Chapter 66. Regional Anesthesia in Austere Environment Medicine

Regional anesthesia has played a pivotal role in the development of anesthesiology as a medical specialty since the discovery of the local anesthetic properties of cocaine by Carl Köller in 1884. In the decades since this landmark discovery, surgeons and anesthesia providers have appreciated the advantages of regional anesthesia in their patients, particularly in surgical situations complicated by limited resources and austere environmental conditions. War, more than any other human endeavor, has driven the need to provide effective anesthesia for surgery in austere environments. Indeed, the development of anesthesiology as a distinct specialty has been attributed to the medical experience obtained in World War II.1 The physician–anesthetists of that era quickly recognized that regional anesthesia imparted the least physiologic insult to the wounded soldier and allowed a more awake patient to be returned to the recovery ward, thus reducing the burden on limited wartime medical resources.1 As anesthesiology matured as a medical specialty and departments of anesthesiology began to break away from departments of surgery in academic centers, regional anesthesia continued to evolve. During the Vietnam War, the value of regional anesthesia in harsh medical conditions was reestablished. In one series of 1000 battle casualties, nerve block, spinal, or local anesthesia was used in 49% of cases. “This allowed increased anesthesia coverage of more surgical procedures at any one time as well as decreasing the demands on postoperative ward personnel in a multiple casualty situation.”2 The role of regional anesthesia in combat casualty care continues to expand in modern conflicts. Consequently, military medical planners are understandably interested in austere environment anesthesia due to the realities of military wartime missions. Civilian anesthesiologists are also interested in the advantages of regional anesthesia in austere environments for disasters, civil defense, or missions to medically underserved regions of the world.

In the last 15 years regional anesthesia has undergone a renaissance. New equipment, such as peripheral nerve stimulators and ultrasound technology have facilitated block placement and enhanced resident training in regional anesthesia. Continuous peripheral nerve block catheters and peripheral nerve infusion pumps have extended the benefits of regional block techniques beyond the immediate perioperative period to days after an operation and even into the home.3 In this chapter the advantages and application of advanced regional anesthesia in austere environment medicine will be examined. The role of recent advances in regional anesthesia equipment and techniques in facilitating anesthesia in less than ideal conditions will also be discussed.

The practice of medicine in an austere environment requires a significantly different approach than that used for medicine practiced in the major medical centers or in developed countries in general. This is especially true for the practice of anesthesiology. In developed countries, the anesthesiologist has a tremendous resource base that is readily available and largely transparent to the production of an anesthetic plan. The utilities, roads, computers and other wonders of modern infrastructure common to developed nations are rarely noticed by anesthesiologists, but they impart a tremendous advantage in ensuring a successful anesthetic outcome. In contrast, the anesthesiologist practicing austere environment anesthesiology (AEA) becomes very aware of the effect limited resources can have on anesthetic decisions. In AEA, the anesthesiologist must factor local infrastructure realities into anesthetic plans. Anesthetic choices and plans that work well in state-of-the-art operating rooms can have disastrous consequences if applied to austere environments without due consideration of local resources and conditions. The available roads; electrical, sanitation, medical gas services; climactic conditions; and operating room facilities, among other issues, will greatly affect the anesthetic plan in AEA.

The influence of local environmental and weather conditions on AEA is a particularly important consideration, especially during medical missions following natural disasters. Temperature and terrain extremes, along with dangerous faunae and disease must be included in any successful anesthetic plan in these environments. Temperature extremes can affect patient health directly and degrade equipment, medication, and anesthesiologist function. Rough terrain can affect practitioner and patient travel, impede communication, and limit resupply of consumable medical supplies. Finally, local geopolitics, in its most extreme form, war, can have a tremendous influence on AEA.

One approach to overcoming the realities of AEA is to surmount local resource limitations by transporting the modern anesthesia infrastructure to the AEA location, thus freeing the anesthesiologist from many if not all of these considerations. This approach is best illustrated by the U.S. military in caring for wounded soldiers on the battlefields of Iraq and Afghanistan through the fielding of combat support hospitals (CSH) that have capabilities similar to civilian hospitals in developed countries (Figure 66–1). While the CSH is a successful approach to caring for injured patients anywhere in the world, the logistics required to place and support such a facility are well beyond the capability of most humanitarian medical mission planners or disaster medicine planners.

Because of the logistical constraints and the environmental realities inherent to AEA, anesthesiologists involved in these types of missions must find anesthetic and analgesic techniques that require minimal logistical support, provide adequate surgical conditions, afford postoperative pain control, and result in a patient that is alert in the postoperative recovery room. Modern advanced regional anesthesia has many characteristics that make it an attractive choice for AEA missions (Table 66–1).

