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Critical Care |

Influence of Head-of-Bed Elevation on the Measurement of IVC Diameter and Collapsibility

Peter Lee, MD; Khyati Gupta, MD; Jaspreet Ahuja, MD; Angela Love, MD; Pierre Kory, MD
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Beth Israel Medical Center, New York, NY


Chest. 2013;144(4_MeetingAbstracts):372A. doi:10.1378/chest.1704636
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Abstract

SESSION TITLE: Critical Care Posters

SESSION TYPE: Original Investigation Poster

PRESENTED ON: Wednesday, October 30, 2013 at 01:30 PM - 02:30 PM

PURPOSE: Inferior vena cava (IVC) diameter and variation are commonly measured in the supine position to estimate the intravascular volume status of critically ill patients. However, critically ill patients are rarely placed in the supine position due to concerns for aspiration risk, worsened respiratory mechanics, increases in intracranial pressure, and the time constraints of changing patient position. We assessed the influence of head of bed (HOB) elevation on IVC measurements.

METHODS: We conducted a prospective observational study of critically ill patients undergoing general critical care ultrasound exams in a medical ICU. In the supine position with HOB at 0°, IVC maximum (IVCmax0°) and minimum (IVCmin0°) diameters were measured at a point just distal to the hepatic vein using 2D ultrasound with cine review. Measurements were then repeated with HOB elevated to 30° and 45° for two minutes prior to measurement. Collapsibility index was calculated for each HOB elevation (IVC-CI). Mean differences were compared with student’s two-tailed t-test of matched groups.

RESULTS: A convenience sample of 47 patients was studied. 66% were on vasopressors and 33% were spontaneously breathing. The IVCmax diameters increased with HOB elevation by a small but statistically significant extent, mean IVCmaxdiff 30°-0°= 1.8mm (range:0-5.7mm), p=.04, mean IVCmaxdiff 45°-0°=2.1mm (range:0-7.2mm) , p<.01. The collapsibility index significantly decreased from supine only when HOB was elevated to 45°, IVC-CI(0°)=41%, IVC-CI(30°)=29% (p=.54), and IVC-CI(45°)=15% (p=.03).

CONCLUSIONS: In a population of critically ill patients undergoing goal-directed ultrasound exams, elevating the HOB to 30° increased the measured IVCmax diameter by 1.8mm and did not significantly alter the collapsibility index. At 45° HOB elevation, IVCmax diameter increased by an average of 2.1mm with a significant decrease in CI from 41% to 15%.

CLINICAL IMPLICATIONS: In critically ill patients, performing ultrasound measurements of the IVC with the HOB elevated to 30° is unlikely to produce clinically meaningful changes. Measuring IVC with the HOB elevated to 45° should be avoided given the large changes observed in the collapsibility Index.

DISCLOSURE: The following authors have nothing to disclose: Peter Lee, Khyati Gupta, Jaspreet Ahuja, Angela Love, Pierre Kory

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