When talking about carbon dioxide (CO₂) reduction in stable hypercapnic COPD patients, we note that studies in the past showed that we need higher pressure levels in order to significantly reduce elevated PaCO₂ levels.  This Figure shows the results of the first study that compared two treatment strategies for NIV in patients with stable hypercapnic COPD using a randomized crossover design.^[3]  The trial compared low-intensity NIV, using a mean inspiratory positive airway pressure (IPAP) of 40.6 mbar, with high-intensity NIV, using a mean IPAP of 28.6 mbar.  The overall aim of high-intensity NIV was to use a step-wise increase in IPAP to significantly reduce elevated levels of arterial carbon dioxide partial pressure (PaCO₂).  

The inset in the lower left panel of Figure 7 shows PaCO₂ values over time.  The white bars show patients who were treated with high-intensity NIV for 6 weeks and then switched to low-intensity NIV for a further 6 weeks.  The white bars clearly show that during the first 6 weeks of high-intensity NIV there is a significant reduction in PCO₂, but once the patients have been switched to low-intensity NIV, PCO₂ increases.  

The gray bars represent the patients who were treated first with low-intensity NIV, then switched to high-intensity NIV.  In these patients there was a slight decrease in PCO₂ on low-intensity NIV, but after they were switched to high-intensity NIV there was a further significant decrease in PCO₂.  

It could be argued that patients with COPD are not tolerating such high levels of IPAP, but the opposite is true.  Patients used high-intensity NIV for a mean of 3.6 hr/night longer than they used low-intensity NIV, apparently because only high-intensity NIV, not low-intensity NIV, was associated with significant improvement in important secondary outcome parameters, meaning dyspnea during exertion, quality of life, and lung function.  

This study showed that high-intensity NIV is better tolerated in patients with severe chronic hypercapnic COPD and is superior to low-pressure NIV in controlling nocturnal hypoventilation.