Comparative effects of flow- versus volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in thoracic surgery: A randomised controlled clinical trial.

BackgroundFlow-controlled ventilation (FCV) allows expiratory flow control, reducing the collapse of the airways during expiration. The performance of FCV during one-lung ventilation (OLV) under intravascular normo- and hypovolaemia is currently unknown. In this explorative study, we hypothesised that OLV with FCV improves PaO2 and reduces mechanical power compared to volume-controlled ventilation (VCV). Sixteen juvenile pigs were randomly assigned to one of two groups: (1) intravascular normovolaemia (n = 8) and (2) intravascular hypovolaemia (n = 8). To mimic inflammation due to major thoracic surgery, a thoracotomy was performed, and 0.5 μg/kg/h lipopolysaccharides from Escherichia coli continuously administered intravenously. Animals were randomly assigned to OLV with one of two sequences (60 min per mode): (1) VCV–FCV or (2) FCV–VCV. Variables of gas exchange, haemodynamics and respiratory signals were collected 20, 40 and 60 min after initiation of OLV with each mechanical ventilation mode. The distribution of ventilation was determined using electrical impedance tomography (EIT).ResultsOxygenation did not differ significantly between modes (P = 0.881). In the normovolaemia group, the corrected expired minute volume (P = 0.022) and positive end-expiratory pressure (PEEP) were lower during FCV than VCV. The minute volume (P ≤ 0.001), respiratory rate (P ≤ 0.001), total PEEP (P ≤ 0.001), resistance of the respiratory system (P ≤ 0.001), mechanical power (P ≤ 0.001) and resistive mechanical power (P ≤ 0.001) were lower during FCV than VCV irrespective of the volaemia status. The distribution of ventilation did not differ between both ventilation modes (P = 0.103).ConclusionsIn a model of OLV in normo- and hypovolemic pigs, mechanical power was lower during FCV compared to VCV, without significant differences in oxygenation. Furthermore, the efficacy of ventilation was higher during FCV compared to VCV during normovolaemia.

Comparative effects of variable versus conventional volume-controlled one-lung ventilation on gas exchange and respiratory system mechanics in thoracic surgery patients: A randomized controlled clinical trial

Application of a ventilation modality that ensures adequate gas exchange during one-lung ventilation (OLV) without inducing lung injury is of paramount importance. Due to its beneficial effects on respiratory mechanics and gas exchange, flow-controlled ventilation (FCV) may be considered as a protective alternative mode of traditional pressure- or volume-controlled ventilation during OLV. We investigated whether this new modality provides benefits compared with conventional ventilation modality for OLV. Ten pigs were anaesthetized and randomly assigned in a crossover design to be ventilated with FCV or pressure-regulated volume control (PRVC) ventilation. Arterial partial pressure of oxygen (Pa o2 ), carbon dioxide (Pa co2 ), ventilation and hemodynamical parameters, and lung aeration measured by electrical impedance tomography were assessed at baseline and 1 hour after the application of each modality during OLV using an endobronchial blocker. Compared to PRVC, FCV resulted in increased Pa o2 (153.7 ± 12.7 vs 169.9 ± 15.0 mm Hg; P = .002) and decreased Pa co2 (53.0 ± 11.0 vs 43.2 ± 6.0 mm Hg; P < .001) during OLV, with lower respiratory elastance (103.7 ± 9.5 vs 77.2 ± 10.5 cm H 2 O/L; P < .001) and peak inspiratory pressure values (27.4 ± 1.9 vs 22.0 ± 2.3 cm H 2 O; P < .001). No differences in lung aeration or hemodynamics could be detected between the 2 ventilation modalities. The application of FCV in OLV led to improvement in gas exchange and respiratory elastance with lower ventilatory pressures. Our findings suggest that FCV may offer an optimal, protective ventilation modality for OLV.

