Renal & Urinary

Metabolic alkalosis: chloride-responsive vs resistant

Clinical Overview and When to Suspect Metabolic Alkalosis

— Chloride-responsive (urine Cl⁻ <20 mEq/L): vomiting/NG suction, diuretics (post-effect), post-hypercapnia, villous adenoma, congenital chloride diarrhea, cystic fibrosis sweat losses. Volume- and Cl⁻-depleted; corrects with saline.

— Chloride-resistant (urine Cl⁻ >20 mEq/L): mineralocorticoid excess (primary aldosteronism, Cushing, licorice, exogenous steroids), Bartter/Gitelman, Liddle, severe K⁺ depletion, active diuretic use. Does NOT correct with saline.

— Persistent vomiting, bulimia, NG suction without HCO₃⁻ replacement

— Loop/thiazide diuretic users with hypokalemia

— Refractory hypertension + hypokalemia + alkalosis → think aldosterone

— Post-extubation patient previously hypercapnic on chronic CO₂ retention

— ICU patient on citrate (massive transfusion, CRRT)

Board pearl: The single most useful test to split chloride-responsive from chloride-resistant is the spot urine chloride, not urine sodium — diuretic-induced natriuresis falsely elevates urine Na⁺ even when the patient is volume-depleted.

Definition: Primary elevation in serum bicarbonate (HCO₃⁻ >26 mEq/L) with compensatory rise in PaCO₂ (~0.7 mmHg per 1 mEq/L ↑HCO₃⁻) and arterial pH typically >7.45.

Why it persists: Generation (acid loss or alkali gain) plus a maintenance factor that prevents renal excretion of excess bicarbonate — usually volume contraction, chloride depletion, hypokalemia, or hyperaldosteronism.

Two-bucket framework (the Step 3 dichotomy):

When to suspect on Step 3:

Clinical clues: Paresthesias, tetany (ionized Ca²⁺ ↓ from alkalemia shifting Ca²⁺ onto albumin), muscle cramps, weakness from hypokalemia, arrhythmias, hypoventilation, seizures if severe.

Severity threshold: HCO₃⁻ >40 or pH >7.55 = severe; mortality climbs sharply >7.65.

Presentation Patterns and Key History

— Young woman, dental erosions, parotid hypertrophy, weight preoccupation → self-induced vomiting (bulimia). Expect low Cl⁻, low K⁺, low urine Cl⁻.

— Elderly woman on HCTZ for HTN with weakness, cramps, polyuria → diuretic-induced; urine Cl⁻ variable (high if actively dosing, low if held >24h).

— Bowel obstruction with high NG output not replaced with isotonic fluid → loss of HCl, classic chloride-responsive picture.

— COPD patient recently extubated after correction of chronic hypercapnia → post-hypercapnic alkalosis; kidneys retained HCO₃⁻ that now appears "excessive."

— Hypertensive 35-year-old with spontaneous hypokalemia → primary aldosteronism workup.

— Normotensive young adult with chronic hypokalemia, cramps, no diuretic, no vomiting → Bartter (loop-like) or Gitelman (thiazide-like).

— Vomiting frequency, NG tube, laxative use, surreptitious diuretics (eating-disorder context)

— Licorice (black licorice candy, chewing tobacco) → 11β-HSD2 inhibition mimics aldosterone

— OTC alkali ingestion (antacids, baking soda, milk-alkali if combined with Ca²⁺)

— Recent blood transfusion (citrate → HCO₃⁻) or CRRT with citrate anticoagulation

— Steroid use, exogenous mineralocorticoid (fludrocortisone)

— Family history of cramps, growth failure → tubulopathies

Step 3 management: When a patient denies vomiting or diuretic use but labs scream chloride-responsive alkalosis, measure urine diuretic screen before pursuing expensive endocrine workup — surreptitious diuretic abuse is a classic Step 3 trap, especially in healthcare workers and patients with eating disorders.

Key distinction: Hypertension + alkalosis + hypokalemia points to mineralocorticoid excess; normotension + alkalosis + hypokalemia points to GI losses, diuretics, or Bartter/Gitelman.

