Sunday 3 December 2017

CO2 retention

#KYJ - CO2 retention
In our #Pirate seminar and #RespNursing we touch on CO2 retention.   It’s a commonly used term, and most nurses will recall hearing it, and associating it with end stage COPD.

That said, do you know what it means to be a carbon dioxide retainer?  Where is the CO2? Where does it come from? And; given that the patient is still breathing, why are they not just blowing it off?

Ok.   Take a deep breath...

Physiology refresh: cells burn glucose with oxygen to make energy (ATP).
Like all engines that burn carbon, (wood on a furnace, petrol in a car, diesel in a truck) so too, glucose in a cell produces   Carbon dioxide (CO2) as a waste gas.

Now stay with me ...

As cells produce CO2, this diffuses into the extra cellular fluid around the cells.   Now capillary blood in close proximity to those cells absorbs this CO2 and two things happen.
The capillary plasma pH drops (CO2 is acidic) so blood becomes acidic.  This also causes micro-vessel dilation.
Entrapped acidic blood in engorged dilated vessels now slows and saturates with CO2, red blood cells off load their oxygen, now freeing up space to absorb the CO2 and transport it to lungs to be blown off (expelled).

So a couple of things here.  
Oxygen binds to haemoglobin;
but so does CO2.  

As the blood cell carrying oxygen starts to off load the oxygen in these peripheral tissues, CO2 hops on because there is space in the RBC.
Think of a bus full of footballers arriving at the field, they get off the bus, and now there is space for the cheerleaders to get on the bus.  

Ok- enter the world of lung disease.  Chronic bronchitis, asthma and alveolar destruction called emphysema.  
Now slowly and insidiously over years, the person with lung disease reduces their oxygen carriage, and subsequently increases CO2 carriage.  They start accumulating more carbon dioxide in blood.  Now this blood should normally just release it’s CO2 in the lungs, but remember, these are the same chronically diseased lungs that had reduced oxygen exchange, so they also have diminished CO2 diffusion and off-gassing.

They start becoming slowly hypoxaemic (lower sats), and slightly CO2 retentive. Slightly more acidic-slightly more vasodilated.  As lower oxygen levels reach the tissues, cells now starving for oxygen (hypoxia), start burning more glucose (carbon) to attempt to make energy anaerobically (lacking oxygen).  
As more glucose is burned, then more carbon dioxide is produced.  This is the cause of increasing levels of carbon dioxide in tissues.  As tissue CO2  levels increase, then blood CO2 levels also increased.

Diseased lungs can’t off gas it, so it becomes retained in tissues and in blood. Now- acidic blood has another interesting property... it won’t carry oxygen.  So this is a downward spiral where the diseased lungs won’t in-gas oxygen, and acidic blood is reluctant to transport it.  Acidosis leads to hypoxia leads to CO2 retention leads to acidosis; and around it goes.

So we think that oxygenating these guys should help, but remember the bus?  If you fill it with footy players, there is no room to transport the cheerleaders.

CO2 retention is worsened by unnecessarily oxygenating end-stage COPD patients.  Allow SpO2 levels of 88-92% in these patients if not distressed. And if you must oxygenate them, just enough (1-2lpm via Nasal prongs) to get their sats into the 88-92% range.

For years we’ve taught the dogma of “Hypoxic Drive” in CO2 retainers; and cautioned clinicians against giving oxygen for fear the patient would stop breathing.  Well we had it wrong.  By all means withhold oxygen as a routine, but it is for worsening of CO2 retention, not loss of drive to breathe.

CO2 retention like the COPD disease pathophysiology is complex, and slow to develop, but one thing is certain, unnecessary oxygen exacerbates it.

#ECT4Health- check out our what’s on page What’s On

Saturday 2 December 2017

Statins and Number Needed to Treat (NNT)

#CageRattler #KYJ
Statins and NNT

The number needed to treat (NNT)  before one person gets any benefit is a pharmacology statistic that drug manufacturers use to to determine that a drug has efficacy (that it does the job it intends).
The same drug can have an NNT that is different depending on the end point you are measuring.  Eg if you measured morphine for the NNT before analgesia is achieved then it is probably about 1 in 3, but if I measured sedation as it’s end point then it might be closer to 1 in 30.
So with younger people being put on statins at an alarming rate (they are the highest selling group of drugs on the planet), the common question in my #CardiacSeminar and #RustyPills pharmacology refresher for Nurses and Paramedics is: “ what is the efficacy of #statin drugs ?”

Now the question is a poisonous chalice, and heavily loaded with misperceived  erroneous opinion about heart disease causes and inappropriate obsolete concepts of cholesterol and it’s evils.

Let’s set the record straight.

Fact: Cholesterol is made in your liver- it is not eaten.  Bacon and eggs for breakfast won’t raise your blood cholesterol like a Glass of fruit juice will raise your blood glucose.   The irony is that that same fruit juice is far far more likely to raise your cholesterol than a serve of pork belly with a butter glaze.... more on that later**.

