Effects Of Pressure-controlled Ventilation On Peak Airway Pressure, Arterial Oxygenation And Intrapulmonary Shunt In Patients With Obstructive Ventilatory Dysfunction During One-lung Ventilation: A Comparison With Volume-controlled Ventilation

Background and objectiveOne-lung ventilation(OLV) can facilitate surgical exposure by collapsing the lung in the operative hemithorax for thoracoscope Surgery, and also accompany hypoxemia, especially for patients with obstructive ventilatory dysfunction. Obstructive ventilatory dysfunction means expiratory flow rate decrease due to airway obstruction or airway constriction. The main respiratory disorders are: ventilation-perfusion ratio(V/Q) mismatching, accrescence of dead space and hyperventilation. During OLV the entire tidal volume must be delivered into the ventilated lung, which may lead to pulmonary hyperventilation of this dependent lung. Nonetheless, it has been reported that patients of obstructive ventilatory dysfunction are vulnerable to barotrauma because of their abnormal pulmonary parenchyma, the heterogeneous distribution of ventilation and their propensity to develop intrinsic positive end expiratory pressure(PEEPi), particularly during OLV. Many studies were carried out on different ventilation modes to improve hypoxemia during OLV, however, no studies were focus on patients with obstructive ventilatory dysfunction.In the present study, the effects of pressure-controlled ventilation (PCV) or volume-controlled ventilation (VCV) of peak inspiratory airway pressure (Ppeak), arterial oxygenation and intrapulmonary shunt(Qs/Qt) on obstructive ventilatory dysfunction patients, who undergoing elective right thoracotomy in the left lateral decubitus position, were observed during OLV, and the better ventilatory settings would be assessed for clinical anesthesia on OLV.MethodsThirty ASA physical status I toШpatients (42⁷6 years old) undergoing elective right thoracotomy were enrolled, whose body mass indexes range from 18～25 kg/m². Exclusion criteria were uncompensated cardiac disease or severe hypertension, without histories of hepatic or renal diseases, with no hypoxemia and pulmonary infection, not taking vasoactive agent. Preoperative fiberoptic bronchoscope(FOB) rule out the patients with tracheal tumors or airway constriction. According to the preoperative pulmonary function, the patients were divided into group N with normal pulmonary function and group O with obstructive ventilatory dysfunction, and randomized into group N-VCV (n=8), group N-PCV (n=8), group O-VCV (n=7), and group O-PCV (n=7) with different OLV modes, subsequently.All patients were premedicated with atropine 0.5mg IM 30min before anaesthesia. Size of left-sided Mallinckrodt double-lumen endobroncheal tubes (DLTs) were determined by measuring the internal tracheal diameter in millimeters at the interclavicular plane from the preoperative posterior-anterior chest radiograph. General anesthesia was target-controlled infused with propofol, remifentanil, and rocuronium IV was given for muscle relaxation. Then Mallinckrodt DLTs of pre-selected size were inserted orally under direct vision. After the patient was intubated and placed in the left lateral position, FOB was used to determine the precise positions of the DLTs. Anesthesia were maintained with target-controlled infusion of propofol 2⁴μg/ml and remifentanil 2⁷ ng/ml intravenously, supplemental rocuronium 0.3 mg/kg were used for maintenance of anaesthesia. A central venous catheter was inserted into the right internal jugular vein, the tip of which was positioned just above the right atrium, and the other catheter in dorsal pedis artery for arterial blood sampling.Mechanical ventilation was with a Mandary WATO EX-60 at a ventilatory rate of 15 breaths/min, tidal volume was 7⁸ ml/kg and adjusted to maintain the end-tidal partial pressure of carbon dioxide (P_ETCO₂) at level of 35-40mmHg during two lung ventilation (TLV), and TLV with VCV (TLV-VCV) in all patients for 30 min in supine position. Then the patients were turned to the left lateral decubitus position and converted to left OLV. Patients in group N-VCV and group O-VCV were initiated with VCV (OLV-VCV) with the above respiratory variables for 30 min and switched to PCV for 30 min, the inspiratory pressure during PCV was adjusted to maintain the same tidal volume as during VCV. The modes of ventilation were performed in the opposite order in those of group N-PCV and group O-PCV. At the measurement time, we used the inspiration:expiration time ratio 1:1.5, fractional inspired oxygen (FiO₂) 1.0, the oxygen flow 2L/min. SpO₂ were kept always >90%. Ppeak, plateau inspiratory airway pressure (Pplat), tidal volume (VT), minute volume (MV), PETCO₂ and PEEPi were continuously monitored with the