76-year-old lady for elective TKR


  • Significant knee pain, impacting QoL
  • COPD, mild. 60 pack year smoking history
  • Ceased smoking to facilitate TKR
  • Peripheral vascular disease, multiple revascularization procedures. On apixaban
  • BMI 46
  • NIDDM. Poor glycaemic control
  • Difficult to obtain accurate history in clinic
  • Some indications of poor medication compliance
  • On ?CPAP for OSA. Advised to bring to hospital.
  • Extensive perioperative work-up, including delay to improve glycaemic control


  • Presented for TKR. Uneventful intraoperative course.
  • Developed Type 2 respiratory failure in PARU
  • Home machine not functioning due to water ingress, sent to biomed
  • Commenced on NFNP with little effect
  • Reviewed by respiratory CNC in PARU. Patient well known to service
  • Patient has significant OHS and is on home BiPAP (IPAP 17, EPAP 9)
  • Device history revealed recent non-compliance with therapy
  • Respiratory department sourced a replacement machine.
  • Patient stable in recovery on usual BiPAP settings and discharged to ward.


Conduct of anaesthesia

  • Spinal with intrathecal morphine 100mcg – consensus opinion that this was the optimal anaesthetic choice as avoided parenteral opioids.
  • Some anaesthetists routinely use 150mcg morphine but would decrease to 100mcg in patients at risk of postoperative respiratory depression
  • Consensus in literature than 100mcg is optimal dose for avoidance of respiratory depression

Could this situation have been avoided?

  • Difficult history, multiple complex comorbidities
  • Patient unaware of differences between CPAP and BiPAP
  • Non-compliant with therapy
  • Respiratory CNC provided extremely valuable input and avoided an unplanned HDU admission

Perioperative management of suspected OSA/OHS

  • Clinic guideline under development, ongoing discussions with respiratory dept
  • Sleep studies are time-consuming and turnaround time from referral to initiation of CPAP is around 6 months
  • No RCT evidence to support reduction in perioperative morbidity and mortality with initiation of CPAP therapy.
  • Observational data would suggest that OSA patients have worse perioperative outcomes and there are benefits to initiating CPAP perioperatively. (Anesth Analg 2015;120:1013–23)
  • Aim is to identify those at highest risk of postoperative pulmonary and cardiac complications
  • OHS – more complex sleep disorder with raised HCO3 and PaCO2. Majority also have OSA. These are patients to identify and treat perioperatively.
  • Perioperative assessment: STOPBANG (>3) then perform ESS. If ESS (>8) – consider referral for sleep studies