Pituitary Disorders: SIADH & Diabetes Insipidus — NCLEX Nursing Lesson Anatomy & Physiology · RN Track · Medical-Surgical Body Systems · Endocrine · Pituitary Disorders: SIADH & DI Condition Lesson · NCLEX-PN / NCLEX-RN

Opposite ends of the same hormone — ADH. One holds water and drowns the brain in dilution, the other wastes water and dries the brain out. Know which is which and your patient stays safe.

In this lesson

Lesson Objectives
Why This Matters
Disease Overview
Pathophysiology
Risk Factors
Signs & Symptoms
Nursing Assessment
Diagnostic Tests
Laboratory Tests
Medications
Nursing Interventions
Potential Complications
Patient Education
Clinical Judgment
Clinical Connections
NCLEX High-Yield
Memory Aids
Case Study
Practice Questions
Key Takeaways
References

Lesson Objectives

Differentiate SIADH vs diabetes insipidus by cause, clinical presentation, and laboratory pattern — and explain WHY each finding occurs.
Explain normal ADH physiology and how too much or too little ADH causes fluid, sodium, and osmolality disturbances.
Identify early, late, and emergency signs of hyponatremia from SIADH and hypernatremia/dehydration from DI.
Prioritize nursing assessment: vitals, I&O, daily weights, urine specific gravity, sodium trends, and neuro checks.
Apply safe medication administration: fluid restriction and hypertonic saline for SIADH, desmopressin and fluid replacement for DI — including WHY each works.
Prevent and manage complications: cerebral edema/seizures from SIADH and hypovolemic shock from DI.

Why This Disease Matters

Prevalence: SIADH is one of the most common causes of hyponatremia, affecting up to 35% of hospitalized patients, especially with small-cell lung cancer, CNS disorders, and post-operative stress. Diabetes insipidus is less common but frequently seen after head trauma, transsphenoidal pituitary surgery, brain tumors, and in critical care.

Patient safety: Both directly threaten the brain. SIADH → water retention → dilutional hyponatremia → brain swelling → seizures, coma, death. Correcting too fast causes osmotic demyelination (central pontine myelinolysis). DI → massive water loss → hypernatremia and dehydration → brain cell shrinkage → seizures, coma, hypovolemic shock. Hourly I&O, weights, and sodium monitoring by the nurse are the safety net.

NCLEX importance: SIADH vs DI is a classic NCLEX comparison: opposite urine output, opposite specific gravity, opposite sodium, opposite fluid status, opposite treatment (fluid restriction vs fluid replacement). Tested heavily on daily weights same scale/time/clothing, I&O hourly, sodium trends, and seizure precautions.

Why nurses encounter it constantly: Head injury, neurosurgery, stroke, meningitis, small-cell lung cancer, pneumonia, post-op pain, nausea, and many medications (SSRIs, carbamazepine, cyclophosphamide, vincristine, opioids, thiazides, lithium) alter ADH.

Connecting to prior lessons From A&P: ADH is made in hypothalamus, stored in posterior pituitary, released when serum osmolality rises or volume drops. ADH inserts aquaporin channels in collecting ducts → water reabsorbed → concentrated urine. From assessment: vitals, I&O, daily weights, mucous membranes, skin turgor, mental status, urine specific gravity and osmolality, serum Na/osmolality tell the ADH story.

Disease Overview

Disorder	What it is	ADH level	Core problem
SIADH	Too much ADH despite low osmolality — kidneys hold water inappropriately	High / inappropriate	Water retention → dilutional hyponatremia, concentrated urine, euvolemic fluid overload
Diabetes Insipidus (DI)	Too little ADH or kidneys resistant — kidneys waste water	Low or ineffective	Water loss → hypernatremia, dilute polyuria, dehydration

Analogy — the dam operator

ADH is the operator who closes the dam gates to keep water in the reservoir (your body). SIADH = operator panics and closes all gates when reservoir is already full — water builds up, floods fields (dilutional low sodium), little water downstream (oliguria, concentrated urine). DI = operator falls asleep, gates wide open — reservoir drains, water rushes downstream (polyuria, dilute urine), fields dry out (dehydration, high sodium).