Datex-Capnomac Ultima-SV multi-function monitor.Mixed-venous and arterial blood sample were taken for blood gas analyses at the end of the following three stages: after 30 min of TLV (T1); after 30 min of the first randomized ventilation mode of OLV (T2); after 30 min of the second ventilation mode of OLV (T3). At the same time, variables including heart rate (HR), mean arterial blood pressure (MAP), SpO₂, Ppeak, Pplat, VT, MV, PETCO₂ and PEEPi were recorded. The shunt fraction was computed using a standard formula based on the three-compartment model: Qs/Qt= ( CcËŠO₂-CaO₂)/( CcËŠO₂- CO₂)×100%.Statistically analysis: All data were expressed as mean and standard deviation. All the quantitative data of the two groups at three stages were compared with two-way analysis of variance (ANOVA) for repeated measures and t-test. The significance was decided when p<0.05.Results1.The average age, weight, height, and hemoglobin of the patients were comparable between four groups (p>0.05). Groups N-VCV and N-PCV, O-VCV and O-PCV were equivalent with regard to gender respectivily (p>0.05). Lung function showed no significant difference between Groups N-VCV and N-PCV, O-VCV and O-PCV; but FEV1% and FEV1/FVC% in group O were lower than those in group N (p<0.01).2.With respect to HR, MAP, SpO₂, MV and PEEPi there were no significant discrepancies between any two of the three stages in the same group and between two groups at the same stage (p>0.05). At the measurement time, SpO₂ were always >90%.3.Ppeak increased in two groups when ventilation modes had been switched from TLV to OLV. Moreover, Ppeak was significantly lower during OLV with PCV compared to that with VCV: at T2, Ppeak in group N-VCV and O-VCV increased by 61.7% and 57.4% compared to those at T1 (p<0.01); Ppeak in group N-PCV and O-PCV increased by 34.5% and 43.8% compared to those at T1(p<0.01). At T3, Ppeak in group N-VCV and O-VCV increased by 39.5% and 46.0% compared to those at T1 (p<0.01), but decreased by 13.7% and 7.2% compared to those at T2 (p <0.01); Ppeak in group N-PCV and O-PCV increased by 57.7% and 55.7% compared to those at T1 (p<0.01), increased by 17.3% and 8.3% compared to those at T2 (p<0.01).4.As to pH, there were no significant differences between any two of the three stages in the same group and between two groups at the same stage (p>0.05).5.PaO₂ decreased in two groups when ventilation modes had been switched from TLV to OLV, but there was no difference during OLV between VCV and PCV in group N and group O. At T2, PaO₂ in group N-VCV, N-PCV, O-VCV and O-PCV decreased by 49.9%, 49.3%, 51.1% and 47.3% compared to those at T1 (p<0.01); decreased by 52.0%, 54.5%, 55.1% and 58.1% compared to those at T3 also (p<0.01); but there were no significant differences between T2 and T3 (p>0.05).6.PaCO₂ in group O was higher than that in group N at three stages (p<0.01). In group N, there were no significant differences between any two of the three stages (p>0.05).In group O, PaCO₂ decreased at T1 compared to those at T2 and T3 (p<0.01).7.PvO₂ decreased in two groups when switched from TLV to OLV, but there were no differences during OLV between VCV and PCV in two groups. At T1, PvO₂ in group O-VCV and O-PCV increased by 29.9% and 50.8% compared to those in group N-VCV and N-PCV respectivily (p<0.01). In group N-VCV, N-PCV, O-VCV and O-PCV, PvO₂ at T2 decreased by 29.0%, 22.7%, 36.7% and 43.9% compared to those at T1 (p<0.01); PvO₂ at T3 decreased by 35.3%, 27.9%, 40.5% and 49.0% compared to those at T1 (p<0.01); there were no differences between stage T2 and T3 (p>0.05). 8.Qs/Qt increased in two groups when switched from TLV to OLV. Moreover, Qs/Qt was significantly increased in group O compared to that in group N at any two of the three stages (p<0.05). In group N-VCV, N-PCV, O-VCV and O-PCV, Qs/Qt at T2 increased by 140.8%, 144.3%, 103.6% and 93.8% compared to those at T1 (p<0.01); Qs/Qt at T3 increased by 149.3%, 153.2%, 83.0% and 111.5% compared to those at T1 (p<0.01). At T1, Qs/Qt in group O-VCV and O-PCV increased by 57.7% and 43.0% compared to those in group N-VCV and N-PCV respectively (p<0.01). At T2, Qs/Qt in group O-VCV and O-PCV increased by 33.3% and 13.5% compared to those in group N-VCV and N-PCV respectively (p<0.01); At T3, Qs/Qt in group O-VCV and O-PCV increased by 15.8% and 19.5% compared to those in group N-VCV and N-PCV respectively (p<0.01). Qs/Qt was decreased during OLV with PCV compared to that with VCV in group N and group O, but there was no statistically significant difference (p>0.05).ConclusionCompared with VCV, PCV conduces a lower Ppeak for patients with obstructive ventilatory dysfunction during OLV, despite no amelioration of arterial oxygenation and Qs/Qt, therefore the risk of lung injury can be minimized by using PCV mode.