Fluid Management After Congenital Cardiac Surgery: The Good, the Bad, and the Indifferent*

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Fluid management remains one of the central tasks following congenital cardiac surgery, while the causes and clinical impact of fluid overload (FO) remain unclear. For example, the adverse effects of cardiopulmonary bypass (CPB) on vascular integrity and the development of a vascular leak syndrome may necessitate the administration of volume to maintain adequate cardiac output, whereas patients with systolic heart failure and pulmonary edema may require aggressive diuresis to maintain adequate cardiopulmonary function. In this issue of Pediatric Critical Care Medicine, Delpachitra et al (1) conducted a case-control study of 182 subjects (46 subjects in the study group; inclusion: all mortalities; 136 subjects in the control group; inclusion: children 0–16 yr old undergoing cardiac surgery and admitted to the PICU directly from the operating room) to further assess the association between postoperative FO and clinical outcomes. The primary aim was to study the association between FO and mortality. The secondary aims studied the association between fluid balance and duration of mechanical ventilation, ICU length of stay (LOS), and hospital LOS. This study (1) was completed in the ICU at the Royal Children’s Hospital in Melbourne, a large, tertiary pediatric cardiac center in Australia performing over 600 operations per year.
With regard to the primary outcome, in multivariable analysis, an increase in cumulative fluid greater than or equal to 5% during the first 7 days following surgery did not find an association between FO and mortality (odds ratio [OR], 0.95; 95% CI, 0.87–1.04; p = 0.30); however, the analysis of the secondary outcomes demonstrated that an increase in cumulative fluid greater than or equal to 5% by day 2 was associated with a longer duration of mechanical ventilation (211 hr [interquartile range (IQR), 97–539]; p < 0.001), longer ICU LOS (11 d [IQR, 8–26]; p < 0.01), and longer hospital LOS (22 d [IQR, 13–39]; p = 0.01). In addition, the authors identified that the late implementation of peritoneal dialysis (PD) after cardiac surgery (OR, 3.65; 95% CI, 1.21–10.99; p = 0.02) was associated with increased mortality.
This study (1) as well as several other studies demonstrate that the development of FO after congenital cardiac surgery is strongly associated with worse outcomes (2–5). However, weighing the importance and implications of these findings is challenging, given the interdependence between FO, comorbidities, and outcomes. This is compounded by our lack of complete understanding of the etiology of FO. The traditionally described mechanism of CPB induced increased vascular leak, leading to third spacing of fluid, and increased fluid requirement is imprecise. Many efforts have been made to distinguish other plausible mechanisms that may contribute to FO, including inflammation, impaired renal and cardiac function, and decreased diuretic response (6, 7). The current study (1) also highlights the potential benefits of early PD. In addition to removing fluid and solutes, PD removes inflammatory mediators, which may be of benefit (8). However, it is not entirely clear if early implementation of PD is advantageous with recently published studies presenting conflicting findings (9, 10).
We identified some limitations to this study (1). The selection of mortality as the primary outcome is challenging and perhaps less informative, particularly, since mortality rates in congenital cardiac surgery are very low outside of patients undergoing single ventricle palliation. Thus, the required study sample size based on mortality is prohibitively large to conduct in a single institution. More relevant to the intensivist may be the analysis of outcomes after stratification of patients by specific physiology.

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