Adaptive Support Ventilation®: la ventilazione si adatta al paziente

BACKGROUND

Adaptive support ventilation (ASV) allows the clinician to set a maximum plateau pressure (PP) and automatically adjusts tidal volume to keep PP below the set maximum.

METHODS

ASV was compared to a fixed tidal volume of 6 ml/kg. ASV determined the respiratory rate and tidal volume based on its algorithms. Maximum airway pressure limit was 28 cm H2O in ASV. Six sets of lung mechanics were simulated for two ideal body weights: 60 kg, Group I; 80 kg, Group II. Positive end expiratory pressure was 8, 12, and 16 cm H2O, and target minute volume 120%, 150%, and 200% of predicted minute volume.

RESULTS

ASV "sacrificed" tidal volume and minute ventilation to maintain PP in 9 (17%) of 54 scenarios in Group I and 20 (37%) of 54 scenarios in Group II. In Group I, the number of scenarios with PP of 28 cm H2O or more was 14 for ASV (26%) and 19 for 6 ml/kg (35%). In these scenarios, mean PP were ASV 28.8 +/- 0.86 cm H2O (min 28, max 30.3) and 6 ml/kg 33.01 +/- 3.48 cm H2O (min 28, max 37.8) (P = 0.000). In group II, the number of scenarios PP of 28 cm H2O or more was 10 for ASV (19%) and 21 for 6 ml/kg (39%). In these cases, mean PP values were ASV 28.78 +/- 0.54 cm H2O (min 28, max 29.6) and 6 ml/kg 32.66 +/- 3.37 cm H2O (min 28.2, max 38.2) (P = 0.000).

CONCLUSION

In a lung model with varying mechanics, ASV is better able to prevent the potential damaging effects of excessive PP (greater than 28 cm H2O) than a fixed tidal volume of 6 ml/kg by automatically adjusting airway pressure, resulting in a decreased tidal volume.

UNLABELLED

Adaptive support ventilation (ASV) provides an automatic adaptation of the ventilator settings to patient's passive and active respiratory mechanics. In a randomized controlled study, we evaluated automatic respiratory weaning in ASV for early tracheal extubation after cardiac surgery. Eligible patients were assigned to either an ASV protocol or a standard one consisting of synchronized intermittent ventilation followed by pressure support. Eighteen patients completed the ASV protocol, and 16 completed the standard one. There were no differences between groups in perioperative characteristics, lengths of tracheal intubation and intensive care unit stay, and ventilatory variables, except less peak inspiratory pressure during the initial phase in ASV (17.5 +/- 0.8 versus 22.2 +/- 0.8 cm H(2)O; P < 0.01). ASV patients required fewer ventilatory settings manipulations (2.4 +/- 0.7 versus 4.0 +/- 0.8 manipulations per patient; P < 0.05) and endured less high-inspiratory pressure alarms (0.7 +/- 2.4 versus 2.9 +/- 3.0; P < 0.05). These results suggest that in this specific population of patients, automation of postoperative ventilation with ASV resulted in an outcome similar to the control group. The internal logic of the new device resulted in less manipulation of the setting and alarms that could simplify respiratory management.

IMPLICATIONS

Adaptive support ventilation (ASV), a ventilatory mode providing automatic adjustment of the settings was compared with standard management for rapid tracheal extubation after cardiac surgery. The two approaches were equal in terms of outcome. In ASV, we observed fewer ventilator settings manipulations and a smaller amount of alarms, suggesting that this automatic mode may simplify postoperative respiratory management without delaying extubation.

BACKGROUND

Adaptive support ventilation (ASV) is a new mode of mechanical ventilation that seeks an optimal breathing pattern based on the minimum work of breathing (WOB) principle. The operator's manual for the ventilators that provide ASV recommends that the %MinVol setting be started at 100% (the 100%MinVol setting), but it is unclear whether that setting reduces WOB in patients with respiratory failure.

METHODS

We studied 22 hemodynamically stable patients with respiratory failure who were on pressure-support ventilation. We switched the ventilation mode to ASV and started at the 100%MinVol setting. We then increased the %MinVol setting by 10% every 5 min until 1-3 mandatory breaths per min appeared, and called that setting the ASV target point. We then tested 2 additional %MinVol settings: 20% below the ASV target point (target-point-20%), and 20% above the ASV target point (target-point+20%). We tested each %MinVol setting for 10 min. At the end of each 10-min period we measured respiratory variables, pressure-time product (PTP), and airway occlusion pressure at 0.1 s after the onset of inspiratory flow (P(0.1)).

