1.1.1. The Physiological Parameters for Health Status Determination
Vital signs have been widely used as performance indicators of a person’s health. The four main vital signs that are routinely monitored by health care providers are body temperature, pulse rate/heart rate, respiration rate (rate of breathing), blood pressure (non-invasive systolic) [15
The normal body temperature of a person varies depending on the gender, any recent activities that the person has been engaged in, along with food and fluid consumption, the time of the day, and in women, the stage of the menstrual cycle. The pulse rate is a measure of the heart rate, or the heart beats per minute. As the heart pumps blood in and out of the body, this action puts pressure on the arteries, which could be felt as a pulse. Taking a pulse on the wrist measures the heart rate and can indicate heart rhythm and health. The normal pulse for healthy adults ranges from 60 to 100 beats per minute. The pulse rate can fluctuate, and it may increase with exercise, illness, injury, and emotions. The heart rate and pulse rate are technically different, though it is the heart beats that cause the pulse, so for analytical purposes, the heart rate can be used just as effectively as the pulse rate. Pulse rate, however, can use used in heart rate variability measurement [17
]. The respiration rate is the number of breaths taken by a person per minute. It is usually measured when a person is at rest, sometimes in a supine position, and it simply involves counting the number of breaths for one minute. Respiration rates also vary, and can it increase with fever, sickness, and with other medical conditions that influence respiration. The normal respiration rates for an adult person in resting position range from 12 to 20 breaths per minute, and may depend on age. Traditionally, in intensive care units and ambulatory settings, a spirometer has been used to measure the respiration rate; however, there has been a range of modern respiration rate sensing devices that have emerged, even in the consumer market, which are non-invasive in nature [9
]. This research uses the ECG signal to calculate the respiratory rate, also called the ECG-derived respiratory (EDR) rate. Thus, all of the sensors mentioned in this research are ubiquitous, wearable, and accurate, as compared to the traditionally used sensing devices and manual interventions [18
]. Blood pressure is the force of the blood pressurizing the artery walls during the contraction and relaxation of the heart. Each time the heart beats, it pumps blood into the arteries, resulting in an increase and peak in blood pressure as the heart contracts, and when the heart relaxes, the blood pressure falls. Two measures have been traditionally recorded when measuring blood pressure using an instrument called sphygmomanometer. The higher measure, called the systolic pressure, refers to the arterial pressure when the heart contracts and pumps blood through the body. The lower measure, called the diastolic pressure, refers to the arterial pressure due to the heart when it comes to rest and is filled with blood. Both the systolic and diastolic pressures are recorded as “mm Hg” (millimeters of mercury). The research revolves around using modern state-of-the-art measuring methods, and this means that blood pressure is a vital sign [19
]. High blood pressure (or hypertension) increases the risk of cardiac arrest, heart failure, and stroke, and its measurement is used as an important vital sign. Blood pressure can be categorized as normal, elevated, or stage 1 or stage 2 high blood pressure: Normal blood pressure is a systolic pressure of less than 120, and a diastolic pressure of less than 80, which is generally recorded as 120/80. Elevated blood pressure is systolic pressure with a range of 120 to 129, and diastolic pressure of less than 80. Stage I hypertension: Systolic blood pressure (BP) range 130–139 or diastolic BP range 80–89 mm Hg; Stage II hypertension: Systolic BP ≥ 140 or diastolic BP ≥ 90 mm Hg. Pulse oximetry, though not usually considered as a vital sign, can be a very important measure to ascertain an individual’s health status, and hence it is called the fifth vital sign [20
Experiments to determine the use of pulse oximetry as a vital sign have been conducted in the past, for example, in an emergency in geriatric assessments using pulse oximetry to measure the oxygen saturation in geriatric patients, which has led to improved diagnosis and treatment [20
]. Gas measurements in blood provide critical information regarding the oxygenation, ventilation, and acid–base concentration in blood; however, these measurements are not frequent. It is well known that oxygenation can change very quickly, and in the absence of continuous oxygenation measurements, these changes may go undetected until it is too late. Pulse oximeters measure the blood oxygen saturation continuously and noninvasively using SpO2 sensors. The blood-oxygen saturation indicates the hemoglobin concentration, due to the hemoglobin affinity to oxygen in the arterial blood, which becomes saturated with oxygen. In healthy adults, the saturation range can vary from 94% to 100%. The SpO2 sensor has a pair of light-emitting diodes (LEDs) and a photodiode on a probe element that is clipped to the patient’s body (usually a fingertip or an earlobe). The red LED has wavelength of 660 nm, the other is an infrared element with wavelength of 910 nm. Absorptions on each wavelength differs significantly with changes in oxygenated and deoxygenated concentrations of blood; therefore, from the differences in absorption due to red and infrared light, the oxy/deoxyhemoglobin ratio can be calculated. As the amount of blood in the capillaries depends on the actual blood pressure on the capillary wall (due to heartbeats), the heartbeat rate can be measured as well with the pulse oximeter.
