MECHANICAL VENTILATION - INDICATIONS

Applications

Obvious examples

Anticipated examples

Maintain gas exchange

  • Cardiorespiratory arrest
  • Cardiorespiratory disease not responding to supplemental oxygen and maximal medical treatment
  • Major thoraco-abdominal surgery
  • Excessive metabolic requirements (e.g. sepsis)
  • Neuromuscular disorders/Muscle relaxant use

Reduce work of breathing

Cardiorespiratory disease not responding to supplemental oxygen and maximal medical treatment Progressive patient fatigue

Control carbon dioxide elimination

Raised ICP
Pulmonary hypertension

 

Heavy Sedation/Anaesthesia
Neurosurgery

Why control gas exchange?

Oxygenation

  • Oxygen is required to maintain normal cellular function (at critically low levels, cellular function will fail or become irreparably damaged)
  • In disease, oxygen
    • delivery can be impaired (e.g. pneumonia) or
    • demand can be increased (e.g. sepsis)
  • In both situations, the respiratory system may not be able to provide adequate delivery of oxygen to meet demand

Elimination of carbon dioxide

  • High levels of carbon dioxide generally do not cause any permanent damage to cells.  The main complication is progressive but reversible neurological dysfunction (e.g. drowsiness/coma)
  • High levels of carbon dioxide will cause cerebral vasodilation (this becomes significant where cerebral autoregulation is impaired e.g.  neurotrauma/surgery)
  • In disease, carbon dioxide:
    • elimination can be impaired (e.g. pneumonia) or
    • production can be increased (e.g. increased work of breathing from cardiorespiratory disease, sepsis)
  • The decision to ventilation is based more on the observed clinical effect of hypercarbia then the absolute level 

Why control work of breathing (WOB)?

  • Normal spontaneous respiration WOB is minimal but in disease WOB can increase significantly
  • Increased WOB causes
    • increases carbon dioxide production and increased ventilatory demand (vicious circle)
    • increased oxygen demand (reducing oxygen reserves to vital organs)

Criteria for ventilation

The following suggests that respiratory function is significantly taxed or failing but the absence or presence of these should not substitute for expert clinical assessment 

  • Conscious level

Drowsiness

  • Respiratory effort

Severe distress
Extreme fatigue

  • RR 

 > 35

(10-20 breaths/min)
  • Tidal volume 

 < 5

 (5-7ml/kg)
  • SaO2

< 90% (high flow O2)

>97% (air)
  • pO2

< 60 (FiO2< 60%)

(75-100 mmHg on air)
  • pCO2

> 60 (or rising)

(35-45 mmHg )

 

 

 

 
Disclaimer: Note: The information described here relates solely to operational matters in the Emergency Department.  Every effort has been made to verify the accuracy of the content. However, neither the author or the hospital will take responsibility for errors resulting from its use.  Please refer to your own departmental guidelines and verify all clinical decisions with a reliable source.  

Date Last Reviewed: 05/08/2004