The strong ion gap predicts mortality in children following cardiopulmonary bypass surgery.
OBJECTIVE
Stewart's strong ion theory quantifies unmeasured tissue acids produced following hypoxia or hypoperfusion, by calculation of the strong ion gap. Our study objectives were as follows: a) to determine the 24-hr profile of the strong ion gap following cardiopulmonary bypass surgery; and b) to compare the prognostic value in terms of intensive care unit mortality of this variable with blood lactate.


METHODS
Prospective, observational study.


METHODS
Tertiary pediatric intensive care unit.


METHODS
Eighty-five children following surgery for congenital heart disease.


METHODS
None.


RESULTS
Arterial blood samples for lactate and strong ion gap calculation were obtained at intensive care unit admission and at 24 hrs. A raised strong ion gap (>3 mEq/L) was present in 41.1% and 51.7% of admission and 24-hr samples, respectively, being elevated at both time points in 30.5%. Both the strong ion gap and lactate increased with surgical complexity, but neither was correlated with length of bypass (r = .13 and -.02) or aortic cross-clamp (r = .13 and .10). The crude mortality was 5.8% (5/85). Four of the five deaths were associated with a persistently elevated strong ion gap, in contrast to two with ongoing hyperlactatemia (>2 mmol/L). The admission strong ion gap (cutoff, >3.2 mEq/L) was superior to lactate (cutoff, >3.0 mmol/L) as a mortality predictor (area under receiver operating characteristic curve of 0.85 [95% confidence interval, 0.74-0.95] vs. 0.71 [95% confidence interval, 0.44-0.98], respectively).


CONCLUSIONS
An elevated strong ion gap occurs commonly following bypass surgery and appears to be superior to lactate as a mortality predictor.
Durward
Andrew
A
Department of Pediatric Intensive Care, Guy's Hospital, London, United Kingdom.
Tibby
Shane M
SM
Skellett
Sophie
S
Austin
Conal
C
Anderson
David
D
Murdoch
Ian A
IA
D000136:Acid-Base Equilibrium; D000140:Acidosis, Lactic / Q000209:etiology; D002315:Cardiopulmonary Bypass / Q000009:adverse effects* / Q000401:mortality*; D002675:Child, Preschool; D006330:Heart Defects, Congenital / Q000401:mortality* / Q000601:surgery*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D015278:Intensive Care Units, Pediatric; D019344:Lactic Acid / Q000097:blood; D011182:Postoperative Care; D011237:Predictive Value of Tests; D011446:Prospective Studies
D019344:Lactic Acid