Adaptive support ventilation modes

Article

Author: Munir Karjaghli, Kaouther Saihi

Date of first publication: 22.05.2023

In this article, we compare the various adaptive support ventilation modes available on the market.

Adaptive Support Ventilation (ASV)

Adaptive Support Ventilation® (ASV®) was the first commercially available adaptive ventilation mode to use an optimal targeting schema (Mireles-Cabodevila E, Diaz-Guzman E, Heresi GA, Chatburn RL. Alternative modes of mechanical ventilation: a review for the hospitalist [published correction appears in Cleve Clin J Med. 2009 Aug;76(8):445]. Cleve Clin J Med. 2009;76(7):417-430. doi:10.3949/ccjm.76a.080431), which is based on a mathematical model that attempts to find the ventilation pattern (VT, RR) associated with the lowest work and force of breathing needed to move the lung with the set minute ventilation.

ASV is a closed-loop ventilation mode that combines adaptive pressure-controlled ventilation for passive patients, and adaptive pressure-support ventilation for spontaneously breathing patients. This mode has the advantages of optimizing the patient's work and force of breathing, shortening the duration of mechanical ventilation supporting weaning and finally, reducing the workload of ICU staff while improving patient safety and comfort.

Principle of operation

The ASV algorithm was originally based on the lowest work of breathing according to Otis' equation (OTIS AB, FENN WO, RAHN H. Mechanics of breathing in man. J Appl Physiol. 1950;2(11):592-607. doi:10.1152/jappl.1950.2.11.5922) to select the optimal frequency at the lowest breathing power. It was demonstrated that ventilation modes using adaptive targeting based on the Otis equation alone do not always provide lung-protective ventilation (Adaptive Support Ventilation: An Inappropriate Mechanical Ventilation Strategy for Acute Respiratory Distress Syndrome?3,Arnal JM, Garnero A, Novonti D, et al. Feasibility study on full closed-loop control ventilation (IntelliVent-ASV™) in ICU patients with acute respiratory failure: a prospective observational comparative study. Crit Care. 2013;17(5):R196. Published 2013 Sep 11. doi:10.1186/cc128904). In addition, they may lead to automated delivery of tidal volumes greater than what is currently recommended for lung-protective ventilation, especially in patients with more compliant lungs (Dongelmans DA, Paulus F, Veelo DP, Binnekade JM, Vroom MB, Schultz MJ. Adaptive support ventilation may deliver unwanted respiratory rate-tidal volume combinations in patients with acute lung injury ventilated according to an open lung concept. Anesthesiology. 2011;114(5):1138-1143. doi:10.1097/ALN.0b013e31820d86765) (see Table 1),

To reduce the tidal volume (and consequently the driving pressure), the ASV algorithm was modified in 2017 to incorporate Mead's equation for the lowest force of breathing (MEAD J. The control of respiratory frequency. Ann N Y Acad Sci. 1963;109:724-729. doi:10.1111/j.1749-6632.1963.tb13500.x6.Ceylan G, Topal S, Atakul G, et al. Randomized crossover trial to compare driving pressures in a closed-loop and a conventional mechanical ventilation mode in pediatric patients. Pediatr Pulmonol. 2021;56(9):3035-3043. doi:10.1002/ppul.255617). Like Otis, Mead showed that there is an optimal frequency at which the average force per breath required is the lowest. Otis et al. and Mead created their equations to better understand the energetics of breathing and the associated effects on “the imaginary path from health to disease”.

Table showing parameters for different lung conditions — Table 1. Settings, delivered ventilation, and respiratory mechanics according to the lung condition in passive patients ventilated in INTELLiVENT-ASV (based on ASV 1.0) (Arnal et al., 2013)

ASV 1.1

This modification resulted in the new version 1.1, which is the default selection on all Hamilton Medical ventilators. The ASV 1.1 algorithm selects the optimal frequency at which the breathing power and force are lowest and thus delivers ventilation at a lower mechanical power (MP) (Wendel Garcia PD, Hofmaenner DA, Brugger SD, et al. Closed-Loop Versus Conventional Mechanical Ventilation in COVID-19 ARDS. J Intensive Care Med. 2021;36(10):1184-1193. doi:10.1177/088506662110241398,Arnal JM, Saoli M, Garnero A. Airway and transpulmonary driving pressures and mechanical powers selected by INTELLiVENT-ASV in passive, mechanically ventilated ICU patients. Heart Lung. 2020;49(4):427-434. doi:10.1016/j.hrtlng.2019.11.0019,Buiteman-Kruizinga LA, Mkadmi HE, Schultz MJ, Tangkau PL, van der Heiden PLJ. Comparison of Mechanical Power During Adaptive Support Ventilation Versus Nonautomated Pressure-Controlled Ventilation-A Pilot Study. Crit Care Explor. 2021;3(2):e0335. Published 2021 Feb 15. doi:10.1097/CCE.000000000000033510).

