Oxygen Use More Than Expected During Aero-Medevac of COVID Patients

By Scott Baltic

December 15, 2020

NEW YORK (Reuters Health) - During a series of group medevac missions using a military transport aircraft, oxygen use by COVID-19 patients with acute respiratory distress syndrome (ARDS) was higher than anticipated, researchers in France report.

All 36 patients were experiencing mild to moderate ARDS and required mechanical ventilation, but only two experienced episodes of hypoxemia.

Although more than two-thirds of the patients used more than 500L/hr of oxygen, the patients' needs did not exceed the available oxygen, Dr. Madeleine Beaussac of the 10th Military Medical Center, in Istres, and colleagues report.

"Oxygen consumption was higher than expected, despite anticipation and predefined oxygen management measures," they write in Military Medicine. "Management of oxygen in such collective aero-medevac missions should be a permanent concern for the physician."

To the authors' knowledge, this was the first experience of collective aero-medevac of patients with ARDS.

From March 17 to April 3, the French Military Health Service and French Military Air Service conducted their first six pandemic-related group medevac missions. Each of the six flights included six patients with ARDS who were being transferred from overloaded facilities to other hospitals in France or Germany.

Two-thirds of the patients, all civilians, were male; the patients mean age was 64. Four potential patients were excluded from the flights for having severe ARDS.

Before each medevac, two of the six patients were identified as presumed high oxygen consumers, based on clinical factors. To limit oxygen consumption on board, these patients were last on and first off.

The aircraft was an Airbus A330 Multi Role Tanker Transport with six intensive-care modules on board. The medical team consisted of three ICU doctors, two flight surgeons, three nurse-anesthetists, three flight nurses, and two critical-care nurses, along with other personnel.

Oxygen capacity on board was three cylinders (15 L at 200 bars) per patient, for a total of 9,000 L.

The flights (of 700 to 1,080 km) lasted from 52 to 77 minutes, but boarding and disembarking times ranged from 60 to 100 minutes each for every flight. The resulting average time on ventilation for each flight was 185 minutes per patient.

Mean oxygen use was 1,650 L per patient per flight (1,350 to 1,950 L per patient per flight) and 564 L per patient per hour with an interquartile range of 482 to 675 L per patient per hour. Most patients (25; 69%) needed 500 L/hr or more, and four (11%) needed 900 L/hr or more; these were the expected standard and maximum needs, respectively.

There were two episodes of hypoxemia, defined as an oxygen saturation (SpO2) of less than 90% for at least five minutes.

The patients who had been judged to be at risk of higher oxygen consumption did not in fact need extra oxygen.

Dr. Casey Patrick, assistant medical director of the Montgomery County Hospital District, in Conroe, Texas, told Reuters Health by email, "These findings are definitely helpful in that they provide the first descriptive analysis of COVID-19 ARDS medevac flights."

Because both hypoxia and hyperoxia are dangerous for the patient, he continued, "there is a fine line that must be walked . . . This makes pre-planning for the correct oxygen amount needed vital, with some level of emergency reserve as well."

Dr. Patrick noted some limitations to the study, specifically that the sickest ARDS patients were not transported, the small patient population, and the retrospective data evaluation. He concluded, "None of those things totally invalidate their conclusions, but the results are likely not broadly generalizable either."

David Olvera, a certified flight paramedic, board member of the MedEvac Foundation International and chair of the foundation's Research Committee, told Reuters Health by email, "In our experience, having an oxygen calculation tool specific to the oxygen tank you are carrying is key."

It's crucial, he added, to anticipate the possibility of delays, such as wind, changes in a patient's oxygen consumption, and time in transport. If there is a change in the situation, Olvera emphasized, "What is your plan?"

The authors could not be reached for comment.

SOURCE: https://bit.ly/39QVhMx Military Medicine, online November 19, 2020.