Changes in the augmentation index and postoperative orthostatic intolerance in orthopedic surgery: a prospective cohort study

Background Postoperative orthostatic intolerance (OI) can be a major obstacle to early ambulation and its determinants are poorly understood. We aimed to study postoperative changes in vascular tone and their potential association with OI in various orthopedic surgical settings. Methods In this prospective cohort study, 350 patients undergoing total joint arthroplasty under neuraxial anesthesia or spine surgery under general anesthesia were enrolled. We determined the augmentation index (AI) as a measure of vascular tone and studied symptoms of OI using a validated questionnaire at various postoperative time points. Results The AI was significantly reduced postoperatively (at spinal resolution in patients with neuraxial anesthesia or two hours postoperatively in general anesthesia) compared with baseline values in all procedures and did not subsequently return to baseline throughout the postoperative period in the majority of patients [252/335 (75.2%); P < 0.001]. The majority [260/342 (76.0%); P < 0.001] of patients had postoperative symptoms of OI Nevertheless, no association was found between postoperative change in AI from baseline and postoperative symptoms of OI. Conclusions A significantly prolonged decrease in AI and symptoms of OI are common after orthopedic surgery. Nevertheless, an association between the two measures was not observed. While compensatory mechanisms may limit the influence of an AI decrease on symptoms of OI more research is needed to understand the contributing factors and aid in the identification of patients at risk of OI.