Hyperchloraemic metabolic acidosis following open cardiac surgery

Mark Hatherill ^1*, Shamiel Salie ¹, Zainab Waggie ¹, John Lawrenson ¹, John Hewitson ¹, Louis Reynolds ¹ and Andrew Argent ¹

¹ University of Cape Town, South Africa

^* To whom correspondence should be addressed. E-mail: mark{at}rmh.uct.ac.za.

Accepted 1 September 2005

Abstract

Objectives:To describe acid-base derangements in children following open cardiac surgery on cardiopulmonary bypass (CPB), using the Fencl-Stewart strong ion approach.

Methods:Prospective observational study set in the paediatric intensive care unit (PICU) of a university children's hospital. Arterial blood gas parameters, serum electrolytes, strong ion difference, strong ion gap (SIG), and partitioned base excess (BE) were measured and calculated on admission to PICU.

Results:97 children, median age 57 months (0.03- 166), median weight 14 kg (2.1-50), were studied. Median CPB time was 80 min (17-232). Predicted mortality was 2% and there was a single nonsurvivor. These children demonstrated mild metabolic acidosis (median standard bicarbonate 20.1 mmol/L and BE -5.1 mEq/L) characterised by hyperchloraemia (median corrected Cl 113 mmol/L), and hypoalbuminaemia (median albumin 30 g/L), but no significant excess unmeasured anions or cations (median SIG 0.7 mEq/L). The major determinants of the net BE were the chloride and albumin components (chloride effect -4.8 mEq/L and albumin effect +3.4 mEq/L). Metabolic acidosis occurred in 72 children (74%) but was not associated with increased morbidity. Hyperchloraemia was a causative factor in 53 children (74%) with metabolic acidosis. Three (4%) hyperchloraemic children required adrenaline for inotropic support, compared to 8 children (28%) without hyperchloraemia (p=0.005). Hypoalbuminaemia was associated with longer duration of inotropic support (p=0.047) and PICU stay (p=0.009).

Conclusions:In these children with low mortality following open cardiac surgery, hypoalbuminaemia and hyperchloraemia were the predominant acid-base abnormalities. Hyperchloraemia was associated with reduced requirement for adrenaline therapy. We suggest that hyperchloraemic metabolic acidosis is a benign phenomenon that should not prompt escalation of haemodynamic support. By contrast, hypoalbuminaemia, an alkalinizing force, was associated with prolonged requirement for intensive care.

Keywords: acidosis, cardiac surgery, chloride, strong ion

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