Early Enteral Nutrition in Aeromedically Evacuated Critically Ill/Injured Patients With a Resultant Validation Algorithm for the Theater Validating Flight Surgeon.

INTRODUCTION: Early enteral feeding in critically ill/injured patients promotes gut integrity and immunocompetence and reduces infections and intensive care unit/hospital stays. Aeromedical evacuation (AE) often takes place concurrently. As a result, AE and early enteral feeding should be inseparable. MATERIALS AND METHODS: This retrospective descriptive study employed AE enteral nutrition (EN) data (2007-2019) collected from patients who were U.S. citizens and mechanically ventilated. The dataset was created from the En Route Critical Care, Transportation Command Regulating and Command and Control Evacuation System, and Theater Medical Data Store databases. Comparisons were performed between patients extracted and patients not extracted, patients treated with EN and patients treated without EN, and within the EN group, between AE Fed and AE Withheld. The impact of the nutrition support in the Joint Trauma System Clinical Practice Guidelines (CPG) was assessed using the 'before' and 'after' methodology. RESULTS: An uptick in feeding rates was found after the 2010 CPG, 15% → 17%. With the next two CPG iterations, rates rose significantly, 17% → 48%. Concurrently, AE feeding holds rose significantly, 10% → 24%, later dropping to 17%. In addition, little difference was found between those patients not enterally fed preflight and those enterally fed across collected demographic, mission, and clinical parameters. Likewise, no difference was found between those enterally fed during AE and those withheld. Yet, 83% of the study's patients were not fed, and 18% of those that were fed had feeding withheld for AE. CONCLUSIONS: It appeared that the Clinical Practice Guidelines (CPGs) reinforced the value of feeding, but may well have sensitized to the threat of aspiration. It also appeared that early enteral feeding was underprescribed and AE feeding withholds were overprescribed. Consequently, an algorithm was devised for the Theater Validating Flight Surgeon, bearing in mind relevant preflight/inflight/clinical issues, with prescriptions designed to boost feeding, diminish AE withholding, and minimize complications.

Decompression Sickness Risk Assessment and Awareness in General Aviation.

INTRODUCTION: Decompression sickness (DCS) can occur during unpressurized flight to altitudes >18,000 ft (FL180; 5486 m). To our knowledge, this has not been studied in general aviation (GA). This knowledge gap may have public health and safety implications because the most popular models of GA aircraft by sales volume are capable of flying >FL180.METHODS: Data from a 1-yr period in a commercial flight tracking database were analyzed to identify flights >FL180 in unpressurized, piston aircraft in the United States. Peak altitude and duration at that altitude were used to calculate DCS risk employing the U.S. Air Force (USAF) Altitude Decompression Sickness Risk Assessment Computer (ADRAC). Registration numbers were cross referenced in publicly available federal databases to identify any events that might be attributable to impairment due to DCS. A web-based survey of practices and associated symptoms was also made available to GA pilots through an online discussion forum.RESULTS: During the data collection period, 1696 flights occurred. The DCS risk was calculated to be 1.9 4.2%. There were 42 responses to the survey. Of these, 25 (59.5%) pilots reported having flown at altitudes >FL180 and 21 (84%) of them reported symptoms possibly attributable to DCS. None sought medical attention. No safety events were identified for any of the aircraft during the study period.CONCLUSION: The risk of DCS in the GA community is not zero. As GA aircraft performance profiles advance and sales increase, this may have significant implications from a public health and safety perspective. Further study is warranted.Harrison MF, Butler WP, Murad MH, Toups GN. Decompression sickness risk assessment and awareness in general aviation. Aerosp Med Hum Perform. 2021; 92(3):138145.

Clinical Impact of Cabin Altitude Restriction Following Aeromedical Evacuation.

