Pressure Support Ventilation Group Research Articles

Effects of pressure support ventilation on ventilator-induced lung injury in mild acute respiratory distress syndrome depend on level of positive end-expiratory pressure: A randomised animal study.

Harmful effects of spontaneous breathing have been shown in experimental severe acute respiratory distress syndrome (ARDS). However, in the clinical setting, spontaneous respiration has been indicated only in mild ARDS. To date, no study has compared the effects of spontaneous assisted breathing with those of fully controlled mechanical ventilation at different levels of positive end-expiratory pressure (PEEP) on lung injury in ARDS. To compare the effects of assisted pressure support ventilation (PSV) with pressure-controlled ventilation (PCV) on lung function, histology and biological markers at two different PEEP levels in mild ARDS in rats. Randomised controlled experimental study. Basic science laboratory. Thirty-five Wistar rats (weight ± SD, 310 ± 19) g received Escherichia coli lipopolysaccharide (LPS) intratracheally. After 24 h, the animals were anaesthetised and randomly allocated to either PCV (n=14) or PSV (n=14) groups. Each group was further assigned to PEEP = 2 cmH2O or PEEP = 5 cmH2O. Tidal volume was kept constant (≈6 ml kg). Additional nonventilated animals (n=7) were used as a control for postmortem analysis. Ventilatory and mechanical parameters, arterial blood gases, diffuse alveolar damage score, epithelial integrity measured by E-cadherin tissue expression, and biological markers associated with inflammation (IL-6 and cytokine-induced neutrophil chemoattractant, CINC-1) and type II epithelial cell damage (surfactant protein-B) were evaluated. In both PCV and PSV, peak transpulmonary pressure was lower, whereas E-cadherin tissue expression, which is related to epithelial integrity, was higher at PEEP = 5 cmH2O than at PEEP = 2 cmH2O. In PSV, PEEP = 5 cmH2O compared with PEEP = 2 cmH2O was associated with significantly reduced diffuse alveolar damage score [median (interquartile range), 11 (8.5 to 13.5) vs. 23 (19 to 26), P = 0.005] and expressions of IL-6 and CINC-1 (P = 0.02 for both), whereas surfactant protein-B mRNA expression increased (P = 0.03). These changes suggested less type II epithelial cell damage at a PEEP of 5 cmH2O. Peak transpulmonary pressure correlated positively with IL-6 [Spearman's rho (ρ) = 0.62, P = 0.0007] and CINC-1 expressions (ρ = 0.50, P = 0.01) and negatively with E-cadherin expression (ρ = -0.67, P = 0.0002). During PSV, PEEP of 5 cmH2O, but not a PEEP of 2 cmH2O, reduced lung damage and inflammatory markers while maintaining epithelial cell integrity.

Weaning of chronic obstructive pulmonary disease patients after coronary artery bypass graft surgery

Background Cardiac surgery has become more common in chronic obstructive pulmonary disease (COPD) patients, but this category is still at a high risk of postoperative prolonged ventilation. Finding of the appropriate mode for faster weaning is important to improve a patient’s outcome. Objective This study aimed to evaluate the effect of adaptive support ventilation (ASV) as a weaning mode in comparison with the pressure support mode in COPD patients in the postoperative period after a coronary artery bypass grafting (CABG) surgery. Patients and methods A randomized-controlled trial was conducted on 90 COPD (stage I and II) patients between 40 and 65 years old in the postoperative cardiothoracic ICU after CABG surgeries. Patients were initially ventilated with synchronized intermittent mandatory ventilation and were then allocated randomly to two equal groups to wean either by ASV group or pressure support ventilation group. The primary outcome was the number of patients weaned successfully from the first trial. The secondary outcomes were duration of mechanical ventilation, duration of weaning, number of arterial blood gas samples before extubation, length of ICU stay, cardiac and respiratory parameters at extubation, and mortality. Result In the ASV group, significantly higher numbers of patients were weaned from first trial, there was a shorter duration of weaning and mechanical ventilation and ICU stay, with fewer times of manual ventilator adjustments and arterial blood gas samples drawing during weaning. At extubation, this group showed a significantly lower respiratory rate, higher tidal volume, and lower peak airway pressure, with less tachycardia and lower systolic blood pressure compared with the pressure support ventilation group. Conclusion The ASV mode improves the quality of weaning and shortens ICU stay in COPD patients after CABG surgery.

