Assessing and optimizing respiratory drive at the bedside

Irene Telias, Canada

Respiratory drive is the output of respiratory centers that control the magnitude of inspiratory effort

Why assess respiratory drive?

  • Derangements are frequent
  • Can have adverse consequences on diaphragm/lungs/ sleep

Respiratory control is complex

  • Chemoreflex – pH, pCO2 and pO2 via central and peripheral chemoreceptors control the output of the respiratory center
  • Multiple factors modify the drive in ICU patients (inflammation, metabolic demands, mechanical ventilation etc)

Monitoring

  • Respiratory center cannot be monitored directly. Respiratory drive is a surrogate
  • Measures of respiratory drive can be used to estimate inspiratory effort and vice versa

Techniques

  • Electrical activity of the diaphragm (EAdi)
  • Mechanical activation of diaphragm (Diaphragm Ultrasound)
  • Esophageal or gastric pressure measurement
  • P0.1 or Pocc
  • P0.1 specific for respiratory drive
  • Respiratory rate is not a good measure of the drive (except when it is <17 or >30 in ICU patients)

How is it done?

  • Majority of vents do it
  • P0.1 is the drop in airway pressure in the first 100 msec; Pocc is the drop in airway pressure during an end expiratory occlusion maneuver
  • P0.1 – Surrogate of respiratory drive, validated

High Respiratory drive

  • P0.1 > 3.5 – 4 cmH2O– High respiratory drive
  • Identify modifiable factors (adjust flow and tidal volume, reduce dead space, treat infection, pain etc)
  • PEEP and FiO2 adjustment
  • Sedation and analgesia

Low respiratory drive

  • 1 <1 cmH20
  • Typically, in patients recovering from respiratory failure – usually on high levels of PS – causes apnea and disrupted sleep
  • Reduce PS or use other modes