Fact:  your liver is genetically programmed to produce cholesterol and a bunch of proteins (Lipoproteins) that transports the cholesterol around in your blood.  If you have familial high cholesterol (hypercholesterolaemia #scrabblewordoftheday), then nothing you eat will lower it.  Whether you have high cholesterol or not, your basal cholesterol level is preset genetically, and any attempt to reduce it will cause your liver to attempt to make more.  It does this even to the detriment of breaking down your muscle and fat stores to seek ingredients for your liver to to replenish what your body is programmed to make.

Fact:  Cholesterol is essential for three main functions.
1- it makes steroid hormones (oestrogen, progesterone, Testosterone, cortisol, and aldosterone)
2- it is the primary ingredient in bile which is used by the gut to emulsify fats in your diet preparing them for absorption in your small intestine.
3- and this is the Big one. Cholesterol is a chief ingredient in every (EVERY) cell in your body.  As surgery, injury, infection, trauma or wear and tear occurs in your body, those very cells need repair, so cholesterol is the bricks and mortar that the liver must make to fix you.  That is where lipoproteins like LDL and HDL come into play.   They transport cholesterol in the blood to the site of tissue repair. 

Think of your liver as Bunnings
Think of cholesterol as building materials
Think of low density lipoproteins (LDL) as the delivery trucks that transport the building supplies (cholesterol).

Fact:  if I had a blood vessel injury (coronary or cerebral as just one example), the walls of the blood vessel needs to be repaired.  Cholesterol production will be stimulated to facilitate this repair.  It often gets trapped and deposited in pockets of inflammation and over years and years of injury and reinjury, it’s accumulation develops the atheroma that you commonly call a plaque.   It is a cholesterol rich scar that is brittle and can rupture- stimulating a clot that becomes the blockage that is called a heart attack or stroke.

Phew!! 
Summarise: Cholesterol made not eaten, and used for really important things. It’s essential!

At the scene of every stroke or heart attack you will find cholesterol.

But ... at the scene of the building fire, you’re likely to find a firefighter.   The firefighter was there to help.  The fire fighter didn’t start the fire.
Cholesterol is there to repair injury, of course it’s there at the scene, but it didn’t cause the MI or stroke.
Ok... if you are still with us. 
NNT.

Statin drugs lower cholesterol - they are great at doing this job. So if cholesterol lowering is your end point, then they are the best we have.   But if they are being taken to reduce heart attack /stroke risk, is there enough efficacy to take them? 
Back to NNT.
If you believe, like some, that cholesterol causes the heart attack or stroke, then you will appreciate that cholesterol lowering statins might lower your risk of heart attack and stroke.

Do they? In short yes.  But enough? Well.... 
Well let’s look at the NNT data:
If you are under 50 these are the numbers for MI and CVA.

Preventing MI or stroke death 
Women - 1 in 5000 on statins will have their life saved.
Men - 1 in 1000 taking a statin will have their deaths avoided.
We must remember that the major decline of deaths from CHD occurred before the introduction of statins.

That said, most people with strokes and heart attacks don’t die first event.
So what about having a non-fatal heart attack or stroke?
Debilitating, but not deadly-
NNT for MI = 1 in 217.
NNT for CVA = 1 in 313

Can you see efficacy changes whether you are looking at death or non-fatal vessel events?  NNT also alters with age and previous history.

What remains is the balance between the costs and benefits of any medication you take.
Statins cause muscle pain (1:21 people on statins) and links to memory loss, impotence, early menopause and digestive upset... nothing fatal in that list, but lately a very sinister phenomenon has emerged in the literature with respect to statin induced type 2 diabetes.

These numbers are not small. 
0.5% or (1 in 200).

A one in 200 risk of getting diabetes (the #1 risk factor of Heart attack) taking a pill that give you a 1 in 217 chance of having a non fatal heart attack.... I’m going to leave that there for you to mull over.

If you are a woman under 50 
5000 of you need to take a statin for one death to be prevented.
But 250 if you will get diabetes while hoping you are that one.

In all things, if risks are less than benefits then that medicine might be a good idea, but if risks are higher- go for a walk, eat some salad, enjoy your bacon, reduce your stress and ponder a little before blindly believing what we were told about cholesterol in the 1980s.

Cholesterol didn’t cause your fire... why on earth would you try and lower it?  Target the real cause of vessel injury, not the scapegoat trying to repair damage.

By now you might be thinking that statins are not that great; but let me remind you that they are the best at doing what they were designed to do- lower cholesterol production in the liver.    They never claimed to lower heart attack rates.

Now.  What can you do to slash your risk.  

Cut Sugar!  Remember that fruit juice**

Fructose in sweets and juice is not metabolised to fuel, it is stored as fat.  Not just the jiggly, wobbly fat, but visceral organ coating fat.

Glucose is used as fuel, and in high amounts, makes blood viscous, and red blood cells sticky. So sticky and abrasive that high HbA1c values (red blood cell sugar) cause the  erosion and vessel damage that stimulates cholesterol production.
If the food you eat converts to quickly to glucose, it is damaging vessels.  Any excess is (like fructose) stored as fat .  But it’s causing vessel injury along that journey.

Im off for some avocado and salmon for lunch.  I might even sauté in butter.  Mmmmm butter.

Fat is your friend