Adaptive support ventilation (ASV) is highly impactful in the context of the respiratory therapist shortage in intensive care units. ASV allows automation to take over the controls rather than to depend on human resources for minute setting changes. ASV is also associated with lesser alarms, and manual setting changes are evident in many studies of the past.[6][7][8] 

When the patient begins the attempts to spontaneous breaths, there occurs an automatic decrease of PS. Such subtle reductions in ventilator demand are often missed by non-automated and human-operated modes of ventilation, thus taking more time for weaning. ASV  allows a reduced requirement for skilled human resources in the care of the ventilated patient.

Operating Principles

Based on the IBW (according to the Radford normogram), the provider must set the target minute ventilation, PEEP, FiO, and maximum pressure alarm (P). With these provided variables, ASV selects the respiratory rate (RR), inspiration-expiration ratio (I: E ratio), and tidal volume (V).

Otis et al. and Mead et al. Equations:

Adaptive support ventilation (ASV) uses the equation by Otis et al.[9] and Mead et al., which was derived in the 1950’- 60’s respectively, which states that for a given set of alveolar ventilation, there is a particular RR that achieves a lower work of breathing (WOB).

General Principles

In ASV, the inspiratory pressure and the respiratory rate (RR) are automatically adjusted by a microprocessor to help minimize the WOB. The microprocessor switches from controlled ventilation (CV) to assisted ventilation (AV). Hence, in general, if the patient’s RR is higher than the target, pressure-controlled ventilation if there is no spontaneous breathing, and a synchronized intermittent mandatory ventilation (SIMV) when the patient’s RR is lower than the target. The rationale is to provide a natural respiratory pattern to the patient and thereby reduce the WOB on the respiratory muscles and therefore stimulate spontaneous breathing. The optimal RR-V combination associated with the least WOB is derived from the Otis equation.[9]

ASV maintains an operator preset minimum minute ventilation. Having MMV, the device administers mandatory volume or pressure-controlled mandatory breaths to maintain the preset minute ventilation. The inspiratory pressure and the mandatory rate are fluctuant according to the patient’s lung mechanics – thus providing different tidal volumes (V) and respiratory rates (RR).[10] 

The automation in ASV has a high potential to select adequate ventilatory patterns based on the condition suffered by the patient – i.e., normal lungs, restrictive or constrictive diseases.[11][12] It takes into account of spontaneous breathing, and it is useful to prevent tachypnea, development of auto-PEEP, and excessive dead-space ventilation. In comparison to other modes of ventilation, it has demonstrated to be superior or equally efficacious to SIMV with pressure support (PS).[13][6]

The goal of adaptive support ventilation (ASV) mode is to ensure adequate alveolar ventilation, minimizing the WOB and transitioning the patient to an optimal ventilatory pattern by deductively preventing barotrauma, volutrauma, and air-trapping.[10] Damage of the lung tissue due to high-volume ventilation occurs with surfactant inactivation and increased microvascular permeability.[14]

1. Post-Cardiac Surgery: A randomized control trial of post-operative weaning of patients after planned and uncomplicated non-fast-track coronary artery bypass graft, weaning with ASV was found to take a similar time to tracheal extubation compared to that of standard weaning – SIMV and PS.[15] Whereas in the case of fast-track patients after cardiac surgery, it was seen that there is a reduction in time to tracheal extubation. Rapid tracheal extubation is of implicative clinical importance because it has shown to reduce ICU length of stay, hospital length of stay, resource utilization, and cost.[16] The time to extubation is determined by various factors such as rewarming, post-operative bleed, and control of hemodynamic problems, which comprise the “window of opportunity.” ASV has also been shown equally efficient to the pressure control (PC) followed by PS [15] for those who have undergone cardiac surgery. Petter et al. conducted a study comparing the ventilator extubation of post-cardiac surgery patients in ASV mode and SIMV + PS mode. It demonstrated equivalent outcomes, although there were fewer alarms and ventilator setting manipulations in the ASV mode.[6] Dongelman et al. demonstrated in an RCT that ASV is safer and more useful even when extubation times were the same in post-coronary artery bypass graft surgery patients when compared to those placed in PC with PS.[15]

2. ASV for Weaning: Patients with chronic respiratory illnesses requiring ventilation can be placed on ASV mode. It has shown benefit as of lesser costs and requirement of respiratory therapists and intensive care personnel.[17]

3. Lung Protective Strategy: ASV provides a better patient-ventilator interaction and lowers WOB compared to SIMV.[18] On the other hand, barotrauma due to high plateau pressure seldom occurs in ASV as it automatically adjusts the airway pressure, thus lowering the tidal volume. In a recent randomized control trial by Dai et al., it was shown that there is no significant difference in mortality in acute respiratory distress syndrome patients placed on either ASV or PC ventilation modes. Moreover, it was understood in animal studies that ASV had induced lower alveolar strain compared to volume-control ventilation, hence lesser lung injury. ASV mode of ventilation controls tidal volume in the range of 6-8 mL/kg of IBW. This implies that patients with ARDS would benefit from opting for the ASV mode of ventilation compared to other modes.[14]

4. Acute Exacerbation of COPD: Non-invasive ventilation (NIV) compared to invasive positive pressure ventilation (IPPV) decreases the risk of ventilator-associated pneumonia (VAP), sepsis, sinusitis and hence reduces the rate of hospitalization and mortality.[19] NIV is the standard for acute exacerbations of COPD (AECOPD). A randomized control trial comparing NIV support of PSV vs. ASV demonstrated that both are viable options without significant differences in mortality.[20] This study by Sehgal et al. also confirmed that there was a lower tracheal intubation rate in patients who were provided ASV.

5. Pediatric Conditions: Proper studies and literature are inadequate for advocating the use of ASV in children. However, there have been reports of positive outcomes from case reports and small observational studies.

Ventilator management is a multidisciplinary effort. When you put a patient on adaptive support ventilation (ASV) mode on a ventilator, it requires the clinical staff to be trained and familiar with this mode of ventilation. At the same time, this is an extremely safe mode of ventilation and weaning. A point to consider is, there is no backup mode while you wean a patient on this mode. There is a risk of hypoventilation and hypercapnia if you have set the patient on the lower percent of minute ventilation support. Familiarity and training regarding this mode of the ventilator are essential among the staff when they are managing the patient on the adaptive mode of the ventilator.