Breath stacking is caused by patient-ventilator asynchrony. It typically happens with respiratory failure associated with bronchospasm and high respiratory rates. It can lead to auto-positive end-expiratory pressure Auto-PEEP, which can interfere with weaning. It may also result in hypoxemia, increased workload on respiratory muscles, and compromised cardiovascular function.
If breath stacking is not resolved, it can lead to increased intrathoracic pressure that causes hypotension or barotrauma, a potentially life-threatening condition.
This is why Hospital Procedures Consultants highly recommends that ED and ICU physicians learn the identification and management of breath stacking on the ventilator to ensure favorable outcomes. Before we dive into it, let’s review the types of patient-ventilator asynchrony.
Types of Patient-Ventilator Asynchrony
There are 7 types of patient-ventilator asynchrony:
- Auto-cycling (auto triggering) – when a ventilator delivers a breath that goes beyond the patient’s requirements. It can be the result of cardiac oscillations.
- Double trigger, also called breath-stacking in Assist/Control (A/C) ventilation – happens when a ventilator delivers 2 breaths consecutively, with or without a full expiration in between, in response to the patient’s high ventilatory demand.
- Flow starvation – when the ventilator fails to meet the patient’s flow requirements.
- Delayed cycling – the ventilator’s set inspiratory time exceeds the patient’s neurological requirements.
- Ineffective effort – when a patient’s inspiratory muscle effort fails to trigger the ventilator. This is the most common and occurs in 45% of patients with neuromuscular diseases.
- Premature cycling – happens when the ventilator terminates the breath sooner than the patient’s required neural inspiratory time.
- Reverse triggering – instead of the patient’s effort triggering a breath, a passive ventilator-delivered breath prompts a neural response.
Among these, double-triggering and premature cycling occur more frequently in patients with severe lung injury and increased respiratory drive.
Detecting the Amount of Breath-Stacking
The qualitative visual evaluation through frequent observations of ventilator waveforms could provide important information about airway resistance, lung compliance, and patient-ventilator synchrony. It should always be used as the first step in detection.
Researchers also assessed the diaphragmatic muscle contractions caused by ventilator insufflations as a type of patient-ventilator interaction. During the observation period, researchers noticed varying degrees of reverse triggering from 12% to 100% of breaths.
Since the clinical implications have yet to be documented, it is recommended to use the BREATHE criteria to further characterize breath-stacking dyssynchrony.
It looks at five components:
- Expiratory time
- Inspiratory time
- Ventilator cycling
- Interval expiratory volume
- Cumulative inspiratory volume
In a 2016 study of 33 patients with ARDS, the BREATHE criteria proved more useful in identifying high-volume breaths than other methods. It outperformed visual waveform inspection when it came to identifying occult high-volume insufflation from breath stacking dyssynchrony (BSD).
Primary Interventions To Treat Breath Stacking
Breath stacking can generate higher volumes than intended, increasing the risk of ventilator-induced lung injury, which can increase morbidity and mortality.
To lower this risk, medical practitioners must first correct any external disturbances.
As an example, let’s suppose that a ventilated patient has metabolic acidosis, which is simulating the respiratory drive and increasing air hunger. In such an event, correcting disturbances in acid-base equilibrium could prevent asynchrony.
In the absence of motivating pathophysiology, switching to pressure-support ventilation together with increasing the levels of continuous positive airway pressure, could help promote diaphragm shortening. Practitioners can also increase the inspiratory time in the assist-control mode, an approach that has been found to be effective.
Other methods commonly employed, such as using a neuromuscular blocking drug or increasing the depth of sedation, may not work well for reducing dyssynchrony.
Ventilator management can be simplified to some extent, but it could have serious consequences for patients. For starters, it can make them susceptible to critical illness myopathy, which can make it more difficult to wean them off mechanical ventilation. Additionally, it can increase the length of stay and mortality.
Alternative Interventions To Consider
Though less practiced, the techniques listed below can be quite effective. They require a good understanding of the patient demand-ventilator delivery dyssynchrony and the enhancement of the ventilator’s ability to meet the breath-by-breath requirements of the patient. By adapting the ventilator to the patient, sufficient augmentation of spontaneous breathing can be achieved without analgesia and with minimal sedation. This can be done by switching from MV to:
- Proportional-assist ventilation with load-adjustable gain factors – associated with fewer interventions for ventilator settings and sedative dose changes.
- Neurally Adjusted Ventilatory Assist (NAVA) which has fewer asynchronies.
Research has also shown that patient-ventilator asynchrony could be efficiently dealt with by changing the ventilator. This was more effective than deepening the level of sedation (assynchrony index dropped from 41% to 21%).
Learn the Nuances of Mechanical Ventilation With HPC
Mechanical ventilation can support the patient’s breathing until their clinical condition improves, but recent research uncovered that the patient’s spontaneous efforts may not be matched by the ventilator breath-delivery patterns.
If unaddressed, this could lead to diaphragmatic fatigue or occult lung injury. To combat this risk, practitioners must develop a keen understanding of the causes of patient–ventilator dyssynchrony. They should also learn how to identify and manage breath stacking on the ventilator for timely ventilator optimization.
If you want to learn more about this aspect of intraoperative management, consider taking our Mechanical Ventilation Course which includes ventilator management.
Resources
Bulleri, E. Fusi, C. Bambi, S. Pisani, L. Patient-ventilator asynchronies: types, outcomes and nursing detection skills. Acta Biomed. 2018; 89(Suppl 7): 6–18. doi: 10.23750
Emrath, E. The Basics of Ventilator Waveforms. Curr Pediatr Rep. 2021; 9(1): 11–19. Published online 2021 Jan 5. doi: 10.1007
Cox, C. E. Carson, S. S. Ely, E. W. Govert, J. A. Garrett, J. M. Brower, R. G. Morris, D. G. Abraham, E. Donnabella, V. Spevetz, A. Hall, J. B. Effectiveness of medical resident education in mechanical ventilation. Am J Respir Crit Care Med. 2003 Jan 1;167(1):32-8. doi: 10.1164
Bein, T. Weber-Carstens, S.The BREATHE-appeal: harmonize interaction between patient and ventilator! J Thorac Dis. 2016 Dec;8(12):E1647-E1650. doi: 10.21037
Bailey, J. M. Management of Patient-Ventilator Asynchrony. Anesthesiology. 2021 Apr 1;134(4):629-636. doi: 10.1097
Wrigge, H. Girrbach, F. Hempel, G. Detection of patient-ventilator asynchrony should be improved: and then what? J Thorac Dis. 2016 Dec;8(12):E1661-E1664. doi: 10.21037