Ultrasonographic measurement of the subclavian vein diameter for assessment of intravascular volume status in patients undergoing gastrointestinal surgery: comparison with central venous pressure.

BACKGROUND: Previous studies have demonstrated that ultrasonographic measurement of the inferior vena cava diameter is a useful tool for the evaluation of intravascular volume status in preoperative patients. However, ultrasonographic measurement of inferior vena cava diameter could be limited by factors including obesity, bowel gas, or complex abdominal wounds. Our study sought to determine whether subclavian vein (SCV) diameter measured by ultrasound correlate with central venous pressure (CVP), as another indicator of intravascular volume status in patients undergoing gastrointestinal surgery.

METHODS: Forty patients (American Society of Anesthesiologists I-II) who underwent elective gastrointestinal surgery and 40 healthy volunteers were enrolled in the study. In the patient group, SCV diameters, during both expiration (dSCVe) and inspiration (dSCVi), were measured with ultrasonography before and after fluid resuscitation. Volunteer baseline measurements were conducted without liquid therapy and the subsequent measurement.

RESULTS: Forty patients (mean age 46 y; 40% female) and 40 volunteers (mean age 43 y; 45% female) underwent SCV sonographic measurements. The average diameters of the SCVe and SCVi in hypovolemic patients (0.68, 0.48 cm) were significantly lower as compared with the SCVe and SCVi diameters of healthy volunteers (0.92, 0.73 cm), whereas the SCV-collapsibility index (0.35) was higher in the hypovolemic patients as compared with the healthy volunteers (0.20). After fluid resuscitation, the SCVe and SCVi diameters in hypovolemic patients (0.88, 0.67 cm) significantly increased, whereas the SCV-collapsibility index decreased (0.23). The pre-SCVe and the post-SCVe were closely correlated to the CVP (R = 0.612 and R = 0.547, respectively). Similarly, the pre-SCVi and the post-SCVi were correlated to the CVP (R = 0.452 and R = 0.507, respectively).

CONCLUSIONS: SCV diameter is consistently low in patients undergoing gastrointestinal surgery as compared with healthy subjects. Measuring the SCV diameter maybe an important addition to the ultrasonographic evaluation of hypovolemia and other potentially volume-depleted patients.