How to treat hypercapnia in a mechanically ventilated (ventilated) patient?

From the Guidelines

To treat hypercapnia in a ventilated patient, permissive hypercapnia is acceptable, allowing pH to remain above 7.20, as evidenced by the most recent and highest quality study 1.

Treatment Approach

When managing hypercapnia in mechanically ventilated patients, the primary goal is to balance the need to reduce CO2 levels with the risk of causing lung injury due to over-distension or repetitive recruitment/de-recruitment of lung units. The approach should be tailored to the individual patient's condition, such as ARDS, obstructive disease, or neuromuscular disease.

Ventilator Settings

• Adjust ventilator settings to achieve a tidal volume of 6-8 mL/kg and a respiratory rate of 10-15 breaths per minute, as recommended for initial settings in acute hypercapnic respiratory failure 1.
• Ensure an inspiratory to expiratory (I:E) ratio that favors adequate expiratory time, typically 1:2 or 1:3, to prevent air trapping.
• In cases of obstructive disease, consider prolonging the expiratory phase to reduce dynamic hyperinflation.

Permissive Hypercapnia

• Permissive hypercapnia, with a pH target above 7.20, is a safe and effective strategy in certain patients, particularly those with ARDS, as it reduces mortality by avoiding ventilator-induced lung injury 1.
• This approach may also be beneficial in other conditions where lung protective strategies are crucial.

Additional Considerations

• Regular arterial blood gas monitoring is essential to assess the effectiveness of interventions and guide further adjustments.
• Address the underlying cause of hypercapnia, whether it's increased CO2 production, decreased elimination, or ventilator-related issues.
• Optimize sedation to prevent patient-ventilator dyssynchrony while avoiding respiratory depression.
• Consider extracorporeal CO2 removal in severe cases where other measures are insufficient.

Evidence-Based Practice

The recommendation for permissive hypercapnia is based on the most recent and highest quality evidence available, specifically the BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults 1, which provides a consensus target for pH control and supports the use of low tidal volume strategies to improve survival in ARDS patients.

From the Research

Treatment of Hypercapnia in Mechanically Ventilated Patients

To treat hypercapnia in mechanically ventilated patients, the following approaches can be considered:

• Non-invasive ventilation (NIV) is the primary treatment for hypercapnic respiratory failure, unless there are contraindications 2, 3
• The initial settings for NIV therapy to treat stable hypercapnia are: Pressure Support Ventilation Modus, EPAP 5 cmH2O, IPAP 15 cmH2O, Back Up rate 15/Minute 4
• The goal of NIV treatment is to reduce CO2 levels, which can be achieved by adjusting the ventilator settings, such as increasing IPAP, backup respiratory rate, or using assisted pressure-controlled ventilation mode (APCV) 4
• In cases of severe respiratory acidosis, invasive mechanical ventilation may be necessary, and ventilator settings should aim to prevent overinflation and increase of intrinsic PEEP 2, 3
• Extracorporeal CO2 removal (ECCO2R) is an experimental therapy that may be considered in individual situations, but its significance is still ambiguous and it should only be applied by a specialist team trained in its use 2, 3

Ventilator Settings

The ventilator settings for hypercapnic patients depend on the underlying cause and pathophysiological situation:

• In acute exacerbation of COPD, ventilator settings need a long expiration and short inspiration time to avoid further hyperinflation and an increase in intrinsic PEEP 3
• In patients with obesity hypoventilation syndrome (OHS) or overlap syndrome, ventilation must be adapted to the pathophysiological situation 3
• Limited peak inspiratory pressure (PIP) and permissive hypercapnia may be used in patients with severe pulmonary blast injury, with the goal of maintaining PIP at less than 40 cm H2O and correcting arterial pH by increasing the ventilator rate 5

Monitoring and Management

Close monitoring is necessary to avoid missing the indications for intubation and invasive ventilation:

• Patients with severe respiratory acidosis require a skilled and experienced team and close monitoring to perceive a failure of NIV 2, 3
• The use of NIV is the predominant treatment in patients with hypercapnic respiratory failure, but close monitoring is necessary to adjust the treatment as needed 3