Conventional Volume-controlled Ventilation Research Articles

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

BackgroundMechanical ventilation with variable tidal volumes (V-VCV) has the potential to improve lung function during general anesthesia. We tested the hypothesis that V-VCV compared to conventional volume-controlled ventilation (C-VCV) would improve intraoperative arterial oxygenation and respiratory system mechanics in patients undergoing thoracic surgery under one-lung ventilation (OLV). MethodsPatients were randomized to V-VCV (n = 39) or C-VCV (n = 39). During OLV tidal volume of 5 mL/kg predicted body weight (PBW) was used. Both groups were ventilated with a positive end-expiratory pressure (PEEP) of 5 cm H2O, inspiration to expiration ratio (I:E) of 1:1 (during OLV) and 1:2 during two-lung ventilation, the respiratory rate (RR) titrated to arterial pH, inspiratory peak-pressure ≤ 40 cm H2O and an inspiratory oxygen fraction of 1.0. ResultsSeventy-five out of 78 Patients completed the trial and were analyzed (dropouts were excluded). The partial pressure of arterial oxygen (PaO2) 20 min after the start of OLV did not differ among groups (V-VCV: 25.8 ± 14.6 kPa vs C-VCV: 27.2 ± 15.3 kPa; mean difference [95% CI]: 1.3 [−8.2, 5.5], P = 0.700). Furthermore, intraoperative gas exchange, intraoperative adverse events, need for rescue maneuvers due to desaturation and hypercapnia, incidence of postoperative pulmonary and extra-pulmonary complications, and hospital free days at day 30 after surgery did not differ between groups. ConclusionsIn thoracic surgery patients under OLV, V-VCV did not improve oxygenation or respiratory system mechanics compared to C-VCV.Ethical Committee: EK 420092019.Trial registration: at the German Clinical Trials Register: DRKS00022202 (16.06.2020).

Flow-controlled expiration reduces positive end-expiratory pressure requirement in dorsally recumbent, anesthetized horses.

Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated. Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmH2O until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured. The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmH2O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH2O) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min). We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.

Flow-controlled expiration improves respiratory mechanics, ventilation, and gas exchange in anesthetized horses.

Mechanical ventilation is usually achieved by active lung inflation during inspiration and passive lung emptying during expiration. By contrast, flow-controlled expiration (FLEX) ventilation actively reduces the rate of lung emptying by causing linear gas flow throughout the expiratory phase. Our aim was to evaluate the effects of FLEX on lung compliance and gas exchange in anesthetized horses in dorsal recumbency. 8 healthy horses. All animals were anesthetized twice and either ventilated beginning with FLEX or conventional volume-controlled ventilation in a randomized, crossover design. Total anesthesia time was 3 hours, with the ventilatory mode being changed after 1.5 hours. During anesthesia, cardiac output (thermodilution), mean arterial blood pressures, central venous pressure, and pulmonary arterial pressure were recorded. Further, peak, plateau, and mean airway pressures and dynamic lung compliance (Cdyn) were measured. Arterial blood gases were analyzed every 15 minutes. Data were analyzed using ANOVA (P < 0.05). FLEX ventilation resulted in significantly higher arterial oxygen partial pressures (521 vs 227 mm Hg) and Cdyn (564 vs 431 mL/cm H2O) values compared to volume-controlled ventilation. The peak and plateau airway pressure were lower, but mean airway pressure was significantly higher (4.8 vs 9.2 cm H2O) in FLEX ventilated horses. No difference for cardiovascular parameters were detected. The results of this study showed a significant improvement of the Pao2 and Cdyn without compromising the cardiovascular system when horses were ventilated by use of FLEX compared to conventional ventilation.

