CANNULATION of an artery for frequent blood gas analysis, hemodynamic studies and continuous pressure monitoring is becoming a routine part of the care of the critically ill patient. In our experience the usual methods for cannulation of the femoral, brachial, ulnar and radial arteries have been unsatisfactory for prolonged use because of leakage, thrombosis in the cannula and ischemia. Ideally, the arterial cannula should remain patent for three days or more without leaking, permit free movement of the patient, not embarrass the arterial supply distal to the site of cannulation, even if the vessel thromboses at that level, and be . . .