MEDICAL EVACUATION: ORGANIZATION AND TRANSPORTABIITY CRITERIA FOR PATIENTS WITH SEVERE INJURY Kasimov R.R., Makhnovskiy A.I., Minnullin R.I., Chuprina A.P., Lyutov V.V., Blinda I.V., Usoltsev E.A., Kovalenko S.A., Khaustov M.V., Shapovaalov N.S.

442 Military Clinical Hospital, Saint Petersburg, Russia,

Main Military Medical Department of the Ministry of Defense of Russia, Moscow, Russia

Organization of timely interhospital transfer (IT) for patients with severe injury (SI) is an important link in functioning of trauma system. Medical evacuation (ME) includes sanitary aviation evacuation (SAE) with air vehicles (AV), sanitary evacuation (SE) with ground, water and other types of vehicles [1-3]. Owing to severity of condition, patients with SI are transferred to the nearest medical facility (MF), not specialized usually [4-6]. Results of diagnostics and treatment in such MFs are significantly worse than in trauma centers, with mortality exceeding 30 % [7-10]. However ME is not considered as a positive factor for patient’s health and usually is a necessary procedure [11-12]. Absence of possibility for rendering specialized care on site dictates the necessity for almost hundred per cent evacuation regardless of severity of injury. It is usually observed in difficult medical and tactical situation. The main problems are estimation of transportability and coordination of action of services dealing with ME [4-5, 13-15]. The issue of estimation of transportability remains the most disputable.

Objective – generalization of experience in organization of medical evacuation of victims with severe trauma, as well as presentation of own experience and opinion on the problem.

ORGANIZATIONAL ASPECTS

A structural unit, which immediately deals with ME, is a medical (aeromedical) team [16, 17]. The participants are “giving”, “transporting” and “accepting” parties. The task of arrangement of ME is given to administration of a “giving” MF [2]. At the same time, a solution about patient’s transportability is made by a specialist who performs MT. This party has to conduct MT, which is the most unprotected stage of ME. It is believed that medicotactical recommendations of “the transporting” team are mandatory. In Military Forces of the Russian Federation, ME is realized by units of emergency medical service of regional and central MFs, and non-staff critical care and surgical teams of other MFs. In the Western Military District (WMD), most patients with SI are primarily admitted to trauma centers of Health Ministry of Russia. Then a team including intensivists and a specialist of prevailing profile of injuries arrives there. Depending on severity of condition and medicotactical situation, s decision on ME is made and its way is selected. One should note the fact that SAE is more often used in WMD now. There are some problems: absence of a regulatory framework, which defines the status of a medical team in-flight [6. 11].

In surgery of injuries, optimal management for patients with severe injuries is based on prediction methods, the terms polytrauma and traumatic disease (TD) [14]. E.K. Gumanenko and I.M. Samokhvalov recommend to predict the course of TD with use of Military Field Surgery-Injury (MFS-I) (for estimation of injury severity) and Military Field Surgery-Condition on Admission (MFS-COA) (for estimation of condition). The “international standard” for prediction of outcome is injury severity score (ISS), Revised Trauma Score (RTS) and complex predictive score TRISS [18-20]. We adhere to the concept of TD and try to realize ME in acute period. These solutions are confirmed by the following study. The study of acute period of TD showed that predictive criteria of poor outcome of acute period course in severe associated injury (SAI) and potential non-transportability were severity of injuries with MFS-I > 15 points, ISS > 24, RTS < 4.1. Such patients have to be evacuated to level 1 trauma center as fast as possible [9. 14].

So called check-list is registered for patients who are admitted to Burdenko Main Military Clinical Hospital in preevacuation period. It contains the data on condition of main vital systems and indications for ME. This approach to arrangement of ME is common in our civilian colleagues [15]. There are three phases of ME: preparatory phase; IT; condition stabilization after IT [13]. The phase of IT is the most unprotected one. All unexpected situations appear at this stage and usually they are caused by equipment. All precautions are to be strengthened during moving the patient since problems appear at the moment of his/her displacement.

