Factors affecting the first 24-hour mortality of patients receiving emergency medical service (EMS) in a sub-urban area: a retrospective cohort study

Study setting and participants

The study analyzed the medical records of 2,500 individuals who sought emergency assistance between May 2017 and July 2019. These patients contacted the EMS center of Saraburi Hospital through various means, including the emergency number 1669. Specifically, the study focused on both regular emergency cases and severe emergencies. To ensure accurate results, the collected data excluded patients whose ambulance dispatch was canceled, those who passed away before the ambulance’s arrival, and individuals who refused service or requested transportation to alternative healthcare facilities. The chosen timeframe predates the onset of the COVID-19 pandemic, allowing for the elimination of potential confounding variables such as the use of personal protective equipment, which could extend response times. The study flow is shown in Figure 3.

Figure 3. Study flow.

Male sex

The study results indicate that male patients had a higher risk of death within 24 hours than female patients. The subgroup analysis revealed that males had a higher ratio of trauma cases, accounting for 63% of trauma patients in the study. This subgroup of patients also had significantly higher mortality rates. The findings align with a previous study,¹¹ which demonstrated that males faced an increased mortality risk in traumatic cases with on-scene hypotension. Furthermore, several other studies^12–32 have reported similar results, indicating that males are more likely to develop severe conditions such as traumatic brain injury, myocardial infarction, or out-of-hospital cardiac arrest. These collective findings suggest that there may be gender-based differences in the susceptibility and severity of certain diseases and injuries, with males exhibiting a higher risk of developing severe conditions and experiencing worse outcomes. However, it’s important to note that individual factors, genetic predisposition, lifestyle choices, and other variables could also contribute to these differences. Further research is needed to explore the underlying reasons behind these gender-based disparities in disease severity and mortality rates.

The time from symptom onset to calling for medical assistance

The time from symptom onset to calling for medical assistance can vary depending on several factors, including the individual’s awareness of symptoms, severity, and decision-making process. It is crucial to seek immediate medical attention by calling emergency services (1669) to ensure timely and appropriate care. Ideally, supposing someone experiences severe or life-threatening symptoms, such as chest pain, difficulty breathing, sudden loss of consciousness, or signs of a stroke, they should call for emergency medical assistance immediately. These situations require urgent attention, and delays in seeking help can have serious consequences. However, the time from symptom onset to calling for assistance can be longer for less severe or non-emergency situations. Some individuals may initially try to manage their symptoms at home or seek advice from non-emergency medical helplines or healthcare professionals. Others may delay seeking medical assistance due to fear, uncertainty, or underestimating the severity of their symptoms. It is important to note that early medical intervention is often crucial in many medical conditions to achieve the best possible outcomes.

Based on study findings, there was an increased hazard ratio for patients who delayed calling for medical assistance beyond two hours compared to those who sought help within two hours. This suggests that earlier medical intervention within the first two hours of symptom onset was associated with a higher severity of the diseases. On the other hand, patients who waited for more than eight hours since the onset of symptoms were found to have less severe symptoms. This finding could be attributed to patients with milder symptoms who can wait longer before seeking medical attention. It is important to note that these findings may not apply universally to all medical conditions and situations. The response time and urgency for seeking medical assistance can vary depending on the specific condition, individual factors, and clinical guidelines. It is always recommended to promptly seek medical advice in cases of severe or life-threatening symptoms, regardless of the elapsed time since symptom onset. Further research and consideration of various factors are necessary to fully understand the implications of delayed or early medical intervention in different medical conditions and to develop appropriate guidelines for prompt and effective care.

Vital signs

Based on the study findings, DBP below 60 mmHg was associated with an increased risk of death within 24 hours, even when accounting for other factors that could affect the outcome, such as pre-hospital life-saving interventions. The administration of intravenous fluids during transportation, a standard resuscitation measure, may not be sufficient to mitigate this effect. The decrease in DBP suggests a decrease in left ventricular diastole, which can occur in cardiogenic shock. Additionally, it may be associated with low vascular resistance resulting from the systemic inflammatory response seen in prolonged shock or distributive shock, such as that caused by sepsis.^33,34 The prehospital team cannot effectively treat both conditions with adequate fluid administration alone. Patients needed the appropriate vasopressor drug, intravenous thrombolysis or primary percutaneous transluminal coronary angioplasty, intra-aortic balloon pump, or extracorporeal membrane oxygenation, which required specific treatment and referral to the high-level critical care unit.