ASV 1.1 evaluates the patient's respiratory mechanics by measuring the expiratory time constant (RCexp) (Brunner JX, Laubscher TP, Banner MJ, Iotti G, Braschi A. Simple method to measure total expiratory time constant based on the passive expiratory flow-volume curve. Crit Care Med. 1995;23(6):1117-1122. doi:10.1097/00003246-199506000-0001911) breath by breath. This is made possible by the proximal flow sensor from Hamilton Medical. For any given minute ventilation set by the clinician, ASV 1.1 determines the combination of VT, RR, and the resulting ΔP that minimizes the work and force of breathing.

Recently, various other manufacturers have released adaptive ventilation modes similar to ASV 1.0, including “Adaptive Ventilation Mode” (IMT, Buchs, Switzerland), “Work of Breathing Optimized Ventilation” (Salvia Medical, Kronberg, Germany), and “Adaptive Minute Ventilation” (Mindray, Shenzhen, China). All these modes select a combination of RR and VT according to Otis’ equation and may therefore deliver a large VT, as observed in ASV by Dongelmans et al. (Dongelmans DA, Paulus F, Veelo DP, Binnekade JM, Vroom MB, Schultz MJ. Adaptive support ventilation may deliver unwanted respiratory rate-tidal volume combinations in patients with acute lung injury ventilated according to an open lung concept. Anesthesiology. 2011;114(5):1138-1143. doi:10.1097/ALN.0b013e31820d86765).

AVM and AVM2 from IMT

The AVM algorithm was originally based on the lowest work of breathing according to Otis' equation as in the ASV mode. However, it was then modified in AVM2 to incorporate the concept of mean inspiratory power, whereby the optimal frequency is selected for the lowest inspiratory power. Inspiratory power is defined as the sum of the resistive and tidal power that is transmitted from the ventilator to the patient, assuming intrinsic PEEP is equal to zero.

AVM2 was announced in 2017 (The Next Step to Optimal Ventilation: AVM 212) when van der Staay and Remus compared AVM2 with both AVM and ASV (version 1.0) using a lung simulator that modeled a patient with restrictive lung disease (12). They demonstrated that minimizing the inspiratory power (with AVM2) results in higher frequencies, lower inspiratory pressure targets, and lower VT compared with minimizing the work of breathing (AVM and ASV 1.0). The tidal volume dropped from 7 to 5.3 ml/kg. AVM2 with automated minimization of inspiratory power may consequently lead to more lung-protective ventilator settings when compared with AVM (Becher T, Adelmeier A, Frerichs I, Weiler N, Schädler D. Adaptive mechanical ventilation with automated minimization of mechanical power-a pilot randomized cross-over study. Crit Care. 2019;23(1):338. Published 2019 Oct 30. doi:10.1186/s13054-019-2610-713).

Comparison of targeting schemes

Van der Staay and Chatburn performed a comparison of three targeting schemes during selected simulation scenarios with ASV 1.0, AVM2, and MFV (van der Staay M, Chatburn RL. Advanced modes of mechanical ventilation and optimal targeting schemes. Intensive Care Med Exp. 2018;6(1):30. Published 2018 Aug 22. doi:10.1186/s40635-018-0195-014). They calculated the optimum frequency with Otis equation for ASV, and optimal frequency for minimal inspiratory power for AVM2. They found that AVM2, which optimizes the rate by minimizing inspiratory power, does not always have the lowest inspiratory power. The tidal volume seemed to be too low for normal lungs and COPD (see Figures 1a, b, c).

The green area highlights the range which is normally used for these patients according to Arnal et al. (Arnal JM, Garnero A, Saoli M, Chatburn RL. Parameters for Simulation of Adult Subjects During Mechanical Ventilation. Respir Care. 2018;63(2):158-168. doi:10.4187/respcare.0577515).

Graphs showing comparioson of VT, tidal pressure, and inspiratory power in ASV, AVM2, and MFV in normal adult patient — Figure 1a: VT, tidal pressure, and tidal/inspiratory power in ASV, AVM2, and MFV in an adult normal lung (van der Staay et al., 2018)

Graphs showing comparison of VT, tidal pressure, and inspiratory power in ASV, AVM2, and MFV in adult ARDS — Figure 1b: VT, tidal pressure, and tidal/inspiratory power in ASV, AVM2, and MFV in an adult ARDS lung (van der Staay et al., 2018)

Graphs showing comparioson of VT, tidal pressure, and inspiratory power in ASV, AVM2, and MFV in adult COPD — Figure 1c: VT, tidal pressure, and tidal/inspiratory power in ASV, AVM2, and MFV in an adult COPD lung (van der Staay et al., 2018)

