This is a single center retrospective cohort study. Patient data were obtained from April 1st 2010 to March 31st 2017 for 7-year period in Toyooka Hospital. Data sources were hospital medical charts. Ethical committee in Toyooka Hospital approved the study (ID: 137). The requirement for informed consent was waived. Study results are presented according to the STROBE guidelines for observational studies.
HEMS system in japan
The Japanese HEMS system was introduced in 2001. The number of medical helicopters are increasing since then and by October 2019, 53 helicopters had been deployed in 43 prefectures. Each base tertiary medical center corresponds to one helicopter. HEMS system is only available during the day light hours, and night-time flight is prohibited. The system also does not allow to flight during periods of poor visibility or bad weather. Typically, HEMS system receives the dispatch request from a ground Emergency Medical Service (EMS) service, such as the public EMS service, then takes off from the hospital and lands at the predefined place (RP: rendezvous point). At the RP, the HEMS staff makes contact with the patient transported by the ground ambulance, stabilizes the patient, then transports the patient to the hospital. If the HEMS team reaches the RP earlier than ground EMS, the HEMS staff may move from the RP to the scene to contact the patient (Figure 1). The Role of Japanese paramedics (public EMS) has been described in the previous literature[7]. Japanese ground transport is mainly conducted by local public paramedics. The activities of the paramedics are dictated by local protocols. Japanese paramedics are not permitted to perform endotracheal intubation for patients except for patients in cardiac arrest (CA).
Service area and protocol of Toyooka HEMS system
Toyooka HEMS system is responsible for the northern region of Hyogo and Kyoto Prefecture, the eastern region of Tottori Prefecture covering approximately 6,226 km2 in area with a population of approximately 784 thousand people. This area is rural and mountainous with only a few hospitals. HEMS system was introduced in 2010 with Public Toyooka Hospital serving as the base hospital. The EC145 (BK117C2 Airbus Group SE, The Netherlands) type helicopter is 13.00 m long, 11.00 m wide, and 3.85 m high with a maximum takeoff weight of 3350 kg and an effective payload of 1586 kg. Its cruise range is 550 km with a cruise duration of 2.5 h. It accommodates 7 passengers: a pilot, mechanic, doctor, nurse and patient with room for 2 others. Most severe cases are seen by the HEMS system including the cases with stroke, cardiovascular disease, sepsis, trauma, and CA. Medical crews consist of one or two physicians with one nurse with specialty training in emergency medical care. Endotracheal intubation is performed in a variety of situations including airway obstruction, regurgitation, respiratory failure (< percutaneous oxygen saturation [SpO2] 90%), circulatory failure (< systolic blood pressure [sBP] 90mmHg), and coma (< Glasgow Coma Scale 8). Patients are intubated using sedatives (midazolam, or ketamine), analgesics (fentanyl), and neuromuscular blockade (rocuronium or vecuronium). Rapid sequence induction was applied to most of the patients. Video laryngoscope: The Pentax Airway Scope® (AWS-S100®; Pentax Corporation, Tokyo, Japan) is available for the intubation at the discretion of the attending physician.
Patient selection
Patients who were intubated by the Toyooka HEMS physician in the prehospital settings over 18 years of ages were included. Exclusion criteria were as follows: inter-facility transport, ground transport, declaration of death at the scene, not transported by HEMS helicopter. We excluded cases such as intubated on scene during extrications, since the times were confounded by long extrications times or other procedures contributing to total prehospital time.
Measurements
Successful ETI attempt was verified by auscultation and end tidal carbon dioxide (ETCO2) measurement. We divided patients into two groups. In the In-Flight Group (FG), patients were intubated during the flight, after take-off (IFI). In the On-Ground Group (GG), patients were intubated on the ground, usually in the ambulance at RP prior to take-off (Figure 1). The following measured data was collected according to database: age, gender, etiology (endogenous/exogenous). Endogenous/exogenous were decided by HEMS physician in charge: endogenous illness include heart disease, respiratory disease, stroke, sepsis, etc., and exogenous illness include trauma, suffocation, etc. For the ETI procedure, we recorded success rate, number of attempts, use of video laryngoscopy or direct laryngoscopy, training level of the emergency physician who performed the intubation, percentage of patients experiencing hypotension or hypoxia during intubation. We recorded prehospital times including: scene time (the time from HEMS staff arrival at the RP to patient loading onto helicopter) and total prehospital time (the time helicopter dispatch from base hospital to arrive with patient at destination hospital) were recorded.
We defined hypoxia and hypotension during intubation as the patient’s SpO2 dropping below 90% or sBP below 90mmHg during the procedure[8][9][10][11]. The primary outcome was the proportion of successful ETI. The secondary outcomes included scene time, total prehospital time and incidence of complications such as hypoxia or hypotension.
Data Analysis
Continuous variables were described as medians with Inter Quartile Range (IQR) and compared using the Mann–Whitney U-test. Categorical variables were described as numbers or percentages using Fisher’s exact test. All statistical analyses were performed with EZR version 1.40 (Saitama Medical Center, Jichi Medical University; http://www.jichi.ac.jp/saitama-sct/SaitamaHP.files/statmed.html; Kanda, 2012), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria, version 2.13.0). More precisely, it is a modified version of R commander (version 1.6-3) that was designed to add statistical functions frequently used in biostatistics[12]. All p-values were two sided and p-values of less than 0.05 were considered statistically significant.