Pathophysiology

Normal: High serum osmolality >295 or low BP/volume → ADH released → V2 receptors in collecting duct → aquaporin-2 channels → water reabsorbed → urine concentrated (SG high), serum osm falls. Low osmolality → ADH suppressed → dilute urine. ↓ SIADH: Non-osmotic ADH release (ectopic tumor, CNS disease, drugs, stress/pain/nausea) → continuous water reabsorption despite low osmolality → dilutional hyponatremia Na <135, low serum osm <275, concentrated urine osm >100 often >300, SG >1.030, low UOP, weight gain, brain cells swell. WHY Na low: same Na diluted in more water. ↓ DI — Central: decreased ADH production (trauma, neurosurgery, tumor, meningitis). Nephrogenic: kidneys resistant (lithium, hypercalcemia, hypokalemia). Result: no water reabsorption → massive dilute polyuria 3-20 L/day, SG <1.005, urine osm <200, serum osm >295-300, hypernatremia >145, dehydration. WHY thirst: high osmolality triggers thirst center. ↓ Symptoms: SIADH: water into brain cells → headache, confusion, seizures. DI: water out of brain cells → thirst, dry mucosa, tachycardia, hypotension, seizures if severe. ↓ Progression: Untreated SIADH Na <120 → seizures, respiratory arrest. Too-fast correction → osmotic demyelination → quadriparesis, locked-in. Untreated DI → hypovolemic shock → AKI → death.

Risk Factors

Non-modifiable	Modifiable / Preventable	High-risk populations
History of brain tumor, pituitary surgery, head trauma, small-cell lung cancer, genetic nephrogenic DI, elderly sensitive to ADH	Medications that increase ADH or cause DI, dehydration, excess hypotonic fluids, stress/pain/nausea stimulating ADH, inadequate monitoring post-neurosurgery	Post-transsphenoidal surgery, head trauma/TBI, CNS infection/stroke, small-cell lung cancer, post-op patients, ICU patients, SSRIs/carbamazepine/cyclophosphamide/vincristine/opioids/thiazides, lithium (nephrogenic DI)

Signs and Symptoms

Category	SIADH — WHY	DI — WHY
Early	Anorexia, nausea, headache, malaise, oliguria <0.5 mL/kg/hr, dark concentrated urine SG >1.030, weight gain without edema — water retained. WHY: too much ADH.	Extreme thirst, polyuria 3-20 L/day, nocturia, dilute pale urine SG <1.005, dry mouth — water wasted. WHY: too little ADH.
Expected	Confusion, lethargy, muscle cramps/weakness, decreased DTRs — hyponatremia impairs brain/muscle. Crackles/JVD if overload.	Dry mucosa, poor turgor, tachycardia, hypotension, orthostasis, weight loss, fatigue, dizziness — dehydration/hypovolemia.
Emergency	Seizures, coma, respiratory depression, Cheyne-Stokes if Na <120 — severe cerebral edema from water into brain.	Severe hypernatremia >150-160, fever, seizures, coma, hypovolemic shock, AKI — brain shrinkage + hypoperfusion.

Red flags SIADH: Na <120, confusion, seizures, weight gain >2kg/24h. DI: UOP >250 mL/hr x2, SG <1.005, Na >150, HR >120, BP <90/60, altered LOC.

Nursing Assessment

Subjective: head trauma, pituitary surgery, brain tumor, stroke, meningitis, lung cancer, post-op state, meds (SSRIs, carbamazepine, cyclophosphamide, vincristine, opioids, thiazides, lithium), fluid intake, thirst, polyuria/oliguria, nocturia, headache, nausea, cramps, weakness, confusion, weight change.

Objective: vitals + orthostatics, LOC, mucous membranes, turgor, edema, lung sounds, daily weights, strict I&O hourly, urine color/SG, labs Na/osmolality.