The selection of a way of ME depends on tasks. The factor of time and distance counts in favor of SAE. However “the problems of a megapolis”, weather conditions, problems of arrangement of air vehicle fly and bad conditions during fly can equalize the time factor [6]. Selection of a type of AV in arrangement of SAE mainly depends on four factors: number of patients who need for evacuation; evacuation route; availability of air strips (AS) adapted to acceptance of specific types of AV; metereologic conditions and time of the day. According to our opinion, one of main criteria in election of a type of AV is a possibility for minimization of bad clinical and physiological reactions of fly. For evacuation over the distance > 500 km and high amount of patients it is appropriate to use evacuation by plane [16-17]. One should consider that not all air vehicles can land in conditions of a city, mainly because of safety considerations and the fact that air traffic control forbids flies during hours of darkness.

UNFAVORABLE FACTORS OF SANITARY AVIATION EVACUATION

The main unfavorable clinical and physiological factors of SAE are low atmospheric pressure and its variations, acceleration and deceleration, low humidity [12, 16]. Noise, vibrations, tightness and bad light decrease the efficiency of visual tracking of a patient and equipment.

During making decision on SAE it is necessary to consider some physiological features: possible expansion of gases in cavities (pleural cavity, intubation tube cuff, air cavities, gastrointestinal tract and others); it is advisable to change air to water; the decrease in density and amount of O₂ at a height > 2 km; low atmospheric pressure in hermetic cockpits; thereat of non-drained pneumothorax; draining should be with active aspiration; danger of presence of air in the intracranial cavity (after neurosurgical operations); influence of deceleration and acceleration on the body. Moreover, technical and natural factors can influence on SAE: problems of operation of medical equipment; rapid deterioration of meteorological conditions; “problems of megapolis” in arrangement of intermediate SE to AS and from AS. Most healthy people tolerate the height of 3,600 m above sea level without consequences for their bodies. The optimal height, which supports the adequate oxygenation in non-hermetic cockpits of AV, is 2,000 m above sea level. Lower height can be a cause of limitations due to turbulence and weather conditions. Boyle, Henri, Dalton and Charles’ laws make differences between physical and chemical properties and gas behavior at a height [6, 12, 16]. At a height of 3,000 m above sea level, PaO₂ decreases to 60 mm Hg, hypoxia develops and worsens in patients with blood loss, and oxygen transport function of the blood decrease twice at the hemoglobin level of 70 g/l. Such patients need for hemotransfusion until the targeted level of hemoglobin (100 g/l) is achieved. If hemotransfusion is impossible, it is appropriate to maintain SpO₂at the level not lower than 90 % by means of increasing level of O₂. Gas expansion in gastrointestinal tract, which is one and half time higher than the initial volume, is usually observed at a height > 3,045 above sea level. It should be considered in patients who experienced surgery for hollow abdominal organs (preventive nasogastrointestinal intubation) and in presence of abdominal compartment syndrome. For each 100 meters of height, the air temperature decreases by 1°С. Therefore, it decreases in AV too. Patients with severe TBI should receive prevention of increase in intracranial pressure. It is achieved with medications, physical methods and hyperventilation.

Transportability criteria

There are not any uniform criteria for transportability. Most researchers recommend to emphasize the subsequent development of available scores and systems and to adapt them to existing conditions [21]. This way was chosen by the specialists in WMD. We developed the criteria of condition severity on the basis of modified score RTS – New RTS [4, 5, 20]. Some criteria were added to the available ones, i.e. the criteria, which efficiently estimate the condition severity and transportability of patients (the table 1). However there are situations where ME is necessary for patients in critical or terminal conditions. New RTS is not without disadvantages: complexity of interpretation in severe TBI. For such patients, the indications for ME depend on need for neurosurgery.