Low SBP (Systolic Blood Pressure) seems to be associated with high mortality in our study. However, the study results were not statistically significant when the SBP was adjusted for another factor. This suggests that the relationship between SBP and mortality may not be significant when considering the influence of this confounding factor. One possible reason for the lack of significance could be the high confounding factor, which means that there is another variable influencing the relationship between SBP and mortality. Additionally, it is mentioned that most patients with a SBP lower than 90 mmHg received early-volume resuscitation as a lifesaving intervention. This intervention might have affected the association between SBP and mortality, potentially reducing the magnitude of the association. The relationship with respiratory rate is also mentioned. Patients with a respiratory rate of ≤8 breaths per minute or ≥25 breaths per minute showed a similar pattern in the study result. It was further stated that endotracheal intubation or oxygen therapy with ventilatory support was performed for these patients when they were detected at the trauma scene, following an offline protocol. Overall, the study found that confounding factors and interventions such as early-volume resuscitation and ventilatory support influenced the association between SBP and mortality. These factors may have affected the significance of the relationship observed in the study.

Our study initially found that an at-scene oxygen saturation level of less than 60% was associated with a significantly higher first 24-hour mortality rate than an at-scene oxygen saturation level of 60% or higher. The hazard ratio (cHR) for this relationship was 43.66, with a 95% confidence interval (CI) of 29.37-64.90, and the p-value was less than 0.001, indicating a strong association. However, after adjusting for other factors in the analysis, the at-scene oxygen saturation level of less than 60% was no longer statistically significant as a risk factor. Instead, it was identified as a protective factor, but this association did not reach statistical significance. One possible explanation for this finding is that patients with lower at-scene oxygen saturation levels were recognized more quickly, leading to a more rapid assessment, intubation, and ventilation. These interventions may have improved their chances of survival, ultimately resulting in no significantly different survival rates compared to patients with higher at-scene oxygen saturation levels. It’s important to note that further research and analysis may be necessary to fully understand the relationship between at-scene oxygen saturation levels, recognition time, interventions, and patient outcomes.

An at-scene PR below 50 or above 120 bpm is associated with a higher mortality rate. This correlation is consistent with Dharod et al.’s retrospective cohort study involving 6,733 patients with arteriosclerosis.³⁵ In that study, it was found that a PR below 50 or above 80 bpm was associated with a 2.42-fold and 3.55-fold higher mortality rate for 9-12 months. These findings were statistically significant, particularly among patients receiving medications that affect pulse, such as digitalis, beta-blockers, non-dihydropyridine calcium channel blockers, and drugs used to treat arrhythmias. Moreover, previous studies have also shown a correlation between rapid pulse (arrhythmia) and increased mortality.^36–41 Zhang et al. found that a rapid resting pulse rate increases the risk of all-cause mortality by 6% and cardiovascular mortality by 8%. This increase in mortality is believed to be caused by an imbalance between the vagus nerve, the sympathetic nervous system, and the autonomic nervous system, which leads to a rapid pulse. Myocardial ischemia, atherosclerosis, and arrhythmias are mentioned as conditions associated with a rapid pulse. A rapid pulse has also been linked to an increased mortality rate in patients with chronic renal failure and pulmonary hypertension.

The results of this study can be applied to improve the unstable vital sign treatment process in the next operation. For example, there are increasing numbers of precaution and guidelines for patients with cardiogenic and distributive shock during the pre-hospital phase, including developing a shock monitoring procedure for the emergency room that requires continuous care from the pre-hospital team.

Level of consciousness

The GCS is commonly used in the EMS system to assess the level of consciousness in patients.⁴² Our study demonstrated that a GCS score of 8 or lower, indicating a reduced level of consciousness, was associated with a significantly higher risk of death within the first 24 hours compared to patients with GCS scores of 13-15 after adjusting for other factors. This finding aligns with previous studies on different patient groups, including ischemic stroke, traumatic brain injury, and non-traumatic brain injury. These studies have consistently shown that a decreased GCS score is associated with a higher likelihood of admission to the intensive care unit and increased mortality rates.^43–45 Based on the results of our study, it is recommended to establish instructions for managing patients with a GCS score of 8 or lower at the incident scene. These instructions should focus on monitoring this specific group of patients for appropriate ventilation and conducting rapid investigations, such as a quickly computed tomography (CT) brain scan.⁴⁶ Definitive treatments, including surgery, should be promptly administered to improve the timing process and reduce patient mortality. By implementing such measures, it is hoped that the early identification and intervention for patients with a reduced level of consciousness will lead to improved outcomes and a decreased risk of death.

Physical distance

Interestingly, our study indicated that the distance from the scene to the hospital did not impact patient mortality. This result contradicts previous studies that suggested a correlation between distance and mortality rates.^47,48 One possible explanation for the observed lack of impact could be the resuscitation process during transportation.⁴⁹ We hypothesized that performing resuscitation procedures in the vehicle while en route to the hospital could have alleviated the potential negative effects of longer distances on patient survival. This implies that even when the distance to the hospital is longer, the availability of skilled medical professionals and necessary equipment in the vehicle plays a crucial role in maintaining patient stability and minimizing mortality rates. However, it is essential to consider that each study has its limitations and unique circumstances, so further research is necessary to validate these findings and understand the specific factors at play in different situations.