Focus	SIADH	DI
Vitals/Weight	HR normal, BP normal/high, weight gain	Tachy, hypotension, orthostasis, weight loss, fever
I&O / Urine	Oliguria, dark urine SG >1.030, urine osm high >300	Polyuria >250 mL/hr, pale SG <1.005, urine osm low <200
Neuro	Headache, confusion, lethargy, seizures if Na <120	Thirst, irritability, confusion, seizures if Na >150
Skin	Moist mucosa, euvolemic	Dry mucosa, poor turgor, tenting, sunken eyes

Diagnostic Tests

Test	Purpose / Findings / Nursing
Serum + urine osmolality, SG, I&O, urine Na simultaneous	Distinguish SIADH vs DI. SIADH: low serum osm <275, high urine osm >300, SG >1.030, urine Na >40, low UOP. DI: high serum osm >295, low urine osm <200, SG <1.005, high UOP. Need same-time samples, strict I&O, daily weight same scale/time/clothing.
Fluid deprivation + desmopressin challenge (monitored)	Central DI: dilute urine persists after restriction, then urine osm rises >50% after DDAVP. Nephrogenic: no response. Risky — monitor vitals/Na/weight, stop if unstable.
Head CT/MRI, Chest X-ray	Finds CNS cause (tumor, bleed, post-op) or lung cause (small-cell lung cancer, pneumonia).

Laboratory Tests

Lab	Purpose / Normal / Abnormal / Priority
Serum Na 135-145	SIADH low <135 often <120 severe. DI high >145 often >150-160. Correct slowly: SIADH ≤8-12 mEq/L/24h to avoid demyelination. DI ≤0.5 mEq/L/hr.
Serum osmolality 275-295	SIADH low <275. DI high >295-300.
Urine osmolality 300-900	SIADH high >300 despite low serum osm (inappropriate). DI low <200 despite high serum osm (cannot concentrate).
Urine Na 20-40, SG 1.005-1.030	SIADH urine Na >40, SG >1.030. DI urine Na low, SG <1.005. Quick bedside SG clue.
BUN/Cr, K+, Glucose	BUN/Cr low dilutional in SIADH, high in DI dehydration. Glucose to rule out osmotic diuresis.

Medications

SIADH

Class	Mechanism / Safety
Fluid restriction 800-1000 mL/day first-line	Limits free water → prevents further dilution. Count ice, IV, foods liquid at room temp. Monitor I&O, weight, Na q4-6h. WHY fixes dilution at source.
3% NaCl hypertonic saline	Raises Na by adding Na + pulling water from cells. For severe symptomatic hyponatremia Na <120 with seizures/coma. Risk: overload, HTN, pulmonary edema, rapid correction → demyelination. Give via central line per facility, pump, cardiac monitor, Na q2-4h, stop if rise too fast.
Tolvaptan (Samsca), Conivaptan (Vaprisol) — V2 antagonists	Blocks V2 → water excreted (aquaretic). For euvolemic SIADH when restriction fails, inpatient only. Risk rapid Na rise, liver injury, thirst/polyuria. Black box: osmotic demyelination, liver injury, initiate in hospital, monitor Na q4-6h, LFTs.

Diabetes Insipidus

Class	Mechanism / Safety
Desmopressin acetate DDAVP — synthetic ADH first-line central DI	V2 agonist → water reabsorption, concentrates urine. Forms PO, nasal, IV. Side: hyponatremia/water intoxication if too much water, headache, HTN, overload. Monitor I&O hourly, SG, weight, Na, thirst, headache/confusion. Teach nasal technique.
Vasopressin (Pitressin) IV	Short-acting ADH ICU for DI. Pump, cardiac monitor, monitor HTN, brady, chest pain, oliguria, hyponatremia.
Thiazides + low-salt diet, NSAIDs, Amiloride — nephrogenic DI paradoxical	Thiazides cause mild volume depletion → proximal reabsorption ↑ → less water lost. Low-salt enhances effect. Monitor K+, Na. Stop lithium if possible.
Isotonic fluids 0.9% NaCl then hypotonic free water 0.45% or D5W cautiously	Restore perfusion first then replace free water deficit slowly. I&O hourly, orthostatics, daily weight, Na q2-4h, do NOT correct Na faster than 0.5 mEq/L/hr.