RESULTS

In 18 patients (82%), at the 100%MinVol setting, the actual minute volume (V(E)) was greater than the target V(E). At the ASV target point the mean +/- SD %MinVol setting was 165 +/- 54% and was associated with a 40% decrease in PTP and P(0.1), but V(E) did not change. At target-point+20%, V(E) increased slightly, primarily due to a small increase in tidal volume, and PTP and P(0.1) further decreased. At target-point-20%, PTP and P(0.1) were similar to those at the 100%MinVol setting. At the ASV target point the 6 patients with chronic obstructive pulmonary disease had a lower mean %MinVol setting (125 +/- 23%) than the 16 patients who did not have chronic obstructive pulmonary disease (180 +/- 55%).

CONCLUSIONS

The 100%MinVol setting was frequently not associated with lower WOB in patients with respiratory failure. The %MinVol setting that significantly reduced WOB could be detected by increasing the %MinVol setting until a few mandatory breaths began to appear, and was on average 165% of the MinVol setting.

OBJECTIVE

To compare the effects of adaptive support ventilation (ASV) and synchronized intermittent mandatory ventilation plus pressure support (SIMV-PS) on patient-ventilator interactions in patients undergoing partial ventilatory support.

DESIGN

Prospective, crossover interventional study.

SETTING

Medical intensive care unit, university tertiary care center.

PATIENTS

Ten patients, intubated and mechanically ventilated for acute respiratory failure of diverse causes, in the early weaning period, ventilated with SIMV-PS and clinically detectable sternocleidomastoid activity suggesting increased inspiratory load and patient-ventilator dyssynchrony.

INTERVENTIONS

Measurement of respiratory mechanics, P0.1, sternocleidomastoid electromyographic activity, arterial blood gases, and systemic hemodynamics in three conditions: 1) after 45 mins with SIMV-PS (SIMV-PS 1); 2) after 45 mins with ASV, set to deliver the same minute-ventilation as during SIMV-PS; 3) 45 mins after return to SIMV-PS (SIMV-PS 2), with settings identical to those of the first SIMV-PS period.

MAIN RESULTS

The same minute ventilation was observed during ASV (11.4 +/- 3.1 l/min [mean +/- sd]) as during SIMV-PS 1 (11.6 +/- 3.5 L/min) and SIMV-PS 2 (10.8 +/- 3.4 L/min). No parameter was significantly different between SIMV-PS 1 and 2, hence subsequent results refer to ASV vs. SIMV-PS 1. During ASV, tidal volume increased (538 +/- 91 vs. 671 +/- 100 mL, p <.05) and total respiratory rate decreased (22 +/- 7 vs. 17 +/- 3 breaths/min, p <.05) vs. SIMV-PS. However, spontaneous respiratory rate increased in six patients, decreased in four, and remained unchanged in one. P0.1 decreased during ASV in all patients except three in whom no change was noted (1.8 +/- 0.9 vs. 1.1 +/- 1 cm H2O, p <.05). During ASV, sternocleidomastoid electromyogram activity was markedly reduced (electromyogram index, where SIMV-PS 1 = 100, ASV 34 +/- 41, SIMV-PS 2 89 +/- 36, p <.02) as was palpable muscle activity. No changes were noted in arterial blood gases, pH, or mean systemic pressure during the trial.

CONCLUSION

In patients undergoing partial ventilatory support, with clinical and electromyographic signs of increased respiratory muscle loading, ASV provided levels of minute ventilation comparable to those of SIMV-PS. However, with ASV, central respiratory drive and sternocleidomastoid activity were markedly reduced, suggesting decreased inspiratory load and improved patient-ventilator interactions. These preliminary results warrant further testing of ASV for partial ventilatory support.

BACKGROUND

Adaptive support ventilation (ASV) facilitates ventilator liberation in postoperative patients in surgical intensive care units (ICU). Whether ASV has similar benefits in patients with acute respiratory failure is unclear.

METHODS

We conducted a pilot study in a medical ICU that manages approximately 600 mechanically ventilated patients a year. The ICU has one respiratory therapist who manages ventilators twice during the day shift (8:00 am to 5:00 pm). No on-site respiratory therapist was present at night. We prospectively enrolled 79 patients mechanically ventilated for ≥ 24 hours on pressure support of ≥ 15 cm H(2)O, with or without synchronized intermittent mandatory ventilation, F(IO(2)) ≤ 50%, and PEEP ≤ 8 cm H(2)O. We switched the ventilation mode to ASV starting at a "%MinVol" setting of 80-100%. We defined spontaneous breathing trial (SBT) readiness as a frequency/tidal-volume ratio of < 105 (breaths/min)/L on pressure support of ≤ 8 cm H(2)O and PEEP of ≤ 5 cm H(2)O for at least 2 h, and all spontaneous breaths. The T-piece SBT was considered successful if the frequency/tidal-volume ratio remained below 105 (breaths/min)/L for 30 min, and we extubated after successful SBT. The control group consisted of 70 patients managed with conventional ventilation modes and a ventilator protocol during a 6-month period immediately before the ASV study period.

