How to wean with ASV®

Article

Author: Dr. med. Jean-Michel Arnal, Senior Intensivist, Hopital Sainte Musse, Toulon, France

Date of first publication: 30.08.2017

Two American societies recently provided recommendations to help optimize liberation from mechanical ventilation in adult ICU patients.

Screening readiness-to-wean criteria

The recocommendations issued by the American Thoracic Society and the American College of Chest Physicians suggest using a ventilator liberation protocol and performing spontaneous breathing trials (SBTs) with modest inspiratory pressure support (5-8 cmH2O) (Schmidt GA, Girard TD, Kress JP, et al. Official Executive Summary of an American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from Mechanical Ventilation in Critically Ill Adults. Am J Respir Crit Care Med. 2017;195(1):115-119. doi:10.1164/rccm.201610-2076ST1). So how do we implement these recommendations using the Adaptive Support Ventilation (ASV) mode?

The following parameters are constantly screened and displayed in the Vent Status panel (Ely EW, Baker AM, Dunagan DP, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med. 1996;335(25):1864-1869. doi:10.1056/NEJM1996121933525022):

For oxygenation: Oxygen and PEEP
For CO2 elimination: Minute volume (MinVol) and pressure support above PEEP (Pinsp)
For spontaneous activity: Rapid Shallow Breathing index (RSB) and percentage of spontaneous breathing (%fSpont)

You can set the thresholds yourself in configuration. The range of values in between (shown in light blue) is known as the weaning zone. In short-term ventilated patients, you can use these parameters as a guide for extubation. In long-term ventilated patients, the parameters indicate when you can consider performing an SBT.

When all the values are within this set range, the timer appears and shows you how long the patient has been in the weaning zone for. If a parameter moves out of the weaning zone for longer than two minutes, the timer will reset to 00:00.

Screenshot showing Vent Status panel on ventilator display — Vent Status panel

Other weaning criteria at the bedside

Other non-respiratory weaning criteria also need to be screened at the bedside. These are:

Absence of sedation or comfort sedation
Patient awake or Coma Glasgow Score > 8 for brain-injury patients
Absence or low dose of vasopressor drugs
Patient able to cough when suctioning

If all these conditions are fulfilled, you can start an SBT.

Spontaneous breathing trial

You can carry out an SBT in ASV by decreasing PEEP to 5 cmH2O and lowering the target minute volume (%MinVol) setting to reduce the pressure support as needed. If the pressure support on the current %MinVol setting is higher than 15 cmH2O, the %MinVol setting can be lowered first to 70% and then 25% to reduce pressure support gradually to 5-8 cmH2O for the SBT.

Screenshot showing ASV Graph panel on ventilator display — ASV Graph panel

Continue clinical and respiratory monitoring

The patient should be monitored both clinically and using the Vent Status panel. Clinical monitoring includes neurological status, effort to breathe, heart rate, and arterial blood pressure. Respiratory monitoring includes SpO2, PetCO2, respiratory rate, and tidal volume. Patient exhaustion may lead to an increase in the respiratory rate with a small tidal volume, and cause an increase in pressure support according to the ASV algorithm.

If the patient remains stable for 30 minutes, you can consider extubation (Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Spanish Lung Failure Collaborative Group.3).

Footnotes

References

1. Schmidt GA, Girard TD, Kress JP, et al. Official Executive Summary of an American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from Mechanical Ventilation in Critically Ill Adults. Am J Respir Crit Care Med. 2017;195(1):115-119. doi:10.1164/rccm.201610-2076ST
2. Ely EW, Baker AM, Dunagan DP, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med. 1996;335(25):1864-1869. doi:10.1056/NEJM199612193352502
3. Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Spanish Lung Failure Collaborative Group.

Official Executive Summary of an American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from Mechanical Ventilation in Critically Ill Adults.

Schmidt GA, Girard TD, Kress JP, et al. Official Executive Summary of an American Thoracic Society/American College of Chest Physicians Clinical Practice Guideline: Liberation from Mechanical Ventilation in Critically Ill Adults. Am J Respir Crit Care Med. 2017;195(1):115-119. doi:10.1164/rccm.201610-2076ST

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BACKGROUND

This clinical practice guideline addresses six questions related to liberation from mechanical ventilation in critically ill adults. It is the result of a collaborative effort between the American Thoracic Society and the American College of Chest Physicians.