1.1.2. Injury Severity and Trauma Scoring for Prediction of Survival Based on Physiological Parameters
The scoring measures, such as the NEWS, the GCS, the ISS, the TRISS, the SAPS II/III, and Ps have been successfully used to identify high health risks in patients that have suffered injury and trauma, and who have been admitted to ICU. The trauma scores used in this research, and the physiological parameters involved, have been presented in Table 1
for comparison. In the case of emergency, it would be a great advantage if the early warning scores could be calculated in time, and if the healthcare units could be made aware of these scores as soon as possible, to prepare for emergency, even before the patient arrives.
The NEWS score is based on an aggregate scoring system in which a score is calculated using physiological measurements, recorded in a routine check-up in a hospital or under prehospital settings. Six simple physiological parameters that are used for NEWS calculations are: the respiration rate, the oxygen saturation, the systolic blood pressure, the pulse rate, the level of consciousness or confusion, and the body temperature. In the case that the patient is in a confused state of mind or disoriented, where the patient may respond to the questions, but is confused, a score of 3 or 4 is assigned to the GCS scale. The normal GCS score equals 5 for a verbal response. NEWS scoring takes the GCS score into consideration, and in the case of trauma, the GCS scores can be very low, which can affect the NEWS scoring. A score is allocated to each measured parameter, with the magnitude reflecting how the parameter varies from the normal values. These act as weights for each measured parameter. Two additional points are added for people requiring supplemental oxygen to maintain oxygen saturation in blood. There is also an AVPU score (Alert, Voice, Pain, Unresponsive) that can be added to the calculation, depending on the alertness of the patient.
The interpretation of the NEWS score: A low score (NEWS 1–4) would ideally require assessment by a competent registered nurse who would further decide how often clinical monitoring would be required, and whether the case should be referred to the next level of diagnosis. A medium score (i.e., NEWS of 5–6 or a RED score) would prompt an urgent review by a clinician that was skilled with the relevant competencies for the assessment of the kind of illness that the patient is suffering from, which would usually be a ward-based doctor or an acute team nurse, who would further assess the patient’s health, and if required, would refer the patient to the critical care team. A RED score refers to an extreme condition in one of the physiological parameter (e.g., a score of 3 on the NEWS chart in any one physiological parameter). A high NEWS score (NEWS ≥ 7) should prompt an emergency assessment by a critical care staff with critical-care skills and competencies, and in such cases, the patient has to be transferred to higher critical care settings for diagnosis and treatment [6
The use of physiologic scoring systems for identifying high-risk patients for mortality detection has been considered using the Acute Physiology and Chronic Health Evaluation II (APACHE II) and Simplified Acute Physiologic Score (SAPS II) models, and they are currently used in a large number of hospitals worldwide. Although these scores are not very exact or perfect, they do enable the estimation of the health status of a patient who has had a recent episode of trauma or a similar condition.
Patients brought to the accident and emergency wards may have suffered multiple injuries, in which case the Injury Severity Score (ISS) is used to assess the trauma levels. Such patients who have been injured may have one or multiple injuries, and the ISS is an anatomical scoring method that provides estimates and measures of the overall severity of injured patients. All injuries are assigned an Abbreviated Injury Scale (AIS) score, and the codes of injuries have been derived from an internationally recognized and accepted dictionary that describes over 2000 injuries, and ranges from 1 (minor injury) to 6 (an extreme life threatening injury). Patients with multiple injuries are scored by adding the squares of the three injuries with the highest AIS scores in predetermined regions of the body, and in the order of the severity of injuries. The ISS score can range from 1 to 75, and a score of 75 represents an extreme condition. The maximum score is 75 (25 + 25 + 25), as the maximum severity is 5 for each anatomical part. By convention, a patient with an AIS 6 in one body region is given an ISS of 75. The injury severity score is non-linear, and scores of 9 and 16 are common, while scores of 14 and 22 unusual. The AIS grades are 0—no injury, 1—minor, 2—moderate, 3—severe (not life-threatening), 4—severe (life-threatening, survival probable), 5—severe (critical, survival uncertain), 6—maximal, possibly fatal.
