Sonographic measurement of the inferior vena cava as a marker of blood loss

Detecting and monitoring blood loss in trauma patients can often be challenging when an obvious source of hemorrhage is not readily seen. To provide a noninvasive measurement of circulating blood volume and of drop therein by measuring the change in the inferior vena cava diameter (IVCd) in relationship to blood loss. This was a prospective observational study on blood donors at a donation center. The IVCd, both during inspiration (IVCi) and during expiration (IVCe), was measured in volunteers both before and after blood donation of 450 mL. All actual blood donors aged 18 years and older were eligible for enrollment. Persons who were younger than 18 years, who declined to participate in the study, or who did not meet blood center criteria for blood donation were excluded. All examinations were performed in the supine position with the ultrasound transducer placed in a subxyphoid location. Sagittal sections of the IVC behind the liver were imaged and the maximal diameter of the IVCe and the minimal diameter of the IVCi were measured. Statistical analysis included test for normality, paired t test, and correlation analysis. A total of 31 volunteers (18 male) with a mean age of 49.5 years (range, 18-73) were studied. The mean IVCe before blood donation was 17.4 mm (95% CI, 15.2-19.7 mm) and after blood donation was 11.9 mm (95% CI, 10.3-13.6 mm). The mean IVCi before blood donation was 13.3 mm (95% CI, 11.3-15.3 mm), but after blood donation was 8.13 mm (95% CI, 6.7-9.6 mm). The difference between IVCe before and after blood donation (dIVCe) was 5.5 mm (95% CI, 4.3-6.3 mm) yielding a P <. 0001. The difference between IVCi before and after donation (dIVCi) was 5.16 mm (95% CI, 4.2-5.9 mm) yielding a P <. 0001. The dIVCe and the dIVCi were closely correlated (r = 0.83). Similarly, the pre-IVCe correlated well to the post-IVCe (r = 0.74) and the pre-IVCi correlated well to the post-IVCi (r = 0.75). Our data indicates that the measurement of the IVC diameter is a reliable indicator of blood loss, even in small amounts of 450 mL. On average, there was about a 5-mm decrease in both the IVCe and IVCi after donation of 450 mL of blood. The measurement of the IVCe may be an important addition to the ultrasonographic evaluation of trauma and other potentially volume-depleted patients.