Evidence

Several studies have been conducted to investigate the benefits of ASV 1.1 over conventional modes. These studies show that ASV 1.1 can select individualized VT-RR combinations, and reduce the metabolic load and mechanical power delivered to the patient when compared to conventional ventilation modes (Arnal JM, Saoli M, Garnero A. Airway and transpulmonary driving pressures and mechanical powers selected by INTELLiVENT-ASV in passive, mechanically ventilated ICU patients. Heart Lung. 2020;49(4):427-434. doi:10.1016/j.hrtlng.2019.11.0019,Buiteman-Kruizinga LA, Mkadmi HE, Schultz MJ, Tangkau PL, van der Heiden PLJ. Comparison of Mechanical Power During Adaptive Support Ventilation Versus Nonautomated Pressure-Controlled Ventilation-A Pilot Study. Crit Care Explor. 2021;3(2):e0335. Published 2021 Feb 15. doi:10.1097/CCE.000000000000033510, Chen YH, Hsiao HF, Hsu HW, Cho HY, Huang CC. Comparisons of Metabolic Load between Adaptive Support Ventilation and Pressure Support Ventilation in Mechanically Ventilated ICU Patients. Can Respir J. 2020;2020:2092879. Published 2020 Jan 28. doi:10.1155/2020/209287916). In a randomized crossover trial of pediatric patients with various lung conditions, ∆P in ASV 1.1 was lower than ∆P in a physician-tailored APV-CMV mode (Ceylan G, Topal S, Atakul G, et al. Randomized crossover trial to compare driving pressures in a closed-loop and a conventional mechanical ventilation mode in pediatric patients. Pediatr Pulmonol. 2021;56(9):3035-3043. doi:10.1002/ppul.255617).

Footnotes

References

1. Mireles-Cabodevila E, Diaz-Guzman E, Heresi GA, Chatburn RL. Alternative modes of mechanical ventilation: a review for the hospitalist [published correction appears in Cleve Clin J Med. 2009 Aug;76(8):445]. Cleve Clin J Med. 2009;76(7):417-430. doi:10.3949/ccjm.76a.08043
2. OTIS AB, FENN WO, RAHN H. Mechanics of breathing in man. J Appl Physiol. 1950;2(11):592-607. doi:10.1152/jappl.1950.2.11.592
3. Sulemanji D, Kacmarek R (2010) Adaptive support ventilation: an inappropriate mechanical ventilation strategy for acute respiratory distress syndrome? Anesthesiology 111(5):1295–1296
4. Arnal JM, Garnero A, Novonti D, et al. Feasibility study on full closed-loop control ventilation (IntelliVent-ASV™) in ICU patients with acute respiratory failure: a prospective observational comparative study. Crit Care. 2013;17(5):R196. Published 2013 Sep 11. doi:10.1186/cc12890
5. Dongelmans DA, Paulus F, Veelo DP, Binnekade JM, Vroom MB, Schultz MJ. Adaptive support ventilation may deliver unwanted respiratory rate-tidal volume combinations in patients with acute lung injury ventilated according to an open lung concept. Anesthesiology. 2011;114(5):1138-1143. doi:10.1097/ALN.0b013e31820d8676
6. MEAD J. The control of respiratory frequency. Ann N Y Acad Sci. 1963;109:724-729. doi:10.1111/j.1749-6632.1963.tb13500.x
7. Ceylan G, Topal S, Atakul G, et al. Randomized crossover trial to compare driving pressures in a closed-loop and a conventional mechanical ventilation mode in pediatric patients. Pediatr Pulmonol. 2021;56(9):3035-3043. doi:10.1002/ppul.25561
8. Wendel Garcia PD, Hofmaenner DA, Brugger SD, et al. Closed-Loop Versus Conventional Mechanical Ventilation in COVID-19 ARDS. J Intensive Care Med. 2021;36(10):1184-1193. doi:10.1177/08850666211024139
9. Arnal JM, Saoli M, Garnero A. Airway and transpulmonary driving pressures and mechanical powers selected by INTELLiVENT-ASV in passive, mechanically ventilated ICU patients. Heart Lung. 2020;49(4):427-434. doi:10.1016/j.hrtlng.2019.11.001
10. Buiteman-Kruizinga LA, Mkadmi HE, Schultz MJ, Tangkau PL, van der Heiden PLJ. Comparison of Mechanical Power During Adaptive Support Ventilation Versus Nonautomated Pressure-Controlled Ventilation-A Pilot Study. Crit Care Explor. 2021;3(2):e0335. Published 2021 Feb 15. doi:10.1097/CCE.0000000000000335
11. Brunner JX, Laubscher TP, Banner MJ, Iotti G, Braschi A. Simple method to measure total expiratory time constant based on the passive expiratory flow-volume curve. Crit Care Med. 1995;23(6):1117-1122. doi:10.1097/00003246-199506000-00019
12. van der Staay M, Remus C (2017) Adaptive ventilation mode 2
13. Becher T, Adelmeier A, Frerichs I, Weiler N, Schädler D. Adaptive mechanical ventilation with automated minimization of mechanical power-a pilot randomized cross-over study. Crit Care. 2019;23(1):338. Published 2019 Oct 30. doi:10.1186/s13054-019-2610-7
14. van der Staay M, Chatburn RL. Advanced modes of mechanical ventilation and optimal targeting schemes. Intensive Care Med Exp. 2018;6(1):30. Published 2018 Aug 22. doi:10.1186/s40635-018-0195-0
15. Arnal JM, Garnero A, Saoli M, Chatburn RL. Parameters for Simulation of Adult Subjects During Mechanical Ventilation. Respir Care. 2018;63(2):158-168. doi:10.4187/respcare.05775
16. Chen YH, Hsiao HF, Hsu HW, Cho HY, Huang CC. Comparisons of Metabolic Load between Adaptive Support Ventilation and Pressure Support Ventilation in Mechanically Ventilated ICU Patients. Can Respir J. 2020;2020:2092879. Published 2020 Jan 28. doi:10.1155/2020/2092879

