The significance of creatine kinase in cardiac patients with acute limb ischaemia.

OBJECTIVE: The value of creatine kinase (CK) and aspartate transaminase (AST) has not been previously evaluated following cardiac surgery in the diagnosis of acute limb ischaemia. Our objective was to assess the value of CK and AST with reference to the diagnosis of limb ischaemia, effect on renal function and prognosis following cardiac surgery.

DESIGN: all patients entering ICU had daily CK and AST measurements over a two -year period. A retrospective study of patients with CK values >5,000 U/L was performed.

SETTING: adult intensive care unit of a secondary and tertiary referral centre for cardiothoracic surgery with on site facilities for vascular surgery.

PATIENT: twenty-seven patients had CK values greater than 5,000 U/L. A further random sample of 35 patients, with no limb ischaemia were used to give medians for CK and AST following cardiac surgery.

INTERVENTIONS: twelve of twenty-seven (44%) patients were noted to have acutely ischaemic limbs; 6 of these (CK>16,000 U/L) underwent surgical intervention.

MEASURES: serum levels of CK, Peak CK, AST, Peak AST and CK/AST ratios. Related to procedure and outcome in terms of mortality and morbidity including, acute limb ischaemia defined on clinical grounds and renal failure defined as creatinine >200 pmoles/L.

RESULTS: The median values for CK and AST immediately following uncomplicated cardiac surgery were 135 (IQR 36-383) and 43 (IQR 26-58) respectively. Median CK for the patients (CK>5,000) without clinical ischaemia was 7,440 U/L compared to the group with ischaemia 17,472 U/L (p<0.05). Renal failure developed in 48% of all patients. Eight of the 9 patients with CK>15,000 developed renal failure compared to 5 of the 13 with CK 5,000-15,000 U/L (p<0.01). 30% of patients underwent haemofiltration; of these, 87% died. For patients with ischaemia peak CK and creatinine correlated. (r = 0.83, p<0.05) Day of peak CK and peak AST correlated (r = 0.92, p<0.01). Logged values of CK with log values of AST showed a highly significant relationship (beta = 1.16, p<0.001). The overall mortality was 33%.

CONCLUSIONS: PATIENTs who develop limb ischaemia following cardiac surgery have a high morbidity and mortality. A CK of 17,000 U/L (5667-46539) is indicative of serious limb ischaemia. Renal failure is likely to develop in patients with CK>15,000 U/L. AST may become a useful additional marker of limb ischaemia.