Perioperative trends in neck and leg fluid volume in surgical patients: a prospective observational proof-of-concept study

Purpose The severity of obstructive sleep apnea (OSA) may increase postoperatively. The changes in segmental fluid volume, especially neck fluid volume, may be related to increasing airway collapsibility and thus worsening of OSA in the postoperative period. Our objective was to evaluate the feasibility of performing bioelectrical impedance analysis (BIA) and to describe the trend and predictors of changes in segmental fluid volumes in patients receiving general anesthesia for noncardiac surgery. Methods We conducted a prospective observational proof-of-concept cohort study of adult patients undergoing elective inpatient noncardiac surgery. Patients underwent a portable sleep study before surgery, and segmental fluid volumes (neck fluid volume [NFV], NFV phase angle, and leg fluid volume [LFV]) were measured using BIA at set time points: preoperative period (preop), in the postanesthesia care unit (PACU), the night following surgery at 10 pm (N 0), and the following day at 10 am (POD 1). Linear regression models were constructed to evaluate for significant predictors of overall segmental fluid changes. The variables included in the models were sex, preoperative apnea–hypopnea index (AHI), fluid balance, body mass index (BMI), cumulative opioids, and the timepoint of measurement. Results Thirty-five adult patients (20/35 females, 57%) were included. For the feasibility outcome, measure of recruitment was 50/66 (76%) and two measures of protocol adherence were fluid measurements (34/39, 87%) and preoperative sleep study (35/39, 90%). There was a significant increase in NFV from preop to N 0 and in LFV from preop to PACU. Neck fluid volume also increased from PACU to N 0 and PACU to POD 1, while LFV decreased during the same intervals. The overall changes in NFV were associated with the preop AHI, BMI, and opioids after adjusting for body position and pneumoperitoneum. Conclusions This proof-of-concept study showed the feasibility and variability of segmental fluid volumes in the perioperative period using BIA. We found an increase in NFV and LFV in the immediate postoperative period in both males and females, followed by the continued rise in NFV and a simultaneous decrease in LFV, which suggest the occurrence of rostral fluid shift. Preoperative AHI, BMI, and opioids predicted the NFV changes. Study registration ClinicalTrials.gov; NCT02666781, registered 25 January 2016; NCT03850041, registered 20 February 2019.