Symptom profile is often nonspecific — metabolic alkalosis is usually discovered on labs ordered for another reason. Symptoms reflect alkalemia, hypokalemia, and volume status rather than the alkalosis itself.

Classic history vignettes:

Key questions to drive the history:

Physical Exam Findings and Hemodynamic Assessment

— Hypovolemic clues (chloride-responsive): orthostatic hypotension, flat neck veins, dry mucous membranes, decreased skin turgor, oliguria, tachycardia. Seen in vomiting, NG suction, diuretic abuse.

— Euvolemic/hypervolemic clues (chloride-resistant): hypertension (primary aldosteronism, Cushing, Liddle, licorice), no edema typically because aldosterone escape limits Na⁺ retention. Cushingoid features (moon facies, striae, central obesity, buffalo hump) when relevant.

— Bartter/Gitelman: normotensive despite renal salt wasting — paradoxical because RAAS is activated but vascular response blunted.

— Chvostek sign (facial twitch on tapping CN VII) and Trousseau sign (carpopedal spasm with BP cuff) from reduced ionized Ca²⁺

— Perioral and digital paresthesias

— Hyporeflexia, flaccid weakness, ileus from hypokalemia

— Tetany, laryngospasm in severe cases

— Compensatory hypoventilation (shallow, slow breathing) — but rarely drives PaCO₂ above 55 mmHg

— Arrhythmias: PVCs, AF, torsades if QT prolonged from hypokalemia/hypomagnesemia

— Digitalis toxicity exacerbated by hypokalemia

Board pearl: A hypertensive patient with proximal muscle weakness and spontaneous hypokalemia should prompt aldosterone:renin ratio (ARR) >20 as the screening test for primary aldosteronism — confirm with saline suppression or oral salt loading.

CCS pearl: On a CCS case, document orthostatic vitals and a focused volume exam early — it triages your fluid choice (NS vs hold fluids, start spironolactone).

General appearance: Often well-appearing; severe alkalemia (pH >7.55) may produce confusion, lethargy, or seizures.

Volume status — central to the Cl⁻-responsive vs resistant split:

Neuromuscular signs of alkalemia and hypokalemia:

Cardiopulmonary:

Dental/parotid exam: lingual enamel erosion (perimylolysis) and parotid swelling support self-induced vomiting.

Skin: Russell sign (knuckle callus from induced vomiting); hyperpigmentation if adrenal pathology.

Diagnostic Workup — Initial Labs

— pH >7.45, HCO₃⁻ >26, PaCO₂ rises ~0.7 mmHg per 1 mEq/L ↑HCO₃⁻ (max ~55 mmHg)

— If PaCO₂ deviates from predicted, suspect mixed disorder (e.g., respiratory acidosis from COPD + metabolic alkalosis from diuretic)

— Hypokalemia almost universal (intracellular K⁺ shift + renal wasting)

— Hypochloremia out of proportion to Na⁺ → classic chloride-responsive

— Anion gap typically normal; alkalemia can slightly elevate gap via lactate

— Mild hypocalcemia (ionized) despite normal total Ca²⁺

— Hypomagnesemia common with diuretics, Gitelman — must correct to fix hypokalemia

— Urine Cl⁻ <20 mEq/L → chloride-responsive (saline-responsive)

— Urine Cl⁻ >20 mEq/L → chloride-resistant (saline-unresponsive)

— Urine Na⁺ is unreliable: vomiting causes bicarbonaturia which obligates Na⁺ loss, falsely suggesting volume repletion

Step 3 management: Order spot urine chloride before giving IV fluids — once you've given saline, urine Cl⁻ rises and the diagnostic window closes. This is a frequent CCS sequencing trap.

Key distinction: Vomiting at presentation → urine Cl⁻ low AND urine Na⁺/K⁺ high (active bicarbonaturia). Vomiting days ago → urine Cl⁻, Na⁺, and K⁺ all low. Either way, urine Cl⁻ remains the reliable marker.

