Elevated Pulmonary Dead Space and Coagulation Abnormalities Suggest Lung Microvascular Thrombosis in Patients Undergoing Cardiac Surgery

Objective: Inflammation has been shown to trigger microvascular thrombosis. Patients undergoing cardiac surgery sustain significant inflammatory insults to the lungs and in addition are routinely given anti-fibrinolytic agents to promote thrombosis. In view of these risk factors we investigated if evidence of pulmonary microvascular thrombosis occurs following cardiac surgery and, if so, whether a pre-operative heparin infusion may limit this.

Design: Double-blind randomised controlled trial.

Setting: Tertiary university affiliated hospital.

Patients: Twenty patients undergoing elective cardiac surgery.

Interventions: Patients were randomised to receive a pre-operative heparin infusion or placebo. All patients were administered aprotinin.

Measurements And Results: Pulmonary microvascular obstruction was estimated by measuring the alveolar dead-space fraction. Pulmonary coagulation activation was estimated by measuring the ratio of prothrombin fragment levels in radial and pulmonary arterial blood. Systemic tissue plasminogen activator (t-PA) levels were also assessed. In the placebo group cardiac surgery triggered increased alveolar dead-space fraction levels and the onset of prothrombin fragment production in the pulmonary circulation. Administration of pre-operative heparin was associated with a lower alveolar dead-space fraction (p < 0.05) and reduced prothrombin fragment production in the pulmonary circulation (p < 0.05). Pre-operative heparin also increased baseline t-PA levels (p < 0.05).

Conclusion: The changes in the alveolar dead-space fraction and pulmonary coagulation activation suggest that pulmonary microvascular thrombosis develops during cardiac surgery and this may be limited by a pre-operative heparin infusion.