The Evolution of Pre-Primed Circuits…My Experience by Gary Grist RN CCP Emeritus

By Gary Grist RN CCP Emeritus

I recently received an inquiry from a manufacturer’s representative asking me about pre-primed ECMO circuits.  I have paraphrased his question below.

The Question.

“I’ve learned that in some institutions it has become common practice to pre-prime oxygenators and circuits in preparation for possible cases, with equipment sometimes being left for days or weeks (he saw this on the ELSO web page) …..  and maintaining sterility during set up would be a major factor but after speaking with colleagues we also agreed that surely leaving equipment in a clinical area where it could potentially be tampered with/compromised is also something to consider?…..I’m really interested to hear if you’re aware of this practice and what your thoughts are on it.”

Common Practice?

Yes, it is common practice to set-up dry circuits and often wet, pre-primed circuits as well and to leave them set-up for up to 30 days.  Since it has been common practice to do this in the USA, you might say it has become an accepted practice.

Before Pre-primed Circuits Were Used.

It probably started with neonatal ECMO many years ago.  At one time neonatal ECMO was the primary outside-of-the-OR bedside ECLS.  Usually, the disease progression in neonates was relatively slow.  So a physician could schedule the start of ECMO by saying…”If this infant is not better by 1500 this Friday (it always seemed to be a FRIDAY afternoon !), we are turning him over to the ECMO team.”  So the ECMO team could begin to set up the pump early Friday afternoon and be ready when the decision finally was made.  I remember attending the instructional clinic for ECMO providers in Ann Arbor in 1986. They showed us how they crystalloid primed their pump. But air bubbles were a big problem for them.  Their perfusionist showed us how to take a Taylor reflex hammer and tap it on the tubing all over the circuit to get the bubbles dislodged and moved to the disposable priming bag where they could be safely removed.  This one part of their priming procedure alone took about 20 minutes.

Sick Patients Transported In.

Unfortunately, as ECMO became more accepted, outlying hospitals which had no ECMO program would keep their sick neonates until they were on the verge of dying and then rapidly transport the neonate to an ECMO center. Upon arrival, there was no time left to wait until ‘Friday afternoon.’  The baby was often dying when it came through the door, sometimes even coding.  Initially, the feeling was “We can’t put a coding neonate on ECMO, it’s probably already dead.”  But after a while, the parade of dying or dead neonates arriving at the ECMO center became too much, despite pleas to the outlying hospitals to send the children earlier. The ECMO docs decided to go ahead and put the child on ECMO, poor survival score or not, ongoing CPR or not.  So it became obvious that the ECMO pump needed to be ready a lot quicker than it had been previously. Dry set-ups were used initially, but that often was still not fast enough.  Surgeons constantly complained that they were waiting on the “pump people.” So the “pump people” started pre-priming to save more time and to shut the surgeons up! The fastest emergent VA ECMO cannulation I ever witnessed was seven minutes from incision to starting the pump. That kind of ECMO team success could not have been achieved without a pre-primed pump.

ECMO For Larger Patients.

Then larger patients were referred to ECMO. The same pattern followed.  As long as they were in-house, the system could be properly timed.  But when out-of-house patients arrived, it was a ‘fire drill’ to get everybody moving quickly.  Again, wet pre-priming was needed.

ECPR Came Next.

Then guess what happened next? Extracorporeal cardiopulmonary resuscitation (ECPR) came along.  Suddenly, any in-house patient who coded and who did not have a terminal diagnosis became a potential ECPR candidate.  Mine was a children’s hospital.  Imagine a doctor telling a mother that her child’s heart had stopped or the lungs had ceased to work.  The child was undergoing CPR, and there was little hope of reviving the child…….except for the remote hope of ECMO if it can be immediately commenced.  Guess what any mother would say? And the “pump people” had better be ready because compressions had already been on-going for 30 minutes. Pre-primed pumps to the rescue again!

Priming And Storing.

Circumstances evolved to dictate the use of pre-primed ECMO circuits in emergent situations, which had become the norm rather than the exception.  We only primed with normal saline because all the other crystalloids contain a potential substrate for bacterial growth. We also kept our circuits covered and in a restricted area and they were inspected every shift change by an ECMO Specialist. We did spot checks and cultured the circuit prime.  We never had any growth.

Reducing Errors.

There are systems that claim a quicker setup and prime.  But in many instances, the primer must still hurry. By performing many of the setup steps needed ahead of time by pre-priming, the primer is less likely to make mistakes like hurrying through the checklist or drug errors or accidentally contaminating the entire system by screwing up a tubing connection.

Contamination?

As far as contaminating the patient, whenever a skin incision is made the patient’s blood system becomes contaminated with skin flora. These bacteria are not normally pathogenic but can cause opportunistic infections in patients with compromised immune systems like many ECMO patients have.  There is no such thing as a ‘sterile wound.’  Living skin cannot be completely sterilized. So which is the greater risk…letting hazardous ventilator pressures or CPR go on longer before starting ECLS support or infecting the patient with an unlikely but potentially unsterile prime?

Dry Setups In Cardiac Surgery.

Here is where I ended my answer to the manufacturer’s representative.  However, there is still more to the story.  In pediatric heart surgery, we always set up a dry circuit similar to the one we just used and discarded after the patient arrived in the ICU.  The reason we did this was that about 3-4 times every year the patient would return to the OR within a few hours for emergent surgery that might require bypass.  These were usually failed Fontan completions or excessive bleeding from arterial switches.  But there were other less common returns which might still need the pump.

Less Risk Of Return In The Early Days.

In my early days the types of procedures were quite limited; ASDs, VSDs, AV canals, Tetralogy of Fallot and Mustard or Senning procedures.  Fontan type procedures for univentricular hearts were not performed by our team back then.  BT shunts without CPB were the primary offerings for univentricular hearts, often with the child outgrowing the shunt.

Interventions In The Cath Lab.

In the days before ECMO, the cath lab started doing a lot of interventions and occasionally would get into trouble and need to put the patient on CPB emergently. Since we were a pediatric hospital, we needed to have dry setups for infants, children, and adults. We used dry set-ups because our CPB circuits were designed to be crystalloid primed and de-aired in less than one minute. The smaller circuits were used for scheduled surgery within 24-48 hours if not required in the cath lab.  The adult circuits were used much less often.  So we left them set up for as long as 30 days, dry.  But these circuits were usually utilized before the 30 days passed.  We covered these dry setups and checked them every day and kept them in a secured area.

Summary.

Some of our patients did develop infections during the course of their treatment over the 30+ years that we used dry CPB setups and pre-primed ECMO circuits.  But these infections were never traced to the extracorporeal circuits.  Back in the 1980’s we had an episode of Pseudomonas infections in our nursery.  Initially, it was blamed on the ECMO pumps.  But soon other non-ECMO patients were getting infected.  Eventually, it was discovered that the source of the infections was the aerators that the hospital placed on the handwashing faucets at the bedsides. Apparently, the aerators and the warm water passing through them was a perfect dark area for the germs to grow.  So every time healthcare workers washed their hands they were unknowingly contaminating their hands with Pseudomonas.  This is a good example of jumping to conclusions that the pump was responsible when it was not. In fact, the decision to place aerators on each faucet to cut down on water use and save money had a serious unintended consequence. It was discovered that Pseudomonas was growing in faucets of other areas, including the scrub sinks in the OR. All the aerators were removed from clinical areas, and cost-conscious hospital administrators learned an important lesson.