76-year-old lady for elective TKR

Background

• 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

Issues

• 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.

Discussion

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 PaCO_2. 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