Patient Care

Evaluating Temperature is Essential in the Prehospital Setting

Issue 11 and Volume 42.

Evaluating temperature is essential in the prehospital setting

The measurement of patient temperature is, and has been, throughout the history of modern medicine, one of the four core physiological measurements that we collectively call “vital signs.”

Over the past decade we’ve added the measurement of oxygen saturation (transcutaneous pulse oximetry, or SpO2) as the fifth vital sign and we hope that in the near future we’ll add end-tidal carbon dioxide (EtCO2) measurement as the sixth vital sign.

Our review and discussion in this article will concentrate on the renewed importance, implications and technical measurement of a patient’s body temperature, and explore how fever serves as an important and concerning finding.

What Is Temperature?

Temperature can best be defined as the temperature of the body when measured by either an infrared or conductive method. In terms of relating temperature to more meaningful physiological parameters, the parameter most closely aligned to temperature is basal metabolic rate (BMR).

BMR is essentially an estimate of how much oxygen we consume, and therefore the calories we burn, at any sustained activity level. The higher our BMR, the higher our temperature, and vice versa.

Since we routinely measure temperature at the skin surface, however, we have to take into consideration physiological responses to disease and injury, which can substantially influence skin perfusion and thereby the measured temperature.

It’s important for emergency personnel to be aware that a person’s normal body temperature may be vary anywhere from 0.5 degrees F to 1.0 degrees F according to the time of day and activity. (Table 1 indicates the normal body temperature mean and range for adult males and females.)

Although all vital signs are an important part of your toolbox when you conduct an objective patient assessment, measuring and understanding a patient’s temperature can provide you with important insight into the patient’s clinical picture. Normothermia, hyperthermia and even hypothermia are all extremely relevant factors in your assessment. In order to demonstrate this let’s review some simple scenarios.

Case #1

A 29-year-old female passes out in her office. There’s no significant medical or surgical history. In addition to the current new onset syncope, she complains of bilateral low back pain. She denies shortness of breath, but complains of dizziness for the past few hours. She reportedly “passed out” when she stood up after being seated at her desk for “a few hours.”

Exam findings: The patient’s height is 5’5″ and her weight is 145 lbs. Her blood pressure is 137/68 mmHg, heart rate is 96, and respiratory rate of 24 breaths per minute. Her SpO2 is 98% on room air and her EtCO2 is 32 mmHg. She has an oral temperature of 101.2 degrees F (38.4 degrees C).

Field diagnosis: You suspect impending septic shock of unknown origin, but probably due to a renal or urinary tract infection-a key precursor to septic shock.

The strong prognostic indicators here are a body temperature > 101 degrees F, heart rate > 90, and respiratory rate > 20. The secondary indicator is the EtCO2 < 35 mmHg.

In this case, with the early signs of septicemia, the patient is trying to compensate for the infectious process by increasing BMR and cardiac output, as well as a myriad of anti-infection factors, all thereby increasing CO2 production, which causes a compensatory increase in respiratory rate and a decrease in EtCO2.

Case #2

A 79-year-old female who lives with her daughter has an altered mental status and is lying in her bed, unresponsive, when she’s discovered by her daughter, who calls 9-1-1.

She has well-controlled hypertension but is otherwise healthy. Her daughter states that her mother has been coughing quite a bit over the past two days, but she has refused to go to her primary care physician.

Exam findings: The patient’s height is 5’2″ and her weight is 125 lbs. Her blood pressure is 147/86 mmHg, heart rate is 110 and respiratory rate is 28 breaths per minute. Her SpO2 is 90% on room air and EtCO2 is 32 mmHg. She has an oral temperature of 96.8 degrees F (36 degrees C). You immediately administer oxygen via nasal cannula at 2 L/min and her SpO2 rises to 97%; however, she remains unconscious.

Field Diagnosis: Impending septic shock of unknown origin, but a pulmonary infection is probably the source.

The strong prognostic indicators here are body temperature of < 97.7 degrees F, heart rate > 90, and respiratory rate > 20. The secondary indicator is the EtCO2 < 35 mmHg.

