Critical Care in the Sky
HEMODYNAMIC MONITORING SYSTEMS AND OTHER CUTTING-EDGE TECHNOLOGY IS HELPING SAVE PATIENTS THOUSANDS OF FEET UP IN THE AIR.
An Air Force critical care air transport team (CCATT) once picked up a patient at Tallil Air Base, Iraq. The patient had a very high blood pressure and chest pain. While treating him on an emergency flight to Kuwait, Captain David Whitehorn saw that his blood pressure was not coming down despite the use of numerous vasoactive intravenous medications. “I had to do some in-flight troubleshooting and found that his IV had come unhooked,” recalls Whitehorn. It was a common enough occurrence during bumpy flights. Whitehorn—who is the interim CCATT nurse manager of the 59th Medical Wing based at Wilford Hall Medical Center at Lackland Air Force Base, Texas—discovered the problem thanks in part to a hemodynamic monitoring system.
“During one flight, we got shot at, struck by lightning and lost an engine, all on one mission,” recounted Whitehorn. Amid such conditions, CCATTs arm themselves with a highly advanced bank of technology such as hemodynamic monitoring systems, saving lives in mid-flight.
CCATTs are responsible for transporting critically ill patients to major medical centers, for example from Iraq to Germany and/or to the United States. A CCATT typically consists of a critical care physician (surgeon, anesthesiologist, emergency physician or pulmonologist), a critical care nurse and a cardiopulmonary technician. The CCATTs must be able to transport up to six unventilated (up to three ventilated) patients for 10-12 hours by air, using various aircraft including the C-17 Globemaster III, C-130 Hercules, KC-135 Stratotanker and C-141 Starlifter.
There are a total of 20 CCATTs based at Wilford Hall Medical Center. Two of them are continuously on call 24 hours a day for U.S. missions, while four teams are deployed in support of operations in Iraq and Afghanistan.
The CCATTs are a contributing factor to the highest survival rate of combat-wounded service members in any U.S. military conflict. During the first Gulf War, 22 percent of injured soldiers would die, but now that statistic has come down to 10 percent. “Combined with small, elite surgical/trauma teams positioned on the ground and close to the battlefield, the Air Force’s Aeromedical Evacuation System (AES) can move the grievously wounded from battlefield to field hospitals to Germany to the U.S. in record time,” said a report in NurseWeek News.
Whitehorn has tended to a number of Army and Marine patients who were the victims of IEDs. One patient he flew to Germany had been hit by an IED and had taken shrapnel through his back. “His belly was surgically left open, and we flew him from Mosul to Germany,” he said. “And once we flew to Afghanistan to pick up a patient who fell from a forklift and severed her spinal cord. She was paralyzed from the belly button down. We had to fly her to Qatar. We also had an interesting case where we flew to Yemen and picked up an active-duty Army soldier who had a dissecting aortic aneurysm with a flap that could have ruptured at any time.”
CCATTs are also sometimes charged with transporting civilians; they swung into action during hurricanes Rita, Katrina and Wilma, transporting about 100 civilian ICU patients.
HEMODYNAMIC LIFELINE
For CCATTs, there is a pressing need for portable, accurate, non-invasive equipment. Prominent among that equipment are hemodynamic monitoring systems, which measure parameters like central venous pressure, inter-cranial pressures, arterial blood pressure, oxygen saturation and hemoglobin counts. Such systems help achieve the early detection, identification and treatment of life-threatening conditions such as heart failure and cardiac tampenade. Through hemodynamic monitoring, medical personnel are able to evaluate the patient’s immediate response to treatment such as drugs and mechanical support. Personnel can evaluate the effectiveness of cardiovascular function such as cardiac output and cardiac index.
There is invasive and noninvasive hemodynamic monitoring. The former involves inserting a pulmonary artery catheter, a.k.a. Swan-Ganz catheter, through a vein and getting it to the artery connecting the heart to the lungs by floating a small balloon there and deflating it. This enables the monitoring of lung artery blood pressure. Non-invasive hemodynamic monitoring systems, to monitor arterial blood pressure, typically involve inserting a thin tube (cannula) into an artery, usually via the wrist.
The CCATT’s hemodynamic monitoring system of choice currently is the Propaq 206EL, enabling technicians to keep a constant check on a patient’s condition and administer emergency treatments accordingly without waiting for the plane to touch down. The Propaq is a 12 inch by 12 inch battery-operated monitor. “We carry two of them, and also use the Zoll defibrillator as a monitor. That gives us the capability to monitor the hemodynamics of up to three patients,” said Whitehorn.
The arterial blood pressure is what Whitehorn calls “our gold standard.” In field hospitals as well as for CCATTs, arterial blood pressure gives a precise indication of the hemodynamic status of a patient. “In particular, IED victims or burn patients are really susceptible to rapid hemodynamic changes, because they lose their vascular status,” said Whitehorn. “They can’t hold any fluid into their vascular space, so it’s imperative that we stay ahead of that game. And in addition to their burns, these same patients may also have broken bones, an open abdomen and head injuries as well. So it’s imperative that we monitor their intercranial pressures, their bowel pressures and everything on top of that.”
