Home Feature Too much free water?

Too much free water?

April 2008

Published in the April 2008 issue of Today’s Hospitalist

For more than 50 years, physicians have taken for granted how to manage maintenance fluids in pediatric inpatients. As long as doctors followed what’s known as the Holliday-Segar regimen, which has been canon since it was published in 1957, giving maintenance IV fluids seemed to be the easy part of patient care.

Now, however, many are questioning whether that standard practice “which typically involves the use of hypotonic fluids for IV maintenance “is benign after all. Some even contend that the Holliday-Segar regimen, which advises indexing maintenance fluid requirements to patients’ estimated calorie expenditure, may cause iatrogenic hyponatremia, brain damage or even death in some children.

The first study to raise concerns set off a firestorm of controversy that continues today. In a 2003 review of the literature, Michael L. Moritz, MD, and Juan C. Ayus, MD, concluded that using hypotonic fluids is “potentially dangerous and may not be physiologic for the hospitalized child.”

The authors added that the conditions that most commonly result in pediatric hospitalization (and the need for maintenance fluids) naturally increase secretion of antidiuretic hormone (ADH). That ADH secretion, combined with the Holliday-Segar formula for hypotonic fluids, they concluded, can lead to free-water retention and hyponatremia.

“If our method of calculating maintenance allows for the possibility of death from iatrogenic hyponatremia, that’s an issue,” says Shawn L. Ralston, MD, a pediatric hospitalist at Community Medical Center in Missoula, Mont. Along with Lisa B. Zaoutis, MD, assistant professor of pediatrics and chief of the inpatient services division at Children’s Hospital of Philadelphia, Dr. Ralston spoke at a recent pediatric hospitalist conference about maintenance IV fluids.

Although some physicians point to the Moritz-Ayus study as a reason to throw out the Holliday-Segar formula and instead use isotonic maintenance fluids, Dr. Zaoutis says that reaction may be just as wrong-headed.

“We don’t know if Holliday-Segar is bad for everybody or just for a subpopulation with certain risk factors that we can identify,” she points out. Those subpopulations, she speculates, likely include children who predictably have higher ADH levels.

Instead, Drs. Ralston and Zaoutis suspect, the answer may have more to do with cutting back on the volume of maintenance fluids administered than with increasing the salt content of the maintenance solution. Some of the problems children have with sodium imbalance may have less to do with giving them too little sodium, Dr. Zaoutis adds, than with giving them too much free water.

Drs. Ralston and Zaoutis talked to Today’s Hospitalist about the controversy and about the strategies they use for maintenance IV fluids.

Q: What is the problem with the Holliday-Segar regimen?

Dr. Ralston: The question is whether we are causing harm with our current method of calculating patients’ maintenance needs for salt and free water. When Drs. Moritz and Ayus reviewed a relatively small body of literature “much of it surgical and quite a bit related to encephalitis “they noticed a lot of morbidity related to the fact that patients became hyponatremic.

There were a few other studies looking at both surgical and medical patients that did find some risk of inducing hospital-acquired hyponatremia. The literature on certain known causes of excess ADH and iatrogenic hyponatremia collided.

Q: Should hospitalists throw Holliday-Segar out and use isotonic saline as the maintenance fluid of choice, as Moritz and Ayus proposed?

Dr. Zaoutis: Some say it would be safer to shift to isotonic maintenance fluids. But if we moved everybody routinely to this new approach, we don’t know whether there would be a risk of hypernatremia because we would be giving a lot more salt to kids than we are used to.

Anecdotally, there are ICUs that now routinely run normal saline for their maintenance fluid. But we are starting to see kids with hypernatremia after days of continuous isotonic IV fluids. This hypernatremia is probably better tolerated than hyponatremia, but it is still an iatrogenic imbalance.

Also, we need to keep in mind that this hypernatremic state is very different from what most doctors are familiar with: the hypernatremia we see in kids who come in dehydrated because they have lost so much free water that their sodium level climbs. That is very different from iatrogenic hypernatremia caused by overhydration with solutions that have a high salt content. We don’t know nearly as much about that condition.

Q: You say another alternative may be to focus on the quantity, not the type, of fluid used. Why?

Dr. Zaoutis: It’s understandable to think that the problem with hyponatremia with Holliday-Segar is that we are giving fluid that has too much free water. One thought is to increase the salt content of the IV fluid to address that.

But if we instead treat with smaller quantities of fluids, we may solve the problem. If high levels of ADH are reducing the body’s ability to eliminate free water, then reducing the quantity of IV fluids administered may be more appropriate.

