Convulsive Patients Transported by a Physician-staffed Helicopter in Japan Had Better Outcomes in the Keyword-triggered Dispatch Compared to Postcontact Emergency Medical Technician-triggered Dispatch

Abstract

Introduction:

We retrospectively analyzed convulsive patient outcomes transported by a physician-staffed Helicopter Emergency Medical Service (doctor helicopter [DH]) using the keyword-triggered dispatch with data from the Japan DH Registry System (JDRS). Upon receiving an emergency call containing critical keywords, such as an ongoing convulsion at the firefighting central command room, immediate dispatch of the DH is requested, in addition to dispatching an ambulance. The keyword-triggered dispatch relied on data obtained from the JDRS.

Methods:

Details from the JDRS database included patient age, sex, cardiac arrest presence upon DH contact, vital signs, DH dispatch timing (keyword-triggered dispatch/emergency medical technician [EMT]-triggered dispatch), medical intervention details, and 1-month outcomes (cerebral performance category [CPC]; CPC1, 2: Good; CPC 3–5: Poor). Subjects were divided into keyword (keyword-triggered dispatch) and control (EMT-triggered dispatch) groups for comparison.

Results:

Of 1201 patients, all evacuated from the scene, 617 were in the keyword group, and 584 in the control group. No significant differences existed between groups for cardiac arrest, respiratory and heart rates, CPC, or mortality. The keyword group had lower average age, systolic blood pressure, and medical intervention ratio but a higher median Glasgow Coma Scale and good outcome ratio.

Conclusion:

This first report on the keyword-triggered dispatch as a prognostic factor for convulsive patients evacuated by DH using the JDRS.

INTRODUCTION

The physician-staffed Helicopter Emergency Medical Service (HEMS), known as the doctor helicopter (DH) in Japan, transports a flight doctor and flight nurse to the scene of an emergency during the daytime (HEM-NET, https://hemnet.jp/en). As of April 2023, 56 DHs have been deployed in 47 prefectures across Japan. The Japan DH Registry System (JDRS), managed by the Japanese Society for Aeromedical, prospectively collected data on dispatches, especially for trauma, acute coronary syndrome, and stroke but not for convulsions. The data, including the outcome at 1 month, were registered by all DH base hospitals in Japan from April 2015 to March 2020.[1] The collected data have been available to each base hospital since December 2022.

In Japan, there are two main types of dispatched DHs: one sent to a rendezvous point near the scene that evacuates patients from the rendezvous point and one for interhospital transportation. In most cases, interhospital transportation is performed to transport patients to medical institutions that provide more advanced medical care. When a DH is dispatched to a rendezvous point, there are two dispatch subtypes. The first subtype involves dispatch after emergency medical technicians (EMTs) establish contact with a patient and assess the severity of the patient’s condition. The second subtype of dispatch is based on keywords. This subtype aims to initiate early requests for DH dispatch and facilitate prompt medical intervention by physicians. It is referred to as keyword-triggered dispatch. In our previous study, the keyword-triggered dispatch showed an association with survival in patients evacuated by a DH using the JDRS.[2] The keywords for the Eastern Shizuoka DH (where our facility serves as a primary base hospital) encompass instances of unconsciousness, suffocation, and persistent convulsions. Upon receipt of an emergency call containing these critical keywords at the firefighting central command room, an ambulance is promptly dispatched to the specified location. Moreover, the firefighting central command room has the authority to request the immediate dispatch of the DH in response to such cases. However, this study did not show the types of diseases or trauma for which the keyword method was most effective.

Evidence-based guidelines concerning the treatment of convulsive status epilepticus recommend the administration of anticonvulsants as early as possible to minimize brain injury.[3,4] However, in Japan, EMTs cannot perform anticonvulsant infusion for convulsive patients; thus, a DH is often called to evacuate such patients to provide early medical intervention.[5,6] The use of the keyword-triggered dispatch when the DH is dispatched might result in an improved outcome for patients with convulsions. Accordingly, we retrospectively investigated the outcome of convulsive patients transported by a physician-staffed helicopter using the keyword-triggered dispatch based on JDRS data.

METHODS

The protocol of this retrospective study was approved by our institutional review board, and examinations were conducted according to the standards of good clinical practice and the Declaration of Helsinki. The approval number was 733.