Combat medical care relies on aeromedical evacuation (AE). Vital to AE is the validating flight surgeon (VFS) who warrants a patient is "fit to fly." To do this, the VFS considers clinical characteristics and inflight physiological stressors, often prescribing specific interventions such as a cabin altitude restriction (CAR). Unfortunately, limited information is available regarding the clinical consequences of a CAR. Consequently, a dual case-control study (CAR patients versus non-CAR patients and non-CAR patients flown with a CAR versus non-CAR patients) was executed. Data on 1,114 patients were obtained from TRANSCOM Regulating and Command and Control Evacuation System and Landstuhl Regional Medical Center trauma database (January 2007 to February 2008). Demographic and clinical factors essentially showed no difference between groups; however, CAR patients appeared more severely injured than non-CAR patients. Despite being sicker, CAR patients had similar clinical outcomes when compared with non-CAR patients. In contrast, despite an equivocal severity picture, the non-CAR patients flown with a CAR had superior clinical outcomes when compared with non-CAR patients. It appeared that the CAR prescription normalized severely injured to moderately injured and brought moderately injured into a less morbid state. These results suggest that CAR should be seriously considered when evacuating seriously ill/injured patients.

Patient-Centric Side Effect Risk Assessment for Medications Used During Aeromedical Evacuations.

BACKGROUND: The U.S. Air Force performs more than 6000 aeromedical transport flights annually, both internationally and domestically. Many of these flights include patients requiring pain relief medications. The risk of side effects from such medications administered at altitude is unknown, but understanding these risks is vital when selecting the safest pain management strategies to achieve optimal postflight outcomes. METHODS: Using an evidence-based medication side effect risk assessment model, we compared our patient-centric approach to an aircrew-centric approach using medications approved for use in U.S. Navy aircrew. We then determined the patient-centric side effect risk of medications commonly used during Air Force aeromedical evacuation (AE). RESULTS: The patient-centric approach to medication side effect risk assessment demonstrates that the majority of medications currently approved for use during AE have an acceptable side effect risk for the patient (18/22, 82%). Four approved drugs displayed significantly elevated patient risk, with risk scores between 2.0- and 3.2-fold greater than the statistically determined upper allowable ("acceptable") limit and between 1.2- and 2.0-fold above the upper control ("tolerable") limit. DISCUSSION: Our results suggest that pain management strategies during AE should be tailored individually to minimize the risk associated with pain medications administered en route.Huntsberger SA, Butler WP, Chapleau RR. Patient-centric side effect risk assessment for medications used during aeromedical evacuations. Aerosp Med Hum Perform. 2017; 88(4):423-426.

A Retrospective Cohort Analysis of Battle Injury Versus Disease, Non-Battle Injury-Two Validating Flight Surgeons' Experience.

Today, military combat medical care is the best it has ever been. Regulated U.S. Air Force aeromedical evacuation (AE) is one important reason. The Theater Validating Flight Surgeon (TVFS) validates that a patient is ready for flight. Two TVFSs' experiences, successively deployed in 2007, are the focus of this study. A unique operational worksheet used to manage the AE queue was used for approximately 5 months. A descriptive analysis of the worksheet's 1,389 patients found the majority male (94%), median age 30 years, and mostly Army enlisted soldiers (63%). U.S. civilians made up 9%. Battle Injury (55%) surpassed Disease, Non-Battle Injury (45%); most frequently seen were extremity injuries (73%) and cardiac illness (31%), respectively. Common to both Battle Injury and Disease, Nonbattle Injury were several TVFS prescriptions including no "remain overnights" (79%), head of bed elevation (78%), cabin altitude restriction (57%), no stops (44%), Critical Care Air Transport Team (27%), and supplemental oxygen (22%). This study is a first look at the TVFS experience and it offers up an initial accounting of the TVFS clinical and prescriptive practices. It is also a jumping point for future TVFS investigations using the available AE databases.

Complication Rates in Altitude Restricted Patients Following Aeromedical Evacuation.

