You are preparing to intubate a morbidly obese patient for respiratory failure.
Describe the strategies for minimising hypoxaemia in the period immediately pre- and post-intubation.
Ensure optimal treatment of the underlying cause of respiratory failure where possible, e.g.
• Diuretics and CPAP for acute pulmonary oedema
• Bronchodilators for asthma
1. Optimise pre-oxygenation/ intra procedure oxygenation
• Longer time of pre-oxygenation
• Use of PSV or CPAP pre-intubation (peak Pi not >15 cmH2O recommended)
• Nasal prong and/or high-flow oxygenation during intubation (e.g. THRIVE or simple prongs at 15l/min)
• Monitoring end tidal oxygen; target FeO2 >80%
2. Minimising time to first breath
• Positioning (essential point to mention)
• Ramping (or similar) achieving tragus-sternal angle in horizontal plane Important in obese patient
• Experienced operator
• Equipment ready (expect candidate to have fall-back equipment such as VL, bougies, second generation LMA. No specific right or wrong re which device they should use first)
• Use of rapidly acting skeletal muscle relaxant (or use of spontaneously breathing technique e.g. LA) • Monitoring for intra-tracheal placement of ETT; capnography
• Ventilator set up with appropriate settings for immediate use including FiO2 1.0 and appropriate level PEEP, Vt and inspiratory airway pressure
• Teamwork management – clear roles in primary and backup plans
• NB: Delay with use of video-laryngoscopy
3. Rescue strategies
• Plan A, Plan B, Plan C
• Preparations for supraglottic and infraglottic rescue (more credit if specific algorithm is mentioned e.g. Vortex, DAS)
4. Optimise cardiac output for improved V/Q matching
• Judicious fluid loading
• Vasopressors (e.g. Nor-adrenaline, metaraminol)
• Awareness of fall in output with induction of anaesthesia and institution of IPPV
• Invasive arterial pressure monitoring
The details of this answer are explored in the chapter on the prevention of hypoxia during airway management. For a proper literature reference, the time-poor candidate is directed to "Preoxygenation and prevention of desaturation during emergency airway management" by Weingart and Levitan (2011).
- Head up 20-25° (especially valuable in the obese patients)
- 100% FiO2
- Deep breaths × 8
- Or, 3-4 minutes of breathing the oxygen-rich mixture
- The effect is enhanced by positive airway pressure
- There is no benefit in extending this period beyond 4 minutes
- Use NIV unless contraindicated
- PEEP 5-10 cm H2O
- Not to exceed 25 cm H2O
- Alternatively, use a PEEP valve on the bag-valve mask
Minimisation of metabolic demands
- Use generous amounts of muscle relaxant
- The use of non-depolarising agents is preferred, as fasciculations can increase the total body oxygen demand
Anticipation of hypoxia
- Preparation of staff and equipment for rapid desaturation
- Continued application of CPAP during the apnoeic period (i.e. while waiting for optimal intubating conditions)
- Use of bag-valve mask to gently ventilate the patient, promoting flow of fresh oxygen into the FRC
Preparation for failure
- Extend invitation to ENT or senior anaesthetic staff to be present at the intubation
- Make surgical airway equipment easily available
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