The Impact of Fluid Volume Shifts on Upper Airway Collapse and Obstructive Sleep Apnea in Surgical Patients

The objective of this study is to examine the contribution of intravenous (IV) fluid administration and rostral fluid shift from the legs to the neck thereby leading to worsening of sleep apnea following surgery. In this prospective, observational cohort study, 50 consecutive preoperative adult obstructive sleep apnea (OSA) patients, requiring at least one night hospital stay post surgery, will be recruited. Recent research from general population suggests that intravenous (IV) fluid administration worsens the severity of OSA by shifting of fluid from the legs to the neck thus increasing neck size and causing airway collapse. The results of this study will be used to design future clinical trials evaluating methods to decrease postoperative OSA worsening, as well as decreasing OSA-related postoperative complications.

The study investigators hypothesize that in obstructive sleep apnea (OSA) patients undergoing elective non-cardiac surgery, preferential increase in neck fluid volume following intravenous administration during general anesthesia results in worsening apnea-hypopnea (AHI) and postoperative respiratory complications.This is a two-center study where the study population will be drawn from patients visiting preoperative clinic at University Health Network Hospitals, Toronto Western Hospital, and Toronto General Hospital.

Objectives of the study

* Measure the change in the leg, neck and total fluid volume from preoperative baseline, postoperative care unit (PACU), first postoperative night (Night 1) and the morning after surgery (Day 2)
* Assess the impact of the change in neck fluid volume on respiratory mechanics and postoperative apnea-hypopnea index (AHI) the first postoperative night (Night 1) In this study, the investigators will perform serial measurements of segmental and total body water shifts occurring after surgery, at various time-points on the night and the morning after surgery. The investigators will monitor indices such as the Apnea Hypopnea index (AHI) and oxygen desaturation index (ODI) to examine changes in the severity of OSA. Internal validity of this study will be made more robust by use of well-validated methods such as Bioelectrical Impedance Analysis (BIA) for fluid measurements, portable Apnea Link for OSA severity and tremflow airway oscillometry for the airway resistance.

Eligibility Criteria:
Inclusion Criteria:

1. Adult patients (\>18 yrs)
2. Previously diagnosed OSA (AHI \> 10), untreated or non-compliant to treatment, or patients screened as suspected OSA (STOP Bang \>3, and confirmed to have OSA with AHI \> 10 on a portable sleep study)
3. ASA physical status I - IV
4. Patients undergoing elective non-cardiac surgery under general anesthesia;
5. Patients requiring overnight admission.

Exclusion Criteria:

1. Patients compliant on OSA treatment such as continuous positive airway pressure therapy or an oral appliance
2. Vascular surgery on the lower limbs, or metal implants in lower limbs
3. Pregnant or lactating patients
4. Cardiac, intra-cranial, or neck procedures.
5. Inability to communicate: with health care providers or the research personnel, inability to perform breathing maneuvers such as spirometry, or inability to follow instructions.