But results should be interpreted with caution, researchers note

No significant 1-year mortality benefit was seen for helicopter emergency medical services (HEMS) versus ground EMS (GEMS) in a nationwide retrospective Danish cohort study.

“This study found that 1 year after dispatch, the use of HEMS, compared with the use of GEMS, was not associated with a statistically significant difference in mortality overall or mortality among patients with critical illness or injury,” wrote Karen Alstrup, MD, PhD, of Prehospital Emergency Medical Services, in Aarhus, Denmark and co-authors in JAMA Network Open.

Alstrup and colleagues studied 10,618 patients in Danish national registries who were transported between Oct. 2014 and April 2018. HEMS was dispatched for all patients in the study; researchers compared those for whom a helicopter was used for transport (89.3%) and those for whom ground transport was used due to weather conditions that precluded flying (10.7%).

Adjusted cumulative 1-year mortality was 23.2% (95% CI 22.4%-24.1%) for HEMS versus 24.5% (95% CI 21.9%-27.1%) for GEMS, a non-significant difference (HR 0.94, 95% CI 0.84-1.06).

For the subgroup of patients with critical illness or injury, adjusted cumulative 1-year mortality was 25.1% (95% CI 23.5%-26.7%) for HEMS (n=2,260), compared with 27.1% (95% CI 22.0%-32.1%) for GEMS (n=315), also with a non-significant difference in mortality risk (HR 0.91, 95% CI 0.73-1.14).

“The wide 95% CIs in our study, which include the value of 1 revealing nonsignificant results, could be associated with the low number of patients in the GEMS group. As a result, our study results should be interpreted with caution,” Alstrup and colleagues said.

“We believe that our findings may have a clinical impact,” they continued. “We suggest that efforts put into improved education of staff making triage decisions in emergency medical dispatch centers or in the field, together with the creation of validated dispatching tools, may be important in selecting the patients who are most likely to benefit from HEMS dispatch.”

This study “stands out from prior research on this subject,” noted Michael Abernethy, MD, of the University of Wisconsin in Madison, in an accompanying editorial.

“Owing to inherent ethical concerns, an actual randomized clinical trial of HEMS versus GEMS has never been and most likely never will be done,” Abernethy observed. “Although the study by Alstrup et al is retrospective, by using adverse weather to naturally select HEMS versus GEMS, it is one of only two studies found in the literature that use weather to approximate a randomized design.

“Another unique aspect of this article is that the level of medical care provided on the ground and in the air is well defined and, more importantly, identical,” he continued. “In Denmark, as in many countries with socialized medicine, the education of personnel and the structure of prehospital care tend to be more standardized than in the United States. For research purposes, this can effectively eliminate the inherent difference in HEMS versus GEMS staffing as a major factor shaping research results.”

The first study of HEMS versus GEMS outcomes in the U.S. was published in 1983; it found a substantial reduction in the predicted mortality of trauma patients transported by air. But since the early days of EMS air transportation, all aspects of prehospital care including tasking, technology, and finances have changed radically, Abernethy pointed out.

“There is a major problem with almost all large studies that use national and/or state-level trauma data banks: the comparison of HEMS and GEMS is based on the common faulty premise that HEMS and GEMS are each uniform, homogenous entities,” he wrote. “There can be a huge disparity in the education, training, and qualifications of HEMS medical crews from program to program.”

“During the last 2 decades there has been a massive shift in HEMS from the traditional hospital-based model to for-profit, free-standing community bases,” he added, with more than half of HEMS programs now owned by two large private equity firms,” he added.

“The financial structure of a HEMS program has a tremendous influence not only on the type of aircraft and medical equipment used but also the education, level of experience, and specialty training of the personnel,” Abernethy wrote. “Quality, aviation or medical, comes with a price.” Because of its regulation and funding, GEMS is even more fragmented, he noted.

In their analysis, Alstrup and colleagues evaluated patients with a median age of 60; 64.4% were men. Transport was for trauma (27%), cardiovascular emergency (51.3%), and neurovascular emergency (21.7%). Overall, 6,381 (60.1%) patients had no previously reported comorbidities.

The destination was a university hospital for 82% of those transported by HEMS and 49% by GEMS. Secondary transfer to a university hospital within 24 hours was seen for 3.0% of the HEMS and 4.9% of the GEMS group.

Limitations include lack of follow-up on patients with missing civil registration system numbers, especially patients receiving GEMS, who were excluded from the analysis which may have led to selection bias. In addition, the patient groups selected for this study as being time critical may not represent the only patients who were truly time critical, the researchers noted.

  1. No significant 1-year mortality benefit was seen for helicopter emergency medical services (HEMS) versus ground EMS (GEMS) in a nationwide retrospective Danish cohort study.

  2. Wide confidence intervals in the study could be associated with the low number of patients in the GEMS group and results should be interpreted with caution, the researchers said.

Paul Smyth, MD, Contributing Writer, BreakingMED™

Alstrup received funding from the Danish Helicopter Emergency Medical Service Research Foundation and the Health Research Foundation of Central Denmark Region.

Alstrup reported no conflicts.

Abernethy reported no conflicts.

Cat ID: 358

Topic ID: 74,358,254,730,358,5,8,914,130,38,192,925