Differential Dx: Tachypnea Part 1

In the wide world of EMS calls we encounter a lot. The intent of this posting will be to differentiate and treat patient's with rapid respirations appropriately. This doesn't sound like a hard thing to do, but why not make it easier? If we treat the wrong patient the wrong way, we are effectively doing nothing to improve the patient's outcome.

As you read through these blog posts, you will notice quotes, videos, links, and research abstracts. This is just a way to let you know that the information is factual and not based on my own anecdotal evidence. It is my intention to spread the practice of evidence-based medicine amongst the world of prehospital clinicians. So lets get started...

You are dispatched to a 17 year old female complaining of difficulty breathing. Upon arrival you find a conscious patient with respirations at about 40 per minute. No audible wheezing or stridor. What do you do next?

This is a very frequent call type. A few things that stand out are the patient's young age and sex. This age coupled with the female gender may alert many that this could be something stress induced. This demographic is highly sensitive to relationship-induced stress. This is not a conclusive finding however, and we should always consider the worst. This patient also fits into a category of patient's that may take birth control. If she is on birth control and is a smoker, than she would be at increased risk of developing a pulmonary embolism.

To create a differential diagnosis, and treat this patient effectively, we need a clear understanding of what conditions may be causing her signs and symptoms. With this we can develop an adequate assessment to figure out what exactly is going on.

Causes of rapid respirations: there are tons but I'm going to list the most common
source: wrongdiagnosis.com, In a page: Signs & Symptoms, 2004
  • Cardiovascular etiologies (pulmonary embolism, CHF, AMI, HTN)
  • Pulmonary etiologies (COPD, asthma, pneumothorax, restrictive lung disease)
  • Metabolic/Toxicologic etiologies (DKA, dehydration, salicylate toxicity, acidosis)
  • Neurologic etiologies (CVA, head trauma)
  • Anxiety/Hyperventilation (panic attack)
  • Sepsis
  • Hyperthyroidism
  • Medications/Drugs

I like to place these patients in two, very basic categories:

Patient's that need O2
Patient's that need CO2

Now, I know that we don't give patient's CO2. That isn't what I am implying. Instead, I am referring to the body's physiological need to maintain a PH balance. CO2 is an essential ingredient to maintain homeostasis. I'll explain:

The image above describes where certain elements lie on the PH scale. It also explains that the lower the number, below 7, the more acidic something is. The higher the number, above 7, the more alkaline (basic) something is. Don't ask why the higher numbers are always on the bottom, maybe because that is considered the base, I dunno.

Normal PH for human blood is around 7.4. The common range used is 7.35 to 7.45.

Not on there is oxygen & carbon dioxide. It is important to know that
CO2 is acidic, and O2 is alkaline.

The healthy body will react according to the PH(depending on the amount) of what enters the body. The body uses it's metabolic and respiratory systems to assist in maintaing a normal acid-bas balance. Consequently, respiratory alkalosis will not appropriately fix metabolic acidosis, and visa versa; even though the body will sometimes try to attempt this type of regulation, it's a feeble attempt.

CO2 + H2O → H2CO3 → H+ + HCO3

When CO2 is disolved in water(H2O), carbonic acid (H2CO3) is formed. This prcoess is regulated by the respiratory and metabolic systems. Bicarobonate(HCO3-) and hydrogen (H+) can cause this effect in reverse. Take a look at this image.

It's not going to be the end of your career or anything if you don't memorize the equation. It is important, however, to remember that CO2 is a vital ingrediant to maintain homeostasis. This image describes how the buffering system works. The most basic thing we usually remember is that O2 is used by the body and CO2 is the waste product. Well, the hyperventilating patient teaches us something else. Some of that CO2 is needed!!

We have all seen the paper bag breathers. These people are attempting to rebreath their expired CO2 to self-regulate their CO2 level. This sounds like a good treatment and may even work.

In Part 2 I will describe why this isn't the best course of action. I will also give a detailed description of hyperventilation syndrome and how to develop a differential diagnosis.

If you have any questions or find something incorrect with the information I provide, please let me know.

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