For adverse environments such as those involving CCATT, the invasive hemodynamic monitoring procedure is accomplished on the ground prior to flight. “One of the goals of CCATT is to make sure we properly assess our patients on the ground in order to avoid trying anything invasive in flight,” said Whitehorn. “Flying over a war zone is really not conducive to the patient’s health because it’s not a sterile environment by any means and it’s dark. People are shooting at you, the plane is going up and down, and the patient is highly susceptible to the stresses of flight—the vibrations, the temperature changes, the altitude changes, the pressure changes and everything else. It makes it very difficult.”
HEART MONITORING
Until recently, the most reliable way to measure arterial blood pressure and other critical cardiac parameters was the pulmonary artery catheter. This invasive procedure has a comprehensive set of parameters that can be measured that describe how the heart’s working. One of those key parameters is cardiac output, which is how many liters in a minute the heart is pumping. Another related parameter is stroke volume, which is how much blood is being pumped per beat.
There has been a concerted effort to develop systems that are more suited to more adverse conditions, such as those involving air transport. Roy Wallen, director of critical care at Edwards Lifesciences Corporation, said that last year, his company introduced a product that works by a very different principle than that involving the pulmonary artery catheter, also made by Edwards Lifesciences “Rather than have to float a catheter through the heart, you can connect up a sensor to where you’d normally measure the patient’s blood pressure, and measure that pressure and cardiac output on a continuous basis.”
Called the FloTrac sensor, a small catheter is placed in the patient’s wrist to measure the blood pressure. This kind of device can thus also measure cardiac output and stroke volume, “So the clinician knows whether patients should get blood or fluids, or how they’re doing in terms of how well their heart is pumping.” He continued, “If a patient is losing a lot of blood or requires more fluids (therefore a lot of IVs) or a blood replacement product, you want to know what that effect is on the cardiac output value.”
He explained that “in a military application, especially in a battlefield kind of application, it’s often not appropriate to try and get a patient lying flat and very stable and to try and thread a catheter through the heart. But there is often this continuous blood pressure measurement that would be made by connecting up a device to the patient’s wrist. And now, rather than just measure the blood pressure, we can also measure the cardiac output and some other related parameters. So you can’t measure the pressures of what’s going on in the heart, but you can measure how well the heart is working. And that’s what FloTrac does.”
This degree of accuracy and reliability, especially under adverse conditions, is a relatively new development, said Wallen. “Also, it takes about 20 or 30 minutes to place a Swan-Ganz catheter in a critically ill patient. But it takes just minutes to set up a FloTrac sensor.”
The FloTrac device is also coupled with a special type of video monitor called the Vigileo monitor, which shows an updated value for cardiac output every 20 seconds and charts a trend for that output over time. “And it’s easy to use,” said Wallen. “You simply enter the patient’s age, gender, height and weight to initiate continuous cardiac output monitoring. No calibration is required, and FloTrac automatically calculates key flow parameters. It also continuously compensates for changes in the patient’s vascular physiology.”
Wallen said that a lot of military people have expressed interest in the ability to use this technology, especially in air transport. It’s a small, lightweight monitor that’s very easy to use so it can be put almost anywhere in that kind of air transport environment.
IN-FLIGHT EQUIPMENT
The CCATTs use a host of innovative technological aids. They include the following:
• Propaq Encore 260EL: two temperature lines (generally only one used), noninvasive BP, two invasive pressures (often used for arterial line and central venous pressure), ECG rhythm, O2 saturation, end-tidal CO2
• Zoll M series CCT monitor/defibrillator: ECG, noninvasive BP, O2 saturation, two invasive pressures, end-tidal CO2
• Codman Interface Control Unit (with Codman ECS 2 or ECS 3 drainage system): intracranial pressure and trend
• Impact 754 M Uni-Vent ventilator
• Impact suction unit
• IVAC MedSystem III multi channel infusion pump
• Mini-OX 3000 oxygen monitor
• iSTAT blood analysis system
The iSTAT machine is a device to gauge arterial and venous blood values, said Whitehorn. It’s also compact, measuring just 4 inches by 10 inches. The Impact 754 ventilator allows patients to oxygenate easier in mid-flight, and Impact’s suction machine is hooked up to wound evacuations, nasal and gastric tubes to drain fluid. “There’s also the Mini-OX,” said Whitehorn. “That’s basically like a carbon-dioxide detector. It tells us the oxygen concentration, and the device is not much bigger than a deck of cards.” The teams also use an Alaris IV pump, which allows medical personnel to plug in three medications and simultaneously run them into the patient all at once.
Size is often paramount. CCATTs may have to treat multiple patients simultaneously, or share their precious space with pallets of cargo or soldiers in an already small space.
The CCATTs’ emphasis on technology evidently has paid off. Whitehorn estimates that in the entire history of CCATT, there have only been a handful of patients who could not last the duration of the flight. “Our goal is to get them stabilized, and we’ve done that very well,” he said. “We get them stabilized, and then we fly them to location with a higher echelon of medical treatment capabilities, while maintaining the same level of care in-flight.” ♦