Type 1 Diabetes at High Altitude: Performance of Personal Insulin Pumps and Patient Metabolic Control

Introduction

Participation in high-altitude trekking activities may expose people with type 1 diabetes mellitus (T1DM) to extreme environmental conditions, such as low temperature and hypobaric hypoxia. These conditions impose a number of unique challenges for individuals with T1DM that make it more difficult for them to avoid hyper and hypoglycemia. In addition, factors, such as high elevation, low temperature, dust, wind, and relative humidity, may affect the performance of insulin pumps and continuous glucose monitoring (CGM) systems. ¹ For example, some researchers have reported excess insulin delivery or bubble formation with some insulin pumps in hypobaric conditions. ^2,3 Regarding CGM systems, in vitro studies have shown that the Enlite sensor performed adequately in hypobaric conditions. ⁴ However, data from patients are very scarce and do not concern very high altitude. ⁵ Therefore, whether altitude has a significant impact on the performance of personal insulin pumps, including ones equipped with CGM systems, remains unclear. As such, frequent blood glucose monitoring (BGM) is imperative in these cases as a measure of caution.

In this study, we report data on metabolic control and describe the performance of insulin pumps in 19 patients with T1DM during the final step of the “5000 meters above sugar level” initiative, which involved trekking Damavand Mountain (5670 meters above sea level [m.a.s.l.]).

Materials and Methods

Nineteen patients with T1DM, who were all treated with personal insulin pumps, participated in the “5000 meters above sugar level” expedition; 18 of them reached the Damavand peak (5670 m.a.s.l.). All patients completed a questionnaire during the trek, with data regarding blood glucose measurements, total daily insulin dose, percentage of basal insulin, and acute mountain sickness (AMS), among others. At certain points during the expedition, we also measured patients' ketone and lactate levels in the blood (Lactate Scout, EKF-Diagnostics).

Patients used different types of insulin pumps: 4 used Accu-Chek Combo (Roche Diagnostics, Mannheim, Germany), 7 used Medtronic 640G (Medtronic, Northridge, CA), 5 used Medtronic Paradigm 715 (Medtronic), 2 used Medtronic Paradigm 722 (Medtronic), and 1 used Medtronic Paradigm VEO (Medtronic). All Medtronic pumps are registered to work at temperatures ranging from 3°C (37°F) to 40°C (104°F), at 20%–95% humidity, and up to an altitude of 3000 m.a.s.l. (as per the instruction manuals). The Roche pump is registered to work at temperatures ranging from 5°C (41°F) to 40°C (104°F), at 20%–90% humidity, and up to an altitude of 5643 m.a.s.l. (as per the instruction manual).

All patients were using the blood glucose meters that are recommended for their pumps, including: Accu-Chek Performa Combo (for Roche pumps; Roche Diagnostics; registered up to an altitude of 3094 m.a.s.l., as per the instruction manual), Contour Link (for Medtronic Paradigm pumps; Bayer HealthCare LLC, Diabetes Care, Whippany, NJ; registered up to an altitude of 3048 m.a.s.l., as per the instruction manual), and Contour Plus Link 2.4 (Medtronic 640G; Bayer HealthCare LLC, Diabetes Care; registered up to an altitude of 6301 m.a.s.l., as per the instruction manual). One patient treated with the Medtronic 715 pump was using the Contour Plus One glucose monitoring device (Bayer HealthCare LLC, Diabetes Care; registered up to an altitude of 6301 m.a.s.l., as per the instruction manual).

Regarding CGM, 10 patients were using CGM systems being a part of Medtronic personal insulin pumps (with the Enlite 2 Sensors). Finally, 11 patients were using a flash glucose monitoring (FGM) system utilizing FreeStyle Libre technology (Abbott Diabetes Care, Alameda, CA; registered to work at temperatures ranging from 10°C [50°F] to 39°C [103°F], at 10%–90% humidity, and up to an altitude of 3048 m.a.s.l.).

Results

The mean age of the patients was 32.5 years (range, 23–48 years), with a mean body mass index of 23.8 kg/m² (range, 19.7–30.2 kg/m²), and a mean HbA_1c level of 6.6% (range, 5.9%–7.1%). Detailed characteristics of this group were previously described. ⁶

Good weather conditions occurred during the expedition in July. There was no wind or snow, and based on values recorded on patients' sports watches, the temperature remained above 0°C even at the peak (for most of the time it was >10°C). This eliminated the potential influence of low temperatures, but no other environmental factors, on all devices used in this study.