Effect of inverse ratio ventilation on hemodynamics and respiratory mechanics in obese patients undergoing laparoscopic sleeve gastrectomy

BackgroundObesity has become a global epidemic problem affecting every system and is associated with many consequences including coronary artery disease, hypertension, diabetes mellitus, dyslipidemia, obstructive sleep apnea, and socioeconomic and psychosocial impairment. Laparoscopic sleeve gastrectomy is one of the best and most commonly done operations for weight loss. Elevated peak airway pressure and hypoxemia are common problems that anesthesiologists face during laparoscopic surgeries with conventional volume-controlled ventilation. This study aimed at the use of the prolonged I:E ratio as an alternative strategy to improve gas exchange and the respiratory mechanics of obese patients undergoing laparoscopic sleeve gastrectomy.ResultsThe study was a prospective randomized controlled trial and was performed between April 2019 and March 2020. After the approval of the departmental ethical committee and the informed written consent had been taken from the patients, fifty-two obese patients undergoing laparoscopic sleeve gastrectomy were enrolled in this study. After endotracheal intubation, the patients were randomly divided into the IRV group (n=26) and the VCV group (n=26). Respiratory parameters were adjusted as tidal volume (Vt) 8mL/kg ideal body weight, respiratory rate 12 breaths/min, positive-end expiratory pressure (PEEP) 0, fractional inspired oxygen (FiO2) 0.6, and I:E ratio 1:2 for the VCV group and 2:1 for the IRV group; hemodynamics and respiratory mechanics were monitored and recorded after intubation (0 min), before pneumoperitoneum (10 mins), and after pneumoperitoneum (20 mins), 30, 40, 50, and 60 mins. IRV significantly improves the respiratory mechanics during pneumoperitoneum in the form of decreasing the peak pressure (Ppeak) and plateau pressure (Pplat) and improving the dynamic compliance, but the mean pressure (Pmean) was increased; it also increased the partial pressure of oxygen (arterial PO2) significantly. No statistical significance was found regarding the demographic data or the hemodynamics.ConclusionIRV is superior to conventional VCV in morbidly obese patients undergoing laparoscopic sleeve gastrectomy as it improves respiratory mechanics and oxygenation.

The Effects of Alveolar Recruitment Maneuver Versus Low Tidal Volume Ventilation on Oxygenation and Lung Mechanics in Patients Undergoing Laparoscopic Surgeries: A Prospective Randomized Controlled Study.

Different ventilatory strategies have been studied to improve gas exchange and compliance of the lungs in patients undergoing laparoscopic surgeries. This study aimed to test the impact of alveolar recruitment maneuver versus low tidal volume ventilation combine with PEEP on arterial oxygenation and lung mechanics in patients undergoing laparoscopic surgeries. Sixty patients were randomly allocated into three equal groups according to the type of ventilation strategy used during surgery. In the control group, patients received conventional volume-controlled ventilation with 10ml/Kg VT and zero PEEP (ZEEP). In group II ( LTV ), patients received low tidal volume ventilation in the form of 6-8 ml/Kg VT and PEEP 5cmH2O. In group III (REC), patients received 6-8 ml/Kg and recruitment maneuvers were done every 10 minutes after intubation till extubation by manual inflation to 40cmH2O peak inspiratory pressure for 15 seconds then the patient was placed back to the same ventilation settings with PEEP of 5cmH2O. The primary outcome is the dynamic compliance. The secondary outcome measures include PaO2, PH, PCO2, SPO2, HR and MAP. Demographic characteristics and duration of surgery were comparable among groups. PaO2 was highly significantly increased (p <0.001) in the recruitment group (Rec) compared to the conventional group (C) and low tidal volume ventilation group (LTV). There was significant increase in dynamic compliance in the recruitment group (REC) compared with the conventional (C) and low tidal volume (LTV) groups. SpO2, PaCO2 showed a highly statistical significance differences between the three ventilated groups. There were no statistically significant differences between the three ventilated groups in terms of PH. There were no statistically significant differences between the three ventilated groups in terms of Mean arterial blood pressure and HR. repeated recruitment maneuvers combined with 5 cm H2O of PEEP increased respiratory system compliance and PaO2 in patients undergoing laparoscopic surgeries without hemodynamics adverse effects.

Dorsal recruitment with flow-controlled expiration (FLEX): an experimental study in mechanically ventilated lung-healthy and lung-injured pigs

BackgroundConcepts for optimizing mechanical ventilation focus mainly on modifying the inspiratory phase. We propose flow-controlled expiration (FLEX) as an additional means for lung protective ventilation and hypothesize that it is capable of recruiting dependent areas of the lungs. This study investigates potential recruiting effects of FLEX using models of mechanically ventilated pigs before and after induction of lung injury with oleic acid.MethodsSeven pigs in the supine position were ventilated with tidal volume 8 ml·kg− 1 and positive end-expiratory pressure (PEEP) set to maintain partial pressure of oxygen in arterial blood (paO2) at ≥ 60 mmHg and monitored with electrical impedance tomography (EIT). Two ventilation sequences were recorded - one before and one after induction of lung injury. Each sequence comprised 2 min of conventional volume-controlled ventilation (VCV), 2 min of VCV with FLEX and 1 min again of conventional VCV. Analysis of the EIT recordings comprised global and ventral and dorsal baseline levels of impedance curves, end-expiratory no-flow periods, tidal variation in ventral and dorsal areas, and regional ventilation delay index.ResultsWith FLEX, the duration of the end-expiratory zero flow intervals was significantly shortened (VCV 1.4 ± 0.3 s; FLEX 0.7 ± 0.1 s, p < 0.001), functional residual capacity was significantly elevated in both conditions of the lungs (global: healthy, increase of 87 ± 12 ml, p < 0.001; injured, increase of 115 ± 44 ml, p < 0.001; ventral: healthy, increase of 64 ± 11 ml, p < 0.001; injured, increase of 83 ± 22 ml, p < 0.001; dorsal: healthy, increase of 23 ± 5 ml, p < 0.001; injured, increase of 32 ± 26 ml, p = 0.02), and ventilation was shifted from ventral to dorsal areas (dorsal increase: healthy, 1 ± 0.5%, p < 0.01; dorsal increase: injured, 6 ± 2%, p < 0.01), compared to conventional VCV. Recruiting effects of FLEX persisted during conventional VCV following FLEX ventilation mostly in the injured but also in the healthy lungs.ConclusionsFLEX shifts regional ventilation towards dependent lung areas in healthy and in injured pig lungs. The recruiting capabilities of FLEX may be mainly responsible for lung-protective effects observed in an earlier study.

Comparison between Variable and Conventional Volume-Controlled Ventilation on Cardiorespiratory Parameters in Experimental Emphysema.

Emphysema is characterized by loss of lung tissue elasticity and destruction of structures supporting alveoli and capillaries. The impact of mechanical ventilation strategies on ventilator-induced lung injury (VILI) in emphysema is poorly defined. New ventilator strategies should be developed to minimize VILI in emphysema. The present study was divided into two protocols: (1) characterization of an elastase-induced emphysema model in rats and identification of the time point of greatest cardiorespiratory impairment, defined as a high specific lung elastance associated with large right ventricular end-diastolic area; and (2) comparison between variable (VV) and conventional volume-controlled ventilation (VCV) on lung mechanics and morphometry, biological markers, and cardiac function at that time point. In the first protocol, Wistar rats (n = 62) received saline (SAL) or porcine pancreatic elastase (ELA) intratracheally once weekly for 4 weeks, respectively. Evaluations were performed 1, 3, 5, or 8 weeks after the last intratracheal instillation of saline or elastase. After identifying the time point of greatest cardiorespiratory impairment, an additional 32 Wistar rats were randomized into the SAL and ELA groups and then ventilated with VV or VCV (n = 8/group) [tidal volume (VT) = 6 mL/kg, positive end-expiratory pressure (PEEP) = 3 cmH2O, fraction of inspired oxygen (FiO2) = 0.4] for 2 h. VV was applied on a breath-to-breath basis as a sequence of randomly generated VT values (mean VT = 6 mL/kg), with a 30% coefficient of variation. Non-ventilated (NV) SAL and ELA animals were used for molecular biology analysis. The time point of greatest cardiorespiratory impairment, was observed 5 weeks after the last elastase instillation. At this time point, interleukin (IL)-6, cytokine-induced neutrophil chemoattractant (CINC)-1, amphiregulin, angiopoietin (Ang)-2, and vascular endothelial growth factor (VEGF) mRNA levels were higher in ELA compared to SAL. In ELA animals, VV reduced respiratory system elastance, alveolar collapse, and hyperinflation compared to VCV, without significant differences in gas exchange, but increased right ventricular diastolic area. Interleukin-6 mRNA expression was higher in VCV and VV than NV, while surfactant protein-D was increased in VV compared to NV. In conclusion, VV improved lung function and morphology and reduced VILI, but impaired right cardiac function in this model of elastase induced-emphysema.

The effects of inverse ratio ventilation on cardiopulmonary function and inflammatory cytokine of bronchoaveolar lavage in obese patients undergoing gynecological laparoscopy

BackgroundHigh peak airway pressure (Ppeak) and high end-tidal carbon dioxide tension (PETCO2) are the common problems encountered in the obese patients undergoing gynecological laparoscopy with conventional volume-controlled ventilation. This study was designed to investigate whether volume-controlled inverse ratio ventilation (IRV) with inspiratory to expiratory (I:E) ratio of 2:1 could reduce Ppeak or the plateau pressure (Pplat), improve oxygenation, and alleviate lung injury in patients with normal lungs. MethodsSixty obese patients undergoing gynecological laparoscopy were enrolled in this study. After tracheal intubation, the patients were randomly divided into the IRV group (n = 30) and control group (n = 30). They were ventilated with an actual tidal volume of 8 mL/kg, respiratory rate of 12 breaths/min, zero positive end-expiratory pressure and I:E of 1:2 or 2:1. Arterial blood samples, hemodynamic parameters, and respiratory mechanics were recorded before and during pneumoperitoneum. The concentrations of tumor necrosis factor-α, and interleukins 6 and 8 in bronchoalveolar lavage fluid were measured immediately before and 60 minutes after onset of CO2 pneumoperitoneum. ResultsIRV significantly increased arterial partial pressure of oxygen, mean airway pressure, and dynamic compliance of respiratory system with concomitant significant decreases in Ppeak and Pplat compared to conventional ventilation with I:E of 1:2 (p < 0.05). Additionally, the levels of tumor necrosis factor-α, and interleukins 6 and 8 were significantly lower than those in control group (p < 0.05). ConclusionVolume-controlled IRV not only reduces Ppeak, Pplat, and the release of inflammatory cytokines, but also increases mean airway pressure, and improves oxygenation and dynamic compliance of respiratory system in obese patients undergoing gynecologic laparoscopy without adverse respiratory and hemodynamic effects. It is superior to conventional ratio ventilation in terms of oxygenation, respiratory mechanics and inflammatory cytokine in obese patients undergoing gynecologic laparoscopy.

Pressure-Controlled vs Volume-Controlled Ventilation During Laparoscopic Gynecologic Surgery

Study Objective To quantify and compare the effects of conventional volume-controlled ventilation (VCV) with the alternative mode, pressure-controlled ventilation (PCV), on respiratory mechanics and noninvasive hemodynamic parameters in patients undergoing laparoscopic gynecologic surgery. Design Randomized controlled trial (Canadian Task Force classification I). Setting Respiratory mechanics and hemodynamic parameters were recorded for each patient at time T1, 10 minutes after induction, in the supine position; T2, 15 minutes after pneumoperitoneum, in the Trendelenburg position; and T3, 10 minutes after pneumoperitoneum withdrawal, in the supine position. Patients Sixty women, aged 20 to 50 years, undergoing laparoscopic gynecologic surgery, with American Society of Anesthesiologists classes I and II disease. Interventions Patients were randomly allocated to 1 of 2 groups. In the VCV group (n = 30), ventilation mode was maintained, whereas in the PCV group (n = 30), ventilation mode was changed to PVC. Measurements and Main Results Both groups were comparable insofar as patient characteristics, operating time, pneumoperitoneum time, anesthesia time, and mean operative time. VCV was associated with a significant increase in peak airway pressure, plateau pressure, and airway resistance at T2 (p < .05). Compliance was significantly higher in the PCV group at T2 (p < .05). No other statistically significant differences were found between the groups. Conclusions Both VCV and PCV seem to be equally suited for use in patients undergoing laparoscopic gynecologic surgery. However, lower peak airway pressure, plateau pressure, and airway resistance, and higher compliance are observed with PCV in laparoscopic gynecologic surgery.

A Comparison of Adaptive Support Ventilation (ASV) and Conventional Volume-Controlled Ventilation on Respiratory Mechanics in Acute Lung Injury/ARDS

Background: ASV is a closed-loop ventilation system that guarantees a user-set minimum per-minute volume in intubated patients, whether paralyzed or with spontaneous breathing. Here, we tested the effects of ASV onrespiratory mechanics and compared them with volume-controlled ventilation (VCV). Methods: Thirteen patients meeting the criteria for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) were enrolled. All patients were paralyzed to eliminate spontaneous breathing. We started with VCV (VCV1), then used ASV followed by VCV modes (VCV2), maintaining minute volume as much as that of VCV1. Results: During ASV, compared with VCV1, the inspiratory and expiratory tidal volumes and expiratory resistance increased. Conversely, the total respiratory rate and maximum pressure decreased. No changes in the arterial blood gases, heart rate, or mean systemic pressure were noted during the trial. Conclusions: In ALI/ARDS patients, although no differences were observed in the arterial blood gas analysis between the two modes, ASV provided better respiratory mechanics in terms of peak airway pressure and tidal volume than VCV.

Respiratory and haemodynamic effects of volume-controlled vs pressure-controlled ventilation during laparoscopy: a cross-over study with echocardiographic assessment

The effects of pressure-controlled (PC) ventilation on the ventilatory and haemodynamic parameters during laparoscopy procedures had not been carefully assessed. This prospective cross-over study was undertaken to compare how volume-controlled (VC) and PC modes could affect pulmonary mechanics, gas exchange, and cardiac function in patients undergoing laparoscopy. Twenty-one patients undergoing laparoscopic urological procedures had their lungs ventilated at the beginning with VC ventilation. PC ventilation was instituted at the end of the VC sequence. Ventilator settings were adjusted to keep tidal volume, respiratory rate, and Fi(o(2)) constant in every mode. A complete set of ventilatory, haemodynamic, and gas exchange parameters was obtained under VC after 40 min of pneumoperitoneum and 20 min after switching for PC. Transoesophageal echocardiography was performed in order to evaluate systolic and diastolic function of the heart. When VC was switched to PC, peak airway pressure decreased [mean (sd) 32 (6) vs 27 (6) cm H(2)O; P < 0.0001], peak inspiratory flow increased [17 (3) vs 48 (8) litre min(-1); P < 0.0001), and dynamic compliance improved [+15 (8)%]. No difference was noted for static airway pressure, static compliance, and arterial oxygenation. No significant change could be demonstrated in the systolic [left ventricular end-systolic wall stress 66 (16) vs 63 (14) x 10(3) dyn cm(-2) m(-2)] or diastolic function [early diastolic velocity 10.3 (2.5) vs 10.5 (2.7) cm s(-1)]. In this study, no short-term beneficial effect of PC ventilation could be demonstrated over conventional VC ventilation in patients with pneumoperitoneum.

Cerebral blood flow during partial liquid ventilation in surfactant-deficient lungs under varying ventilation strategies.

OBJECTIVE: To test the hypothesis that cerebral and other regional organ blood flow would be maintained during partial liquid ventilation (PLV) in an animal model of acute lung injury during different ventilation strategies. DESIGN: A prospective, randomized study. SETTING: Animal research facility. SUBJECTS: Sixteen piglets, 2 to 4 wks of age. INTERVENTIONS: Severe lung injury was induced in infant piglets by repeated saline lavage and high tidal volume ventilation. Animals were then randomized to either conventional volume-controlled ventilation or PLV. MEASUREMENTS AND MAIN RESULTS: Organ blood flow was determined in both groups using radiolabeled microspheres under four conditions: high mean airway pressure, Paw; high Paco(2), high Paw; normal Paco(2); low Paw, high Paco(2); low Paw, normal Paco(2). There were no differences in cerebral blood flow during conventional ventilation and PLV, regardless of ventilation strategy. CONCLUSIONS: These results suggest in an acute lung injury model, PLV does not affect cerebral blood flow or other regional organ blood flow over a range of airway pressures.

Pressure-controlled ventilation via a mini-tracheostomy tube for patients with neuromuscular disease.

The authors managed 10 patients with Duchenne muscular dystrophy (DMD) and five with MG with pressure-controlled ventilation (PCV) via mini-tracheostomy tube (MTT). The arterial partial pressure of CO2 (PaCO2) of the patients with DMD decreased after conversion to PCV via MTT from biphasic positive airway pressure (BIPAP) or a body ventilator. The MG patients could be converted from conventional volume-controlled ventilation to PCV via MTT. PCV via MTT achieves more effective ventilation than either BIPAP or a body ventilator and is as effective as ventilation via a conventional tracheal tube.

Effects of Inverse Ratio Ventilation on Cardiorespiratory Parameters in Severe Respiratory Failure

Inverse ratio ventilation, with prolonged inspiratory times, appears to improve gas exchange and arterial oxygenation in patients with severe respiratory failure; however, in previous studies, pressure-controlled inverse ratio ventilation (PC-IRV), which uses a rapidly decelerating inspiratory flow pattern, was compared to conventional volume-controlled ventilation, which uses a constant inspiratory flow rate. Pressure-controlled ventilation (PCV), with a decelerating inspiratory flow pattern and conventional inspiratory-to-expiratory (I/E) ratios, also has been shown to produce improvement in PaO2 when compared to volume-controlled ventilation. It therefore is unknown if the potentially beneficial effects of PC-IRV are due to the reversal of I/E ratios or to the use of the rapidly decelerating inspiratory flow pattern. In order to investigate this issue, cardiorespiratory values were measured in ten patients with severe respiratory failure ventilated first with PCV, then PC-IRV, and finally with a second period of PCV. Tidal volume, respiratory rate, end-expiratory pressure, and fraction of oxygen in inspired gas (FIO2) were maintained at the same value for both ventilatory modalities. The PC-IRV was associated with significant increases in PaO2, arterial pH, and mean airway pressure. Significant decreases in pulmonary shunt fraction, PaCO2, and cardiac index were found with PC-IRV. No significant changes in tissue oxygen delivery or consumption occurred with either PCV or PC-IRV. These results demonstrate that inversion of conventional I/E ratios produces no significant improvement in the overall cardiorespiratory profile of critically ill patients. This study also suggests that the clinical utility of PC-IRV is limited except in the setting of the adult respiratory distress syndrome with hypoxemia or hypercapnia refractory to other therapeutic options.

Clinical Evaluation of High-Frequency Positive-Pressure Ventilation (HFPPV) in Patients Scheduled for Open-Chest Surgery

Comparisons were made in 10 patients scheduled for thoracotomy between a prototype of a low-compressive system (Bronchovent Special) for volume-controlled, high-frequency positive-pressure ventilation (HFPPV; fixed frequency of 60/min; fixed relative insufflation time of 22%), and a conventional respirator (SV-900) for intermittent positive-pressure, volume-controlled ventilation at a frequency of 20/min, after induction of anesthesia, but before surgery. With both ventilator systems intratracheal, intrapleural, systolic, diastolic, and mean arterial systemic and central venous pressures were measured at normoventilation (normocarbia). Mean intratracheal pressure and mean intrapleural pressure were significantly lower with volume-controlled HFPPV (1.3 +/- 0.5 and -4.0 +/- 2.1 (SD) cm H2O, respectively) than with conventional volume-controlled ventilation with SV-900 (2.1 +/- 1.2 and -3.0 +/- 1.5 cm H2O, respectively). No significant differences between the two ventilators were found with respect to arterial systemic and central venous pressures, arterial oxygen and carbon dioxide tensions, or alveolar-arterial oxygen tension difference. With the thorax open, during volume-controlled HFPPV the exposed lung was moderately expanded and exhibited only minor movements during insufflation. Repeated blood gas analyses during surgery showed normocarbia and good oxygenation even during compression of the exposed lung. After compression the lung was readily re-expanded with the aid of a brief period of positive end-expiratory pressure (PEEP). Thus, even relatively low intrapulmonary pressures during volume-controlled HFPPV without PEEP are adequate to keep the open-chest lung expanded during intrathoracic surgery. This creates optimal conditions for the surgeons.