US of the IVC and Hemodynamic Response to Early Hemorrhage
US of the IVC and Hemodynamic Response to Early Hemorrhage
The study was approved by the Central Region Ethical Committee of Denmark (journal no. M-20110110), and enrollment was conditional upon written consent. The study was conducted in accordance with the Helsinki Declaration. All donors from the blood bank were eligible for inclusion (participants). Standard exclusion criteria for blood donation included any disease that may affect the cardiovascular system, including hypertension, diabetes mellitus, any cardiac or renal disease, previous cerebral stroke, and pregnancy. Additional criteria were blood pressure above 180/100 mm Hg or below 100/50 mm Hg, heart rate outside the range of 50–110 min, and body weight below 50 kg.
In addition, a control group of 10 volunteers (controls) with identical exclusion criteria was recruited for evaluation of the effects of an identical resting protocol on IVC dynamics and CO.
Upon arrival at the blood bank, participants rested in the supine position for at least 15 min before examination. Participants were subject to ultrasonographic measurement of the IVC and CO before blood donation and immediately after needle withdrawal, thereby minimizing volume re-distribution. The IVC was visualized from the transhepatic, subcostal view during quiet breathing. Longitudinal 2-dimensional (2D) cine loops spanning at least one respiratory cycle were stored for off-line analysis (Figure 1). Participants were then placed in the left lateral position for imaging of the left ventricular outflow tract (LVOT) in the cardiac apical five-chamber view. The velocity time integral (VTI) of the LVOT was acquired, employing pulsed wave Doppler (Figure 1). All examinations were performed by one of two sonographers experienced in echocardiography using a vivid E9 echocardiography system fitted with an M5S phased array transducer (1.5–4.5 MHz) (GE Healthcare, Horten, Norway).
(Enlarge Image)
Figure 1.
Left: Sagittal image of the inferior vena cava with calibration of the diameter during expiration (IVCe). Right: Measurement of the velocity time interval of the left ventricular outflow tract (LVOT), enabling calculation of stroke volume and cardiac output.
(Enlarge Image)
Figure 2.
Scatter plot of the baseline collapsibility index of the inferior vena cava (IVC) and the relative change in cardiac output facilitated by blood donation. No significant correlation was seen.
(Enlarge Image)
Figure 3.
Scatter plot of the baseline expiratory diameter of the inferior vena cava (IVC) and the relative change in cardiac output facilitated by blood donation. No significant correlation was seen.
An identical scanning protocol, in terms of resting periods and timing of imaging, was applied to the controls.
Images and cine loops were analyzed off-line by an observer blinded to the time of examination in relation to blood donation. Analyses were reanalyzed by a second observer, similarly blinded, for calculation of inter-observer variation. Commercially available software (Echopac, GE Healthcare) was used. The IVC was calipered with tracings perpendicular to the vessel walls approximately 2 cm caudal to the inflow of the hepatic veins. The maximal expiratory (IVCe) and inspiratory (IVCi) diameters of the IVC were meticulously found by frame-by-frame analysis. The inner-edge to inner-edge technique was used.
The collapsibility index of the IVC was calculated as IVC-CI = (IVCe−IVCi)/IVCe. The VTI was averaged from triplicates, and the CO was found by the equation CO = VTI*cross-sectional area of the LVOT*heart rate.
Measurements before and after blood donation were compared with a paired-samples Student's t-test. Correlations were analyzed with Spearman's rank correlation coefficient, as the IVC-CI and the relative difference in CO were not normally distributed. Interobserver variation was calculated as the mean difference in readings divided by the mean, expressed as a percentage and presented as mean variation with its corresponding 95% limits of agreement (LoA) and 95% confidence interval (CI). Statistical significance was set at p < 0.05. Calculations were performed with STATA software (StataCorp LP, College Station, TX).
Methods
The study was approved by the Central Region Ethical Committee of Denmark (journal no. M-20110110), and enrollment was conditional upon written consent. The study was conducted in accordance with the Helsinki Declaration. All donors from the blood bank were eligible for inclusion (participants). Standard exclusion criteria for blood donation included any disease that may affect the cardiovascular system, including hypertension, diabetes mellitus, any cardiac or renal disease, previous cerebral stroke, and pregnancy. Additional criteria were blood pressure above 180/100 mm Hg or below 100/50 mm Hg, heart rate outside the range of 50–110 min, and body weight below 50 kg.
In addition, a control group of 10 volunteers (controls) with identical exclusion criteria was recruited for evaluation of the effects of an identical resting protocol on IVC dynamics and CO.
Ultrasound Data Collection
Upon arrival at the blood bank, participants rested in the supine position for at least 15 min before examination. Participants were subject to ultrasonographic measurement of the IVC and CO before blood donation and immediately after needle withdrawal, thereby minimizing volume re-distribution. The IVC was visualized from the transhepatic, subcostal view during quiet breathing. Longitudinal 2-dimensional (2D) cine loops spanning at least one respiratory cycle were stored for off-line analysis (Figure 1). Participants were then placed in the left lateral position for imaging of the left ventricular outflow tract (LVOT) in the cardiac apical five-chamber view. The velocity time integral (VTI) of the LVOT was acquired, employing pulsed wave Doppler (Figure 1). All examinations were performed by one of two sonographers experienced in echocardiography using a vivid E9 echocardiography system fitted with an M5S phased array transducer (1.5–4.5 MHz) (GE Healthcare, Horten, Norway).
(Enlarge Image)
Figure 1.
Left: Sagittal image of the inferior vena cava with calibration of the diameter during expiration (IVCe). Right: Measurement of the velocity time interval of the left ventricular outflow tract (LVOT), enabling calculation of stroke volume and cardiac output.
(Enlarge Image)
Figure 2.
Scatter plot of the baseline collapsibility index of the inferior vena cava (IVC) and the relative change in cardiac output facilitated by blood donation. No significant correlation was seen.
(Enlarge Image)
Figure 3.
Scatter plot of the baseline expiratory diameter of the inferior vena cava (IVC) and the relative change in cardiac output facilitated by blood donation. No significant correlation was seen.
An identical scanning protocol, in terms of resting periods and timing of imaging, was applied to the controls.
Data Analysis
Images and cine loops were analyzed off-line by an observer blinded to the time of examination in relation to blood donation. Analyses were reanalyzed by a second observer, similarly blinded, for calculation of inter-observer variation. Commercially available software (Echopac, GE Healthcare) was used. The IVC was calipered with tracings perpendicular to the vessel walls approximately 2 cm caudal to the inflow of the hepatic veins. The maximal expiratory (IVCe) and inspiratory (IVCi) diameters of the IVC were meticulously found by frame-by-frame analysis. The inner-edge to inner-edge technique was used.
The collapsibility index of the IVC was calculated as IVC-CI = (IVCe−IVCi)/IVCe. The VTI was averaged from triplicates, and the CO was found by the equation CO = VTI*cross-sectional area of the LVOT*heart rate.
Statistical Analysis
Measurements before and after blood donation were compared with a paired-samples Student's t-test. Correlations were analyzed with Spearman's rank correlation coefficient, as the IVC-CI and the relative difference in CO were not normally distributed. Interobserver variation was calculated as the mean difference in readings divided by the mean, expressed as a percentage and presented as mean variation with its corresponding 95% limits of agreement (LoA) and 95% confidence interval (CI). Statistical significance was set at p < 0.05. Calculations were performed with STATA software (StataCorp LP, College Station, TX).
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