Abstract PR088

Background & Objectives: Proportional Assist Ventilation (PAV+) delivers positive pressure ventilation in proportion to instantaneous inspiratory effort, with some studies suggesting PAV+ may reduce ventilator dyssynchrony and the duration of weaning from the ventilator. This trial compared the time taken to wean critically ill patients from invasive mechanical ventilation using PAV+ as opposed to Pressure Support Ventilation (PSV). Secondary objectives were to compare the rate of tracheostomy, failed extubation, ICU and hospital length of stay (LOS), ICU and hospital mortality in patients studied. Materials & Methods: This study was conducted in a 15-bed Australian metropolitan ICU that admits approximately 1100 medical and surgical patients per year. Patients were included in the study if they had been ventilated on a controlled mode of ventilation and were deemed suitable for at least 48 hours of weaning on a spontaneous mode of ventilation. Patients were excluded if they were unlikely to survive for 24 hours, had a neuromuscular disease or injury, or a tracheostomy in-situ. Results: Fifty patients were randomised, with 25 randomised into each arm. There was no statistical difference in age (median = 65 vs 61 years; p = 0.76) and APACHE-III illness severity score (median = 76 vs 77.5, p = 0.75) between the PAV+ and PSV groups. There was no significant difference in the duration of weaning from mechanical ventilation (78.2 vs 130.5 hours; p = 0.53). There was a non-significant trends towards lower in-hospital mortality (12% vs 37.5%, p = 0.08). There was no significant difference in the ICU LOS (median = 9.3 vs. 11.8 days; p = 0.57) among patients in the PAV+ arm when compared to those in the PSV arm. Three patients in the PAV+ group did not respond to this ventilation mode and were changed to PSV. There was no significant difference in the proportion of patients requiring tracheostomy (20% vs 29.2%; p = 0.68) or reintubation (4% vs 8.3%; p = 0.97). Conclusion: The duration of weaning from mechanical ventilation was comparable with PAV+ and PSV ventilation. A trend towards reduced hospital mortality was noted with PAV+ weaning. A larger study may provide further information on the advantages and disadvantages of PAV+ compared to other modes of spontaneous ventilation.

Low-positive pressure ventilation improves non-hypoxaemic apnoea tolerance during ear, nose and throat pan-endoscopy: A randomised controlled trial.

It has been suggested that oxygenation using pressure support ventilation (PSV) before general anaesthesia can reduce the duration of non-hypoxaemic apnoea. The objective was to determine whether or not pre-oxygenation with PSV increases the duration of non-hypoxaemic apnoea in non-obese patients during pan-endoscopy. A randomised, controlled trial. Amiens University Hospital, France. Fifty patients scheduled for ENT pan-endoscopy with a BMI lower than 35 kg m(-2). Patients scheduled for pan-endoscopy were enrolled to receive either 100% oxygen at neutral pressure (the control group) or 100% oxygen with positive-pressure ventilation (a positive inspiratory pressure of 4 cmH2O and a positive end-expiratory pressure of 4 cmH2O; the PSV group) during spontaneous ventilation with a face mask. The goal of pre-oxygenation was to obtain an end-tidal oxygen concentration of more than 90% prior to induction of anaesthesia. The primary efficacy criterion was the duration of non-hypoxaemic apnoea (i.e. before the peripheral capillary oxygen saturation fell to 90%). Secondary outcomes were duration of pre-oxygenation, pre-oxygenation failure and tolerance. The mean (interquartile range) duration of non-hypoxaemic apnoea was longer in the PSV group [598 (447 to 717) s] than in the control group [310 (217 to 451) s] (P < 0.001). Oxygenation time was shorter in the PSV group [190 (159 to 225) s] than in the control group [245 (151 to 435) s] (P = 0.037). Pre-oxygenation was unsuccessful (i.e. end-tidal oxygen concentration was < 90%) in 20% of the patients in the control group but none in the PSV group. The intergroup difference in the duration of pan-endoscopy was not significant. Tolerance was good or very good in all patients. Our results show that pre-oxygenation with PSV is associated with a longer duration of non-hypoxaemic apnoea and a lower frequency of manual reventilation during ENT pan-endoscopy. CLINICALTRIALS. NCT02167334.

