Q. What clinical and waveform clues should alert you early to patient ventilator asynchrony at the bedside and which patterns are most commonly missed?

When looking at ventilator waveforms, we usually have three to assess: pressure on top, flow in the middle, and then volume at the bottom. Asynchrony can occur at three key stages: triggering (how the patient initiates a breath), inspiratory flow delivery (whether flow meets patient demand), and cycling (how the ventilator transitions to exhalation).

I believe the most commonly missed asynchrony is false triggering, in which the ventilator falsely detects patient effort and delivers a breath, but in reality is detecting a leak in the circuit or another factor. This is very difficult to pick up on the newer generation ventilators, because they are so sensitive, and many times we’re not alerted until we get a blood gas with respiratory alkalosis.

Another asynchrony which does not receive enough attention is cycle asynchrony, where the ventilator cycles to exhalation. In years gone by, especially in pressure support, the ventilator was preset as to how it would cycle to exhalation. Now therapists have much more control over cycling, but the practice is lagging a little bit behind the technology.

Q. When you identify ineffective triggering, what are the key ventilator adjustments or patient-related factors you should address first to improve synchrony?

Firstly, there are a lot of different terminologies to describe asynchronies; ineffective triggering, missed triggering, delayed triggering, and there is not one accepted term, even synchrony has been interchanged with terms such as asynchrony, desynchrony, and discordance. But ineffective triggering simply implies that the patient made an effort and either there was a significant delay in the ventilator identifying it or the ventilator never detected the effort.

The first thing to check would be the sensitivity setting. Nowadays, ventilators are very sensitive and responsive. Often the sensitivity is set and left as is, if the patient looks well, but the sensitivity should be continually assessed. Patients with an obstructive airways pattern (e.g., COPD or asthma) may have intrinsic positive end-expiratory pressure (PEEP) or auto PEEP build up in the chest, which they have to overcome before the ventilator detects an effort and triggers a breath.

Identifying ineffective triggering requires clinical assessment at the bedside; you can put your left hand on the diaphragm and eyes on the ventilator to feel any delay or even a missed trigger. To correct ineffective triggering, you would start with sensitivity settings. Sometimes you can add applied PEEP, which reduces the pressure gradient between the intrinsic PEEP in the patient’s chest and the circuit pressure level. In this case, you have to be aware of tidal volumes going up, but it can be done at the bedside without esophageal monitoring. Sometimes, small adjustments to PEEP can help.

Q. How do you rapidly troubleshoot flow mismatch or flow starvation, and which ventilator settings are most effective for correcting it?

The most common mode used is Volume Assist Control, where the volume is set, the flow is set, and the patient has no control over how the breath is delivered. The volume control is very effective when you need to control the arterial blood gases, but this mode is not very interactive with the patient. It is not inherent to normal breathing; we don’t normally take the same breath or have the same flow every time. At the bedside, you might see the patient pulling down on the pressure tracing in an effort to increase flow, because the only thing that they can change is the pressure. This is reflected as a downward dip in the pressure tracing.

Usually the problem is a lack of flow, rather than an excess, so a lot of people will advise turning up the flow to correct it, but this can result in consequences elsewhere. If the patient has an active drive to breathe, their efforts are probably not the same every time, which could cause asynchrony with a fixed flow. The inspiratory time will also shorten, because the same volume will be delivered faster and that may lead to problems with cycle asynchrony.

My solution would be to set the pressure through Pressure Support Ventilation or Pressure Assist Control, leaving the flow variable. This way, the ventilator will respond to patient efforts as opposed to having a fixed flow. The downside is that the tidal volume could go up initially and to unsafe levels, but this should settle out to a normal range as flow starvation abates and if the inspiratory pressure level is set appropriately. This “normal” tidal volume won’t be the same every time, but we can look for the patient’s usual range.

Q. What strategies help prevent or manage cycle asynchrony and reverse triggering, and how do you decide when to make corrective adjustments?

Cycle asynchrony occurs when the ventilator transitions to exhalation at a time that does not match the patient’s inspiratory effort. Look at the patient and match up their effort with what the ventilator is doing. If you are in Volume Assist Control or Pressure Assist Control mode with a fixed inspiratory time, monitor the patient. If they are trying to exhale in Pressure Assist Control, you should see a little bump in the pressure tracing. If that happens on the majority of breaths, I would be inclined to change the inspiratory time. In Volume Assist Control, you can either change the volume or the flow for the same effect.

If a patient is having trouble cycling and going to exhalation, consider pressure support because it is more attuned to their way of breathing. The patient triggers every breath, achieving the flow they want, and the ventilator cycles the exhalation based on flow degradation. You can also adjust the expiratory sensitivity to closely match what the patient wants.

Reverse triggering is a breath that is triggered by the patient after a mandatory ventilator breath. The time-triggered ventilator breath stimulates a reflex on the patient’s part. We don’t know what causes it or how to fix it. If it happens near the end of the ventilator breath and results in a second breath, this can cause breath stacking, which gives a very high tidal volume. If it doesn’t result in a second breath, there are two opinions; some say we should still correct it and others say maybe it is helping as the diaphragm is active and not atrophying. We don’t know the answer to that.

Essentially, you need to consider whether you can reduce the respiratory rate and allow the patient to trigger their own breaths, and whether transitioning to pressure support is feasible. The challenge is that this often occurs in very unwell, deeply sedated patients, where the alternative may be to paralyze them and take full control of ventilation. It ultimately depends on where the patient is in their clinical path. If they can tolerate pressure support and potentially higher levels, that may be beneficial, but there is no single right answer. In most cases, this requires bedside assessment by a multidisciplinary team to decide on the best approach.

Q. How should you balance sedation, analgesia, and spontaneous breathing support when asynchrony persists despite ventilator adjustments?

Ventilator adjustment is the first step, followed by assessing why the patient is asynchronous before moving to sedation. Are they in pain? Are they febrile? Are there issues with family members contributing to this? There may be external factors driving the asynchrony, and once these are ruled out, you can try different modes, such as pressure support, or other adjustments you think may help.

In my opinion, the best approach is to titrate sedation and adjust it as needed, reserving neuromuscular blockade for when all else fails. These situations depend on where the patient is clinically. Another important question, if they remain asynchronous, is whether they could be extubated. Ultimately, there are several clinical questions to consider at the bedside when asynchrony persists, but neuromuscular blockade should probably be the last step, especially if the patient is still interacting with the ventilator.