Advances in anesthesia delivery in the deployed setting.
DEPLOYABLE ANESTHESIA EQUIPMENT
The evolution of mission requirements and the fluid nature of the battlefield has directed surgical and advanced resuscitation capability to move increasingly forward. Often located within minutes of the point of injury, surgical teams are frequently deployed in elements smaller than the traditional Role 2 forward surgical team. Military anesthesia providers have consistently sought to find the optimal anesthesia equipment set to meet mission requirements, increase mobility, and still maintain the highest standard of anesthetic care. The traditional combat anesthetic is a balanced technique of volatile inhalation gas and intravenous anesthetic adjuncts. In the early phases of Operation Enduring Freedom and Operation Iraqi Freedom, many anesthesia providers deployed with the Ohmeda Universal Portable Anesthesia Complete (PAC) draw-over anesthesia system to deliver volatile inhalation anesthetics. The draw-over meets the requirements discussed above. Since its development in the 1970s, the PAC has proven to be durable, dependable, and relatively lightweight. Additionally, it does not require power or gas flow to deliver an anesthetic. However, the draw-over does have limitations, which include the requirement to scavenge waste gases and the potential, as with all volatile gases, to trigger malignant hyperthermia, a potentially lethal metabolic crisis in susceptible individual. Perhaps the greatest barrier to the continued use of this device is that it is no longer being manufactured by Ohmeda and no commercial vendor has offered a replacement; meanwhile, stockpiles of replacement parts are rapidly being depleted. A similar problem occurred with the Narkomed M anesthesia machine (Dragerwerk AG, Lubeck, Germany) secondary to the manufacturer discontinuing its production. The device was simple and safe and similar in design to anesthesia machines familiar to providers used in the United States. Unfortunately, the Narkomed M failed to meet the criteria for agile surgical teams on many levels. First, the machine and its components weigh close to 200 pounds. Secondly, it requires compressed gas and power for sustained operations. Consequently, the Narkomed M was limited to use by Role 2 (forward surgical team) and Role 3 (combat support hospital/field hospital) medical facilities.
In response to continued requirements for a suitable field anesthesia machine, the Defense Medical Standardization Board convened a Theater Care Anesthesia Working Group to evaluate commercial, off the shelf, anesthesia machines suitable for use in austere environments. The purpose was to quickly field a unit that would replace the Narkomed M while maintaining the standards for safety and mobility. The recommendation forwarded was the Draeger Fabius Tiro M. The most noticeable differences from the Narkomed M was that the Tiro M provided alternative ventilation modes and integrated safety features absent in earlier generations of field anesthesia machines. The familiar technology provided by the Trio M appealed to most anesthesia providers, however, once again this device was designed for Role 2 and higher medical facilities with limited requirements for mobility. The newly fielded Tiro M weighs 200 pounds, has regular maintenance requirements, and requires electrical power to operate the ventilator (battery charge limited to 45 minutes.) There are similar limitations found with the Magellan anesthesia machine. Although it weighs only 45 pounds, which makes it more appealing for field anesthesia, the protective case required for transport adds an additional 65 pounds. As with all other volatile gas machines, this makes the Magellan suitable for Role 2 medical facilities but not practical for mobile surgical teams with weight and cubic restrictions. For these reasons, TIVA, rather than volatile gas anesthetics, may be a more desirable method for providing anesthesia in deployed mobile surgical teams.
The development and implementation of commercially available oxygen concentrators have reduced many of the requirements to maintain large quantities of compressed gas. All commercially available anesthetic machines, however, require a compressed gas source. Most mobile surgical units deploy with E size compressed gas cylinders, which weigh on average 8 pounds empty. Some Role 2 (forward surgical team) facilities deploy with H size compressed gas cylinders, which are over 100 pounds each. The use of compressed gas by surgical teams can create a burdensome logistical problem by introducing the requirement for a robust infrastructure with capability to refill and procure replacement cylinders. In some cases, a local vender may be available, however, a quality control issue is introduced when relying on an outside source.
Patient air and ground transport add an additional consideration when using compressed gas. A traditional alloy-encased bottle may become compromised and suffer catastrophic failure. The explosive release of metal fragments can create safety concerns for air and ground crew personnel. (1) Consequently; the use of Kevlar oxygen bottles has gained support for long distance transport. Kevlar is approximately half the weight of an ordinary, alloy-encased oxygen cylinder. Additionally, the Kevlar casing may help reduce ductile failure, limiting cylinder disintegration and the risk of fragmentation if compromised. (1) However, the unacceptable risk of fragmentation remained, especially for patient transport via aircraft. In an effort to reduce reliance on compressed gas, US Army Medical Department leadership invested in systems that actually generate oxygen through room air concentration at the point of use. This initiative ensured that the supply of oxygen was uninterrupted on the battlefield. (2) Portable oxygen concentrators were subsequently developed, including the Eclipse and Saros (Sequal Technologies, Ltd, Taipei City, Taiwan). The implementation of oxygen concentrators resolved several problems created by compressed gas cylinders. First and foremost, they clearly reduced explosive risk and personnel endangerment. Secondly, they reduced or eliminated logistical requirements incumbent with the use of compressed oxygen cylinders. Finally, the concentrators that have been fielded have demonstrated their ability to remain functional in extreme temperatures and harsh environments, which make them a perfect complement for TIVA administration.