BackgroundAnesthesia for thoracic surgery routinely involves one lung ventilation (OLV). Volume controlled ventilation (VCV) was and still the most common method of performing OLV. We assumed that pressure controlled ventilation-volume guaranteed (PCV-VG) is a better ventilation strategy for OLV than VCV as regard the inspiratory pressures, oxygenation parameters and post-operative ventilatory outcome.MethodsForty patients undergoing elective thoracic surgery in the lateral position requiring at least 1 h of OLV were randomly assigned into two groups. Group VCV: VCV was performed throughout the operation. Group PCV-VG: PCV-VG was performed throughout the operation. Blood gas analysis, peak inspiratory pressure (Ppeak), mean inspiratory pressure (Pmean), plateau inspiratory pressure (Pplateau) were measured: (1) During two lung ventilation (TLV1) 30 min after turning the patient to the lateral decubitus prior the beginning of OLV; (2) 30 min after initiation of OLV(OLV); (3) End of surgery: 30 min after reestablishing TLV (TLV2).ResultsThe Ppeak and the Pplateau were significantly lower in PCV-VG compared with VCV in all stages of the study (P value < 0.05). There was significant increase in all pressure values in OLV compared with TLV1 in the two groups (P value < 0.05). There were significant decrease in the mean Pao2 values during OLV and TLV2 compared with TLV1 in the two groups (P value < 0.05). Yet the Pao2 was significantly higher in the PCV-VG group at OLV and TLV2 compared to the OLV and TLV2 in VCV group. Also Pao2 was significantly lower in TLV2 compared with TLV1 in both groups (P value < 0.05).ConclusionIn patients undergoing thoracic surgery with OLV, pressure controlled volume guaranteed mode of ventilation decreases inspiratory pressure parameters and improve arterial oxygenation better than volume controlled ventilation.

Flow-controlled ventilation (FCV) is a new ventilation mode that provides constant inspiratory and expiratory flow. FCV was shown to improve gas exchange and lung recruitment in porcine models of healthy and injured ventilated lungs. The primary aim of our study was to verify the influences of FCV on gas exchange, respiratory mechanics and haemodynamic variables in mechanically ventilated lung-healthy patients. After obtaining ethical approval and informed consent, we measured arterial blood gases, respiratory and haemodynamic variables during volume-controlled ventilation (VCV) and FCV in 20 consecutive patients before they underwent abdominal surgery. After baseline (BL) ventilation, patients were randomly assigned to either BL-VCV-FCV or BL-FCV-VCV. Thereby, BL ventilation settings were kept, except for the ventilation mode-related differences (FCV is supposed to be used with an I:E ratio of 1:1). Compared to BL and VCV, PaO2 was higher [PaO2 : FCV: 38.2 (7.1), BL ventilation: 35.0 (5.8), VCV: 35.2 (7.0) kPa, P<.001] and PaCO2 lower [PaCO2 : FCV: 4.8 (0.5), BL ventilation: 5.1 (0.5), VCV: 5.1 (0.5) kPa, P<.001] during FCV. With comparable plateau pressure [BL: 14.9 (1.9), VCV: 15.3 (1.6), FCV: 15.2 (1.5) cm H2 O), P=.185], tracheal mean pressure was higher during FCV [BL: 10.2 (1.1), VCV: 10.4 (0.7), FCV: 11.5 (1.0) cm H2 O, P<.001]. Haemodynamic variables did not differ between ventilation phases. Flow-controlled ventilation improves oxygenation and carbon dioxide elimination within a short time, compared to VCV with identical tidal volume, inspiratory plateau pressure and end-expiratory pressure.

Objective To compare volume-controlled ventilation (VCV) versus pressure-controlled ventilation (PCV) improved by PEEP during one-lung ventilation (OLV).Methods Fifty ASA physical status Ⅰ-Ⅲ patients,aged 25-64 yr,weighing 40-80 kg,undergoing elective thoracotomy,were randomly divided into 2 groups (n =25 each) using a random number table:VCV + PEEP group (group Ⅴ) and PCV + PEEP group (group P).Those in group Ⅴ underwent OLV initially with VCV for 20 min followed by 4cm H2O PEEP for 20 min and then PEEP was removed.Those in group P underwent OLV initially with PCV for 20 min followed by 4cm H2O PEEP for 20 min and then PEEP was removed.At the beginning of two-lung ventilation before chest opening (T1),at 20 min of OLV before PEEP (T2),and at 20 min of ventilation with PEEP (T3),arterial blood samples were collected for blood gas analysis and the peak airway pressure (Ppeak) and development of SpO2 ＜ 95 ％ from beginning of OLV to T3 were recorded.Results Compared with group P,Ppeak at T2,3 and PaO2 at T3 were significantly increased in group Ⅴ (P ＜ 0.05).Compared with the baseline value at T1,PaO2 was significantly decreased and Ppeak was increased at T2.3 in Ⅴ and P groups (P ＜ 0.05).The incidence of SpO2 ＜ 95％ was significantly decreased and PaO2 was increased at T3 than at T2 in Ⅴ and P groups (P ＜ 0.05).Conclusion 4 cm H2O PEEP can improve VCV and PCV during OLV and the improved efficacy is better for VCV in patients undergoing thoracotomy. Key words: Positive pressure respiration; Pulmonary gas exchange; Respiration, artificial