Compared with general anesthesia using a volatile anesthetic, regional anesthesia is particularly suited for AEA because of its small logistics footprint. The equipment for regional anesthesia (peripheral nerve stimulator, single-injection or continuous peripheral nerve block needle and tubing, local anesthetic, and infusion pump) is compact, lightweight, and easily transported. In contrast, the equipment used to deliver volatile anesthetics does not posses these attributes (Figure 66–2). Though general anesthesia remains the gold standard for AEA, this capability must be planned for and surgical cases that demand general anesthesia carefully triaged. The availability of compressed oxygen can often dictate the number and types of cases that can be managed in austere environments. Many anesthetic ventilators are pneumatically driven and can consume significant quantities of compressed oxygen during a typical general anesthetic. Oxygen cylinders or oxygen generation equipment (eg, the portable oxygen generation system [POGS] shown in Figure 66–2B which required six men to lift into place) can represent a significant logistics challenge to any AEA mission. Possible alternatives to pneumatically driven volatile anesthetics include draw-over anesthesia or total intravenous anesthesia (TIVA) using target-controlled infusion (TCI) pumps. These alternatives remain in development and may not be available to many anesthesiologists. Whenever possible, regional anesthesia is the preferred technique for most cases during an AEA mission because it allows conservation of resources that may be required for more complicated surgeries or emergencies.4

Regional anesthesia provides excellent operating conditions for the surgeon. With the establishment of a surgical block, motor, sensory, and sympathetic nerves to a body region are blocked. This provides muscle relaxation,5 preemptive analgesia,6 reduced overall stress response to surgery,7 a reduction in thromboembolic complications,8 and reduced blood loss.9,10 Because afferent nociceptive stimulation from the surgical site is greatly attenuated or eliminated during the operative procedure, stable hemodynamics are characteristic of regional anesthesia. In AEA, when monitoring capability is often constrained, intraoperative hemodynamic stability is important. Regional anesthetic techniques allow the procedure to be performed on an awake or lightly sedated patient who can communicate with the anesthesiologist, providing the best monitor of patient well-being.

Postoperatively, the advantages of regional anesthesia in AEA become even more apparent. Unlike general anesthesia, which provides for little to no postoperative analgesia, regional techniques with long-acting local anesthetics maintain analgesia for hours following the operation. If continuous peripheral nerve block (CPNB) techniques are employed, analgesia can be extended for days postoperatively. Another important benefit of regional anesthesia in the postsurgical recovery area is the improved alertness and reduced nausea and vomiting associated with these techniques compared with the affects from general anesthesia. In the modern ambulatory surgery setting, the increased incidence of postoperative nausea and vomiting, drowsiness, and pain are the most frequent causes of prolonged postoperative stay.11,12 Although these issues have economic significance in developed countries, in the resource-limited practice of AEA, difficult recovery can have a profoundly negative effect on mission success. Recovery area personnel and monitoring capability are usually limited in AEA. Anesthesiologists working in this environment favor techniques, like regional anesthesia, that facilitate sending alert patients, free of pain and nausea, who can be active proponents in their recovery despite limited resources. Rapid recovery of the patient's own airway protective reflexes is a significant advantage of regional compared with general anesthesia in AEA.

Effective perioperative pain management is an important consideration following any operative procedure regardless of the location and conditions under which it is performed. Since Serturner, a German pharmacist, first identified and isolated morphine from opium in 1803, morphine and other opioid drugs have played a major role in pain management in austere environments, especially in the military. Although the preeminence and success of opioid medications in pain management is well established, their use is not without significant side effects that are undesirable in the best medical environments but can be potentially devastating in AEA. International regulations concerning the transportation of opioids and limited monitoring capability can further complicate the use of these drugs in AEA. Studies have demonstrated a reduced requirement for opioid pain medication following surgery when regional anesthesia techniques are used.3,13 Using CPNB techniques, pain relief can be extended for days, further reducing the need for opioid pain medications. The efficacy of CPNB infusions have been demonstrated in the ambulatory surgery setting, allowing anesthesiologists to extend the benefits of peripheral nerve block following surgery well into the patient's recovery at home.14–16

