Lactate levels

I have no idea what these things are, but they are causing us problems.  Everything else seems to be going well: (i) she had the left drainage tube removed this morning, leaving on the right tube in (the one that was inserted a couple of days post-op), (ii) she is eating better, she had cheerios and yogurt this morning, much like a usual breakfast for her, (iii) she is down to minimal oxygen, and (iv) she is seeming more herself.  She was telling me this morning that she can see the water out her window (the Hudson river) and can also see birds flying around.

The lactate levels, however, are a little perplexing.  They were the reason she was not moved yesterday, as her values were too high (and increasing) and so they put her on a drug to improve heart function.  At the rounds this morning, they said her lactate was down to 0.9 (it was 2.7 and they like it under 1).  However, at the next blood draw her lactate was reading 2.9.  They run it on three different machines and found values between 2.2 and 2.9.  They also sent a sample to the lab and the lab results came back without a lactate value...