High Flow Nasal Cannula in Thoracic Surgery: a Physiologic Study

The goal of this study is to evaluate the role that high-flow nasal cannulas (HFNC) have on respiratory drive, work of breathing and neuromuscular efficiency after lung resection surgery. The main question the investigators aim to answer is whether HFNC decrease respiratory drive by at least 15% in these patients, assessed by a special diaphragmatic electromyography (EMG) device (NAVA catheter). In order, to perform this study, the investigators will perform a physiological study in 40 patients. These patients will be assessed in the immediate postoperative period and HFNC will be compared to conventional face-mask therapy.

Single centre, physiological crossover clinical trial in 40 patients in the immediate postoperative period after lung resection, equipped with a NAVA catheter to monitor diaphragm electrical activity (EAdi) and assess the effects that HFNC have on the respiratory drive and work of breathing as compared to conventional facemask oxygen therapy. Once in the postoperative care unit (PACU) and 1) after recovery from anaesthesia, 2) cardiorespiratory stable and 3) pain-free (see below), the intervention will start. The study will assess the effect of HFNC and oxygen via face mask on EAdi and diaphragm function, as measured by ultrasonography. HFNC and oxygen via face mask order will be randomized in a sequence (A-B or B-A) with the aid of a website (www.randomization.com). Each intervention will last for 30 minutes. The oxygen-inspired fraction (FiO2) will be adjusted to maintain a pulse oximetry (SpO2) between >92%. In the case of the high-flow nasal cannula, the study will be carried out with a flow of 50 L/min. EAdi signal will be continuously monitored and its signal later exported to a laptop for further analysis. At the end of the 30-minute period, a blood sample will be obtained for gas analysis from the arterial line and the investigators will perform a diaphragm ultrasonography. Ultrasonography will consist of measurement of diaphragm thickness and thickening on the right side during quiet breathing and diaphragmatic excursion on both sides.

To provide high-flow nasal cannula in the immediate postoperative period after lung resection surgery as compared to conventional face-mask therapy, in a randomized sequence, for 30 minutes.

Respiratory drive will be assessed as maximal EMG activity during each respiratory cycle (peak EAdi of the NAVA catheter)

Diaphragm thickness will be assessed at end-inspiration and end-expiration and presented as percentage of change.

The presence of dyspnea will be assessed by a visual analog scale (VAS). This scale presents a range of discrete values from 0 to 10; with lower values indicating less symptoms and higher values indicating more symptoms. Participants will subjectively rate their own level of dyspnea.

Dyspnea presence by VAS will be assessed at the 30-minute mark of each condition (end of each condition) and will evaluate dyspnea for the whole condition (30 minutes).

Inclusion Criteria: Subjects submitted to lung resection with an expected mechanical ventilation time of more than 180 minutes. Exclusion Criteria: Patient refusal to participate Contraindications to nasogastric tube placement (i.e. oesophageal varices) Patients less than 18 years old Pregnancy Neuromuscular disease Prior thoracic surgery