Pediatric Fluids & Electrolytes: Maintenance Fluids

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Holliday–Segar Maintenance Requirements

The Holliday–Segar method links fluid needs to metabolic rate, which tracks with weight.

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Daily Requirements 

• Fluids:

  • 100 mL per 100 kcal expended

• Electrolytes (per 100 mL of maintenance fluid):

  • Sodium: ~3 mEq

  • Potassium: ~2 mEq​

 

This translates to daily electrolyte needs of approximately (+ balance needed fro growth and losses in urine, sweat stool yields):

• Sodium: 2–3 mEq/kg/day 

• Potassium: 1–2 mEq/kg/day

  • adults do not require as much as they are no longer growing (taller)​

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• This is significant when considering the fluids we give. For example, if we give a 10kg patient 0.9% NS running at maintenance (~40ml/hr=1L a day), they will receive 154mEq of sodium (see fluid composition below).  However, his daily requirement is only ~33mEq/day! (see AAP recommendations below).​

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• An aside, the way I think of electrolytes and the kidneys is, your urine is abnormal so that your serum could be normal. I.e. if one person eats 500gm of sodium per day vs another who eats 3000gm of sodium the urine composition will be different (3000gm intake guy will dump sodium vs 500gm guy who will reabsorb all of it), yet the serum sodium will be essentially the same.​​

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From Holliday–Segar to the 4–2–1 Rule

To make this usable at the bedside, the daily fluid calculations were converted into hourly rates → the 4–2–1 rule.​

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What Are We Replacing With “Maintenance Fluids”?

Maintenance fluids replace ongoing physiologic losses, not deficits. I liken it to maintenance calories: what comes in, must go out for us not to lose or gain weight. Same with fluids:

• Fluid retention->fluid overload

• Fluid deficit->volume depletion

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Approximate Breakdown of Daily Losses

Source Percent of Total

Urine~55-60%

Insensible losses (skin + lungs)~30%

Stool~5-10%

This is why maintenance fluids:

• Contain water

• Include sodium and potassium

• Are not meant to correct dehydration or shock

 

Why is this important?

      When We Do Not Give Full Maintenance?

             Example: Anuric or Nephrotic Patient

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In patients with:

• Anuria / severe oliguria

• Nephrotic syndrome with edema- (slightly different conceptually as we want to limit the worsening of edema by limiting to ~ insensible losses while also diuresing from the fluid overload)

• ESRD

 

In anuria/oliguria/some ESRD patients, urinary losses are minimal or absent. Depending on the circumstance, we may therefore provide enough fluid to cover their insensible losses + urine output replacement ml:ml or some variation of that while we begin to manage fluid removal whether with lasix (e.g. in the fluid overload patient with nephrotic syndrome) or dialysis, etc. Once another method of fluid removal is found (Dialysis improving renal function/injury, resolution of AKI with improving urination, remission of nephrotic syndrome etc.) we can liberalize the fluid restrictions.

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• Insensible losses ≈ 400-600ml/m2/day. I often use 500 mL/m²/day for ease of calculation.

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Isonatremic hypovolemia (See Hypernatremia and Hyponatremia pages for said topics)

 

• Now that we've discussed maintenance and baseline fluids, lets discuss isonatremic dehydration, which is relatively straightforward. 

• While ideally you would have a previous weight to determine % dehydration, in reality that often doesn't happen, and actual reality, the weights don't often correlate anyway (different scales, the way ED weights are taken, etc.) In which case, you have to guess-timate.

• 1ml:1gm, therefore a child who weighed 10kg and now weighs 9kg is 10% dehydrated, and is down 1000ml, which you now have to replace. 

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Fluid Replacement Strategy for Isonatremic Dehydration

After initial stabilization, fluid therapy includes maintenance fluids, replacement of the estimated deficit, and replacement of ongoing losses.

Remember: You must ensure patient is making urine before adding K+ (typically ordered as 20mEq/L) to IVF

 

Estimated Fluid Deficit

 

This is the classic teaching:

 

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Replacement of Ongoing Losses

Consider replacing ongoing losses mL‑for‑mL

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Putting it all together

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Patient: 5 year old Male with 2 day history of vomiting. Looks tired, dry, per mom making urine but less than usual. He is tachycardic but BP is wnl for age. 

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• Amazingly you have the perfect baseline weight: 20 kg

• Current weight 18.4kg, = Dehydration: 8% (moderate, which fits with the presentation)

• Serum sodium: 138 mEq/L (isonatremic)

 

Step 1 — Calculate Fluid Deficit

Deficit=%dehydration×weight 

8% × 20 kg=1600gm= 1600 mL deficit

 

Step 2 — Replace Deficit

Time Period                        Fluid

First 8 hours                          800 mL

Next 16 hours                       800 mL

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Step 3 — Calculate Maintenance (4-2-1 rule)

Weight                                Rate

First 10 kg                    4 mL/kg/hr = 40

Next 10 kg                   2 mL/kg/hr = 20

 Maintenance = 60 mL/hr

 

Step 4 — Hourly Rates

    First 8 Hours

     Deficit replacement:

     800 ÷ 8 = 100 mL/hr

     Component         Rate

      Maintenance        60 mL/hr

      Deficit                    100 mL/hr

      Total =                 160 mL/hr as tolerated

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Next 16 Hours

     Deficit replacement:

      800 ÷ 16 = 50 mL/hr

     Component          Rate

     Maintenance          60 mL/hr

     Deficit                        50 mL/hr

     Total =                 110 mL/hr

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Maintenance Fluid Choice: 

American Academy of Pediatrics Recommendations

For children >28 days old, the AAP recommends:

Isotonic fluids (e.g., NS or Plasmalyte) for maintenance despite containing much more sodium than the child likely requires to avoid hyponatremia- see below. 

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Of note, while adult studies demonstrate preference for balance solutions in resuscitation and perioperative critically ill patients, (LR or plasmalyte that have electrolytes and osmolality closer to physiology)  pediatric data is mixed.

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Why?

• Hospitalized children often have elevated ADH

  • Pain

  • Nausea

  • Stress

  • Pulmonary disease

• Hypotonic fluids increase risk of:

  • Hospital-acquired hyponatremia, which may have adverse effects (see "Hyponatremia".

 

When Might ½ NS Still Be Used?

• Selected nephrology patients

• Carefully monitored settings

• Explicit sodium targets

• Stable patients without ADH excess

 

Even then, close sodium monitoring is essential.

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Common IV Fluids: Electrolyte Composition