This is an important issue. We have been struggling with the use of NIV on the wards. From my personal observation there are 3 issues that must be addressed.
1. The 2 most common causes of hypercapnic failure are COPD and obesity hypoventilation syndrome (OHS). I am not sure that NIV should be set similarly or used at the same time of the day. Most patients with OHS have severe OSA and require high levels of CPAP (10-20 cmH2O) when they are asleep. Once the upper airway is open they might require some inspiratory support if there tidal volumes were low. On the other hand, patients with COPD usually have intrinsic PEEP that can be overcome with EPAP of 5-8 cmH2O. If their tidal volumes remain high despite EPAP, then high inspiratory support of 8--10 cmH2O might be needed.
2. In patients with OHS, airway obstruction and hypoventilation occurs mostly when they sleep and this is when they need NIV the most. on the other hand, patients with COPD have airway obstruction all around the day and will need NIV awake or asleep.
3. When were the blood gases measured? On NIV, off NIV, an hour off NIV, 2 hours after NIV? many times the ward team measures blood gases on NIV, and not so surprisingly, they show improvement. When they are repeated few hours after removing the NIV, they frequently worsen.
Article Does Noninvasive Ventilation Delivery in the Ward Provide Ea...
I have noticed that the PCO2 improves on NIV during the hospitalization but with the price of causing alkalosis. Once the the NIV is removed, the PCO2 increases probably in response to the alkalosis.
In sum, what I am trying to say is that hypercapnic respiratory failure is complex and in treating it the etiology and the compensation should be considered before setting NIV, interpreting blood gases, and giving other therapies.
I would agree with the idea for non-invasive monitoring in this situation but I have no experience in using transcutaneous monitors in adult patients. It would be my guess that this would be particularly problematic in obese patients. I do have a lot experience with the use of end-tidal CO monitors in patients who are receiving NIV for treatment of acute-on-chronic hypercapnia, The end-tidal monitors made by Covidien and Oridian are able to measure reliably (using a proprietary nasal cannula) while the patient is receiving mask ventilation. Initially we would observe a significant disparity between end-tidal and arterial CO2 values. As the patient improves, the disparity narrows. Use of this monitor presumes that the staff who will care for the patient is comfortable with this technology. With regard to your comment on post-NIV alkalosis, could you describe its etiology (respiratory or metabolic)? If metabolic, is Diamox a therapeutic option (assuming K+ and Cl are WNL)?
- Badges
- Science topic