The effect of airway pressure release ventilation on respiration and circulation in post-operative heart surgery patients

INTERVENTION: Patients who receive cardiothoracic surgery and need invasive mechanical ventilation after admission to the ICU are randomly divided into routine ventilation group (PCV group) and APRV group. The random scheme is generated by referring to the random comparison table without any restriction, intervention or adjustment in advance or in the process of implementation. All patients are supported by Evita4 ventilator, and the initial parameters of a ventilator in the PCV group are set as follows: respiratory frequency 12 times/min, tidal volume 6‐8ml/ ideal kg body weight, inhalation oxygen concentration and positive end‐expiratory pressure (PEEP) are set according to the needs of patients. The initial respiratory rate, tidal volume, and inhaled oxygen concentration of the APRV group are set the same as that of the conventional ventilator group, with the low pressure set to 0, and the low pressure time (Tlow) is set at the time required to reduce the flow rate at pressure release to 50%‐75% of the peak flow rate. The distribution of functional residual gas and tidal gas is measured by EIT equipment at the time of enrollment, 30min and 1h after enrollment. Vital signs and respiratory physiological indicators are also recorded as well as the incidence of ventilator‐associated pneumonia, atelectasis, mechanical ventilation duration, length of ICU stay, and final prognosis. CONDITION: Postoperative pulmonary complications and cardiovascular complications ; Respiratory PRIMARY OUTCOME: Electrical impedance imaging (EIT) was used to determine the difference in pulmonary gas distribution in patients undergoing cardiothoracic surgery before and after admission to the ICU after APRV SECONDARY OUTCOME: ; From patient records:; 1. Incidence of ventilator‐associated pneumonia; 2. Incidence of atelectasis; 3. Duration of mechanical ventilation; 4. Length of ICU stay; 5. Final outcome (death/survival); INCLUSION CRITERIA: 1. Age above 18 2.Received cardiothoracic surgery and needed invasive mechanical ventilation after admission to the ICU