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The Vital Signs, Part 3: Respiratory Rate, Temperature and Beyond
Vital signs give EMS providers insight to what's going on inside our patients and let us evaluate their responses to our interventions. This multipart series takes a fresh look at these vital signs and what they actually tell us in terms of changing our prehospital treatment, predicting the severity of presenting problems and even predicting survival.
RESPIRATION (RATE AND DEPTH)
In one way, respiratory rate is similar to pulse: It's measured by simply counting, yet studies indicate that even professionals often measure it wrong. A study comparing the counting of respirations by ED triage nurses and electronic devices at a teaching hospital in New York City concluded that neither were accurate for detecting abnormal respiratory rates of less than 12 breaths per minute (bradypnea) or greater than 20 breaths per minute (tachypnea).1 The importance of respiratory rates was brought into question by a study finding that respiratory rate measurements correlated poorly with oxygen saturation measurements and did not screen reliably for desaturation. Patients with low SaO2 did not usually exhibit increased respiratory rates. Similarly, increased respiratory rates were unlikely to reflect desaturation. Overall, only 33% of subjects with oxygen saturations below 90% exhibited increased respiratory rates.2 With regard to pediatric patients, a study found that in babies under six months old, respiratory rates counted using a stethoscope were 20%–50% higher than those counted from the patient's bedside by observation only. The authors theorized that bedside observers were counting only respirations that moved large amounts of air.3 The review also called into question the value of the respiratory rate as a vital sign.
There are a few notable respiratory patterns that providers may have heard of. Most are associated with specific disorders or syndromes, and they can be useful in determining extent of injury in coma patients. They include Kussmaul's, Cheyne-Stokes, central neurogenic hyperventilation, Biot's (ataxic) and apneustic breathing patterns.
TEMPERATURE
While temperature is commonly referred to as the fourth vital sign and recorded on call sheets, there is little research to support its importance to EMS personnel or the need for expensive temperature-recording equipment. One study conducted in a Zambian hospital evaluated the ability of mothers and medical students to detect fever in children using only touch. Both groups were highly accurate, comparable to a mercury thermometer.4 Skin temperature is documented as cool, normal or warm, and on some forms cold and hot.
PAIN
Pain as the "fifth vital sign" was an idea introduced in 1995 by the American Pain Society. American hospitals are now obligated to assess pain in their patients. EMS has started to address this symptom with prehospital pain management research and protocols, especially for burns and extremity fractures.
As with the previous vital signs, there are problems with identifying and treating this fifth one. Significant disparity exists between paramedics' perceptions of acute pain assessment and frequency of providing analgesia and their actual practice. Children and adolescents have less documentation of pain assessment and receive fewer analgesic interventions compared with adults. Inability to assess pain may be an important barrier to providing analgesia.5 Few pediatric patients receive prehospital analgesia, although most ultimately get it in EDs.6 Research and education must be done to allay fears about side effects. Prehospital pain management is an important QA/QI/call review topic for agencies.
APGAR
Virginia Apgar, a physician and anesthesiologist, developed the Apgar scoring system in 1952 to evaluate a newborn's condition at birth. The Apgar score is performed at one and five minutes of life. Newborn infants are evaluated based on five variables: appearance (color), pulse (heart rate), grimace (reflex irritability), activity (muscle tone) and respiratory effort. A numerical score of 0–2 is assigned in each category. The maximum score is therefore 10, with higher numbers being better. Authors have noted that great variability exists in how individual healthcare providers score the assessment.