High-Level Pressure Support Ventilation Attenuates Ventilator-Induced Diaphragm Dysfunction in Rabbits

BackgroundThe effects of different modes of mechanical ventilation in the same ventilatory support level on ventilator-induced diaphragm dysfunction onset were assessed in healthy rabbits. MethodsTwenty New Zealand rabbits were randomly assigned to 4 groups (n = 5 in each group). Group 1: no mechanical ventilation; group 2: controlled mechanical ventilation (CMV) for 24 hours; group 3: assist/ control ventilation (A/C) mode for 24 hours; group 4: high-level pressure support ventilation (PSV) mode for 24 hours. Heart rate, mean arterial blood pressure, PH, partial pressure of arterial oxygen/fraction of inspired oxygen and partial pressure of arterial carbon dioxide were monitored and diaphragm electrical activity was analyzed in the 4 groups. Caspase-3 was evaluated by protein analysis and diaphragm ultra structure was assessed by electron microscopy. ResultsThe centroid frequency and the ratio of high frequency to low frequency were significantly reduced in the CMV, A/C and PSV groups (P < 0.001). The percent change in centroid frequency was significantly lower in the PSV group than in the CMV and A/C groups (P = 0.001 andP =0.028, respectively). Electromyography of diaphragm integral amplitude decreased by 90% ± 1.48%, 67.8% ± 3.13% and 70.2% ± 4.72% in the CMV, A/C and PSV groups, respectively (P< 0.001). Caspase-3 protein activation was attenuated in the PSV group compared with the CMV and A/C groups (P = 0.035 andP= 0.033, respectively). Irregular swelling of mitochondria along with fractured and fuzzy cristae was observed in the CMV group, whereas mitochondrial cristae were dense and rich in the PSV group. The mitochondrial injury scores (Flameng scores) in the PSV group were the lowest among the 3 ventilatory groups (0.93 ± 0.09 in PSV versus 2.69 ± 0.05 in the CMV [P < 0.01] and PSV versus A/C groups [2.02 ± 0.08,P <0.01]). ConclusionsThe diaphragm myoelectric activity was reduced in the PSV group, although excessive oxidative stress and ultrastructural changes of diaphragm were found. However, partial diaphragm electrical activity was retained and diaphragm injury was minimized using the PSV mode.

Different spontaneous breathing trials in patients with atrial fibrillation

IntroductionWeaning from mechanical ventilation is one of the most important and challenging problems for most intensive care unit (ICU) patients. Spontaneous breathing trial (SBT) is the most common method used to evaluate patients’ ability to breathe by themselves and plays an important role in decision making for weaning. The aim of our study was to investigate the effect of different methods of SBT in respiratory care unit (RCU) patients with atrial fibrillation (AF) on weaning outcome. MethodsWe retrospectively analyzed different methods of SBT in patients with and without AF. We enrolled RCU patients who required mechanical ventilation and had undergone transthoracic echocardiography from January 2011 to January 2012. ResultsThere was a higher SBT passing rate among AF patients who received pressure support ventilation (PSV) trial than in those who received T-piece trail (92.5% vs. 73.1%, p=0.041). The weaning rates between these two groups were not significantly different (83.8% vs. 94.7%, p=0.403). Total ventilator days were longer in T-piece group than in PSV group (median 40.0, IQR: 18.2–125.1 days vs. 33.0, IQR: 29.6–51.0 days respectively, p=0.580), but this difference was not statistically significant. These results were not found in patients without AF. ConclusionsThe use of PSV trial might be considered first instead of T-piece trial for SBT when AF patients were ready to wean.