One-lung ventilation is limited by hypoventilation and hypoxemia because of increasing airway pressure and intrapulmonary shunt. Previous clinical studies compared pressure-controlled versus volume-controlled ventilation during one-lung ventilation in patients with pre-existing pulmonary disease. We studied 50 patients undergoing thoracotomy and one-lung ventilation because of cardiovascular disease. After two-lung ventilation with volume-controlled ventilation, patients were divided randomly into two groups. In one group, ventilation was switched to pressure-controlled ventilation after starting one-lung ventilation. In the other group, volume-controlled ventilation was continued. Parameters of ventilation, pulmonary function and systemic and pulmonary hemodynamics were recorded. We observed, that peak airway pressure, dead space ventilation and arterial carbon dioxide partial pressure were significantly higher during volume-controlled ventilation. After one-lung ventilation patients with pressure controlled ventilation had lower alveolar-arterial oxygen tension difference and a higher arterial oxygen partial pressure with significant differences for those patients in the intensive care unit. We conclude that pressure-controlled ventilation may be useful to improve gas exchange and alveolar recruitment during one lung ventilation.

Comparison of Pulmonary Gas Exchange According to Intraoperative Ventilation Modes for Mitral Valve Repair Surgery via Thoracotomy With One-Lung Ventilation: A Randomized Controlled Trial

We hypothesized that pressure control ventilation allows a more even distribution in the lung and better maintenance of the mean airway pressure than is achieved with volume control ventilation. We try to compare the effect of pressure control ventilation (PC) with that of volume control ventilation without an end-inspiratory pause (VC) during one-lung ventilation (OLV) in an anesthetized, paralyzed patient for performing thoracopic bullectomy of the lung. We ventilated 20 patients with VC and PC after the insertion of a thoracoscope in continual order for, at least for 15 minutes, for each, VC and PC procedure. At the end of VC and PC, the respiratory mechanics, gasometrics, and hemodynamic parameters were measured and collected. We found no significant differences between VC and PC except for the peak inspiratory airway pressure (PIP), the mean airway pressure and the arterial oxygen partial pressure (PaO2). The PIP was significantly decreased from 27.0 +/- 6.0 cmH2O (VC) to 21.8 +/- 5.4 cmH2O (PC). The mean airway pressure was significantly increased from 8.6 +/- 1.6 cmH2O (VC) to 9.4 +/- 2.0 cmH2O (PC), and the PaO2 was significantly increased from 252.9 +/- 97.3 mmHg (VC) to 285.2 +/- 103.8 mmHg (PC). If PC allows mechanical ventilation with the same tidal volume and respiratory rate as VC during OLV, then PC significantly increases the PaO2 but this is not clinically significant, and the PC significantly decreases the PIP, which induces barotrauma or volutrauma when the PIP is excessively high.

Objective To explore the effects of two different modes for one-lung ventilation on airway pressure and oxidative stress factors during thoracoscopic radical resection of right lung cancer. Methods Sixty-two patients who needed one-lung ventilation after thoracoscopic radical resection of right lung cancer were divided into volume-controlled ventilation (VCV) group and pressure-controlled ventilation (PCV) group by random number table.VCV was used in both groups during dual lung ventilation.In VCV group, tidal volume was 6 ml/kg, positive end-expiratory pressure was 0 cmH2O (1 cmH2O=0.098 kPa). In PCV group, VCV mode was firstly used to regulate airway pressure to tidal volume at 6 ml/kg, then PCV mode was used, positive end-expiratory pressure was 0 cmH2O, and ventilation frequency was adjusted to maintain the value of end-tidal carbon dioxide partial pressure at 30-45 mmHg (1 mmHg=0.133 kPa). Radial artery blood was collected for blood gas analysis at 10 minutes (T1) before dual lung ventilation and 30 minutes (T2), 60 minutes (T3) and 120 minutes (T4) after one-lung ventilation.Malondialdehyde (MDA) and superoxide dismutase (SOD) in radial artery blood serum were measured at T1, T3 and T4 time points in the two groups. Results There was no significant difference in hemodynamic parameters between the two groups at different time points.At T3 and T4, the peak airway pressures of PCV group were (22.00±4.44) and (21.68±4.55) cmH2O, which were significantly lower than those of VCV group [(25.00±4.14), (25.00±4.03) cmH2O]. At T3 and T4, MDA of PCV group was (6.64±2.15), (7.11±1.50) μmol/L, which was significantly lower than that of VCV group [(7.31±2.09), (8.00±1.83) μmol/L], and SOD of PCV group was (39.42±15.36), (37.49±13.02) U/ml, which was significantly higher than that of VCV group [(35.94±8.47), (31.72±7.83) U/ml]. There was no significant difference in arterial partial pressure of oxygen and carbon dioxide between the two groups during one-lung ventilation. Conclusions PCV in thoracoscopic radical resection of lung cancer is helpful to reduce peak airway pressure and levels of oxidative stress factors, which may be helpful to reduce airway injury. Key words: One-lung ventilation; Volume-controlled ventilation; Pressure-controlled ventilation; Blood gas analysis; Oxidative stress mediators

