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  • Dr Niraj Mistry

Ventilation of the Obese Patient

Updated: Mar 20

Dr Niraj Mistry

Emergency Registrar

Peer review: Dr Nick Erskine

Editor: Dr Dave McCreary


THE CASE

You’re on for resus in the middle of a night shift and you receive an alert for a shocked diabetic male with respiratory sepsis and DKA who has been intubated and will be arriving soon. Your initial reaction to this news probably wouldn’t worry you too much (aside from how severe the DKA must be to lead to a tube) knowing that the hard work has been done pre-hospital until the paramedic ends the call with a very casual, “Oh by the way the patient is 280kg.”



Suddenly, managing the patient has become that much harder and you’re in for a night of complicated respiratory physiology and unexpected challenges. I recently encountered just such a situation and the myriad of problems I encountered during the case left a lasting impression that motivated me to share my experiences in this blog post.


FIRST, WHAT IF THE PARAMEDICS HADN’T BEEN SO KIND AS TO TUBE THIS PATIENT FOR ME?

Intubation of the morbidly obese patient is a high-risk situation. You need an experienced airway operator and there are some considerations to optimise pre-oxygenation. Schetz et al.(1) recommend:

  • At least 5 minutes of non-invasive ventilation (NIV) in an upright seated position with positive end-expiratory pressure (PEEP) support of 5-10cmH20 (3).

  • Apnoeic oxygenation via the addition of high-flow nasal cannula (NC) to pre-oxygenation with NIV provided more effective pre-oxygenation and subsequently less oxygen desaturation then NIV alone (4).

Furthermore, simple manoeuvres to improve the positioning of the patient such as ramping will optimise your first-pass success when it comes to intubating these tricky airways.

OBESITY, THE RESPIRATORY SYSTEM & MECHANICAL VENTILATION

The main issue with this patient was optimising ventilation. After trialling various modes of ventilation and PEEP settings to little avail I can honestly say that at the end of the night the Hamilton ventilator and I were not the best of friends. The physiological changes to the respiratory system in obesity explain why ventilating can be so difficult in these situations. Including(2):

  • Increased oxygen consumption and carbon dioxide production

  • Increased work of breathing

  • Increased intraabdominal and intrathoracic pressures

  • Decreased compliance

  • Decreased functional residual capacity

Schetz et al. eloquently summarise the most effective intubation/pre-oxygenation and ventilation techniques in obese individuals as such:

PROTECTIVE VENTILATION

The key to mechanical ventilation is a protective ventilation strategy using low tidal volumes of 6ml/kg of ideal body weight (as our image above illustrates, inside every obese patient is the non-obese patient we're trying to ventilate) with moderate-to-high PEEP support of >10cmH2O. This approach improves respiratory mechanics, alveolar recruitment, and gas exchange (6). Whilst Schetz et al proposed using PEEP flows of 10 or more it should be noted one study found that PEEPs around this level were inadequate in minimising atelectasis and optimising ventilation in obese ICU patients, and PEEPs as high as 20 cmH2O significantly improved lung volumes and oxygenation (7).