In this case, with the early signs of pulmonary septicemia with hypoxia, the patient is trying to compensate for the infectious process by increasing BMR and cardiac output, as well as a myriad of anti-infection factors, all thereby increasing CO2 production, which causes a compensatory increase in respiratory rate and a decrease in EtCO2.

Remember, however, that increases in the temperature of elderly patients are a late sign in septicemia. Often, as in this case, the patient will be hypothermic first, and they may or may not develop hyperthermia throughout the course of the illness.

Case #3

An 89-year-old male in a skilled nursing facility is found unresponsive to commands during morning rounds.

The patient has an extensive medical and surgical history, including hypertension, coronary heart disease, myocardial infarction, stroke, diabetes and chronic obstructive pulmonary disease (COPD).

Exam findings: The patient’s height is 5’10” and his weight is 160 lbs. His blood sugar is normal. His blood pressure is 189/98 mmHg, heart rate is 110, and his respiratory rate is 34 breaths per minute. His SpO2 is 85% on room air and his EtCO2 is 28 mmHg. He has an oral temperature of 101.2 degrees F (38.4 degrees C).

You immediately place him on 100% oxygen administered via non-rebreather mask and his SpO2 rises to 98%.

As you turn the patient to place him on your scoop stretcher, you notice a large decubitus ulcer on his sacrum.

Field diagnosis: Advanced septic shock of unknown origin, but the untreated decubitus ulcer is likely the source.

The strong prognostic indicators here are body temperature > 100.9 degrees F, heart rate > 90, and respiratory rate > 20. The secondary indicator is the EtCO2, which is < 35 mmHg.

In this case, with the late signs of intravenous septicemia with hypoxia, the patient is trying to compensate for the infectious process by increasing BMR and cardiac output, as well as a myriad of anti-infection factors, all increasing CO2 production, which causes a compensatory increase in respiratory rate and a decrease in EtCO2.

Complicating the field diagnosis here are his chronic hyperglycemia from his diabetes, with likely peripheral vascular disease, and his chronic hypoxemia from his COPD. These are relative distractors to his advanced underlying condition of septicemia, of which, as stated previously, increased temperature is a late physical indicator in the elderly.

Infrared tympanic measurement temperature monitors are relatively inexpensive, reliable, not overly intrusive and quick. Photo courtesy Mike Legeros

Kids Are Different

Although EMS may be called to the home of an ill child due to markedly elevated temperatures as high as 105-107 degrees F, providers are more likely to encounter patients with lower grade fevers (101-103 degrees F) and who have had a seizure. (Table 2 indicates the normal body temperature range for pediatric patients at various age ranges.)

Fever is commonly encountered in children, and more often represents a benign viral illness vs. more serious pathologies such as sepsis, meningitis or leukemia. Despite this, fever is a considerable source of stress for parents and providers who don’t frequently care for children.

There’s also considerable variability in the appearance of the febrile child. Some children can present with an ill appearance and lethargy with moderate temperatures, while others are playful and happy despite markedly elevated temperatures.

Further, fever can significantly impact other presenting vital signs, most notably the heart rate and respiratory rate, making strict criteria for sepsis difficult, especially knowing that these vital signs are already age and body habitus dependent.

There are, however, aspects of the febrile child that should warrant further evaluation in the prehospital setting and may impact your treatment and transport decisions.

There are a number of important points to consider. First, does the maximum temperature matter? In children who are both ill-appearing or well-appearing, a markedly elevated temperature gives most parents and providers some pause.

We know, however, that the ability to mount a fever response-our body’s way of fighting most infections-varies between individual children. Influenza, adenovirus and roseola are some of the more common causes of high fever in children.

With that in mind, most physicians will evaluate children with high-grade fever, especially those with hyperpyrexia, which is defined as > 106 degrees F.