INTRODUCTION: Military aeromedical evacuation, especially that associated with the present Middle East conflict, is seeing increasing research. This ecological study initiates research into the validating flight surgeon by looking at cabin altitude restriction (CAR), arguably the validating flight surgeon's prescription with the highest patient-mission impact, and its association with postflight complications. METHODS: CAR rates from January 2006 through February 2008 were determined from the U.S. Transportation Command Regulating and Command and Control Evacuation System database. Postflight complication rates-the rate of patients with postflight complications (PFC) and the postflight complications per 100 patients (PFC-100)-from January 2007 through June 2008 were calculated from the Landstuhl Regional Medical Center trauma database. CAR and complication rates were examined before, during, and after the authors' deployment. In addition, the relationship between CAR and postflight complication rates was investigated; as the rates were nonlinear, a Spearman correlation was performed. RESULTS: CAR rates during the authors' deployments were significantly up compared to the authors' predecessors or successors; their predecessors and successors did not differ statistically. Likewise, the PFC rate during the authors' deployments was significantly lower than that of the before or after time frames. Furthermore, a statistically significant inverse relationship between CAR and PFC rates (Spearman rho = -0.587) as well as CAR and PFC-100 rates (Spearman rho = -0.568) was demonstrated. DISCUSSION: CAR rate was inversely correlated to PFC and PFC-100 rates. This finding suggests that aggressive prescribing of CARs may have a salutary effect on postflight complication rates and bears further investigation.

Altitude decompression sickness incidence among U-2 pilots: 1994-2010.

INTRODUCTION: The U-2 aircraft exposes its pilots to cabin pressures equivalent to 29,500 ft (8992 m) during flight, placing them at risk for decompression sickness (DCS). Historical data documenting DCS in the U-2 pilot community is lacking. This study assesses how rates and types of DCS have changed temporally in the U-2 flight program. METHODS: We created a database of all DCS cases among U-2 pilots from 1994 through 2010. Cases were analyzed by date of occurrence and symptoms experienced. Flight data were collected to calculate DCS incidence rates. RESULTS: From 1994-2010, there were 73 documented DCS cases in U-2 pilots. Between 1994 and 2005, the number of annual cases ranged from 0-5; between 2006 and 2010, the number of annual cases increased to 6-10. Additionally, there was a trend toward more severe (neurologic and pulmonary) cases between 2006 and 2010 with 22 cases compared to 10 cases the preceding 12 yr. The most common presentations of U-2 DCS were joint pain (59%), mainly involving large joints, and generalized neurologic symptoms (44%). From 2006-2010, there was an increase in the average annual flight hours per pilot to meet wartime operational needs that correlated temporally with the increase in number and severity of DCS cases. The DCS risk per flight was 0.076% from 1994-2005 but increased to 0.23% from 2006-2010. CONCLUSIONS: DCS remains prevalent among U-2 pilots. An increase in number and severity of cases correlated temporally with increased operational tempo of the U-2 squadron. Changes in cockpit pressurization and limiting the length and frequency of hypobaric exposure may reduce future incidence.

Aeromedical decision making--it may be time for a paradigm change.

Recent events in the U-2 and F-22 fleets have challenged aeromedical experts, highlighting the need for better in-flight aircrew physiologic and cognitive monitoring capability. Existing aerospace medicine risk assessment tools, while necessary, are no longer sufficient to affect positive safety changes given the evolving nature of the aerospace environment. Cognition and its sub-elements are now primary measures for the "Fit to Fly" decision. We must investigate practical methodologies for determining dynamic aircrew physiologic and cognitive function preflight (selection, retention) and in-flight (selection, retention, performance enhancement). In 2010, a panel of aeromedical experts met to address current paradigms and suggest possible solutions. This commentary briefly summarizes panel findings and recommendations.

Pressurized flight immediately after splenic infarction in two patients with the sickle cell trait.

