odern warfare has brought both new advancements and new challenges for acute pain management in the combat setting. While survivability has increased thanks to improvements in body armor, the necessarily exposed limbs of soldiers become even more vulnerable to progressively more destructive explosive devices. The lethality of improvised explosive devices (IEDs), explosively formed penetrators (EFPs) and other weapons has clearly increased during the course of the current conflict. Rapid air evacuation of combat wounded to critical care facilities outside of the war theater is one key factor that has resulted in a died-of-wound-rate of less than 10 percent. Unfortunately, the relatively austere medical environment of the Air Force evacuation aircraft makes the management of acute pain in these multitrauma patients particularly difficult. Pain management with morphine only, which has served the military well in the past, fails in the complex evacuation systems used in today’s conflicts. Transport from the battlefield has evolved into the most efficient system seen in history. At the core of this system lies the aeromedical evacuation, or “aerovac,” system — likened to a 6,000-mile-long ICU in the sky, stretching from staging areas in the middle east to Landstuhl Regional Medical Center in Germany and finally to Washington, D.C.

Aeromedical Evacuation Mission A C-17 Globemaster III is marshaled into its parking spot at Ramstein Air Base, Germany, after completing an aeromedical evacuation mission on September 18. U.S. Air Force photo by Master Sgt. John E. Lasky.

At the point of injury, soldiers are moved off the battlefield by any means necessary — armored vehicle, helicopter or simply carried by other soldiers. After initial resuscitation and stabilization at a combat surgical hospital (CSH), patients are transported to staging areas at airfields for aerovac to Landstuhl for further management, and finally they are transported to major military hospitals in the United States. Modern military aeromedical evacuation provides many lessons for effective patient transport. This is particularly true for response plans to mass casualty, an area in which civilian critical care providers are increasingly involved.

While the focus in aerovac tends to be on the critical care patient, it must be remembered that the majority of injured soldiers require transport without mechanical ventilation, inotropic medications or other measures typically associated with critical care. However, these patients often have sustained massive injury such as multiple amputations of limbs and complicated orthopedic injuries. While “hemodynamically stable,” their needs for in-flight monitoring and aggressive pain management remain acute.

Until recently, morphine was essentially the only pain management therapy available for injured soldiers in transport. Patients would often be narcotized for long transport, with the inherent risks of morphine monotherapy — such as respiratory depression — made even more insidious by the difficulty of patient monitoring within the flight environment. Safer, more effective opioid delivery systems such as morphine and hydromorphone patient-controlled analgesia (PCA) pumps are now in use. While PCA technology is decades-old in civilian medical systems, this pain management technology is new to the aerovac system.

The most significant advance in aerovac pain management has been the expansion of regional anesthesia strategies, both neuraxial and peripheral, into the air transport arena. Patients are now transported with epidural catheters and continuous peripheral nerve block (CPNB) catheters. The most common types of CPNB used today are interscalene, supraclavicular, femoral, sciatic and lumbar plexus. Less common are infraclavicular, paravertebral and popliteal (lateral sciatic) catheters. Indeed, the synergism of systemic opioid via PCA combined with the targeted (but nonrespiratory depressant) effects of CPNB therapy seems to offer the most powerful degree of pain relief available to multitrauma patients. CPNB on military aircraft has enjoyed an excellent safety record in wounded soldiers since it was first introduced on October 7, 2003.

The detailed case report of this first use of CPNB during aerovac describes implementing continuous sciatic and lumbar plexus nerve blocks in-theatre at the CSH level, continued use of both catheters during aerovac to Landstuhl, bolus dosing for operation at Landstuhl, aerovac to Walter Reed Army Medical Center, and use for both surgical anesthesia and analgesia at Walter Reed. The CPNB catheters were used for 16 days¹

The aerospace environment presents numerous physiologic and psychological challenges to medical personnel. These factors are compounded in the trauma patients for which they care. Altitude changes, extremes of temperature, noise, vibration, lighting, power, and space and equipment restrictions are just a few of the myriad issues that confront providers of in-flight medical care.

Constant vibration and the cramped conditions aboard the aircraft can make a painful injury excruciating. Appropriate padding and securing of wounded extremities helps to both reduce pain and protect the patient from compression injuries in this cramped environment. Some soldiers have even gone as far as posting signs for aerovac personnel stating, “Don’t bump the stump!” Attention to simple details such as this goes far in the management of pain in this complex environment.

Another complexity of the military aerovac environment relates to aircraft. All equipment aboard the aircraft must be certified as airworthy for both functionality and flight safety. The complex engineering systems aboard an aircraft can be adversely affected by medical equipment, occasionally with disastrous consequences. The exhaustive testing process includes, but is not limited to, performance under prolonged vibration, testing for radiofrequency emissions and safety should explosive decompression occur. A typical monitoring package for aerovac is shown, effectively converting the standard stretcher into a mobile ICU (see photo on page 16). Currently, the ambIT pump serves the function of epidural, CPNB and I.V. PCA during aerovac.

Finally, communication to maintain continuity of care is paramount. Providers at all points of the aerovac chain need timely and accurate information about their patients’ pain management therapies. As an example, an anesthesiologist in Washington, D.C. receiving a patient from Germany needs to know:

1. The type of catheter(s) in place. (A tunneled paramedian epidural can resemble a lumbar plexus catheter, and vice-versa. The management of the two is clearly different and fundamentally important to patient safety.)

2. The duration such therapies have been in place.

3. Whether any technical issues (with catheter placement, for example) exist that need to be known for future interventions.

4. Pertinent considerations relating to regional anesthesia. Compartment syndrome risk and anticoagulation are common examples.

To this end, the Regional Anesthesia Tracking System (RATS) was started in September 2005. RATS serves as an online medical record for regional anesthesia patients, available at all medical facilities along the aerovac chain. Providers of regional anesthesia input and update the database online so that providers downstream will have accurate information for making patient care decisions. As of this writing, RATS has been used for nearly 1,000 patients.

Placement of a continuous peripheral nerve block.

Never before has pain management for our combat wounded been so aggressively pursued. Certification of an airworthy portable infusion pump paved the way for implementation of epidural and CPNB regional anesthesia during aeromedical evacuation on military aircraft. The revolution in pain management for aeromedical evacuation represents a sea change in our thinking of the battlefield management of pain. Recently, a command-level decision was made to integrate RATS into the combat medical record known as TDMS, or Theatre Data Management System. Twenty-first century military planning for medical care of the wounded now recognizes pain as a disease process, not a symptom. As such, aggressive treatment of pain is part of every wounded soldier’s care plan.

But our work is far from done. More anesthesiologists trained in regional anesthesia are needed to put these technologies into practice. Ensuring that all acute pain management options are exercised as early as possible in the aerovac chain is critical. Building on the lessons of combat trauma, both military and civilian anesthesiologists can increase use of CPNB for management of acute pain. The experience in pain management during combat aeromedical evacuation has brought innovative and effective pain management solutions into common use. Regardless of where you practice, these strategies can benefit patients through the entire perioperative period.

References:
1. Buckenmaier C, McKnight G, Winkley J, et al. Continuous peripheral nerve block for battlefield anesthesia and evacuation. Reg Anesth Pain Med. 2005; 30(2):202-205

Gregory J. Malone, M.D., is a fellow, Regional Anesthesia and Acute Pain Management, Walter Reed Army Medical Center, Washington, D.C.