ISS > 15 has been associated with a mortality of 10%. The advantage of using ISS is that it uses anatomical areas of injury to help in formulating a prediction of survival, though at the same time it is difficult to calculate this during the initial evaluation when the patient arrives at the emergency ward, and during resuscitation. In addition, it is difficult to predict the outcomes for patients with a severe single body area injury, though the New Injury Severity Score (NISS), which takes the three highest scores regardless of anatomic area, overcomes this deficit [11
]. The injury severity scoring can be classified as the following:
Physiologic: RTS, APACHE, Emergency Trauma Score
Anatomical: AIS, ISS, NISS
Combined: TRISS, A Severity Characterization of Trauma (ASCOT), the International Classification of Diseases Injury Severity Score (ICISS)
The composite device in this research can calculate the early warning scores and injury severity scores in real time, when the individual has had an episode of trauma. The NEWS, RTS, and TRISS models have been considered in this research presented in Table 1
. In the Materials and Methods section, these scores have been calculated and discussed, along with the severity levels that are associated with these scores. The statistical scores associated with these scores have been compared, and the analytical results have been presented. The correlation and regression scores between the NEWS and RTS scores have been studied and are later discussed. The measurements of the physiological parameters associated with these trauma scores have been measured in real time, and the scores have been calculated and presented in real time.
In the calculation of injury severity, the TRISS score [22
] remained the most commonly used tool for benchmarking trauma fatality outcome. The survival prediction power of TRISS could be substantially improved by re-classifying the measured physiological parameters and altering the coefficients for the environmental conditions, the demographics or the situations (e.g., combat). Despite some variations in the scoring mechanism in TRISS, due to the influence of demographics and environmental conditions on the patients, it remains a widely used model. Anatomic injury, age, injury mechanism, and pre-injury comorbidity are well-founded predictors of trauma outcome and for calculating the TRISS score. Statistical prediction models may have some inaccuracies, though these may be due to inaccurate calibration and inaccuracy due to applications of these models with influence on the environmental conditions [12
Early warning scores have largely been used in cardiac emergencies, as these patients, along with other fatal injuries, require medical attention and lead to the emergent incident response [15
]. Recognizing the early signs of clinical deterioration of patients is thought to improve patient treatment outcomes. The Early Warning System (EWS) scores and the impact of EWS outcomes were studied on the 48 hr mortality rate for respiratory failure and cardiac arrest patients. It was found that the early warning system scores performed well for predicting cardiac arrest and death within 48 hr. For ailments like cardiac arrests, early warning scoring mechanisms become relevant and applicable as these patients may enter trauma at any time, and healthcare service providers need to prepare ahead of time with readiness to attend to this trauma [23
For patients admitted to ICU and facing deterioration of health, physiological parameters such as pulse rate, blood pressure, temperature, and respiratory rate could be used to assess mortality, and serious adverse events (SAEs) such as cardiac arrest could be prevented. The EWS is a scoring system which assists with the detection of physiological changes, and it may help to identify patients who are at risk of further deterioration [24
]. In cardiac ailments, reduced heart rate (HR) is an established predictor of trauma and further mortality. However, the relationship between the predictors and trauma scoring is poorly understood, hence it becomes important to establish the relationship between heart rate variability and trauma scores [13
The importance of using injury severity, comorbidity, and prediction-of-survival scores becomes paramount in military operations when troops who engaged in combat may require medical attention. The situation aggravates when the location of the troops is not known and a soldier requires medical attention, if the time frame of the arrival to the base camp is uncertain. In such cases, predicting survival and the measures related to injury severity scores become very important, and the wearable vital signs and physiological measurement kits that can calculate and perform further analysis become a very crucial instrument [13
The TRISS) methodology has been used in both the UK and US Military trauma registries. The method relies on dividing the casualties according to their survival probability (penetrating (Ps_penetrating) or blunt (Ps_blunt)), though the use different weighing mechanisms based on experiences in combat-related environments. The UK Military Joint Theatre Trauma Registry (JTTR) and the US Military use the same scoring mechanism with some variations in coefficients for soldiers who have been injured in explosions. This study aimed to use the UK Military JTTR to calculate new TRISS coefficients for contemporary battlefield casualties who were injured by either gunshot or explosive mechanisms. The secondary aim of this study was to apply the revised TRISS coefficients to examine the survival trends of UK casualties from recent military conflicts. Such systems and early warning scoring kits can be very useful to forces who are deployed in combat zones where the scores can be calculated in real time in the event of an emergency [27
] . The composite sensor kit in this research enables the measurement of physiological parameters that can determine the injury and trauma scores.
These studies emphasize the importance of using trauma scores in predicting the mortality and in calculating the probability of survival in injury and trauma situations.