Need help understanding these

[nurs1ng]

Had a pt who was admitted for septic shock due to PNA. Initial ScVo2 was 89% and crept up to as high as 94%. Pt was on levo maxed at 30 and SBP was sustaining above 90 (goal SBP > 90). According to the MD, he wanted the pt to be on both levo & vasopressin even though levo in itself was sustaining pt's blood pressure.

Since we were using pressors on this pt, that may have been a contributing factor for why the pt's ScVo2 was high... since the body isn't able to properly utilize the O2. Just trying to get a rationale for why the MD prefers to have two pressors (btw, we're talking about a very potent pressor - Vaso) instead of just leaving the pt on levo.

Although this pt's ScvO2 was really high, lactate trended down after about 4L bolus. Is this because the bolus helped push O2 to the tissues? I know that lactate is a byproduct of anaerobic metabolism, but what exactly normalizes lactate?

Also, is So2 (on an i-STAT) the same as SaO2?

Thanks in advance for your help.

[PaSSiNGaS, MSN]

Without getting into a ton of physiology and pharmacology of these drugs you do need to look into their actions at the cellular level. Levophed works on beta and alpha where Vasopressin works on V1 and V2 receptors. Levophed is first line treatment and basically he wanted to add the Vasopressin so you could wean down the Levophed instead of having it so high.

In regards to SvO2 you need to remember in septic shock there is a low O2 extraction rate and normally a high CO. This in turn causes a normal to high SvO2 in most situations until the septic shock progresses into later states.

And finally yes sO2 is the same as SaO2, both measure oxygen saturation in arterial blood. SpO2 is the oxygen saturation measured by pulse oximetry which looks at two different wave lengths.

[PaSSiNGaS, MSN]

I need to know more about the different tests and uses of iStats because we only use venous blood for ours, so I would have said no.

First question would be why only use venous blood for an i-stat abg? If you are using it for the Hgb then ok, but not sure why else you would run an abg from venous blood.

But if you measure sO2 on an istat that was drawn from venous blood then just compare it to what normal venous SaO2 would be which would be 40-70. Venous blood can have a large difference of 30-45 points lower with the SaO2 compared to an ABG.

[nurs1ng]

Without getting into a ton of physiology and pharmacology of these drugs you do need to look into their actions at the cellular level. Levophed works on beta and alpha where Vasopressin works on V1 and V2 receptors. Levophed is first line treatment and basically he wanted to add the Vasopressin so you could wean down the Levophed instead of having it so high.

So I understood that the doc wanted to wean down on the Levo, but is this because Levo by itself can cause renal failure due to too much constriction?

Thanks again for your response.

[PaSSiNGaS, MSN]

There are a lot of different studies showing better mortality rates when vasopressin is used in conjunction with levophed than if it was just Levo. Some show better urine output and renal perfusion but then some even show the opposite but I would much rather run low dose Vaso with a little Levo than a large amount of Levo by itself. If I start to see myself using a lot of Levo and having to keep titration get up I will start Vaso

[Dranger]

Levo at 30 is pretty high, if I get around 20 I better have Vaso on board with neo ready. You can only vasoconstrict so much (there are side effects) and these drugs do have diminishing returns. Having Levo lowered with other drugs like vaso running is a much better option than maxed levo.