Chronic hypercapnia, characterized by elevated levels of CO2, poses a significant challenge for individuals with conditions like chronic obstructive pulmonary disease (COPD), neuromuscular disorders (NMD), and obesity. Although the negative effects of chronic hypercapnia are widely acknowledged, researchers at the University of Michigan are shedding light on the true urgency of its management.

Their findings call for a reconsideration of existing approaches to partial pressure carbon dioxide (PCO2) reduction, specifically target thresholds and the prioritization of ongoing assessment of PCO2 values. By optimizing these strategies, caregivers can yield benefits beyond symptom management, with data reinforcing the significant impact they can have on improving survival rates for patients.

Research has demonstrated that using noninvasive ventilation (NIV) to reduce PCO2 is an effective approach for improving outcomes in individuals with COPD, a patient population in which chronic hypercapnia is frequently observed.1 While these previous findings have important implications for the care strategies of this patient group, the team of researchers at University of Michigan set out to dig a little deeper: What could this mean for other patients with chronic hypercapnia?

To investigate the link between reducing PCO2 levels and survival rates across a broader spectrum of patients, this retrospective cohort study examined data from 337 individuals who utilized NIV for the treatment of chronic hypercapnic respiratory failure. The cohort consisted of patients with diverse underlying conditions such as neuromuscular disorders, ALS, spinal cord injuries, and cystic fibrosis. By utilizing patient databases, medical records, and public death records, researchers were able to examine the relationship between recorded PCO2 levels over time and mortality among these individuals.

The results were striking, with PCO2 reductions exhibiting a strong link to increased survival over time, across diverse patient populations. After analyzing the data, the authors found that patients who attained PCO2 levels below 50 mmHg exhibited an improvement in survival rates beyond the 90-day follow-up mark. 

Patients who reduced PCO2 to <50 mmHg showed:

• 94% reduction in mortality between 90-179 days
• 69% reduction in mortality between 180-364 days
• 73% reduction in mortality between 365-730 days

Researchers further highlighted that even individuals who did not reach normocapnia saw a survival benefit. Correlation was found between percentage reduction from baseline PCO2 levels and improved survival rates:

• Reduction of PCO2 >20% was associated with a 92% reduction in mortality rate between 180-364 days. 
• Reduction of PCO2 >20% was associated with a 76% reduction in mortality rate after 365 days. 
• Reduction of PCO2 between 10-19.9% was associated with a 77% reduction in mortality rate after 365 days. 

These findings go beyond reinforcing the significance of achieving normocapnia to demonstrate the impact that even relative reductions in PCO2 can have in the long term for chronic hypercapnic patients. And while this data is impactful on its own, it also begs an important question: Is PCO2 currently being monitored enough to support better long-term outcomes for these patients?

Although the authors of this study recognize the need for additional research, the data suggests that implementing effective strategies to decrease PCO2 levels, particularly through the use of NIV, could have a substantial impact on improving survival rates for individuals affected by chronic hypercapnia. This link calls for healthcare professionals to potentially shift their perspective on chronic hypercapnia. Rather than viewing it solely as a benign marker of disease severity, they should recognize it as a critical aspect of patient care that demands proactive attention. In this regard, the study’s findings prompt us to pose a few questions regarding the optimization of care for this patient population.

Is ongoing PCO2 monitoring prioritized enough for chronic hypercapnic patients?

It has been demonstrated that sustained reductions in PCO2, even if the patient does not reach normocapnic levels, contribute to improved survival rates. (Some possible explanations are that the body’s ability to respond to acute illnesses is improved when the reserve of total body stores of CO2 isn’t compromised. Chronic hypercapnia has also been shown to have a negative impact on respiratory and non-respiratory skeletal muscle regeneration.) However, such reductions necessitate ongoing monitoring of PCO2 levels to ensure that patients are consistently maintaining these reductions. And in many cases, PCO2 monitoring is either being done too infrequently or not at all.

By integrating regular and ongoing PCO2 monitoring, healthcare providers can gain visibility into fluctuations and trends, which in turn can support fine-tuned NIV titrations for optimized treatment strategies and timely adjustments to settings. Close monitoring allows clinicians to prioritize sustained reductions over time, potentially leading to enhanced patient outcomes and improved survival, as this study suggests. The authors note that transcutaneous monitoring (tcPCO2) can serve as a vital tool to support these strategies, as it allows clinicians to regularly monitor PCO2 noninvasively over time – without the need for frequent blood draws. 

Can current NIV strategies be optimized for outcome improvement?

While NIV is commonly used to alleviate symptoms in individuals with chronic hypercapnia, the research also suggests a need to reconsider how care teams approach this treatment strategy. The authors highlight that the emphasis of NIV treatment for chronic respiratory failure has predominantly revolved around the duration of daily usage, rather than considering “specific physiological variables.” These factors, including underlying condition and severity, can lead to fluctuations in CO2 levels throughout the day, potentially rendering typical NIV strategies inadequate, especially if CO2 isn’t being closely monitored. Consequently, it might be necessary to reevaluate NIV treatment approaches, taking into consideration the level of intervention required to successfully achieve sustained reductions.