more prolonged with longer duration of infusion.[ii] This pilot study aims to characterize the effect of 1L of IV normal saline (NS) administered in a bolus versus continuous infusion on CO, heart rate (HR), and systemic blood pressures in 7 healthy volunteers. We hypothesize that an infusion of 1L of NS given over 120 minutes will produce a more sustained increase in CO when compared to a rapid bolus given over 30 minutes. Materials & Methods: Seven healthy male volunteers between aged 18–65 years participated in 2 experiments each on separate days where 1L NS was given either over 30min or 120min. Haemodynamic data was gathered using a non-invasive finger arterial pressure monitor. Results: When compared to baseline, rapid infusion of 1L of saline over 30 min produced a fall in CO by 0.62L/min (p<0.0001), whereas there was a marginal but significant increase in CO during infusion of 1L NS over 120min of 0.02L/min (p<0.0001). The difference in CO between the groups was also significant with a higher CO seen in the infusion group (p<0.0001) (Figure 1). This effect was mirrored by changes in systolic blood pressure (SBP) measurements for each group (p<0.0001).Conclusion: Continuous infusion of 1L NS in healthy male volunteers produced a greater increase in both SBP and CO than rapid infusion, which produced a paradoxical fall in both of these haemodynamic parameters.
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