Efficacy of pressure support ventilation in infants undergoing laparoscopic hernia repair under sevoflurane anesthesia

Objective To evaluate the efficacy of pressure support ventilation (PSV) in the infants undergoing laparoscopic hernia repair under sevoflurane anesthesia. Methods Thirty ASA physical status Ⅰ pediatric children, aged 9 months-1 yr, weighing 8.0-11.5 kg, undergoing elective laparoscopic hernia repair, were randomly assigned into 3 groups (n=10 each) using a random number table: pressure control ventilation (PCV) used for muscle relaxants in combination with low-concentration sevoflurane group (group PCV1) , PCV used for high-concentration sevoflurane group (group PCV2) , and PSV used for low-concentration sevoflurane group (group PSV) . Anesthesia was induced with inhalation of 4%-6% sevoflurane and iv fentanyl 2 μg/kg and succinylcholine 1.5 mg/kg.The pediatric children were endotracheally intubated and mechanically ventilated.In PCV1 and PCV2 groups, PCV was used during operation.In group PSV, PCV was used first after intubation, and then PSV was applied after spontaneous breathing recovered.Anesthesia was maintained as follows: in group PCV1, the end-tidal concentration of sevoflurane was maintained at 2.5%-3.0%, and cisatracurium besylate 0.1 mg/kg was injected intermittently as required; in group PCV1, the end-tidal concentration of sevoflurane was maintained at 3.5%-4.0%; in group PSV, the end-tidal concentration of sevoflurane was maintained at 2.5%-3.0%, and succinylcholine 1.0 mg/kg was injected intravenously before pneumoperitoneum.Narcotrend index value was maintained at 50-60 in PCV1 and PSV groups, or at 37-45 in PCV2 group.Heart rate (HR) and mean arterial pressure (MAP) were recorded before induction of anesthesia (baseline) , at the beginning of pneumoperitoneum, at 5 and 10 min of pneumoperitoneum, at the end of pneumoperitoneum, at the end of operation and immediately after extubation.The time interval from the end of surgery to extubation was recorded. Results Pulse oxygen saturation was 100% during anesthesia, and>95% during recovery from anesthesia in the three groups.Compared with the baseline value, HR was significantly faster, and MAP was increased during extubation in PCV1 and PCV2 groups, and no significant change was found in HR and MAP at each time point in group PSV.The time interval from the end of surgery to extubation was 30.3±5.4, 18.4±4.3 and (4.1±1.2) min in PCV1, PCV2 and PSV groups, respectively.Compared with PCV1 and PCV2 groups, the time interval from the end of surgery to extubation was significantly shortened in group PSV. Conclusion When PSV is applied in the infants undergoing laparoscopic hernia repair under sevoflurane anesthesia, it can provide adequate ventilation, recovery from anesthesia is rapid, and no cardiovascular responses occur during extubation. Key words: Anesthetics, inhalation; Anesthesia, general; Infant; Laparoscopy; Pressure support ventilation

Effects of pressure support ventilation mode on emergence time and intra-operative ventilatory function: a randomized controlled trial.

We tested the hypothesis that pressure-support ventilation (PSV) allows a reduction in emergence time and laryngeal mask airway (LMA) removal time after general anesthesia compared to volume-controlled mechanical ventilation (CMV). Because spontaneous breathing (SB) is often used with LMA under general anesthesia, patients were allocated randomly to three groups (CMV, SB and PSV). Thirty-six consecutive ASA I–II patients scheduled for knee arthroscopic surgery under general anesthesia with a LMA and breathing throughout the ventilator circuit were included. Hemodynamic and ventilatory variables were recorded before and 10-min after general anesthesia-induction, at the surgical incision, at the end of anaesthetic drugs infusion and when the patient was totally awake (which defines emergence time). LMA removal time, drug consumption were recorded at the end of the surgical procedure. Leak fraction around the LMA was also evaluated. LMA removal time was significantly higher in the CMV-group (18±6 min) compared to both SB (8±4 min) and PSV (7±4 min, P<0.05) groups as well as for emergence time: CMV-group (32±12 min), SB (17±7 min) and PSV (13±6 min, P<0.05) groups. Total propofol consumption was significantly lower in the PSV-group (610±180 mg) than in both CMV (852±330 mg) and SB (734±246 mg, P<0.05) groups. Air leaks around the LMA was significantly higher in the CMV-group than in the SB and PSV groups (16% vs 3% and 7%, all P<0.05). In conclusion, in knee arthroscopic surgery, in comparison to CMV, PSV use during general anesthesia in unparalyzed patients decreases LMA removal time, propofol consumption and leaks around LMA while improving ventilatory variables without adverse effects.Trial RegistrationControlled-Trials.com ISRCTN17382426

