iSTAT Capillary BGs on peds patients

With any form of lab testing, preanalytical concerns must be addressed. A syringe drawn sample can also clot, especially with NICU babies. Heparinized samples can clot if not mixed properly or collected too slowly. IV fluids can dilute samples and impact other ISTAT (and main lab) results. Bad venous sticks can cause hemolysis. 

Our hospital uses the ISTAT exclusively for blood gas testing. We use venous, arterial and capillary. Of course, each sample type has its own set of normal ranges. We educate proper collection of the samples (avoid air bubbles, allow the sample to flow from the capillary collection tube, not go drip, drip, drip which would introduce ambient air. If sample volume is of concern (as with preemies), capillary collection uses the least amount of blood with minimum waste.

Validation occurred long before I was in point of care so I cannot help there. You cannot compare your results to the other two sources since they do have different ranges though arterial would be the closest. I would not personally volunteer for that. :)

Per the iSTAT system manual: "There are conflicting reports in the literature regarding the validity of PO2 analysis performed on arterialized skin puncture specimens compared to arterial PO2 . The process of capillary collection may change PO2, PCO2, and the calculated sO2. Arterial specimens are preferred for blood gas analysis. See CLSI documents H4-A5, C-46A, and H11-A4 listed in the References section for further discussion."
and "Avoid hemolysis (bursting of red cells) due to vigorous massaging or “milking.” Hemolysis will cause an increase in potassium results and a decrease in calcium results."
and "Avoid drawing air into the capillary tube."
and "Test samples collected in capillary tubes immediately to avoid clotting (especially in neonates whose blood may clot more quickly)."
and "Most heparinized capillary tubes are not suitable for electrolyte measurements, especially ionized calcium, due to the high concentration of heparin (50 U/mL or more). Use balanced heparin tubes."

Essentially what the iSTAT system manual is saying is that hemolysis will not have an affect on blood gas values, but if you use a cartridge that also measures potassium then you could have problems. Secondly, clotted specimens on the iSTAT simply error out - there would not be an issue of erroneous results due to clotting, you would instead get <> as a result or "Cartridge Error", etc. The only contaminant for blood gases is exposure to room air and in some instances, ice.

At Children's Hospital Colorado we performed capillary gases extensively, collected via heparinized Saf-Wrap capillary tubes and G3+ cartridges when I was there. On the Sample Type selection screen the testing operator could select "CAP" as the specimen type to apply the appropriate reference ranges. Our reference ranges matched our Arterial ranges.  With that said, I have not kept up with the limitations and changes to FDA approval for all cartridge types, and am not able to comment on whether or not the G3+ cartridge is still approved for use with Capillary specimens.

We would focus on CG8s, so hemolysis would be a concern. Right now we do not have our ABL in the lab validated for capillary samples, so figuring out a validation would be challenging. I've reached out to the company and haven't received much help, so I figured I'd open it up to this forum. Our areas currently use the cartridge for venous and arterial, and have for years, but it was never worked up for cap. We did briefly discuss comparing art vs cap (so long as an art sample was already being taken from the patient). It would be the closest comparison. 

Yep, and you wouldn't necessarily need to validate on newborns/peds either - as that sort of primary validation is on the vendor to perform, and has already been approved by the FDA. You would be doing a secondary validation - so if it was me, I would be looking at my adult ICU and/or patients with an arterial line, and work with those areas to collect a simultaneous capillary specimen in a Saf-Wrap capillary tube tested immediately at the bedside.

We switched from the ISTAT blue CG4 to the white CG4 cartridge a couple years back.  We ran 10 capillary samples during that validation.  We used volunteers for capillary sticking (not too many want to volunteer!).  We did use the heel stick lancets to do this as the other ones used for fingerstick glucose didn't allow us to collect enough to run a gas.  We did not go to the NICU to collect due to logistics with POC and Main Lab equipment to be run at the same time.  Our neonatal ranges are set up the same as Main Lab ranges so we did not establish new reference ranges, just verified them.  Every 6 months we do patient correlations with our POC to Main Lab equipment and we do 2 arterial, 2 venous and 1 capillary - that capillary is from whoever volunteers.  

 We run tons of capillary gases here in the main labs and these gases are only drawn by our phlebotomists. There are a lot of barriers here to transitioning collection of cap samples to RNs or RTs. So as long as we can maintain this practice, we will.

I do have one off site NICU where the RNs only have an iSTAT and have to be trained on capillary collection. This works well here as it is a small group, and they have great educators. One thing that made a HUGE difference for us years ago was switching from using a standard cap tube with open ends to using this Sarstedt product with the iSTAT. It is virtually impossible to get air bubbles in this device, and the sample doesn't run out the other end if tipped too far, etc. It collects the exact volume needed for the cartridge. We have virtually no cartridge errors using this. 

Sarstedt Minivette 100uL lithium heparin, capillary collection device

481_d_Minivette_US_0616.pdf

Hi everyone. Are you using the white CG4 cartridge for the i-Stat 1 System?

Yes I am just starting