METHODS

A multidisciplinary panel posed six clinical questions in a Population, Intervention, Comparator, and Outcomes format. A comprehensive literature search and evidence synthesis was performed for each question, which included appraising the certainty in the evidence (i.e., the quality of evidence) using the Grading of Recommendations, Assessment, Development, and Evaluation approach. The Evidence-to-Decision framework was applied to each question, requiring the panel to evaluate and weigh the importance of the problem, the confidence in the evidence, the certainty about how much the public values the main outcomes, the magnitude and balance of desirable and undesirable outcomes, the resources and costs associated with the intervention, the impact on health disparities, and the acceptability and feasibility of the intervention.

RESULTS

Evidence-based recommendations were formulated and graded initially by subcommittees and then modified after full-panel discussions. The recommendations were confirmed by confidential electronic voting; approval required that at least 80% of the panel members agree with the recommendation.

CONCLUSIONS

The panel provides recommendations regarding liberation from mechanical ventilation. The details regarding the evidence and rationale for each recommendation are presented in the American Journal of Respiratory and Critical Care Medicine and Chest.

Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously.

Ely EW, Baker AM, Dunagan DP, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med. 1996;335(25):1864-1869. doi:10.1056/NEJM199612193352502

Link to article

BACKGROUND

Prompt recognition of the reversal of respiratory failure may permit earlier discontinuation of mechanical ventilation, without harm to the patient.

METHODS

We conducted a randomized, controlled trial in 300 adult patients receiving mechanical ventilation in medical and coronary intensive care units. In the intervention group, patients underwent daily screening of respiratory function by physicians, respiratory therapists, and nurses to identify those possibly capable of breathing spontaneously; successful tests were followed by two-hour trials of spontaneous breathing in those who met the criteria. Physicians were notified when their patients successfully completed the trials of spontaneous breathing. The control subjects had daily screening but no other interventions. In both groups, all clinical decisions, including the decision to discontinue mechanical ventilation, were made by the attending physicians.

RESULTS

Although the 149 patients randomly assigned to the intervention group had more severe disease, they received mechanical ventilation for a median of 4.5 days, as compared with 6 days in the 151 patients in the control group (P=0.003). The median interval between the time a patient met the screening criteria and the discontinuation of mechanical ventilation was one day in the intervention group and three days in the control group (P<0.001). Complications -- removal of the breathing tube by the patient, reintubation, tracheostomy, and mechanical ventilation for more than 21 days -- occurred in 20 percent of the intervention group and 41 percent of the control group (P=0.001). The number of days of intensive care and hospital care was similar in the two groups. Total costs for the intensive care unit were lower in the intervention group (median, $15,740, vs. $20,890 in the controls, P=0.03); hospital costs were lower, though not significantly so (median, $26,229 and $29,048, respectively; P=0.3).

CONCLUSIONS

Daily screening of the respiratory function of adults receiving mechanical ventilation, followed by trials of spontaneous breathing in appropriate patients and notification of their physicians when the trials were successful, can reduce the duration of mechanical ventilation and the cost of intensive care and is associated with fewer complications than usual care.

Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Spanish Lung Failure Collaborative Group.

Link to article

The duration of spontaneous breathing trials before extubation has been set at 2 h in research studies, but the optimal duration is not known. We conducted a prospective, multicenter study involving 526 ventilator-supported patients considered ready for weaning, to compare clinical outcomes for trials of spontaneous breathing with target durations of 30 and 120 min. Of the 270 and 256 patients in the 30- and 120-min trial groups, respectively, 237 (87.8%) and 216 (84.8%), respectively, completed the trial without distress and were extubated (p = 0.32); 32 (13.5%) and 29 (13.4%), respectively, of these patients required reintubation within 48 h. The percentage of patients who remained extubated for 48 h after a spontaneous breathing trial did not differ in the 30- and 120-min trial groups (75.9% versus 73.0%, respectively, p = 0.43). The 30- and 120-min trial groups had similar within-unit mortality rates (13 and 9%, respectively) and in-hospital mortality rates (19 and 18%, respectively). Reintubation was required in 61 (13.5%) patients, and these patients had a higher mortality (20 of 61, 32.8%) than did patients who tolerated extubation (18 of 392, 4.6%) (p < 0.001). Neither measurements of respiratory frequency, heart rate, systolic blood pressure, and oxygen saturation during the trial, nor other functional measurements before the trial discriminated between patients who required reintubation from those who tolerated extubation. In conclusion, after a first trial of spontaneous breathing, successful extubation was achieved equally effectively with trials targeted to last 30 and 120 min.