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Permissive hypercapnia

Robert C Hyzy, MD
Jorge Hidalgo, MD
Section Editor
Polly E Parsons, MD
Deputy Editor
Geraldine Finlay, MD


Mechanical ventilation was traditionally applied with the aim of normalizing blood gas values, particularly the arterial carbon dioxide tension (PaCO2). However, this is no longer the primary goal of mechanical ventilation. The emphasis is now on maintaining adequate gas exchange while minimizing the risks of mechanical ventilation. Acceptance of the hypercapnia and continuation of the ventilation strategy is called permissive hypercapnia [1]. Permissive hypercapnia is supported by the observation that hypercapnia is well tolerated and may be advantageous to patients with pulmonary disease [2].

Examples of strategies to reduce the risk of mechanical ventilation include (1) low tidal volume ventilation to protect the lung from ventilator-associated lung injury in patients with acute lung injury and (2) reduction of the tidal volume, respiratory rate, or both to minimize intrinsic positive end-expiratory pressure (ie, auto-PEEP) in patients with obstructive lung disease, thereby protecting the lung from barotrauma.

Typical clinical situations in which permissive hypercapnia may be used are reviewed here, as well as the contraindications, technique, benefits, and potential harms. The use of permissive hypercapnia in patients with acute respiratory distress syndrome and asthma is reviewed separately. (See "Mechanical ventilation of adults in acute respiratory distress syndrome" and "Invasive mechanical ventilation in adults with acute exacerbations of asthma".)


Clinical scenarios in which permissive hypercapnia may be appropriate include acute respiratory distress syndrome (ARDS) managed with low tidal volume ventilation and obstructive lung disease (asthma and chronic obstructive pulmonary disease [COPD]) managed with a low tidal volume and/or a low respiratory rate to minimize intrinsic positive end-expiratory pressure (ie, auto-PEEP); :

ARDS – Low tidal volume ventilation improves important clinical outcomes in patients with ARDS. The respiratory rate is routinely increased during low tidal volume ventilation in an effort to maintain adequate minute ventilation. However, the increased respiratory rate may be insufficient to compensate for the low tidal volumes and hypercapnia may develop. (See "Mechanical ventilation of adults in acute respiratory distress syndrome", section on 'Low tidal volume ventilation'.)

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Literature review current through: Nov 2017. | This topic last updated: Aug 16, 2016.
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