Transport time

Our study found that when the transport time from the scene to the hospital was longer than 15 minutes, there was a two-fold increase in mortality within 24 hours. This finding suggests a longer transport time is associated with poorer patient outcomes. Further subgroup analysis revealed that a greater distance and extended response time were factors contributing to the longer transport time. Patients with transport times longer than 15 minutes had a 19% and 12% increase in mortality, respectively, with statistical significance. This suggests that distance and response time affect patient outcomes during transportation. The study also found that patients with a GCS score of 8 or less, indicating a more severe neurological condition, had a transport time of 15 minutes or less. These patients experienced a 49% reduction in 24-hour mortality. This finding implies that in cases where patients have unclear warning signs but are still awake with early abnormal hemodynamics, a shorter transport time can lead to improved outcomes. The shorter transport time allows for timely detection of unstable status and prompt resuscitation. Various challenges encountered during transportation can lead to delays in providing care and observation. One such challenge is the constrained space available for patient care within the ambulance, which can hinder immediate attention and observation. Additionally, the requirement for ambulance staff to sit in positions other than the designated chair further exacerbates these obstacles. If the duration of transport is excessively long, it could potentially lead to a higher mortality rate, possibly due to the obstacles in providing immediate care. Previous studies have also shown that prolonged transport times exceeding 20 minutes and prehospital times exceeding 65 minutes are associated with poor patient outcomes.^9,50–53 These findings emphasize the importance of minimizing transport time and time spent during transportation to improve patient outcomes.

Synchronized operation with the BLS team

The study found that prior transfer of patients by the basic-level operation team, in a synchronized operation with the BLS team, resulted in a statistically significant reduction of 24-hour deaths compared to cases where no previous transfer occurred. When the distance between the ambulance base and the scene is considerable, the dispatcher and medical commander may instruct the basic-level operation team closest to the scene to start transferring the patient along the way rather than waiting for the higher-level operations team, which might take longer to arrive. During this transfer, the patient receives primary assessment and basic life support management, including interventions like chest compressions and airway opening, without waiting for the arrival of higher-level teams. This highlights the importance of rapid resuscitation and access to basic-level operations teams. The findings of this study align with a meta-analysis conducted by Tannvik et al. in 2012.⁵⁴ Their analysis focused on primary resuscitation of patients with accidents and found that patients who received primary care, including interventions such as hemostasis and airway opening, had a 5.8% reduction in mortality compared to those who did not receive primary care. Additionally, two separate fatal and post-mortem studies supported the notion that primary resuscitation at the scene led to a reduction in accidental death rates of 4.5% and 1.8%, respectively. It should be noted that different studies may have variations in the geographical area, the composition of first responders, and incident prevalence, which can affect the mortality rate differently. However, overall, the evidence suggests that providing primary resuscitation at the scene, especially by basic-level operations teams, can significantly reduce mortality rates and improve outcomes for patients experiencing emergencies or accidents.

Pre-hospital life-saving intervention

The study found that patients who received prehospital life-saving interventions, including cardiopulmonary resuscitation, endotracheal intubation, rapid hydration, or resuscitative drug administration, were more severely ill and had unstable vital signs compared to those who did not receive resuscitation. Additionally, these patients were associated with a statistically significant higher risk of death within 24 hours. However, it’s important to note that this finding does not imply that out-of-hospital advanced life-support procedures in severely ill patients do not reduce mortality within 24 hours and does not contradict a previous study.⁵⁵ In other words, our study does not suggest that advanced life-support procedures are ineffective in reducing mortality within the first 24 hours for severely ill patients. It’s crucial to carefully interpret the study’s results and consider other factors and variables that might affect the outcomes. Further research and analysis are necessary to fully understand the relationship between out-of-hospital advanced life-support procedures and mortality rates for severely ill patients within a specific time frame.

Limitations

Our study was conducted in the central region of Thailand, specifically in a suburban area. It’s important to note that the findings of this study may not apply to other areas with different topography and population distribution. The emergency medical services (EMS) system in this study relied heavily on the central hospital, and all operational team members were affiliated with a high-level hospital. Additionally, the patients involved in the research were transported to the only hospital in Saraburi that had adequate medical equipment and provided multidisciplinary care. Consequently, the mortality rate might vary in other areas due to factors related to the destination hospital. It’s crucial to consider the capabilities and resources of different hospitals when interpreting the impact on mortality rates. Furthermore, this study was observational and focused solely on identifying factors that could be associated with mortality. A predictive model may be developed to assess the mortality rate of individuals receiving EMS. Such a model could be utilized to measure and evaluate the quality of prehospital patient care, thereby enhancing the potential and effectiveness of prehospital care. It’s important to recognize the study’s limitations and consider these factors when applying its findings to other regions or making broader conclusions about EMS systems and mortality rates.