The strong ion gap and outcome after cardiac arrest in patients treated with therapeutic hypothermia: a retrospective study.

OBJECTIVE: This study investigates whether the strong ion gap (SIG) is associated with long-term outcome after cardiac arrest in patients treated with therapeutic hypothermia. The hypothesis of the study was that an elevated SIG was associated with unfavourable outcome after cardiac arrest.

DESIGN: Retrospective review of records from 1995 to 2007 of patients who received cardiopulmonary resuscitation.

SETTING: Emergency department of a university hospital.

PATIENTS: Patients who were successfully resuscitated after cardiac arrest (n = 288) and treated with mild therapeutic hypothermia.

INTERVENTIONS: None.

MEASUREMENTS AND RESULTS: Acid-base variables were calculated according to Stewart's approach, as modified by Figge and Fencl, and were determined immediately on admission and 12 h after the return of spontaneous circulation. Acid-base variables were determined at 37 degrees C and are reported without correction for patient temperature. Differences in SIG were compared between patients with favourable (survival 6 months with cerebral performance category 1 or 2) and unfavourable outcomes. SIG on admission and 12 h after return of spontaneous circulation was higher in patients with unfavourable outcome (n = 151; 52%). SIG 12 h after return of spontaneous circulation was identified as an independent predictor of outcome. A SIG > 8.9 mmol/L was associated with an increased cumulative hazard of death.

CONCLUSIONS: An elevated SIG 12 h after return of spontaneous circulation may be associated with unfavourable outcome in patients after cardiac arrest treated with mild therapeutic hypothermia. The unmeasured anions hidden behind an elevated SIG may represent markers of tissue damage.