First, before we discuss the IO further, please check out Practical POCUS at PracticalPOCUS.com
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There is a great systematic review available that covers many of the details on the basics of IOs.
The main contraindications are skin infection at the site of insertion, fracture of the bone used (or potentially proximally), severe bone disease, osteogenesis imperfecta, osteoporosis, osteomyelitis of the bone involved, compartment syndrome to the extremity, prior surgery, burns to the area involved, or recent failed attempt at the same bone.
Although rare the major complications are compartment syndrome due to fluid extravasation, skin infection, and osteomyelitis. However, there have been rare complications up to death from sternal access due to injuries or the heart or aorta. Mediastinitis is another potential complication seen with older devices. Fat emboli has been questioned but in certain studies this was found in animals both with and without IO access.
There are a variety of devices but the EZ-IO is very simple to use with multiple approved sites (except for the sternum). The five signs that indicate correct placement are loss of resistance on entering the marrow cavity, ability of the needle to remain upright without support, bone marrow or blood easily sampled using a syringe, administration of 2ml of saline without tissue swelling, and easy administration of 8ml of saline without resistance.
When it comes to drawing blood off of the IO, this is possible and is the main portion of our discussion today. In a 2010 study, there was a significant correlation for many labs. The RBC, hemoglobin, and hematocrit counts in the CBC profile were the same but WBCs and platelets did not correlate. Glucose, BUN, creatinine, chloride, total protein, and albumin in the chemistry profile were well correlated but sodium, potassium, CO2, and calcium concentrations were not. However, sodium was within 5%, calcium within 10%, and the rest were within 25%. With these differences, the WBC is elevated and both CO2 and platelets are low in the IO compared to IV. There are several important limitations of that study. It was small with only 10 healthy volunteers, was all drawn from the humeral site, and it being unknown if the lower CO2 level would have changed with evaluation of arterial blood.