Getting a little sciencey…
So I’ve been talking about a lot of different techniques for increasing inflation, ventilation, and (ultimately) perfusion that therapists can utilize with patients. However, I’ve been mentioning here and there that some of these need to be utilized with caution in patients who have obstructive lung conditions. Please heed my warning. Here’s one of the reasons why…
What is Hypercapnia?
Hypercapnia, also known as hypercarbia and CO₂ retention, is a condition of abnormally elevated carbon dioxide levels in the blood. PaCO2 > 45 mmHg.
What this basically results in physiologically is that the normal respiratory drive no longer exists. The changes in PaCO2 that the body experiences over the long term destroy certain receptors, so the only force keeping a CO2 retainer breathing is a lower O2 saturation. Titrating someone who is a retainer to above 95% can actually STOP them from breathing! Their body realizes a lack of NEED for oxygen.
What causes Hypercapnia?
- COPD (chronic bronchitis + emphysema)
- Interstitial lung disease
- Narcotic overdose
- Obstructive Sleep Apnea (OSA)
Symptoms of hypercapnia
- Acute hypoxic respiratory failure (ARF – we’ve mentioned this before) / ARDS
- Irregular Heart Rate/Rhythm
What Can You Do?
- Obtain “titrate to” oxygen orders for a tailored approach to maintaining resting and active saturation between 88-92% (or whatever other parameters the pulmonologist decides upon) to reduce risk of hypoxemia but also manage hypercapnia.
- Refer the patient for Sleep Study if they have a history of Acute Hypoxic Respiratory Failure
- Encourage the use of CPAP/BiPAP (Non-Invasive Ventilation (NIV) treatment)
Did you know?
Daytime hypercapnia and nocturnal hypoxia are predictors of CPAP failure in patients with OSA-COPD overlap syndrome. An increase of CT90% (defined as the time with SpO2 < 90% of total sleep time) by 1% increases the likelihood of CPAP failure by ∼6%.
Bilevel positive airway pressure (BiPAP) therapy effectively alleviates hypercapnia in patients with primary CPAP failure.
What about COVID-19?
BiPAPs have been found to not be effective for the treatment of patients with COVID-19 (WCPT, 2020 – see resources page). However, NIPPV has been utilized in certain circumstances which is a similar intervention that uses a CPAP or BiPAP machine. High Flow Nasal Oxygen (HFNO) has also been utilized due to the severe desaturation COVID patients experience. We will talk more about these in another post.
This becomes a risk vs benefit analysis. If you are seeing a patient who has COPD and is or is not a CO2 Retainer, but you feel they may need some of these inspiratory or hyperinflation interventions, then provide them. But do so knowing that you should be monitoring oxygen levels, limiting hyperinflation as much as possible to obstructed segments, and know the signs and symptoms of decline in your patient.
As we’ve discussed in other posts, patients who have COPD are at particular risk of decline when also affected by COVID-19 because of their long-term use of corticosteroids. When they return home or if they are being treated in the home primarily, you may end up treating a COPD exacerbation more than the effects of COVID-19. It will be patient-dependent. Keep your AGP precautions in mind.
As PTs and other rehab professionals, we cannot diagnose someone as a CO2 retainer, but we can definitely look at the ABGs and find our answers. Have you had any difficulty obtaining altered orders or parameters for patients who are CO2 Retainers? Let me know your stories in the comments!
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