Kawano et al. Intraosseous Vascular Access Is Associated With Lower Survival and Neurologic Recovery Among Patients With Out-of-Hospital Cardiac Arrest. Ann Emerg Med. 2018;71:588-596.
THE BOTTOM LINE
This study was a secondary analysis of a large EMS trial conducted in 7 sites in the US and Canada. This is a really interesting study that looks at the association between outcome and IO access. They looked at 12,500 pts with IV access and 660 pts with IO access. The primary outcome measure was favorable neurologic outcome at hospital discharge with a mRS of 0 to 3. In the IO group 24% had rosc, 4% survived to hospital discharge, and 1.5% had a favorable neurological outcome. In the IV group 38% had ROSC, 10% survived, 8% had a favorable neurological outcomes. In the UNADJUSTED propensity matched model IO vs IV access was associated decreased probability of ROSC (25% vs 34%,OR=0.66), survival to discharge (4.5% vs 8.6%, OR=0.5), and favorable neurologic outcome (1.8% vs 5.9%, OR=0.29). The two groups differed in interventions very noticeabley in that the IO group were an almost 15% LESS therapeutic hypothermia and 9% less interventional catheterization. This is JUST AN ASSOCIATION and maybe IO is just a marker of sicker patients, HOWEVER, I think this is enough to allow for an RCT looking directly at this topic.
Difficult IV access in cardiac arrest? Just drill it! Utilize intraosseous vascular access that is. The IO has become the go to for rapid IV access in cardiac arrest patients. We can deliver drugs quickly and not muck around looking for a vein either peripherally or centrally. But are there down stream consequences? Is it REALLY better? This study takes a look at outcomes of non-traumatic cardiac arrest patients who had an IO placed.
This study was a secondary analysis of a publicly available registry conducted in 7 sites in the US and Canada. The original trial looked at the timing of the first analysis for defibrillation and application of an impedance threshold device. The original data was prospectively collected. Exclusion criteria were the typical ones including trauma, prisoners, pregnant, dnr, and hypovolemia. To the study’s benefit the obtained a cohort whose access route was the INTENDED PRIMARY CHOICE and excluded failed attempts at either route of access. The importance of this is that it MIGHT equal out the bias of a sicker patient or delays in care where a failed access attempt delays the care. The primary outcome measure was favorable neurologic outcome at hospital discharge with a mRS of 0 to 3. This is an interesting outcome change point because normally mRS is 0 to 2 is the cutoff in stroke studies. Because out-of-hospital vascular access was not randomly assigned across this cohort, they applied propensity matching to decrease selection bias and unmeasured confounder.
They found after exclusions 13,155 patients with 660 pts (5%) and 12,495 (95%) pts. Note that patients with IO access had a higher proportion of nonshockable initial rhythms, fewer public location and shorter times from call to first provider. In the IO group 24% had rosc, 3.8% survived to hospital discharge, and 1.5% had a favorable neurological outcome. In the IV group 38.3% had ROSC, 10% survived, 7.6% had a favorable neurological outcomes. They found after multiple regression with multivariate analysis that IO access was ASSOCIATED with a DECREASED probability of ROSC [OR 0.6 (CI: 0.49 to 0.74)] and DECREASED favorable neurological outcome [OR 0.24 (CI: 0.13to 0.46)].
They found 1116 patients in the propensity match. In the UNADJUSTED model IO vs IV access was associated decreased probability of ROSC (25% vs 34%,OR=0.66), survival to discharge (4.5% vs 8.6%, OR=0.5), and favorable neurologic outcome (1.8% vs 5.9%, OR=0.29). Looking at the propensity matching these groups for the
Baseline characteristics are quite well matched and markers of their propensity matching were well correlated. They did differ in some ways in the interventions. The very noticeable differences in the IO group were an almost 15% LESS therapeutic hypothermia, 5% less fibrinolytics, and 9% less interventional catheterization.
Although the propensity scoring appears quite well and there were multiple calculations to correct for confounders there are still significant biases. I think foremost the discrepancy between the number of of IO vs IV’s performed is hard to overcome (660 vs 12500). Also there were some big differences in the patients receiving hypothermia and cardiac catheterizations. I still think the data is not definitive for those two interventions but certainly this may be a marker of quality of care and attention to care. Still the OR for survival with favorable neurological outcome is impressively in favor of IV access. It is interesting that some EMS systems used IO as their first line and it would be interesting to know why IO was first line. I also wonder WHY the IO patients got less interventions. Was the IV access the reason or were they initially deemed to be sicker? Also it would be nice to know how long the IO was in and what was the time frame to when it was swapped out for IV access. Lastly, I can’t get away from the thought that sicker patients are going to get IO’s and are going to do worse.
So what’s the bottom line? IO access is critical to establishing vascular access to care for patients (depending on what you think the validity of ACLS drugs are, oh HEY OPALS TRIAL). Maybe IO access is a marker for sicker patients or maybe worse IO access biases providers against the same level of care as those with an IV…We all know the drill… but does it make our patients better? I think this is enough to allow for an RCT looking directly at this topic.