Despite the benefits of regional anesthesia techniques, information regarding the use of CPNB in AEA is limited. Recently, the use of CPNB for surgical anesthesia and analgesia on the modern battlefield and throughout the evacuation chain back to the United States has been demonstrated successfully.17 Since this first success, CPNB catheters have been increasingly used to treat a number of patients within the Iraq combat theater. The application of regional anesthesia, CPNB in particular, has been one of the medical success stories to emerge from the military's experience in the Iraq war. Although the technology remains new to the modern battlefield and is far from being universally accepted, many soldiers have enjoyed the benefits of advanced regional anesthesia and CPNB in the management of their combat wounds in the austere battlefield environment of Iraq. Advances in soldier body armor and the Iraq insurgent's preference for using improvised explosive devices has resulted in a preponderance of extremity wounds and traumatic amputations. The application of CPNB catheters in many of these patients has facilitated the multiple operative procedures they often undergo since reestablishment of a surgical block can be easily accomplished via the existing catheter(s). Additionally, the analgesic block provided by CPNB allows for far superior pain control on the long, jarring evacuation flights to Germany and the United States compared with morphine alone, which until recently was the only option for pain control on an evacuation aircraft.

Despite this initial success, the military has been slow to embrace advanced regional anesthesia as a viable battlefield medicine standard of care. The reasons for this reluctance are numerous and not easily defined, but worth exploring since the military medical community's concerns over advanced regional anesthesia will also provide insight into why, despite its many advantages, advance regional anesthesia is not the predominate anesthetic for AEA. First, general anesthesia with volatile anesthetics is the “gold standard” anesthetic in developed countries. The safety and efficacy of general anesthesia has been established over the decades with countless successful applications. Anesthesiology training programs focus on general anesthesia techniques, and most practitioners are very comfortable with its use for all surgical indications. Unfortunately, the technology and personnel support needed to employ general anesthesia successfully can quickly exhaust the resources available during AEA as previously noted. In the U.S. military, a tremendous investment has been made in technology to safely provide general anesthesia to war casualties, regardless of the environment. Additional requirements on the military medical supply system, such as advanced regional anesthesia, are less attractive to medical logistical planners when so much effort has been directed toward volatile-anesthetic-based general anesthesia. Although the capability to perform general anesthesia in AEA is vital, general anesthesia is not necessarily the best choice for every clinical situation encountered on the mission. The availability of other options is a key to AEA mission success.

Lack of training in advanced regional anesthesia has also hampered the development of this anesthetic in the AEA environment.18,19 Advanced regional anesthesia training, at least in U.S. anesthesiology residency programs, is far from what it needs to be for these techniques to become ubiquitous within the anesthesia community and not just the domain of a select few regional anesthesia specialists. A considerable investment is required by the anesthesiologist to learn block techniques and detailed human anatomy before advanced regional anesthesia can become part of routine anesthesia practice. The increased availability of regional anesthesia courses, the development of regional anesthesia fellowship training programs, and the explosion of interest in the medical literature suggests that this issue may become moot in the not too distant future. In the military, the Army Regional Anesthesia and Pain Management Initiative, a Congressionally sponsored program established in 2000, has done much to establish advanced regional anesthesia and other modern pain management techniques on the modern battlefield.

During the last decade, along with and complimentary to the resurgence of interest in regional anesthesia, there has been an upsurge in available technology to support and enhance the practice of advanced regional anesthesia. Although these technologies, such as peripheral nerve stimulators, stimulating catheters, portable infusion pumps, and ultrasound, to name just a few, have revolutionized the practice of regional anesthesia, the plethora of equipment to choose from can be confusing. This situation is made worse by the lack of consensus among regional anesthesiologists as to what technologies and practices are best for physician and patient alike. Stimulating versus nonstimulating catheters, ultrasound-directed versus stimulating needle placement, needle sharpness and design, CPNB catheter infusion rates, and bolus parameters are just a few of the topics that often pervade regional anesthesia conference floor discussions. Unlike general anesthesia, modern regional anesthesia (particularly CPNB) does not enjoy decades of safe application and experience in use. This relatively new frontier in anesthesiology and perioperative analgesia attracts many anesthesiologists to the study of advanced regional anesthesia techniques, but it is the discomfort of challenging new technologies and ideas that deters many. Considerable effort is needed to take the “art” out of regional anesthesia and establish its “science” before these techniques can become generally accepted.