One study compared the consistency (interrater reliability) of Apgar scoring among various healthcare disciplines. In this study, groups of providers were visually shown case presentations involving infants, then asked to assign them Apgar scores. Pediatricians and pediatric house staff had a consistency rating of 68%. Obstetricians and obstetric house staff had a consistency rating of 46%. Intensive care nursery staff had a consistency score of 42%, obstetric nurses 36%, and community hospital nurses 24%. The authors concluded that improper scoring limits the usefulness of the Apgar calculation in comparing neonates within and between hospitals.7
Another study evaluated the consistency against each other of two healthcare providers assigning scores. In this study, the consistency of scores ranged from 55% to 82%, with heart rate showing the best rate (82% for the one-minute scores). For five-minute scores, consistency ranged from 36% to 100%, with heart rate again the most consistent. Heart rate measures likely have greater consistency due to the ease of understanding and defining exactly what is being assessed, while things like appearance and activity are subjective. Between full-term and premature newborns, providers were found to have better consistency when assessing full-termers.8
CAPILLARY REFILL
Capillary refill was first advocated as a parameter for grading shock in 1947.9 That article is from a collection of data from the experiences of the Army medical services in North Africa during WWII. They correlated normal, definite slowing and very sluggish capillary refill with no, slight-to-moderate and severe shock in wounded military personnel. No values for capillary refill were included in this report; however, major texts and reference materials state that the normal value for capillary refill is less than two seconds. This number is included in trauma scores and the Basic and Advanced Trauma Life Support courses. It has since been determined that the two-second figure was an arbitrary number put forward by a nurse, with absolutely no experimentation or attempts to validate it. A study in 1988 determined that a refill time of one second was appropriate for all children and adult males, while 2.9 seconds was appropriate for adult females and 4.5 seconds for the elderly.10
The trauma score was revised in 1989, and capillary refill was excluded because it was difficult to assess at night. A follow-up study of voluntary blood donors conducted by the same authors in 1991 found that for this group, mean capillary refill time was 1.4 seconds before donation and 1.1 seconds after. It concluded that capillary refill does not appear to be a useful test for detecting mild-to-moderate hypovolemia in adults—it's about as useful as a coin toss.11
Capillary refill was removed as an indicator of shock in adults, but remains one in pediatrics. A 2005 study concluded that capillary refill is an unreliable indicator of cardiovascular status in term neonates, and that capillary refill time varies considerably with age, ambient and skin temperature, anatomical site of measurement, and duration of pressure.12 A 2004 study of almost 5,000 children at a pediatric emergency room found that prolonged capillary refill time is a poor predictor of the need for IV fluid bolus or hospital admission.13 While not specifically addressing capillary refill, a 2006 study concluded that ATLS guidelines may not always be appropriate for the fluid resuscitation management of pediatric trauma.14 Adding more confusion was a study from late 2006 introducing a technique known as digital videography capillary refill, which proved more accurate in detecting dehydration in children in an emergency room setting than the entire clinical exam by a pediatric emergency physician!15
Again, this clinical sign is not an absolute, and while it's no longer taught as an indicator of hypovolemia in adults, its value in the pediatric population must be further scrutinized.
NEW VITAL SIGNS
PULSE OXIMETRY
Pulse oximetry noninvasively measures the arterial oxygen saturation of hemoglobin. Pulse oximeters were used in special care units in hospitals for years before being introduced to the prehospital arena. In assessing whether pulse oximetry is a vital sign, we must ask if care changes based on knowledge of this value. Studies have shown it to be important in emergency departments, influencing decisions to increase or decrease oxygenation and order chest radiographs or additional studies. Prehospital, one study found that respiratory rate measurements correlated poorly with oxygen saturation measurements and did not screen reliably for desaturation. Patients with low oxygen saturations did not usually exhibit the increased respiratory rates that might be expected. Increased respiratory rate was also unlikely to reflect desaturation. Paramedics were more likely to appropriately base oxygen therapy on oximetry measurements than were EMT-Bs, and both groups failed to decrease supplemental oxygen with patients in EMS systems with highly explicit protocols for considering oximetry to guide oxygen therapy.
The results further suggested that pulse oximetry could be used to prevent unnecessary oxygen therapy on a significant number of patients transported by EMS who are already well saturated on room air. In addition, pulse oximetry information caused EMTs to request ALS dispatch in 11 cases, cancel previously dispatched ALS responses in eight cases, and not to request ALS responses from the scene when they otherwise would have in 16 cases.16 East Carolina University's Lawrence Brown found in a study of 180 patients transported by EMS without pulse oximeters that 30 (16%) had hypoxemia (saturation less than 95%). Only 3 of those 30 had interventions to combat it. Twenty-four of those 27 others did not complain of respiratory distress. Thus, there are patients whose hypoxemia is unrecognized by EMS providers, and this occurs most frequently in patients who do not complain of respiratory distress.17
In another study, EMS attendants recognized hypoxemia without a pulse oximeter only 28% of the time.18 A study of pediatric asthmatics concluded that the initial oxygen saturation of wheezing children presenting to an emergency room predicted their need for hospitalization.19
COMA SCORE
EMS providers are familiar with the Glasgow Coma Scale. Recent studies have evaluated the GCS and postulated its potential as a vital sign. One concluded that the GCS score was the only prehospital physiologic parameter that was different between patients admitted to hospitals and discharged home.20 A change from field GCS to ER-arrival GCS is highly predictive of outcome.21 Several studies suggested the GCS motor score was the most important value, and equally indicative of the patient's severity as the entire score.22–24
Based on these findings, a relatively new tool has been developed called the Simplified Motor Score. With this tool, "obeys commands" counts for 2 points, "localizes pain" for 1, and a "withdrawal to pain or less" response is 0. This simplifies the GCS into its most valid component for predicting extent of injury, and the SMS has already been validated as comparable to the total GCS and GCS motor scores for these predictions.25 While the SMS will have to be validated in larger studies, the authors of this first study have already called for replacing the GCS with the SMS.
