Haemodynamics, Haemodynamics, Haemodynamics: Critical Care’s New Mantra?

Saying it three times seems to cut through… whether it was the old “education education education” or the WHO’s rather more recent “Test, Test, Test.”

So here’s a new mantra that is growing in recognition as vital in treating critically ill COVID-19 patients: Haemodynamics, Haemodynamics, Haemodynamics. And it’s not just those of us in the industry who are saying it.

(No) time for new approaches?

Critical care practitioners have never been more tightly focused on the urgency that faces them every minute of every day. And when you’re right up against it, it’s very difficult to throw another therapy into the works. Haemodynamic monitoring though, isn’t a new therapeutic approach… it’s just that some can view it as either a luxury or a forgotten man in the front line of the critical care war zone. But far from being a nuanced option, we’d argue it’s a powerful weapon. What follows is the “why?”

“Too much or too little fluid can have a negative impact on patient outcomes”

There are thousands of live situations ongoing right now. Each one is a patient needing the most urgent critical care, mostly falling into recognisable and repeatable treatment categories. However COVID-19 patients are sometimes different to the expected norms of the typical ARDS sufferer. They actually fall into two symptomatic “phenotypes” which suggest different approaches. Reversion to the ARDS treatment norms for so-called non-ARDS-type lungs (normal respiratory compliance, normal chest X-Ray) may do more harm than good.

COVID-19 non-ARDS-type lung support requires “lung-protective” measures including reduced tidal volume and lower PEEP (pressure). These patients arrive dehydrated in any case and do not need to be “kept dry.” There needs to be a focus on achieving haemodynamic stability, because poor fluid control is in the spotlight for contributing to poor outcomes. Indeed clinical discussion suggests that some haemodynamic instability is iatrogenic – caused as much by applying the ARDS treatment approach to non-ARDS patients – as it is by the disease.

In the most recent edition (April 18th) of professional medical news forum, TopMedTalk, Editor-in-Chief Prof Monty Mythen says “some clinicians, on reflection, are saying that if they had kept it simple, focusing on the ABCs of Airway, Breathing, Circulation, but applied haemodynamic monitoring to assess preload, afterload and contractility, they may have done better.”

Worryingly high renal failure rates are probably caused by a combination of hypovolaemia resulting from severe dehydration on arrival as much as by the virus itself. Or the clinical tradition of minimising fluid… kidneys don’t like hypovolaemia.

So, if it’s as much about perfusion as ventilation, haemodynamic stability is vital. Indeed paper after paper, presentation after presentation tell us that maintaining the “right” circulating blood volume delivers the best outcomes. We often quote from the many surgical references, but here’s one specific to critical care setting:

“Fluid therapy, which is provided to restore and maintain tissue perfusion, is part of routine management for almost all critically ill patients. However, because either too much or too little fluid can have a negative impact on patient outcomes, fluid administration must be titrated carefully for each patient.” Vincent, JL., Fluid Management in the Critically Ill, Kidney International July 2019

Finding the Haemodynamic “Sweet Spot”

The relatively new wisdom is that the haemodynamic “sweet spot” (or alternatively the “Goldilocks zone”) is very narrow. Moreover, outwith those parameters, too much fluid (hypervolaemia) can lead to as many, but different, problems as too little (hypovolaemia). “Just right” and you’ve got a chance.

But how many intensive care beds feature any form of monitoring that is required to hit the sweet spot? The answer is undoubtedly “not enough”… when it should probably be all.

As haemodynamic expert Dr Manuel Ignacio Monge Garcia puts it, in the TopMedTalk interview “If we are changing the concept of how this virus is affecting the lung, we should also consider changing the approach to haemodynamic monitoring. It’s not a matter of trying to keep the lungs dry or wet. It should be to keep the right amount of fluid, and use haemodynamic monitoring parameters to influence when intervention is necessary.”

He adds “You can’t do that by just using diuretics or giving fluids without any rationale or because you think it’s right.”

Monty Mythen neatly summarises: “when people are so busy and so overwhelmed, things we consider ‘every-day-at-the-office’ – cardiac output, stroke volume, fluid challenges – are also overwhelmed, so we have to select patients for more meticulous haemodynamic management.”

If you need a precision tool, which you do… use a precision tool

So how to do haemodynamic management? How best to assess circulating blood volume? Deltex Medical’s long-established oesophageal Doppler-based monitor (ODM+) derives its data right from source, cardiac output straight from the heart, measured from the aorta via a probe that sits in the (helpfully adjacent) oesophagus. Other systems that back-calculate flow data from peripheral pressure transducers etc. can’t hope to deliver the same level of accuracy or timeliness. They can even less expect to deliver meaningful data from these fundamentally unstable patients.

Consider Monty Mythen’s words from a recent (2018) speech relating to ODM:

“…we’re heavily conflicted in discussing oesophageal Doppler because it’s been our house technology for as long as I can remember. We also use other technologies, but in using ODM what we recognise is it is a precision tool… it measures velocity directly. You are not deriving anything… You do something with that number and I think everyone accepts the fact that it is the most precise tool so everything else that we use which may have greater utility or user-friendliness is a sort of wannabe technology.”

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