There are parallels to other types of conditions, such as the syndrome of inappropriate ADH secretion. When these kids become hyponatremic due to high levels of ADH, we typically fluid-restrict them. We don’t pour more salt into the patient to even it out “unless it’s a dire situation, such as hyponatremic seizures.

Dr. Ralston: We don’t have an answer yet, so my take-home message is this: Don’t treat IV fluids as if they are a completely benign intervention. We have to be a lot more careful than just putting everybody on IV fluids and deciding whether to use normal saline or Holliday-Segar.

You have to identify high-risk groups where normal saline may be appropriate. You also have to identify opportunities to decrease or stop fluids earlier than we do. Physicians should ask themselves: Do children need to be left on maintenance IV fluids for their entire hospitalization? We need to stop treating with maintenance IV fluids as a knee-jerk, no-thought-required action.

Q: What do you do personally in your practice?

Dr. Ralston: As a community hospitalist, I lean more toward rehydrating a patient in the emergency setting and then not using a maintenance regimen, or I consider a maintenance regimen in smaller increments. I still use Holliday-Segar, but I use it for eight hours rather than a full day, and I then reconsider.

Dr. Zaoutis: Sometimes we feel kids are safer if they are left on maintenance IV fluids when their oral intake is limited. But there can be downsides to that approach.

Hospital stays may be prolonged if there are missed opportunities for patients to demonstrate that they can meet their fluid needs by oral intake. For kids who are adequately rehydrated, allowing them trials off IV fluids earlier, more frequently or for longer periods of time may have earlier success with oral intake. And clinicians can consider re-bolusing with isotonic IV fluids if needed, instead of automatically hooking kids back up to continuous maintenance fluids.

The other thing to consider is the nasogastric [NG] tube. Interestingly, families often would rather have an IV in their child than an NG tube. But if there is nothing wrong with a patient’s gut, an NG tube may be a more benign intervention in some circumstances.

Q: How do you make a decision to stop maintenance fluid? Do you test patients’ sodium status and electrolyte levels more often?

Dr. Ralston: I hate that approach. I think that if a child is sick enough, yes, you need to test. But I would hate the examination of current practice to lead to more testing and more intervention, when our response really ought to be: Do we really need to be doing anything?

Dr. Zaoutis: Some people are trying to identify subpopulations at higher risk for hyponatremia so we can say, “I can use Holliday-Segar for 80% of my patients,” or 60%, or whatever it turns out to be. But for children at increased risk, I won’t use this approach.

We think these high-risk kids will be those who have elevated levels of ADH, identified either by diagnosis “such as encephalitis “or by initial decreased sodium levels. But we don’t know if we are going to miss kids at increased risk for hyponatremia that way.

Q: What are some non-osmotic triggers for increased ADH secretion that hospitalists should consider?

Dr. Zaoutis: The literature shows that there are higher levels of ADH in some patients without fluid or electrolyte imbalances. Perhaps this can help us predict which kids will have a harder time handling routine maintenance IV fluids. Kids who are post-op often have several risk factors, including hypoglycemia, pain, nausea or vomiting, all of which can trigger ADH release.

In addition, kids who have something going on with their brains “neurosurgical patients or kids with CNS infections “often have increased ADH release. And anything that will stimulate the pulmonary system, such as infection, tumor or trauma, can cause increased ADH release. If we took those higher risk kids and treated them with IV fluid solutions or rates that are different than Holliday-Segar, would they do better while the rest of the kids would be safe? There are not enough data yet to say.

Q: Is this debate also about IV fluid resuscitation?

Dr. Zaoutis: No. Initial resuscitation is about restoring circulating volume, and the fluid of choice is an isotonic solution such as normal saline or Lactated Ringer’s solution. During initial fluid resuscitation, we may start to move toward normalizing sodium imbalances, but most of the correction of osmotic abnormalities is done more slowly over the maintenance phase.

Q: What future research is needed?

Dr. Ralston: We’ve never investigated the impact of careful control of free water. Because sodium and free water are linked in the human system in ways that are so complex, we haven’t asked whether it’s the type of fluids or the amount that is causing the problem.

There will be much research on this in the next 10 years, but we don’t know if we are even asking the right questions. Should we be randomizing children to normal saline or Holliday-Segar? Should we be stopping IV fluids earlier? What if we decide to treat IV fluids as a more dangerous intervention and require orders every eight hours to continue them?

An intervention like that might be just as effective as changing to normal saline, and it might not cause any danger at all, as opposed to the hypothetical danger of hypernatremia.

Deborah Gesensway is a freelance writer reporting on U.S. health care from Toronto, Canada.