Table 1

The modified variant of New RTS

Criteria for estimation of vital functions	0 points	1 point			2 points	3 points	4 points
M-Mention
Glasgow coma scale	3	4-5			6-8	9-14	15
C-Circulation
MAP, mm Hg	Bleeding arrest	< 70			70-89	90-99	≥ 100
Hemoglobin, g/l	-	< 60			60-79	80-119	≥ 120
Platelets, 10³/ml	-	< 30			30-79	80-119	≥ 120
Ultrasonic sings of internal bleeding	-	≥ 1,5 l / l			0,5-1,5 l / l	< 0,5 l / l	No
ECG – cardiac contusion signs	-	Ventricular extrasystoles, early and grouped, AB blockade of degree 3			ST segment elevation or depression > 2 mm, absent R wave or QS	Non-specific changes	No
Vasopressor and inotropic therapy: in equivalent of dopamine, µg/kg/min	-	≥ 15			5-14	< 5	No
Risk of thromboembolic complications	-	Suspected PE			High	Middle	Low
R-Respiration
Respiratory rate	Respiratory arrest	Abnormal breathing			≥ 30	25-29	10-24
Pulmonary radiography: proportion of lesioned (collapsed) pulmonary tissue	> 75 %	Up to 75 %			Up to 50 %	Up to 25 %	0
Pleural drainage	-	Active air aspiration			Bilateral drainage	Unilateral drainage	No
ALV	-	ALV with PEEP ≥ 15			ALV with PEEP < 15	Non-invasive ALV	Without ALV
PaO₂/FiO₂ × 100	-	< 100			100-224	225-299	≥ 300
or SpO₂/FiO₂ × 100	-	< 70			70-270	280-440	≥ 450
NRTS = M + C_min + R_min
Condition estimated with NRTS
Terminal (critical)			0-2	Non-transportable
Extremely severe			3-5	Potentially transportable
Severe			6-8	Transportable
Middle			9-11
Satisfactory			12

Orientation to more detailed and functional changes and wide spectrum of laboratory values, according to our opinion, is needless since time can be lost. Other authors adhere to this opinion [13, 21]. The contraindications for IT are ongoing bleeding, tension pneumothorax, decrease in arterial pressure by more than 20 % from age norm at the background of absent effect from cardiotonic and vasopressor therapy, impossibility of hypoxia correction in ALV, epistatus, hyperthermic syndrome (39.5°С and higher) [22]. At the same time, the authors note the high incidence of complications in ME: increasing events of cerebral edema, hypotension, convulsive disorder and others. The proportion of complications was higher in the group of conditionally transportable patients.

The estimation of transportability should be oriented to degree of compensation of the main vital systems: cardiovascular, respiratory and CNS [13]. But even in decompensated state, the patients were estimated as conditionally transportable, and ME was successfully carried out after preevacuation preparation. There were not any lethal outcomes during IT. The short term mortality was 40 %. The authors note that those evacuations were necessary since all patients in decompensated state could die (earlier or later). However the authors separate only two criteria of non-transportability: agonal state and ongoing bleeding.

According to S.V. Kemerov and I.Yu. Noskov (2004), the unfavorable factors for IT are MAP < 60 mm Hg, CVP < 0 or > 14 mm H₂O, unstable hemodynamics with vasopressors in conversion to dopamine > 10 µg/kg/min, saturation index < 184, signs of heart contusion, dieresis rate < 20 ml/hour, rash blanching at pressure symptom 5 sec. and higher [23]. These criteria are easy and determined in MF of any level.

Currently, there is a persistent trend to decrease in number of absolute contraindications for IT. So, the use of extracorporeal membrane oxygenation (ECMO) for temporary treatment of respiratory function allowed successful realization of IT in a patient with severe respiratory failure [24]. The first positive experience with critical endovascular balloon aortal occlusion (CEBAO) was published by British physicians dealing with helicopter prehospital transfer [25]. In 2018, during the experimental educational and practical course in trauma surgery, we cooperated with specialists from Kirov Military Medical Academy and researched big animals with CEBAO (modeling of circulatory and respiratory arrest).

We conducted the analysis of ME in peaceful time. MEs were conducted by specialists of WMD for the past two years. The statistical data of non-parametrical values (indices) are presented as the median with interquartile range of 75%-25% – Ме (Q3-Q1) and parametric (age) test – М ± ơ. Totally, 73 patients with SAI and severe single and multiple injuries with shock (ISS ≥ 17) were evacuated. There were not any fatal incidents during IT. All patients were men, age of 27.7 ± 9.1. SE was conducted in 52 cases (71 %), SAE – in 21 cases (29 %). 22 patients (42 %) experienced long distance transportation (more than 200 km). SAE was conducted with helicopters in 14 cases, with planes – in 7 cases. SAE was considered as tactical – within the limits of territorial zone of the main military medical facility (MMF) – 13 cases; operative and tactical – between territorial zones of the main MMF of the district – 8 cases. Patients with SAI presented 43 (59 %) cases, with severe single and multiple injuries – 25 (34 %) cases, 5 (7 %) cases –severe burns. The table 2 presents the distribution of the patients according to morphology.