Splenic infarction in individuals harboring the sickle cell trait can occur in the setting of exposure to low oxygen tension at high altitudes. While this is a concern in unpressurized aircraft flight, it has not been well documented in pressurized flight. What has not been addressed is whether this relative safety of pressurized flight extends to the postinfarction period and whether or not pressurized flight in the immediate post-infarction period, especially air evacuation, would change the patient's outcome. We present two cases of splenic infarction suffered during climbing Mt. Fuji (12,388 ft, 3776 m) in patients harboring the sickle cell trait. Both patients were initially assessed and misdiagnosed by a local hospital. They then voluntarily took a 2-h, 30-min pressurized commercial flight [cruising altitude 40,000 ft (12,192 m), minimal cabin pressure: 0.73 atmospheric pressure] within 48 h of their initial presentation. Shortly after their arrival in their final destination they underwent a full workup, including a contrast enhanced CT scan, and were found to have the above-mentioned diagnosis. In both cases, supportive care was sufficient; both patients recovered without sequelae and did not deviate from what would be considered the standard, expected natural history of splenic infarction in patients with the sickle cell trait. It would seem from this anecdotal experience that pressurized commercial flights undertaken in the immediate post-splenic infarction period by individuals with the sickle cell trait may not change either the disease course or the patient's outcome and might be safe.

Decompression sickness rates for chamber personnel: case series from one facility.

During 2004, a case series of decompression sickness (DCS) meeting the definition of epidemic DCS was observed in the Shaw AFB Physiological Training Program. There were 10 cases of chamber-induced altitude DCS observed. Internal and external investigations focused on time, place, person, and environment. No temporal trend was observed. Chamber, masks, regulators, crew positions, and oxygen sources revealed no defects. Among the cases, mean age was 27 yr. Peak altitude in four cases was 35,000 ft and in the other six cases was 25,000 ft. Six had joint pain, one skin symptoms, and three neurological findings. Four were treated with 100% ground-level oxygen and six with hyperbaric oxygen. Four were students and six were inside observers (IO). Four were women and six men. In the IO, where four of the six were women, no gender effect was seen. Examining the IO monthly exposure load (exposures per month) against DCS suggested a dose-response relationship. This relationship held true when 4 yr of Shaw AFB IO data was studied. Indeed, Poisson regression analysis demonstrated a statistically significant 2.1-fold rise in DCS risk with each monthly exposure. Consequently, the number of exposures per month may need to be considered when devising IO schedules.

Frostbite in a mountain climber treated with hyperbaric oxygen: case report.

We describe a case of frostbite to all fingers of a mountain climber, treated with hyperbaric oxygen (HBO). All fingers eventually healed to full function, with only some cosmetic deformity to the tip of the most severely affected finger. Because few cases of frostbite treated with HBO have been reported, we hope that such case reports will stimulate future research in this area. It is hoped that multiple anecdotal cases may help guide future research in this area. Sequential digital photographs were taken at various stages of healing during HBO treatments. We raise the possibility of photographic techniques and standards that may facilitate planning of therapy for frostbite with improved treatment comparisons, resulting in more consistency in the future. For example, a graphical software application is described that allows morphing of sequential images to demonstrate healing progress in a concise movie format. The morphing allows concise demonstration of healing to the referring provider and patient and helps in teaching and research on frostbite treatment outcomes.

Headache and altitude decompression sickness: joint pain or neurological pain?

INTRODUCTION: Exposure to reduced ambient pressure may result in decompression sickness (DCS). Headache is among the DCS symptoms encountered and is usually regarded as neurological DCS, which is traditionally classified as serious DCS. Since cranial sutures may be considered joints, it is possible that some headaches are actually joint pain and when associated with decompression sickness need not be neurological DCS. METHODS: Records were individually recovered from the Davis Hyperbaric Laboratory at Brooks City-Base, TX. Information was extracted using a detailed survey instrument. Possible joint pain headache cases were identified using three criteria: headache localized at a suture, normal neurologic exam, and resolution within 30 min of hyperbaric oxygen treatment. RESULTS: A total of 729 records documenting treatment for DCS were scrutinized. Of these, 70 cases of altitude DCS with headache were examined. Analysis, using the three criteria, showed 23% (16 cases) of altitude headache DCS symptoms could potentially be re-classified as joint pain. CONCLUSION: Generally, headache DCS is considered neurological DCS. However, since cranial sutures are joints, both histologically and functionally, and since DCS most commonly affects joints, headache DCS may, at times, be joint pain DCS. Indeed, retrospective data analysis suggests that this possibility exists. Such a reclassification from neurological to joint pain DCS would lessen the aeromedical impact of a DCS headache.

