Fluid management

Cardiac index decreases in prone position due to reduced venous return and left ventricle compliance. Crystalloid should be used for maintenance and colloid for replacement of blood loss. Albumin seems to be the suitable colloid during spine surgery. Glycocalyx is better maintained by avoiding hyper- and hypovolemia. Goal-directed fluid therapy is the ideal way to guide fluid management during spine surgery especially in prone position. Introduction Fluid management during spine surgery is very important and difficult at the same time. Most spine surgeries are performed in prone position. Prone position induces a decrease in cardiac index and cardiac output. Maintaining stable hemodynamics with proper tissue perfusion requires adequate fluid management without fluid overloading. The best way to ensure normovolemia in prone position is by utilizing goal-directed fluid therapy for fluid management during spine surgery in prone position. This chapter will cover the pathophysiological changes during prone position, the physiology and the importance of the endothelial glycocalyx, the different types of fluid, and the most recent advances in goal-directed fluid therapy. Pathophysiology of prone position Prone position decreases cardiac index and venous return. Wadsworth et al. measured cardiac index (CI) in unanesthetized volunteers. CI was reduced mostly in the knee-chest position by 20% and decreased by 3% on the Jackson table (the Jackson table allows free abdominal excursion in the prone position, which enhances the venous return). Using transesophageal echocardiography (TEE), Toyota and Amaki demonstrated a decrease in left ventricular volume and compliance in prone position for lumbar laminectomy. These changes can be explained by inferior vena caval compression and decreased let ventricular compliance due to increased intrathoracic pressure in the prone position. These results have been coni rmed using a thermodilution pulmonary artery catheter. Cardiac output decreased from 17% to 24% using this technique. It should be mentioned that vena cava pressures vary between 0 – 40 mmH 2 O in prone position with the abdomen hanging free and >300 mm H 2 O with abdominal compression in prone position. 4 Consequently the increase in venous pressure not only will increase bleeding during spine surgery but also can impair spinal cord perfusion.