Slow, big breaths ain’t what the doctor’s ordering

This is part of a recurring series examining landmark articles in Emergency Medicine, in the style of ALiEM’s 52 Articles.

Discussing:  The Acute Respiratory Distress Syndrome Network. “Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome” N Eng J Med, May 2000; 342(18): 1301-08

Main Points

This landmark study was stopped early! It determined that in patients with acute respiratory distress syndrome (ARDS) who are treated with lower tidal volumes than those treated with traditional volumes:

  1. Mortality is decreased by 31.0% vs 39.8% (P = 0.007)
  2. Breathing without assistance increases by the 28th day by 65.7% vs 55.0%
  3. The number of ventilator free days increases by 12 ± 11 vs 10 ± 11. days (P = 0.007)

ARDS is a life-threatening condition for which the mortality was quoted in this study to be approximately 40 to 50 percent.  (To be blunt, any study that uses death as its primary outcome is looking at a very ill cohort.) 

Much has been learned about the pathophysiology of ARDS, but very little headway has been made in the treatment of it. The authors of this study looked at adjusting ventilatory tidal volume and plateau pressures for treatment for ARDS.  The authors also measured plasma interleukin-6 in the first 204 of 234 patients as a measure of lung inflammation. The results were significantly in favor of the lower tidal volume group.  

Details

This was a prospective, randomized controlled study that assorted 861 patients into two groups.  Patients were randomly selected to be treated with tradition ventilation treatments, initial tidal volumes of 12 ml per kilogram of predicted body weight and a plateau pressure of 50 cm of water or less, versus lower tidal volumes of 6 ml per kilogram of predicted body weight and a plateau pressure of 30 cm of water or less.

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ED Ventilator Settings

Quality Control editors at work.

Quality Control editors at work.

All excited for intubation but forget to optimize the ventilatory settings?

Important for those that are not rapidly taken away to the ICU.

Ventilation
Tidal Volumes: low tidal volumes 6 ml/kg (ideal body weight) even without acute lung injury is even beneficial.  Study by Determann et al. 2010 Critical Care.  Looked at 150 patients, randomized trial of 10 vs 6 ml/kg.  Development of Acute lung injury in 13.5 in the 10 ml/kg group and 2.6 in the 6 ml/kg group.  Stopped early because of difference.
Respiratory Rate: Minute ventilation is RRxTV.  You want a MV of 5-6L/min in a normal patient, but if need to increase for metabolic derrangement may need much higher.  Permissive hypercapnea is okay in those with ARDS.  Caution in those with brain injury and severe metabolic acidosis.  Don’t go higher than RR of 35.  Keep ph>7.15, as done in ARDSnet. Continue reading