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.

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College answer

 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 
 

Discussion

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).

Positioning

  • Head up 20-25° (especially valuable in the obese patients)

Denitrogenation

  • 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

Positive pressure

  • 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

Apnoeic oxygenation

  • 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

References

References

Weingart, Scott D., and Richard M. Levitan. "Preoxygenation and prevention of desaturation during emergency airway management." Annals of emergency medicine 59.3 (2012): 165-175.

Heller, Morris L., and T. Richard Watson Jr. "Polarographic study of arterial oxygenation during apnea in man." New England Journal of Medicine 264.7 (1961): 326-330.

Cherniack, NEIL S., and G. S. Longobardo. "Oxygen and carbon dioxide gas stores of the body." Physiological reviews 50.2 (1970): 196-243.

Enghoff, H., and L. RISHOLM. "Diffusion respiration in man." Nature 168.4280 (1951): 830-830.

Draper, William B., and Richard W. Whitehead. "The Phenomenon of Diffusion Respiration.." Anesthesia & Analgesia 28.6 (1949): 307-318.

Lane, S., et al. "A prospective, randomised controlled trial comparing the efficacy of pre‐oxygenation in the 20° head‐up vs supine position." Anaesthesia 60.11 (2005): 1064-1067.

Ramkumar, Venkateswaran, Goneppanavar Umesh, and Frenny Ann Philip. "Preoxygenation with 20º head-up tilt provides longer duration of non-hypoxic apnea than conventional preoxygenation in non-obese healthy adults.Journal of anesthesia 25.2 (2011): 189-194.

Mort, Thomas C. "Preoxygenation in critically ill patients requiring emergency tracheal intubation." Critical care medicine 33.11 (2005): 2672-2675.

Mort, Thomas C., Barbara H. Waberski, and Jonathan Clive. "Extending the preoxygenation period from 4 to 8 mins in critically ill patients undergoing emergency intubation." Critical care medicine 37.1 (2009): 68-71.

Nielsen, Niels D., et al. "Apneic oxygenation combined with extracorporeal arteriovenous carbon dioxide removal provides sufficient gas exchange in experimental lung injury." ASAIO journal 54.4 (2008): 401-405.

Eger, E. I., and J. W. Severinghaus. "The rate of rise of PaCO2 in the apneic anesthetized patient." Anesthesiology 22.3 (1961): 419-425.

Russotto, Vincenzo, et al. "Respiratory support techniques to avoid desaturation in critically ill patients requiring endotracheal intubation: A systematic review and meta-analysis.Journal of Critical Care (2017).

Altermatt, F. R., et al. "Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea." British journal of anaesthesia 95.5 (2005): 706-709.

Dixon, Benjamin J., et al. "Preoxygenation Is More Effective in the 25° Head-up Position Than in the Supine Position in Severely Obese PatientsA Randomized Controlled Study." The Journal of the American Society of Anesthesiologists 102.6 (2005): 1110-1115.

Duggan, Michelle, and Brian P. Kavanagh. "Atelectasis in the perioperative patient." Current Opinion in Anesthesiology 20.1 (2007): 37-42.

Baillard, Christophe, et al. "Noninvasive ventilation improves preoxygenation before intubation of hypoxic patients." American journal of respiratory and critical care medicine 174.2 (2006): 171-177.

Tang, L., et al. "Desaturation following rapid sequence induction using succinylcholine vs. rocuronium in overweight patients." Acta Anaesthesiologica Scandinavica 55.2 (2011): 203-208.