Finally, perhaps the most unusual reason for the slow acceptance of regional anesthesia in AEA and in the military is our professional and social attitudes toward pain. The science of understanding pain and its management is a relatively new phenomenon. Before the advent of modern anesthesia practice, surgeons were instructed to not display excessive concern over a patient's discomfort during surgery and to operate fast, since a speedy surgery limited suffering.20 Even after the development of anesthesiology as a medical specialty, pain has been, and still is, considered an unfortunate and unavoidable consequence of surgical intervention. In the AEA environment, expending limited medical resources on the management of pain can seem a luxury. As evidence mounts on the destructive aspects of pain, particularly as it contributes to the overall surgical stress response and postoperative morbidity, effective pain control is fast becoming less a luxury and more a necessary component of successful surgical care.21,22 Though compassion and the relief of suffering is reason enough to provide good pain control, in the twenty-first century it is just good medicine.

The successful application of regional anesthesia in austere environments requires anesthesiologists to embrace their role as physicians of perioperative medicine. Simply put, the anesthesiologist must accept responsibility for the patient's operative care before, during, and long after his or her surgical procedure. Although this extended role for the anesthesiologist beyond the operating room and recovery area is nontraditional, the anesthesiologist is uniquely trained to manage perioperative pain and enhance recovery using a multimodal approach that includes advanced regional anesthesia techniques and technologies. The anesthesiologist's perioperative role is enhanced through the establishment of a regional anesthesia/acute pain section. The anesthesiologist working outside of the operating room in the regional anesthesia/acute pain section facilitates the introduction of advanced regional anesthesia both in modern hospitals and in AEA. This location is equipped with regional anesthesia supplies and should have basic monitors, oxygen, suction, airway and resuscitation equipment and medications in the event of an emergency. This investment in resources has profound advantages in the AEA environment. The regional anesthesia section facilitates patient preparation for surgery, and, if appropriate, blocks with long-acting local anesthetics or CPNB can be established before previous surgery patients are out of the operating room, thus improving efficiency. The block area anesthesiologist is also available to serve as a perioperative medical consultant, critical care provider, and acute pain specialist for recovering patients.

The need for this expanded role of anesthesiologists in perioperative analgesia is exemplified by the austere military medical environment that currently exists in Iraq. In previous conflicts, wounded American soldiers often spent days recovering from combat wounds before they were deemed fit to be evacuated to higher levels of medical care outside of the war theater. In the current War on Terror a soldier's evacuation from point of injury to a major medical facility outside of the combat theater is often measured in hours. This aggressive evacuation policy has contributed significantly to the salvage of many soldiers who likely would have died in previous conflicts. Unfortunately, traditional opioid-based pain management techniques alone are not well suited to the difficult air evacuation environment that makes rapid removal of casualties to distant major medical facilities possible. Medical personnel on evacuation flights are often faced with many wounded patients in significant pain. In the low light, high noise, high vibration, and difficult monitoring environment of evacuation aircraft, the significant side effects associated with opioid-only pain control become magnified. The advantage of CPNB and modern peripheral nerve infusion pumps that allow patients to manage their own pain control is obvious. These catheters also facilitate repeated operations and dressing changes by allowing reestablishment of surgical blocks through bolus administration of local anesthetic via established CPNB catheters. Military anesthesiologists are actively pursuing this technology.

Patients receiving regional anesthesia, as part of their care, should be warned to avoid weight bearing on blocked extremities. They should also be advised to take special precautions to avoid further injury to the blocked region of the body since normal protective sensations and proprioception will be diminished or absent. Patients should also be cautioned about possible side effects that may be associated with specific block procedures. For example, patients receiving an interscalene block should be warned of the possibility of developing Horner's syndrome and a hoarse voice. They should be reassured that these conditions are temporary and will resolve completely with resolution of the block. These warnings are especially important in AEA where cultural differences can heighten patient fears and negatively affect the patient's perception of their anesthetic care. Planning for adequate translator resources is vital for any medical mission in which language differences exist between caregivers and patients.

