Suction event

[psychRN-PMHNP]

When working with a VAD can someone explain what exactly a suction event is?

[renardeau, BSN, RN]

I'm a relatively new nurse on a floor that deals with a lot of VADs, so I might give a completely coherent answer, but here goes. (And I wish I could draw pictures here haha.) Also, someone please correct me if I get something wrong! My understanding is that suction events can be caused by different things.

If the VAD speed is set too high for instance, there isn't enough blood volume to sustain the left ventricular flow---imagine that there is a certain amount of blood supplied to the left ventricle, but the pump is shuttling the blood to the aorta way too fast, and pulling blood out at such a rate that it creates "suction" in the ventricle. This same situation can occur if the patient is dehydrated, e.g. being diuresed too aggressively (not enough blood volume and VAD is "pulling" blood from the left ventricle too quickly/faster than the LV can replace the blood being pulled).

Suction events can also occur when there is some sort of obstruction blocking blood flow. Again, this is the LVAD pump trying to pull more blood than the ventricle can supply (esp. if something is in the way), thus creating a "suction" force in the ventricle. This can happen if the VAD cannula isn't placed properly and hits/sucks at the heart wall or septum (e.g. VAD tries to pull at what would be ~4L/min, but is only getting heart muscle in way and little or no blood = we see drops in flow; VAD subsequently drops pump speed).

Basically anything that decreases blood volume to the ventricle that the VAD is pulling from can cause a suction event (e.g. dehydration, obstruction, tamponade, arrhythmia...) The suction event itself is when the VAD pulls too much too quickly, and you'll usually see a drop in speed and flow. And while I explained mostly in terms of the LVAD, same principles would apply to the RVAD.

[DogLover17]

I'm a relatively new nurse on a floor that deals with a lot of VADs, so I might give a completely coherent answer, but here goes. (And I wish I could draw pictures here haha.) Also, someone please correct me if I get something wrong! My understanding is that suction events can be caused by different things.

If the VAD speed is set too high for instance, there isn't enough blood volume to sustain the left ventricular flow---imagine that there is a certain amount of blood supplied to the left ventricle, but the pump is shuttling the blood to the aorta way too fast, and pulling blood out at such a rate that it creates "suction" in the ventricle. This same situation can occur if the patient is dehydrated, e.g. being diuresed too aggressively (not enough blood volume and VAD is "pulling" blood from the left ventricle too quickly/faster than the LV can replace the blood being pulled).

Suction events can also occur when there is some sort of obstruction blocking blood flow. Again, this is the LVAD pump trying to pull more blood than the ventricle can supply (esp. if something is in the way), thus creating a "suction" force in the ventricle. This can happen if the VAD cannula isn't placed properly and hits/sucks at the heart wall or septum (e.g. VAD tries to pull at what would be ~4L/min, but is only getting heart muscle in way and little or no blood = we see drops in flow; VAD subsequently drops pump speed).

Basically anything that decreases blood volume to the ventricle that the VAD is pulling from can cause a suction event (e.g. dehydration, obstruction, tamponade, arrhythmia...) The suction event itself is when the VAD pulls too much too quickly, and you'll usually see a drop in speed and flow. And while I explained mostly in terms of the LVAD, same principles would apply to the RVAD.

You're spot on. We frequently have a patient who has runs of v-tach and has suction events with those runs.

[ghillbert, MSN, NP]

Renardeau - excellent explanation!

Dysrhythmias are difficult because it's a case of chicken or egg - VT causes decreased preload to the VAD so in a fixed speed device you can have suction events because the pump can't adjust to less flow coming in. Or if you are overpumping with a patient who is hypovolemic or has the pump speed set too high, you can induce VT by literally pulling the LV walls and causing irritation leading to VT.

In general, suction events are usually cause by too much pump speed and/or not enough pump preload (LVEDP). However if you get into nuances, they can also be caused by alterations in heart rate or in afterload (SVR or BP).

It's important to note which device you're talking about also.

In a Heartmate II LVAD which is an axial flow device, a "PI event" is not the same as a suction event. Anything which causes the PI to change by more than 40% within a set time frame (from memory I think it's a few second cycle) will induce a "PI event". The manufacturer has been careful to get away from calling these "suction events" because they simply may not be - they may be caused by several things, and may be totally clinically insignificant. Heartmate II has an algorithm that detects these and will drop to the low speed limit that you set (several RPMs lower than the set speed) just in case they are suction events, in order to relieve the suction by not sucking as hard.

With a Heartware LVAD (centrifugal flow device) - suction event is clearly a true suction event. You can see the pulsatility on the monitor waveform go too low (should be >2L between max and min flow on the waveform) and then when a suction event occurs the waveform literally drops into negative numbers below the baseline. This is because centrifugal flow devices put out more flow at lower speeds than axial flow devices, but are also much more sensitive to changes in pump preload and afterload.