Comparison of Pressure Support Ventilation and T-piece in Determining Rapid Shallow Breathing Index in Spontaneous Breathing Trials

BackgroundThe threshold values of rapid shallow breathing index (RSBI) were compared in pressure support ventilation (PSV) and T-piece assessments for spontaneous breathing trials (SBT). The ability of DRSBI to also predict successful weaning was evaluated. MethodsTwo hundred eight patients were weaned from mechanical ventilation through oral intubation. They were randomly divided into PSV group (n = 93) and T-piece group (n = 115). The RSBI was calculated as f/VT at SBT of 3 and 30 minutes. Receiver operating characteristic curves of RSBI were also generated, cutoff values were determined and the changes in the RSBI were calculated. ResultsOf the 208 patients, 168 (80.77%) were successfully weaned from mechanical ventilation, 78/93 (83.9%) in the PSV group and 90/ 115 (78.3%) in the T-piece group (P > 0.05). In the PSV and T-piece groups, the average RSBI at 30-minute SBT was 67.18 ± 11.55 breaths per min/L and 99.11 ± 15.53 breaths per min/L, respectively (P < 0.01), and the average DRSBI was 69 ± 33% and 119 ± 35%, respectively (P < 0.01). Additionally, in the 2 groups, an RSBI of 75 breaths per min/L (PSV) and 100 breaths per min/L (T-piece) yielded a diagnostic accuracy of 87% and 82% respectively. However, a DRSBI of 90% (PSV) and 130% (T-piece) yielded a diagnostic accuracy of 82% and 77% respectively. ConclusionsThe threshold values of RSBI, thus 75 breaths per min/L (PSV) and 100 breaths per min/L (T-piece), for predicting successful weaning were more accurate than other values. Similarly, the change in the RSBI could also predict such successes.

Proportional assist ventilation versus pressure support ventilation in the weaning of patients with acute exacerbation of chronic obstructive pulmonary disease

BackgroundPatients with COPD are frequently hospitalized for acute exacerbations (AECOPD), which may cause respiratory failure and death. Proportional assist ventilation (PAV) is a relatively new mode of ventilator-based, inspiratory support designed to assist spontaneous breathing in patients with intact neural drive. It is a form of synchronized partial ventilatory assistance with peculiar characteristic that ventilator generates pressure in proportion to patient’s instantaneous effort. Pressure support ventilation (PSV) is an attractive weaning mode, however at higher pressure support levels, many patients displayed expiratory muscle activation indicating that the patient is “fighting the ventilator”. ObjectiveTo compare PAV and PSV in the weaning of AECOPD patients. Patients and methodsThe study was conducted on 60 patients admitted to the Department of Critical Care Medicine, at the Alexandria Main University Hospital with the diagnosis of AECOPD. Exclusion criteria included those with severe cardiac or neurological disease, and those managed by non-invasive ventilation. All patients were subjected on admission to complete history taking, complete physical examination and laboratory investigations and were treated according to guidelines of treatment of AECOPD. At the time of weaning patients were randomly categorized into two equal groups; Group A: patients weaned using PAV and Group B: patients weaned using PSV and the two groups were assessed for weaning success, patient–ventilator dys-synchrony, MV days, ICU, and hospital stay. ResultsThe weaning success rate was 90% in group A, and 66.7% in group B. PAV was associated with less patient–ventilator dys-synchrony and was associated with 1.5day reduction in the mean days of mechanical ventilation, 2day reduction in the mean days of ICU stay, and 1.8day reduction in the mean days of hospital stay in comparison to PSV group. ConclusionPAV was associated with less patient–ventilator dys-synchrony and associated with reduction of days of mechanical ventilation, ICU, and hospital stay.

