Overview:

Promote more natural breathing.

A full 71% of ventilated patients in the ICU show signs of agitation at least once during their stay,([FOOTNOTE=Siegel MD. Management of agitation in the intensive care unit. Clin Chest Med. 2003;24(4):713-725.],[ANCHOR=],[LINK=]) often leading to the need for sedation. One cause of agitation in ventilated patients may be patient-ventilator asynchrony.

Puritan Bennett™ PAV™*+ software can help clinicians address patient-ventilator asynchrony. It considers how a patient is breathing and enables the patient to determine the rate, depth and timing of each breath.

By improving the patient-ventilator relationship, clinicians can potentially make their patients more comfortable and help them breathe more naturally.

Promote more natural breathing

At Covidien, we believe mechanical ventilation can and should be more natural. Our PAV™*+ software is a breath type that better manages work of breathing in spontaneously breathing patients and promotes natural breathing compared to conventional mechanical ventilation.††,([FOOTNOTE=Pohlman MC, et al. Excessive tidal volume from breath stacking during lung-protective ventilation for acute lung injury. Crit Care Med. 2008;36(11):3019-3023.],[ANCHOR=],[LINK=]) PAV™*+ software manages the patient’s work of breathing differently than other traditional modes of mechanical ventilation†† in the following ways.([FOOTNOTE=Puritan Bennett™ 980 Ventilator Operator's Manual],[ANCHOR=],[LINK=])

    With PAV™*+ breath type the patient defines rate, depth and timing.

  • Flow is an indicator of demand. It tells us when the patient wants to begin inspiration, how deep the breath should be, when to end the breath and how often to breathe.([FOOTNOTE=Wilkins RL, Stoller JK, Scanlan CL. Egan’s Fundamentals of Respiratory Care. 8th ed. Louis, MO: Mosby; 2003.],[ANCHOR=],[LINK=])
  • The PAV™*+ software continuously monitors patient demand by measuring flow and volume every 5 milliseconds and by knowing the %Support set.
  • As patient demand changes, PAV™*+ software can change support pressure within the same breath.

    When the %Support is set, the patient and the ventilator are sharing the work of breathing as defined by the clinician.

  • Work of breathing can be calculated using the equation of motion.([FOOTNOTE=Younes M, et al. Proportional Assist Ventilation. In: Tobin MJ. Principles And Practice of Mechanical Ventilation, Third Edition. McGraw Hill Professional; 2012.315-346.],[ANCHOR=],[LINK=])
  • When R and C are known, it’s possible to calculate patient-generated pressure (PMUS) and work of breathing in real time using the equation of motion.([FOOTNOTE=Younes M, et al. Proportional Assist Ventilation. In: Tobin MJ. Principles And Practice of Mechanical Ventilation, Third Edition. McGraw Hill Professional; 2012.315-346.],[ANCHOR=],[LINK=]),([FOOTNOTE=Bosma K, Ferreyra G, Ambrogio C, et al. Patient-ventilator interaction and sleep in mechanically ventilated patients: pressure support versus proportional assist ventilation. Crit Care Med. 2007;35(4):1048-1054.],[ANCHOR=],[LINK=]),([FOOTNOTE=Younes M, Webster K, Kun J, Roberts D, Masiowski B. A method for measuring passive elastance during proportional assist ventilation. Am J Respir Crit Care Med. 2001;164(1):50-60.],[ANCHOR=],[LINK=]),([FOOTNOTE=Grasso S, Ranieri WM, Brochard L, et al. Closed loop proportional assist ventilation (PAV): Results of a phase II multicenter trial. Am J Respir Crit Care Med. 2001, 163:A303.],[ANCHOR=],[LINK=]),([FOOTNOTE=Younes M, Riddle W, Polacheck J. A model for the relationship between respiratory neural and mechanical outputs: III. Validation. J Appl Physiol. 1981;51(4):990-1001.],[ANCHOR=],[LINK=])

    PMUS + PVENT = (flow x resistance) + (volume ÷ compliance)

  • PAV™*+ software measures resistance and compliance every 4-10 breaths.
  • Once %Support is set, clinicians can use the work of breathing (WOB) bar for real-time feedback on how much work the patient is doing.
  • The work of breathing bar displays both total work of breathing (WOBTOT) and the patient work of breathing (WOBPT).
  • Adjust the % Support setting to maintain the patient’s WOB (WOBPT) within the green zone.
  • Associated fatigue values for work of breathing are shown as being outside the green zone.