Nursing Interventions — Prioritized

Priority	SIADH	DI
Circulation / Fluids	Fluid restriction 800-1000 mL/day, strict I&O hourly, daily weight same scale/time, no isotonic overhydration. If 3% saline: central line, pump, monitor Na q2-4h, lung sounds, stop if rise >8-12/24h.	Fluid replacement priority: isotonic first to restore perfusion then free water per order slowly. Replace UOP mL for mL if ordered, I&O hourly, orthostatics, daily weight.
Labs / Safety	Na q4-6h (q2-4h if 3% saline), serum/urine osmolality, SG, BUN/Cr. Seizure precautions if Na <120, neuro checks q1-4h.	Na q4-6h, serum/urine osm, BUN/Cr for AKI, SG. Fall precautions from hypotension, seizure precautions if Na >150.
Comfort / Meds	Mouth care for thirst despite restriction, ice chips counted, small sips. Give tolvaptan per order inpatient only, monitor thirst/polyuria.	Mouth care for dry mucosa, keep water available if allowed, keep urinal close, skin care perineal irritation. Give DDAVP per schedule, monitor for water intoxication.

Potential Complications

Complication	Early signs	Response
Severe hyponatremia → seizures/coma (SIADH)	Na <120, headache, confusion, cramps, decreased DTRs	Seizure precautions, neuro checks q1h, notify STAT, prepare 3% saline per order, Na q2h, stop free water, fluid restriction.
Osmotic demyelination from rapid correction	Dysarthria, dysphagia, quadriparesis 2-6 days post-rapid rise	Stop hypertonic/tolvaptan, monitor Na rise ≤8-12/24h, supportive care — prevention key.
Hypovolemic shock / AKI (DI)	Tachy, hypotension, poor turgor, rising BUN/Cr, Na >150	Large-bore IV isotonic per order, I&O hourly, daily weight, BUN/Cr q4-6h, monitor overload but perfusion priority.
Hypernatremia → brain shrinkage seizures (DI)	Na >150, thirst, confusion, fever, seizures	Correct slowly ≤0.5/hr, free water per order, neuro checks, seizure precautions.
Water intoxication DDAVP overdose	Headache, confusion, weight gain, oliguria, low Na, SG rises after being dilute	Hold DDAVP, fluid restriction, monitor Na, weight, neuro, notify provider.

Patient Education

Process: SIADH = too much water held → low sodium → brain swelling. DI = too much water lost → high sodium → dehydration. Opposite treatments.
Lifestyle: SIADH: fluid restriction 800-1000 mL/day — measure all, ice chips count, spread through day. DI: carry water, don't ignore thirst, medical alert.
Meds: SIADH tolvaptan only inpatient, report polyuria/thirst. DI DDAVP same time daily, nasal technique, report headache/confusion/weight gain/oliguria (intoxication) or return polyuria/thirst (dose low).
Home: Daily weight same scale/time, I&O log, urine color/SG, oral care, skin care.
Emergency: SIADH: headache, confusion, seizures, weight gain >2lb/day, dyspnea. DI: UOP >250 mL/hr x2, extreme thirst, dizziness, tachy, hypotension, confusion.

