To the Editor:
The recent update of the report “Practice Advisory for Perioperative Visual Loss Associated with Spine Surgery” by the American Society of Anesthesiologists Task Force on Perioperative Visual Loss did not present any new guidelines.1It did, however, continue a recommendation regarding the management of intraoperative fluid therapy from the 2006 Practice Advisory,2which states that “central venous pressure (CVP) monitoring should be considered in high-risk patients.” Although there is a relationship between CVP and intraocular pressure,3there is little data supporting the utility of CVP in guiding fluid therapy, particularly in patients undergoing spine surgery in the prone position.
Recognizing that the heart is the target organ of intravenous fluids, the goal of fluid therapy is to ensure adequate cardiac output for perfusion of vital organs. Furthermore, additional fluids should only be administered in a patient who is “fluid-responsive,” meaning that an increase in preload will cause a commensurate increase in cardiac output. This is the rationale for “goal-directed therapy.”
Unfortunately, CVP does not predict fluid responsiveness.4,5Furthermore, CVP monitoring in the prone position may be particularly misleading to clinicians. A previous study comparing CVP and left ventricular end diastolic volume demonstrated that when a patient is turned from supine to prone, CVP rises, whereas left ventricular end diastolic volume falls.6Thus, in the prone position, the CVP suggests that the left ventricle is more full when in fact it is more empty.
In addition to a lack of utility, CVP catheters present additional risks to patients, including both mechanical injury and infection. It is therefore difficult to recommend CVP monitoring when a host of minimally and noninvasive hemodynamic monitors, using a variety of technologies, are available for goal-directed fluid therapy.