RESULTS

Extubation was attempted in 73% of the patients in the ASV group, and 80% of the patients in the non-ASV group. The re-intubation rates in the ASV and non-ASV groups were 5% and 7%, respectively. In the ASV group, 20% of the patients achieved extubation readiness within 1 day, compared to 4% in the non-ASV group (P = <.001). The median time from the enrollment to extubation readiness was 1 day for the ASV group and 3 days for the non-ASV group (P = .055). Patients switched to ASV were more likely to be liberated from mechanical ventilation at 3 weeks (P = .04). Multiple logistic regression analysis showed that, of the independent factors in the model, only ASV was associated with shorter time to extubation readiness (P = .048 via likelihood ratio test).

CONCLUSIONS

Extubation readiness may not be recognized in a timely manner in at least 15% of patients recovering from respiratory failure. ASV helps to identify these patients and may improve their weaning outcomes.

Adaptive support ventilation (ASV) is a closed-loop ventilation mode that can act both as pressure support ventilation (PSV) and pressure-controlled ventilation. Weaning with ASV shows promising results, mainly in post-cardiac surgery patients. The aim of the present randomised controlled study was to test the hypothesis that weaning with ASV could reduce the weaning duration in patients with chronic obstructive pulmonary disease (COPD) when compared with PSV. From among 435 COPD patients admitted to the intensive care unit (ICU) during a 20-month period, 97 were enrolled. Patients were assigned at random to either ASV or PSV as a weaning mode. Compared with PSV, ASV provided shorter weaning times (median 24 (interquartile range 20-62) h versus 72 (24-144) h, p=0.041) with similar weaning success rates (35 out of 49 for ASV and 33 out of 48 for PSV). Length of stay in the ICU was also shorter with ASV but the difference was not statistically significant. This study suggests that ASV may be used in the weaning of COPD patients with the advantage of shorter weaning times. Further studies are needed to investigate the role and potential advantages of ASV in the weaning period of different patient groups.

BACKGROUND

Adaptive-support ventilation (ASV) is a minute ventilation-controlled mode governed by a closed-loop algorithm. With ASV, tidal volume and respiratory rate are automatically adjusted to minimize work of breathing. Studies indicate that ventilation in ASV enables more rapid weaning. The authors conducted a randomized controlled trial to determine whether ventilation in ASV results in a shorter time to extubation than pressure-regulated volume-controlled ventilation with automode (PRVCa) after cardiac surgery.

METHODS

Fifty patients were randomly assigned to ASV or PRVCa after elective coronary artery bypass grafting. Respiratory weaning progressed through three phases: phase 1 (controlled ventilation), phase 2 (assisted ventilation), and phase 3 (T-piece trial), followed by extubation. The primary outcome was duration of intubation (sum of phases 1-3). Secondary outcomes were duration of mechanical ventilation (sum of phases 1 and 2), number of arterial blood gas samples, and manual ventilator setting changes made before extubation.

RESULTS

Forty-eight patients completed the study. The median duration of intubation was significantly shorter in the ASV group than in the PRVCa group (300 [205-365] vs. 540 [462-580] min; P < 0.05). This difference was due to a reduction in the duration of mechanical ventilation (165 [120-195] vs. 480 [360-510] min; P < 0.05). There were no significant differences between the ASV and PRVCa groups in the number of arterial blood gas samples taken or manual ventilator setting changes made.

CONCLUSIONS

ASV is associated with earlier extubation, without an increase in clinician intervention, when compared with PRVCa in patients undergoing uncomplicated cardiac surgery.

BACKGROUND

Adaptive support ventilation (ASV) is a microprocessor-controlled mode of mechanical ventilation that maintains a predefined minute ventilation with an optimal breathing pattern (tidal volume and rate) by automatically adapting inspiratory pressure and ventilator rate to changes in the patient's condition. The aim of the current study was to test the hypothesis that a protocol of respiratory weaning based on ASV could reduce the duration of tracheal intubation after uncomplicated cardiac surgery ("fast-track" surgery).

METHODS

A group of patients being given ASV (group ASV) was compared with a control group (group control) in a randomized controlled study. After coronary artery bypass grafting during general anesthesia with midazolam and fentanyl, patients were randomly assigned to group ASV or group control. Both protocols were divided into three predefined phases, and weaning progressed according to arterial blood gas and clinical criteria. In phase 1, ASV mode was set at 100% of the theoretical value of volume/minute in group ASV, and synchronized intermittent mandatory ventilation mode was used in group control. When spontaneous breathing occurred, ASV setting was reduced by 50% of minute ventilation (phase 2) and again by 50% (phase 3), and the trachea was extubated. In group control, the ventilator was switched to 10 cm H2O inspiratory pressure support (phase 2), then to 5 cm H2O (phase 3) until extubation.