Clinical Judgment (NCSBN CJMM)

Recognize cues: 62yo small-cell lung cancer, 3 days nausea, headache, confusion, weight gain 2kg, intake 800 mL output 400 mL, urine dark SG 1.032, Na 118, serum osm 260 low, urine osm 500 high, urine Na 45, euvolemic.
Analyze cues: Lung cancer ectopic ADH → SIADH. Low Na dilutional, low serum osm, high urine osm inappropriate, oliguria, weight gain water retention. Nausea/headache/confusion early cerebral edema. Risk seizures/coma if lower, demyelination if corrected too fast.
Prioritize hypotheses: #1 SIADH with severe hyponatremia cerebral edema risk. #2 Seizure risk. #3 Demyelination risk with treatment.
Generate solutions: Fluid restriction 800-1000 mL/day, seizure precautions, neuro checks q1-2h, Na q2-4h, strict I&O hourly, daily weight, hold hypotonic fluids, prepare 3% saline if Na <120 with symptoms per provider, monitor overload, treat underlying cancer, review meds.
Take action: Notify provider STAT, implement restriction signage, seizure precautions, cardiac monitor, vitals q4h, neuro q1-2h, I&O hourly, daily weight, Na q2-4h, lung sounds.
Evaluate: Na rises slowly 4-6/24h toward 135, serum osm toward 275-295, urine osm decreasing, SG to 1.015-1.025, UOP 0.5-1 mL/kg/hr, weight decreasing slightly, headache/confusion improving, no seizures.

Clinical Connections — commonly confused

Feature	SIADH	DI Central	Nephrogenic DI	Cerebral Salt Wasting (CSW)
Cause	Too much ADH	Too little ADH	Kidneys resistant (lithium)	Brain injury → salt wasting
Volume	Euvolemic/slightly hypervolemic	Hypovolemic dehydrated	Hypovolemic	Hypovolemic — key vs SIADH
Serum Na/Osm	Low Na, low osm	High Na, high osm	High Na, high osm	Low Na, low osm but hypovolemic
Urine	Low UOP, SG >1.030 high, urine osm high	High UOP >250/hr, SG <1.005 low, urine osm low	Same central	High UOP, high urine Na
Weight/BP/HR	Gain, BP normal/high	Loss, hypo, tachy	Same central	Loss, hypo, tachy
Treatment	Fluid restriction, 3% saline if severe, tolvaptan	DDAVP + fluids	Stop lithium, thiazides + low salt	Fluid + salt replacement — NOT restriction

NCLEX High-Yield Review

What the NCLEX Wants You to Know

SIADH = SOAKED Low Na, low serum osm, high urine osm, SG >1.030, oliguria, weight gain.
DI = DRY High Na, high serum osm, low urine osm, SG <1.005, polyuria, weight loss.
Daily weights same scale/time/clothing Best fluid indicator + I&O hourly.
Correct Na slowly SIADH ≤8-12/24h → demyelination. DI ≤0.5/hr → cerebral edema.
Seizure precautions both Na <120 and >150 cause seizures.

Memory Aids

SIADH = SOAKED: Low Na, Low serum Osm, High urine Osm, High SG, Oliguria, Weight Gain, Euvolemic, Dilutional.
DI = DRY: High Na, High serum Osm, Low urine Osm, Low SG, Lots urine, Weight Loss, Thirsty.
SIADH treatment = RESTRICT fluids; DI treatment = REPLACE fluids + DDAVP.
Tolvaptan makes you Toli-pee water but can fry pons if too fast.
DDAVP overdose = headache + confusion + weight gain + oliguria + low Na + SG up after dilute.

Case Study

Patient: Mr. Lee, 45, s/p transsphenoidal pituitary adenoma resection 24h ago, extreme thirst, urinating large amounts hourly, HR 108, BP 96/64, dry mucosa, poor turgor, weight loss 1.5kg overnight, I&O 8h: in 1200 out 3200 dilute pale SG 1.002, Na 152, serum osm 310 high, urine osm 150 low.

Recognize & Analyze

Post-pituitary surgery → central DI 24-48h. Polyuria >250/hr, SG 1.002 dilute, urine osm 150 low despite serum osm 310 high, Na 152 high, dry mucosa, tachy, hypotension, weight loss = water loss. No ADH.

Prioritize & Plan

#1 Hypovolemia hypernatremia. #2 Shock/seizure risk. Plan: I&O hourly, daily weight, orthostatics, Na q2-4h, serum/urine osm, BUN/Cr, isotonic fluids then free water per order slowly, DDAVP per order, monitor for water intoxication.

