Page 417 - Clinical Application of Mechanical Ventilation

Management of Mechanical Ventilation 383

Initiate Continuous Positive Airway
Pressure (CPAP)

Continuous positive airway pressure (CPAP) provides positive airway pressure
CPAP is only suitable for throughout the spontaneous breathing cycle. It increases the functional residual
patients who have adequate
respiratory mechanics and can capacity and is useful to correct hypoxemia due to intrapulmonary shunting. Since
sustain prolonged spontane- CPAP does not provide mechanical ventilation, it is suitable only for patients
ous breathing.
who have adequate respiratory mechanics and can sustain prolonged spontaneous
breathing. Adequacy of spontaneous ventilation can be documented by trending a
patient’s PaCO . An increasing PaCO over time indicates that the patient is tiring,
2
2
and continuation of CPAP must be reevaluated.
Initiate Positive End-Expiratory Pressure (PEEP)

Positive end-expiratory pressure (PEEP) provides positive airway pressure at the end
CPAP and PEEP increase of exhalation from a mechanical breath. It is similar to CPAP with the exception
the functional residual
capacity and are useful to that PEEP is used in conjunction with mechanical ventilation. With PEEP, sponta-
correct hypoxemia due to neous breathing is not required because the patient relies on the ventilator for ven-
intrapulmonary shunting.
tilatory support. Similar to CPAP, PEEP increases the functional residual capacity
and is therefore useful to correct hypoxemia due to intrapulmonary shunting.
In order to minimize the cardiovascular complications associated with excessive
pulmonary pressures, the optimal PEEP should be used in uncomplicated intra-
optimal PEEP: The lowest PEEP
level leading to the best oxygen- pulmonary shunting (e.g., post-operative atelectasis). Optimal PEEP may be deter-
ation status (or other indicators) mined by evaluating different parameters, such as PaO , compliance, O saturation,
without causing significant 2 2
cardiopulmonary complications. and ventilator waveforms. Table 12-4 shows that 10 cm H O is the optimal PEEP
2
since the next level of PEEP (12 cm H O) causes a decrease of PaO and compliance.
2
2

TABLE 12-4 Titration of Optimal PEEP Using PaO 2 and Compliance as Indicators

PEEP (cm H O) PaO (mm Hg) Compliance (mL/cm H O)
2
2
2
0 43 26
5 67 33
8 77 37

10* 83 43

12 79 41

*In this example, 10 cm H 2 O is the optimal PEEP since the PaO 2 and compliance show a continuing upward
trend with the increasing PEEP level from 0 to 10 cm H 2 O. Beyond the optimal PEEP, the next PEEP setting (12 cm
H 2 O) causes the PaO 2 to drop from 83 to 79 mm Hg and the compliance to fall from 43 to 41 mL/cm H 2 O. It is not
necessary to use more than one indicator to titrate the optimal PEEP. As shown above, the PaO 2 indicator is more
time-consuming and invasive than the compliance indicator. Since compliance is a function of DV/ DP, the volume-
pressure waveform may be used to titrate the optimal PEEP. (See Chapter 15 for titration of optimal PEEP using the
decremental recruitment maneuver.)
© Cengage Learning 2014

Copyright 2013 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).
Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.