Arterial or venous blood gas (ABG/VBG):

Basic metabolic panel:

Spot urine electrolytes — the decisive test:

Urine K⁺ and TTKG: elevated urine K⁺ (>20 mEq/day) with hypokalemia confirms renal wasting (diuretics, mineralocorticoid excess, Bartter/Gitelman); low urine K⁺ suggests GI loss or transcellular shift.

ECG: flattened T waves, U waves, prolonged QT, ST depression from hypokalemia; watch for digoxin toxicity if on digoxin.

Glucose, Mg²⁺, phosphate routinely.

Diagnostic Workup — Advanced/Confirmatory Studies

— Plasma aldosterone concentration (PAC) and plasma renin activity (PRA) in morning, seated, off interfering meds when feasible

— Aldosterone:renin ratio (ARR) >20 with PAC >15 ng/dL → screen positive for primary aldosteronism

— Confirmation: oral salt loading + 24h urine aldosterone, or IV saline suppression test, or fludrocortisone suppression

— Adrenal CT after biochemical confirmation; adrenal vein sampling if surgery considered and patient >35 or imaging equivocal

— Liddle syndrome (ENaC gain-of-function) — responds to amiloride/triamterene, NOT spironolactone

— Apparent mineralocorticoid excess (licorice, 11β-HSD2 deficiency)

— Exogenous mineralocorticoid (fludrocortisone)

— Gitelman: hypocalciuria (urine Ca/Cr <0.1), hypomagnesemia, adult-onset, mild → thiazide-like (NCC defect)

— Bartter: hypercalciuria, normal/low Mg²⁺, presents in childhood with polyhydramnios/growth failure → loop-like (NKCC2 defect)

— Genetic testing confirms; urine diuretic screen rules out surreptitious abuse

Board pearl: Spironolactone-responsive HTN with hypokalemia and family history → primary aldosteronism or glucocorticoid-remediable aldosteronism (GRA). GRA is confirmed by genetic testing for the CYP11B1/CYP11B2 chimeric gene and treated with low-dose dexamethasone.

Key distinction: Hypocalciuria = Gitelman; hypercalciuria = Bartter. Both have alkalosis, hypokalemia, normotension, and high renin/aldosterone — but the urine calcium splits them.

When chloride-resistant (urine Cl⁻ >20) and not on active diuretics — pursue mineralocorticoid workup:

Suspected Cushing syndrome: 24-h urine free cortisol, late-night salivary cortisol, low-dose dexamethasone suppression.

Low renin AND low aldosterone with HTN + hypokalemia + alkalosis:

Normotensive chloride-resistant alkalosis (Bartter vs Gitelman):

Imaging: Adrenal CT, sellar MRI if Cushing suspected, renal US for tubulopathies/cystic disease.

Risk Stratification and First-Line Management Logic

— Stop NG suction or add PPI/H2 blocker to reduce gastric acid loss (omeprazole, famotidine)

— Stop diuretic or switch class

— Treat vomiting (antiemetics, address underlying cause)

— Discontinue exogenous alkali (bicarbonate, citrate, antacids)

— <20 mEq/L → Chloride-responsive: Give 0.9% NaCl to restore volume and provide Cl⁻; add KCl to replete potassium. Most cases resolve once volume and Cl⁻ replete.

— >20 mEq/L → Chloride-resistant: Saline will NOT correct it and may worsen HTN/edema. Target underlying mineralocorticoid excess: spironolactone or eplerenone; amiloride for Liddle; adrenalectomy for aldosteronoma.

— Mild (HCO₃⁻ 26–35, pH <7.50): treat outpatient with oral KCl, fluid as needed

— Moderate (HCO₃⁻ 35–45): IV fluids, IV KCl if symptomatic

— Severe (HCO₃⁻ >45 or pH >7.60): ICU; consider acetazolamide 250–500 mg IV/PO, HCl infusion via central line, or hemodialysis with low-bicarbonate bath if renal failure

— Volume overload + alkalosis (CHF on loop diuretic): saline contraindicated — use acetazolamide or KCl + spironolactone

— Mechanical ventilation: avoid hyperventilation that maintains alkalemia; correct alkalosis to facilitate weaning

CCS pearl: In a CHF patient with diuretic-induced alkalosis, ordering "0.9% NaCl" will lose you points — the correct order is acetazolamide 250–500 mg IV daily plus KCl repletion, since the patient is chloride-depleted but volume-overloaded.