Table 2

Distribution of patients according to injury morphology

Prevailing injury	Severe associated injury	Severe single and multiple injuries	Всего Total
Prevailing injury	43	25	68 (100 %)
Head and neck	19	18	37 (54 %)
Chest	9	1	10 (15 %)
Abdomen	5	4	9 (13 %)
Pelvis	2	-	2 (3 %)
Spine	1	1	2 (3 %)
Extremities	7	1	8 (12 %)

The median of ISS was 22 (29-17). Injury severity > 17 – 48 patients (66 %), other 25 patient – 17. 23 (32 %) and 25 (34 %) were in prognostically unfavorable zone (MFS-I > 15, ISS > 24). New RTS was 8 (9-2) initially and was classified as (the table 1): terminal – 3 (2), extremely severe – 5 (2), severe – 39 (6), average – 25 (1), satisfactory – 1 (1). The statistics of lethal outcomes is presented in the brackets. Condition improved insignificantly after preevacuation preparation – 8 (10-0) points (p > 0.05). Condition was achieved to stabilize in 27 cases (37 %); it was without changes in 26 cases (36 %) and worsened in 20 (27 %). SAE was used more often in case of worsening condition – in 8 cases (40 %). The absolute amount of patients (66 persons, 90.4 %) were transferred from trauma centers of level 3 (48.5 %) and level 2 (51.5 %). The indication for ME was impossibility of arrangement of appropriate medical care in these MFs.

12 patients died after ME (16.4 %). The patients in satisfactory and middle severity condition had thermical flame burns with square of 84 % (72 %) and 80 % (52 %). The mean score in other deceased patients was 4.5, i.e. unfavorable prognosis. 3 patients showed improvement in their condition, 3 patients – worsening, other 6 – without changes. 4 patients (50 %) with unfavorable prognosis survived. After adequate preevacuation preparation of the patient in terminal condition (2 points), the severity of condition was extremely severe (5 points). SE was conducted and the patient survived. ISS was 27 (34-17), MFS-I – 18 (22-7), meaning the poor outcome. A half of the patients had some prognostic signs of poor outcome according to MFS-I, 8 patients (67 %) – according to ISS. The relationship between poor outcome according to ISS and a lethal outcome was reliable (p = 0.03). A half of deceased patients were evacuated with AV. The table 3 shows the detailed statistics of distribution of ME cases according to injury severity.

Table 3

Distribution of patients with favorable and unfavorable prognosis

Objective criterion		Medical evacuation		Outcome
Objective criterion		Urgent evacuation	Urgent aviation evacuation	Survived	Died
Unfavorable outcome	Military Field Surgery-Injury ≥ 15 (n = 23*)	19	4	17	6*
	ISS ≥ 24 (n = 25**)	19	6	17	8**
	NRTS ≤ 4 (n = 7***)	5	2	4	3***
Favorable outcome	Military Field Surgery-Injury < 15 (n = 50*)	33	17	44	6*
	ISS < 24 (n = 48**)	33	15	44	4**
	NRTS ˃ 4 (n = 66***)	47	19	57	9***

Note: *, *** – unreliable differences (p ≥ 0.05); ** – reliable differences.

SE in unfavorable prognosis according to injury severity was realized in 19 cases (83 % of cases for MFS-I, 76 % of cases for ISS) with mean transfer distance of 165 km. It testified that AVs for arrangement of tactical ME in severe trauma were used insufficiently. At the same time, long term SE was only in 1 case with extremely severe condition of patients (NRTS ≤ 4). In other 4 cases, the transfer distance was not more than 200 km (79 km on average) that was tactically substantiated. The higher use of AV for evacuation of patients with favorable prognosis was associated with the fact that urgent measures were not required and ME was arranged according to availability of AV.

CONCLUSION

There is a current substantiated opinion that the notion of non-transportability has been becoming quite relative, considering the presence of modern equipment with ability for complete maintenance vital functions and presence of trained medical staff. Our criteria of transportability show their efficiency. Other authors indicate the similar data. Prediction of outcome of SI is a key factor for selection of indications and a method of ME. It is necessary to continue the research of uniform normative criteria of transportability.

Information on financing and conflict of interests

The study was conducted without sponsorship. The authors declare the absence of any clear or potential conflicts of interests relating to publication of this article.