Assessment of Volume Status During Prone Spine Surgery via a Novel Point-of-care Ultrasound Technique.

Background Operations performed with the patient in the prone position can pose a significant challenge to the anesthesiologist. Hypotension is a commonly encountered complication. Intravascular volume depletion and decreased cardiac output secondary to decreased preload are thought to be the most likely cause of hypotension in the prone position. Measurement of inferior vena cava (IVC) diameter via point-of-care ultrasound examination (POC_US) has been used to provide an estimate of intravascular volume status. However, this measurement is most often obtained with the patient in the supine position. Materials and methods In this study, we describe a technique for evaluating IVC diameter via POC_US in the prone position. Right lateral long axis imaging of the IVC was used to assess the intravascular volume status of 10 patients undergoing lumbar spine surgery in the prone position. In addition, we used a non-invasive measure of cardiac output to correlate changes in IVC width with changes in cardiac output. Results Images of the IVC in the prone position were obtainable in all 10 patients. IVC diameter increased in six out of 10 patients on going from supine to prone position. The increase in IVC diameter corresponded to an increase in cardiac output, measured noninvasively in five out of the six patients. Conclusions Our findings indicate that POC_US examination of the IVC is possible in the prone position. Further study of a larger patient population could demonstrate the utility of this technique in assessing intravascular volume status in patients undergoing surgery in the prone position.