Iodine toxicity secondary to continuous povidone-iodine mediastinal irrigation in dogs

Abstract

Mediastinitis is a devastating complication following median sternotomy. Continuous povidone-iodine (PVP-I) irrigation has been advocated as therapy because of its broad antimicrobial spectrum and its apparent safety. However, several recent clinical reports have warned of suspected local and systemic iodine toxicity. The purpose of this study is to determine if significant amounts of iodine can be absorbed systemically via the mediastinum, and if so, what toxicity (local and/or systemic) may result. PVP-I (0.5%) was continuously irrigated into the pericardial sacs of three dogs via catheters for 48 hr. Serial serum and urine iodine levels were determined. The serum steady-state concentration ( C 88), the rate elimination constant ( k), the urinary clearance (Cl), and the serum half-life ( t 1 2 ) for iodine were assessed. Serum electrolytes, Bun, Cr, and arterial pH were measured to assess systemic iodine toxicity. Tissue samples of the heart, pericardium, liver, and kidney were examined histologically for evidence of local or end organ iodine toxicity. This study demonstrated that the absorption of iodine during continuous mediastinal irrigation with PVP-I follows zero-order pharmacokinetics, just as if it were being given by continuous intravenous infusion. The baseline serum iodine concentration was 145.9 ± 64.3 μg/dl, C 88 was 29,290 ± 101.4 μg/dl, k was 0.0996 ± 0.009/hr, Cl was 872.4 ± 119.3 ml/hr, and t 1 2 was 6.22 hr. Urinary excretion of iodine increased in proportion to the serum iodine. Measured serum chloride increased in a linear manner ( r = 0.949), while serum Na, K. Bun, Cr, and pH were unchanged. Histological sections of the pericardium and the heart showed marked acute inflammation and fat necrosis in the epicardial adipose tissue and the subepicardial myocardium; the kidney and the liver were normal. We conclude that during continuous PVP-I irrigation of the mediastinum, free iodine is absorbed in significant quantities and a severe chemical pericarditis is produced. Continued clinical use of this technique is cautioned.