Take Action & Evaluate

Notify neurosurgery/endocrine STAT, hourly I&O, daily weight, cardiac monitor, NS bolus 500 mL then 0.45% per order, DDAVP 1mcg IV per order, UOP 400→80 mL/hr, SG 1.002→1.015, urine osm 150→400, Na 152→145 over 24h slowly, HR 88 BP 110/70, mucosa moist. UOP 0.5-1 mL/kg/hr, SG 1.010-1.020, Na 135-145, no seizures/overload. Teach DDAVP technique, daily weight, I&O, signs intoxication vs recurrence, medical alert, follow-up.

NCLEX Practice Questions

Answers are shuffled — no sequential pattern. Each correct answer is marked with its number.

1. A client with small-cell lung cancer has Na 118 mEq/L, serum osmolality 260, urine osmolality 520, SG 1.032, and low urine output. Which finding best supports SIADH?

High serum osmolality with low urine osmolality and polyuria
Low urine Na and dilute urine with weight loss
Low serum Na with low serum osmolality and high urine osmolality with oliguria
High serum Na with high serum osmolality and low urine osmolality

Rationale

Answer: 3. SIADH = too much ADH → water retained → dilutional hyponatremia Na 118, low serum osmolality 260, concentrated urine high osmolality 520 and SG 1.032 despite low serum osmolality, oliguria, weight gain. Option 1 and 4 are DI pattern (high serum osm, low urine osm, polyuria, high Na). Option 2 is hypovolemia or DI, not SIADH.

2. A client 24 hours post-transsphenoidal pituitary surgery has urine output 350 mL/hr x3 hours, SG 1.002, extreme thirst, HR 110, BP 94/62, Na 151. What is the priority nursing action?

Notify provider STAT, continue strict I&O hourly, daily weight, and prepare for desmopressin and fluid replacement per order
Encourage 2L free water bolus orally quickly
Restrict fluids to 800 mL/day and give 3% saline
Give furosemide to increase urine output

Rationale

Answer: 1. This is central DI post-pituitary surgery: polyuria >250 mL/hr, dilute SG <1.005, hypernatremia 151, tachycardia, hypotension, dehydration. Priority notify provider STAT, strict I&O hourly, daily weight, orthostatics, Na q2-4h, prepare for desmopressin which replaces ADH plus isotonic fluids then free water per order correcting Na slowly. Restriction and 3% saline (3) are for SIADH and would worsen DI. Rapid 2L free water (2) risks too-fast correction → cerebral edema. Furosemide (4) worsens dehydration.

3. A client with SIADH has Na 116 mEq/L and confusion. Provider orders 3% NaCl infusion. Which nursing action is essential?

Encourage 2L water during infusion to maintain hydration
Give hypotonic fluids concurrently to prevent overload
Give the infusion rapidly to correct Na to 135 within 6 hours
Give via infusion pump with cardiac monitoring, monitor Na q2-4h, and ensure rise no faster than 8-12 mEq/L per 24h

Rationale

Answer: 4. 3% hypertonic saline for severe symptomatic hyponatremia must be given slowly with pump, cardiac monitor, Na q2-4h, I&O hourly, lung sounds, daily weight, limit rise to 8-12 mEq/L/24h to prevent osmotic demyelination (central pontine myelinolysis). Rapid correction (3) causes demyelination. Hypotonic fluids (2) and excess water (1) worsen hyponatremia.

4. A client with DI is receiving desmopressin acetate (DDAVP). Which finding indicates water intoxication from overdose?

Weight loss, tachycardia, SG <1.005
Polyuria, SG 1.001, thirst, Na 152
Headache, confusion, weight gain, oliguria, Na 122, SG 1.030
Dry mucosa, poor turgor, hypotension, Na 150

Rationale

Answer: 3. DDAVP overdose → too much water reabsorbed → water intoxication → dilutional hyponatremia Na 122, weight gain, oliguria, concentrated urine SG 1.030, headache, confusion, possible seizures. Option 2 is untreated DI (polyuria dilute high Na). Options 1 and 4 are DI dehydration patterns.

