Differences between non invasive mechanical ventilation in the hypoxemic and hypercapnic respiratory failure

Introduction Clinically and pathophysiologically there are differences between a hypoxemic or hypercapnic respiratory failure. In both, the application of non invasive mechanical ventilation (NIMV) can be indicated. Our objective is to analyze the characteristics of these differences in our patients.

Material and method This is a one-year descriptive study of patients with acute respiratory failure (ARF) or acute exacerbation of chronic respiratory failure (AECRF) treated with NIMV. We collected general data (age, sex, Unit), clinical data (basic pathology, NYHA functional level, level of consciousness, respiratory work and chest radiology), gasometric data and operational data (type of respirator, involvement of the Intensive Care Unit-ICU), and the final result of the process.

Result Were studied 242 cases of ARF or AECRF treated with NIMV. The respiratory failure was hypoxemic in 45 cases (18.6%) and hypercapnic in 197 (81.4%). Mean age 64 years (hypoxemic patients), 69 (hypercapnic patients). There were no differences in terms of sex. There was primary respiratory pathology in 42% of hypoxemic patients and 66% of hypercapnic (p < 0.05). 10 cases (22.2%) of hypoxemic without limitation according to NYHA and 14 hypercapnic (7.1%), p = 0.01.

20% of hypoxemic patients had severe respiratory work compared to 11.7% of hypercapnic patients. 15.5% of hypoxemics had moderate or severe alteration of consciousness compared to 41% of hypercapnics. 40% of hypercapnic failures were ventilated in Pulmonology, and 26.6% of hypoxemic failures, p < 0.001. Of the 45 hypoxemic failures, in 60% ICU was consulted and 33.3% were admitted to this Unit, compared to 20.5% and 9.7% in the hypercapnics, p < 0.001. 20% of hypoxemic failures were ventilated with Trilogy 100 respirator and 73.3% with V60 respirator, compared to 52.8% and 18.4% in hypercapnic, p < 0.001. Mortality of the hypoxemic patients was 42.2%, and 14.3% in the others.

Conclusion Hypoxemic patients are younger. They are ventilated in other Units of hospitalization, have less respiratory history, more radiological involvement and more respiratory work. Hypercapnic patients have a higher altered level of consciousness. Although the Intensive Care Unit is more involved in hypoxemic patients, their mortality is three times bigger than the one of hypercapnic patients.