Interesting Tidbits from My On-Going CT Surg Report (2)

Cerebral Oximetry - Used to indirectly measure the cerebral oxygenation during surgery. As the blood flow examined is predominantly venous, the readings are lower than that measured by the SpO2 monitor. An initial reading is taken at the beginning of surgery, and its trend is then monitored. A significant drop in cerebral oximetry measurements may be an indicator of poor oxygenation of blood or poor cerebral perfusion delivered by the heart/heart lung machine.

CVP - A measurement of the filling pressure of the right ventricle and thus an indirect measurement of left ventricular preload. Estimates intravascular volume status which is an interaction of circulating blood volume, venous tone and right ventricular function. As cardiac surgery involves large amounts of fluid shifts into and out from the vascular system, CVP is a valuable measurement to properly adjust fluid interventions.

PAW - An direct measurement of the left atrial pressure and thus preload; this is because there are no valves separating the pulmonary valves and the left atrium. An increase in this measurement indicates left ventricular failure, of which very high pressures indicate possible presence of pulmonary edema. The catheter may also be used to perform cardiac output studies.

CO, SVR, CI - These are parameters determined by performing cardiac output studies intraoperatively via the thermodilution method. At the heart of these studies is the cardiac index, which is used to judge whether the heart is pumping enough cardiac output to meet the needs of the body. To optimize blood delivery, the anaesthesiologist may adjust the cardiac output by manipulating the stroke volume/heart rate, or adjust the systemic vascular resistance. These are all achieved with intravenous drugs.

(You may refer to this pdf for normal intracardiac values (copy-pasting the pdf table into the report, too lazy to type it out here in Blogger))

Heart Lung Machine - A machine used to replace the functions of the heart and lungs during cardiac surgery. The heart-lung machine in Serdang Hospital uses 4 pumps controlled by the perfusionist, all of which are peristaltic pump heads that produce a pulsatile flow of fluids. The first pump sucks blood from the central venous (right auricular) catheter (or alternatively, 2 catheters inserted into the SVC & IVC), the second is the pump sucker, the third the vent sucker, and the 4^th the cardioplegia delivery system. The venous pump delivers blood into a venous reservoir, and then into an oxygenator/head exchanger assembly, followed by a pump into the patient’s aorta via an aortic catheter. A pump sucker functions to suck blood present in the operating field for auto-transfusion. A vent sucker serves to collapse the heart by sucking fluids out of the RV via a catheter that may be attached to the aortic root/pulmonary vein, helping to create a bloodless field. The vent sucker may also be used during massive hemorrhage intra-op to suck blood for auto-transfusion. The 4^th pump serves to deliver the cardioplegia fluid. Cardioplegia is delivered via 2 directions, namely antegrade and retrograde. Antegrade cardioplegia is delivered via an aortic root cannula, while retrograde cardioplegia is delivered via a coronary sinus catheter. During cardiopulmonary bypass, heparin is used to prevent the blood from clotting, especially within the bypass circuit. After bypass, protamine is used to reverse the anticoagulation.

Transesophageal Echocardiography:

A device used to examine the heart during cardiac surgery. Used in cardiac surgery to examine the cardiac structure, ventricular function, valvular condition, and to search for pericardial fluid to be suctioned prior to closing of sternotomy.