Is hypocapnia a risk factor for non-invasive ventilation failure in acute heart failure?

Abstract Introduction Non-invasive ventilation (NIV) has become a standard treatment for acute respiratory failure. Multiple factors associated with failure of this ventilatory technique have been described. Some authors postulate that the presence of hypocapnia at the onset of NIV increases the mortality of patients with acute heart failure (AHF). Purpose To analyse whether the presence of hypocapnia is a risk factor for failure of NIV in the patient with AHF. Methods Observational, retrospective study on a prospective database. All patients with AHF admitted to Intensitive Care Unit (ICU) between January 1997 and December 2017 for respiratory failure and requiring NIV are included. The inclusion criteria were the presence of dyspnea, respiratory rate ≥30 and PaO2/FiO2 <250 mmHg. The exclusion criteria were the presence of cardiogenic shock and AHF due to involvement of the right ventricle. Hypocapnia is defined as the presence of PaCO2 <35 mmHg) in basal gasometry prior to NIV, normocapnia as PaCO2 between 35 and 45 mmHg and PaCO2 hypercapnia greater than 45 mmHg. NIV failure is defined as the need for endotracheal intubation or death in ICU. Quantitative variables are expressed as means ± standard deviation, and qualitative variables as percentages. Comparison between variables has been made using the Ji2 linear trend test and single factor ANOVA. Multivariate analysis was performed using logistic regression with the calculation of odds ratios (OR) and their 95% confidence intervals (CI-95%). Results A total of 1009 patients with AHF, 158 (15.7%) normocapnic, 361 (35.8%) hypocapnic and 490 (48.5%) hypercapnic were analyzed. The age in the 3 groups was 73.3±10.4, 73.3±11.2 and 75.6±8.9 years (p=0.001), respectively. In the normocapnic group the respiratory rate was 36±4, PaCO2 40±3 and PaO2/FiO2 125±31. In the hypocapnic group 37±3, 28±3 and 134±30; and in the hypercapnic group 37±6, 65±16 and 126±36, respectively. NIV failure was observed in 15 (9.5%) of normocapnic patients, 56 (15.5%) of hypocapnic patients and 54 (11%) of hypercapnic patients (p=0.070). Independent risk factors for NIV failure were SAPS II (OR=1.07, CI-95%=1.04–1.09), order of non-intubation (OR=2.88, CI-95%=1.45–1.81), baseline SOFA (OR=1.76, CI-95%=1.48–2.08), HACOR index at 1 hour NIV (OR=1,62, CI-95%=1.45–1.08), the presence of acute coronary syndrome (OR=2.18, CI-95%=1.18–4.01), the presence of NIV-related complication (OR=6.42, CI-95%=3.47–11.89) and hypocapnia at the onset of NIV (OR=3.842, CI-95%=2.02–7.27). Conclusions Hypocapnia at the beginning of NIV in the patient with AHF is a frequent finding. Among the risk factors for poor prognosis, the presence of hypocapnia is a strong predictor of NIV failure. Funding Acknowledgement Type of funding source: None