The work of breathing bar, when coupled with good clinical assessment, can help take the guesswork out of determining the appropriate level of mechanical ventilation support. Providing real-time feedback on work of breathing helps the clinician keep the patient at a sustainable level of work—reducing the risk for respiratory muscle atrophy, but off-loading enough work to avoid fatigue.([FOOTNOTE=Hermans G. Increased duration of mechanical ventilation is associated with decreased diaphragmatic force: a prospective observational study. Crit Care. 2010;14:R127.],[ANCHOR=],[LINK=]),([FOOTNOTE=Anzueto A, Peters JI, Tobin MJ, et al. Effects of prolonged controlled mechanical ventilation on diaphragmatic function in healthy adult baboons. Crit Care Med. 1997;25(7):1187-1190.],[ANCHOR=],[LINK=]),([FOOTNOTE=Haitsma JJ. Diaphragmatic dysfunction in mechanical ventilation. Curr Opin Anaesthesiol. 2011;24(2):214-218.],[ANCHOR=],[LINK=])

Learn more about how PAV™*+ works.

Understanding patient-ventilator asynchrony

People display normal variability in their breathing patterns even at rest. In contrast, although a necessary medical intervention, mechanical ventilation uses some sort of fixed parameter in almost all currently available modes. If the mechanical breath is delivered in a fashion that the patient doesn’t want or expect (too short, not enough flow, too long, etc.), asynchrony between the ventilator and the patient, discomfort, anxiety and fatigue can result.1

Eight out of 10 ventilated patients come off the vent within three to four days with little difficulty.2,3 They might be uncomfortable under mechanical ventilation, but they are able to wean from the ventilator. Still, in these patients, improving patient-ventilator synchrony may potentially result in less anxiety and need for sedation.4

Those who stay on ventilation longer (~25%) and continue to fail to wean use 50% of our ICU resources, accounting for 40% of all ICU costs.3,5 In these patients, asynchrony may have a greater impact.2,6,7,8

 

What is asynchrony?

The best way to describe asynchrony is to call it poor patient-ventilator interaction. Patient-ventilator interaction is dependent upon many variables. Some of those are:
  • The patient’s pathophysiology
  • The ventilator settings
  • The patient-ventilator interface used

How often does asynchrony occur?

Asynchrony occurs at varying degrees depending on the patient population and the mechanical ventilation strategy employed. The most common types of asynchrony are ineffective efforts and double triggers. (See TABLE 2 for definitions.)
Here is a look at the findings of different researchers. Please note that a variety of modes and approaches were used. TABLE 1

What does asynchrony look like?

Patients experiencing patient-ventilator asynchrony may present one or more symptoms. The patient may appear uncomfortable,15 have severe hypercapnia,13 have an increased need for sedation, and show confusion during the weaning process.15
(For a fuller discussion of the signs of asynchrony, see the Asynchrony Assessment Tool.)
Today’s ventilators offer graphics that can be used by the clinician to identify the presence and potential cause of asynchrony. Here are some common forms of asynchrony and examples of what they might look like in clinical practice. TABLE 2

Why is asynchrony important?

Patient-ventilator asynchrony is typically uncomfortable for the patient. In addition, it may have an impact on patient outcomes. Epstein14 put together a list of adverse effects associated with poor patient-ventilator interaction:
  • A higher or wasted work of breathing
  • Patient discomfort
  • An increased need for sedation
  • Confusion during the weaning process
  • Prolonged mechanical ventilation
  • A longer stay
  • The possibility of higher mortality

Investigators have examined the relationship between patient-ventilator asynchrony and outcomes. Thille et al2 found patients with an asynchrony index >10% had a longer duration of mechanical ventilation and were more likely to need a tracheostomy. de Wit et al1 found that those patients who had an ineffective trigger index of >10% had a longer duration of mechanical ventilation, a worse 28-day ventilator-free survival, and a longer ICU time and hospital stay. Patients in the ineffective trigger group were less likely to be discharged to home. Varon et al14 found that mortality was higher in patients with an asynchrony index >30%.

What are the key takeaways?

Patients experiencing patient-ventilator asynchrony can be very uncomfortable, exhibit wasted effort and fatigue easier. Asynchrony, or poor patient-ventilator interaction, may occur as a result of the patient’s pathophysiology, the settings of the ventilator and/or the patient-ventilator interface used. Failure to address/resolve asynchrony may result in patient discomfort, longer duration of ventilator days, a worse 28-day ventilator-free survival rate, a longer ICU time and a longer hospital stay.6