5. Which intervention is appropriate for mild SIADH with Na 128 mEq/L and mild headache?

Give desmopressin acetate nasal spray
Give 0.45% NaCl 1L bolus rapidly
Restrict fluids to 800-1000 mL/day per order, strict I&O, daily weight, seizure precautions
Encourage 3L fluid intake per day

Rationale

Answer: 3. Mild-moderate SIADH first-line is fluid restriction 800-1000 mL/day per order, strict I&O hourly, daily weight same scale/time/clothing, neuro checks, seizure precautions, Na q4-6h, SG/osmolality trends. Encouraging fluids (4) and hypotonic bolus (2) worsen hyponatremia. Desmopressin (1) is for DI, not SIADH, and would worsen retention.

6. SATA. Which findings are expected in SIADH? Select all that apply.

Low serum Na and low serum osmolality
High serum Na and high serum osmolality with polyuria
High urine osmolality and SG >1.030 with oliguria
Confusion, headache, muscle cramps from hyponatremia
Weight gain and euvolemic fluid status with possible crackles if overload

Rationale

Answers: 1, 3, 4, 5. SIADH water retained → dilutional low Na, low serum osmolality, concentrated urine high osmolality/SG >1.030, oliguria, weight gain, euvolemic, neuro symptoms headache/confusion/cramps/seizures if severe. Option 2 is DI pattern high Na high serum osm polyuria low SG.

7. SATA. Which findings are expected in central diabetes insipidus? Select all that apply.

Extreme thirst and nocturia
Low serum Na and high urine osmolality with oliguria
Polyuria >250 mL/hr with dilute urine SG <1.005 and low urine osmolality
Dry mucosa, poor turgor, tachycardia, hypotension, weight loss
High serum Na and high serum osmolality

Rationale

Answers: 1, 3, 4, 5. DI no ADH → water wasted → polyuria >250/hr, SG <1.005 dilute, low urine osm <200, high serum Na >145 and high serum osm >295, dehydration dry mucosa poor turgor tachy hypo weight loss, extreme thirst nocturia. Option 2 is SIADH pattern.

8. Priority. The nurse has four clients. Who should be seen first?

Client with SIADH, Na 130, mild headache, on fluid restriction, alert
Client with SIADH, Na 126, on 3% saline with Na rise 6 mEq/L in 24h, lung sounds clear
Client with DI on desmopressin, Na 140, UOP 60 mL/hr, alert, mucosa moist
Client with DI post-pituitary surgery, Na 154, HR 120, BP 88/60, UOP 400 mL/hr x2, confused

Rationale

Answer: 4. Client 4 DI post-op Na 154 high, HR 120, BP 88/60 hypotension, UOP 400 polyuria, confused = severe hypernatremia with hypovolemic shock and brain shrinkage → seizures, coma, AKI risk. Needs immediate fluid replacement and desmopressin per order, strict I&O, neuro checks. Others stable: SIADH mild headache Na 130 stable, SIADH Na 126 with appropriate slow correction 6/24h clear lungs, DI on DDAVP improving Na 140 UOP 60.

9. Delegation. Which task can the RN delegate to LPN/VN for a client with SIADH on fluid restriction?

Interpret serum and urine osmolality and adjust 3% saline infusion
Check vital signs, strict I&O hourly, daily weight same scale/time/clothing, and reinforce fluid restriction teaching per plan
Assess for osmotic demyelination and manage emergency
Teach initial disease process of SIADH and tolvaptan side effects

Rationale

Answer: 2. LPN/VN can check vitals, strict I&O hourly, daily weight, give PO meds per order, reinforce teaching per plan, report changes. Interpreting osmolality and adjusting hypertonic saline (1), assessing demyelination emergency (3), and initial teaching (4) require RN.