TOTAL INTRAVENOUS ANESTHESIA
The technique or specific drugs used when designing an anesthesia plan for a trauma patient may often appear irrelevant. (3) Experienced providers argue that the best results are achieved by familiarity and experience of the anesthetist. Based on the modality of administration, anesthetics agents can be divided into 2 subclasses: those delivered by inhalation via volatile gases and those delivered intravenously (TIVA). (3) Whether using TIVA or inhalation, either technique must be carefully titrated to the hemodynamic profile while assuring adequate sedation/hypnosis and analgesia. (4) Unfortunately, in some percentage of patients it is nearly impossible in early resuscitation efforts to adequately address all pillars of anesthesia while maintaining hemodynamic stability. Total intravenous anesthesia provides the anesthetist with a unique flexibility. The provider can select individual intravenous agents and concentrations that address analgesia, amnesia, and akinesia with reduced detriment to the patient's hemodynamic stability.
Historically, a typical trauma anesthetic may have been accomplished using 2 simple intravenous medications, scopolamine and a narcotic. However, in the past year, the manufacture of intravenous scopolamine has become very limited leaving anesthesia providers in search of alternative agents for trauma patients in extremist. Intravenous anesthetic management of the trauma patient is still preferred over volatile anesthetic management for emergent airway facilitation and damage control surgery. There are several alternative intravenous agents that have been implemented with varied success. Intravenous medications such as propofol, etomidate, midazolam, and fentanyl have been administered alone and in combination for induction and anesthetic maintenance during trauma resuscitation. One of the most promising intravenous anesthetic agents for trauma is ketamine, an older medication that was previously avoided because of undesired side effects. However, as the clinical management of ketamine administration improves and renewed research provides refutable evidence from previous claims, anesthesia providers have taken a second look at ketamine use in trauma. (5) In fact, some evidence suggests that ketamine may provide a neuroprotective quality by improving cerebral perfusion in neurologic injury. (6)
A number of studies have compared TIVA and volatile anesthetics. The results demonstrated in Englehart et al showed that a TIVA regimen produced less pronounced hypotension then isoflurane in uncontrolled hemorrhagic shock. (6) The study suggested that in circumstances of limited resources, such as mobile surgical teams, a ketamine-based TIVA regimen might be a viable option. Ketamine is a noncompetitive antagonist of the N-methyl-D-Aspartate (NMDA) receptor. It demonstrates several beneficial pharmacodynamic effects in the setting of hypotension due to the fact that it increases sympathetic tone, which leads to an increase in heart rate, blood pressure, and cardiac output. (7) This is a significant advantage in a cohort of trauma patients including adults, children, and polytrauma patients who are hypotensive secondary to hypovolemia. (7) A popular medication used in the induction of anesthesia and maintenance of general anesthesia is propofol. Propofol is a short acting, hypnotic/amnestic agent. Although propofol has an appealing pharmacokinetic profile, it has been associated with hypotension. Shearin et al (8) determined that 16.5% of trauma patients who were administered propofol only infusions developed hypotension. Therefore, an alternative to propofol alone is the mixture of ketamine with propofol known as "ketofol". According to Smischney et al, (9) propofol was more likely to generate a 20% reduction in systolic blood pressure compared to "ketofol" which was associated with significantly improved hemodynamic stability.
Total intravenous anesthesia in the deployed setting has additional practical advantages over volatile anesthetics. In wartime trauma resuscitation, the ability to continue to provide anesthesia despite loss of power or equipment failure is crucial. A total intravenous technique can be accomplished without additional equipment or power supply. Occasionally, the deployed setting introduces additional tactical considerations such as environments that require light and noise discipline. An intravenous anesthetic may prove to be a better option than a cumbersome anesthesia machine. The total intravenous technique also allows the anesthesia provider the ability to continuously provide en route patient transport by litter, ground, or air without interruption of amnesia and analgesia.
Recent changes in tactical combat casualty care doctrine have increased the recognition and availability of ketamine in the deployed setting. First line medics are now more familiar with ketamine and frequently include it as a first line adjunct in their medic aid kits. The consorted use of ketamine across the continuum of combat care enables the consolidation of resources in extreme conditions where resupply may be constrained.
