A perfect example of this is with noninvasive ventilation (NIV) for treatment of acute respiratory distress due to chronic obstructive pulmonary disease (COPD). Savi et al, 2014, notes the following:
Noninvasive ventilation benefits patients with COPD, and it seems reasonable to expect that NIV would increase tidal volume and improve CO2 elimination, and thus reduce respiratory drive.The note the studies have proven that NIV results in the following when used on COPD patient's presenting to the emergency room with flare-ups:
- Reduction of treatment failure
- Lower mortality
- Fewer complications
- Lower Intubation rates
However, the studies also conclude that: "In these patients CO2 elimination is increased but overall ventilation-perfusion mismatch is not changed during NIV.
What does improve ventilation, the authors note, are the following:
- Treating precipitating factors (eg, infection with antibiotics)
- Increase expiratory flow (eg, with beta agonists)
- Reduce pulmonary inflammation (eg, with corticosteroids)
- Manage gas exchange (eg, improve oxygenation)
Without NIV, studies have shown, patient's who have COPD with CO2 retainers should receive an FiO2 just enough to maintain an SpO2 of 88-92%, as higher FiO2s (either due to the loss of hypoxic drive, or V/Q mismatching) have been shown to cause a rise in PaCO2.
However, this effect is negated with NIV. Savi et al concludes:
During NIV with an FiO2 sufficient to maintain a normal PaO2, a further increase in FiO2 does not result in an increase in PaCO2 in CO2-rataining COPD patients, since no changes occur in (minute ventilation).Crossley et al had similar results, concluding, that "CO2-retaining COPD patients following a period of mechanical ventilation with PaO2 in the normal range can safely receive supplemental oxygen without retaining CO2 or a depression of respiratory drive. A new ventilation-perfusion relationship is established during ventilation to normoxia, and it is not altered by further increasing FiO2," Savi et all reports.
Since NIV helps COPD patients take deeper breaths, thus improving their ventilation (allowing them to blow off CO2), high levels of oxygen do not cause rising PaCO2 levels while a patient is receiving NIV therapy. However, we often find that, while using NIV, many patients require less oxygen compared to prior to the NIV start.
Bottom line: NIV is beneficial to CO2-retaining COPD patients because it increases their tidal volume, increases CO2 elimination, and reduces their drive to breathe. By treating these symptoms, caregivers are provided an opportunity to do whatever is necessary to treat the cause of the exacerbation (even if that means utilizing higher oxygen levels).
- Savi, Augusto, Jucara Gasparetto Maccari, Tulio Frederico Tonietto, Ana Carolina Pecanha Antonio, Roselaine Pinheiro de Oliveira, Marcelo de Mello Rieder, Evelyn Cristina Zignani, Emerson Boschi da Silva, and Cassiano Teixeira, "Influence of FiO2 on PaCO2 During Noninvasive Ventilation in Patients With COPD," Respiratory Care, March, 2014, volume 59, number 3, pages 383-387