Home-Based Mechanical Ventilation and Neuromuscular Disease
Transcutaneous Carbon Dioxide Monitoring: New Era for Home Ventilation
A primary objective of noninvasive home ventilation is normalization of arterial blood gas tensions, night and day. Pulse oximetry has long enabled estimation of arterial oxygen saturation (SpO2) in outpatient offices and overnight at home; however, until recently, measurement of the partial pressure of carbon dioxide (PCO2) has been limited to invasive arterial blood gas testing (PaCO2) or end-tidal CO2 (PetCO2) measurements. Assessment of PetCO2 has been limited by challenges in accessing true end-tidal exhaled gas under a face mask during noninvasive ventilation, particularly for patients with parenchymal lung diseases such as COPD.
Thanks to recent technological advances, transcutaneous measurement of carbon dioxide (PtcCO2) is emerging as the method of choice for assessing the adequacy of noninvasive ventilation. PtcCO2 monitoring is a standard assessment for pediatric patients in the sleep lab, and it is increasingly being utilized in adults to complement diagnostic and treatment purposes. The transcutaneous CO2 sensors work by heating underlying skin to approximately 43° C, increasing blood flow through the underlying dermal capillary bed. Within 2 to 5 minutes, the “arteriolized” capillary PtcCO2 approximates PaCO2. Commercially available devices for measuring PtcCO2 reliably estimate PaCO2 in patients undergoing noninvasive ventilation to within 5 mm Hg (95% CI) ().
PtcCO2 measurement has limitations. Measured PtcCO2 can drift upward (i.e., technical drift) during continuous monitoring; however, currently available devices adequately adjust for this phenomenon. Arterialization may be limited by thickened skin, edema, or hypoperfusion.
Currently, U.S. insurance companies do not accept PtcCO2 for documentation of hypercapnia, and the cost of measuring PtcCO2 is not reimbursed. Nevertheless, PtcCO2 technology promises a new era for home mechanical ventilation guided by accurate and practical assessment of PCO2, in particular for chronic respiratory failure syndromes. In this setting, home PtcCO2 monitoring potentially can be utilized in place of in-laboratory sleep studies for assessment of nocturnal hypoventilation and optimizing home mechanical ventilation.
Jason Ackrivo, MD
Steering Committee Member
Interstitial and Diffuse Lung Disease
Electronic Patient Education
The management of patients with an interstitial lung disease (ILD) is challenging. A provider must examine the fine details about current and prior medication history, explore various occupational and environmental exposures, perform a thorough physical examination that includes a careful dermatologic and rheumatologic review, and peruse the objective data, such as the high-resolution CT scan of the chest and pulmonary function tests. Then, the pulmonologist and the patient (plus often multiple family members) discuss diagnostic possibilities, any future testing for confirmation, and prognostic implications. Understandably, the patient may leave the office bewildered, overwhelmed, and in search of clarification.
Bewilderment may lead to the internet. In 2001, 4.5% of all internet searches were determined to be health-care-related (). It is reasonable to presume the percentage is higher today. Just as with any nonmedical website, the choices for digital health-care information are sometimes not contemporaneous and vary in quality. By exploring the most common “hits” on popular search engines when searching for idiopathic pulmonary fibrosis, a 2016 study found that not only is information presented at a high reading level – 12th grade – but often outdated or simply wrong (). Adding to a patient’s possible confusion is that websites expected to be the most helpful, foundation or advocacy websites, were more likely to suggest disproven and even harmful therapies years after those conclusions were published.
CHEST and the Interstitial and Diffuse Lung Disease NetWork are committed to patient education both in and out of the clinical setting. An ongoing redesign of ILD patient education on the CHEST Foundation website is nearing completion and will ensure patients have the most accurate and understandable information available.
Corey Kershaw, MD
Steering Committee Member