Alternative modes of mechanical ventilation: a review for the hospitalist.

Mireles-Cabodevila E, Diaz-Guzman E, Heresi GA, Chatburn RL. Alternative modes of mechanical ventilation: a review for the hospitalist [published correction appears in Cleve Clin J Med. 2009 Aug;76(8):445]. Cleve Clin J Med. 2009;76(7):417-430. doi:10.3949/ccjm.76a.08043

Newer ventilators can be set to modes other than the pressure-control and volume-control modes of older machines. In this paper, the authors review several of these alternative modes (adaptive pressure control, adaptive support ventilation, proportional assist ventilation, airway pressure-release ventilation, biphasic positive airway pressure, and high-frequency oscillatory ventilation), explaining how they work and contrasting their theoretical benefits and the actual evidence of benefit.

Mechanics of breathing in man.

OTIS AB, FENN WO, RAHN H. Mechanics of breathing in man. J Appl Physiol. 1950;2(11):592-607. doi:10.1152/jappl.1950.2.11.592

Adaptive Support Ventilation: An Inappropriate Mechanical Ventilation Strategy for Acute Respiratory Distress Syndrome?

Sulemanji D, Kacmarek R (2010) Adaptive support ventilation: an inappropriate mechanical ventilation strategy for acute respiratory distress syndrome? Anesthesiology 111(5):1295–1296

Feasibility study on full closed-loop control ventilation (IntelliVent-ASV™) in ICU patients with acute respiratory failure: a prospective observational comparative study.

Arnal JM, Garnero A, Novonti D, et al. Feasibility study on full closed-loop control ventilation (IntelliVent-ASV™) in ICU patients with acute respiratory failure: a prospective observational comparative study. Crit Care. 2013;17(5):R196. Published 2013 Sep 11. doi:10.1186/cc12890

Link to article

INTRODUCTION

IntelliVent-ASV™ is a full closed-loop ventilation mode that automatically adjusts ventilation and oxygenation parameters in both passive and active patients. This feasibility study compared oxygenation and ventilation settings automatically selected by IntelliVent-ASV™ among three predefined lung conditions (normal lung, acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD)) in active and passive patients. The feasibility of IntelliVent-ASV™ use was assessed based on the number of safety events, the need to switch to conventional mode for any medical reason, and sensor failure.

METHOD

This prospective observational comparative study included 100 consecutive patients who were invasively ventilated for less than 24 hours at the time of inclusion with an expected duration of ventilation of more than 12 hours. Patients were ventilated using IntelliVent-ASV™ from inclusion to extubation. Settings, automatically selected by the ventilator, delivered ventilation, respiratory mechanics, and gas exchanges were recorded once a day.

RESULTS

Regarding feasibility, all patients were ventilated using IntelliVent-ASV™ (392 days in total). No safety issues occurred and there was never a need to switch to an alternative ventilation mode. The fully automated ventilation was used for 95% of the total ventilation time. IntelliVent-ASV™ selected different settings according to lung condition in passive and active patients. In passive patients, tidal volume (VT), predicted body weight (PBW) was significantly different between normal lung (n = 45), ARDS (n = 16) and COPD patients (n = 19) (8.1 (7.3 to 8.9) mL/kg; 7.5 (6.9 to 7.9) mL/kg; 9.9 (8.3 to 11.1) mL/kg, respectively; P 0.05). In passive ARDS patients, FiO2 and positive end-expiratory pressure (PEEP) were statistically higher than passive normal lung (35 (33 to 47)% versus 30 (30 to 31)% and 11 (8 to 13) cmH2O versus 5 (5 to 6) cmH2O, respectively; P< 0.05).

