Preventing desaturation during ED intubation

Author: Maha Salama, PGY-3

Article Reviewed:

Preoxygenation allows a safety buffer during periods of hypoventilation and apnea

In a patient breathing room air before RSI (PaO2 ~90-100 mmHg), desaturation will
occur in the 45-60 sec after sedative/paralytic administration
Preoxygenation extends duration of safe apnea (time until a patient reaches a saturation level of 88% to 90%)
In the short term, shunt physiology (perfusing but not ventilated) can be partially
overcome by augmenting the mean airway pressure
3 goals of preoxygenation in the ED:
- Bring saturation as close to 100% as possible
- Denitrogenate residual capacity of the lungs
  - Leads to maximal oxygen storage in the lungs
- Denitrogenate and maximally oxygenate the bloodstream
  - Bloodstream is a comparatively small oxygen reservoir compared to lungs (5% vs 95%)
Patients with adequate respiratory drive should receive preoxygenation for 3 minutes or take 8 breaths with maximal inhalation and exhalation
Should receive preoxygenation in a head elevated position whenever possible
- If immobilized for possible spinal injury, reverse Trendelenburg position
When a patient is breathing room air, 450 cc of oxygen is present in the lungs;
- Increases to 3000cc when a patient breathes 100% oxygen for a sufficient time to replace the alveolar nitrogen

Oxygen consumption during apnea is approximately 250cc/min (3cc/kg/min)

Healthy patients- safe apnea time on RA is 1 min compared to 8 min when breathing at high FiO2
A nasal cannula set at 15 L/min is the most readily available and effective means of providing adequate apneic oxygenation during ED tracheal intubations
In hypoxemic patients, low pressure/low volume/low rate bag mask ventilation will be required during the onset phase of muscle relaxants

Alveoli will continue using oxygen even without diaphragmatic excursion or lung expansion
- 8-20 cc/min of CO2 moves into alveoli during apnea with the remainder being
  buffered in the bloodstream
- On average, PaCO2 increases 8-16 mmHg in the first minute of apnea and then
  approximately 3 mmHg/min subsequently

One comment