Come learn about the most prescribed medicine in pediatrics, IV fluids! Dr. Michelle Starr (Indiana) returns to teach us about maintenance fluids, adding electrolytes to fluids, and why Justin shouldn’t worry so much about his medical decision-making. Listen now to find out if you’d like to be a member of Team LR!
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IV fluids are medicines! They are one of the most prescribed medicines in a children’s hospital and must be treated as such. For rehydrating the volume-depleted patient, most guidelines recommend using isotonic crystalloid fluid (matching our fluid’s osmolarity and osmolality with the serum).
Normal Saline (NS)
Lactated Ringers (LR)
Dr. Starr stamps out a few common concerns about giving lactated ringers. For patients with elevated serum lactate, LR is very safe in those with functioning livers! Does LR cause hyperkalemia? Nope! Note only does LR contain very little potassium at 4 mEq/L, it actually causes less hyperkalemia than NS because it is less acidic (OMalley et al 2005). In an acidic environment, H+ is exchanged for K+ in an attempt to normalize pH, leading to hyperkalemia.
Due to its more physiologic pH, Dr. Starr recommends lactated ringers as fluid of choice for volume resuscitation in most volume-depleted children (expert opinion). However, this clinical decision is most important when giving high volumes of fluid. Dr. Starr has no contraindications to giving a first bolus of normal saline if that’s all you think you’ll need. Once you are moving onto subsequent boluses, that’s when you need to think of the acidity and tonicity of your fluids.
Although trials such as SALT-ED, SMART, and Australia-New Zealand’s PLUS exist in adults, we do not have definitive evidence in children at this time (multicentered PRoMPT BOLUS trial is currently underway).
For all patients expected to be admitted to the hospital for IV fluids, Dr. Starr recommends obtaining a basic metabolic panel with the initial IV placement. IV fluids are medicines, and require monitoring if they will be used for longer than 24-48 hours.
Clinical Pearl: Dr. Starr believes the most useful marker for volume depletion in young children is patient weight. If a patient is 1.5kg lighter, that patient is approximately 1.5L depleted.
“Maintenance” is the assumption of fluids a healthy child with well functioning kidneys needs to maintain euvolemia. This is a calculated volume, most commonly using the 4:2:1 rule or Holliday-Segar method. Although this calculation has become standard of care, it was created by adjusting adult maintenance fluid rates for body surface area. There were no direct pediatric clinical trials involved! This is a great starting point, but remember, this really only applies to patients with normal renal function.
Dr. Starr recommends starting maintenance fluids after a patient has returned to euvolemia. She recommends bolusing until euvolemia, and then starting maintenance at that time. Multiples of maintenance should not be used for volume resuscitation.
Without an exact replica of serum, often we need to choose between slightly hypotonic fluids and slightly hypertonic fluids. In general, that poses a risk of either hypernatremia or hyponatremia. 2018 AAP guidelines currently recommend normal saline for all patients 1mo-18yrs in order to mitigate the risk of hyponatremia. Patients are at risk of hyponatremia when they have elevated levels of antidiuretic hormone (ADH). ADH causes retention of free water, leading to hyponatremia. Elevated levels occur during physiologic stress.
Dr. Starr believes this is a conservative stance to apply universally as normal saline is not very physiologic. The guidelines were created with a primary endpoint of avoiding hyponatremia, but not necessarily kidney dysfunction, acidemia, or hospital length of stay. Dr. Starr recommends making an individualized evaluation of the risk for dysnatremia in your patient. For example, patients going to the ICU will have prolonged physiologic ADH stress states, putting them at higher risk of hyponatremia.
For most patients, Dr. Starr recommends ½ NS as the sodium component of her maintenance fluids in patients with normal renal function. However, patients will need monitoring and adjustments as necessary based on changing electrolytes. LR can also be used for maintenance fluids, but its absence in the guidelines is likely culture-based rather than evidence-based at this time.
In babies less than 28 days old, Dr. Starr points out that neonatal kidneys are worse at excreting and concentrating sodium. Therefore, these infants can tolerate a lower sodium content in their fluids. Dr. Starr continues to recommend ½ NS, but some infants in the NICU will receive ¼ NS. In addition, they have a decreased ability to secrete potassium due to immature Na-K transporters in distal nephron. In general, we are conservative when giving electrolytes to babies due to their immature kidneys.
Dr. Starr recommends checking daily BMPs in patients at risk for dysnatremia or receiving potassium supplementation to assess for efficacy of therapy and changing if necessary. This should be in addition to measuring Ins/Outs and daily weights.
The good news is the functioning kidney is smarter than even the best nephrologist! It will figure out how much is too much and excrete the rest. Most patients will be able to handle extra volume, sodium, and potassium. With functioning kidneys, you won’t be able to create clinical signs of volume overload in a child unless you get them at least 10-15% above euvolemia. However, anyone with kidney impairment will need to be monitored and their fluids adjusted like any other medicine.
Concerned about hyperkalemia? If a patient with AKI has improved vital signs and begins to urinate after volume resuscitation, chances are high that the calculated GFR has improved significantly. Remember, a Creatinine level is just a single snapshot in time – repeating it can help establish a timeline/trend.
There is little evidence to support our clinical decision at this juncture. When the underlying illness is resolving and the patient no longer needs the hospital, Dr. Starr recommends stopping fluids entirely rather than weaning slowly. Although there’s no data here, she believes this is more physiologic to help the patient drink again.
Although not common in the United States, access to IV fluids is not always available and able to be a part of standard of care.
Dr. Starr also points out there is a difference between ADH release in males and females. Females often have higher risk of elevated physiologic ADH release due to their underlying sex hormones. She recommends being mindful of dysnatremia in teenage females when choosing fluids.
In high urine output states, such as post ATN diuresis, post transplant, some urologic conditions, or patients who have received excess IV fluids, Dr. Starr recommends choosing a maintenance fluid by matching it to the urine sodium. For example, if urine sodium is 70 mEq, then give them ½ NS, which has 154/2 = 77 mEq/L in order to maintain the serum sodium.
Listeners will understand the composition of IV fluids, when to start “maintenance” treatment, and how to choose a starting crystalloid fluid to improve fluid management strategies inside the hospital.
After listening to this episode listeners will…
Dr Starr reports no relevant financial disclosures. The Cribsiders report no relevant financial disclosures.
Masur S, Starr M, Chiu C, Berk J. “76: IV Fluids – Salty and Sweet”. The Cribsiders Pediatric Podcast. https:/www.thecribsiders.com/ December 28, 2022.
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