MECHANICAL VENTILATION
Process by which air is moved into and out of the lungs by a mechanical ventilator
- FiO2 >21% up to 100% oxygen!
- Purpose is to optimize gas exchange by maintaining ventilation and oxygen delivery
- The ventilator has tubing that attaches to an advanced airway (endotracheal tube or
tracheostomy) through which the ventilator delivers oxygen to the lungs
- NOT a cure, just a means of support so, once goal is met, patient must be weaned off
Indications:
a. Apnea or impending apnea
b. Acute respiratory failure
c. Severe hypoxia
d. Shock
e. Respiratory muscle fatigue
Types:
May be positive or negative pressure breathing device
1) Negative pressure ventilation – not used anymore
2) Positive-pressure ventilators
Inflate the lungs by exerting positive pressure on the airway, pushing air in and forcing the
alveoli to expand while expiration occurs passively
!!!!Using positive pressure ventilation, intrathoracic pressures are increased causing venous
return to decrease and consequent hypotension RAAS activation*
*RAAS explained at the end
, POSITIVE PRESSURE VENTILATORS
Ventilator settings include:
1. Tidal volume (Vt)
o Volume of air set to be delivered with each breath (usually 6-15 ml/kg)
2. Rate
o Number of breaths per minute (usual 6-20 breaths/min)
3. Minute ventilation
o Amount of air delivered per minute
o Respiratory rate x tidal volume = minute ventilation
4. FiO2
o Oxygen concentration
o 21%-100%
o Levels higher than 60% constantly can lead to toxicity and cause alveolar
damage)
o At the least amount required and adjusted to maintain SaO2 > 90%
5. PEEP (positive end expiratory pressure)
o Constant pressure applied throughout expiration to prevent closure of alveoli
o At least 5 cm H20
o Increased when SaO2 isn’t high enough but high levels should not be
discontinued suddenly bc alveoli may not be ready
o Gas trapped in the lungs at the end of exhalation can result in auto-PEEP
(additional PEEP over set) and a total PEEP level that is excessive.
o Auto PEEP may be avoided by sedation, analgesia, bronchodilators etc.
o Helps in pulmonary edema but not to be used with COPD, hypovolemia
Advantages:
- Alveolar recruitment
- Improved gas exchange
- Decreased work of breathing (alveoli stay a little open during expiration making
inspiration easy)
- Decrease FiO2
Process by which air is moved into and out of the lungs by a mechanical ventilator
- FiO2 >21% up to 100% oxygen!
- Purpose is to optimize gas exchange by maintaining ventilation and oxygen delivery
- The ventilator has tubing that attaches to an advanced airway (endotracheal tube or
tracheostomy) through which the ventilator delivers oxygen to the lungs
- NOT a cure, just a means of support so, once goal is met, patient must be weaned off
Indications:
a. Apnea or impending apnea
b. Acute respiratory failure
c. Severe hypoxia
d. Shock
e. Respiratory muscle fatigue
Types:
May be positive or negative pressure breathing device
1) Negative pressure ventilation – not used anymore
2) Positive-pressure ventilators
Inflate the lungs by exerting positive pressure on the airway, pushing air in and forcing the
alveoli to expand while expiration occurs passively
!!!!Using positive pressure ventilation, intrathoracic pressures are increased causing venous
return to decrease and consequent hypotension RAAS activation*
*RAAS explained at the end
, POSITIVE PRESSURE VENTILATORS
Ventilator settings include:
1. Tidal volume (Vt)
o Volume of air set to be delivered with each breath (usually 6-15 ml/kg)
2. Rate
o Number of breaths per minute (usual 6-20 breaths/min)
3. Minute ventilation
o Amount of air delivered per minute
o Respiratory rate x tidal volume = minute ventilation
4. FiO2
o Oxygen concentration
o 21%-100%
o Levels higher than 60% constantly can lead to toxicity and cause alveolar
damage)
o At the least amount required and adjusted to maintain SaO2 > 90%
5. PEEP (positive end expiratory pressure)
o Constant pressure applied throughout expiration to prevent closure of alveoli
o At least 5 cm H20
o Increased when SaO2 isn’t high enough but high levels should not be
discontinued suddenly bc alveoli may not be ready
o Gas trapped in the lungs at the end of exhalation can result in auto-PEEP
(additional PEEP over set) and a total PEEP level that is excessive.
o Auto PEEP may be avoided by sedation, analgesia, bronchodilators etc.
o Helps in pulmonary edema but not to be used with COPD, hypovolemia
Advantages:
- Alveolar recruitment
- Improved gas exchange
- Decreased work of breathing (alveoli stay a little open during expiration making
inspiration easy)
- Decrease FiO2
