Rules to Live By – Transfusion Triggers in Cardiac Kids Having Non-Cardiac Surgery

This post is the written version of a talk for PACSA 2019 in Johannesburg. Andrew Weatherall was asked to cover transfusion triggers and anaemia stuff in cardiac kids having non-cardiac surgery. 

I am pretty sure that at some point when I was a medical student I thought some things would remain certain. Cheddar cheese was never going to be turkey stuffing. Prince would be ripping out ridiculous guitar solos forever. Coffee would be great. Actually coffee and I are still on good terms.

Oxygen was also just a pretty great thing back then. Also, clever people would always be around to provide us with guidance. And anaemia was basically pretty easy in the operating suite. People bleed. We have blood. We give blood. Patients don’t have anaemia. Blood is good.

I don’t think much is certain any more.

I even worry about coffee a bit.

 

Take this ….

So to examine this lets think about a 4 year old patient and for an extra bit of aftertaste (or is it pretaste?) the patient has cardiac disease. At some point early in their life they had the slightly unfortunate plumbing arrangement of a left ventricle that didn’t turn up for duty and now they have a long line of plumbing rearrangements happening with the cardiac surgeons. It started with a conduit from the right ventricle to the pulmonary artery and these days there is a Glenn shunt involved. The Fontan will come later.

Oh, and they need an operation for their hip involving a bit of pelvic osteotomy work. Because… well, I have to sustain this narrative for a while and I couldn’t really work in a trusty speaking animal companion in a way that supports the whole anaemia chat thing.

So this is the case we’re presented with a patient with cardiac disease and the surgeons will try their hardest but there will be blood. So much blood.

So we’d better know in detail just how much blood we have to give to keep patients in their safe zone beause blood is good, right?

Luckily for me experts are still experts and a bunch of them have just recently got together in whatever collective grouping noun you call experts (a pontification? A waffle?) and handed down instructions. Guidance on how to approach transfusion and triggers in the critical care settings.

And while I sort of had a crack there the fairer reflection would be that the experts are really a bunch of passionate and knowledgeable people working really hard to provide useful, evidence-based guidance for the rest of us so we don’t have to go the trouble of looking up everything ever.

Yes, please give me the instructions.

Which I am really delighted about because now I can just go and read this paper and this paper and really roll around in the magnificent summary of the literature which could be best summarised by ….

 

The Big Reveal

 

¯\_(ツ)_/¯

 

Yeah, that’s the target.

And that’s just a marker of how hard it is to find actual evidence for things as seemingly innocuous as targets. In the Valentine et al paper which is a more general population thing, the group comes up with 102 recommendations. 45 are related to the need for research. 57 are clinical but only 20 of those are on the basis of some sort of quasi-strong (maybe) evidence.

Look even closer and the statements they do make are sometimes …. what’s that colour that’s like beige but actually more beige than beige so that beige looks quite exciting by comparison? That colour.

I mean things like “When deciding to transfuse an individual critically ill child, we recommend considering not only the haemoglobin concentration but also the overall clinical context … and the risks, benefits, and alternatives to transfusion.” Wow.

Other gems include ‘measure haemoglobin’. They do feel pretty strong about saying transfuse if the Hb is under 5 g/dL (yikes). By the time they discuss maybe avoiding transfusion if the Hb is above 7 g/dL in a stable patient (weak recommendation with low quality paediatric evidence) or accepting 7-9.5 g/dL more broadly (weak recommendation, low quality evidence) it feels almost desperate.

This is no criticism of those producing the guidelines. They spent 2 years trying.

That second publication specifically tackles the pediatric cardiac patient. They hit the same problem with their 21 recommendations, the particular highlight being that only 93% of the experts could agree with the following:

“We recommend that for all children with congenital heart disease the benefits and risks of transfusion are considered before transfusion. Whenever possible, adoption of blood sparing and conservation procedures and guidelines should be implemented.

93%. Wot??

So before we get back to the rules to live by, maybe we should get to know ourselves better.

 

The Way We Think

To really embrace the idea that we don’t need to transfuse quite so much, it’s pretty important to understand the way we think about things and in particular the way our biases and previous experience impact on our perceptions of what works, what doesn’t and the risk of change.

