Some good news for remote, rural, prehospital, and retrieval medicine clinicians who rely on point of care testing with the i-STAT® device. An animal study confirmed the reliability of testing aspirates from intraosseous samples taken from the tibia(1).
This is also good news for hospital practitioners when it comes to the acquisition of blood gas results, since there are concerns over the potential damage to blood gas analysers by bone marrow contents in the samples.
The researchers tested blood gases, acid–base status, lactate, haemoglobin, and electrolytes, and compared these with results from an arterial sample.
There was no malfunction of the equipment. Most of the acid–base parameters showed discrepancies between arterial and osseous samples: the average pH and base excess were consistently lower whilst pCO2 and lactate were higher in the intraosseous samples compared to the arterial. However the overall small degree and predictable direction of discrepancy in these values should preserve the clinical usefulness of intraosseous gases if these findings can be replicated in human subjects. pO2 was obviously very different between osseous and arterial samples.
They noted that aspiration of intraosseous samples was generally straightforward, especially immediately after placement of the cannulae, but on a few occasions more forceful aspiration was needed. They point out that this could possibly cause cellular lysis and affect the potassium analysis.
The authors consider the issue of how much aspirate should be discarded before taking a sample after intraosseous cannula insertion, and refer to a prior study which suggested that 2mL is adequate.
- Intraosseous aspirate can be tested on an i-STAT® point-of-care analyser
- Haemoglobin and electrolytes show good correlation with arterial samples
- Acid-base, pCO2, and lactate differ slightly from arterial results but in a predictable direction and results are still likely to be clinically useful in an emergency
- It may be worth discarding the first 2 ml of aspirate
- These results require validation in human subjects
Analysis of intraosseous samples using point of care technology–an experimental study in the anaesthetised pig
Resuscitation. 2012 Nov;83(11):1381-5
BACKGROUND: Intraosseous access is an essential method in emergency medicine when other forms of vascular access are unavailable and there is an urgent need for fluid or drug therapy. A number of publications have discussed the suitability of using intraosseous access for laboratory testing. We aimed to further evaluate this issue and to study the accuracy and precision of intraosseous measurements.
METHODS: Five healthy, anaesthetised pigs were instrumented with bilateral tibial intraosseous cannulae and an arterial catheter. Samples were collected hourly for 6h and analysed for blood gases, acid base status, haemoglobin and electrolytes using an I-Stat point of care analyser.
RESULTS: There was no clinically relevant difference between results from left and right intraosseous sites. The variability of the intraosseous sample values, measured as the coefficient of variance (CV), was maximally 11%, and smaller than for the arterial sample values for all variables except SO2. For most variables, there seems to be some degree of systematic difference between intraosseous and arterial results. However, the direction of this difference seems to be predictable.
CONCLUSION: Based on our findings in this animal model, cartridge based point of care instruments appear suitable for the analysis of intraosseous samples. The agreement between intraosseous and arterial analysis seems to be good enough for the method to be clinically useful. The precision, quantified in terms of CV, is at least as good for intraosseous as for arterial analysis. There is no clinically important difference between samples from left and right tibia, indicating a good reproducibility.