During the entire trek, we did not observe a single case of severe diabetic decompensation; only once did the ketone levels in the blood exceed 0.6 mmol/L in one patient (i.e., 0.9 mmol/L at 4200 m.a.s.l.), but this normalized a few hours later. Furthermore, no severe hypoglycemia was observed in the patients, although weak hypoglycemia did occur at a frequency of 1.6 episodes per 3 days.

The blood glucose levels remained on average moderately elevated throughout the expedition. The mean blood glucose level measured with hand blood glucose meters were 153 ± 33 mg/dL for day 1 (from 3200 to 4200 m.a.s.l.), 183 ± 40 mg/dL for day 2 (from 4200 to 4700 m.a.s.l., and then returning to 4200 m.a.s.l.), and 202 ± 31 mg/dL for day 3 (from 4200 to 5671 m.a.s.l., and then returning to 4200 m.a.s.l.). The average number of strips used during this expedition by our patients was 12.4 for days 1 and 2, and 14.6 for day 3. For individuals who used CGM systems, the results were 153 ± 19, 163 ± 19, and 202 ± 30 mg/dL for days 1, 2, and 3, respectively. For patients who used FGM, the values for days 1, 2, and 3 were 168 ± 36, 219 ± 42, and 264 ± 45 mg/dL, respectively.

During the 3 days of expedition, including the peak (5671 m.a.s.l.), patients did not experience any alarms or errors or problems with their insulin pumps or infusion sets (no occlusion; all patients changed their infusion sets on the starting day). It is worth noting that almost all patients experienced symptoms of AMS, starting from day 1 (the day we changed altitude to ∼2000 m.a.s.l.) until reaching 4200 m.a.s.l.; 77% of patients felt weakness (light to heavy), 72% had some difficulties with sleep, 66% had headache (light to heavy), 55% experienced dizziness (light to heavy), and 27% reported stomach problems (light to heavy).

SmartGuard Technology, which saves the patients from severe hypoglycemia episodes, was turned on 3.3 times per patient per day, with the “Suspend Before Low” option mostly set to 70 mg/dL.

Discussion

In this observational study, we found that high-altitude mountain trekking without extreme weather conditions caused no clinically significant problems in T1DM individuals with good prior glycemic control and was not associated with any noticeable malfunction of personal pumps. Not a single case of severe diabetes decompensation or clinically significant hypoglycemia occurred among the 19 patients with T1DM in our study, and glucose levels stayed within the reasonable range.

We assume that the episodes of moderate hyperglycemia observed in our patients were due to AMS rather than due to improper functioning of the insulin pumps or CGM system. Importantly, all pump models, including the newest one with SmartGuard Technology, worked well without any disruption. We previously reported a single case of patient who climbed an even higher mountain (6961 m.a.s.l.) with the Medtronic 640G pump and the SmartGuard function working safely and properly. ⁷

It is worth noting that the absence of an alarm from an insulin pump does not mean that the insulin pump has delivered insulin properly; however, all patients did not notice any improper functioning of their devices. Furthermore, patients did not report any problems with the ability of their pumps to lower blood glucose levels in cases of hyperglycemia; that is, no patient had to use an insulin pen during the trek.

The obvious limitation of the study was the lack of an appropriate reference device for the blood glucose concentration measurements. Thus, all reported biochemical measurements should be treated with some caution as glucose monitoring devices were used outside of the range of their registration altitude. This also made testing of the accuracy and precision of BGM, FGM, and CGM at high altitude not possible. In future, one could consider taking additional capillary blood samples, deep freezing them, and then measuring them with an appropriate method upon return from the expedition. However, this was not an option for our expedition as all participants were amateur climbers. Therefore, participants were advised to reduce their load and only take essential equipment that was crucial for their comfort or safety for the final ascent. Furthermore, freezing the blood samples at the shelter, where we spent four nights was not an option due to weak and inconsistent power supply. Finally, legal issues relating to blood sample transportation would have made this process very difficult.

Conclusions

Despite the risks, healthy, physically fit, and experienced individuals with T1DM and good prior glycemic control should not be discouraged from participating in mountain trekking activities and attaining their summit goals. Modern personal insulin pumps, including ones equipped with CGM systems, appear to work properly even at high altitudes.