Dry Lungs?

Fluid in Thoracic Surgery: Time to overthrow Immortan Joe?

The Classic Teaching from Miller 8th Edition ch 66 Anesthesia for Thoracic Surgery

Total positive fluid balance in the first 24-hour perioperative period should not exceed 20 mL/kg.

For an average adult patient, crystalloid administration should be limited to less than 3 L in the first 24 hours.

No fluid administration for third-space fluid losses during pulmonary resection.

Urine output greater than 0.5 mL/kg/h is unnecessary.

If increased tissue perfusion is needed postoperatively, it is preferable to use invasive monitoring and inotropes rather than to cause fluid overload.

And so the above was also consistent with the clinical teaching at my institution. Keep them dry, regardless of whether it was a wedge resection, lobectomy or esophagectomy (I haven’t had the pleasure of a pneumonectomy yet).

But further reading in Barash (Clinical Anethesia Fundamentals), calls this into question in ch 34 Anesthesia for Thoracic Surgery, with the following one liner broadside:

“Fluid management for all thoracic procedures should follow either a restricted or a goal-directed protocol. However, recently, concerns about acute kidney injury have called into question the strategy of fluid restriction in thoracic surgery.”

And later in the same chapter, a “Did You Know?” sidebar reinforces the same point, specifically mentioning esophageal surgery and the controversy around restrictive fluid management.

When asked about this in the operating room, the Thoracic Surgery team even indicated that anesthesiologists in this practice are being too restrictive, especially with the esophagectomies (which are for the most part, abdominal surgery).

So what is one to make of this?

Digging into the literature, there was a nice summary of the controversy and recent data at Current Opinion in Anaesthesiology  (doi: 10.1097/ACO.0b013e32835c5cf5) from a team of anesthesiologists at Yale. The article provides a nice run down on the basis of the fluid restrictive strategies (mainly studies from the 198os) and how these studies were performed before the advent of lung protective ventilation strategies (6-8cc/kg and use of peep). They do agree that fluid restriction in Pneumonectomy is logical:

In pneumonectomy, the whole cardiac output will be directed to the remaining lung. This volume in the presence of a decreased vital capacity may overwhelm the remaining lung’s protective mechanisms resulting in a rise in the pulmonary capillary filtration pressure.

However, this may not be the case in lesser lung resections, with a restrictive therapy threatening to cause Acute Kidney Injury. In fact, the belief that renal injury is low in thoracic surgery appears misplaced, as old data only counted kidney injury if patients required renal replacement therapy. Newer evidence shows thoracic patients are at higher risk of AKI than previously thought and that this may cause increased M&M in the longer term.

The authors then go on to promote a Normovolemia and Goal-Directed fluid therapy regiment. One study showed a simple normovolemia method of replacing ongoing losses and use of maintenance fluids i/o and post-op until PO intake, reduced both AKI and extravascular lung water (EVLW). The goal-directed therapy targets Cardiac Index through either Thermodilution, PiCCO, Transesophageal Doppler, SVV or PPV.  The authors point out that while controversy remains, there is some evidence showing no increase in EVLW with goal-directed fluid therapy when lung protective ventilation strategies are used.

The remainder of the article goes into the colloid vs. crystalloid debate, which is beyond the scope of this post, and it appears there is no evidence of which is better to use in thoracic surgery (potential for future research questions!).

So in conclusion, it appears that Dry Lungs may not be the Best Lungs and Best Kidneys for Thoracic Surgery.

Renal Replacement Therapy – Considerations

Indications for Renal Replacement Therapy (notes from TrueLearn)

-broad term : hemodialysis, peritoneal dialysis, hemofiltration, renal transplant
-CRRT is over 24hrs, best for HD unstable patients

Chronic Renal Failure indications
-fluid overload
-uremic symptoms
-ftt
-malnutrition
-GFR criteria

Indications in ICU patient
-oliguria/anuria
-pulmonary edema unresponsive to diuretics
-uncompensated metabolic acidosis (ph35, creatinine >400, hyperkalemia >6.5

Succ will raise K same as normal patient
watch fluid status and hemodynamics
avoid nephrotoxic agents (some a/b, nsaids)

Lactated Ringer’s: All Good, All the time

Great post from emcrit.org on the myths of using LR in renal failure, specifically pointing out the physiology then backing it up with clinical trials:

the primary reason that this myth is wrong has to do with potassium shifting between the cells and the extracellular fluid.   About 98% of the potassium in the body is present inside the cells, with an intracellular potassium concentration of ~140 mEq/L.   Therefore, even a tiny shift of potassium out of the cellular compartment will have a major effect on extracellular potassium levels.   NS causes a non-anion gap metabolic acidosis, which shifts potassium out of cells, thereby increasing the potassium level.   On the other hand, LR does not cause an acidosis, but instead may have a mild alkalinizing effect given that it contains the equivalent of 28 mEq/L of bicarbonate.   Potassium shifts have a greater effect on the serum potassium than the actual concentration of potassium in the infused solution.

The trials were quite excellent, with one comparing LR vs NS use in patients undergoing renal transplant.. the trial was actually stopped early as the LR patients were doing so much better than the NS patients:

 

_{They performed a prospective, randomized, double-blind controlled trial of NS versus LR among 52 patients undergoing renal transplant surgery.   The mean change in serum potassium during the procedure was +0.5 mEq/L in the NS group compared to -0.5 mEq/L in the LR group (p < 0.001; figure below).   Patients in the NS group also had lower pH levels following surgery.}     

0

 

More detailed explanation at EMCRIT ( http://emcrit.org/pulmcrit/myth-busting-lactated-ringers-is-safe-in-hyperkalemia-and-is-superior-to-ns/ )

 

Another common myth associated with LR has to do with blood transfusions, according to this the calcium in LR can cause clots by overwhelming the chelating capability of the citrate in stored blood. But as a trial from 1998 demonstrated, this is also false and blood banks should recommend using LR for its advantages during trauma resuscitation vs. NS.  See: http://www.aafp.org/afp/1998/0801/p502.html

So next time someone tells you to use NS for whatever reason in the OR or elsewhere, let them know LR is the best!

Renal Tubular Acidosis

From: http://www.anaesthesiamcq.com/AcidBaseBook/ab8_5.php

The table below provides a useful summary of some of the key points in differentiating the types of renal tubular acidosis.

Comparison of Major Types of RTA
	Type 1	Type 2	Type 4
Hyperchloraemic acidosis	Yes	Yes	Yes
Minimum Urine pH	>5.5	<5.5 (but usually >5.5 before the acidosis becomes established)	<5.5
Plasma potassium	Low-normal	Low-normal	High
Renal stones	Yes	No	No
Defect	Reduced H+excretion in distal tubule	Impaired HCO3reabsorption in proximal tubule	Impaired cation exchange in distal tubule