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Insulin pump delivery potentially affected during airplane travel
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Changes in atmospheric pressure that occur during airplane travel may lead to insulin pumps unintentionally delivering insulin while flying, recent data suggest.
After becoming aware of 50 cases in which patients with type 1 diabetes using insulin pumps developed recurrent hypoglycemia during commercial air travel, researchers in Australia sought to investigate the effect that atmospheric pressure has on insulin pumps. They included five Animas 2020 pumps (IR1200/2020) and five Medtronic Paradigm pumps (1.8 mL cartridge) with 60-cm infusion systems in their analysis.
Effect of pressure changes
To gauge the effect that changes in pressure may have in the pumps, the researchers conducted a hypobaric chamber study in which they mimicked normal flight in a commercial airliner, as well as abnormal flight with catastrophic decompression. Results revealed that during ascent, from 760 mm Hg to 560 mm Hg, the Animas pumps delivered 0.776 excess units of insulin (P<.000001), whereas the Medtronic pumps delivered 0.709 excess units of insulin (P<.000001). During descent, from 560 mm Hg to 760 mm Hg, the pumps delivered 0.663 units less than expected and the Medtronic pumps delivered 0.533 units less than expected, the researchers said. Catastrophic depressurization, a decrease in pressure from 760 mm Hg to 260 mm Hg during 1 minute, however, led to the delivery of more than eight excess units due to plunger movement.
In a second pressure study, the researchers examined the pumps’ insulin delivery during actual flight of a Boeing 767-338. Findings from this analysis showed that Animas pumps delivered 1.37 units of excess insulin (0.685% of cartridge volume; P<.001) and Medtronic pumps delivered 1.01 units of excess insulin (0.561% of cartridge volume; P<.001) during ascent. In contrast, during descent, insulin appeared to be sucked back into pumps, leading to deficits of 0.87 units and 0.58 units of insulin for Animas and Medtronic pumps, respectively.
The researchers also performed a bubble study in which they found gas bubbles in all syringes after 50-mm Hg decreases in pressure. Bubbles disappeared after an atmospheric pressure of 760 mm Hg was restored. Changes in bubble size were consistent with Boyle’s law, they said.
Plunger movement was also examined. According to the researchers, the Animas cartridge plunger moved after a 273.48-mm Hg decrease in pressure.
Because of their findings, the researchers said the insulin pump cartridge should contain only 1.5 mL of insulin, and patients should disconnect the pump before takeoff. When at cruising altitude, remove the cartridge from the pump and ensure that there are no air bubbles before reconnecting. After landing, disconnect the pump, prime the line with two units and then reconnect. If cabin decompression occurs, disconnect the pump.
Cautious interpretation
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These data, although concerning, should be viewed cautiously, Irl B. Hirsch, MD, professor of medicine at the University of Washington School of Medicine, wrote in an editorial in Diabetes Technology & Therapeutics.
“The study was implemented in such a small number of people that large conclusions may not be justified,” Hirsch wrote. “It is possible the authors overreacted in their recommendations.”
He also said the changes in insulin delivery were less than one unit, except for during ascent on an actual plane, and therefore the recommendations may be more harmful than helpful, considering the amount of time the researchers recommend being disconnected from the pump.
“My hope is that providers, patients and the regulatory bodies do not overreact to this single report,” Hirsch wrote. “Let’s wait for more data, with the ultimate goal of hitting our dartboard with better accuracy.”
For more information:
- Hirsch IB. Diabetes Technol Ther. 2011;doi:10.1089/dia.2011.0190.
- King BR. Diabetes Care. 2011;34:1932-1933.
Disclosures: Animas and Medtronic supplied insulin pumps on a loan basis. The researchers report no relevant financial disclosures. Dr. Hirsch reports receiving grant support from Novo Nordisk, Halozyme and Sanofi-Aventis. He also received consulting fees from Roche, Abbott, Johnson & Johnson and Cellnovo.