 Initially, univariate analysis will be performed on the variables recorded in the patients and control groups. The results of the categorical variables will be expressed in percentages and those of the continuous variables as means standard deviation, as median or range depending on the form of their distribution. Groups will be compared with the chi-squared text or through means comparison as required. Subsequently, the variables for which relations are found and those considered clinically important will be included in the multivariate logistical regression model in order to determine a predictive model of the presence of hypercapnia. 