First, convulsive patients were selected from the JDRS database. The dispatch activity details collected from the JDRS database included various parameters. These parameters encompassed whether the request for the DH dispatch was initiated before (keyword-triggered dispatch) or after the EMTs contacted the patient (EMT-triggered dispatch). In addition, the data comprised the duration from the first call to when DH staff made contact with the patient.

Other key elements incorporated in the data collection were the patient’s age, sex, the presence or absence of cardiac arrest when contacted by DH staff, and vital signs at the time of contact. Vital signs encompassed the Glasgow Coma Scale (GCS), systolic blood pressure, heart rate, and respiratory rate. Furthermore, the information encompassed the specific medical interventions administered by DH staff, such as securing venous routes, tracheal intubation, and infusion of drugs.

The final outcomes of the dispatched cases were also recorded, considering the Cerebral Performance Category (CPC) at 1 month and the survival outcome. The CPC categories included CPC1 for good cerebral performance, CPC2 for disabled but independent, CPC3 for conscious but disabled and dependent, CPC4 for vegetative state, and CPC5 for deceased. A favorable outcome was defined as CPC 1 and 2, whereas an unfavorable outcome was defined as CPC 3–5. Patients with missing CPC data were excluded. Subjects were divided into the keyword (keyword-triggered dispatch: the DH dispatch before EMTs make contact with the convulsive patients) and control (EMT-triggered dispatch: the DH dispatch after EMTs make contact with the convulsive patients) groups, and variables were compared between the two groups. The main objective of the study was to examine whether keyword-triggered dispatch had an impact on the outcomes of the convulsive patients. This entails investigating whether early medical intervention, prompted by keyword-triggered dispatch, influences the outcomes of convulsive individuals.

The data were analyzed using Wilcoxon’s test for the duration from the first call to contact, age, systolic blood pressure, heart rate, and respiratory rate; the median test was used for the GCS and CPC; the Chi-squared test was used for sex, cardiac arrest on contact, medical intervention, ratio of patients with a good outcome, and mortality rate. P < 0.05 was considered statistically significant. Data were presented as the mean ± standard deviation or the median with interquartile range.

RESULTS

During the investigation period, a total of 41,592 patients were registered in the JDRS. Among them, 1377 were convulsive patients. After excluding patients whose final CPC data were missing, a total of 1201 patients were enrolled as subjects. All of these were evacuated from the scene, and there was no interhospital transportation. Among them, 617 subjects were in the keyword group, and 584 patients were in the control group.

The results of the analysis of the two groups are presented in Table 1. There were no significant differences between the two groups concerning cardiac arrest on contact, respiratory rate, heart rate, CPC, and mortality rate. However, the duration from the first call to contact, average age, average systolic blood pressure, and the ratio of medical intervention in the keyword group were significantly smaller compared to those in the control group. The median GCS and the ratio of patients with a good outcome in the keyword group were significantly greater compared to the Control group.

Table 1.

Results of analysis

	Key word (n=617)	After contact (n=584)	P
First call to contact (min)	26.1±10.0	34.5±13.3	<0.0001
Age (years)	39.5±33.2	45.8±31.3	0.001
Sex male/female	369/247	366/281	0.28
Cardiac arrest on contact, n (%)	1 (0.1)	5 (0.8)	0.19
GCS	12 (7–14)	9 (6–13)	<0.0001
Systolic blood pressure (mmHg)	136.1±32.8	141.8±34.9	0.01
Respiratory rate (breath/min)	23.5±8.2	23.7±7.8	0.45
Heart rate (beat/min)	111.3±34.8	113.4±32.3	0.27
Medical intervention
Securing venous route yes, n (%)	480 (77.7)	511 (87.5)	<0.0001
Securing airway yes, n (%)	64 (10.3)	128 (21.9)	<0.0001
Administrating drug yes, n (%)	258 (41.8)	348 (59.5)	<0.0001
Good outcome, n (%)	562 (91.0)	507 (86.8)	0.01
CPC	1 (1–1)	1 (1–1)	0.19
Mortality, n (%)	2 (0.3)	4 (0.6)	0.37

GCS: Glasgow Coma Scale, CPC: Cerebral performance category

DISCUSSION

This is the first report to describe the keyword-triggered dispatch as a prognostic factor in convulsive patients who were evacuated by a DH using the JDRS. Previous reports on convulsive patients transported by helicopters have been limited in number, investigating only small cohorts with short outcomes during transportation and often reported from small geographic areas.[5,6,7,8] The present study, in contrast, involved the largest number of convulsive patients, followed them for 1 month, and collected data from across Japan.

