Control group  Inclusion criteria.:  -Patients over the age of 18 who did not have COVID-19 and who are going to undergo scheduled surgery  Exclusion criteria:  Patients under the age of 18. Unstable patients in shock Patients in current state of pulmonary hypertension or heart failure Patients with moderate-severe pulmonary pathology prior to surgery. Patients previously surgery for chest surgery Patients in current state of respiratory infection  Post-COVID group Inclusion criteria  -Post-COVID-19 patients (confirmed by PCR) >18 years undergoing scheduled surgery without pulmonary disease prior to SARS-CoV-2 infection, that at the time of surgery present negative PCR and absence of clinic due to SARS-CoV-2 infection.  Exclusion criteria:  Patients under the age of 18 Unstable patients in shock Patients in current state of pulmonary hypertension or heart failure Patients with moderate-severe pulmonary pathology prior to SARS-CoV-2. Patients previously surgery for chest surgery Patients in current state of respiratory infection