Hyperchloremic metabolic acidosis after cardiac surgery

Background

Hyperchloremic metabolic acidosis (HCMA) after cardiac surgery is iatrogenic and is due to large volumes of saline infused perioperatively [1]. The aim of the study was to determine the incidence, the clinical implications and the duration of this acid–base disorder in cardiac surgery.

Methods

One hundred patients who underwent cardiac surgery with cardiopulmonary bypass (CPB) were included prospectively. Exclusion criteria were: diabetes mellitus, pre-existing acid–base abnormalities, postoperative renal failure or low cardiac output syndrome. All patients received crystalloid (0.9% saline or Ringer's) and colloid solutions (gelatin). Sampling of arterial blood for gas, acid–base parameters and serum electrolytes were performed at four time points: 30 min after induction of anesthesia (T1), after completion of CPB (T2), at 6 hours (T3) and at 24 hours postoperatively (T4). Values are given as the mean ± SD. We registered the volume of solutions administered intraoperatively and in the first 24 hours postoperatively as well as complications: bleeding, cardiac arrhythmias and organ dysfunctions. (renal, pulmonary or neurological). For statistical analysis we used a t test (P < 0.05).

Results

Sixty-six patients (66%) presented a simple normal-anion gap hyperchloremic acidosis. Twenty-seven patients had no acidosis. The results of the arterial blood sampling are presented in Table 1. The infused volumes are presented in Table 2.

Table 1.

	T1	T2	T3	T4
Chloride (mmol/l)	103 ± 3.5	113 ± 5.1	111.8 ± 3.6	108.5 ± 4.1
pH	7.4 ± 0.04	7.34 ± 0.06	7.35 ± 0.06	7.4 ± 0.03
paCO2 (mmHg)	37.2 ± 5.01	34.8 ± 4.5	37.3 ± 5.9	37.5 ± 4.6
Base excess (mmol/l)	-1.4 ± 1.2	-5.9 ± 2.1	-6.33 ± 2.3	-0.9 ± 3.5
Bicarbonate (mmol/l)	22.7 ± 2.0	19.2 ± 1.8	20.6 ± 3.7	23.8 ± 2.9
Anion gap (mmol/l)	11.4 ± 3.1	8.4 ± 2.1	12.7 ± 2.5	10.6 ± 2.9

Table 2.

	Intraoperative (ml)	Postoperative (ml)
Crystalloids	2680 ± 853	1687 ± 696
Colloids	500 ± 254	805 ± 420
Bicarbonate	40 ± 15	35 ± 25
Tromethamol	0	613 ± 156

Cardiac arrhythmias were more frequent in patients with HCMA compared with those with no acidosis. There were no statistical differences in the incidence of bleeding or organ dysfunctions.

Conclusion

HCMA due to saline infusion is common after cardiac surgery. However it is transient (less than 24 hours). Due to the low number of patients in our study, the clinical relevance of this metabolic acidosis is not clear. The major risk is of undesirable interventions.