Adaptive and Automated Weaning Systems (AWS)

While transition to pressure support or T-piece has traditionally been used, more recently “adaptive modes” have been advocated for weaning. Available “adaptive modes” are listed in Table 9.1.

The first adaptive modes with feedback were volume-targeted pressure control modes such as “pressure-regulated volume control” which titrated pressures to achieve a TV. Subsequent iterations targeted MV. Adaptive support ventilation (ASV) is a partially automated mode available from Hamilton Medical. ASV targets

Table 9.1 Available advanced “adaptive” modes used in weaning

Name	Company	Principles	Ref.
Mandatory minute ventilation (MMV)	Drager Medical, Lubeck, Germany	Closed loop control of the mandatory breath rate while considering the patient’s spontaneous breath rate based on a prescribed minute ventilation	[132]
SmartCare/ PSTM	Drager Medical, Lubeck, Germany	Closed loop control of pressure support based on monitoring of respiratory rate, tidal volume, and end-tidal carbon dioxide. Tests for extubation readiness using a 1-h spontaneous breath trial adaptive	[12]
Adaptive support ventilation (ASV)	Hamilton Medical, Bonaduz, Switzerland	Closed loop control to maintain preset minimum minute ventilation by adjusting inspiratory pressure and mandatory breath rate on a breath-by-breath basis. Pressure support ventilation based on respiratory rate and tidal volume. Adjusts I:E ratio based on RC	[133]
IntelliVent- ASV®	Hamilton Medical, Rhazuns, Switzerland	Extension of ASV that uses closed loop control to adjust minute ventilation using end-tidal carbon dioxide and oxygenation by adjusting PEEP and inspired O2 concentration. Conducts automated SBT	[134]
Automode	Siemens, Solna, Sweden	PC, PRVC, or VC switches to a support mode such as (either VS or PS ventilation) on detection of patient-initiated ventilation of two consecutive breaths	[135]
Neurally adjusted ventilatory assist	Maquet, Solna, Sweden	Partial ventilatory support proportional to inspiratory diaphragmatic electrical activity measured via an esophageal catheter	[136]
Proportional assist ventilation (PAV)	The University of Manitoba, Canada	Adjusts airway pressure based on measurement of compliance and resistance throughout the inspiratory cycle to maintain an clinician selected % degree of support	[137]
Proportional pressure support (PPS)	Drager Medical, Lubeck, Germany	Germany pressure support is provided proportionately to changes in airway resistance and lung compliance. PPS is based on the PAV algorithm	[137]
Mandatory rate ventilation (MRV)	Taema-Horus Ventilator® Air Liquide, France	Closed loop control to titrate pressure support based on a set respiratory rate target	[138]

minute ventilation with an algorithm using the “Otis equation,” to target the least work of breathing. Studies comparing ASV weaning to standard care found that ASV could shorten weaning in post-cardiac surgery or chronic lung disease patient. When ASV was compared to assist control in patients with ARDS, no differences were found [133]. Of concern is that ASV allows TV of up to 22 mL/kg and in ARDS delivered median tidal volumes greater than the recommended 8 mL/kg [55, 133-135, 139, 140].

The most recent fully AWS incorporates feedback loops that titrate to ventilation and oxygenation targets and provides interesting opportunities. Two AWS are currently available the SmartCare® from Drager Medical and IntelliVent from Hamilton Medical [141, 142].

While they differ slightly, the principles of the AWS are to establish ventilation through titration of adaptive ventilation: when stable, the sequential application of a SBT and then if successful conversion to titrated pressure support weaning. An early study of SmartCare® found that closed-loop weaning resulted in more rapid weaning, whereas a similar study carried out in an extremely well-staffed unit demonstrated no benefit [12, 142]. Differences in the nursing intensity and clinical governance may be explain this discrepancy. This development highlights two possibilities:

Firstly, a more consistent weaning system, which if calibrated correctly, could provide rapid weaning.

Compared to nonautomated weaning methods, these systems demonstrated positive advantages in weaning time, time to successful extubation, and possibly assisted in reducing ICU length of stay and the number of patients requiring prolonged MV [54, 143] However, most patients studied received relatively short-term ventilation after surgery or ventilation for exacerbation of COPD. Clinical evidence from patients who have suffered ARDS is scarce [144, 145].

Secondly, when skilled personnel are scarce, equivalent outcomes may be achieved with less clinician input. Adaptive weaning systems follow a computerized protocol and as such could be viewed as being identical to a “manual” weaning protocols, with more assured compliance. If “weaning protocols” are non-inferior to standard care, an automated form of these should also demonstrate at least equivalent outcomes.

While the automated weaning systems show promise and some evidence of efficacy, proprietary systems are generally available only on a single manufacturer’s ventilator, and for multiple reasons, these systems have not been widely adopted [54].