Interesting Case - Pheochromocytoma

[Brenna's Dad]

I had the opportuity to assist with the anesthesia of a child with pheochromocytoma last week. Three tumors all together, one on each adrenal and then one on her left pregnaglionic sympathetic chain at L1.

A few things I didn't know and thought would be interesting to share.

1. The kids are usually dry, dry, dry. This patient was admitted the night before to get lines placed and for fluid management. This in fact did not happen because the PICU doc couldn't get the central line in. So her initial CVP was 3. The doc I was with wanted her CVP up around 12. Before we achieved this, we actually had more problems with hypotension.

2. Magnesium bolus and drip are highly recommended in the literature to prevent dysrhythmias in adults. We gave a gram on induction and ran the drip at 0.5 grams per hour. Seemed to work great. I would think that the magnesium would also be helpful in antagonizing calcium and the effects of the catechols.

3. For induction we ran Nipride at 1 mcg/kg/min, 150 of propofol, 40 mg Lidocaine, 5 mg Labetolol, 250 mcg of fentanyl, and 20 mg of esmolol. Worked very well. Her pressure in fact dipped for a few beats to 66/40 but easily increased with the metalephrine. Her BP was very stable though and only went as high as the 120s with larygoscopy.

4. The patient had been on Desmer and phenoxybenzamine for 2 weeks prior to surgery.

5. We used phentolamine, labetolol, and nipride throughout the case to control BP.

Now for the cupie prize... Which alpha antagonist would you use and what would be your rationale???

[athomas91]

good question - but i am up to my ears in osmoles, molality and the such....so i will just read the replies... :imbar

[Tenesma]

he wanted a CVP of 12 and it was only 3...???? easy solution: change the height of the transducer or add about a PEEP of 20.... sigh... CVP is useless... now discuss...

[charles-thor]

I'm going to go out on a limb here with Tenesma's comment, so here goes. Since CVP is a combined function of venous compliance, volume, and right ventricular function; any alteration(s) of one or more of these variables will influence transduced CVP values and thus may not necessarily correlate with intravascular volume. Furthermore, this value is greatly influenced by intrathoracic pressure. I guess all of the potentially confounding variables lead to a number that really doesn't signify a whole lot of anything. Am I on the right track?

[Brenna's Dad]

I will have to disagree somewhat with Tenesma's comment. We all know that the CVP isn't a very good indicator of fluid status. But I do think it is one thing we can use to trend fluid therapy, especially in the patient with a normal heart and if we assume that contractility and cardiac output have not changed dramatically.

Would I use CVP in the patient with an EF of 20%, probably not, would I use it a 12 year old with Pheo, probably.

[charles-thor]

I guess what I should've added is that context makes all the difference.

[Cabgman]

One would want to use a drug that antagonizes the alpha 2 receptor located on the presynaptic nerve terminal because it is this receptor that will ultimately lead to a release of presynaptic Ca++. The Ca++ then mediates as a second messenger to release NE to sustain the patient after the tumor is removed thus preventing cardiovascular collapse related to decreased levels of circulating catecholamines.

[aRNnAR]

One would want to use a drug that antagonizes the alpha 2 receptor located on the presynaptic nerve terminal because it is this receptor that will ultimately lead to a release of presynaptic Ca++. The Ca++ then mediates as a second messenger to release NE to sustain the patient after the tumor is removed thus preventing cardiovascular collapse related to decreased levels of circulating catecholamines.

How bout...Phentolamine!

[allapeyre]

Phentalomine............ a potent presynaptic alpha-2 blocker that would counteract the excess catacholamine release from the tumors intraoperatively.

[Passin' Gas]

Alpha-2 receptors function to reduce release of NE into presynaptic ending. They function as autoreceptors, when NE is present, binds to receptor, and in effect, reduces further release of NE. An antagonist at an alpha-2 receptors would actually ENHANCE further release of NE.

Using a selective alpha-1 antagonist will prevent NE from binding to the post-synaptic receptor, decrease vascular contractility on the venous and arteriolar beds, thereby reducing preload and SVR. Plus by using a competetive antagonist, the alpha-1 effects of e.g. prazosin (alpha-1 selective antagonist) can be overcome by phenylephrine. I.e. get the 'squeeze' back once the offending tumor is excised and the source of excess NE removed.

The venous vascular beds have a high density of alpha-1 receptors. Blocking these will increase capacitance and allow 'tank refilling' since these patients are really intravascular volume depleted.

PG

[Cabgman]

Thanks for the insight! I stand corrected humbled by your knowledge. We just received a portion of this lecture in class this week.