Adaptive support ventilation modes

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.
 

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”. 

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​).

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​​).

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​).

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​).