A Study of Noninvasive Cardiac Output and Other Cardiorespiratory Parameters in Various Neurosurgical Positions

ABSTRACT Background Neurosurgical patients are operated in supine, prone, lateral, and sitting positions, which cause physiological changes in cardiorespiratory parameters. Noninvasive cardiac output (NICO) monitor developed by Novametrix Medical System Inc is a noninvasive cardiac output monitor, which also measures and displays other parameters like stroke volume, cardiac index, pulmonary capillary blood flow, alveolar and dead space ventilation, peak flow rates, airway pressures, and respiratory volumes. We felt that a study using the NICO monitor in anesthetized patients undergoing neurosurgery in different positions would quantify the cardiopulmonary changes, identify risk factors, and improve intraoperative management. Materials and methods A total of 40 consecutive patients undergoing neurosurgical procedures—20 in prone, 16 in lateral and 4 in sitting position—were studied. The hemodynamic and cardiorespiratory parameters were noted in supine position about 15 minutes after induction of general anesthesia using standard protocol and 15 minutes after giving surgical position using NICO monitor. Conclusion We conclude that under anesthesia, the prone and sitting positions negatively affect derived cardiac parameters like cardiac output, cardiac index, and stroke volume, and lateral position tends to improve these parameters while the respiratory parameters are not significantly affected. How to cite this article Karnik HS, Nerurkar AA, Bawankule N. A Study of Noninvasive Cardiac Output and Other Cardiorespiratory Parameters in Various Neurosurgical Positions. Res Inno Anaesth 2016;1(1):19-24.

Pulmonary Capillary Blood Flow and Cardiac Output Measurement by Partial Carbon Dioxide Rebreathing in Patients with Acute Respiratory Distress Syndrome Receiving Lung Protective Ventilation

Background Partial carbon dioxide rebreathing noninvasively measures the pulmonary capillary blood flow and estimates the cardiac output with the use of a predicted shunt value. It has been reported that the accuracy of the method is decreased in patients with high pulmonary shunt. The aim of this study was to investigate the agreement between partial rebreathing and thermodilution for the determination of pulmonary capillary blood flow and cardiac output in the setting of acute respiratory distress syndrome. Methods Twenty consecutive patients with the acute respiratory distress syndrome were enrolled. Ventilator settings include low tidal volume (6 ml x kg(-1)) and positive end-expiratory pressure + 2 cm H2O higher than the lower inflection point if present or 10 cm H2O if not. Seven pairs of cardiac output and pulmonary capillary blood flows were recorded every 20 min over a 2-h period. The authors determined bias, SD, limit of agreement (95% confidence interval) and percentage error. Results Bias and agreement for cardiac output measurement were 0.8 +/- 1.2 l x min(-1) (-2.1 to 3.7 l x min(-1)), and percentage error was 36%. Bias and agreement for pulmonary capillary blood flow measurement were -0.1 +/- 0.8 l x min(-1) (-2.1 to 1.9 l x min(-1)), and percentage error was 35%. Dead space, arteriovenous oxygen content difference, mean pulmonary arterial pressure, and baseline cardiac output were independently associated with differences between methods. Conclusions In patients with the acute respiratory distress syndrome, partial rebreathing cannot yet replace thermodilution for measuring pulmonary capillary blood flow or cardiac output. However, accuracy of the method is close to the boundary of clinical relevance.

Intravital microscopic observations of 15-μm microspheres lodging in the pulmonary microcirculation

Vascular infusions of 15-μm-diameter microspheres are used to study pulmonary blood flow distribution. The sites of microsphere lodging and their effects on microvascular perfusion are debated but unknown. Using intravital microscopy of the subpleural surface of rat lungs, we directly observed deposition of fluorescent microspheres. In a pump-perfused lung model, ∼0.5 million microspheres were infused over 30 s into the pulmonary artery of seven rats. Microsphere lodging was analyzed for the location in the microvasculature and the effect on local flow after lodging. On average, we observed 3.2 microspheres per 160 alveolar facets. The microspheres always entered the arterioles as singlets and lodged at the inlets to capillaries, either in alveolar corner vessels or small arterioles. In all cases, blood flow continued either around the microspheres or into the capillaries via adjacent pathways. We conclude that 15-μm-diameter microspheres, in doses in excess of those used in typical studies, have no significant impact on pulmonary capillary blood flow distribution.