V/Q Matching

With new evidence emerging hourly in some cases, the more we learn about treating COVID-19, the more we need to know from a clinical intervention perspective for those in the rehabilitation fields. There is a lot of information out there for doctors and nurses and respiratory therapists. Unfortunately, many Rehab Therapists are being told to stay away. But the truth is: we have a lot to offer!

COVID-19 is presenting as a restrictive lung disease with some other confounding factors. But what that means is that consolidation is not a huge concern. Of course, if the patient has other comorbidities (COPD, CHF, PNA…) we definitely want to make sure we are addressing the exacerbated states of those conditions which will likely involve secretion management. But for the majority of patients, consolidation will not be a concern.

---

So what can we do for them instead?

---

V/Q Matching

V = Ventilation
Q = Perfusion

Ventilation is the literal act of what we consider breathing: moving air into and out of our lungs. Perfusion is the rate at which the oxygen we inspire is delivered to our organs via our blood stream. There is an incredibly important step that happens between V and Q, called diffusion, or the process by which oxygen passes through the alveolar membrane from lung to vessel. Diffusion is ultimately what is impacted here.

People who have ventilatory problems can’t get air in for one reason or another. Some examples may be a blocked airway, too many secretions, or too much dead air (think COPD). Some people have perfusion issues so they cannot get blood to where is needs to go. These may include diabetic arterial calcifications, peripheral vascular disease, or extraneous compression of the tissues (think edematous compression on arteries or a tourniquet). Diffusion deficits results from destruction of the alveolar membrane.

V/Q matching issues can present for many reasons like a PE blocking a lung segment or secretions covering too much alveolar surface area. Ultimately, V and Q values need to match or we get short of breath.

---

So what does this have to do with COVID-19?

---

We now know that COVID-19 presents like a restrictive lung disease, causing poor V/Q matching by preventing lungs to fully expand with air (they are restricted). The lung tissues (parenchyma) in patients with COVID-19 become edematous. The fluid is not in the airways, but in the interstitial spaces. This collapses the alveoli and stiffens the lung tissues preventing them from expanding properly (called diffuse alveolar damage). Therefore, oxygen cannot get in. This is marked clinically by oxygen desaturation after activity. However, as the condition progresses, less and less activity are required for desaturation. Ultimately, if this progresses too far and too wide, it results in ARDS. You can learn more about that here.

---

So what can Rehab Clinicians do about this?

---

Rehab clinicians can play a pretty important role in improving V/Q matching. We are currently hearing a lot about proning patients. Proning is simply the act of turning the patient prone. You can imagine that in the ICU, this is intensely difficulty and can be risky for the patient. Proning typically takes a team to achieve in this setting and rehab professional need to be part of this team. Management of lines, leads, and ventilator tubing is only part of the battle. These patients are chemically paralyzes so are completely non-participatory in the process. Positioning to prevent skin breakdown and contractures will be important here.

Outside of the acute setting, patients will be working toward recovery and some parts of their lung parenchyma may be recovering faster than others. We can use lung auscultation to determine where less ventilation is taking place (we would call this area “diminished”).

• First off, if there is consolidation, it needs to be cleared. Consolidation blocks small airways and impairs V/Q matching.
• Second, we need to reduce external constriction to the affected segments. Laying on the affected segment will compress it and not allow for expansion during inspiration. Tight clothing should be removed.
• Third, if needed, we should apply interventions to help expand the collapsed segments. This may include segmental breathing (targeting breath toward the segment) to recruit more alveolar units, utilizing positive expiratory pressure (even simply pursed lip breathing when done properly), or manual interventions (see my video on ACBT for some ideas) to improve diaphragm activation to deepen the breath and improve rib cage expansion.
• Intentional dynamic hyperinflation using glossopharyngeal breathing may also be advantageous to increase open alveoli that had been collapsed. (This was also used during the Polio epidemic!)
  However, use this with caution in patients with concurrent obstructive disease.
• IMTs and manual resistance can be used to increase diaphragm strength.
• Visual feedback (like a mirror) can help with re-education of muscle recruitment and coordination.

Intermittent Positive Pressure Breathing (IPPB) may sound like a good idea, but it is not currently recommended due to the open loop system which could aerosolize particles and increase your risk of infection. Most clinicians wouldn’t have this available to them in the home environment, anyway.

---

Have you ever intentionally provided an intervention to target V/Q matching? How did you document it? Let me know in the comments!

image credit

• WordPress
• Twitter
• LinkedIn
• Instagram

Follow @DoctorBthePT on Twitter for regular updates!

Resources:
Dail CW. Glossopharyngeal breathing by paralyzed patients. Calif Med;1951:75217–218.

Maltais, F. (2010). Glossopharyngeal Breathing. American Journal of Respiratory and Critical Care Medicine. 184(3). https://doi.org/10.1164/rccm.201012-2031IM 

Mukhopadhyay, S. (2020). A Pulmonary Pathologist’s Perspective on COVID-19. Cleveland Clinic: Consult QD. https://consultqd.clevelandclinic.org/a-pulmonary-pathologists-perspective-on-covid-19/