A 2007 study conducted by researchers at the Texas Children’s Hospital found that hyperpyrexia occurs in approximately 1 of every 1,200 patients presenting to the ED. Somewhat surprisingly, it was noted that 18% of patients had a confirmed serious bacterial infection with positive cultures from the blood or urine.1

In evaluating the workup of these patients, the authors found no aspect of the physical exam (i.e., the presence of viral symptoms), or the laboratory evaluation (i.e., total white blood cell count, acute phase reactants) that allowed practitioners to distinguish between patients with bacterial or viral illnesses.1

They did note that a known viral illness (i.e., influenza) reduced the likelihood of bacterial co-infection.1 As a result, these patients will often receive empiric antibiotics, and, if ill-appearing, will likely be hospitalized.

A frequent reason for EMS requests for children are febrile seizures, or seizures in the setting of febrile illness where no prior seizure history exists.

Seizures in the setting of fever are common in children from six months to six years of age, with an incidence of approximately 2-5% in North America and Europe.

Simple febrile seizures, defined as a tonic- clonic (and previously referred to as “grand mal”) seizure that last < 15 minutes and doesn’t recur or rest in any deficit, are often disconcerting to parents and providers. These seizures are provoked by rapid elevations in temperature, and aren’t thought to be related to the height of fever (i.e., some children have febrile seizures at 102 degrees F, others at 105 degrees F).

A common misconception is that these seizures can be prevented by over-the-counter antipyretics, however numerous studies have shown that antipyretics don’t reduce the risk of febrile seizures.2 In other words, if they’re going to happen, they’re going to happen.

The evaluation of these children in the field consists of airway protection, oxygenation, evaluation for hypoglycemia and seizure control, if needed. In the ED, with a child who returns promptly to baseline and is an otherwise neurologically normal child, little diagnostic evaluation is needed beyond the search for an obvious source (e.g., otitis media, influenza or urinary tract infection).

Complex febrile seizures are those that last > 15 minutes, are focal in nature, present in status epilepticus, or result in a postictal deficit.

The presence of both simple and complex febrile seizures increases the risk of epilepsy (i.e., seizure disorder), but only marginally (from 0.5-1% to 1-2%).

Historically, emergency medicine providers have performed more detailed ED evaluations, including CT scans of the brain, blood work and diagnostic lumbar punctures (i.e., spinal taps), and many institutions still admit these children for electroencephalography and evaluation by a pediatric neurologist.

There is, however, evidence that the need for a lumbar puncture to evaluate for meningitis is unnecessary, especially in children who return to baseline in the ED. An article published in the Annals of Emergency Medicine in 2017 found that the incidence of bacterial or herpetic meningitis/encephalitis in more than 1 million children evaluated for complex febrile seizures, was the same as the rest of the population.3 This means that if the children aren’t meningitic appearing, they likely don’t have meningitis. Ill-appearing children and those in febrile status epilepticus continue to have more significant evaluations and are more frequently hospitalized.

The duration of fever is another common cause of concern, and there are numerous approaches to the child with prolonged fever. The problem is that there’s little agreement on how long is too long.

Once again, this obviously pertains to the well-appearing child. Perhaps most common in academic pediatric EDs is the initiation of a laboratory and radiologic workup in the setting of five days of documented fever > 100.4 degrees F.

Although viral illnesses are still by far the most common cause, you should begin to consider the possibilities of other issues including bacteremia (i.e., bacteria in the blood), pneumonia, urinary tract infections, leukemia and inflammatory disorders including Kawasaki disease.

Another common question is whether or not the absence of vaccines increases the risk for bacterial infections. Let’s be super clear about this: All vaccines reduce the risk of serious and invasive bacterial or viral infections.

A 2015 evaluation of the 13-valent pneumococcal conjugate vaccine, which covers 13 different strains of the bacterial Streptococcus pneumoniae, dramatically reduced the incidence of invasive pneumococcal disease (e.g., meningitis, bacteremia, pneumonia). In children, rates of reduction varied from 64-93% compared to the prior period where only seven types of pneumococcal strains were covered, and in adults, the decline was 12-72%.4,5

There are a select few groups of children for whom the presence of fever suggests the need for urgent evaluation, though the need for emergent prehospital care is likely limited. Patients under two months of age, those with cancer and certain blood disorders, such as sickle cell disease, and those with complex medical needs are at higher risk for serious bacterial infections, and require urgent evaluation in the ED.

