PulmCrit (EMCrit)
PulmCrit - June 20, 2016 - By Josh Farkas
"ARDS causes shunting of deoxygenated blood through the lungs. Most therapies for ARDS naturally combat this shunting (e.g. opening alveoli with PEEP). However, there is often a limit to which pulmonary shunting is treatable.
Jujitsu is a Japanese martial art based on flexibility and technique, rather than a directly confronting an opponent with force. In the spirit of jujitsu, this post explores how to support ARDS patients without directly confronting lung dysfunction. This is useful in refractory ARDS, when frontal assault has failed.
- Four variables determine systemic oxygen delivery in ARDS:
- cardiac output
- hemoglobin concentration
- systemic oxygen consumption (VO2)
- fraction of blood shunted through the lungs without being oxygenated
- Therapies for ARDS focus on reducing the shunt fraction (e.g., PEEP, proning, APRV). Patients with refractory shunting will be refractory to these therapies.
- Among patients with refractory ARDS, manipulations of other variables could improve systemic oxygen delivery:
- reduced systemic oxygen consumption (paralysis, temperature control)
- increased hemoglobin concentration (blood conservation, possibly transfusion)
- increased cardiac output (inotropes)
- Arterial oxygen saturation is not a reliable measurement of systemic oxygen delivery (DO2).
- It’s notable how little we know about oxygenation goals when treating ARDS. Over-emphasis on normalizing arterial oxygen saturation may be leading us astray."