Appropriate Tidal Volume for Patients with Obesity Hypoventilation Syndrome
For patients with obesity hypoventilation syndrome (OHS), a tidal volume of 6-8 ml/kg of predicted body weight (PBW) is recommended to reduce pulmonary complications. 1
Ventilation Strategy for OHS Patients
Tidal Volume Selection
- Use predicted body weight (PBW) rather than actual body weight when calculating tidal volumes, as lung volume does not increase proportionally with body weight in patients with obesity 1
- Target tidal volumes of 6-8 ml/kg PBW to provide lung-protective ventilation and reduce pulmonary complications 1
- For volume-targeted BiPAP, the recommended tidal volume target is 8 ml/kg using ideal body weight 1
- Avoid excessive tidal volumes (>10 ml/kg PBW), which can cause overdistension and lung injury without improving oxygenation 2
Calculating Predicted Body Weight
- For males: PBW = 50 + 0.91 × (height in cm - 152.4) kg 1
- For females: PBW = 45.5 + 0.91 × (height in cm - 152.4) kg 1
- Using arm demispan to calculate height can be helpful when direct height measurement is difficult 3
Additional Ventilation Parameters
- Consider individualized PEEP settings to reduce postoperative atelectasis and improve gas exchange 1
- Monitor driving pressure (plateau pressure minus PEEP), as patients with obesity may require higher cut-off values than non-obese patients 1
- For non-invasive ventilation, increase pressure support if tidal volume remains below the 6-8 ml/kg PBW target 1
- Use ST mode (backup rate) if frequent central apneas are present or if the patient fails to reliably trigger the device due to muscle weakness 1
Clinical Considerations and Pitfalls
Common Pitfalls
- Using actual body weight instead of PBW leads to excessive tidal volumes, especially in obese patients 1, 3
- Women are at higher risk of receiving excessive tidal volumes when actual body weight is used for calculations 3, 4
- Failure to adjust ventilation parameters based on clinical response may result in persistent hypoventilation 1
Monitoring and Adjustments
- Increase pressure support if arterial PCO2 remains 10 mmHg above goal for 10 minutes or more 1
- Target PCO2 values less than or equal to the awake PCO2 1
- Increase pressure support if SpO2 remains below 90% for 5 minutes or more and tidal volume is low (<6-8 ml/kg) 1
- Monitor for adequate respiratory muscle rest, indicated by resolution of tachypnea and excessive inspiratory effort 1
Treatment Modalities
- CPAP is considered first-line treatment for OHS patients with concomitant severe obstructive sleep apnea 5
- NIV is preferred for OHS patients with hypoventilation during sleep with no or milder forms of obstructive sleep apnea 5
- For acute-on-chronic hypercapnic respiratory failure, NIV is typically the treatment of choice 5
By adhering to these lung-protective ventilation strategies with appropriate tidal volumes based on predicted body weight, clinicians can reduce the risk of ventilator-induced lung injury and improve outcomes in patients with obesity hypoventilation syndrome.