The discussion about anesthesia in the deployed austere environment is not a new concept. In 2009, Barras et al (10) summarized many of the same discussion points made in this paper. New paradigms in Army medicine and emergent tactical requirements necessitate smaller, more agile surgical teams to conduct missions with a reduced logistical footprint. Complacency with current practice and equipment should not be status quo for the next conflict. An increased investment in time and resources should be expended on predeployment training and the continued pursuit of alternative anesthetic techniques. Demonstrated success with total intravenous anesthesia remains one of the most promising developments from years of combat lessons learned. Continued educational and training efforts should focus on ensuring that every military anesthesia provider is comfortable delivering TIVA in an unstable trauma patient. Doctrine should support formal TIVA education in military anesthesia curricula for both nurse anesthetist and physician anesthesiologists. Prior to deployment, anesthesia providers should demonstrate proficiency in the administration of TIVA to trauma patients as part of predeployment training.
The effectiveness of any anesthesia provider, however, is also dependent on the effectiveness of the tools they have. Research and development should focus on new and innovative ways of delivering combat anesthesia. Promising investigative projects such as closed loop inhalation anesthesia and racemic versus +S isomer ketamine have been documented in anesthesia journals, however, continued research is necessary. The increased interest in TIVA across the field of anesthesia has prompted several biomedical manufactures to develop target controlled infusers. Target controlled infusers use specifically programmed syringe drivers to enable a more precise titration of anesthetic medication. The infuser operates on algorithms based upon pharmacokinetic and pharmacodynamic data to an estimated target concentration in blood. (11) With continued development and clinical trials, this type of infuser shows tremendous promise for future military use in the deployed setting.
Collaborative triservice efforts should guide future studies and focus on the effectiveness of different anesthetics throughout the continuum of care on the battlefield. Future education and deployment training should focus on physiological endpoints and be informed by clinical outcomes. Numerous technological advances have occurred in anesthetic delivery throughout the past decade of war. It is now imperative that we retain these lessons, learn from our missteps, and continue to develop techniques that allow for quicker adaptation to meet future battlefield requirements.
(1.) More Durable Aerospace, Marine, and Rail Equipment [internet]. Du Pont Corporation Website; 2014. Available at: http://www.du pont.com/products-and-services/fabrics-fibersnonwovens/fibers/uses-and-applications/aero space-marine-rail.html. Accessed September 24, 2015.
(2.) Arnold M. US Army Oxygen Generation System Development. Defense Technical Information Center Website; 2010. Report RTO-MP-HFM-182. Available at: http://dtic.mil/dtic/tr/fulltext/u2/ a581789.pdf. Accessed September 24, 2015.
(3.) Schifilliti D, Grasso G, Conti A, Fodale V. Anaesthetic-related neuroprotection: intravenous or inhalational agents?. CNS Drugs. 2010;24:893-907.
(4.) Joint Theater Trauma System Clinical Practice Guideline [internet]. Fort Sam Houston, TX: US Army Institute of Surgical Research; 2014. Available at: http://www.usaisr.amedd.army.mil/cpgs/ Trauma_Anesthesia_16Jun2014.pdf. Accessed September 24, 2015.
(5.) Himmelseher S, Durieux ME. Revising a dogma: ketamine for patients with neurological injury? Anesth Analg. 2005;101:524-534.
(6.) Englehart MS, Allison CE, Tieu BH, et al. Ketamine-based total intravenous anesthesia versus isoflurane anesthesia in a swine model of hemorrhagic shock. J Trauma. 2008;65:901-909.
(7.) McDermott P, Sebastian J. Should Ketamine be used as an induction agent in traumatic brain injury? Br J Hosp Med. 2013;74(9):538.
(8.) Shearin AE, Patanwala AE, Tang A, Erstad BL. Predictors of hypotension associated with propofol in trauma patients. J Trauma Nurs. 2014;21(1):4-8.
(9.) Smischney NJ, Beach ML, Loftus RW, Dodds TM, Koff MD. Ketamine/propofol admixture (ketofol) is associated with improved hemodynamics as an induction agent: a randomized, controlled trial. J Trauma Acute Surg. 2012;73:94-101.
(10.) Barras P, McMasters J, Grathwohl K, Blackbourne L. Total intravenous anesthesia on the battlefield. US Army Med Dep J. January-March 2009:68-72.
(11.) Morton NS. Total intravenous anesthesia (TIVA) and target controlled infusion (TCI) in children. Paediatr Anaesth. 2013;3:37-41.
MAJ Wilson is assigned to the San Antonio Military Medical Center, Joint Base San Antonio-Fort Sam Houston, Texas.
COL Barras is Chief, Clinical Operations, US Army Forces Command Surgeon's Office, Fort Bragg, North Carolina.
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|Title Annotation:||PERSONNEL CHANGES THAT IMPACTED CARE AND OUTCOMES|
|Author:||Wilson, John E., Jr.; Barras, William P.|
|Publication:||U.S. Army Medical Department Journal|
|Date:||Apr 1, 2016|
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