Background One-lung ventilation (OLV)-associated hypoxemia is a major concern and a challenge for the anesthesiologist. Lung recruitment maneuvers (RMs) are ventilator strategies in which the main goal is to restore the functional residual capacity and improve arterial oxygenation. Hemodynamic side effects are mainly associated with ‘fast’ RM not with ‘slow’ cycling RM and their effects are self-limited; therefore, they must be performed repetitively. Aim The aim of this study was to evaluate the efficacy and safety of single versus repeated stepwise cycling RMs during OLV in patients with normal lung function. Settings and design The study design is a randomized, double-blinded, controlled one. Patients and methods Sixty adult patients of ASA I–II who were scheduled for elective thoracoscopic lung surgery were randomized into groups C, single recruitment maneuver (SRM), and repeated recruitment maneuver (RRM) comprising 20 patients each. Group C patients received standard ventilation protocol: volume-controlled ventilation mode, VT 6 ml/kg, I : E ratio 1 : 2, positive end expiratory pressure (PEEP) 5 cmH2O, and respiratory rate 10–12 breaths/min. SRM patients received standard ventilation protocol with one alveolar RM 10 min after initiation of OLV with a PEEP of 10 cmH2O until end of surgery. RRM patients received standard ventilation protocol with first RM 10 min after initiation of OLV and then repeated every 30 min during OLV and a PEEP of 10 cmH2O until end of surgery. The following were assessed: hemodynamic parameters – heart rate, mean arterial blood pressure, and central venous pressure; respiratory mechanical parameters – peak airway pressure (Paw-peak), plateau pressure (Paw-plat), and static lung compliance; and oxygenation parameters – partial arterial oxygen tension (PaO2), PaO2/FiO2, and oxygen saturation (SpO2). Results PaO2 and PaO2/FiO2 ratio increased in the SRM and RRM groups after RM from T2 (10 min after first RM) to T4 (45 min from first RM), with a significant difference compared with group C (P Conclusion Single or repeated cycling RM was considered effective with high safety profile in patients with normal pulmonary function undergoing thoracoscopic lung surgery using OLV.

Objective To evaluate the effects of pressure controlled ventilation(PCV) and volume control ventilation(VCV) on the respiratory mechanics and circulation of patients during one-lung ventilation(OLV). Methods We searched the PubMed, Embase and Cochrane libraries for all randomized controlled trials(RCT) from the establishment of library to February 2016 about the use of PCV and VCV during operation. The quality of the studies was evaluated by the method recommended by Cochrane Collaboration. Meta-analysis was conducted using the Cochrane Collaboration′s RevMan 5.0 software. Results A total of 14 studies were selected, including 964 patients(480 for PCV and 484 for VCV). Compared with group VCV, group PCV showed lower mean airway pressure(Pmean) [odds ratio(OR)=-0.22, 95%CI(-0.42,-0.01), P<0.05] before chest opening(T1), lower peak airway pressure(Ppeak)[weighted mean difference(WMD)=-1.37, 95%CI(-1.69,-1.05)], lower plateau pressure(Plateau) airway pressure[WMD=-0.29, 95%CI(-0.51,-0.07)] but higher pressure of arterial oxygen[WMD=0.52, 95%CI(0.08, 0.95)] during OLV(T2), and lower Ppeak[WMD=-0.63, 95%CI(-1.09, 0.17)] after chest closing(T3). Conclusions Compared with VCV, PCV results in low airway pressure during OLV, which may be a good ventilation model. Key words: Volume-controlled ventilation; Pressure-controlled ventilation; One-lung ventilation; Respiratory mechanics; Meta-analysis