CONCLUSIONS

IntelliVent-ASV™ was safely used in unselected ventilated ICU patients with different lung conditions. Automatically selected oxygenation and ventilation settings were different according to the lung condition, especially in passive patients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01489085.

Adaptive support ventilation may deliver unwanted respiratory rate-tidal volume combinations in patients with acute lung injury ventilated according to an open lung concept.

Dongelmans DA, Paulus F, Veelo DP, Binnekade JM, Vroom MB, Schultz MJ. Adaptive support ventilation may deliver unwanted respiratory rate-tidal volume combinations in patients with acute lung injury ventilated according to an open lung concept. Anesthesiology. 2011;114(5):1138-1143. doi:10.1097/ALN.0b013e31820d8676

BACKGROUND

With adaptive support ventilation, respiratory rate and tidal volume (V(T)) are a function of the Otis least work of breathing formula. We hypothesized that adaptive support ventilation in an open lung ventilator strategy would deliver higher V(T)s to patients with acute lung injury.

METHODS

Patients with acute lung injury were ventilated according to a local guideline advising the use of lower V(T) (6-8 ml/kg predicted body weight), high concentrations of positive end-expiratory pressure, and recruitment maneuvers. Ventilation parameters were recorded when the ventilator was switched to adaptive support ventilation, and after recruitment maneuvers. If V(T) increased more than 8 ml/kg predicted body weight, airway pressure was limited to correct for the rise of V(T).

RESULTS

Ten patients with a mean (±SD) Pao(2)/Fio(2) of 171 ± 86 mmHg were included. After a switch from pressure-controlled ventilation to adaptive support ventilation, respiratory rate declined (from 31 ± 5 to 21 ± 6 breaths/min; difference = 10 breaths/min, 95% CI 3-17 breaths/min, P = 0.008) and V(T) increased (from 6.5 ± 0.8 to 9.0 ± 1.6 ml/kg predicted body weight; difference = 2.5 ml, 95% CI 0.4-4.6 ml/kg predicted body weight, P = 0.02). Pressure limitation corrected for the rise of V(T), but minute ventilation declined, forcing the user to switch back to pressure-controlled ventilation.

CONCLUSIONS

Adaptive support ventilation, compared with pressure-controlled ventilation in an open lung strategy setting, delivers a lower respiratory rate-higher V(T) combination. Pressure limitation does correct for the rise of V(T), but leads to a decline in minute ventilation.

The control of respiratory frequency.

MEAD J. The control of respiratory frequency. Ann N Y Acad Sci. 1963;109:724-729. doi:10.1111/j.1749-6632.1963.tb13500.x

Randomized crossover trial to compare driving pressures in a closed-loop and a conventional mechanical ventilation mode in pediatric patients.

Ceylan G, Topal S, Atakul G, et al. Randomized crossover trial to compare driving pressures in a closed-loop and a conventional mechanical ventilation mode in pediatric patients. Pediatr Pulmonol. 2021;56(9):3035-3043. doi:10.1002/ppul.25561

Link to article

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.

Closed-Loop Versus Conventional Mechanical Ventilation in COVID-19 ARDS.

Wendel Garcia PD, Hofmaenner DA, Brugger SD, et al. Closed-Loop Versus Conventional Mechanical Ventilation in COVID-19 ARDS. J Intensive Care Med. 2021;36(10):1184-1193. doi:10.1177/08850666211024139

Link to article

BACKGROUND

Lung-protective ventilation is key in bridging patients suffering from COVID-19 acute respiratory distress syndrome (ARDS) to recovery. However, resource and personnel limitations during pandemics complicate the implementation of lung-protective protocols. Automated ventilation modes may prove decisive in these settings enabling higher degrees of lung-protective ventilation than conventional modes.

METHOD

Prospective study at a Swiss university hospital. Critically ill, mechanically ventilated COVID-19 ARDS patients were allocated, by study-blinded coordinating staff, to either closed-loop or conventional mechanical ventilation, based on mechanical ventilator availability. Primary outcome was the overall achieved percentage of lung-protective ventilation in closed-loop versus conventional mechanical ventilation, assessed minute-by-minute, during the initial 7 days and overall mechanical ventilation time. Lung-protective ventilation was defined as the combined target of tidal volume <8 ml per kg of ideal body weight, dynamic driving pressure <15 cmH2O, peak pressure <30 cmH2O, peripheral oxygen saturation ≥88% and dynamic mechanical power <17 J/min.

