The Capped Bicarbonate Volcano
Let’s talk about baking soda, we use it to clean laundry, brush our teeth, and absorb those odd and unpleasant smells coming from the fridge after that last piece of lasagna gets forgotten in the back. Baking soda, is at a chemical level a solid constitute of NaHC03, Sodium Bicarbonate. If you asked any street wise medic from the 90’s, this would be one the drugs routinely used in cardiac arrest and part of the “coma cocktail” alongside dextrose and naloxone (for a feather-ruffling look at narcan, read Sam’s blog “Stop Using Narcan!”).
But, as clinicians interested in best practice, not common practice, lets look at how bicarb works physiologically, and how appropriate or inappropriate this alkaline solution is in the pre-hospital setting.
Sodium bicarbonate, at the physiological level, is naturally produced in our body as a regulatory anion that functions to control pH, because of its metabolic effects on carbon dioxide in the body. These functions make it one of the most important and first line features of the sodium bicarbonate buffer system.
Like EVERYTHING else in our bodies, we need balance, and we need equilibrium. In order for appropriate cellular respiration to occur, our body has a specific pH range that it has to meet (a narrow 7.35-7.45). Outside of this balance, whether the body is in acidosis or alkalosis, cellular respiration is inhibited as proteins and enzymes become denatured and fail to function properly.
Sodium bicarbonate is an important “kid” on the “see-saw” of our acid-base balance. Chemoreceptors, both central (medulla oblongata), and peripheral (within the arterio-venous endothelium) function to detect major pH deviations. If a deviation is detected, the body will begin the process of returning the body to its regular balance by use of the buffer system. The medulla oblongota will then signal two major systems in our body to begin their work in maintaining this system, the respiratory system and the renal system. Bicarb is a part of the renal response to correct a pH deviation. Let’s look at this see-saw and how it functions.
So, this buffer system is going to function in both directions, completing one cycle.
Looking back at the see-saw, lets say there is an increase in carbon dioxide from inhibited respiration. As carbon dioxide fails to be removed from the blood plasma, it will begin to bond with water and form carbonic acid. Carbonic acid as a weak acid will not maintain form and will immediately look for a way to break down. While not a perfect example, imagine those vinegar/baking soda volcanos you made in school. Now picture placing a cap on the top of the volcano, preventing it to off gas.
As this carbonic acid shifts to the right, it will be broken down into a hydrogen ion and bicarbonate. And what does an increase in hydrogen ions cause...ding ding ding, acidosis. The central nervous system immediately detects this increase in hydrogen ions and causes the renal system to react, stimulating the release of bicarbonate, this excess bicarbonate will begin a shift of this buffer system back to the left, bonding with hydrogen ions to create carbonic acid. But remember! Carbonic acid is not stable, its going to continue to cycle to the left, breaking down into water and carbon dioxide.
We know as clinicians that there are four different types of alkalosis and acidosis, respiratory and metabolic. The above example was the response of the body as a result of respiratory acidosis. Inhibited respiration resulted in increased plasma carbon dioxide causing the buffer system to cycle to the right!
So now, following our physiology lesson, lets look at the use of sodium bicarbonate in the field. When is it indicated? When is it truly beneficial?
Let’s think about a cardiac arrest patient. This patient enters a possible non-perfusing rhythm secondary to long term ischemia from an arterial occlusion. For the time that this patient is down with no pulse and not breathing, no oxygen is being taken in, nor carbon dioxide being removed from the body. Furthermore, cells enter anabolic respiration, further increasing the serum carbon dioxide. Carbon dioxide begins to bond with water, shifting this buffer system to the right in an attempt to combat this excess carbon dioxide. The unstable carbonic acid formed as a result is broken down into hydrogen ions and bicarbonate, your patient is now acidotic. Is this the time to give bicarbonate? No! We know this. It is not a metabolic issue, its a respiratory one! This patient needs quality CPR and optimal ventilations to restore proper cellular respiration and remove that carbon dioxide.
Let’s imagine that you do give this cardiac arrest patient sodium bicarbonate. The blood is flooded by the bicarbonate, binding with those free flowing hydrogen ions. We know this is gonna force the buffer system to the left. The end result? A high serum carbon dioxide. But this patient isn’t getting adequate respiration. He’s in cardiac arrest. You’re now left with high concentrations of carbon dioxide with will force it to the right. It will break down again leaving you with more hydrogen ions than before you administered the bicarbonate. your patient is more acidotic than before.
The first rule of bicarbonate administration. These patients need patent airways! They need to be able to remove the carbon dioxide resulting from the left shifting buffer system from excess bicarbonate. DON'T CAP THE VOLCANO! LET THAT SUCKA BREATHE!
In the case of someone who has experienced profound fluid loss, such as from extended instances of diarrhea following infectious disease process within the GI. These patients can experience a profound loss of bicarbonate, reducing their ability to combat acidity within the blood (this fluid loss can also result, eventually, in rising lactic acid levels). They also experience copious losses of sodium and chloride. if both cation and anion are traveling in their same direction this results in non anion gap metabolic acidosis. These patients need balanced fluid therapy to restore their acid-base balance. Restoration of normal fluid balance will allow the kidneys to begin normal function within the distal tubules to properly regulate bicarbonate retention. Josh Farkas did an excellent post on choosing the correct fluid/bicarb ratio in respect to the recent BICAR-ICU study. Sam Ireland also made a fantastic chart to help guide you through gap or non-gapped MA.
In the pre-hospital setting, sodium bicarbonate is a valuable drug, but it is a drug of limited efficacy and particular therapeutic index. Remember these rules. If it is a respiratory acidosis, manage their airway! (No giving codes bicarbonate because “they’ve been down for a while”) Will this patient benefit from strictly bicarbonate? Or is their an underlying process that needs to be treated. As with any patient, procedure, or medication; use good judgment, critical thinking, and stay educated.
Stay balanced everyone!
Jay Nance (@j_dakotes) is currently a paramedic student in North Carolina. Avid digester of FOAMed, medical journals, and dedicated to absorbing as much information as possible. This is his first time blogging for FOAMfrat, and we look forward to hearing from him more in the future!