Surgical intervention is a treatment option for many diseases of the thorax . After thoracotomy, ventilatory patterns change, lung volumes and pulmonary capacities decrease due to the reflex inhibition of the diaphragm muscle, and the sigh mechanism becomes impaired, even if the procedure does not include pulmonary resection . These changes often lead to postoperative pulmonary complications, which may increase length of stay in the hospital. The role of physical therapy in minimizing these risks is critical, and several techniques are available to improve both lung volume and capacity and to make coughing more effective. The air stacking technique allows enough air to be accumulated in the lungs to generate an acceptable cough peak flow (CPF). Several studies have shown that the use of this technique in patients with neuromuscular disease positively impacts the biomechanical components of peak expiratory flow (PEF) and CPF. This study aimed to evaluate the effectiveness, safety and feasibility of the air stacking technique application and its effect on PEF and CPF during the postoperative period in patients undergoing elective noncardiac intrathoracic surgery We conducted an interventional experimental study involving hospitalized patients for thoracic surgery in a teaching hospital. The study was approved by the Ethics Committee in Human Research (42693015.0.000.5505), and the patients freely signed an informed consent form prior to participation. Maximal inspiratory and expiratory pressure (MIP and MEP) were measured with a previously calibrated aneroid manometer (GER-AR®), ranging from 5 to ± 300 cmH2O. A mouthpiece was attached to the manovacuometer, and the nasal clip was used during the maneuvers following previous recommendations. (12) For maximal inspiratory and expiratory pressures assessment, maximum effort was requested from the residual volume and total lung capacity, respectively. Results were compared to predicted values according to the equation proposed by Neder et al. PEF and CPF were measured with a peak flow meter ranging from 100 to 900 L/min following the literature recommendations. The patient remained seated at 90º with a nasal clip and was asked to force maximum expiration as fast as he could through the mouthpiece after maximum inspiration to measure PEF. To measure cough peak flow, the patient repeated the inspiratory maneuver and was asked to cough as hard as he could. At least three measurements of both variables were performed, provided that the last measurement was not higher than others. The highest obtained value was considered as the result. To perform the air stacking technique, an air manual breathing unit (AMBU) was used, attached to a unidirectional valve and nasal/oral mask. The technique was performed with the patient in a sitting position, head resting on a smooth surface to avoid neck hyperextension. The mask was fit to the patient's face, and the AMBU one-way valve was kept closed. For each AMBU manual compression (three in the total), the patient was instructed to breathe in deeply and hold the air inside the lungs. Immediately after the first manual compression, the second and third were performed while the patient is deep breathing in together, without exhaling the air. PEF was measured immediately after the technique. The patient rested for 5 minutes, and the air staking technique was repeated. The same procedure was performed to measure CPF followed by a clinical evaluation including vital signs, visual lung expansion and auscultation, dyspnea, and pain evaluation. Sample size calculation was based on previous study performed by Brito et al. A minimum difference of 4% and a maximum difference of 47% were found between PEF and CPF means before and after air stacking technique. Considering a power of 90% and an alpha error of 5%, a power analysis revealed that a minimum number of 17 patients should be included in the study.