| | 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
|
|
|
|
Drowsiness
|
|
|
Severe distress
Extreme fatigue
|
|
|
> 35
|
(10-20 breaths/min) |
|
< 5
|
(5-7ml/kg) |
|
< 90% (high flow O2)
|
>97% (air) |
|
< 60 (FiO2< 60%)
|
(75-100 mmHg on air) |
|
> 60 (or rising)
|
(35-45 mmHg ) |
|