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Too little oxygen is a common cause of serious, unstable patient status in the prehospital environment. There are two related low-oxygen conditions that are clinically important to the Emergency Medical Dispatcher (EMD): hypoxemia and hypoxia. In order to best understand them, one must know how they are related, the major causes, which symptoms they elicit, and which Key Questions the Medical Priority Dispatch System™ (MPDS® ) provides to identify patients in these states.
Hypoxemia is defined as a low level of oxygen in the blood, while hypoxia is a low level of oxygen in body tissues and organs.1 The two conditions are related; hypoxemia can lead to hypoxia when a low blood-oxygen level persists for too long.1
The main reason hypoxemia and hypoxia are so important in the prehospital setting is that many medical emergencies and deaths are linked directly to low oxygen levels in vital body organs—particularly the heart, brain, and lungs.1-7
A number of the Key Questions in the MPDS are there to identify low oxygen states. Indeed, if you review nearly any Chief Complaint Protocol in the MPDS, you will find Key Questions that query for symptoms of hypoxemia or hypoxia because their presence is of such importance. For trauma patients—those who have been injured—hypoxia is mostly due to severe bleeding or injury to the respiratory system (the lungs and airway), or in some cases, both. Either will deprive the heart and/or brain of the oxygen it needs to function normally.
For non-trauma patients, there are many causes of hypoxemia and hypoxia that are internal and physiologically complex and are, therefore, not always easy for an average emergency caller to recognize. However, the symptoms of severe hypoxemia and hypoxia can be uncovered by a well-trained EMD who follows Protocol and listens carefully to callers’ answers to Key Questions.
There are many underlying causes of hypoxia and hypoxemia, such as respiratory failure, respiratory distress, and reduced blood flow (hypoperfusion, also known as ischemia). These are often due to heart problems such as cardiac arrest, congestive heart failure, and obstruction of blood vessels by clots and emboli, as occurs in a heart attack, angina, or pulmonary embolism.1-7,9
Cerebral hypoxia—a low oxygen level in the brain—is a life-threatening emergency. Since the brain needs a constant supply of oxygen to function properly, even a short period of cerebral hypoxia can be life threatening. The most common symptoms of cerebral hypoxia are decreased level of consciousness; abnormal breathing; and blue, gray, or ashen skin (the latter is also a clear sign of hypoxemia).5,6
In addition to cerebral hypoxia, the heart can also become hypoxic from several causes, including heart attack, angina, heart failure, and respiratory distress.2,3,7,9
Using the MPDS
Let’s look at several non-trauma hypoxic conditions and how they are identified and managed by the MPDS.
Consider the case of a 72-year-old male who is awake but having difficulty breathing. How do we tell if his breathing problem may be causing hypoxemia and/or hypoxia, which would in turn make this patient higher in severity and require DELTA-level coding? The answers to the Key Questions on Protocol 6: Breathing Problems will give us that information. The Key Question “Is he responding normally (completely alert)?” indicates potential cerebral hypoxia when answers other than a clear yes are given. Key Questions “Is he changing color?” and “(Yes) Describe the color change” will give us the information needed to confirm low oxygen in the blood (hypoxemia) when that condition exists. This is because blood loses its bright red color as it loses oxygen, causing the patient’s skin to change color. “Is he clammy or having cold sweats?” may also be an indication of hypoxemia when answered yes, although it can also be a symptom of other serious conditions such as heart attack, allergic reaction, or sepsis (body-wide infection).8
Now, let’s take the case of a 56-year-old male with crushing chest pain who is conscious and breathing. Protocol 10: Chest Pain/Chest Discomfort (Non-Traumatic) queries for heart attack symptoms. In a heart attack, a blockage of one of the coronary arteries leads to less oxygen supplied to the heart muscle (myocardium), which in turn means the heart pumps less blood and oxygen to the brain. The Key Question “Is he responding normally (completely alert)?” will tell you if the patient has been affected by low oxygen to the brain, a sign of a severe condition. “Is he breathing normally?” will tell you if the lungs are attempting to compensate for the lack of oxygen to the heart by working harder, which is often manifested by rapid or labored breaths. Key Questions “Is he changing color?” and “Describe the color change” are, as mentioned before, looking for hypoxemia.