Now the field of looking at cognitive decision making in anaesthesia is just massive so there are other prisms with which to view the way we make decisions. The reason I’m focussing on the bias bit is that before we can think about adopting specific decision-making approaches or reasoned logic to arrive at a plan, we need to think about bias. If we don’t pick up on how bias might influence what we perceive as our ‘next rational decision’, then we’re sort of going into the thinking bits without the helicopter rotor on the top of our hats whirring.

What? What does your thinking hat look like?

Now in this instance the way we think about the value or otherwise of transfusion will be influenced very much by our previous experience, both in terms of what we’ve learnt but also our prior clinical experience when we’ve looked after patients.

To point at just a few really relevant bits of our thought patterns:

  • We transfer our feelings about our patients. In the paediatric setting where we develop positive feelings about the patient our desire to ‘do that little bit more’ for them might well influence our decisions and actions.
  • We reconstruct our memories. This is a feature of every time access a memory. The process of filling in gaps in the memory or even embedding false bits of information or data that is falsely elevated in its importance can influence the way we perceive past experiences where transfusion did or didn’t work.
  • We’re also susceptible to confirmation bias where we more strongly imprint events that confirm what we already thought would be what happened.
  • We really like certainty. The red cell transfusion may be perceived as being certain to make a difference that you can see, rather than waiting longer on a ‘wait and see’ basis.
  • We also really don’t like loss. This is particularly relevant to the way we ‘frame’ a treatment. If we frame a lower transfusion target as risking the ‘loss’ of major morbidity because there’s a small chance bleeding will occur, we’re more likely to want to transfuse. If we frame it as a ‘gain’ because we’ve taken onboard that transfusions cause problems, our mindset will be substantially different.
  • We get hit hard by feedback bias. We see the here and now (‘patient bleeds, patient responds to being given blood’) and not the myriad of long-term complications described in the literature. Out of sight, out of mind.

So now that we appreciate that we are quivering beings whose ‘rational’ decisions are pre-determined by a series of influences from our lives up until this point that assail our subconscious decision-making at every turn, how do we address that little voice that says ‘blood is good, and anaemia is a thing we avoid’? Let’s bring the focus back on the patient and think about things in a broad fashion that sort of works for lots of other parts of looking after congenital heart disease kids.

 

The Key Questions

  1. What is the benefit of transfusing to treat anaemia?

Easy. Anaemia drops delivery of oxygen to tissues and that sucks. Giving red cells is effective at helping with this and in the operative setting we might lose a bit of blood so I’m better off running with a safety margin anyway. Plus I’ve seen it work.

  1. What problems might result from giving blood?

Well, there is more and more evidence that red cell transfusion is associated with excess mortality. There’s a range of non-infectious complications (circulatory overload, immunological effects, that pesky death bit) that really suck. When I give blood it might not just be a positive thing. It might be that I don’t see the negative part because it comes later. I should at remember (*irony alert*) that sometimes the cases I recall might have had other significant things that made an immediate difference and I just didn’t see that bit.

  1. What is normal for this kid?

Really this is a particularly key question. It’s relevant here and it’s relevant when thinking about lots of things in cardiac kids like how much oxygen to give the patient or how to target blood pressure. ‘When I chatted to this patient before what was their normal? They were breathing 21% oxygen a few minutes ago and I know their blood pressure, then that’s a baseline I can keep working towards, offsetting the effects of anaesthesia and the surgery to keep hitting those targets.’

In the context of this, for bigger surgery you should know the underlying Hb. If they were getting around fine with a Hb of 10 g/dL how much Hb do you need swimming around to be at the lower limits of what is ‘normal’?

  1. What is about to happen?

In the context of the surgery they are about to have how much bleeding might happen and in what phases of the operation? If they are stable when the bloodthirsty bit is done then a ‘top-up because they’ll probably just need it on the ward’ might be something worth reconsidering.

  1. What about the targets?

So there are some recommendations that are both weak and not universally supported by the experts that they throw out there. They really are weak though and we have to keep in mind that at times the Hb won’t be our guide because bleeding is bleeding.

