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Resuscitating the Obese Patient

In this episode, Mitchell Zekhtser, and Michael E. Winters, MD FAAEM, discuss resuscitating the obese patient. Mr. Zekhtser is a student at Western University and Western Regional Representative on the ’18-’19 RSA Medical Student Council. Dr. Winters is Associate Professor of Emergency Medicine and Medicine Program Director, Combined EM/IM Program, Co-Director, Combined EM/IM/CC Program, University of Maryland School of Medicine, Baltimore, MD.

 

Show Notes

Dr. Michael Winters: Resus of the Obese Patient

Twitter: @critcareguys

Check out more from Dr. Winters at www.criticalcareinem.com


Clinical Pearls:

Anatomy:

  1. Obese patients have a high chance of collapse in the glottic opening due to extra tissues. Obese patients have a large tongue and excess cervical fat, creating a constricted glottic opening.
  2. Obese patients have a decreased cardiopulmonary reserve meaning they will quickly and critically de-saturate. These patients have an increased amount of adipose tissue causing it to push up on the diaphragm. So even when you pre-oxygenate them be aware these patients have a rapid onset of hypoxemia.
  1. Normal body habitus patients have a safe apnea time of 6-7 min if adequately pre-oxygenated to 88-90%
  2. Morbidly obese patients have an apnea time of 3-4 min. However, when they are sick you only have 60-90 seconds!

Physiology:

  1. Obese patients increase their total work of breathing in order to get a normal tidal volume. Obese patient’s lung volumes are decreased due to the decreased functional residual capacity (FRC), which drops about 3-5% for every unit increase in BMI. This causes intrapulmonary shunting at baseline, which leads to decreased lung compliance. This decreased lung compliance is coupled with the decreased chest wall compliance from the anatomical restriction from all the excess adipose tissue.
  2. Obese patients also have a V/Q mismatch where the obese patient’s upper lung zones are preferentially aerated and the lower lung fields are preferentially perfused. 
  3. Given that obese patients have a V/Q mismatch, intrapulmonary shunting, and increased work of breathing, their respiratory muscles are consuming anywhere up to 5x the amount of O2 that non-obese patients would utilize.
  4. In summary, obese patients have a markedly decreased endurance of their respiratory system.

Rapid Sequence Intubation:

  1. Pre-oxygenation should occur in a sitting rather than a supine position. It helps decrease airflow limitations, helps limit air trapping, and atelectasis.
  2. For pre-oxygenation try to use CPAP at about 10 cm of H2O for at least 5-10 minutes. It is not effective if you only pre-oxygenate for 1-2 minutes.
    1. If you do not have CPAP available, you can use another non-rebreather at flush rate or BVM with a PEEP valve.
  3. Meds: Which meds are dosed through ideal vs total body weight

 

Ideal Body Weight

Total Body Weight

Sedative

Ketamine (1.5 mg/kg)

Etomidate (0.3 mg/kg)

Paralytic

Rocuronium (1 mg/kg)

Succinylcholine (1.5 mg/kg)

  1. Ideal body weight for males: 50 kg + 2.3 kg for every inch over 5 ft.
  2. Ideal body weight for females: 45.5 kg + 2.3 kg for every inch over 5 ft.
  1. Prior to intubation, make sure you position them appropriately. You want the head of the bed up to 25-30 degrees. However, if you do not have a stretcher that can raise the head of the bed, then use some blankets to artificially raise it.
    1. The OPTIMAL INTUBATING POSITION is the external auditory canal is in line with the sternal notch.

The Vent:

  1. Tidal Volume should be based of Ideal Body Weight. Obese patients have the same sized lungs as non-obese patients, so keep their tidal volume at their ideal body weight.
  2. Respiratory Rate needs to be high at around 15-20 Breaths per min. Since obese patients have an increased work of breathing they are generating more CO2. Therefore, obese patients will have a higher spontaneous respiratory rate compared to non-obese patients.
  3. PEEP needs to be 10-15 cm H2O. Obese patients have lower lung volumes, so you need to keep their airway open. Normal patients would have a starting PEEP of 5.
  4. Put the patient in reverse Trendelenburg. When the patient is supine you are closing their regional lung segments, which can impair your ability to mechanically ventilate them. You will be able to pull higher tidal volumes and have a lower spontaneous respiratory rate.

 

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