There are many misconceptions in the fluid therapy world. We continue our conversation from last month with Dr. Sean Smarick, a board-certified criticalist at AVETS in Monroeville, Pa., to clarify them.
When should you use LRS vs. saline vs. Normosol-R?
There is no question that this is a controversial topic. Ultimately, what matters most is probably how much we give rather than what we give. What also matters is knowing what we are trying to achieve.
One could argue that if giving a shock dose to restore effective circulating volume, Normosol-R is not ideal as resuscitation fluids, because the acetate buffer, as well as the magnesium it contains, reportedly can cause vasodilatation and therefore hypotension. If we have a patient in the hospital for days on maintenance (or some multiple thereof), LRS may be of benefit since it contains less sodium. Saline is the highest in sodium and not buffered, so I don’t find myself reaching for it very often.
Is it appropriate to deny IV fluids to a cat or a dog with urinary blockage?
No, it is not. Fluids are critical to dilute potassium, reduce acidemia and support the effective circulating volume. Early fluid therapy is crucial to the successful treatment of “blocked” patients.
What is better with urinary blockage, saline or LRS?
The main goal is to restore an effective circulating volume, to fight metabolic acidosis and to dilute potassium in these hyperkalemic patients. Several studies have shown that LRS is a better choice as it is balanced, i.e. buffered.
If a patient on crystalloids needs Hetastarch, can we give it in the same IV port?
Hetastarch is diluted in 0.9 percent sodium chloride, so there are no incompatibility issues.
Speaking of Hetastarch, which dose do you like to use?
A dose of 5-10 ml/kg/hour is a good place to start for volume expansion. But as always, rather than blindly following a recipe, I prefer to titrate based on the patient’s needs. Here again, we need to know the end points of our fluid therapy plan. For colloidal support, 1 ml/kg/hr should avoid some of the coagulopathies seen with higher doses.
Can colloids really cause coagulopathies?
Yes, they can. In fact, any type of fluid can alter coagulation by diluting coagulation factors. This is called a dilutional coagulopathy. In addition to this dilutional effect, colloids can interfere with platelets and alter their ability to form a clot, especially when we give more than 20 ml/kg/day.
What is the controversy in human medicine about falsified studies about colloids?
One of the most prolific writers who advocated synthetic colloids over simple crystalloids had his research revoked after he was found guilty of fraud. This amplifies the never-settled debate of whether crystalloids or synthetic colloid containing solutions are superior.
What is the ideal intraop fluid rate with heart disease?
Again, looking at each patient as an individual is important. Heart disease is not necessarily heart failure. We want to keep our surgical patients hydrated with an effective circulating volume while they are under anesthesia. To address this, a place to start is often 10 ml/kg/hr. When we give too many fluids to a cardiac patient, we increase the intravascular volume, which may lead to congestive heart failure. In this example, perhaps start a little more conservatively and navigate between intraop hypotension and volume overload, based on vital signs and careful monitoring.
Is using dextrose and saline recommended for patients with liver disease?
The concern is that with end-stage liver disease, the liver will not be able to process the lactate, which is the buffering agent in LRS. Developing a fluid plan with a patient in liver disease can be a challenge, as they may be hypoglycemic, hypoalbuminemic, hyponatremic, with a decreased colloid osmotic pressure. Starting with 2.5 percent dextrose in 1/2 strength saline may be a good maintenance rate, but with all plans, re-evaluate and change as needed.
What would you like every colleague to know about fluid therapy?
1. Severely dehydrated patients are often hypovolemic. If they look shocky, with pale gums, prolonged CRT, fast heart rate and weak pulses, then treat them with ”shock fluids.”
2. “Shock fluids” means using boluses, such as 20 ml/kg given over a few minutes, re-evaluated and repeated. Think “lather, rinse, repeat.”
3. Recognize that although “twice maintenance rate” LRS is often adequate to address many of our hospitalized sick patients, there are others, such as very large and small patients and those with kidney, heart or liver disease, which deserve further consideration. By asking ourselves, “Which type? How much? How fast?” our fluid therapy plans will be better suited for each individual patient.
4. Last but not least, fluid plans are just plans. They should be adjusted as dictated by reassessments of hydration and perfusion of the patient.
Dr. Phil Zeltzman is a mobile, board-certified surgeon near Allentown, Pa. He is the co-author of “Walk a Hound, Lose a Pound.”