But what they did come up with was:

  • There’s no convincing evidence that if you have a patient with a biventricular repair or biventricular circulation outcomes are any better if you drive that Hb anywhere above 7 g/dL.
  • There’s no convincing evidence that there’s a benefit to driving the Hb to > 9 g/dL if the patient is on a single ventricle pathway.
  • For everything else (pulmonary hypertension etc) there’s just even less info.

So now that we know there’s not convincing evidence for better outcomes at levels in those higher regions, it becomes far more reasonable to focus on the potential ‘wins’ of avoiding that extra bit of red cell product.

The things to aim for are not that definite just yet.

What about avoiding the whole mess?

Of course preventing the need for transfusion might be an even better way forward.

I’m not going to touch on red cell conservation strategies like cell salvage because it is both self-evidently a good idea and deserves more time than you can wrap up in a throwaway line. There are a couple of things to chat about though.

Thing 1 is ‘get the surgeon to shed less blood’. Sounds flippant but it isn’t. Having surgeons really focus on blood loss is useful. In some procedures there might also be a role for antifibrinolytics like tranexamic acid but that’s a bit beyond the scope here. There is a little on dosing of TXA over in this trauma post here.

Thing 2 is worth talking about. That’s screening for anaemia and doing the replacing of factors like iron when you can. One retrospective review mentioned in that cardiac patients guidelines paper suggested anaemia rates in VSD and AVSD patients of around 23% so there might be scope to look at that. Cyanotic patients can of course have high Hb but low stores (but at that point a clever haematologist might be worth chatting with).

So screening for both Hb and iron studies (particularly ferritin to reflect stores) makes sense. Ideally you’ll want to treat for 6 weeks plus so the earlier the better.

How much? Well if that ferritin is < 50 micromol/L it’s probably worth replacement at 3 mg/kg/day. Unless it’s under 20 micromol/L where we’re thinking about programs with 6 mg/kg/day. The downside of replacement is of course it tastes great and can result in non-exciting GI symptoms. From a practical point of view it might be necessary to divide the iron doses (as long as the daily intake is the same) and using a straw with liquid versions so those teeth don’t become …. their own story.

There are now some IV iron preparations that let you give IV iron over a few minutes but the exact niche for those is still a little unclear at our joint. While appealing as an option to give even in theatres for a boost there is still a lag in effect. There are also some policies that preclude use at operation because of concerns that patients display muscle weakness after the infusion for a short period of time.

At the end of all of that our patient with that hip that needs fixing should be able to avoid blood entirely. It’s all so simple…

  • Screen before and top up things like iron where we need to.
  • Remember that it’s OK not to give blood.
  • Ask ourselves how the patient was going with their version of ‘normal’ before this operation. We don’t need to aim above that.
  • Remember that there isn’t evidence that says we need to travel above 10 g/dL anyway. Lower seems fine and might be a way we actively avoid other problems on behalf of our patient.

And now we have something to be certain about all over again. Until we don’t.

Except for coffee. Coffee is our friend.

 

The References:

The first of those expert group papers is this one:

Valentine SL, Bembea MM, Muszynski JA, et al. Consensus Recommendations for Red Blood Cell Transfusion Practice in Critically Ill Children from the Pediatric Critical Care Transfusion and Anemia Expertise Initiative. Pediatr Crit Care Med. 2018;19:884-98.

The specific cardiac one is this one:

Cholette JM, Willems A, Valentine S, et al. Recommendations on Red Blood Transfusion in Infants and Children with Acquired and Congenital Heart Disease from the Pediatric Critical Care Transfusion and Anaemia Expertise Initiative. Pediatr Crit Care Med. 2018;19:S137-S148. 

The Australian National Blood Authority module on Patient Blood Management in Kids is this one. A long read but a good one (note it’s presently under review).

The work on cognitive decision making and bias for anaesthetists is this one:

Stiegler MP, Tung A. Cognitive Processes in Anesthesiology Decision Making. Anesthesiology. 2014;120:204-17. 

 

 

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