Cardiovascular Response to Hyperoxemia, Hemodilution and Burns A clinical and experimental study

Bak, Zoltan. Cardiovascular Response to Hyperoxemia, Hemodilution and Burns – A clinical and experimental study. Linköping University Medical Dissertations No.1013, Ed: The Dean of Faculty of Health Sciences, Sweden 2007. During the last decades less invasive monitoring and analytical tools have been developed for the evaluation of myocardial mechanics in clinical practice. In critical care, these are complements to pulmonary artery catheter monitoring, additionally offering previously inaccessible information. This work is aimed, during fluid-replacement and oxygen treatment, to find out the physiological interface of ventricular and vascular mechanical properties that result in the transfer of blood from the heart to appropriate circulatory beds. We investigated in prospective clinical studies previously cardiovascular healthy adults during hyperoxemia and patients with severe burns during fluid resuscitation, and before spine surgery during preoperative acute normovolemic hemodilution. Echocardiography was used in all studies, transthoracic for healthy volunteers and transesophageal for patients. For vascular variables, and for control purposes, pulmonary artery Swan-Ganz catheter, calibrated external pulse recordings, whole body impedance cardiography, and transpulmonary thermodilution method were used. We detected no significant change in blood pressure or heart rate, the two most often used variables for monitoring patients. During preoperative acute normovolemic hemodilution a reduction in hemoglobin to 80 g/l did not compromise systolic or diastolic myocardial function. Cardiac volumes and flow increased with a coexisting fall in systemic vascular resistance while oxygen delivery seemed maintained. Supplemental oxygen treatment resulted in a linear dose-response between arterial oxygen and cardiovascular variables, suggesting a direct vascular effect. Cardiac flow decreased and vascular resistance increased from hyperoxemia, and a reduction in venous return implied extracardial bloodpooling. Severe burns result in hypovolemic shock if not properly treated. The commonly used Parkland fluid replacement strategy, with urinary output and mean arterial pressure as endpoints, has recently been questioned. Applying this strategy, only transient early central hypovolemia was recorded, while dimensional preload, global left ventricular systolic function, and oxygen delivery or consumption, remained within normal ranges during the first 36 hours after the accident. Signs of restrictive left ventricular diastolic function were detected in all patients and regional unstable systolic dysfunction was recognized in every other patient, and was consistent with leakage of myocardial markers. Severe burns cause myocardial stiffness and systolic regional dysfunction, which may not be prevented by central normovolemia and adequate oxygenation alone.