Ventilación con presión de soporte y ventilación proporcional asistida durante la retirada de la ventilación mecánica

ObjectivesTo compare tolerance, duration of mechanical ventilation (MV) and clinical outcomes during weaning from MV in patients subjected to either pressure support ventilation (PSV) or proportional assist ventilation (PAV). DesignA prospective, observational study was carried out. SettingIntensive Care Unit. PatientsA total of 40 consecutive subjects were allocated to either the PSV or the PAV group until each group contained 20 patients. Patients were included in the study when they met the criteria to begin weaning and the attending physician decided to initiate the weaning process. The physician selected the modality and set the ventilatory parameters. InterventionsNone. Variables of interestDemographic data, respiratory mechanics, ventilatory parameters, duration of MV, and clinical outcomes (reintubation, tracheostomy, mortality). ResultsBaseline characteristics were similar in both groups. No significant differences were observed between the PSV and PAV groups in terms of the total duration of MV (10 [5-18] vs. 9 [7-19] days; P=.85), reintubation (5 [31%] vs. 3 [19%]; P=.69), or mortality (4 [20%] vs. 5 [25%] deaths; P=1). Eight patients (40%) in the PSV group and 6 patients (30%) in the PAV group (P=.74) required a return to volume assist-control ventilation due to clinical deterioration. ConclusionsTolerance, duration of MV and clinical outcomes during weaning from mechanical ventilation were similar in PSV and PAV.

Effect of pressure support ventilation during weaning on ventilation and oxygenation indices in healthy horses recovering from general anesthesia

ObjectiveTo determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses. Study designProspective randomized clinical study. AnimalsTwenty client‐owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg. MethodsIn the control group (CG; n = 10) weaning was performed by a gradual decrease in respiratory rate (fR) and in the PSV group (PSVG; n = 10) by a gradual decrease in fR with PSV. The effect of weaning was considered suboptimal if PaCO2 > 50 mmHg, arterial pH < 7.35 plus PaCO2 > 50 mmHg or PaO2 < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested. ResultsPressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO2 41 ± 3 mmHg at weaning and the average lowest PaO2 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO2 57 ± 6 mmHg at weaning and the average lowest PaO2 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for fR (p = 0.3474), minute volume (p = 0.1153), SaO2 (p = 0.1737) and PaO2/PAO2 (p = 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for VT > 10 L (p = 0.0001), fR/VT ratio ≤ 0.60 breaths minute−1 L−1 (p = 0.0001), VT/bodyweight > 18.5 mL kg−1 (p = 0.0001) and PaO2/FiO2 > 298 (p = 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for VT < 10 L (p = 0.0001), fR/VT ratio ≥ 0.60 breaths minute−1 L−1 (p = 0.0001) and Pe′CO2 ≥ 38 mmHg (p = 0.0001) at weaning. Conclusions and clinical relevancePressure support ventilation (PSV) weaning had a better respiratory outcome. A higher VT, VT/body weight, PaO2/FiO2 ratio and a lower fR/VT ratio and Pe′CO2 were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.

Non-invasive determination of respiratory system mechanics in pressure support ventilation using the expiratory time constant?

In the previous issue of Critical Care, we read with interest the article by Al-Rawas and colleagues [1], who proposed a method for the determination of respiratory system mechanics (RSM) in diff erent ventilatory modes. We have some concerns regarding the applicability of the described method during pressure support ventilation (PSV). In particular, all equations proposed in the article contain a term called ‘inhaled fl ow rate’. Since there is no constant inspiratory fl ow during PSV, it is unclear how the authors determined its exact value. Furthermore, all of these equations are transformations of the equation of motion of the respiratory system and require the knowledge of the inspiratory driving pressure, for which the authors apparently used the inspiratory airway pressure. However, in PSV, the patients’ spontaneous breathing activity contributes to inspiratory driving pressure to a variable degree [2]. It would be interesting to know how the authors took the patients’ muscular eff ort (P mus ) into account. Finally, we would like to know why the numbers of patients in the PSV and in the volume-controlled continuous mandatory ventilation groups diff er from the numbers of measurements plotted in the corresponding fi gures. For example, 23 patients were in the PSV group (according to Table 1), but 25 measure ments are shown in Figure 4a,b and only 14 are shown in Figure 4c. A non-invasive determination of RSM during PSV is certainly helpful in a clinical setting, and we would appreciate if the authors provided a detailed description of how they handled the non-constant qualities of fl ow and P mus during PSV.

