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Abstract

Introduction: Originally, the casual mechanism for the acidosis occurs after fluid challenges with normal saline was ascribed to the dilution of bicarbonate. Differently, Stewart approach explains that as due to a change in the strong ion difference. In the present study, we aimed to compare the acid base changes elicited by 2 crystal fluids: normal saline and sodium octanoate solution which does not generate bicarbonate through the Krebs cycle immediately after infusion like those commercially available balanced solutions such as Ringer’s lactate solution. Hypothesis: We hypothesized that sodium octanoate fluid infusion will not change acid base status while normal saline will, although the two fluids were given in identical volume and no complementary bicarbonate would be produced. Methods: We conducted a cross-over animal study in eight female Merino ewes. After baseline measurement, animals were randomly assigned to receive a rapid intravenous infusion (1L in half an hour) of either normal saline or sodium octanoate solution. Additional arterial blood samples were collected at 0.5, 1, 2, 4, 6 hours after the start of the infusion for blood gas analyses and biochemical measurements. Hemodynamic profiles were recorded continuously before and after the infusion. Results: Animals in the normal saline group developed metabolic acidosis on delivery of the fluid (pH from 7.48 to 7.42), while no acidosis could be detected in the octanoate group (pH from 7.47 to 7.50). The octanoate group also showed higher strong ion difference (36.2 mEq/l vs. 32.7 mEq/l). Additionally, the octanoate group showed a much higher peak global renal blood flow (209.0 ± 36.3 ml/min vs. 171.1 ± 28.2 ml/min, P<0.05) after infusion, although no difference could be seen in terms of cardiac output between the two groups. Conclusions: Our findings provide evidence that the acidosis induced by crystalloids like saline is not due to dilution but to changes in strong ion difference. Once a solution is given with a chloride substitute (octanoate) which can be removed rapidly from the circulation but does not generate large amount of bicarbonate immediately, this difference is clear and can only be logically explained according to the Stewart methodology.