CAPNOGRAPHY
Capnography is the monitoring of respiratory carbon dioxide concentration as a time-concentration curve. It is a direct monitor of the inhaled and exhaled concentration of CO2, and an indirect monitor of the CO2 concentration in a patient's blood. End-tidal CO2 levels fall abruptly at the onset of cardiac arrest, increase with effective CPR and return to normal at return of spontaneous circulation. During effective CPR, EtCO2 has been shown to correlate with cardiac output, coronary perfusion pressure, efficacy of cardiac compressions, ROSC and even survival.26 Colorimetric detectors (shown to correlate with infrared capnometry) have demonstrated prognostic value in both adult and pediatric CPR. The higher the initial value of EtCO2, the greater short-term survival was. EtCO2 is a useful tool during resuscitation for evaluating the current and potential effects of treatment, and potentially could be useful in determining when to terminate resuscitation efforts.
Beyond its use in cardiac arrest, EtCO2 is beneficial in recognizing misplaced intubations and is being studied for its value in trauma and shock.27 In one study, no unrecognized misplaced intubations were found in patients for whom paramedics used continuous EtCO2 monitoring; conversely, failure to use continuous EtCO2 monitoring was associated with a 23% unrecognized misplaced intubation rate.9 Another study found changes in EtCO2 prior to oxygen desaturation or clinically observed hypoventilation. A preliminary study of 190 blunt trauma patients found specific EtCO2 levels to be predictive of survival.28 One author stated that "capnography is the single monitoring modality that provides a visual reference to a patient's ABCs in less than 15 seconds," and that capnography has proved useful as a diagnostic tool for the respiratory system in the same way that changes in ECG shape are used for the cardiac system.29
Review Points for Vital Signs
- There is evidence that respiratory rates are not being recorded accurately.
- Only a third of patients with oxygen saturations below 90% exhibit increased respiratory rate.
- Agencies should include pain management in their QA/QI call reviews.
- Different providers give the same infant different Apgar scores, which limits the usefulness of this test.
- In adults, capillary refill is as useful an indicator for shock as a coin toss. Its usefulness in pediatrics has never been proven.
- In one study, EMS recognized hypoxemia without a pulse oximeter only 28% of the time.
- The Glasgow Coma Scale score, especially the motor component, is useful in predicting patient outcomes. A new tool, the Simplified Motor Score, is on the horizon.
- Capnography has shown its usefulness in cardiac arrest and recognizing misplaced intubations. It is being studied for usefulness in asthma, laryngospasm and COPD.
CONCLUSION
EMS providers have limited time with patients, limited instrumentation and resources, and lack access to blood gases, bedside ultrasound and echocardiography, lab tests and blood results. We must make wise use of the tools we do have to make decisions in our patients' best interests. Knowing the correct procedures for obtaining vital signs and knowing what that data tells you—and, at times, does not tell you—is critical to your patient and their receiving emergency department team.
The future in patient assessment looks to be coming from the military. Military physicians and engineers are designing devices that can gather data so that wounded soldiers can be remotely triaged for extraction and monitored while en route to receiving facilities. A possible new vital sign, heart rate variability, has been mentioned as a course of study, as well as the amplitude of the R wave in lead II of an ECG being an indicator of hypovolemia.
References
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Rob Curran, DC, EMT, is a human anatomy and physiology instructor at CUNY-Brooklyn College.