RESULTS

Forty COVID-19 ARDS patients, accounting for 1,048,630 minutes (728 days) of cumulative mechanical ventilation, allocated to either closed-loop (n = 23) or conventional ventilation (n = 17), presenting with a median paO2/ FiO2 ratio of 92 [72-147] mmHg and a static compliance of 18 [11-25] ml/cmH2O, were mechanically ventilated for 11 [4-25] days and had a 28-day mortality rate of 20%. During the initial 7 days of mechanical ventilation, patients in the closed-loop group were ventilated lung-protectively for 65% of the time versus 38% in the conventional group (Odds Ratio, 1.79; 95% CI, 1.76-1.82; P < 0.001) and for 45% versus 33% of overall mechanical ventilation time (Odds Ratio, 1.22; 95% CI, 1.21-1.23; P < 0.001).

CONCLUSION

Among critically ill, mechanically ventilated COVID-19 ARDS patients during an early highpoint of the pandemic, mechanical ventilation using a closed-loop mode was associated with a higher degree of lung-protective ventilation than was conventional mechanical ventilation.

Airway and transpulmonary driving pressures and mechanical powers selected by INTELLiVENT-ASV in passive, mechanically ventilated ICU patients.

Arnal JM, Saoli M, Garnero A. Airway and transpulmonary driving pressures and mechanical powers selected by INTELLiVENT-ASV in passive, mechanically ventilated ICU patients. Heart Lung. 2020;49(4):427-434. doi:10.1016/j.hrtlng.2019.11.001

Link to article

BACKGROUND

Driving pressure (ΔP) and mechanical power (MP) are predictors of the risk of ventilation- induced lung injuries (VILI) in mechanically ventilated patients. INTELLiVENT-ASV® is a closed-loop ventilation mode that automatically adjusts respiratory rate and tidal volume, according to the patient's respiratory mechanics.

OBJECTIVES

This prospective observational study investigated ΔP and MP (and also transpulmonary ΔP (ΔPL) and MP (MPL) for a subgroup of patients) delivered by INTELLiVENT-ASV.

METHODS

Adult patients admitted to the ICU were included if they were sedated and met the criteria for a single lung condition (normal lungs, COPD, or ARDS). INTELLiVENT-ASV was used with default target settings. If PEEP was above 16 cmH2O, the recruitment strategy used transpulmonary pressure as a reference, and ΔPL and MPL were computed. Measurements were made once for each patient.

RESULTS

Of the 255 patients included, 98 patients were classified as normal-lungs, 28 as COPD, and 129 as ARDS patients. The median ΔP was 8 (7 - 10), 10 (8 - 12), and 9 (8 - 11) cmH2O for normal-lungs, COPD, and ARDS patients, respectively. The median MP was 9.1 (4.9 - 13.5), 11.8 (8.6 - 16.5), and 8.8 (5.6 - 13.8) J/min for normal-lungs, COPD, and ARDS patients, respectively. For the 19 patients managed with transpulmonary pressure ΔPL was 6 (4 - 7) cmH2O and MPL was 3.6 (3.1 - 4.4) J/min.

CONCLUSIONS

In this short term observation study, INTELLiVENT-ASV selected ΔP and MP considered in safe ranges for lung protection. In a subgroup of ARDS patients, the combination of a recruitment strategy and INTELLiVENT-ASV resulted in an apparently safe ΔPL and MPL.

Comparison of Mechanical Power During Adaptive Support Ventilation Versus Nonautomated Pressure-Controlled Ventilation-A Pilot Study.

Buiteman-Kruizinga LA, Mkadmi HE, Schultz MJ, Tangkau PL, van der Heiden PLJ. Comparison of Mechanical Power During Adaptive Support Ventilation Versus Nonautomated Pressure-Controlled Ventilation-A Pilot Study. Crit Care Explor. 2021;3(2):e0335. Published 2021 Feb 15. doi:10.1097/CCE.0000000000000335

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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.

Simple method to measure total expiratory time constant based on the passive expiratory flow-volume curve.

Brunner JX, Laubscher TP, Banner MJ, Iotti G, Braschi A. Simple method to measure total expiratory time constant based on the passive expiratory flow-volume curve. Crit Care Med. 1995;23(6):1117-1122. doi:10.1097/00003246-199506000-00019

Link to article

OBJECTIVE

In intubated, mechanically ventilated patients, inspiration is forced by externally applied positive pressure. In contrast, exhalation is passive and depends on the time constant of the total respiratory system. The expiratory time constant is thus an important determinant of mechanical ventilation. The aim of this study was to evaluate a simple method for measuring the expiratory time constant in ventilated subjects.

DESIGN

Prospective study using a lung simulator and ten dogs.

SETTING

University hospital.

SUBJECTS

Commercially available lung simulator and ten greyhound dogs.

INTERVENTIONS

Different expiratory time constants were set on the lung simulator. In the dogs, the endotracheal tube was clamped to increase airways resistance by 22.5 cm H2O/(L/sec) and the lungs were injured with hydrochloric acid to decrease total respiratory compliance by 16 mL/cm H2O. This procedure resulted in a wide range of expiratory time constants.

