POOR ORAL INTAKE / DEHYDRATION

Inadequate fluid/caloric intake leading to intravascular volume depletion — common precipitant of AKI, electrolyte disorders, delirium, and falls

SYMPTOMS / ASSOCIATED SX

  • Thirst, dry mouth, dark/concentrated urine, decreased urine output (<0.5 mL/kg/h)

  • Orthostatic lightheadedness, presyncope, syncope

  • Fatigue, lethargy, AMS (severe)

  • Exam: dry mucous membranes, tachycardia, orthostatic hypotension, decreased skin turgor (unreliable in elderly)

DENIES

  • Chest pain/dyspnea (cardiogenic — not dehydration)

  • Fever/diarrhea/vomiting (identify GI/infectious precipitant)

  • Dysphagia (mechanical cause — NPO without evaluation)

SOCIAL HISTORY

  • Ability to access and prepare fluids independently; cognitive status; caregiving situation

  • Alcohol use; recent vomiting or diarrheal illness

MAIN ETIOLOGY

  • Reduced intake: AMS, dysphagia, reduced thirst sensation (elderly), NPO/fasting, functional dependence

  • GI losses: vomiting, diarrhea, NGT drainage, high-output ostomy/fistula

  • Insensible losses: fever, burns, sweating, hyperventilation

  • Renal losses: DI (central or nephrogenic), osmotic diuresis (DKA), diuretics

  • Third-spacing: ascites, pleural effusion, bowel obstruction, burns

MOST COMMON DDX

  • AKI prerenal (BUN:Cr >20; FeNa <1%; responds to fluids)

  • Hypernatremia (Na >145 — free water deficit; coexists with dehydration in elderly)

  • DKA/HHS (hyperglycemia, ketonemia, osmotic diuresis)

  • Central/nephrogenic DI (polyuria, urine specific gravity <1.005)

  • Adrenal insufficiency (hypoNa + hyperK + hypotension)

  • Sepsis (third-spacing, reduced intake)

DATA

  • BMP (BUN:Cr >20 = prerenal); urine Na + Cr → FeNa = (urine Na × plasma Cr)/(plasma Na × urine Cr) × 100

  • Urine specific gravity; serum osmolality; orthostatic VS

  • Weight trend (1 kg ≈ 1 L fluid); strict I&Os; urine output

  • CBC (hemoconcentration); glucose; HbA1c; bladder scan if oliguria unexplained

HOME MEDS

  • Diuretics — hold until euvolemic; reassess dose

  • ACE inhibitors/ARBs — hold if AKI or hypotension

  • NSAIDs — hold (worsen AKI)

  • Metformin — hold if AKI or contrast planned; digoxin — hold (levels rise with dehydration)

PLAN

  • Fluid selection (SMART and SALT-ED trials — prefer balanced crystalloids for large-volume resuscitation):

    • Isotonic depletion: LR or PlasmaLyte preferred over NS (lower hyperchloremic acidosis risk)

    • Hypovolemia + hyponatremia: NS 0.9% initially; correct Na no faster than 6–8 mEq/L/24h

    • Hypovolemia + hypernatremia: D5W or 0.45% NaCl; correct no faster than 10–12 mEq/L/24h

    • Severe hemodynamic instability: NS FIRST to restore perfusion, then switch to hypotonic/balanced

  • IV bolus: 500 mL–1 L LR or NS; reassess after each bolus; maintenance 125–150 mL/h after correction

  • Electrolyte replacement as needed (K, Mg, Phos)

  • Oral route preferred when tolerated; speech therapy if dysphagia; ORT for mild-moderate dehydration

  • Antiemetics: ondansetron 4 mg IV q6h PRN; loperamide 4 mg then 2 mg after loose stool (non-infectious only)

  • Target urine output 0.5–1 mL/kg/h

  • DISCHARGE:

    • Ensure oral intake adequate (≥1.5–2 L/day) before discharge

    • Restart held meds only after renal function confirms safety

    • BMP in 3–5 days if electrolyte abnormalities at discharge

RED FLAGS

  • SBP <90 + tachycardia + oliguria → hypovolemic shock; 1–2 L IV bolus rapidly; ICU if no response

  • Anuria + no response to fluid bolus → obstruction or intrinsic AKI; bladder scan; nephrology

  • Dysphagia + aspiration → NPO; speech therapy urgently

  • Large-volume NS (>3 L): monitor for hyperchloremic metabolic acidosis; switch to balanced crystalloid

SENIOR IM RESIDENT PEARLS

  • SMART trial (NEJM 2018): balanced crystalloids reduced MAKE vs. NS in ICU patients

  • SALT-ED trial (NEJM 2018): similar findings in non-ICU — shift to balanced crystalloids in standard practice

  • BUN:Cr >20 = prerenal but poor sensitivity/specificity; FeNa <1% more specific but unreliable on diuretics — use FeUrea <35% instead

  • Common mistake: giving NS to all dehydrated patients regardless of Na — check Na before choosing fluid

  • ORT (WHO solution): sodium 75 mEq/L + glucose 75 mmol/L — equivalent to IV in mild-moderate dehydration