Automatic Tube Compensation versus Pressure Support Ventilation and Extubation Outcome in Children: A Randomized Controlled Study

Background. Automatic tube compensation (ATC) has been developed to overcome the imposed work of breathing due to artificial airways during spontaneous breathing trials (SBTs). Objectives. This study aimed to assess extubation outcome after an SBT (spontaneous breathing trial) with ATC compared with pressure support ventilation (PSV) and to determine the risk factors for extubation failure. Methods. Patients ready for extubation were randomly assigned to two-hour spontaneous breathing trial with either ATC or pressure support ventilation. Results. In the ATC group (n = 17), 11 (65%) patients passed the SBT with subsequent extubation failure (9%). While in PSV group (n = 19), 10 (53%) patients passed the SBT with subsequent extubation failure (10%). This represented a positive predictive value for ATC of 91% and PSV of 90% (P = 0.52). Five (83%) of the patients who failed the SBT in ATC group were reintubated. This represented a higher negative predictive value for ATC of 83% than for PSV which was 56%. None of the assessed risk factors were independently associated with extubation failure including failed trial. Conclusion. ATC was equivalent to PSV in predicting patients with successful extubation. A trial failure in ATC group is associated with but does not definitely predict extubation failure.

Pressure support-ventilation versus spontaneous breathing with “T-Tube” for interrupting the ventilation after cardiac operations

ObjectiveTo compare pressure-support ventilation with spontaneous breathing through a T-tube for interrupting invasive mechanical ventilation in patients undergoing cardiac surgery with cardiopulmonary bypass. MethodsAdults of both genders were randomly allocated to 30 minutes of either pressure-support ventilation or spontaneous ventilation with "T-tube" before extubation. Manovacuometry, ventilometry and clinical evaluation were performed before the operation, immediately before and after extubation, 1h and 12h after extubation. ResultsTwenty-eight patients were studied. There were no deaths or pulmonary complications. The mean aortic clamping time in the pressure support ventilation group was 62 ± 35 minutes and 68 ± 36 minutes in the T-tube group (P=0.651). The mean cardiopulmonary bypass duration in the pressure-support ventilation group was 89 ± 44 minutes and 82 ± 42 minutes in the T-tube group (P=0.75). The mean Tobin index in the pressure support ventilation group was 51 ± 25 and 64.5 ± 23 in the T-tube group (P=0.153). The duration of intensive care unit stay for the pressure support ventilation group was 2.1 ± 0.36 days and 2.3 ± 0.61 days in the T-tube group (P=0.581). The atelectasis score in the T-tube group was 0.6 ± 0.8 and 0.5 ± 0.6 (P=0.979) in the pressure support ventilation group. The study groups did not differ significantly in manovacuometric and ventilometric parameters and hospital evolution. ConclusionThe two trial methods evaluated for interruption of mechanical ventilation did not affect the postoperative course of patients who underwent cardiac operations with cardiopulmonary bypass.

Spontaneous Breathing during General Anesthesia Prevents the Ventral Redistribution of Ventilation as Detected by Electrical Impedance Tomography

