Metabolic Alkalosis in the Pediatric Cardiac Intensive Care Unit-A Prospective Observational Study

Metabolic alkalosis in pediatric patients following cardiac surgery warrants a comprehensive study. Newer methods of arterial blood gas (ABG) assessment can offer more insights into the mechanisms behind such derangement.

To study the incidence of metabolic alkalosis in postsurgical infants admitted to the pediatric cardiac intensive care unit and analyze factors associated with its development and its effect on prognosis.

Prospective observational study.

Tertiary care teaching hospital in India during 2020-2021.

One hundred four infants < 1 year of age undergoing elective cardiac surgery and who required more than 6 h of postoperative mechanical ventilation were included. Infants on preoperative mechanical ventilation or with metabolic alkalosis were excluded.

Incidence of metabolic alkalosis and causative preoperative, intraoperative, and postoperative factors were studied along with their morbidity profile.

Metabolic alkalosis was detected in 23 (22.1%) subjects. In group MA (who developed metabolic alkalosis), 73.9% of infants belonged to risk adjustment for congenital heart surgery-1 (RACHS-1) category 3 and above (p = 0.009). They also had longer cardiopulmonary bypass time (200.04 ± 83.35 min vs. 144.59 ± 64.77; 95% confidence interval of the difference in means [23, 87.9]), longer cross-clamp time (119.78 ± 63.12 min vs. 84.95 ± 48.8; 95% CI [10.4, 59.3]), greater application of modified ultrafiltration (MUF) (91.3% vs. 60.5%, p = 0.005), and larger volume of MUF removed (60 (44.4, 70) ml kg^-1 vs. 44.44 (32.9, 54.3), p = 0.003). Partitioning of base excess showed similar standard base excess due to free water (SBE_FW) (MA -0.18 ± 0.94 vs. No MA 0.25 ± 1.1; confidence interval of the difference in means [-0.95, 0.09]) and due to chloride (SBE_Cl) (MA -5.7 ± 4.8 vs. No MA -5.18 ± 5.05; 95% CI [-2.9, 1.8]) in both groups. A longer period of ventilation, intensive care unit stay, and hospital stay were found in group MA.

This prospective study on postcardiotomy infants revealed a much lower incidence of metabolic alkalosis than historical data. Physicochemical analysis of the blood samples for mechanisms underlying metabolic alkalosis found that its development is not entirely dependent on overt volume depletion or significant chloride loss. The administration of chloride-containing solutions appears to mitigate both the occurrence and severity of metabolic alkalosis.