By David Jaslow
All firefighters and emergency responders performing heavy physical workloads for prolonged periods will manifest some degree of heat stress even if the ambient temperature is cold, assuming that proper PPE is being worn. Heat stress is linked to core body temperature. The greater the degree of heat stress, the more likely it is that body temperature rises. So the measurement or estimation of core body temperature is often cited as one of the basic tenets of firefighter rehabilitation and medical monitoring.
There are several questions often posed in relationship to core body temperature monitoring in the rehab sector:
1) Is it necessary?
2) If so, what is the most reliable method to obtain core body temperature?
3) How do I continuously monitor core body temperature?
4) What is the magic value at which core body temperature elevation (or depression in the case of hypothermia) becomes a problem?
5) Is the phenomenon of core body temperature measurement one in which a single point value becomes the trigger point for action or is a sustained threshold more important?
Since the answers to these questions are usually elusive or not well elucidated, it has been our experience that core body temperature measurement is not usually performed in the rehab sector. Luckily, it is probably not absolutely necessary unless this is a practice that is part of your SOP, it is done correctly and there are defined and medically approved policies about how to act on abnormal values. Let’s review answers to the four basic questions above.
The reason that core body temperature measurement is not absolutely necessary in the rehab sector is that in most cases there is a defined relationship between pulse and temperature, in which both rise in parallel. Clearly, persons who take cardiovascular medications that are designed to block elevations in heart rate (calcium channel blockers, beta blockers, etc.) may not manifest tachycardias in the 140 range, but most will have some degree of elevation. Therefore, we can draw the conclusion that it is very unlikely that a firefighter who has a serious elevation of core body temperature will be missed solely because there was no direct temperature measurement. Pulse measurement becomes a substitute — if heart rate fails to fall, one reason may be inadequate mitigation of heat stress.
Another reason why temperature acquisition is not critical is that the actual value is rarely medically important during routine emergency operations. However, clearly special operations teams and those on long duration incidents may want to screen for signs of infectious illness prior to deployment on a mission. But non-wildland firefighters and those acclimatized to their environment do not get heat stroke accompanied by life-threatening elevations in temperature during standard operations.
They do occasionally suffer from heat exhaustion, which may cause slight elevations in core body temperature that rapidly improve with hydration, removal of PPE and other standard rehab procedures. In these cases, the exact body temperature is irrelevant because the temperature itself is a result of the physiologic process of heat production and not the cause. Hypothermia is a different issue altogether, although there are few if any case reports of firefighters becoming hypothermic due to sub-freezing ambient temperatures while performing operations that last less than one work cycle.
Another reason that core body temperature is rarely obtained in most rehab sectors is that the most commonly available methods to perform this task are also the least reliable
- Oral temperatures will be inaccurate if taken shortly after firefighters drink cool or warm liquids or smoke cigarettes since all three can affect thermometer readings.
- Tympanic thermometers are notoriously unreliable if the reading is lower than normal.
- The ears are most likely to be warmer than normal after exiting a fire if the hood is not worn properly or not warn at all.
By definition, the only two methods to truly obtain core body temperature are rectal and esophageal probe. Rectal probes, the most accurate method to measure core body temperature, will never find their way onto the fireground. Esophageal probes are currently in the research and development phase and they represent the only method to continuously measure core body temperature. Disposable skin thermometers that can be placed on the forehead are not accurate.
Ultimately, temperature measurement should be trended if it is done at all. Let's assume that we will never see a critically low or high temperature in the rehab sector (otherwise, that person belongs in the treatment sector receiving resuscitation) or that a minor fluctuation in body temperature equates to automatic hospital transport. The key is not that a firefighter's core body temperature is one or two degrees above normal at a given point in time, but whether it rapidly returns to normal with appropriate interventions discussed at length in this series. Until the time arrives when firefighters swallow esophageal probes that not only pinpoint their exact location but continuously report temperature, it is unlikely that most rehab sector officers are in a position to mandate trending of core body temperature.
One of the goals of the rehab sector is to identify these individuals who are at greater risk of cardiovascular and cerebrovascular emergency before that event happens. Emergency responders are primarily men and many in this country develop hypertension before they are 40. Aside from heart rate, the other critical “traditional” vital sign that must be measured in the rehab sector is blood pressure. There are two primary reasons to measure BP:
1) Detection of those emergency responders who have pre-existing hypertension and who have developed what is commonly known as hypertensive urgency
2) Discover those emergency responders who have essential hypertension (or some other cause for high blood pressure) who are unaware that they have this condition.
The National Heart, Lung and Blood Institute defines Stage I hypertension as a systolic BP of 140-159 and a diastolic blood pressure of 90-99. Stage II hypertension is defined as a systolic BP greater than 160 and a diastolic BP greater than 100. Both categories assume that BP measurements are taken properly and in patients who are not on any antihypertensive medications.
