2. GOALS OF MECHANICAL VENTILATION
Mechanical ventilation alone does not treat or reverse the underlying pathology
leading to the need for ventilator support. Rather, it is applied as one of the support
systems until the reversal of the pathological condition, so that the patient may
then become weaned from mechanical ventilation.
3. GOAL
Improve gas exchange
Relive respiratory distress
Improve pulmonary mechanics
Permit lung and airway healing
Avoid complication
TARGET
Reverse hypoxemia/Relieve acute respiratory
acidosis
Reverse respiratory muscle fatigue Prevent and
reverse atelectasis
Improve lung compliance/Maintain lung and
airway function
Prevent disuse respiratory muscle dystrophy
5. Mode
full ventilatory support (FVS) or
partial ventilatory support (PVS).
synchronized intermittent mandatory ventilation - provides full ventilatory support if the
patient is not breathing spontaneously between mechanical breaths, and the mandatory
frequency is set at 12/min or higher.
6. Frequency
intended to provide eucapneic ventilation (PaCO2 at patient’s normal).
usually set between 10 and 12/min
Frequencies of 20/min or higher are associated with auto-PEEP and should be avoided
˄ frequency if the PaCO2is too high; ˅ frequency if thePaCO2 is too low.
Minute ventilation
7. Tidal Volume
Initial 6 to 8 ml/kg IBW
IBW = (Ht – 152.4) * 0.91 + 45 for female / + 50 for male
Tidal volumes as low as 6 mL per kg of predicted body weight have been recommended for
ARDS patients
The primary reason for using lower tidal volumes (i.e., permissive hypercapnia) is to minimize
the airway pressures and the risk of barotrauma
8. Conditions That May Require Lower Tidal
Volumes
CONDITION
Increase of airway pressure requirement
Increase of lung compliance
Decrease of lung volumes
EXAMPLES
ARDS / Pulmonary edema
Emphysema
Pneumonectomy
9. Pressure Support
used to augment a patient’s breathing effort by reducing the airflow resistance during
spontaneous breathing
available in modes of ventilation that allows spontaneous breathing (e.g., SIMV).
For weaning
A PSV of greater than 30 cm H2O is rarely needed since these patients are typically not ready for
weaning
the PS level is reduced by 2 to 4 cm H2O increments as tolerated.
Extubation can be considered when the PS level reaches 5 to 8 cm H2O for 2 hours with no signs
of respiratory distress.
10. FIO2
For patients with severe hypoxemia or abnormal cardiopulmonary functions (e.g., post-
resuscitation, smoke inhalation, ARDS), the initial FIO2 may be set at 100%.
evaluated by means of arterial blood gas analyses
adjusted accordingly to maintain a PaO2 between 80 and 100 mm Hg (lower for patients with
chronic CO2 retention).
11. PEEP
Positive end-expiratory pressure (PEEP) increases the functional residual capacity and is useful
to treat refractory hypoxemia (low PaO2 not responding to high FIO2)
initial PEEP level may be set at 5 cm H2O.
PEEP should be based on the patient’s blood gas results, FIO2 requirement, tolerance of PEEP,
and cardiovascular responses.
13. I:E Ratio
I:E ratio is the ratio of inspiratory time to expiratory time
Kept in the range between 1:2 and 1:4
A larger I:E ratio (longer E ratio) may be used on patients needing additional time for exhalation
Inverse I:E ratios have been used to correct refractory hypoxemia in ARDS patients with very low
compliance.
Inverse I:E ratio should be tried only after traditional strategies have failed to improve a patient’s
ventilation and oxygenation status.
Note that the I time and I:E ratio are inversely related. A longer I time leads to a lower I:E ratio
COPD patients may also benefit from a reduced tidal volume setting. These patients
have reduced expiratory flow rates due to decreased alveolar elastic recoil
longer expiratory time is needed for complete exhalation
For patients with a reduction of lung volumes due to lung resection, lower
tidal volumes may also become necessary
The contributing factors of airflow resistance during mechanical ventilation may include the artificial
airway, ventilator circuit, and secretions.
because of the possibility of air
trapping and auto-PEEP. Presence of air trapping during mechanical ventilation
may be checked by occluding the expiratory port of the ventilator circuit at the
end of exhalation.
Depending on the features available on the ventilator, the I:E ratio may be altered
by manipulating any one or a combination of the following controls: (1) flow rate,
(2) inspiratory time, (3) inspiratory time %, (4) frequency, and (5) minute volume
(tidal volume and frequency).