The ex vivo pig eye as a replacement model for laser safety testing.

The purpose of this study was to evaluate the viability of ex vivo pig eyes as a replacement model for in vivo testing in the establishment of laser eye safety standards. Previous studies of pulsed energy absorption at 3.8 microm were performed using rhesus monkey cornea at pulse durations two orders of magnitude shorter than the 8-micros pulses used in the current study. Ex vivo pig eyes were exposed to laser pulses of various energies and then evaluated to establish the statistical threshold for corneal damage. Tissue analysis (histologic evaluation) was used to determine the extent of damage to the cornea. These results can be used in the establishment of safety standards for laser use; our findings also suggest that ex vivo pig eyes are suitable models for this purpose.

Epidemic decompression sickness: case report, literature review, and clinical commentary.

BACKGROUND: Decompression sickness (DCS) is a syndrome of symptoms caused by bubbles of inert gas. These bubbles are produced by a significant ambient pressure drop. Although cases are usually solitary there have been several episodes of DCS clusters. This paper reports an episode of epidemic decompression sickness and reviews the literature. METHODS: The case reported describes six aircrewmen with DCS following an unpressurized AC-130 flight (maximum altitude 17,000 ft). Two obvious concerns-the low altitude at which DCS was encountered and the potential for epidemic hysteria-are discussed and discounted. In addition, factors contributing to this case are recounted in depth. Moreover, the literature was examined for similar cases of epidemic decompression sickness. Four other instances were discovered. Detailed qualitative analysis of these five reports was performed. RESULTS: With this information epidemic decompression sickness is defined and classified. Two types are described-individual-based (Epi-I) and population-based (Epi-P). Epi-I is a cluster of DCS following a solitary exposure; whereas, Epi-P is a cluster of DCS following multiple exposures over time. Investigation of Epi-P follows the classical rules of outbreak investigation (time, place, person, and environment); whereas, Epi-I does not. In fact, the focus in Epi-I is almost entirely the environment. Following this outline should produce an etiology that control measures can be directed against. However, it is prudent to look beyond the etiology. Enter the Haddon Matrix, a classic public health tool that considers counter-measures before, during, and after the event. CONCLUSION: These many concepts are illustrated with the presented case. Following this template, both the expert and the novice flight surgeon have a systematic and reproducible approach to these difficult puzzles.

USAF treatment table 8: treatment for altitude decompression sickness.

INTRODUCTION: Altitude decompression sickness (DCS) has been treated with hyperbaric therapy since 1941. Treatment has essentially followed the diving DCS paradigm. Expanding space operations and higher flying, more remotely placed military aircraft have stimulated a re-examination of this paradigm. Can the oxygen and pressure-producing resources in these austere environs be reduced without sacrificing treatment efficacy? METHOD: A prospective series of 12 patients was treated with a new treatment table. USAF Treatment Table 8 (TT8) consists of 100% oxygen delivered at 2 ATA for four 30-min periods with intervening 10-min air breaks (a total oxygen dose of 2 h). Inclusion spanned 1985-1989. RESULTS: There were 10 patients who were treated 11 times for Type I altitude decompression sickness. Treatment was successful in 91%. There was one failure (a recurrence of elbow pain) requiring further therapy. Two patients were treated for Type II altitude decompression sickness. Treatment was successful in 50%. There was one failure (incomplete clearance of sensory deficits and weakness in the shoulder) requiring further therapy. CONCLUSION: Although TT8 had two failures, its successes suggest that a new protocol for the treatment of altitude decompression sickness is viable. In addition, its successes further suggest that a more extensive clinical trial is in order.