Step 1 — Confirm primary disorder: ABG with HCO₃⁻ >26, pH >7.45, appropriate respiratory compensation.

Step 2 — Identify and stop the generating insult:

Step 3 — Classify by urine Cl⁻:

Step 4 — Severity-based escalation:

Special situations:

Pharmacotherapy — First-Line Regimens

— 0.9% NaCl IV at 100–250 mL/h until volume replete (urine output >0.5 mL/kg/h, normalization of HR/BP); typical total 2–4 L

— Potassium chloride: 10–20 mEq/h IV via peripheral line (max 40 mEq/h via central with monitoring); oral KCl 40–80 mEq/day in divided doses for mild cases. Goal serum K⁺ ≥4.0

— Magnesium sulfate 2 g IV or oral Mg oxide if Mg <2.0 — refractory hypokalemia won't correct without Mg repletion

— For ongoing gastric loss: PPI (pantoprazole 40 mg IV daily) reduces HCl loss from NG suction

— Spironolactone 25–100 mg/day or eplerenone 25–50 mg BID for primary aldosteronism, secondary hyperaldosteronism

— Amiloride 5–10 mg/day or triamterene for Liddle syndrome (ENaC blockade — spironolactone won't work because the defect is downstream of the receptor)

— Glucocorticoid replacement withdrawal/reduction for Cushing; low-dose dexamethasone for glucocorticoid-remediable aldosteronism

— NSAIDs (indomethacin) for Bartter to reduce prostaglandin-driven renin

— Mg and K replacement essential for Gitelman/Bartter

— Carbonic anhydrase inhibitor → bicarbonaturia

— Useful when saline is contraindicated (CHF, COPD with post-hypercapnic alkalosis, edema)

— Monitor for worsening hypokalemia (acetazolamide wastes K⁺) — co-administer KCl

— HCl infusion 0.1–0.2 N via central line, max 0.2 mEq/kg/h

— Ammonium chloride or arginine HCl alternatives (avoid in hepatic failure)

— Hemodialysis with low-HCO₃⁻ bath in renal failure

Board pearl: Liddle syndrome responds to amiloride/triamterene, NOT spironolactone, because the mutation is in ENaC itself (constitutively active), not at the mineralocorticoid receptor.

Chloride-responsive alkalosis:

Chloride-resistant alkalosis:

Adjunct: Acetazolamide 250–500 mg PO/IV daily

Severe refractory cases:

Procedures and Invasive/Refractory Management

— Indications: severe alkalosis (pH >7.55, HCO₃⁻ >45) with neurologic symptoms, arrhythmia, or failure to wean from ventilator

— Concentration: 0.1–0.2 N HCl in D5W via central line only (peripheral causes severe vein necrosis)

— Rate: 0.1–0.2 mEq/kg/h; check ABG q4–6h

— Dose calculation: HCl deficit (mEq) = 0.5 × weight (kg) × (current HCO₃⁻ − desired HCO₃⁻); replace ~half over 12–24h

— Indicated when renal failure prevents bicarbonate excretion or HCl/acetazolamide contraindicated

— Use low-bicarbonate dialysate (25–30 mEq/L) rather than standard 35 mEq/L bath

— CRRT with citrate anticoagulation can paradoxically worsen alkalosis — switch to heparin or regional anticoagulation

— Unilateral laparoscopic adrenalectomy for aldosterone-producing adenoma confirmed by adrenal vein sampling lateralization

— Preop: spironolactone 4–6 weeks to normalize K⁺ and BP; perioperative steroid coverage usually not needed for unilateral

— Cure rate ~50% for HTN, near-100% for hypokalemia/alkalosis

— In post-hypercapnic alkalosis, allow gradual normalization of PaCO₂; do not over-ventilate

— Sedation/paralysis if alkalosis is impairing weaning

CCS pearl: When ordering HCl infusion, also order central line placement, continuous telemetry, q4h ABG, q6h BMP, and a vascular access nursing consult — missing these supportive orders costs CCS points even if the therapeutic order is correct.

