S-Nitrosohemoglobin Levels and Patient Outcome After Transfusion During Pediatric Bypass Surgery

Abstract

Banked blood exhibits impairments in nitric oxide (NO)-based oxygen delivery capability, reflected in rapid depletion of S-nitrosohemoglobin (SNO-Hb). We hypothesized that transfusion of even freshly-stored blood used in pediatric heart surgery would reduce SNO-Hb levels and worsen outcome. In a retrospective review (n = 29), the percent of estimated blood volume (% eBV) replaced by transfusion directly correlated with ventilator time and inversely correlated with kidney function; similar results were obtained in a prospective arm (n = 20). In addition, an inverse association was identified between SNO-Hb and postoperative increase in Hb (∆Hb), reflecting the amount of blood retained by the patient. Both SNO-Hb and ∆Hb correlated with the probability of kidney dysfunction and oxygenation-related complications. Further, regression analysis identified SNO-Hb as an inverse predictor of outcome. The findings suggest that SNO-Hb and ∆Hb are prognostic biomarkers following pediatric cardiopulmonary bypass, and that maintenance of red blood cell-derived NO bioactivity might confer therapeutic benefit.

Figure 1

Transfusion, tissue oxygenation, and organ function. (a) The % eBV replaced by intraoperative transfusion was inversely correlated with kidney StO₂ at the end of surgery (n = 20; r = –0.722, P = 0.0003). (b) There was no correlation between kidney StO₂ and arterial blood oxygen content (r = –0.122, P = 0.651). (c) Scatterplot depicts the inverse correlation between eGFR and % eBV replaced (r = –0.533, P = 0.015).

Figure 2

SNO‐Hb, CPB, and transfusion. (a) Circulating RBC SNO‐Hb concentrations in pediatric patients (n = 20; group means are designated by the bars) at various procedural points before, during, and after CPB. SNO‐Hb levels increased after going on bypass and continued to rise into the postoperative period. *Significant difference compared with baseline, P < 0.05, as determined by repeated‐measures ANOVA followed by Dunnet's test. (b) There was no relationship between SNO‐Hb levels and % eBV replaced. (c) The increase in SNO‐Hb correlated inversely with the magnitude of the pre‐to‐posttransfusion increase in Hb (∆Hb) (r = –0.573, P = 0.010). Retention of more blood (i.e., greater increase in postop Hb) was thus associated with lower SNO‐Hb.

Figure 3

Oxygenation‐related complications. (a) Table enumerating the oxygenation‐related complications. (b) A scatterplot depicting the weak correlation between % eBV replaced and probability of complications (n = 20, r = 0.392, P = 0.08). (c) ∆Hb demonstrates a positive correlation with probability of complications (n = 20, r = 0.587, P = 0.008). (d) SNO‐Hb has a negative correlation with probability of complications (n = 20, r = –0.695, P = 0.0007).