Life, Death and the Bridges in Between - Part II, With Dr Sam Shemie.
Highlights
- Brain Blood Flow Testing in Neurology
Key takeaways:
- There is variability across the world in things like the number of doctors needed to perform an examination, the interval between examinations, and the type of test needed to support an examination.
- There are limitations currently with brain blood flow testing, and if there is no flow, it is unclear whether the patient is in chronic anneurochrenal failure.
Transcript:
Speaker 1
What varies across the world are things like, okay, well how many doctors do you need to do this? Should there be an interval between the examinations and how long should that interval be? What kind of, if you can't complete the examination, what kind of test should you do to support that? Or alternatively, you must do another test to support it and what test should that be? Should it be an EEG, electron sub allography or should it be some type of brain blood flow scan? And we know all the limitations currently with brain blood flow testing, that if there is no flow, okay, but if there is some flow, it's unclear whether how much flow is required to animate, organize neuronal function. I'll give you the analogy as a segue a little bit. If somebody is in chronic anneurochrenal failure and they had some renal blood flow on scan, nobody would say that they're not in chronic anneurochrenal failure. The detection of flow or some penetration of contrast inside the skull, that flow has to perfuse tissues and that perfusion has to lead to function. And this is a concept put forward by Michael Shasse, the distinction between flow, perfusion and function. (Time 0:02:04)
- The Importance of Acknowledging the Difference Between Detection of Flow and That Flow Required to Perfuse Tissues and that Tissue Perfusion Required to Animate Cellular Function
Key takeaways:
- There is a big difference between detection of flow and that flow required to perfuse tissues and that tissue perfusion required to animate cellular function based on nutrient and oxygen delivery to neurons so that they can work in an organized way.
- In most countries around the world, the clinical examination is fundamental to brain death.
- The areas of variability is number of physicians, interval between exams.
- What do you do about ancillary or supportive testing and the variability of laws around this internationally? That will change in this upcoming report.
Transcript:
Speaker 1
Acknowledging, there is a big difference between detection of flow and that flow required to perfuse tissues and that tissue perfusion required to animate cellular function based on nutrient and oxygen delivery to neurons so that they can work in an organized way. In most countries around the world, the clinical examination is fundamental to brain death. The areas of variability is number of physicians, interval between exams. What do you do about ancillary or supportive testing and the variability of laws around this internationally? That will change in this upcoming report and I'll just tell you that it's a, again, a widely endorsed clinical practice guideline in Canada endorsed by organizations like the Canadian Medical Association, Critical Care Society, the Canadian Neurological Sciences Federation representing neurology, neurosurgery, neurophysiology, child neurology and many other organizations is the following. One is we're moving away from the concept of heart death and brain based death to a unified single definition of the permanent cessation of brain function fulfilling the definition of death. And again, you get there from primary brain injury or secondary to a circulatory arrest. (Time 0:03:40)
- Brain Death: What You Need to Know
Key takeaways:
- Brain function can be impaired after cardiac arrest and DCD cannot be performed to preserve organs for transplantation if there is no flow to the brain.
- CPR is insufficient to restart circulation and brain function must be preserved with circulation restarted.
Transcript:
Speaker 1
Well, if you're dead because your circulation has stopped to the brain, that means anything that can risk resuming circulation to the brain after death after cardiac arrest and DCD cannot be performed. So it's all about brain function and it's all about the absence of flow in cardiac arrest. It's the absence of both flow and perfusion and function and therefore any intervention to preserve organs for transplantation like so-called normothermic regional perfusion or donor ECMO effectively that you cannot resume flow to the brain under those circumstances. And the other thing in response to Peter's comment about, I think you said Supreme Court, that has been tested in Canada, the most widely covered case has been the case of Tkisha McKittie in Ontario, a family of mid-20s women who died after a fentanyl overdose resuscitated out of hospital cardiac arrest, CPR, which by the way is the wrong name for what we do in CPR. And the most common outcome is death and the most common outcome is death because of brain injury. And so they need to change the name of CPR to cardio pulmonary brain resuscitation so people understand that it's necessary but insufficient to restart circulation. What is required is that circulation is restarted to preserve brain function. (Time 0:08:07)
- How much blood pressure is needed to say there is no circulation?
Key takeaways:
- Flow measurement is not currently possible in ICUs,.
- There is a threshold for when compressions should be started in order to generate enough blood flow to the brain.
Transcript:
Speaker 1
So it's a very good question. We don't measure flow in ICU. We're not good yet technologically of measuring volume. We don't have an ability to measure cardiac output reliably. We used to with swan gans and stuff, but the relevant issue is how much blood pressure equals how much flow and how does that flow get distributed and how much of it goes to the brain. So, you know, when we prepared for Sonny's, the Nanny's D part study, we had this working group of cardiovascular scientists to advise us like how much blood pressure on arterial Lyme do you think we need to say there's no circulation? We were really cautious. We defined circulation as follows or we defined the resumption of circulation as follows. A single pulse pressure of greater than five millimeters of mercury. So if an average adult blood pressure is 120 on 80, I can tell you that in a deteriorating circulation, an intensivist will not wait till the pulse pressure drops to five millimeters of mercury before they start CPR. When they become hypotensive to a level of, I don't know what, what the threshold that Peter might use for a blood pressure before he starts compressions, but it's a lot higher than a pulse pressure of 20 and a pulse pressure of five millimeters of mercury, although we did not measure aortic blood flow or carotid blood flow that that was widely seen as lower than the threshold to generate enough flow for any flow to go to the brain. (Time 0:14:16)
- The Limits of CPR in the Treatment of Cardiac Arrest
Key takeaways:
- When someone experiences a sudden cardiac arrest, it takes about 20 to 30 seconds for their brain to stop functioning.
- There is a difference between brain function after withdrawal of life support and after sudden cardiac arrest.
Transcript:
Speaker 1
When they become hypotensive to a level of, I don't know what, what the threshold that Peter might use for a blood pressure before he starts compressions, but it's a lot higher than a pulse pressure of 20 and a pulse pressure of five millimeters of mercury, although we did not measure aortic blood flow or carotid blood flow that that was widely seen as lower than the threshold to generate enough flow for any flow to go to the brain. Having said that, what Teneil Goughton and Morat Slessarab's group in London are doing under the new part study, which is really the brain physiology during the dying process study, is that they're going to measure those things. Is that they're going to measure things like EEG and evoke potentials and transcranial gopplers in the dying process of a deteriorating circulation when CPR will not be restarted to really define that moment when the brain stops functioning. But this is what we know in the previous study in which there was, I think, four patients in the neurological arm of the D part study. So if I have a sudden abrupt cardiac arrest going from normal flow to abruptly zero flow, it takes about 20 to 30 seconds for me to go unconscious and for my EEG to go isoelectric. So the brain stops working after the circulation stops. It's completely different after withdrawal of life support in the (Time 0:15:24)