HCl infusion — when and how:

Hemodialysis:

Adrenalectomy:

Bilateral adrenal hyperplasia: medical management with spironolactone/eplerenone preferred over bilateral adrenalectomy.

Pituitary surgery for ACTH-secreting Cushing disease (transsphenoidal).

Pyloric obstruction / gastric outlet obstruction: endoscopic dilation or surgical bypass for chronic vomiting source.

Ventilator management:

Special Populations — Elderly and Renal/Hepatic Impairment

— Disproportionate burden from thiazide and loop diuretics for HTN/CHF — leading cause of chloride-responsive alkalosis in this group

— Reduced thirst and concentrating ability amplify volume depletion

— Polypharmacy: PPIs, laxatives, antacids, milk-alkali from OTC calcium

— Falls risk from hypokalemia-related weakness and orthostasis

— Start low, go slow with KCl repletion — risk of hyperkalemia if undetected CKD

— Reassess need for diuretic at every visit; deprescribe when possible

— Impaired bicarbonate excretion prolongs alkalosis once generated

— Avoid acetazolamide if eGFR <30 (less effective, risk of metabolic acidosis paradoxically delayed)

— Spironolactone risk: hyperkalemia — contraindicated if K⁺ >5.0 or eGFR <30

— Eplerenone preferred for fewer endocrine side effects but same K⁺ risk

— In dialysis patients, adjust dialysate HCO₃⁻ downward (25–30 mEq/L) to manage chronic alkalosis from citrate/acetate

— Hyperaldosteronism is physiologic in cirrhosis (low effective arterial volume) → chronic mild alkalosis

— Loop diuretics + spironolactone in 40:100 ratio (e.g., furosemide 40 / spironolactone 100) is standard for ascites — adjust based on K⁺ and alkalosis severity

— Avoid ammonium chloride and arginine HCl — risk of precipitating hepatic encephalopathy via ammonia generation

— Hypokalemic alkalosis worsens encephalopathy by increasing renal ammoniagenesis — aggressive K⁺ repletion is part of HE management

Step 3 management: In an elderly CHF patient with HCO₃⁻ 38, K⁺ 3.0, on furosemide — add spironolactone 25 mg daily (treats alkalosis, hypokalemia, AND improves CHF mortality per RALES), rather than acetazolamide as first move.

Board pearl: Avoid HCl-based therapies in cirrhosis; use acetazolamide or spironolactone optimization instead.

Elderly:

Chronic kidney disease (CKD):

Hepatic impairment / cirrhosis:

Heart failure: diuretic-driven alkalosis common; managed with acetazolamide rather than saline.

Special Populations — Pregnancy, Pediatrics, Other Subgroups

— Baseline is chronic respiratory alkalosis (progesterone-driven hyperventilation, PaCO₂ ~30), so superimposed metabolic alkalosis can produce extreme pH elevations

— Hyperemesis gravidarum: classic chloride-responsive alkalosis with ketosis; treat with IV NS + KCl + thiamine before dextrose, ondansetron/doxylamine/pyridoxine

— Pre-eclampsia: avoid spironolactone (antiandrogenic, fetal feminization risk) — use eplerenone if mineralocorticoid blockade needed

— Bartter/Gitelman exacerbates during pregnancy due to volume expansion needs

— Pyloric stenosis: 4–8 week old male, projectile non-bilious vomiting, palpable "olive," hypochloremic hypokalemic metabolic alkalosis. Correct fluids/electrolytes before pyloromyotomy — anesthetic risk if alkalotic

— Cystic fibrosis: chronic Cl⁻ loss in sweat → "pseudo-Bartter" alkalosis during heat exposure or gastroenteritis