Patients may utilize EMS for transport, though interventions are rarely needed. Certainly, fever in the setting of evidence of shock (i.e., end-organ hypoperfusion) should increase our concern for sepsis, and fluid resuscitation (20 mL/kg), blood sugar evaluation and oxygen administration should be considered.

Ultimately, fever should be considered in the context of the bigger clinical picture and, in isolation, may have less relevance in children compared to adults, at least in the prehospital setting.

Measuring Temperature

As eluded to earlier, there are distinct variations in a patient’s measured temperature, depending on where and how the temperature is measured. The ideal measurement of temperature in the human body is to measure the body’s core temperature.

In the operating room with an anesthetized patient, this is ideally measured with an esophageal probe; however, this isn’t practical in the field. Rectal temperature measurements are also very close to core temperature but again, aren’t practical in the field.

This leaves us with four possible modalities: 1) electronic sublingual and/or rectal; 2) temporal artery scan; 3) distant infrared scan; and 4) infrared tympanic measurement. (See Table 3)

Relatively inexpensive and common, electronic thermometers with disposable probes for sublingual or rectal use are very reliable for field use, especially during transport.

Temporal artery scan thermometers can be substantially influenced and invalidated by sweat and/or moisture, so they’re not reliable for field use, especially with a diaphoretic patient.

Distant infrared scan thermometers are very inexpensive, and completely noninvasive, but only measure the temperature at the skin surface, which can be substantially lowered in many physiological and environmental conditions, making it less than desirable for diagnostic purposes.

Out of the four technologies, the two which come closest to accurately measuring the patient’s core temperature, are the high-quality electronic oral thermometers described earlier and infrared tympanic measurement temperature monitors, which are relatively inexpensive, reliable, not overly intrusive and efficient.


The intent of this article is to present important and often neglected facts to EMS providers, educators, medical directors and managers.

First, we’re only as good clinically as the data we acquire and the way we piece it together and recognize deviations and combinations that can be dangerous to our patients.

Second, temperature is an important vital sign. Although this is recognized throughout EMS textbooks and medicine it has been passed over too often by EMS agencies throughout the past several years.

If we’re going to be successful in treating and transporting our patients to a higher level of care, we must be diligent in acquiring and recording all of the data possible.

The initial presentation of a patient can determine how that patient will be managed until definitive diagnostic procedures can be performed and the additional data analyzed. In conjunction with blood pressure, heart rate, respirations and oxygen saturation, temperature completes the clinical picture of our patient in the field, and its role and importance can’t be underestimated.


1. Trautner BW, Caviness AC, Gerlacher GR, et al. Prospective evaluation of the risk of serious bacterial infection in children who present to the emergency department with hyperpyrexia (temperature of 106 degrees F or higher). Pediatrics. 2006;118(1):34-40.

2. Offringa M, Newton R, Gozijnsen MA, et al. Prophylactic drug management for febrile seizures in children. Cochrane Database Syst Rev. 2017;2:CD003031.

3. Geudj R, Chappuy H, Titomanlio L, et al. Do all children who present with a complex febrile seizure need a lumbar puncture? Ann Emerg Med. 2017;70(1):52-62.

4. Moore MR, Link-Gelles R, Schaffner W, et al. Impact of 13-valent pneumococcal conjugate vaccine used in children on invasive pneumococcal disease in children and adults in the United States: Analysis of multisite, population-based surveillance. Lancet Infect Dis. 2015;15(3):301-309.

5. Leibovitz E, Nuphar D, Ribizky-Eisner D, et al. The epidemiologic, microbiologic and clinical picture of bacteremia among febrile infants and young children managed as outpatients at the emergency room, before and after initiation of the routine anti-pneumococcal immunization. Int J Environ Res Public Health. 2016;13(7):723.