Hypertensive urgency is defined as severe elevation of blood pressure without evidence of target organ dysfunction (damage to heart, brain, kidney, etc.) This is the typical situation when paramedics or emergency physicians see a patient with a BP of 180/120 who does not appear to have symptoms and say to themselves, "Wow! That's high. That patient needs medication."
The difficult question to answer is who requires transport to an ED just because their BP is elevated.
Interestingly, there is no exact "panic value" for blood pressure in which emergency medical treatment (in terms of immediate blood pressure lowering) is mandatory, although there are ranges that most physicians act upon. Generally speaking, no patient with a new onset systolic BP greater than 180 or a diastolic BP greater than 120 will be sent out of an ED without either confirming that he/she can be seen by their primary physician within 48 hours or the patient is started on medication prior to discharge.
Similarly, there is no "panic value" for low blood pressure, although most texts define hypotension as a systolic BP < 90 or a diastolic BP < 60. EMS personnel and rehab officers should bear in mind that healthy females, especially those who are of short stature and low body weight, typically have normal blood pressures that run less than 100 systolic. Any responder thought to be truly hypotensive becomes a patient and should be transported to an ED for evaluation and treatment.
The difficult question to answer is who requires transport to an ED just because their BP is elevated. Is there a simple protocol that can be designed to instruct EMS personnel what actions to take based upon abnormal BP readings? The answers to both questions are that there is no EMS literature yet looking at outcomes of firefighters with elevated BP in the rehab sector nor is there much literature on any aspect of the firefighter rehabilitation process. It is not even clear whether emergency responders whose blood pressure does not return to a normal range after sufficient rest and rehydration definitely have pre-existing hypertension. However, I operate under this principle because it is conservative and in the best interest of the responders to have follow-up whenever the possibility of new onset hypertension exists.
Another factor which complicates the evaluation of emergency responders' blood pressure in the rehab sector is that personnel may be taking anti-hypertensive medications but may still be hypertensive for a variety of reasons. Perhaps they missed a dose of medication. They may have been inadequately controlled on the current dose of their medication or require additional drugs. Current recommendations are that most people will require two medications to achieve good blood pressure control. Departments which do not mandate annual fitness for duty exams or follow NFPA 1582 requirements are more likely to find that their personnel are hypertensive in the rehab sector.
I use the algorithm that follows to drive decision-making about how to handle hypertension in the rehab sector. What is most important to recognize is that blood pressure (as well as the other vital signs) should not be taken immediately as firefighters who have just performed heavy manual labor enter the rehab sector because the values will all be abnormal. All this reflects is the adrenaline surge and physical exertion that has just occurred. The issue is not who is hypertensive coming into rehab, it is who is hypertensive when he/she is otherwise ready to exit rehab. It is this group in whom heat stress has been attenuated that is most likely hypertensive at baseline or acutely ill from some other cause even if they have no symptoms. Anybody who is hypertensive and has symptoms of acute illness becomes a patient and should be transported to an ED.
- BP < 140 systolic and < 90 diastolic meet criteria for discharge
- BP 140-60 systolic and 90-100 diastolic are discharged but told to follow-up with their physician for repeat BP measurement
- BP > 160 but < 180 systolic and BP > 100 but < 120 diastolic are placed on light duty and removed from active operations on the fireground. They must bring a fitness for duty note from their primary physician stating that the BP has been addressed prior to returning to duty
- BP > 180 systolic or > 120 diastolic requires transport to the ED for evaluation
The bottom line concerning hypertension in the rehab sector is that there are no clear cut guidelines available for how to handle returning firefighters to the manpower pool versus taking them out of active duty purely for asymptomatic elevations in blood pressure. I urge you to think about the consequences of potential hypertensive crisis that may develop in someone who is found to have hypertensive urgency in rehab that is not acted upon. We should all practice preventive medicine!
Previous articles in this series:
Fireground Medical Screening Exam – Part 1
Fireground Medical Screening Exam – Part 2
Fireground Medical Screening Exam – Part 3
Fireground Medical Screening Exam – Part 4
Fireground Medical Screening Exam – Part 5
Fireground Medical Screening Exam – Part 6
David Jaslow, MD, MPH, FAAEM is a board certified emergency physician who is fellowship trained in EMS and disaster medicine. He is the director of the Division of EMS and Disaster Medicine within the Department of Emergency Medicine at Albert Einstein Medical Center in Philadelphia. Dr. Jaslow is a state-certified Firefighter I and he is credentialed by the Pennsylvania Department of Health as a pre-hospital physician. He functions as a chief officer in several suburban Philadelphia fire and EMS agencies and provides medical oversight as the lead physician for the Bucks County Technical Rescue Task Force as well as Pa. Task Force-1 Urban Search and Rescue.