strategies for craniotomy w/ mannitol & copious UOP.

[gtb]

What is your fluid management strategy for copious urine output following mannitol to relax the brain. This current case is 23yo otherwise remarkably healthy guy w/ skull base tumor and a very technically challenging approach for the surgeons (stealth stereotaxy and 16 hours under the microscope). They requested 1gram/kg of mannitol along with steroids and some mild hypocapnia to relax the brain. Gave 0.5 g/kg first round, then another 0.5g/kg after further relaxation requested. Normal serum and urine electrolytes, normal serum and urine OSM, normal urine specific gravity. Effectively matching ins w/ outs. But, after > 12 liters of UOP, I start wondering whether chasing w/ fluids is the right strategy.

Am I just contributing to excessive urine output by overloading him with fluid, and his completely normal organs are just appropriately dealing the the volume? Six hours after the mannitol, I considered letting him dry out a little to see if things would slow down, however all other parameters were perfect, and at midnight, I did not want to perturb an otherwise stable patient.

Looking for alternative management strategies. Thanks for considering the case.

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[ssmallz]

Why chase the urine in an otherwise healthy 23 y/o patient. That fluid has to go somewhere and if he doesn't pee it out, he's gonna get all puffy and thats not good for extubation. I usually try to keep my fluids to a minimum unless the hemodynamics or surgery indicate it. Minimal EBL, just keep up w/maintanance 1L for NPO, 100-200/hr for basal + exposure losses. I usually ignore the urine made w/mannitol b/c thats the whole point of the manaitol and if we replace the fluid w/crystalloid then we're kinda chasing our tail. As long as the bp and hr are stable and blood loss is minimal, no reason to flood him. If you're really concerned during a long case send off a BUN/Cr after a few hrs to make sure his kidneys aren't getting hurt

 

[gtb]

Definitely considered dropping off on the fluid resuscitation. As outs > ins, started seeing pretty significant systolic variation on the aline, CVP dipped down from baseline, and MAP dropped to low 60's. Easily normalized w/ fluid bolus. Dura opened so MAP ~ 60 mmHg still should be adequate for brain perfusion. Considered vasopressor, but both hemodynamic monitoring and response to fluid challenge seemed to indicate volume down as the root cause.

 

[Idiopathic]

Definitely considered dropping off on the fluid resuscitation. As outs > ins, started seeing pretty significant systolic variation on the aline, CVP dipped down from baseline, and MAP dropped to low 60's. Easily normalized w/ fluid bolus. Dura opened so MAP ~ 60 mmHg still should be adequate for brain perfusion. Considered vasopressor, but both hemodynamic monitoring and response to fluid challenge seemed to indicate volume down as the root cause.

i wouldnt necessarily treat a systolic variation on its own, i would rather trend base deficits and lactate, realize that as long as UOP continues, there is still intravascular fluid to be had (sort of tongue in cheek, but you get the idea). also its extremely hard to manage the 14th hour of these cases up front, which is kind of what you need to do, so at that point, sometimes you are forced into an alternative plan.

i think its okay to run these patients dry, administer low dose phenylephrine infusion with plans to gently hydrate postoperatively. its extremely unlikely that any problems will occur with mild dehydration in this patient but its extremely likely that you will have complications if you go the other way.

i am always surprised how well my frail, comorbid, geriatric patients have done after 12+ hour craniotomies.

 

[Idiopathic]

Effectively matching ins w/ outs.

i just saw this nugget, and i would not typically recommend this plan in craniotomy, if only because of the electrolyte derangement, for one thing, but also the volume is not necessary.

 

[gtb]

Thank you for the recommendations. I failed to mention, that although hemodynamics, pH, and electrolytes were normal, the measured lactate was increasing slightly with each blood gas. This climbing lactate was another reason I continued resuscitating w/ crystalloid.

 

[Idiopathic]

thats appropriate, i would just caution about getting too attached to replacing urine output 1:1 in these cases. clearly if you have signs of decreased perfusion like a steadily climbing lactate or worsening base deficit, then you need to consider volume replacement with blood or saline.

 

[tucker27705]

>12 L of UOP seems like a hell of a lot of UOP. Even after lasix and mannitol. DI? I've not seen that kind of UOP before. Anyone else? When you say crystal, what exactly were you using? NS, add a little bicarb? LR?

Tuck

 

[jennyboo]

Hmm. 12000 ml / 16 hours = 750 ml per hour. Assuming a 75kg guy, that's 10 ml/kg/h. Way too much fluid and UO, even for a 16 hour case.

My volume of crystalloid administered during a crani is frequently close to the volume of urine out, but I don't usually chase this cc by cc. Usually the diuresis has its effect, then the rapid urine output slows down, then I catch up.

I don't trend base deficit or lactate (lactate, imo, shouldn't be rising at all and if it's abnormally high you are way behind). I do check ABG w/electrolytes and serum osms.

 

[Idiopathic]

were you using precedex? profound diruesis can occur, 2/2 ADH blockade.

jenny - many roads lead to rome. i typically do not check osmolality in these patients (although i might after that kind of UOP), if only because it seems fairly early for DI, and the amount of mannitol we give is fairly trivial (usually 1mg/kg max for the case). Now if 3%/mannitol boluses were being used thats obviously a different story, but I probably wouldnt check an osm for this case. Like with any 10 hour case though, I feel DE/lactate trends are extremely helpful (this patients lactate was rising, so something is off).

 

[Arch Guillotti]

I can recall having a similar case once with massive uop. Urine studies were wnl so I really doubted it was DI. Slowed the fluids down, quit chasin my tail and used some neo to prop things up a bit and things really seemed to smooth out.

 

[Narcotized]

I'm thinking that's DI regardless of what your lab values are.

 

[aredoubleyou]

Maybe somebody smart can answer if urine osm can be used in the setting of manitol diuresis. I'd keep an eye on plasma sodium, maybe even osm (same issure - manitol?). DI is not an emergency, just follow trends, see where things lead. I wouldnt be too aggressive on the fluids if the head is tight, otherwise doesnt matter what you do, in the big picture. Can catch up on fluids later, can treat DI as it comes, likely transient anyway. Probably using NS, after a huge diuresis and replacement might get a little acidotic (high cl-, no gap), again, dont worry, check lactate which will probably be normal

 

[tucker27705]

i was wondering the same thing about checking an osm in the setting of mannitol. in this case, however, after so much uop, i doubt there is much mannitol left to cloud the picture. i would assume any osm attributable to mannitol would be scant.

 

[Idiopathic]

Maybe somebody smart can answer if urine osm can be used in the setting of manitol diuresis.

well sure, but its not like how lasix clouds your urine electrolyte pattern. if mannitol is around then your urine will be hyperosmolar compared to serum and if no mannitol is around and you have that kind of UOP then it will be hypoosmolar compared to serum. obviously you CAN have intraoperative DI although its rare especially with this particular operation.

i agree with the assessment that the mannitol effect is gone. i think that its reasonable to check urine osm if it makes one feel better. as long as the patient isnt hypernatremic (hallmark of DI), then you have normally functioning kidneys and youll probably just get back most of what you put in. if you choose to augment bp with volume here you may end up hurting yourself is my only assessment. id rather be a little dry than a little wet with this guy. replacing uop is fine if you diagnose DI.