Inferior vena cava collapsibility loses correlation with internal jugular vein collapsibility during increased thoracic or intra-abdominal pressure.

Abstract

Point-of-care ultrasound evaluates inferior vena cava (IVC) and internal jugular vein (IJV) measurements to estimate intravascular volume status. The reliability of the IVC and IJV collapsibility index during increased thoracic or intra-abdominal pressure remains unclear. Three phases of sonographic scanning were performed: spontaneous breathing phase, increased thoracic pressure phase via positive pressure ventilation (PPV) phase, and increased intra-abdominal pressure (IAP) phase via laparoscopic insufflation to 15mmHg. IVC measurements were done at 1-2cm below the diaphragm and IJV measurements were done at the level of the cricoid cartilage during a complete respiratory cycle. Collapsibility index was calculated by (max diameter-min diameter)/max diameter×100%. Chi square, t test, correlation procedure (CORR) and Fisher's exact analyses were completed. A total of 144 scans of the IVC and IJV were completed in 16 patients who underwent laparoscopic surgery. Mean age was 46±15years, with 75% female and 69% African-American. IVC and IJV collapsibility correlated in the setting of spontaneous breathing (r (2)=0.86, p<0.01). IVC collapsibility had no correlation with the IJV in the setting of PPV (r (2)=0.21, p=0.52) or IAP (r (2)=0.26, p=0.42). Maximal IVC diameter was significantly smaller during increased IAP (16.5mm±4.9) compared to spontaneous breathing (20.6mm±4.8, p=0.04) and PPV (21.8mm±5.6, p=0.01). IJV and IVC collapsibility correlated during spontaneous breathing but there was no statistically significant correlation during increased thoracic or intra-abdominal pressure. Increased intra-abdominal pressure was associated with a significant smaller maximal IVC diameter and cautions the reliability of IVC diameter in clinical settings that are associated with intra-abdominal hypertension or abdominal compartment syndrome.