Pressure and Flow Characteristics of a Novel Bidirectional Cannula for Cardiopulmonary Bypass.

OBJECTIVE: Femoral arterial cannulation is associated with a significant risk of lower limb ischemia. The aim of the study was to assess the pressure and flow in the femoral artery using a novel bidirectional femoral cannula in a sheep model of peripheral cardiopulmonary bypass. METHODS: Peripheral cardiopulmonary bypass was established using a multistage venous cannula inserted into the internal jugular vein and the bidirectional or a conventional arterial cannula into the femoral artery in seven adult ewes. Systemic and distal perfusion pressures and flow rates were measured during cardiopulmonary bypass with flow rates of 1, 2, 3, and 4 L/min. Lower limb venous oxygen saturation and lactate levels were also measured. RESULTS: A significantly higher blood flow in the lower limb using the bidirectional cannula was observed and compared with a conventional cannula at all flow rates (mean flow 115 mL/min vs 10 mL/min, P < 0.05). The mean distal perfusion pressure was also significantly higher in the bidirectional cannula group (86 mm Hg vs 45 mm Hg at 4 L/min of flow, P < 0.05). The bidirectional cannula was associated with higher venous oxygen saturations in the lower limb than in the conventional cannula group; however, lower limb lactate production was similar in the two groups. CONCLUSIONS: This in vivo data demonstrates superior distal flow and pressure characteristics of a novel bidirectional cannula compared with a conventional femoral cannula during peripheral cardiopulmonary bypass.

Transesophageal Echocardiography Guidance of Antegrade Cardioplegia Delivery for Cardiac Surgery.

OBJECTIVES: The initial volume of antegrade cardioplegia used to induce asystole during aortic cross-clamp still is based on empiric methods and may be excessive, potentially leading to hyperkalemia, myocardial edema, and acute left ventricular distention from aortic regurgitation. The objectives were to determine whether the volume of cardioplegia required to induce asystole is proportional to left ventricular mass, and whether the degree of left ventricular distention is proportional to the severity of aortic regurgitation. DESIGN: Prospective observational study. SETTING: Two tertiary university hospitals. INTERVENTIONS: Transesophageal echocardiography was used to estimate left ventricular mass (prolate ellipse revolution formula), quantify aortic regurgitation, and monitor for distention during initial antegrade cardioplegia delivery. The volume of cardioplegia required for asystole was recorded. PARTICIPANTS: Fifty-eight patients aged over 18 years scheduled for cardiac surgery requiring aortic cross-clamping. MEASUREMENTS AND MAIN RESULTS: There was a weak correlation of left ventricular mass and antegrade cardioplegia volume required for asystole (r = 0.35, p = 0.047). The degree of left ventricular distention correlated moderately with the severity of aortic regurgitation (r = 0.55, p = 0.007) and was excessive and stopped early (aborted) in 24% of all patients, including 18% of 39 patients without aortic regurgitation. An aortic regurgitation vena contracta of 0.3 cm predicted aborted cardioplegia with modest accuracy (AUC 0.81, 0.66-0.99, p = 0.02, sensitivity 71%, specifity 81%). CONCLUSIONS: Estimated left ventricular mass is not a useful predictor of the initial volume of antegrade cardioplegia required to induce asystole. However transesophageal echocardiography can predict and monitor for left ventricular distention, which is common.