10. NGN Case Study. A 58-year-old with small-cell lung cancer reports headache, nausea, confusion, weight gain 2kg in 2 days, intake 1000 mL, output 350 mL, urine dark SG 1.034, Na 118, serum osmolality 258 low, urine osmolality 600 high, euvolemic, lung sounds clear, HR 78, BP 126/78.

a) What condition and cues support it?
b) What are 3 priority actions and why?
c) What indicates improvement and what complication to prevent?

Model answer

a) SIADH: Small-cell lung cancer ectopic ADH, low Na 118 dilutional, low serum osm 258, high urine osm 600 inappropriate, SG 1.034 concentrated, oliguria 350 vs intake 1000, weight gain 2kg water retention, euvolemic, headache/nausea/confusion cerebral edema.

b) Priorities: 1) Fluid restriction 800-1000 mL/day per order with signage, strict I&O hourly, daily weight same scale/time — stops further dilution. 2) Seizure precautions, neuro checks q1-2h, cardiac monitor, Na q2-4h, serum/urine osm trends, lung sounds — Na <120 seizure risk, monitor overload if 3% saline needed. 3) Notify provider STAT, prepare for 3% saline only if severe symptoms per order via pump slowly ensuring rise ≤8-12/24h to prevent osmotic demyelination, hold hypotonic fluids, review meds, treat underlying cancer.

c) Improvement: Na rising slowly 4-6/24h toward 135, serum osm to 275-295, urine osm decreasing, SG to 1.015-1.025, UOP 0.5-1 mL/kg/hr, weight stable/decreasing slightly, headache/confusion resolving, no seizures/crackles. Prevent osmotic demyelination from too-rapid correction → monitor Na rise, watch dysarthria/dysphagia/quadriparesis 2-6 days post-correction; also prevent fluid overload and seizures.

Key Takeaways

SIADH = too much ADH → water retained → low Na, low serum osm, high urine osm, SG >1.030, oliguria, weight gain, euvolemic → brain swelling → headache, confusion, seizures. Treatment: fluid restriction 800-1000 mL, severe: 3% saline slowly ≤8-12/24h + tolvaptan inpatient.
DI = too little ADH or resistant → water wasted → high Na, high serum osm, low urine osm, SG <1.005, polyuria >250/hr, weight loss, dehydrated → brain shrinkage. Treatment: isotonic then free water slowly ≤0.5/hr + DDAVP central, thiazides + low salt nephrogenic.
Daily weight same scale/time/clothing + strict I&O hourly + SG + osmolality + Na trends = best monitoring.
Distinguish SIADH vs cerebral salt wasting: both low Na but SIADH euvolemic needs restriction, CSW hypovolemic needs fluids/salt — restriction worsens CSW.
DDAVP overdose = water intoxication: headache, confusion, weight gain, oliguria, low Na, SG rises after dilute → hold and notify.

References

Hinkle, J. L., Cheever, K. H., & Overbaugh, K. J. (2022). Brunner & Suddarth's textbook of medical-surgical nursing (15th ed.). Wolters Kluwer.
Ignatavicius, D. D., Workman, M. L., Rebar, C. R., & Heimgartner, N. M. (2021). Medical-surgical nursing: Concepts for interprofessional collaborative care (10th ed.). Elsevier.
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Pituitary Disorders

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Welcome & Getting Started

Launch RN Simulator

Wellness Center

Nursing Foundations

Fundamentals & Safety

Pharmacology

Dosage Calculations

Leadership, Management & Delegation

Medical-Surgical Body Systems

Neurological System

Sensory System

Endocrine System

Respiratory System

Cardiovascular System

Hematologic/Immune/Lymphatic System

Gastrointestinal (GI) System

Renal & Genitourinary

Reproductive System

Musculoskeletal System

Integumentary System

Specialty Areas

Maternity

Infectious Diseases

Pediatrics

Mental Health

NCLEX Success Center

Clinical Judgment Practice

Prioritization Practice

Delegation Practice

Lab Values

Final Review