Safety of warfarin dosing in the intensive care unit following the Fontan procedure.

OBJECTIVE

To determine the incidence of supratherapeutic international normalized ratio (INR) values in patients initiated on warfarin in the pediatric intensive care unit after the Fontan procedure.

DESIGN

Retrospective chart review.

SETTING

Pediatric intensive care unit in a freestanding pediatric teaching hospital.

PATIENTS

Thirty-two consecutive children with single ventricle physiology with an initial Fontan conversion. All were initiated on warfarin in the postoperative period while in the intensive care unit.

OUTCOME MEASURES

Supratherapeutic INR values, interventions in warfarin dosing to address or prevent supratherapeutic INR values, major and minor bleeding episodes, and venous thromboembolic events.

RESULTS

Supratherapeutic INR values after warfarin initiation occurred in 12.5% (n = 4) of patients with an additional 6.3% (n = 2) requiring dose adjustments due to a rapidly increasing INR. Patients with a supratherapeutic INR were started on warfarin earlier compared with other patients (median postoperative day 2 vs. 5, P = .037, respectively). There were no reported thrombi or thromboembolic events and the only clinically significant bleeding event occurred while the INR value was subtherapeutic.

CONCLUSIONS

Patients undergoing the Fontan procedure may be more sensitive to warfarin dosing when initiated closer to the surgical procedure date. Despite this observation, warfarin appears to be a safe medication for use within the early postoperative period after the Fontan procedure when response to therapy is monitored closely. Clinicians should use caution when initiating warfarin before postoperative day 3 in patients undergoing an initial Fontan operation.