Augmented venous return for minimally invasive open heart surgery with selective caval cannulation

OBJECTIVE: Minimally invasive open heart surgery involves limited intrathoracic cannulation sites necessitating cardiopulmonary bypass to be initiated via peripheral access using percutaneous cannulae with the tip placed into the right atrial cavity. However, surgery involving the opening of the right heart obliges the surgeon to maintain the end of the cannulae into the vena cavae. The impeded venous return due to the smaller diameter may be alleviated by inserting a centrifugal pump in the venous line. METHODS: Right anterior mini-thoracotomy and exposure of the femoral site were performed before the patient was heparinized. Cannulation of the femoral artery, the inferior vena cava via the femoral vein and the superior vena cava through the mini-thoracotomy was performed and cardiopulmonary bypass was initiated. Venous drainage was augmented with the centrifugal pump. Cardiac arrest was provoked and both vena cavae were snared before performing the intracardiac procedure. RESULTS: Twenty consecutive patients were operated on using this technique (15 males/five females; age: 44.8 +/- 14.3 years; bodyweight: 73.5 +/- 15.1 kg; body surface area: 1.8 +/- 0.2 m2; theoretical blood flow rate: 4.4 +/- 0.5 l/min). The cannula sizes were 21.9 +/- 2.2 Fr for the femoral artery, 26.5 +/- 1.7 Fr for the inferior vena cava and 23.8 +/- 2.5 Fr for the superior vena cava. Venous drainage through the single inferior vena cava cannula was 2.1 +/- 0.6 l/min (48.8 +/- 13.3% of the theoretical flow). Adding the superior vena cava cannula increased the venous flow to 3.1 +/- 0.4 l/min (70.7 +/- 9.6% of the theoretical value, P < 0.005). The use of the centrifugal pump increased the flow to 4.1 +/- 0.6 l/min (93.4 +/- 8.9% of the theoretical flow, P < 0.001) with a mean inlet negative pressure of -69 +/- 10.2 mmHg. The mean bypass time was 64.0 +/- 24.6 min for a mean operative time of 226.3 +/- 61.0 min. Minimum venous saturation was 69.4 +/- 8.5%. CONCLUSIONS: Despite the smaller diameter of the vena cavae compared to the right atrium, and a smaller internal diameter of percutaneous cardiopulmonary bypass cannulae compared to classic ones; the centrifugal pump improves the venous drainage significantly so that minimally invasive open heart procedures can be performed under optimal and safe perfusion conditions

The Role of the Frank–Starling Law in the Transduction of Cellular Work to Whole Organ Pump Function: A Computational Modeling Analysis

We have developed a multi-scale biophysical electromechanics model of the rat left ventricle at room temperature. This model has been applied to investigate the relative roles of cellular scale length dependent regulators of tension generation on the transduction of work from the cell to whole organ pump function. Specifically, the role of the length dependent Ca2+ sensitivity of tension (Ca50), filament overlap tension dependence, velocity dependence of tension, and tension dependent binding of Ca2+ to Troponin C on metrics of efficient transduction of work and stress and strain homogeneity were predicted by performing simulations in the absence of each of these feedback mechanisms. The length dependent Ca50 and the filament overlap, which make up the Frank-Starling Law, were found to be the two dominant regulators of the efficient transduction of work. Analyzing the fiber velocity field in the absence of the Frank-Starling mechanisms showed that the decreased efficiency in the transduction of work in the absence of filament overlap effects was caused by increased post systolic shortening, whereas the decreased efficiency in the absence of length dependent Ca50 was caused by an inversion in the regional distribution of strain

Strategies to prevent intraoperative lung injury during cardiopulmonary bypass

During open heart surgery the influence of a series of factors such as cardiopulmonary bypass (CPB), hypothermia, operation and anaesthesia, as well as medication and transfusion can cause a diffuse trauma in the lungs. This injury leads mostly to a postoperative interstitial pulmonary oedema and abnormal gas exchange. Substantial improvements in all of the above mentioned factors may lead to a better lung function postoperatively. By avoiding CPB, reducing its time, or by minimizing the extracorporeal surface area with the use of miniaturized circuits of CPB, beneficial effects on lung function are reported. In addition, replacement of circuit surface with biocompatible surfaces like heparin-coated, and material-independent sources of blood activation, a better postoperative lung function is observed. Meticulous myocardial protection by using hypothermia and cardioplegia methods during ischemia and reperfusion remain one of the cornerstones of postoperative lung function. The partial restoration of pulmonary artery perfusion during CPB possibly contributes to prevent pulmonary ischemia and lung dysfunction. Using medication such as corticosteroids and aprotinin, which protect the lungs during CPB, and leukocyte depletion filters for operations expected to exceed 90 minutes in CPB-time appear to be protective against the toxic impact of CPB in the lungs. The newer methods of ultrafiltration used to scavenge pro-inflammatory factors seem to be protective for the lung function. In a similar way, reducing the use of cardiotomy suction device, as well as the contact-time between free blood and pericardium, it is expected that the postoperative lung function will be improved