RESULTS

Forty-nine patients were enrolled. Sixteen patients completed the ASV protocol, and 20 the standard protocol; 7 patients were excluded in group ASV and 6 in group control according to explicit, predefined criteria. There were no differences between groups in perioperative characteristics or in the doses of sedation. The primary outcome of the study, that is, the duration of tracheal intubation, was shorter in group ASV than in group control (median [quartiles]: 3.2 [2.5-4.6] vs. 4.1 [3.1-8.6] h; P < 0.02). Fewer arterial blood analyses were performed in group ASV (median number [quartiles]: 3 [3-4] vs. 4 [3-6]), suggesting that fewer changes in the settings of the ventilator were required in this group.

CONCLUSIONS

A respiratory weaning protocol based on ASV is practicable; it may accelerate tracheal extubation and simplify ventilatory management in fast-track patients after cardiac surgery. The evaluation of potential advantages of the use of such technology on patient outcome and resource utilization deserves further studies.

INTRODUCTION

In mechanically ventilated patients, driving pressure (ΔP) represents the dynamic stress applied to the respiratory system and is related to ICU mortality. An evolution of the Adaptive Support Ventilation algorithm (ASV® 1.1) minimizes inspiratory pressure in addition to minimizing the work of breathing. We hypothesized that ASV 1.1 would result in lower ΔP than the ΔP measured in APV-CMV (controlled mandatory ventilation with adaptive pressure ventilation) mode with physician-tailored settings. The aim of this randomized crossover trial was therefore to compare ΔP in ASV 1.1 with ΔP in physician-tailored APV-CMV mode.

METHODS

Pediatric patients admitted to the PICU with heterogeneous-lung disease were enrolled if they were ventilated invasively with no detectable respiratory effort, hemodynamic instability, or significant airway leak around the endotracheal tube. We compared two 60-min periods of ventilation in APV-CMV and ASV 1.1, which were determined by randomization and separated by 30-min washout periods. Settings were adjusted to reach the same minute ventilation in both modes. ΔP was calculated as the difference between plateau pressure and total PEEP measured using end-inspiratory and end-expiratory occlusions, respectively.

RESULTS

There were 26 patients enrolled with a median age of 16 (9-25 [IQR]) months. The median ΔP for these patients was 10.4 (8.5-12.1 [IQR]) and 12.4 (10.5-15.3 [IQR]) cmH2O in the ASV 1.1 and APV-CMV periods, respectively (p < .001). The median tidal volume (VT) selected by the ASV 1.1 algorithm was 6.4 (5.1-7.3 [IQR]) ml/kg and RR was 41 (33 50 [IQR]) b/min, whereas the median of the same values for the APV-CMV period was 7.9 (6.8-8.3 [IQR]) ml/kg and 31 (26-41[IQR]) b/min, respectively. In both ASV 1.1 and APV-CMV modes, the highest ΔP was used to ventilate those patients with restrictive lung conditions at baseline.

CONCLUSION

In this randomized crossover trial, ΔP in ASV 1.1 was lower compared to ΔP in physician-tailored APV-CMV mode in pediatric patients with different lung conditions. The use of ASV 1.1 may therefore result in continued, safe ventilation in a heterogeneous pediatric patient group.

OBJECTIVES

The aim of this pilot study was to compare the amount of "mechanical power of ventilation" under adaptive support ventilation with nonautomated pressure-controlled ventilation.

DESIGN

Single-center, observational prospective pilot study adjoining unitwide implementation of adaptive support ventilation in our department.

SETTING

The ICU of a nonacademic teaching hospital in the Netherlands.

PATIENTS

Twenty-four passive invasively ventilated critically ill patients expected to need of invasive ventilation beyond the following calendar day.

MEASUREMENTS AND MAIN RESULTS

In patients under adaptive support ventilation, only positive end-expiratory pressure and Fio2 were set by the caregivers-all other ventilator settings were under control of the ventilator; in patients under pressure-controlled ventilation, maximum airway pressure (Pmax), positive end-expiratory pressure, Fio2, and respiratory rate were set by the caregivers. Mechanical power of ventilation was calculated three times per day. Compared with pressure-controlled ventilation, mechanical power of ventilation with adaptive support ventilation was lower (15.1 [10.5-25.7] vs 22.9 [18.7-28.8] J/min; p = 0.04). Tidal volume was not different, but Pmax (p = 0.012) and respiratory rate (p = 0.012) were lower with adaptive support ventilation.

CONCLUSIONS

This study suggests adaptive support ventilation may have benefits compared with pressure-controlled ventilation with respect to the mechanical power of ventilation transferred from the ventilator to the respiratory system in passive invasively ventilated critically ill patients. The difference in mechanical power of ventilation is not a result of a difference in tidal volume, but the reduction in applied pressures and respiratory rate. The findings of this observational pilot study need to be confirmed in a larger, preferably randomized clinical trial.