Positive-pressure ventilation causes a ventral redistribution of ventilation. Spontaneous breathing during general anesthesia with a laryngeal mask airway could prevent this redistribution of ventilation. We hypothesize that, compared with pressure-controlled ventilation, spontaneous breathing and pressure support ventilation reduce the extent of the redistribution of ventilation as detected by electrical impedance tomography. The study was a randomized, three-armed, observational, clinical trial without blinding. With approval from the local ethics committee, we enrolled 30 nonobese patients without severe cardiac or pulmonary comorbidities who were scheduled for elective orthopedic surgery. All of the procedures were performed under general anesthesia with a laryngeal mask airway and a standardized anesthetic regimen. The center of ventilation (primary outcome) was calculated before the induction of anesthesia (AWAKE), after the placement of the laryngeal mask airway (BEGIN), before the end of anesthesia (END), and after arrival in the postanesthesia care unit (PACU). The center of ventilation during anesthesia (BEGIN) was higher than baseline (AWAKE) in both the pressure-controlled and pressure support ventilation groups (pressure control: 55.0 vs. 48.3, pressure support: 54.7 vs. 48.8, respectively; multivariate analysis of covariance, P < 0.01), whereas the values in the spontaneous breathing group remained at baseline levels (47.9 vs. 48.5). In the postanesthesia care unit, the center of ventilation had returned to the baseline values in all groups. No adverse events were recorded. Both pressure-controlled ventilation and pressure support ventilation induce a redistribution of ventilation toward the ventral region, as detected by electrical impedance tomography. Spontaneous breathing prevents this redistribution.

Randomised weaning trial comparing assist control to pressure support ventilation

ObjectivesTo determine if the work of breathing was lower, respiratory muscle strength greater, but the degree of asynchrony higher during weaning by assist control ventilation (ACV) rather than pressure support...

Effects of neurally adjusted ventilatory assist on subject-ventilator synchrony in rabbits with acute respiratory distress syndrome

To observe the effects of neurally adjusted ventilatory assist (NAVA) on subject-ventilator synchrony in rabbits with acute respiratory distress syndrome (ARDS). The rabbit model of ARDS was induced by intratracheal infusion of hydrochloric acid. After sufficient recruitment, the rabbits were randomly divided into 2 groups: pressure support ventilation (PSV) group and NAVA group. The parameters of subject-ventilator synchrony such as ventilation trigger, ventilation switching and magnitude of assist were observed at 0, 1, 2, 3 h respectively. (1) Ventilation trigger: 1) trigger delay: the trigger delay in the NAVA group were markedly lower than the PSV group at 0, 1, 2, 3 h (P < 0.05); as ventilation time elapsed, the trigger delay changed neither in NAVA nor in PSV group (P > 0.05). 2) Ineffective trigger index: the ineffective trigger index was 17.7% ± 13.7% in the PSV group. While all neural efforts were trigger, there was no ineffective trigger observed in the NAVA group. (2) Off-cycle delay: the off-cycle delay were significantly lower in the PSV group than that in the NAVA group at 0, 1, 2, 3 h (P < 0.05); as the ventilation time elapsed, the off-cycle delay changed neither in the NAVA group nor in the PSV group (P > 0.05). (3) Magnitude of assist: in the NAVA group, peak EAdi and peak pressure were markedly correlated (determination coefficient 0.86 ± 0.07, P < 0.05). But pressure delivery during the PSV group was not correlated with EAdi (P > 0.05). As compared with PSV, NAVA can improve subject-ventilator synchrony in rabbits with ARDS.

Randomised trial comparing assist control and pressure support ventilation during weaning

AimAssist control ventilation (ACV) compared to pressure limited, time cycled ventilation is associated with shorter duration of weaning. During both ACV and pressure support ventilation (PSV), all the infant's breaths...

Effect of intra‐operative pressure support vs pressure controlled ventilation on oxygenation and lung function in moderately obese adults*

Obesity impairs peri-operative lung function. To evaluate the impact of pressure support ventilation vs pressure controlled ventilation in moderately obese adults upon early postoperative lung function, we randomly assigned 68 moderately obese patients (body mass index 25-35 kg x m(-2)) undergoing minor surgery to receive intra-operative ventilation either with pressure support or pressure controlled ventilation. We performed intra-operative blood gas analysis and measured pulse oximetry saturation, spirometry values at pre-operative assessment (baseline) and at 10 min, 30 min, 2 h and 24 h after extubation. The intra-operative oxygenation index (arterial partial pressure of oxygen/fraction of inspired oxygen) in the pressure support ventilation group was significantly improved over time (p < 0.0001). Postoperatively, the pressure support ventilation group also had better lung function and oxygenation values than did the pressure controlled ventilation group (p < 0.005). We conclude that pressure support ventilation better maintains lung function than pressure controlled ventilation in moderately overweight patients scheduled for minor surgery.