Let It Flow! Intraosseous Flow Rates by Insertion Site

Intraosseous (IO) access has become increasingly popular as a ‘safety net’ for failed IV access and has become a go-to procedure in pre-hospital cases of rapidly decompensating patients. Think of the cardiac arrest patient or the hemodynamically unstable trauma patient. The IO has proven a quick and reliable way to gain access to medullary venous plexuses in long bones, which drain into systemic venous circulation. We can basically think of the bone marrow as a vein that will not collapse on us that can be accessed very rapidly, with very little training. We have infused fluids, medications, and blood products successfully through the IO. And now that increased support has grown for the use of IOs prehospitally, the question has become which site is best: Tibia (which many people seem to be most comfortable with due to prominent landmarks and distance from resuscitative efforts), humerus, or sternum. There is literature supporting, and widespread consensus for, proximal tibia as the optimal insertion site in children, but this consensus does not exist in adults. Choice often depends on comfort level of the operator and convenience of the location, but we should also consider the difference in flow rates between sites.

There are few studies comparing IO placement sites but the ones that exist compare proximal to distal tibia, tibia to humerus, and one study which compared IO infusion rates between tibia, humerus and sternum in cadavers. The first study found that IO flow rates in the proximal tibia were significantly faster with and without use of a pressure bag than flow rates the in the distal tibia. The drawback of this study was its small sample size of only 22 patients. Pasley et al did a cadaver study published 1 year ago which utilized 16 cadavers to compare flow rates and found that the sternal site had the highest and most consistent flow rate compared to the humerus and tibia. In fact the average flow rate in the sternum according to this study was 1.6x higher than the humerus and 3.1x higher than the tibia. Additionally, this study showed that the tibia had the greatest number of insertion difficulties (In 3 out of the 16 cadavers, infusion was unsuccessful after insertion and alternate tibia had to be used.) Ong et al did a study in 2009 which had very different results. This study recruited 24 patients who presented to an ED in Singapore, all patients received a tibial IO, and those who needed a second access point were given a humeral IO (which 11 patients received). This study found no significant difference between the flow rates at the tibial and humeral site in contrast to Pasley’s study which did show a significant difference between humerus and tibia with the humeral site achieving a 1.8x greater volume on average than the tibia. Small sample size is an issue in all articles existing on this subject.

It seems that there have been no conclusive studies in human or cadaver studies on best IO insertion site, but, if we believe the most recent study by Pasley et al, the sternal and humeral IO sites, in that order, have better flow rates compared to tibial placement. This higher flow rate could make a difference when rapid fluid resuscitation is imperative and could lead to better survival of our patients. A new device called the FASTResponder was released by Pyng Medical in 2013 to make the sternal IO concept easier. This device is safe on ages 12 years and older and makes site identification easy. Another benefit of the device is, unlike the IO drill system, it requires no batteries, and, anecdotally, there is less pain on fluid delivery compared to other sites. One factor we are still unclear about is if the sternal IO could pose a problem if cervical immobilization is being used in trauma patients, with chest compressions, and for some airway procedures. Pyng Medical advertises on their website that it is “safe” to use in conjunction with cervical immobilization devices and CPR. However, the drill-based EZ-IO is approved for all ages, and many providers are already comfortable with it. According to Pasley’s study, the humeral placement is second best in terms of flow rates and had less insertional difficulties. He also notes that the humeral site had the greatest variability in volumes infused from subject to subject. There doesn’t seem to be enough evidence yet to draw firm conclusions; more studies are needed with a greater number of test subjects to increase reliability.  Furthermore, outcome measures, though often difficult to study, would be nice.

References

Carness J, Russell J, Rodrigo M, et al. Fluid Resuscitation Using the Intraosseous Route: Infusion with Lactated Ringer’s and Hetastarch. Military Medicine 2012; 2:222.

Ong M, Chan Y, Jen J, Ngo A. An observation prospective study comparing tibial and humeral intraosseous access using the EZ-IO. Amer Journal of Emergency Medicine 2009; 27, 8-15. 

Pasley J, Miller C, Dubose J, et al. Intraosseous Infusion Rates under High Pressure: A Cadaveric Comparison of Anatomic Sites. Distribution A: Approved for Public Release 2014: Case Number 88ABW-2014-1139.

Tan B, Chong S, Koh Z, Ong M. EZ-IO in the ED: an observational, prospective study comparing flow rates with proximal and distal tibia intraosseous access in adults. Amer Journal of EM 2012;30(8):1602-6.