Influence of Diaphragmatic Motion on Inferior Vena Cava Diameter Respiratory Variations in Healthy Volunteers

AbstractAbstract In 52 spontaneously breathing healthy adults, respiratory variation of collapsibility of central vena cava (cIVC) was associated with inspiratory effort and diaphragmatic motion. This study identified a gray zone of the diaphragmatic motion ranging from 25 to 43 mm for predicting cIVC more than or equal to 40%. This study suggests, although not tested, inaccuracy of cIVC for determining fluid responsiveness when the diaphragmatic motion is more than 25 mm. Background The collapsibility index of inferior vena cava (cIVC) is widely used to decide fluid infusion in spontaneously breathing intensive care unit patients. The authors hypothesized that high inspiratory efforts may induce false-positive high cIVC values. This study aims at determining a value of diaphragmatic motion recorded by echography that could predict a high cIVC (more than or equal to 40%) in healthy volunteers. Methods The cIVC and diaphragmatic motions were recorded for three levels of inspiratory efforts. Right and left diaphragmatic motions were defined as the maximal diaphragmatic excursions. Receiver operating characteristic curves evaluated the performance of right diaphragmatic motion to predict a cIVC more than or equal to 40% defining the best cutoff value. Results Among 52 included volunteers, interobserver reproducibility showed a generalized concordance correlation coefficient (ρ c ) above 0.9 for all echographic parameters. Right diaphragmatic motion correlated with cIVC (r = 0.64, P < 0.0001). Univariate analyses did not show association between cIVC and age, sex, weight, height, or body mass index. The area under the receiver operating characteristic curves for cIVC more than or equal to 40% was 0.87 (95% CI, 0.81 to 0.93). The best diaphragmatic motion cutoff was 28 mm (Youden Index, 0.65) with sensitivity of 89% and specificity of 77%. The gray zone area was 25 to 43 mm. Conclusions Inferior vena cava collapsibility is affected by diaphragmatic motion. During low inspiratory effort, diaphragmatic motion was less than 25 mm and predicted a cIVC less than 40%. During maximal inspiratory effort, diaphragmatic motion was more than 43 mm and predicted a cIVC more than 40%. When diaphragmatic motion ranged from 25 to 43 mm, no conclusion on cIVC value could be done.