Date Published: April 5, 2017
Publisher: Public Library of Science
Author(s): Angélique M. E. Spoelstra–de Man, Annemieke Smorenberg, A. B. Johan Groeneveld, Kathrin Eller.
Fluid administration in critically ill patients may affect acid-base balance. However, the effect of the fluid type used for resuscitation on acid-base balance remains controversial.
We studied the effect of fluid resuscitation of normal saline and the colloids gelatine 4%, hydroxyethyl starch (HES) 6%, and albumin 5% on acid-base balance in 115 clinically hypovolemic critically ill patients during a 90 minute filling pressure-guided fluid challenge by a post-hoc analysis of a prospective randomized clinical trial.
About 1700 mL was infused per patient in the saline and 1500 mL in each of the colloid groups (P<0.001). Overall, fluid loading slightly decreased pH (P<0.001) and there was no intergroup difference. This mildly metabolic acidifying effect was caused by a small increase in chloride concentration and decrease in strong ion difference in the saline- and HES-, and an increase in (uncorrected) anion gap in gelatine- and albumin-loaded patients, independent of lactate concentrations. In clinically hypovolemic, critically ill patients, fluid resuscitation by only 1500–1700 mL of normal saline, gelatine, HES or albumin, resulted in a small decrease in pH, irrespective of the type of fluid used. Therefore, a progressive metabolic acidosis, even with increased anion gap, should not be erroneously attributed to insufficient fluid resuscitation. ISRCTN Registry ISRCTN19023197
In shock, tissue hypoperfusion and concomitantly lactic acidosis can be treated with fluid administration. However, the type of fluid used for resuscitation in critically ill patients may also affect acid-base balance and can decrease blood pH. The mechanisms and short-term effects among the various fluids of this post infusion or dilution acidosis in clinical practise are largely unknown. This could lead to erroneous conclusions when blood pH is regarded as a marker of evalutating hypovolemia and tissue hypoxia . The effects of fluid types on acid base status are evaluated using the anion gap according to Henderson-Hasselbalch and the strong ion difference (SID) according to Stewart (Fig 1) . The anion gap is influenced by the change in (unmeasured) ions, and increases in the presence of a toxine, lactate, or ketoacids. The SID indicates the difference between strong cations and anions and is influenced by the total plasma concentration of weak non-volatile acids (Atot). It decreases with an increase in unmeasured anions and concomintant acidosis. The difference between sodium and chloride concentration has been shown to correlate good with the SID and corrected anion gap as a measure for the strong ion gap [3,4].
This study was a post hoc analysis of a prospective, stratified, randomized, single blinded and single centre clinical trial concerning the effect of various fluid types in critically ill patients. We studied four groups of patients based upon fluid type given: with saline, gelatine, hydroxyethyl starch or albumin. The primary goal of this trial was to study the pulmonary and cardiac effects of crystalloid and colloid fluid loading in various patient subgroups. In succession, we included patients after cardiac and vascular surgery, with sepsis and other major surgery (S1 and S2 Text). The first part of the study encompassed the inclusion of 68 patients undergoing cardiac and major vascular surgery [22–25]. For the second stage 24 septic patients and 24 patients with major surgery were included [26–28]. For the current analysis, all patients were taken together and analysed based upon fluid type administered. Previous data has been published regarding the prediction of fluid responsiveness [24,25,28] and the cardiac and pulmonary effects of fluid loading in cardiac and major vascular surgery [22,23] and in septic and non-septic patients [24,25] when inclusion in one patient cohort after the other had been completed. This explains publications dated before the end of the complete study.
116 patients were enrolled in the study. 1 patient was excluded due to technical failures and 115 patients were included in the final analysis. Patient characteristics are listed in Table 1. Groups were comparable. Fourteen patients died in the ICU (cardiac surgery: 1, vascular surgery: 1, sepsis: 9, trauma: 3). There were no signs of significant bleeding as blood drainage was < 50 mL/h in all patients. Plasma volume expansion differed between fluid types and was lower in saline compared to colloid fluid loading (P<0.001). In this study in clinically hypovolaemic, critically ill patients, fluid loading of about 1.5–1.7 L only had a mildly metabolic acidifying effect, irrespective whether normal saline, gelatine, HES or albumin was used. This can be attributed to a small increase in chloride concentration in saline- and HES-, and in corrected anion gap in gelatine- and uncorrected anion gap in albumin-loaded patients, independent of lactate concentrations. In our study of clinically hypovolemic, critically ill patients, fluid resuscitation by only 1.5–1.7 L of normal saline, gelatine, HES or albumin, resulted in a small decrease in pH, irrespective of the type of fluid used, due to a small increase in chloride concentration in saline- and HES-, and in (uncorrected) anion gap in gelatine- and albumin-loaded patients. The latter was independent of lactate concentrations. Therefore, progressive metabolic acidosis should not be simply attributed to inadequate fluid resuscitation, even with an increased anion gap and application of relatively small volumes. Source: http://doi.org/10.1371/journal.pone.0174507