Introduction: Measurement of intravascular volume status is an ongoing challenge for physicians in the surgical intensive care unit (SICU). Most surrogates for volume status, including central venous pressure (CVP) and pulmonary artery wedge pressure, require invasive lines associated with a number of potential complications. Sonographic assessment of the collapsibility of the inferior vena cava (IVC) has been described as a noninvasive method for determining volume status. The purpose of this study was to analyze the dynamic response in IVC collapsibility index (IVC-CI) to changes in CVP in SICU patients receiving fluid boluses for volume resuscitation.
Materials and methods: A prospective pilot study was conducted on a sample of SICU patients who met clinical indications for intravenous (IV) fluid bolus and who had preexisting central venous access. Boluses were standardized to crystalloid administration of either 500 mL over 30 min or 1,000 mL over 60 min, as clinically indicated. Concurrent measurements of venous CI (VCI) and CVP were conducted right before initiation of IV bolus (i.e. time 0) and then at 30 and 60 min (as applicable) after bolus initiation. Patient demographics, ventilatory parameters, and vital sign assessments were recorded, with descriptive outcomes reported due to the limited sample size.
Results: Twenty patients received a total of 24 IV fluid boluses. There were five recorded 500 mL boluses given over 30 min and 19 recorded 1,000 mL boluses given over 60 min. Mean (median) CVP measured at 0, 30, and 60 minutes post-bolus were 6.04 ± 3.32 (6.5), 9.00 ± 3.41 (8.0), and 11.1 ± 3.91 (12.0) mmHg, respectively. Mean (median) IVC-CI values at 0, 30, and 60 min were 44.4 ± 25.2 (36.5), 26.5 ± 22.8 (15.6), and 25.2 ± 21.2 (14.8), respectively.
Conclusions: Observable changes in both VCI and CVP are apparent during an infusion of a standardized fluid bolus. Dynamic changes in VCI as a measurement of responsiveness to fluid bolus are inversely related to changes seen in CVP. Moreover, an IV bolus tends to produce an early response in VCI, while the CVP response is more gradual. Given the noninvasive nature of the measurement technique, VCI shows promise as a method of dynamically measuring patient response to fluid resuscitation. Further studies with larger sample sizes are warranted.
Keywords: Central venous pressure; Point-of-care ultrasound; inferior vena cava collapsibility index; intravascular volume status assessment; intravenous fluid bolus.