Hyperchloraemic metabolic acidosis following open cardiac surgery

Abstract

Aims: 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: A total of 97 children, median age 57 months (range 0.03-166), median weight 14 kg (range 2.1-50), were studied. Median CPB time was 80 minutes (range 17-232). Predicted mortality was 2% and there was a single non-survivor. These children showed mild metabolic acidosis (median standard bicarbonate 20.1 mmol/l, BE 25.1 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 24.8 mEq/l, 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 eight children (28%) without hyperchloraemia. Hypoalbuminaemia was associated with longer duration of inotropic support and PICU stay. 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. It is suggested that hyperchloraemic metabolic acidosis is a benign phenomenon that should not prompt escalation of haemodynamic support. By contrast, hypoalbuminaemia, an alkalinising force, was associated with prolonged requirement for intensive care.

Hydrogen ion concentration and coronary artery bypass graft surgery with and without cardiopulmonary bypass

“…A TOT is mainly composed of albumin as the principal extracellular weak acid [17]. During CPB, patients develop a dilutional hypoalbuminaemia as a result of intravascular fluid administration [10,11,18]. This hypoalbuminaemia induces a metabolic alkalosis, which counteracts the acidosis induced by the administration of intravascular fluids [7,10].…”

The base excess gap is not a valid tool for the quantification of unmeasured ions in cardiac surgical patients

“…On the basis of the modern ion selective method, 20,21,26 the following reference values for strong electrolytes and weak acids were adopted: Na 140 mmol l À1 , K 4 mmol l À1 , Cl 108 mmol l À1 , Ca 2.3 mmol l À1 , Mg 0.8 mmol l À1 , lactate 1.5 mmol l À1 , albumin 42 g l À1 and phosphate 1.2 mmol l À1 . Therefore, according to Eqs.1 to 6, the value of SIG at reference state equals to 2.85 meq l À1 and the deviation of the observed SIG from its reference value can be expressed as:…”

“…11 Importantly, several authors have suggested a significant relationship between the concentration of unmeasured anions as assessed by SIG and mortality in critically ill patients. [16][17][18][19][20][21] These efforts capitalized on extensive theoretical work, which has disclosed the quantitative interlinking between the base excess and the SID theory. In order to provide the clinician with easy-to-use tools for the assessment of acid-base equilibrium and, in particular the unmeasured ions, several authors have attempted to unify the SID and the base excess approach.…”

“…In order to provide the clinician with easy-to-use tools for the assessment of acid-base equilibrium and, in particular the unmeasured ions, several authors have attempted to unify the SID and the base excess approach. [19][20][21] Generally, we can write: [22][23][24][25][26] It should be remembered that by definition, the base excess represents the deviation of the metabolic acid-base status from its reference state.…”

Postoperative Compensatory Ammonium Excretion Subsequent to Systemic Acidosis in Cardiac Patients

“…Lactic acidosis might also develop during the operative and postoperative course depending on different parameters like CPB and cross-clamp duration and postoperative hemodynamic status [1, 5, 6]. Nonetheless, acid-base imbalances are present not only during the operation but also commonly in the postoperative phase, which are then of all sorts, with acidosis prevailing [1, 7, 8]. Severe manifestation causes, among others, impairments of the cardiovascular system with concomitant systemic consequences [9–11].…”