AACN Advanced Critical Care:
Mollan, I.A. MBChB, DAvMed, MRAeS, RAF
Wing Commander, Oxfordshire, England
I read with interest Lamb's article on measuring the performance of Critical Care Air Support Teams (CCAST) during extended periods of duty.1 For the past 4½ years, I have been the RAF medical officer solely in charge of the UK Aeromedical Evacuation (AE) Service and laterally for 3 months the coalition validating flight surgeon to the US CENTCOM Joint Patient Movement Requirements Center in Al Udeid.
I would like to make 2 comments about the article: The first concerns fatigue; the second is to correct the statement that “Higher pressurization to provide this lower cabin altitude increases the aircraft's structural weight, which increases fuel consumption.” Fatigue in AE teams (particularly CCAST) is an important issue that is often marginalized because there is an absence of evidence showing any detrimental clinical outcome to patients. AE teams, particularly CCAST, are scarce resources. In the United Kingdom, unlike the United States, there is no protection of AE teams with crew duty regulations; and both lack crew duty regulation for their critical care teams. Notwithstanding this, the method of team employment for the mission is an important factor that requires consideration. UK CCAST is presently employed by positioning from the United Kingdom, collecting the patient and then transporting back to the United Kingdom. If CCAST fatigue was considered to expose patients to clinical risk unnecessarily, the method of CCAST employment could be changed to permanently deploy the CCAST. Deploying the CCAST would ensure that the first sector flown (when the CCAST was least fatigued) was to transport the patient; CCAST redeployment (or recycling) could then be undertaken after the patient had been delivered to the United Kingdom (and when the CCAST was more fatigued).
The most common requirement for a cabin altitude restriction (CAR) is abdominal surgery. For patients who have undergone laparotomy with bowel anastomosis, a ground-level CAR is applied; without anastomosis (and with a closed abdomen), a ground-level plus 2000-ft CAR can be applied. In UK AE, CARs are expressed as a relative altitude to the aircraft's last departure airfield elevation. In US AE, CARs are expressed as an absolute altitude.2,3
The application of a CAR does not increase an aircraft's structural weight. When CARs are applied, the aircraft may be required to fly at a lower than normal altitude; this is to ensure that the cabin pressure differential (the difference between the external pressure and the internal pressure) is maintained below the maximum allowable limit.4
Jet engines are less efficient at lower altitudes (in denser air). If the application of a CAR requires the aircraft to fly at a lower altitude, an increased quantity of fuel would be required to fly the same distance compared with that at higher altitudes.5
There are many factors that contribute to the overall mission length. A good understanding of both the aviation and clinical issues, coupled with quality planning within available Air Transport resources, is required by control center staff to get the correct balance for each patient movement.
I.A. Mollan, MBChB, DAvMed, MRAeS, RAF
Wing Commander, Oxfordshire, England
1. Lamb D Measuring critical care air support teams' performance during extended periods of duty. AACN Adv Crit Care. 2010 21(3): 298–306.
2. AP3394. The Royal Air Force Aeromedical Evacuation Service (AL1 Sep 10). London, UK: Ministry of Defence; November 2009.
3. UK AECC SOP 44—Cabin Altitude Restriction (Version 2). UK: AECC; 2010.
4. Lombardo D Aircraft Systems. 2nd ed. New York: McGraw-Hill Professional; 1998.
5. The Pilot's Handbook of Aeronautical Knowledge. Washington, DC: US Department of Transportation, Federal Aviation Administration; 2009.