Using CPNB, the benefits of regional anesthesia can be extended for days into a patient's recovery from surgery. This advantage can have a profoundly positive influence on the care of patients who require evacuation over long distances or have injuries that necessitate frequent surgical interventions or dressing changes. Although this technique has important advantages in AEA, it also presents the medical team with unique management challenges that are best addressed by the regional anesthesia/acute pain anesthesiologist working outside of the operating room. The decision to use CPNB on AEA patients must be individualized to each patient's clinical situation. During the clinical evaluation of the patient for anesthesia, the anesthesiologist will be able to ascertain if the patient is a suitable candidate for CPNB. Not all patients are willing or able to tolerate CPNB infusions despite the relative simplicity of the technology. If a patient remains resistant to CPNB therapy after thoughtful discussion with a physician, then the technique should be abandoned in favor of more traditional anesthetic and pain management techniques. Additionally, personnel resources must be available to monitor and appropriately manage any development of local anesthetic toxicity following a block. The anesthesiologist must also weigh the benefits of applying CPNB for each surgical situation against the risks of the technique. In the author's practice, all patients are warned, “The use of a block needle can result in injury or infection and because we are working near nerves the possibility of nerve damage does exist, though these complications are rare.” The least invasive intervention that can adequately control a patient's pain should always be sought for each clinical situation. Finally, the anesthesiologist must have an established plan for a follow-up of CPNB patients. Follow-up can be as simple as a telephone call, but CPNB patients and their catheters should be evaluated daily. Patients treated with CPNB catheters should also be educated on signs and symptoms of local anesthetic toxicity. The patient must have 24-h access to an anesthesia provider should problems occur during the infusion. Fortunately, the answer for any CPNB infusion problem is the same, stop the infusion, resort to back-up pain medications, seek medical help. The U.S. Air Force has developed a series of infusion pump labels to provide CPNB patients and their caregivers basic instructions during air evacuation to manage infusion problems when an anesthesiologist may not be immediately available (Figure 66–3). Internet e-mail is also a valuable communication tool when physicians and nurses are required to treat CPNB patients that are being transferred to medical facilities separated by great distance. E-mail can often be accessed in the most remote areas where other forms of long-distance communication are unavailable. Although these CPNB management principles may seem burdensome to apply in the AEA environment, the advantages in pain relief for patients are clear and consistent with compassionate anesthetic care. With proper planning, CPNB works well in austere environments.

One of the frequent complaints concerning CPNB infusions is catheter dislodgement. Poorly secured catheters can migrate or fall out, reducing the effectiveness of the technique, especially when patients require evacuation to other medical facilities. Although many devices and procedures are available to secure catheters, in the military evacuation environment and in military hospitals the following CPNB catheter-securing procedures seem to work best. After placement, all catheters are gently aspirated for blood and 5 mL of local anesthetic containing epinephrine 1:400,000 is injected to diagnose possible intravascular placement. Catheters are tunneled for 3 to 5 cm under the skin in any CPNB patient who will be evacuated or is expected to maintain the catheter for longer then 72 h (this includes epidural catheters). Whether tunneled or not, all catheters are secured with cyanoacrylate glue at the skin puncture site,23 followed by a medical spray adhesive. The catheter is looped at the puncture site and further secured with Steri-Strips and a transparent dressing. All catheters are labeled with the site of the block and the date and time of catheter placement.

A variety of excellent peripheral nerve infusion pumps are available. A discussion of infusion pump technology is beyond the scope of this chapter, more information on comparison and contrasting the devices can be found in Chapter 48 (Equipment for Continuous Nerve Blocks).24,25 Currently in the military two different infusion pumps are in use. The Stryker PainPump II (Stryker Instruments, Kalamazoo, MI) is a single-use, disposable electronic infusion pump and is currently the only peripheral nerve infusion pump approved for flight on military aircraft. The amBit (Sorenson Medical, Inc, West Jordan, Utah) is a multiuse, adjustable electronic infusion pump that is currently being used in fixed military medical facilities in Iraq. These devices were selected because of their consistent infusion performance in temperature extremes and at altitude.

A variety of local anesthetics are available for use in AEA regional anesthesia. Ropivacaine is the long-acting local anesthetic preferred by the author for single-injection blocks and CPNB catheter infusions. Compared with other long-acting local anesthetics such as bupivacaine and levobupivacaine, ropivacaine is the safest long-acting local anesthetic available.26,27 Mepivacaine is the intermediate-acting local anesthetic often selected when a shorter duration block is desirable or when catheters are bolused to reestablish a surgical level block for dressing changes or surgery. Table 66–2 provides some examples of effective single-injection and CPNB infusion rates for a variety of regional anesthetic blocks.

In summary, regional anesthesia has characteristics that make its application in the AEA desirable. Although the rewards for the patient in improved postoperative alertness, pain control, and possibly enhanced recovery are apparent, these benefits are only realized through a significant investment by anesthesiologists in the education and the increased effort advanced regional anesthesia requires for successful application. Anesthesiologists who embrace the challenge of advanced regional anesthesia become more versatile anesthesia providers whether their practice is in a modern, high-technology hospital or an isolated, austere tent. As recent events involving terrorism and natural disaster have demonstrated, the ability to provide safe anesthesia and effective analgesia regardless of environmental circumstances is a valuable twenty-first century skill for all anesthesiologists.