Flow Controlled Ventilation during EVLP Improves Oxygenation and Preserves Alveolar Recruitment

Background: Impairment of gas exchange is a common problem during one lung ventilation (OLV) with a hazardous effect on morbidity and mortality. The current study compares the effect of volume-controlled ventilation (VCV) versus pressure-controlled ventilation volume guaranteed (PCV-VG) on gas exchange during OLV. Settings and Design: This study was a prospective randomized study. Methods: The study was carried out on 30 adult patients who were randomly assigned to two groups. Group VCV: VCV was performed throughout the operation. Group PCV-VG: PCV-VG was performed throughout the operation. Haemodynamic parameters ((HR), MAP), and (CVP)), blood gas analysis, and PaO2/FiO2 were recorded: before induction of anaesthesia (T0); during TLV (T1); ½ an hour after OLV (T2); 1 h after OLV (T3); 20 minutes after resuming TLV (T4); 6, 12, and 24 hours after surgery (T5, 6, and T7). (Ppeak), (Pmean) and (Cdyn) were recorded during (T1, 2, 3, and T4) time intervals. TNFα level was measured in venous Samples in the following times: (1) before induction of anaesthesia (T0); (2) Directly after surgery (T1); (3) 5th postoperative day (T2). The patients were followed for 5 days for recording of PPCs. Results: PCV-VG ventilation leads to a significant decrease in Ppeak and Pmean and significant increase in Cdyn (P ≤ 0.05). However, it had no effect on intra- and postoperative oxygenation values. Conclusion: PCV-VG is superior to VCV as regard respiratory dynamics during one lung ventilation (OLV), while it does not differ as regard items of gas exchange, inflammatory response and PPCs. Abbreviations: OLV: one lung ventilation; TLV: two lung ventilation; VCV: volume-controlled ventilation; PCV-VG: pressure-controlled ventilation volume guaranteed; PaO2: arterial oxygen tension; FiO2: fraction of inspired oxygen; Ppeak: Peak inspiratory pressure; Pmean: mean inspiratory pressure; Cdyn: dynamic compliance TNFα: Tumour necrosis factor α; PPCs: postoperative pulmonary complications.

Introduction: Volume Controlled Ventilation (VCV) is traditionally used during One Lung Ventilation (OLV); however, it is associated with complications such as volutrauma and barotrauma. On the other hand, Pressure Controlled Ventilation (PCV) allows the delivery of a required tidal volume at lower airway pressures, leading to enhanced oxygenation and ventilation. Aim: To compare VCV and PCV modes for OLV in patients undergoing surgery for empyema thoracis. Materials and Methods: A randomised controlled trial was conducted among 50 patients requiring OLV. The participants were divided into two groups, namely Group-V and Group-P, with each group receiving VCV and PCV, respectively. The two groups were compared based on the partial pressure of oxygen (during the intraoperative and post-operative period), peak and plateau airway pressures, lung compliance, and complications. The groups were analysed using the Chi-square test, and the threshold of statistical significance was set at a p-value &lt;0.05. Results: Fifty participants were divided into two groups: VCV (n=25) and PCV (n=25). Both study groups were found to be comparable in terms of demographic details, haemodynamic parameters, and duration of surgery. The mean age of the patients was 27.80 years in Group-V and 31.04 years in Group-P. The authors observed improved PaO2 levels, lung compliance, and reduced peak pressures during OLV in the PCV group. After lung isolation, PaO2 levels of Group-P patients (93.64±5.154 mmHg) were higher compared to Group-V (81.38±7.975 mmHg) at 50% FiO2 (p-value &lt;0.001). Similarly, post-extubation PaO2 levels were better in Group-P (99.24±18.58 mmHg) than in Group-V (84.35±7.677 mmHg) at 36% FiO2 (p-value &lt;0.001). The mean peak pressures were lower in Group-P (25.17±4.34 cm H2 O) than in Group-V (28.22±4.51 cm H2 O). Additionally, there was a statistically significant improvement in lung compliance among Group-P patients (p-value=0.0144). Conclusion: Thus, it can be inferred that PCV improves oxygenation and reduces airway pressures during OLV. However, there was no significant difference seen between the two modes in terms of post-operative pulmonary complications.