The same process of identifying hypoxemia and/or hypoxia using Key Questions exists on most other Protocols. Try this exercise on yourself: Pick any Chief Complaint in the MPDS, try to identify the Key Questions that will give you evidence of the presence of hypoxemia or hypoxia, and identify the corresponding Determinant Codes that go with that presence. Which Chief Complaint Protocols besides Breathing Problems and Chest Pain/Chest Discomfort (as already mentioned here) would hypoxemia and/or hypoxia be most common?
Something else worth noting: The on-scene ambulance crew has a noninvasive device that can measure the oxygen level of the blood called a pulse oximeter. Occasionally a caller or patient may have their own pulse oximeter and provide you with information about the patient’s blood oxygen level. However, these devices can be inaccurate if not used properly, so in general, we don’t currently use this reading by laypeople to determine hypoxemia. The best measure is still the answers to the relevant Key Questions, as discussed here.
Understanding low oxygen states can help you understand when and why the MPDS queries for these conditions. Obtaining clear caller answers to the relevant Key Questions whenever possible can identify more accurately some of the most severe and at-risk patients you will encounter as an EMD, lead to the optimal Determinant Coding, and provide the right information to determine which Dispatch Life Support (DLS) Instructions are needed.
Sources:
1. “Hypoxemia.” Cleveland Clinic. 2022; June 15. my.clevelandclinic.org/health/diseases/17727-hypoxemia (accessed Feb. 27, 2024).
2. “Ischemia; Hypoxia Shock.” London Health Sciences Centre. lhsc.on.ca/critical-care-trauma-centre/critical-care-trauma-centre-181#:~:text=Causes%20for%20hypoperfusion%20include%20low,)%20or%20%22mini%20stroke%22 (accessed March 21, 2024).
3. Ashorobi D, Ameer MA, Fernandez R. “Thrombosis.” NIH – National Library of Medicine. 2023; Aug. 8. ncbi.nlm.nih.gov/books/NBK538430/#:~:text=Thrombosis%20is%20a%20blood%20clot,location%20and%20acuity%20of%20thrombosis (accessed March 21, 2024).
4. Mayo Clinic Staff. “Pulmonary embolism.” Mayo Clinic. 2022; Dec. 1. mayoclinic.org/diseases-conditions/pulmonary-embolism/symptoms-causes/syc-20354647#:~:text=A%20pulmonary%20embolism%20is%20a,another%20part%20of%20the%20body (accessed March 28, 2024).
5. “Cerebral Hypoxia.” Cleveland Clinic. 2024; March 8. my.clevelandclinic.org/health/diseases/6025-cerebral-hypoxia (accessed March 1, 2024).
6. “Cerebral hypoxia.” MedlinePlus. NIH – National Library of Medicine. 2022; July 26. medlineplus.gov/ency/article/001435.htm#:~:text=Cerebral%20hypoxia%20occurs%20when%20there,brain%2C%20called%20the%20cerebral%20hemispheres (accessed March 22, 2024).
7. Ošt’ádal B, Kolář F. “Myocardial Hypoxia And Ischemia.” Springer Nature. Springer Science+Business Media New York. 1999. doi.org/10.1007/978-1-4757-3025-8_1 (accessed March 22, 2024).
8. “Skin - clammy.” Mount Sinai. mountsinai.org/health-library/symptoms/skin-clammy (accessed March 20, 2024).
9. Ojha N, Dhamoon AS. “Myocardial Infarction.” NIH – National Library of Medicine. 2023; Aug. 8. ncbi.nlm.nih.gov/books/NBK537076 (accessed March 22, 2024).
