Use of Hypoglossal Nerve Stimulation for Treating OSA in Military Patient Populations

Limitations to OSA Studies

The reviewed studies have several limitations that warrant caution when determining the possible benefits of HGNS treatment. The primary limitation is the lack of active control groups, therefore precluding a direct comparison of the short- and long-term effectiveness of HGNS vs other treatments (eg, CPAP). This is especially problematic because in the reviewed studies HGNS treatment efficacy is reported as a function of the mean—and SD—percent reduction in the AHI, whereas the efficacy of CPAP treatment usually is defined in terms of “adequacy of titration” as suggested by the AASM.³⁶ It has been reported that with CPAP treatment, 50% to 60% of OSA patients achieve AASM-defined optimal improvement of respiratory disturbance index of < 5/hour during a polysomnographic sleep recording of ≥ 15 minutes duration that includes REM sleep in the supine position.³⁷ In most of the reviewed studies, treatment success was more liberally defined as a decrease of AHI by ≥ 50%, regardless of the resulting AHI. It is notable that among the reviewed HGNS studies, the TJU and UP cohorts achieved the best outcome in short-term follow-up of 2 months with a mean (SD) AHI of 6.3 (11.5) and 6.4 (6.1), respectively. Among those cohortsassessed at a 12-month follow-up, the Munich cohort achieved the best outcome with a mean (SD) AHI of 7.1 (5.9).

Although the metrics reported in the reviewed studies are not directly comparable, the reported findings strongly suggest that HGNS generally is less effective than CPAP. How important are these differences? With findings that HGNS “reliably produces clinically meaningful (positive) effects on daytime sleepiness, daytime functioning, and sleep quality,” does it really matter if the outcome metrics for HGNS are a little less positive than those produced by CPAP?³⁸ For individual military OSA patients the answer is yes. This is because in military operational environments—especially during deployment—sleep restriction is nearly ubiquitous, therefore any mild residual deficits in sleep quality and daytime alertness resulting from nominally adequate, but suboptimal OSA treatment, could be exacerbated by sleep restriction, therefore placing the service member and the mission at increased risk.³⁹

Another limitation is the narrow inclusion criteria these studies employed, which limits the generalizability of the findings. Participants in the reviewed clinical trials were selected from a patient population that was mostly middle-aged, White, and obese or overweight. In a Medical Surveillance Monthly Report study, OSA was found to be highest among service members aged > 40 years, male, obese, and Black/non-Hispanic (although it should be noted that more than one-half of enlisted service members aged ≤ 25 years).^40,41 Obesity has been noted as a growing concern for the military as the military population is beginning to mirror the civilian population in terms of being overweight or obese despite height and weight standards. HGNS might not be as successful in military populations with different demographics. Moreover, HGNS has been shown to have greater AHI reduction among those with higher BMI.³⁰ Although obese service members have a 6-fold higher 12-year incidence rate of OSA than service members without obesity, this nevertheless suggests that general level of HGNS efficacy might be lower among the military patient population, because obesity is less prevalent in the military than the general population.⁹

Ethnicity has been found to be a relevant factor, with the highest incidence rate of OSA among non-Hispanic Black males, a demographic that was underrepresented in cohorts included in this review. Further studies will be needed to determine the extent to which findings from HGNS treatment studies are generalizable to the broader OSA patient population.

HGNS Implementation Challenges

Current impediments to widespread use of HGNS as an OSA treatment include no standardized guidance for titration and follow-on care, which varies based on the resources available. Titrating a new device for HGNS requires experienced sleep technicians who have close relationships with device representatives and can troubleshoot problems. Technical expertise, which currently is rare, is required if there are complications after placement or if adjustments to voltage settings are needed over time. In addition, patients may require multiple specialists making it easy to get lost to follow-up after implantation. This is particularly challenging in a transient community, such as the military, because there is no guarantee that a service member will have access to the same specialty care at the next duty station.

Although some evidence suggests that HGNS is a viable alternative treatment for some patients with OSA, the generalizability of these findings to the military patient population is unclear. Specialized facilities and expertise are needed for the surgical procedure and follow-up requirements, which currently constitute significant logistical constraints. As with any implantable device, there is a risk of complications including infection that could result in medical evacuation from a theater of operations. If the device malfunctions or loses effectiveness in a deployed environment, the service member might not have immediate access to medical support, potentially leading to undertreatment of OSA. In future battlefield scenarios in multidomain operations, prolonged, far-forward field care will become the new normal because the military is not expected to have air superiority or the ability to quickly evacuate service members to a higher level of medical care.⁴²

In deployed environments, the potential limitations of HGNS become increasingly risky for the service member and the overall mission. Considering these factors, it will be important to evaluate the practicality of HGNS as a treatment option in military populations. Military-specific challenges associated with HGNS that require further study, include guidance for patient selection outside academic centers, guidance on long-term postsurgical care and device maintenance, duty limitation and military retention considerations, and limitations in training and combat environments. The military medical community needs to conduct its own studies in appropriately selected service members to guide clinical practice.

CONCLUSIONS

HGNS treatment results in improvement of both AHI and ESS scores and could be a deployable treatment option for military patients with OSA. However, HGNS has not been found to be as effective as CPAP, although the current literature is limited by small sample sizes, homogeneous populations that do not reflect the demographics of the military, and mostly short follow-up periods. Future studies should be focused on collecting data on HGNS from demographic groups that are more representative of the military OSA patient population and identifying the subpopulation of patients who derive the greatest benefit from HGNS, so that this treatment can be better individually targeted. Until data on existing military patients is published, it is not possible to fully weigh risks and benefits in this population and generalize civilian guidance to the military.