MEASUREMENTS AND MAIN RESULTS

Pneumotachography was used to measure flow and volume. The ratio of exhaled volume and peak flow was calculated from these signals, corrected for the limited exhalation time yielding the "calculated expiratory time constant" and compared with the actual expiratory time constant. The typical error was +/- 0.19 sec for the lung simulator and +/- 0.15 sec for the dogs.

CONCLUSIONS

The volume and peak flow corrected for limited exhalation time is a good estimate of the total expiratory time constant in passive subjects and may be useful for the titration of mechanical ventilation.

The Next Step to Optimal Ventilation: AVM 2

van der Staay M, Remus C (2017) Adaptive ventilation mode 2

Adaptive mechanical ventilation with automated minimization of mechanical power-a pilot randomized cross-over study.

Becher T, Adelmeier A, Frerichs I, Weiler N, Schädler D. Adaptive mechanical ventilation with automated minimization of mechanical power-a pilot randomized cross-over study. Crit Care. 2019;23(1):338. Published 2019 Oct 30. doi:10.1186/s13054-019-2610-7

BACKGROUND

Adaptive mechanical ventilation automatically adjusts respiratory rate (RR) and tidal volume (VT) to deliver the clinically desired minute ventilation, selecting RR and VT based on Otis' equation on least work of breathing. However, the resulting VT may be relatively high, especially in patients with more compliant lungs. Therefore, a new mode of adaptive ventilation (adaptive ventilation mode 2, AVM2) was developed which automatically minimizes inspiratory power with the aim of ensuring lung-protective combinations of VT and RR. The aim of this study was to investigate whether AVM2 reduces VT, mechanical power, and driving pressure (ΔPstat) and provides similar gas exchange when compared to adaptive mechanical ventilation based on Otis' equation.

METHODS

A prospective randomized cross-over study was performed in 20 critically ill patients on controlled mechanical ventilation, including 10 patients with acute respiratory distress syndrome (ARDS). Each patient underwent 1 h of mechanical ventilation with AVM2 and 1 h of adaptive mechanical ventilation according to Otis' equation (adaptive ventilation mode, AVM). At the end of each phase, we collected data on VT, mechanical power, ΔP, PaO2/FiO2 ratio, PaCO2, pH, and hemodynamics.

RESULTS

Comparing adaptive mechanical ventilation with AVM2 to the approach based on Otis' equation (AVM), we found a significant reduction in VT both in the whole study population (7.2 ± 0.9 vs. 8.2 ± 0.6 ml/kg, p < 0.0001) and in the subgroup of patients with ARDS (6.6 ± 0.8 ml/kg with AVM2 vs. 7.9 ± 0.5 ml/kg with AVM, p < 0.0001). Similar reductions were observed for ΔPstat (whole study population: 11.5 ± 1.6 cmH2O with AVM2 vs. 12.6 ± 2.5 cmH2O with AVM, p < 0.0001; patients with ARDS: 11.8 ± 1.7 cmH2O with AVM2 and 13.3 ± 2.7 cmH2O with AVM, p = 0.0044) and total mechanical power (16.8 ± 3.9 J/min with AVM2 vs. 18.6 ± 4.6 J/min with AVM, p = 0.0024; ARDS: 15.6 ± 3.2 J/min with AVM2 vs. 17.5 ± 4.1 J/min with AVM, p = 0.0023). There was a small decrease in PaO2/FiO2 (270 ± 98 vs. 291 ± 102 mmHg with AVM, p = 0.03; ARDS: 194 ± 55 vs. 218 ± 61 with AVM, p = 0.008) and no differences in PaCO2, pH, and hemodynamics.

CONCLUSIONS

Adaptive mechanical ventilation with automated minimization of inspiratory power may lead to more lung-protective ventilator settings when compared with adaptive mechanical ventilation according to Otis' equation.

TRIAL REGISTRATION

The study was registered at the German Clinical Trials Register ( DRKS00013540 ) on December 1, 2017, before including the first patient.