— Bartter syndrome: polyhydramnios, premature delivery, failure to thrive, polyuria; treat with KCl, indomethacin, spironolactone

— Congenital chloride diarrhea: rare AR disorder, watery diarrhea high in Cl⁻ → alkalosis (the only diarrhea that causes alkalosis instead of acidosis)

— Bulimia → vomiting-induced; anorexia + laxative abuse → can cause either alkalosis (vomiting) or acidosis (laxatives)

— Surreptitious diuretic use mimics Bartter/Gitelman — urine diuretic screen essential

— Refeeding risk: aggressive correction can worsen hypophosphatemia, arrhythmias

Key distinction: Pyloric stenosis is the prototypical pediatric chloride-responsive alkalosis — never operate before electrolytes/pH normalize (Cl⁻ >100, HCO₃⁻ <30, K⁺ >3.5) due to anesthesia-induced apnea risk from alkalemic hypoventilation.

Pregnancy:

Pediatrics:

Eating disorders:

Athletes/military: profuse sweating with Cl⁻ loss + dehydration; volume + Cl⁻ repletion.

Complications and Adverse Outcomes

— Arrhythmias: hypokalemia and alkalemia together prolong QT, predispose to torsades de pointes, AF, PVCs, ventricular tachycardia

— Digoxin toxicity potentiated by hypokalemia even at therapeutic digoxin levels

— Coronary vasospasm from alkalemia-induced vasoconstriction

— Reduced cardiac contractility at pH >7.6

— Confusion, lethargy, seizures, coma at pH >7.6

— Tetany, carpopedal spasm, laryngospasm from reduced ionized Ca²⁺

— Cerebral vasoconstriction → reduced CBF, exacerbates ischemic stroke

— Compensatory hypoventilation → hypoxemia, hypercapnia

— Impaired ventilator weaning — alkalosis suppresses respiratory drive; targeting HCO₃⁻ <30 facilitates extubation

— Leftward shift of oxyhemoglobin curve → impaired tissue O₂ delivery

— Bicarbonaturia obligates K⁺ and Na⁺ loss, worsening depletion

— Nephrogenic DI from chronic hypokalemia → polyuria, polydipsia

— Hypokalemic nephropathy if chronic (>1 month) — interstitial fibrosis, cysts

— Hypocalcemia (ionized), hypomagnesemia, hypophosphatemia

— Worsened hepatic encephalopathy via increased renal ammoniagenesis and NH₃ shift across BBB

— Glucose intolerance (hypokalemia impairs insulin secretion)

— HCl extravasation → tissue necrosis

— Overcorrection → metabolic acidosis with respiratory compensation lag

— Acetazolamide → hypokalemia, metabolic acidosis if overshoot

Board pearl: A ventilated COPD patient who fails extubation despite good gas exchange may be suppressed by post-hypercapnic metabolic alkalosis — treat with acetazolamide to lower HCO₃⁻ and restore respiratory drive.

Step 3 management: Check ionized Ca²⁺, Mg²⁺, and phosphate in every patient with HCO₃⁻ >35 — repletion of all three is required to safely correct K⁺.

Cardiovascular:

Neurologic:

Pulmonary:

Renal:

Metabolic:

Iatrogenic:

When to Escalate — ICU, Consult, Inpatient Triage

— pH >7.60 or HCO₃⁻ >45

— Arrhythmia, hemodynamic instability, or seizure

— Need for HCl infusion (requires central line and continuous monitoring)

— Mechanical ventilation with alkalosis impeding weaning

— Severe hypokalemia (K⁺ <2.5) with ECG changes

— Concurrent severe hyponatremia, hypomagnesemia, or hypocalcemia with tetany

— Moderate alkalosis (HCO₃⁻ 35–45) with symptomatic hypokalemia

— Need for IV potassium repletion >10 mEq/h

— Hyperemesis gravidarum requiring IV fluids and antiemetics

— Pyloric stenosis awaiting surgery

— Diagnostic workup for new mineralocorticoid excess

— Mild alkalosis (HCO₃⁻ <35) with mild hypokalemia (K⁺ >3.0)

