How do COPD and healthy-lung patients tolerate the reduced volume ventilation strategy during OLV ventilation

Background: Although a strategy of tidal volume (V_t) reduction during the one‐lung ventilation (OLV) period is advised in thoracic surgery, the influence of the pre‐operative respiratory status on the tolerance of this strategy remains unknown. Therefore, the aim of this study was to compare the pulmonary function between chronic obstructive pulmonary disease (COPD) and healthy‐lung patients during the operative and the post‐operative period. Methods: Forty‐eight patients undergoing a planned lobectomy for cancer and presenting either a healthy lung function (n=24) or a moderate COPD stage (n=24) were ventilated without external positive end‐expiratory pressure (PEEP) and received 9 ml/kg V_t during the two‐lung ventilation (TLV) period, secondary reduced to 6 ml/kg during the OLV period. Lung function was assessed by peroperative gas exchange, venous admixture, respiratory mechanical parameters and post‐operative spirometric measurements. Results: Although the PaO₂ was superior in the healthy‐lung group during the TLV, once the OLV was established, no difference was observed between the two groups. Moreover, the PaO₂/FiO₂ was proportionally more impaired in the healthy‐lung group compared with the COPD group (50 ± 13 vs. 72 ± 19% of the baseline values after exclusion and 32 ± 15 vs. 51 ± 25% after the thoracotomy, P<0.05 for each) as well as the venous admixture. In the post‐operative period, a higher decrease was observed in the healthy‐lung group for the forced vital capacity and the forced expiratory volume. Conclusions: Reducing V_t to 6 ml/kg without the adjunction of external PEEP during OLV is associated with better preservation of lung function in the case of moderate COPD than in the case of healthy‐lung status.     

Recruitment and PEEP level influences long‐time aeration in saline‐lavaged piglets: an experimental model

Objectives: To evaluate aeration/ventilation in saline‐lavaged piglets during a 3‐h follow‐up after a recruitment maneuver (RM)/PEEP titration compared with PEEP 10 cmH₂O without a RM. Background: Lung recruitment and PEEP titration are used to find a PEEP preventing repetitive opening/collapsing of lung. Methods: Twenty‐one lung‐lavaged piglets, mean age 7 weeks and mean weight 10 kg; a RM‐group and a PEEP10‐group, were ventilated at PEEP 5 cmH₂O (baseline) followed by zero PEEP ventilation. In the RM‐group, tidal elimination of CO₂ and dynamic compliance (Cdyn) guided recruitment and PEEP titration, respectively. A final 3‐h ventilation followed using PEEP 2 cmH₂O above the first decline of Cdyn and end‐inspiratory pressure (EIP) for a target tidal volume (V_T) of 10 ml·kg^?1. In the PEEP10‐group, PEEP 10 cmH₂O without a RM was used during the final 3‐h ventilation. CT scans and blood gases were repeated every 30 min. Airway pressures, Cdyn and hemodynamics were continuously recorded. Results: Aeration improved without differences between groups. The RM‐group PEEP level of 10 ± 0.6 cmH₂O did not differ from the PEEP10‐group. Compared to baseline EIP was lower in the RM‐group after 3‐h ventilation. In both groups, driving pressure (DP) was lower and Cdyn higher than baseline. In the RM‐group, final EIP and DP were lower and Cdyn higher than in the PEEP10‐group. Conclusions: Both RM/PEEP titration and PEEP elevation resulted in improved aeration without differences between groups at the end point. Lung aeration was achieved at lower EIP and DP and higher Cdyn in the RM‐group than in the PEEP10‐group.     

Effect of PEEP on regional ventilation during laparoscopic surgery monitored by electrical impedance tomography

Background: Anesthesia per se and pneumoperitoneum during laparoscopic surgery lead to atelectasis and impairment of oxygenation. We hypothesized that a ventilation with positive end‐expiratory pressure (PEEP) during general anesthesia and laparoscopic surgery leads to a more homogeneous ventilation distribution as determined by electrical impedance tomography (EIT). Furthermore, we supposed that PEEP ventilation in lung‐healthy patients would improve the parameters of oxygenation and respiratory compliance. Methods: Thirty‐two patients scheduled to undergo laparoscopic cholecystectomy were randomly assigned to be ventilated with ZEEP (0 cmH₂O) or with PEEP (10 cmH₂O) and a subsequent recruitment maneuver. Differences in regional ventilation were analyzed by the EIT‐based center‐of‐ventilation index (COV), which quantifies the distribution of ventilation and indicates ventilation shifts. Results: Higher amount of ventilation was examined in the dorsal parts of the lungs in the PEEP group. Throughout the application of PEEP, a lower shift of ventilation was found, whereas after the induction of anesthesia, a remarkable ventral shift of ventilation in ZEEP‐ventilated patients (COV: ZEEP, 40.6 ± 2.4%; PEEP, 46.5 ± 3.5%; P<0.001) was observed. Compared with the PEEP group, ZEEP caused a ventral misalignment of ventilation during pneumoperitoneum (COV: ZEEP, 41.6 ± 2.4%; PEEP, 44 ± 2.7%; P=0.013). Throughout the study, there were significant differences in the parameters of oxygenation and respiratory compliance with improved values in PEEP‐ventilated patients. Conclusion: The effect of anesthesia, pneumoperitoneum, and different PEEP levels can be evaluated by EIT‐based COV monitoring. An initial recruitment maneuver and a PEEP of 10 cmH₂O preserved homogeneous regional ventilation during laparoscopic surgery in most, but not all, patients and improved oxygenation and respiratory compliance.     

A new non-radiological method to assess potential lung recruitability: a pilot study in ALI patients

Introduction: Potentially recruitable lung has been assessed previously in patients with acute lung injury (ALI) by computed tomography. A large variability in lung recruitability was observed between patients. In this study, we assess whether a new non‐radiological bedside technique could determine potentially recruitable lung volume (PRLV) in ALI patients. Methods: Sixteen mechanically ventilated patients with early ALI/ARDS were subjected to a recruitment manoeuvre and decremental PEEP titration. Electric impedance tomography, together with measurements of end‐expiratory lung volume (EELV) and tracheal pressure, were used to determine PRLV. The method defines fully recruited open lung volume (OLV) as the volume reached at the end of two consecutive vital capacity manoeuvres to 40 cmH₂O. It also uses extrapolation of the baseline alveolar pressure/volume curve up to 40 cmH₂O, the volume reached being the non‐recruited lung volume. The difference between the fully recruited and the non‐recruited volume was defined as PRLV. Results: We observed a considerable heterogeneity among the patients in lung recruitability, PRLV range 11–47%. In a post hoc analysis, dividing the patients into two groups, a high and a low PRLV group, we found at baseline before the recruitment manoeuvre that the high PRLV group had lower compliance and a lower fraction of EELV/OLV. Conclusions: Using non‐invasive radiation‐free bedside methods, it may be possible to measure PRLV in ALI/ARDS patients. It is possible that this technique could be used to determine the need for recruitment manoeuvres and to select PEEP level on the basis of lung recruitability.     

Gravity is an important determinant of oxygenation during one‐lung ventilation

Background: The role of gravity in the redistribution of pulmonary blood flow during one‐lung ventilation (OLV) has been questioned recently. To address this controversial but clinically important issue, we used an experimental approach that allowed us to differentiate the effects of gravity from the effects of hypoxic pulmonary vasoconstriction (HPV) on arterial oxygenation during OLV in patients scheduled for thoracic surgery. Methods: Forty patients with chronic obstructive pulmonary disease scheduled for right lung tumour resection were randomized to undergo dependent (left) one‐lung ventilation (D‐OLV; n=20) or non‐dependent (right) one‐lung ventilation (ND‐OLV; n=20) in the supine and left lateral positions. Partial pressure of arterial oxygen (PaO₂) was measured as a surrogate for ventilation/perfusion matching. Patients were studied before surgery under closed chest conditions. Results: When compared with bilateral lung ventilation, both D‐OLV and ND‐OLV caused a significant and equal decrease in PaO₂ in the supine position. However, D‐OLV in the lateral position was associated with a higher PaO₂ as compared with the supine position [274.2 (77.6) vs. 181.9 (68.3) mmHg, P<0.01, analysis of variance (ANOVA)]. In contrast, in patients undergoing ND‐OLV, PaO₂ was always lower in the lateral as compared with the supine position [105.3 (63.2) vs. 187 (63.1) mmHg, P<0.01, ANOVA]. Conclusion: The relative position of the ventilated vs. the non‐ventilated lung markedly affects arterial oxygenation during OLV. These data suggest that gravity affects ventilation–perfusion matching independent of HPV.     

Hemodynamic effects of medical antishock trousers during mechanical ventilation

Purpose

To compare the hemodynamic effects of medical antishock trousers (MAST) inflation in mechanically ventilated patients with normal and poor left ventricular function.

Methods

Twelve patients requiring respiratory support were divided into two groups according to baseline transesophageal echocardiography (TEE) measurements: normal left ventricular dimensions and fractional area of contraction (FAC=61 ± 5%) (n=7) and dilated cardiomyopathy with reduced FAC (21 ± 1%) (n=5). All patients were studied when two successive levels of load (mild load by inflation of the leg compartment of MAST at 50 cmH₂O and high load by adding the abdominal compartment of MAST inflated at 30 cmH₂O) were applied. Global left ventricular systolic function was assessed on the TEE transgastric short-axis view. End-systolic wall stress (ESWS) was used as an indicator of left ventricular afterload.

Results

Total respiratory, lung and chest wall compliances were reduced by 48%, 51% and 27% respectively at the high load level (P < 0.05). Whereas no hemodynamic changes occurred at mild load, the high load level produced an increase in left ventricular afterload as evidenced by concomitant increases in diastolic arterial blood pressure (66 ± 6 to 79 ± 6 mmHg,P < 0.05) and ESWS (69 ± 12 to 74 ± 12 Kdyn·cm^?2·m^?2,P < 0.05). In patients with dilated cardiomyopathy, this increase in afterload impaired the left ventricular systolic function and end-systolic area increased (19.0 ± 2.5 to 21.4 ± 2.9 cm²·m^?2,P < 0.05) while FAC decreased (22 ± 2 to 16 ± 2%,P < 0.05). Left ventricular end-diastolic area remained unchanged during the study in both groups.

Conclusion

MAST inflation impairs respiratory mechanics and global left ventricular systolic function in cardiac patients without changes in left ventricular preload.     

Protective ventilation to reduce inflammatory injury from one lung ventilation in a piglet model

Objectives: To test the hypothesis that protective ventilation strategy (PVS) as defined by the use of low stretch ventilation (tidal volume of 5 ml·kg^?1 and employing 5 cm of positive end expiratory pressure (PEEP) during one lung ventilation (OLV) in piglets would result in reduced injury compared to a control group of piglets who received the conventional ventilation (tidal volume of 10 ml·kg^?1 and no PEEP). Background: PVS has been found to be beneficial in adults to minimize injury from OLV. We designed the current study to test the beneficial effects of PVS in a piglet model of OLV. Methods: Ten piglets each were assigned to either ‘Control’ group (tidal volume of 10 ml·kg^?1 and no PEEP) or ‘PVS’ group (tidal volume of 5 ml·kg^?1 during the OLV phase and PEEP of 5 cm of H₂O throughout the study). Experiment consisted of 30 min of baseline ventilation, 3 h of OLV, and again 30 min of bilateral ventilation. Respiratory parameters and proinflammatory markers were measured as outcome. Results: There was no difference in PaO₂ between groups. PaCO₂ (P < 0.01) and ventilatory rate (P < 0.01) were higher at 1.5 h OLV and at the end point in the PVS group. Peak inflating pressure (PIP) and pulmonary resistance were higher (P < 0.05) in the control group at 1.5 h OLV. tumor necrosis factor‐alpha (P < 0.04) and IL‐8 were less (P < 0.001) in the plasma from the PVS group, while IL‐6 and IL‐8 were less (P < 0.04) in the lung tissue from ventilated lungs in the PVS group. Conclusions: Based on this model, PVS decreases inflammatory injury both systemically and in the lung tissue with no adverse effect on oxygenation, ventilation, or lung function.     

An individualized recruitment maneuver for mechanically ventilated patients after cardiac surgery

Purpose  The recruitment maneuver (RM) has been shown to improve oxygenation for post-cardiopulmonary bypass (CPB) patients; however, sustained inflation of the lung gives rise to hypotension. The primary goal of our study was to evaluate the safety and efficacy of our proposed RM, defined on the basis of dynamic lung compliance (Cdyn). Methods  Twenty-eight patients undergoing elective cardiac surgery with CPB were assigned to two treatment groups: an individualized RM group, in which a pressure equal to 15 ml × real body weight/Cdyn + positive end-expiratory pressure (PEEP) cmH₂O was applied for 15 s; and a control RM group, in which a pressure of 20 cmH₂O was applied for 25 s. Arterial blood pressure, cardiac output, pulmonary artery pressure, and heart rate (HR) were monitored. Tidal volume (V_T), and airway pressure were continuously obtained from an expiratory flow meter and pressure monitor. Blood samples were obtained and analyzed with a blood gas analyzer. Results  The changes in HR, mean arterial pressure, mean pulmonary artery pressure, and cardiac index at the end of the RM were not significantly different between the two groups. The mean airway pressure of sustained inflation was 28.3 ± 1.3 cmH₂O in the individualized RM group. The individualized RM significantly improved the Cdyn and partial pressure arterial oxygen/inspiratory fraction of oxygen (P/F) ratio compared with values in the control RM group (P = 0.026 and P = 0.012, respectively). Conclusion  The present study indicates that the individualized RM resulted in minimum changes of hemodynamics and brought about improvement in oxygenation and lung compliance.     

Effects of desflurane and propofol on arterial oxygenation during one-lung ventilation in the pig

Background: Desflurane depresses hypoxic pulmonary vasoconstriction (HPV) in vitro. During one-lung ventilation (OLV), HPV may reduce venous admixture and ameliorate the decrease in arterial O₂ tension by diverting blood from the non-ventilated to the ventilated lung. Accordingly, this study compares the effects of desflurane with those of propofol on oxygenation during two-lung (TLV) and OLV in vivo. Methods: Ten pigs (25–30 kg) were premedicated (flunitrazepam 0.4 mg/kg im), anaesthetized (induction: propofol 2 mg/kg iv; maintenance: N₂O/O₂ 50%/50%, desflurane 3%, propofol 50 μg kg^?1 min^?1, and vecuronium 0.2 mg kg^?1 h^?1 iv), orally intubated and mechanically ventilated. Femoral arterial and thermodilution pulmonary artery catheters were placed, and the orotracheal tube was replaced by a left-sided 28-Ch double-lumen tube (DLT) via tracheotomy. After DLT placement, N₂O and propofol were discontinued, FiO₂ was increased to 0.85, and anaesthesia continued randomly with either desflurane (1 MAC) or propofol 200 μg kg^?1 min^?1. Using a cross-over design, in each animal the effects of a), changing from TLV to OLV (left lung) during both desflurane and propofol and b), the effects of changing between the two anaesthetics during OLV were studied. Results: When changing from TLV to OLV, PaO₂ decreased more (P<0.05) during desflurane (mean 75%) than during propofol (mean 60%). Changing between desflurane and propofol during OLV resulted in small but consistent (P<0.05) increases in PaO₂ (mean 15%) during propofol. Conclusion: Consistent with in vitro results on HPV, 1 MAC desflurane impaired in vivo oxygenation during OLV more than did propofol.     

Efficacité d’une manœuvre de recrutement alvéolaire associée à une pression expiratoire positive sur la mécanique respiratoire en cœliochirurgie bariatrique

Objective

To evaluate recruitment manoeuvre (RM) efficiency associated with a 10 cmH₂O positive end expiratory pressure (PEEP) on respiratory mechanic estimated by lung compliance (Ctp) and PEEP to ZEEP expiratory volume delta (Δ VTE) during laparoscopic bariatric surgery in patients with morbid obesity.

Study design

Prospective randomized study.

Methods

Twenty-six obese patients (BMI > 40 kg/m²) undergoing laparoscopic bariatric surgery. The recruitment group received an RM followed by a 10 cmH₂O PEP versus only 10 cmH₂O PEP in the control group. Ctp was measured during the intervention and functional residual capacity (FRC) was estimated measuring Δ VTE during a PEP to ZEP manoeuvre. Mann and Whitney tests as well as a t-test were used (significance p < 0.05).

Results

In the RM group, a significant improvement of 52 ± 14 ml/cmH₂O was noted versus a 36 ± 10 ml/cmH₂O in the PEP group (p = 0,004). This improvement was transitory and no statistically significant Δ VTE difference was noted between the groups at the end of the intervention (360 [90–770] ml [MRA] and 310 [190–450] ml [PEP]).

Conclusion

In patients with morbid obesity undergoing laparoscopic bariatric surgery, an RM conducted prior the pneumoperitoneum temporarily improves lung mechanics but without any change of the end expiratory lung volume at the end of the surgery in comparison with PEP alone. The RM was well tolerated.     

Effect of external high-frequency oscillation on severe cardiogenic pulmonary edema

Effective gas exchange can be maintained in animals without endotracheal intubation using external high-frequency oscillation (EHFO). The aim of this study was to evaluate the effect of EHFO in patients with respiratory failure due to severe cardiogenic pulmonary edema. Seven patients were ventilated with EHFO for 2h at 60 oscillations·min⁻¹, with a cuiras pressure of 36 cmH₂O (−26 to +10) and an inspiratory to expiratory ratio of 1:1, with EHFO. Blood gas values and hemodynamic parameters were measured. Significant increases were noted in cardiac index (2.3±0.5 to 2.5±0.5 l·m⁻²;P<0.05), stroke volume index (24±7 to 28±8 ml·m⁻²;P<0.05), and arterial O₂ pressure (Pao₂) (70±4 to 95±23 mmHg;P<0.01) without a change in pulmonary artery wedge pressure at 1 h after EHFO. The respiratory rate decreased from 28±3 to 22 ±3 breaths·min⁻¹ at 5 min after the termination of EHFO (P <0.01). Arterial CO₂ pressure (Paco₂) did not, however, decrease. Increased stroke volume without a change in pulmonary artery wedge pressure (preload) suggests either improved inotropic function of the left ventricle or reduced left ventricular afterload with EHFO. The use of EHFO may be effective not only for gas exchange but also for left ventricular function in patients with severe cardiogenic pulmonary edema.     

End-expiratory lung volume and ventilation distribution with different continuous positive airway pressure systems in volunteers

Background: Continuous positive airway pressure (CPAP) has been shown to improve oxygenation and a number of different CPAP systems are available. The aim of this study was to assess lung volume and ventilation distribution using three different CPAP techniques. Methods: A high‐flow CPAP system (HF‐CPAP), an ejector‐driven system (E‐CPAP) and CPAP using a Servo 300 ventilator (V‐CPAP) were randomly applied at 0, 5 and 10 cmH₂O in 14 volunteers. End‐expiratory lung volume (EELV) was measured by N₂ dilution at baseline; changes in EELV and tidal volume distribution were assessed by electric impedance tomography. Results: Higher end‐expiratory and mean airway pressures were found using the E‐CPAP vs. the HF‐CPAP and the V‐CPAP system (P<0.01). EELV increased markedly from baseline, 0 cmH₂O, with increased CPAP levels: 1110±380, 1620±520 and 1130±350 ml for HF‐, E‐ and V‐CPAP, respectively, at 10 cmH₂O. A larger fraction of the increase in EELV occurred for all systems in ventral compared with dorsal regions (P<0.01). In contrast, tidal ventilation was increasingly directed toward dorsal regions with increasing CPAP levels (P<0.01). The increase in EELV as well as the tidal volume redistribution were more pronounced with the E‐CPAP system as compared with both the HF‐CPAP and the V‐CPAP systems (P<0.05) at 10 cmH₂O. Conclusion: EELV increased more in ventral regions with increasing CPAP levels, independent of systems, leading to a redistribution of tidal ventilation toward dorsal regions. Different CPAP systems resulted in different airway pressure profiles, which may result in different lung volume expansion and tidal volume distribution.     

Cardiogenic oscillations in spontaneous breathing airway signal reflect respiratory system mechanics

Background: Heartbeat‐related pressure oscillations appear at the airway opening. We investigated whether these cardiogenic oscillations (COS) – extracted from spontaneous breathing signals – reflect the compliance of the respiratory system. Methods: Fifteen volunteers breathed spontaneously at normal or reduced chest wall compliance, i.e. with and without thorax strapping, and at normal or reduced lung compliance, induced by positive end‐expiratory pressure (PEEP). COS‐related signals were extracted by averaging the flow and pressure curve sections, temporally aligned to the electrocardiogram signal. Results: COS‐related airway pressure and flow curves correlated closely for each subject (r²=0.97±0.02, P<0.0001). At the unstrapped thorax, the oscillation's amplitudes were 0.07±0.03 cmH₂O (pressure) and 22±10 ml/s (flow). COS‐related pressure amplitudes correlated closely with the ratio of tidal volume divided by pressure amplitude (r²=0.88, P<0.001) and furthermore increased with either thorax strapping (P<0.001) or with increasing PEEP (P=0.049). Conclusion: We conclude that COS extracted from the pressure and flow signal reflect the compliance of the respiratory system and could potentially allow estimating respiratory system mechanics during spontaneous breathing.     

Live donor study – implications of kidney donation on cardiovascular risk with a focus on lipid parameters including lipoprotein a

In this prospective observational cohort study, we evaluate the change in cardiovascular risk parameters, with a focus on lipids, in live kidney donors 1 year post donation. Body mass index, systolic/diastolic blood pressure, kidney function (chromium‐51 ethylenediaminetetraacetic acid estimated glomerular filtration) and lipid parameters were measured at baseline and 1 year. Data on 87 live kidney donors were collected. Body mass index increased from 26.5 ± 2.7 pre to 27.4 ± 3.0 kg/m² post donation (p < 0.0001). Chromium‐51 ethylenediaminetetraacetic acid estimated glomerular filtration decreased from 111.8 ± 20.0 pre to 72.1 ± 13.1 mL/min/1.73 m² post donation (p < 0.0001). Serum triglyceride levels increased from 0.8 (interquartile range 0.6–1.3) pre to 1.0 mmol/L (interquartile range 0.7–1.6) post donation (p = 0.0004). Statin use increased from 11.5% pre to 21% post donation (p < 0.005). Low‐density lipoprotein remained stable, and other lipids (high‐density lipoprotein, apolipoprotein B and lipoprotein a) did not change post donation.     

Beneficial effects of the prone position on the incidence of barotrauma in oleic acid-induced lung injury under continuous positive pressure ventilation

Background: Factors that contribute to ventilator-induced barotrauma are not well defined. This study investigates the effects of posture on ventilator-induced barotrauma, as well as arterial oxygenation. Methods: Twelve dogs with oleic acid lung injury, lying in the prone position (n=6) and right lateral position (n=6), were mechanically ventilated with continuous positive pressure ventilation for 24 hours. The incidence of pneumothorax and arterial oxygenation were investigated in each position. Results: All animals lying in the lateral position developed pneumothorax in the nondependent thorax, while only one animal in the prone position developed pneumothorax in the left thorax (P < 0.05). Postmortem examination revealed that in the lateral group, the nondependent lung consisted of large areas of emphysematous regions and neutrophil infiltration regions, while the dependent lung was composed of extensive atelectasis and neutrophil infiltration. Lung ruptures occurred in the non-dependent lung at the regions of either emphysematous change or severe neutrophil infiltration. In the prone group, in contrast, both lungs were inflated fairly homogeneously with only small areas of atelectatic and emphysematous changes. In the dog in whom pneumothorax developed, lung ruptures were limited to the regions of severe neutrophil infiltration in the left lung. No animal in either group had a peak airway pressure more than 20 cmH₂O. The peak airway pressures were 17.5 ±1.3 cmH₂O in the lateral group and 16.6±2.1 cmH₂O in the prone group (P>0.05). Tidal volume was comparable between the lateral group (13±2 ml/kg) and the prone group (12±1 ml/kg) before pneumothorax occurred (P>0.05). Arterial oxygenation was much better in the prone group than in the lateral group during the experiment (P < 0.05). Conclusion: It was concluded that in lung injury dogs, the prone position has beneficial effects on the incidence of ventilator-induced barotrauma and arterial oxygenation when compared with the lateral position. Ventilator-induced barotrauma may occur at lower airway pressure.     

The Effects of Pneumoperitoneum on Respiratory Mechanics During General Anesthesia for Bariatric Surgery

Background:The effects of pneumoperitoneum (PPM) on respiratory mechanics during bariatric surgery were investigated. Patients and Methods: 10 patients with BMI 50.5±8 kg/m² (range 40.9- 66.8) who underwent laparoscopic adjustable gastric banding with the Swedish band under general anesthesia were studied. Besides routine monitoring of vital signs and lung volumes, respiratory mechanics (compliance and resistance) were measured during positive pressure ventilation using an anesthesia delivery unit (Datex Ohmeda type A_Elec). Data were recorded at the following stages: 1) before PPM, 2) during PPM, and 3) after gas deflation. One-way analysis of variance was used for analysis of data. P <0.05 was considered significant. Results: The airway, peak inspiratory and plateau pressures increased significantly during PPM. Dynamic lung compliances were 44.6±7.8 SD, 31.8±5.5 and 44.5±8.3 cm/H₂O before, during and after PPM respectively with significant differences (P <0.05). Conclusions: Although significant decrease in lung mechanics was found in the present study,these variations were well tolerated in morbidly obese patients with PPM pressure of 15 mmHg.     

Effect of peak inspiratory flow on gas exchange, pulmonary mechanics, and lung histology in rabbits with injured lungs

Purpose The aim of this study was to evaluate, using a rabbit model, the little-known effect of different levels of peak inspiratory flow on acutely injured lungs. Methods Fourteen male rabbits (body weight, 2711 ± 146 g) were anesthetized and their lungs were injured by alveolar overstretch with mechanical ventilation until Pa_O2 was reduced below 300 mmHg. Injured animals were randomly assigned to: the P group—to receive pressure-regulated volume-control ventilation (PRVCV; n = 7); and the V group—to receive volume-control ventilation (VCV; n = 7). Other ventilator settings were: fraction of inspired oxygen (FI_O2), 1.0; tidal volume, 20 ml·kg⁻¹; positive end-expiratory pressure (PEEP) 5 cmH₂O; and respiratory rate, 20 min⁻¹. The animals were thus ventilated for 4 h. Throughout the protocol, ventilatory parameters and blood gas were measured every 30 min. After the protocol, the lung wet-to-dry ratio and histological lung injury score were evaluated in the excised lungs. Results Throughout the protocol, peak inspiratory flow and mean inspiratory flow values in the P group were significantly higher than those in the V group (26.7 ± 5.0 l·min⁻¹ vs 1.2 ± 0.2 l·min⁻¹, and 4.3 ± 0.3 l·min⁻¹ vs 1.1 ± 0.1 l·min⁻¹; P < 0.05). The wet-to-dry ratio in the P group was also significantly higher than that in the V group (7.7 ± 0.9 vs 6.3 ± 0.5; P < 0.05). More animals in the P group than in the V group had end-of-protocol Pa_O2/FI_O2 ratios below 200 mmHg (43% vs 0%; P = 0.06). Conclusion In rabbits with injured lungs, high peak inspiratory flow with high tidal volume (V_T) reduces the Pa_O2/FI_O2 ratio and increases the lung wet-to-dry ratio.     

Single-lung ventilation with carbon dioxide hemipneumothorax: hemodynamic and respiratory effects in piglets

Objectives: Video‐assisted thoracoscopic surgery (VATS) has become a standard procedure in pediatric surgery. To facilitate surgical access, the dependent lung has to collapse using intrathoracic carbon dioxide insufflation and/or single‐lung ventilation. These procedures can induce hemodynamic deteriorations in adults. The potential impacts of single‐lung ventilation in combination with capnothorax on hemodynamics in infants have never been studied before. Aim: We conducted a randomized experimental study focusing on hemodynamic and respiratory changes during single‐lung ventilation with or without capnothorax in a pediatric animal model. Methods: Twelve piglets were randomly assigned to receive single‐lung ventilation with (SLV‐CO₂) or without (SLV) capnothorax with an insufflation pressure of 5 mmHg for a period of two hours. Before, during, and after single‐lung ventilation, hemodynamic and respiratory parameters were measured. Results: Although mean arterial pressure remained stable during the course of the study and no critical incidents were monitored, cardiac index (CI) decreased significantly with SLV‐CO₂ (baseline 3.6 ± 1.6 l·min^?1·m^?2 vs 2.9 ± 1.1 l·min^?1·m^?2 at 120 min, P < 0.05). Furthermore, global end‐diastolic volume and intrathoracic blood volume (ITBV) decreased as well significantly with SLV‐CO₂, causing a significant between‐group difference in ITBV (P < 0.05). Conclusions: Despite a decrease in CI and preload parameters, the combination of single‐lung ventilation and low‐pressure capnothorax was well tolerated in piglets and could justify further clinical studies to be performed in infants and children focusing on hemodynamic and respiratory changes during VATS.     

Monitoring of vecuronium-induced neuromuscular blockade during one-lung ventilation

Purpose  We investigated the monitoring of neuromuscular blockade caused by vecuronium in patients receiving one-lung ventilation (OLV) anesthesia for lung surgery. Methods  Eighteen adult patients requiring OLV for lung surgery (OLV group) and 18 undergoing two-lung ventilation (TLV) for colon surgery (control group) were enrolled in this study. In the two groups, anesthesia was maintained with sevoflurane, fentanyl, and epidural lidocaine. Time from vecuronium 0.1 mg·kg⁻¹ to the onset of neuromuscular blockade; times to the return of T1, T2, T3, or T4 (the first, second, third, or fourth response of the train-of-four [TOF]); and recovery of T1/control or TOF ratio (T4/T1) were compared between the two groups. Results  Time to the onset of neuromuscular blockade in the OLV group was similar to that in the control group (289 ± 74 vs 270 ± 85 s [mean ± SD]; P = 0.482). Times from vecuronium to the return of T1, T2, T3, or T4 in the OLV group did not significantly differ from those in the control group (21.9 ± 7.0 vs 25.8 ± 6.7 min for T1; P = 0.099). T1/control in the OLV group was significantly higher than that in the control group 50-120 min after vecuronium (P < 0.05). The TOF ratio did not differ significantly between the two groups. Conclusion  During OLV for lung surgery, recovery of T1/control is accelerated in anesthetized patients receiving vecuronium.     

Attenuation of hyperoxic lung injury in rabbits with superoxide dismutase: effects on inflammatory mediators

Background. Superoxide dismutase (SOD) has been shown to attenuate hyperoxic lung injury. This effect is thought to be exhibited by scavenging superoxide released from neutrophils and other aerobic cells. The aim of the current study was to investigate the effect of pre-treatment with SOD on the chemical mediators in hyperoxic lung injury. Methods. Thirty male anesthetized rabbits were allocated to receive one of three treatments (n = 10 for each group): ventilated with 100% oxygen for 36 h with or without recombinant human SOD (rhSOD) treatment, and ventilated with air for 36 h without rhSOD. In the rhSOD-treated group, a single intravenous dose of rhSOD 10,000 U kg BW^-1 was administered immediately after the start of exposure to 100% oxygen and thereafter infused at a rate of 340,000 U kg BW^-1 day^-1 for 36 h until the animals were sacrificed. The lungs of all rabbits were ventilated with 100% oxygen or air. Haemodynamics, Pao₂, and lung mechanics were recorded during the ventilation period. After exposure to 100% oxygen, lung mechanics, cell fraction of bronchoalveolar lavage fluid (BALF), activated complements, cytokines, and arachidonic acid metabolite concentrations in BALF were measured and analyzed. The lung wet-to-dry (W/D) weight ratio and albumin concentrations in BALF were determined as indices of pulmonary oedema. Results. Exposure to the high concentration of oxygen for 36 h caused no significant changes in haemodynamics but decreased compliance and increased A-aDo₂. In the rhSOD-treated group, the decrease in compliance was not observed. At the end of the 36 hrexposure period, however, hyperoxia significantly increased the lung W/ D weight ratio, influx of neutrophils into the lung, BALF concentrations of C3a, C5a, tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-8, thromboxane B₂, and albumin. Pre-treatment with rhSOD attenuated these increases. Exposure to 100% oxygen caused extensive morphologic lung damage (alveolar haemorrhage and hyaline membrane formation), which was lessened by rhSOD. Conclusion. These results indicate that intravenous rhSOD prevented hyperoxic lung injury (decreases in Pao₂ and compliance, increased pulmonary vascular permeability, histopathological damage) in rabbits. This prophylactic effect of rhSOD amy be due, in part, to decreased chemical mediators such as activated complements, cytokines, and arachidonic acid metabolites.