According to the results of the present study, the characteristics of convulsive patients in the control group included older age, more frequent unconsciousness, higher blood pressure, and a higher chance of receiving medical intervention during air evacuation. In practical terms, it is undeniable that keyword-triggered dispatch involves less severe convulsive patients compared to DH dispatch, once EMTs make contact with the patients. The lack of precise information in the report received during the first call appears to be the cause for not accurately understanding the patient’s condition. As age was identified as a prognostic factor for status epilepticus, the present study might exhibit this tendency.[9] However, when employing propensity score matching analysis to control for the significant difference in age [Table 2], a greater percentage of patients in the keyword group demonstrated a good outcome compared to the control group (P = 0.06). Accordingly, this potential bias was minimized.

Table 2.

Results of analysis after propensity score matching (n=378)

	Keyword	After contact	P
First call to contact (min)	26.7±8.1	30.8±11.2	<0.0001
Age (years)	46.7±31.6	47.6±30.3	0.85
Sex male/female	235/143	232/146	0.82
Cardiac arrest on contact, n (%)	1 (0.2)	1 (0.2)	0.68
GCS	11 (7–14)	10 (6.75–14)	0.45
Systolic blood pressure (mmHg)	137.3±32.1	135.9±30.9	0.71
Respiratory rate (breath/min)	22.2±6.8	23.2±7.3	0.08
Heart rate (beat/min)	104.7±31.3	109.32±30.4	0.05
Medical intervention
Securing venous route yes, n (%)	336 (88.8)	344 (91.0)	0.33
Securing airway yes, n (%)	50 (13.2)	62 (16.4)	0.21
Administrating drug yes, n (%)	169 (44.7)	213 (6.3)	0.001
Good outcome, n (%)	345 (91.2)	329 (87.0)	0.06
CPC	1 (1–1)	1 (1–1)	0.48
Mortality, n (%)	2 (0.5)	2 (0.2)	0.55

GCS: Glasgow Coma Scale, CPC: Cerebral performance category

The changes in vital signs observed in the control group may reflect intracranial hypertension, which is known to occur immediately upon convulsive activity. Increased intracranial pressure during convulsions can lead to physiological changes, including hypertension.[10] Intracranial hypertension may also contribute to secondary brain damage and brain herniation.[11,12] Severe brain injury often results in a coma state, requiring tracheal intubation, assisted ventilation, and various drug interventions. These changes and treatments could potentially account for the outcomes observed in the present study.

An early request for dispatch of the DH could enable medical staff to reach the patient at an earlier time point, facilitating earlier medical intervention for convulsive patients. Early administration of anticonvulsants has been shown to minimize brain injury.[3,4] These factors may offer an explanation for the results of the present study. Consequently, initiating an early request for dispatch of the HEMS when receiving an emergency call related to a convulsive patient, where anticonvulsants can be provided, may prove beneficial in improving the outcomes of convulsive patients.

However, the present study has certain limitations. First, the JDRS did not specifically collect data focusing on convulsive patients, leading to a lack of detailed information on the etiology, duration or frequency of convulsions, status epilepticus or not, or the specific drugs administered. In this study, we demonstrated a short duration from the first call to contact; however, the specific timing of the administration of early medication or medical interventions remained unclear due to the absence of specific implementation timelines. In addition, the names of registered hospitals were not accessible to researchers, limiting further investigation. Second, the JDRS did not include data on fees for medical treatments, precluding analysis of the medical economy. Third, the JDRS lacked data on convulsive patients transported by ground ambulance, preventing a comparison of final outcomes between patients evacuated by DH and those evacuated by ground ambulance. Therefore, further prospective studies, incorporating data from patients transported by ground ambulance and considering economic aspects, are warranted.

CONCLUSION

This study represents the initial report describing the keyword-triggered dispatch as a prognostic factor in patients with convulsions evacuated by the DH using the JDRS.

Research quality and ethics statement

This study was approved by the Institutional Review Board (Juntendo Shizuoka Hospital IRB 733). The authors followed applicable EQUATOR Network (https://www.equator-network.org/) guidelines during the conduct of this research project.

Financial support and sponsorship

This work was supported in part by a Grant-in-Aid for Special Research in Subsidies for ordinary expenses of private schools from The Promotion and Mutual Aid Corporation for Private Schools of Japan.

Conflicts of interest

There are no conflicts of interest.