Advanced modes of mechanical ventilation and optimal targeting schemes.

van der Staay M, Chatburn RL. Advanced modes of mechanical ventilation and optimal targeting schemes. Intensive Care Med Exp. 2018;6(1):30. Published 2018 Aug 22. doi:10.1186/s40635-018-0195-0

Pubmed

Recent research results provide new incentives to recognize and prevent ventilator-induced lung injury (VILI) and create targeting schemes for new modes of mechanical ventilation. For example, minimization of breathing power, inspiratory power, and inspiratory pressure are the underlying goals of optimum targeting schemes used in the modes called adaptive support ventilation (ASV), adaptive ventilation mode 2 (AVM2), and MID-frequency ventilation (MFV). We describe the mathematical models underlying these targeting schemes and present theoretical analyses for minimizing tidal volume, tidal pressure (also known as driving pressure), or tidal power as functions of ventilatory frequency. To go beyond theoretical equations, these targeting schemes were compared in terms of expected tidal volumes using different patient models. Results indicate that at the same ventilation efficiency (same PaCO2 level), we expect tidal volume dosage in the range of 7.4 mL/kg (for ASV), 6.2 mL/kg (for AVM2), and 6.7 mL/kg (for MFV) for adult ARDS simulation. For a neonatal RDS model, we expect 5.5 mL/kg (for ASV), 4.6 mL/kg (for AVM2), and 4.5 (for MFV).

Parameters for Simulation of Adult Subjects During Mechanical Ventilation.

Arnal JM, Garnero A, Saoli M, Chatburn RL. Parameters for Simulation of Adult Subjects During Mechanical Ventilation. Respir Care. 2018;63(2):158-168. doi:10.4187/respcare.05775

Link to article

BACKGROUND

Simulation studies are often used to examine ventilator performance. However, there are no standards for selecting simulation parameters. This study collected data in passively-ventilated adult human subjects and summarized the results as a set of parameters that can be used for simulation studies of intubated, passive, adult subjects with normal lungs, COPD, or ARDS.

METHODS

Consecutive adult patients admitted to the ICU were included if they were deeply sedated and mechanically ventilated for <48 h without any spontaneous breathing activity. Subjects were classified as having normal lungs, COPD, or ARDS. Respiratory mechanics variables were collected once per subject. Static compliance was calculated as the ratio between tidal volume and driving pressure. Inspiratory resistance was measured by the least-squares fitting method. The expiratory time constant was estimated by the tidal volume/flow ratio.

RESULTS

Of the 359 subjects included, 138 were classified as having normal lungs, 181 as ARDS, and 40 as COPD. Median (interquartile range) static compliance was significantly lower in ARDS subjects as compared with normal lung and COPD subjects (39 [32-50] mL/cm H2O vs 54 [44-64] and 59 [43-75] mL/cm H2O, respectively, P < .001). Inspiratory resistance was significantly higher in COPD subjects as compared with normal lung and ARDS subjects (22 [16-33] cm H2O/L/s vs 13 [10-15] and 12 [9-14] cm H2O/L/s, respectively, P < .001). The expiratory time constant was significantly different for each lung condition (0.60 [0.51-0.71], 1.07 [0.68-2.14], and 0.46 [0.40-0.55] s for normal lung, COPD, and ARDS subjects, respectively, P < .001). In the subgroup of subjects with ARDS, there were no significant differences in respiratory mechanics variables among mild, moderate, and severe ARDS.

CONCLUSIONS

This study provides educators, researchers, and manufacturers with a standard set of practical parameters for simulating the respiratory system's mechanical properties in passive conditions.

Comparisons of Metabolic Load between Adaptive Support Ventilation and Pressure Support Ventilation in Mechanically Ventilated ICU Patients.

Chen YH, Hsiao HF, Hsu HW, Cho HY, Huang CC. Comparisons of Metabolic Load between Adaptive Support Ventilation and Pressure Support Ventilation in Mechanically Ventilated ICU Patients. Can Respir J. 2020;2020:2092879. Published 2020 Jan 28. doi:10.1155/2020/2092879

Link to article

Purpose

The aim of this study was to compare the metabolic load between adaptive support ventilation (ASV) and pressure support ventilation (PSV) modes in critically ill patients.

Methods

Sequential 20 min ventilation by PSV followed by 20 min ASV in critically ill patients was assessed. ASV was set for full support, i.e., with the minute volume control set at the same level as the minute volume observed during PSV. The trial started from PSV 8 cmH2O and continued with high (PSV 12 cmH2O) to low (PSV 0) conditions or low to high conditions, in random order. The oxygen consumption (VO2), production of carbon dioxide (VCO2), and energy expenditure (EE) were measured by indirect calorimetry (IC).

Results

Twenty-four patients with critical illness participated in the study. Comparing with the PSV mode, the EE in the ASV mode was lower in the level of PSV 0 cmH2O (1069 ± 73 vs. 1425 ± 76 kcal), PS 8 cmH2O (1116 ± 70 vs. 1284 ± 61 kcal), and PS 12 cmH2O (1017 ± 70 vs. 1169 ± 58 kcal) (p < 0.05). The VO2, VCO2, and P0.1 in PSV were significantly higher than those in ASV (p < 0.05). The VO2, VCO2, and P0.1 in PSV were significantly higher than those in ASV (.

Conclusion

In patients with critical illness, the application of ASV set for full support was associated with a lower metabolic load and respiratory drive than in any of the studied PSV conditions.