Page 421 - Clinical Application of Mechanical Ventilation

Management of Mechanical Ventilation 387

Respiratory Acidosis and Compensated
Metabolic Alkalosis

Respiratory acidosis (ventilatory failure) is caused by hypoventilation. The strategy
to correct this abnormality is to improve ventilation. For specific procedures to
improve ventilation, refer to the section on “Strategies to Improve Ventilation” at
the beginning of this chapter.
The strategies to improve ventilation are useful only when respiratory acidosis is
If a patient hypoven- caused by hypoventilation. These strategies should not be used when hypoventila-
tilates to compensate for
metabolic alkalosis, increasing tion occurs as a compensatory mechanism for metabolic alkalosis. Compensated
ventilatory support will further metabolic alkalosis has an elevated PaCO , thus mimicking the elevated PaCO seen
compromise spontaneous 2 2
ventilation. in primary or compensated respiratory acidosis.
Table 12-7 compares the typical blood gases of compensated respiratory acidosis and
-
compensated metabolic alkalosis (both show high PaCO and high HCO ). Note
3
2
-
that in primary respiratory acidosis, the HCO is within its normal range (i.e., early
3
stage; no renal compensation). In compensated respiratory acidosis, the pH (7.37) is
on the acidotic side of its normal range (7.35–7.45). In compensated metabolic alka-
losis, the pH (7.42) is on the alkalotic side of its normal range (7.35–7.45). As with
other blood gas abnormalities, the patient’s clinical data and presentation should be
used to differentiate a respiratory or metabolic problem.

Respiratory Alkalosis and Compensated
Metabolic Acidosis

If hyperventilation is due to Respiratory alkalosis is caused by alveolar hyperventilation. In general, this con-
metabolic acidosis, reducing the
ventilator frequency will cause dition does not require mechanical ventilation intervention and it usually allows
the patient to continue with gradual weaning of the ventilator frequency. However, if the hyperventilation is due
hyperventilation until respiratory
muscle fatigue occurs. to metabolic acidosis, the cause must be identified and treated. Otherwise, weaning
the ventilator frequency will cause further patient hyperventilation due to uncor-
rected and persistent metabolic acidosis.
Additional deadspace tubing between the endotracheal tube and ventilator “Y”
adaptor is sometimes used to partially correct persistent respiratory alkalosis. This

TABLE 12-7 Differentiation of Compensated Respiratory Acidosis and Compensated Metabolic Alkalosis
2
Blood Gas Condition pH PaCO (mm Hg) HCO (mEq/L)
3
2
Primary respiratory acidosis 7.31 53 26
Compensated respiratory acidosis 7.38 52 30
Compensated metabolic alkalosis 7.43 50 32
© 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.