Dynamic variation of the axillary veins due to intrathoracic pressure changes: A prospective sonographic study

Introduction: The ultrasound-guided axillary vein is becoming a compulsory alternative vessel for central venous catheterization and the anatomical position offers several potential advantages over blind, subclavian vein techniques. Objective: To determine the degree of dynamic variation of the axillary vein size measured by ultrasound prior to the induction of general anesthesia and after starting controlled mechanical ventilation. Design: Prospective, observational study. Methods: One hundred ten patients undergoing elective surgery were enrolled and classified according to sex, age, and body mass index. Two-dimensional cross-sectional vein diameter, area, and mean flow velocity were performed using ultrasound on both the left and right axillary veins of each subject before and after induction of anesthesia. Results: There was statistically significant evidence showing that the axillary vein area increases when patients are mechanically ventilated. When considering venous flow velocity as a primary outcome, velocity decreased after patients moved from spontaneous to mechanical ventilation (coefficient = −0.267), but this relationship failed to achieve statistical significance (t = –1.355, p = 0.179). Conclusions: Anatomical variations in depth and diameter as well as the collapsibility due to intrathoracic pressures changes represent common challenges that face clinicians during central venous catheterization of the axillary vein. A noteworthy increase in vessel size as patients transition from spontaneous to mechanical ventilation may theoretically improve first-pass cannulation success with practitioners skilled in both ultrasound and procedure. As a result, placing a centrally inserted central catheter after the induction of anesthesia may be beneficial.