— Stable diuretic-related alkalosis with reliable follow-up

— Confirmed primary aldosteronism without symptoms, awaiting elective surgery

— Nephrology: refractory alkalosis, suspected tubulopathy, need for dialysis modification

— Endocrinology: suspected primary aldosteronism, Cushing, Liddle, GRA

— Surgery: adrenalectomy candidates, pyloric stenosis, gastric outlet obstruction

— Psychiatry/Eating disorders team: bulimia, surreptitious vomiting/diuretic use

— Genetics: suspected Bartter/Gitelman/Liddle/GRA

CCS pearl: Always order continuous telemetry for K⁺ <3.0, q4h K⁺ during IV repletion, and central line placement order before any HCl infusion order — sequencing these correctly is what the CCS scorer rewards.

Admit to ICU when:

Admit to ward when:

Outpatient management acceptable when:

Consultations to request:

Safety triggers for inpatient observation: suicidal ideation in eating disorder, syncope from hypokalemia, inability to tolerate PO.

Key Differentials — Same-Category Causes of Alkalosis

— Vomiting / NG suction: loss of HCl directly generates alkalosis; volume contraction maintains it

— Post-diuretic effect: loop or thiazide diuretic dosed >24h ago — patient still volume/Cl⁻ depleted but no active diuresis, so urine Cl⁻ drops below 20

— Post-hypercapnic alkalosis: rapid correction of chronic CO₂ retention (e.g., aggressive ventilation in COPD) unmasks renal HCO₃⁻ retention

— Villous adenoma of colon: rare; secretes Cl⁻-rich, K⁺-rich fluid → hypokalemic alkalosis with diarrhea

— Congenital chloride diarrhea: AR, neonatal watery diarrhea

— Cystic fibrosis: Cl⁻ loss in sweat, especially with heat stress

— Laxative abuse: can cause either acidosis or alkalosis depending on type

— Active diuretic use (loop or thiazide within last 24h)

— Primary aldosteronism (Conn syndrome, bilateral adrenal hyperplasia): HTN, hypokalemia, suppressed renin

— Secondary hyperaldosteronism: renovascular HTN, malignant HTN, renin-secreting tumor — HTN with HIGH renin

— Cushing syndrome: especially ectopic ACTH (small cell lung cancer) — massive cortisol overwhelms 11β-HSD2

— Apparent mineralocorticoid excess: licorice (glycyrrhizic acid), chewing tobacco, carbenoxolone — inhibit 11β-HSD2

— Liddle syndrome: ENaC gain-of-function — HTN, low renin, low aldosterone

— Bartter syndrome: loop-like, normotensive, hypercalciuria

— Gitelman syndrome: thiazide-like, normotensive, hypocalciuria, hypomagnesemia

— Severe K⁺ depletion (K⁺ <2.0): itself causes alkalosis via increased renal H⁺ secretion

Key distinction: HTN + hypokalemic alkalosis with HIGH renin = secondary aldosteronism (renovascular). HTN + hypokalemic alkalosis with LOW renin = primary aldosteronism, Cushing, Liddle, or licorice. Then split low-renin causes by aldosterone level.

Chloride-responsive (urine Cl⁻ <20) differentials:

Chloride-resistant (urine Cl⁻ >20) differentials:

Key Differentials — Other-Category Causes/Mimics

— Chronic respiratory acidosis: HCO₃⁻ elevated as compensation (not primary alkalosis); pH is low or normal, not high

— Triple disorder: e.g., septic patient with vomiting (alkalosis) + lactic acidosis + respiratory alkalosis — use anion gap and delta-delta to unmask

— Laboratory error: prolonged tourniquet, sample exposed to air → falsely elevated HCO₃⁻

— Contraction alkalosis from aggressive diuresis without HCO₃⁻ loss — essentially a chloride-responsive variant

— Milk-alkali syndrome: ingestion of large Ca²⁺ + absorbable alkali (calcium carbonate, baking soda) → hypercalcemia, alkalosis, renal failure. