Dehydration

• Core 1 (Pre-Clerkship)
  • Microbiology and Infectious Diseases
    • GI bacteria
  • Renal
    • Water Balance and Control of Osmolality
    • Disorders of Water Balance 1: Hyponatremia and Hypotonicity
    • Disorders of Water Balance 2: Hypernatremia and Hypertonicity
    • Small Groups: Sodium Balance and Volume Status Case
    • Acute kidney injury pathophysiology
• Core 2 (Clerkships)
  • Pediatric Clerkship Didactics on the Acutely Ill Child
  • Pediatric Emergency Medicine didactics on Pediatric Trauma
• Core 3 (Post-Clerkship)Electives that may further knowledge
  • Peds SubI, PEM SubI, Pediatric Nephrology, PICU, NICU

The PCP office gets a call from a parent concerned about their 9 month old daughter. Their 4 year old son seems to have “caught a GI bug” at daycare and has been having some vomiting and now diarrhea, but otherwise is appearing okay. Their 9 month old started throwing up last night and is continuing this morning. She is tired appearing and has not had a wet diaper since yesterday afternoon. She is not interested in food or her bottle – she had a few sips this morning and then threw up again.  

What other questions do you want to ask this family? What should they do next?  

Assessing intake: 

• Feeding how often and how many ounces per feed?  

• If breastfeeding, can’t determine exact volumes, but generally: how long is the baby spending breastfeeding per side? Different from typical?  

• Formula mixing: often helps to start by asking open-ended (“how are you mixing the formula?”) 

• • What we need to know:  

• • • What is the ratio of ounces of water to scoops of formula?  

• • • • This will depend on the formula and if fortified to higher calories! Standard is 20 kcal/oz. Ask which formula is being used 

• • • • For MOST formulas, we want 2 oz water for each scoop of (dry) formula 

• • • What is being added into the bottle FIRST? Water or powder? 

• • • • Should be WATER! Should be adding powder TO water. This way we know the exact volume of fluid.  

• Assessing output: vomiting 

• • How often is patient having vomiting or diarrhea? 

• • If vomiting, any blood or green color to it? Think of surgical abdomen emergencies in the differential, if bilious. 

• • How often is this happening? Timing related to feeds? 

• Assessing output: urine and stool  

• • How many wet diapers up to the current point in the day? How many typically?  

• • For toilet trained children, appearance of urine? When was the last time they went to the bathroom/how many times today?  

• • If having diarrhea, how many times today? Appearance of stool, any blood or mucus? Sometimes harder to recognize constipation – ask about last bowel movement, typical pattern of stooling. 

• Associated symptoms: 

• • Any sick contacts? In school/daycare? 

• • Always ask about presence and duration of fever 

• • Longer duration of fever (5 days or more) should always trigger more questions (i.e. assess for major criteria of Kawasaki disease)  

• • Other possible pertinent positives/negatives: rash, abdominal pain, cough/cold symptoms, dysuria, headache or other neurologic changes (don’t want to miss evidence of increased intracranial pressure) 

• Always check the growth curve! Is the child falling off weight or height curve?  

Based on these exam findings, can estimate degree of dehydration: 

Source: https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5216a1.htm#tab1 

The table outlines how dehydration severity progresses from minimal to mild–moderate to severe, with changes in mental status, thirst, heart rate, pulses, breathing, exam features, extremities, and urine output. Mild dehydration shows subtle findings such as increased thirst, slightly sunken eyes, dry mouth, and decreased tears, while severe dehydration presents with lethargy, poor drinking, weak pulses, deep breathing, sunken eyes, delayed capillary refill, cool mottled extremities, and minimal urine output. The layout offers a quick comparison to help determine severity based on physical exam.

Hypernatremia and Hyponatremia 

• Hydration and fluid status does not exist in isolation: when your fluid status is abnormal, you run the risk of disrupting the electrolyte balance in your body too. One of the most significant electrolytes we worry about is sodium. In fact, serum sodium abnormalities are a reflection of water balance! 

• 2 important terms 

• • Osmolality = concentration of solute (particles) dissolved in a solution 

• • • Serum Osmolality in the human body = (1.8 * Na) + (Glucose /18) +  (BUN / 2.8) 

• • • Big take away = sodium has a big effect on serum osmolality! 

• • Tonicity = the affect a solution has on a cell based on movement of water 

• • • Hypertonic solution: causes water to move out of a cell --> cell shrinks 

• • • Hypotonic solution: causes water to move into a cell --> cell swells 

• Sodium can be tricky – having low salt can be from being volume UP or volume DOWN... HUH? Let’s look into this more. 

Hypernatremia 

• Generally Na > 150 mEq/L in extracellular fluid (ECF) 
• Three buckets
  • Not enough water in
  • Too much water out
  • Increases in salt "in" (rare)

Hyponatremia

• Generally Na < 130 mEq/L in extracellular fluid (ECF) 
• Three buckets
  • Too much water in 
  • Not enough water out
  • Dysregulated ADH

Two specific disease processes:

SIADH vs DI 

Let’s focus on two specific disease processes that can result in water and salt dysfunction 

First remember back to physiology: 

• Body experiences dehydration (low blood volume or high blood osmolality) -->  

• Hypothalamus senses an issue in water balance -->  

• Tells Posterior Pituitary Gland to make Anti-Diuretic Hormone (ADH) and release into blood stream -->  

• ADH acts on Kidney (at the distal convoluted tubule & collecting duct) --> 

• Add Aquaporin or water channels into cell membrane --> 

• Water reabsorbed from urine --> blood stream  

• Net result: serum contains more water, urine gets more concentrated 

Hypernatremia

Identifying Cause

• Check urine osmolality to differentiate renal and non-renal causes 
• Assess volume status
• Can also check urine sodium

Management

• Correct Sodium slowly! Calculate and gradually replace free water deficit 
• If you correct hypernatremia too fast, you can cause cerebral edema
• "High to Low your brains will blow"

Hyponatremia

Identifying Cause

• Check serum osmolality (Osm) 

• Assess volume status 

• Can check urine osmolality, urine sodium 

Management 

• If you see an acute change in sodium (> 10 mEq drop) or symptomatic hyponatremia (ex: coma or seizure): Act now! Give hypertonic saline (IV 3% NaCl) 

• If asymptomatic and chronic, first diagnose what is going on, and then correct sodium slowly! 

• If you correct hyponatremia too fast, you can cause central pontine myelinolysis 

• “Low to High your pons will die” 

Dehydration

• Oral fluids – if able to tolerate some oral intake, either with or without receiving an anti-emetic medication like ondansetron, can trial oral rehydration therapy giving small amounts of fluid every 5 minutes. 

• IV Fluids 

• Fluid boluses to address fluid deficit/losses are usually 20 mL/kg (maximum 1L). Consider 10 mL/kg if fluid sensitive, such as a patient with cardiac history. 

• Maintenance fluids are continuous fluids to meet ongoing physiologic needs, including urine losses and insensible losses like sweat.  

• The 4-2-1 rule for maintenance rate: 

• Hourly fluid rate = 4 x (first 10 kg of patient weight) + 2 x (next 10kg of patient weight) + 1 x (remainder of patient weight) 

• For example, hourly rate for a 21kg child = (4 x 10) + (2 x 10) + (1x1) = 61 mL/hr 

• The Holliday-Seger rule for maintenance rate: 

• Total daily fluid = 100 x (first 10kg of patient weight) + 50 x (next 10kg of patient weight) + 20 x (remainder of patient weight) 

• For example, for a 21kg child = (100 x 10) + (50 x 10) + (20 x 1) = 1520 cc over 24 hours = 63 mL/hr 

• We usually use the 4-2-1 rule much more often!  

• Fluid rates are automatically calculated in Epic 

• Types of IV fluids 

• You will commonly see/hear “D5 normal” (Dextrose 5% with 0.9% normal saline” 

• Half normal = 0.45% NS  

• Quarter normal = 0.225% NS (for new/tiny babies)  

• KCl can be added to fluids (“D5 normal with K”). Consider 20 mEq/L KCl if weight > 10kg, 10 mEq/L if < 10kg 

• You may also see D5LR: lactated ringers. This can be appealing if a patient has metabolic acidosis (ex. from GI losses) as LR contains some lactate, unlike normal saline. 

• Not to memorize! Just take note of which fluid types are isotonic to human plasma and which are not  

• Assessing specific intake and output in history questions is key for patients presenting with dehydration. Include specific physical exam maneuvers to assess hydration status. 

• As with most interventions in pediatrics, volumes of IV fluid replacement are weight-based, both for bolus and maintenance fluids. Pediatric patients typically receive isotonic fluids. 

• Abnormal sodium levels are usually related to water balance. When investigating etiology, it is often helpful to assess volume status and measurements of serum and urine osmolality. 

Answers

Q1. A

Q2. B

Q3. C

Q4. B

Q5. D

Q6. B

Articles: 

• AAP Clinical Practice Guideline: Maintenance Intravenous Fluids in Children 

• Peds in Review Hyponatremia/Hypernatremia 

Videos: 

• Osmosis Hydration 

• CHOP Oral Rehydration Therapy 

• Dirty Medicine Hyponatremia 

Podcasts: 

• Cribsiders Pediatrics, Episode 96, Approach to Hyponatremia (70min) 

• • Also comes with a 1-page summary!  

• Clerkship Ready - Pediatrics: Before the First Time You Order Fluids or Electrolyte Replacement (21min) 

Pathways: 

• Dehydration in gastroenteritis CHOP pathway  

• Inpatient IV fluid management CHOP pathway 

Dehydration Case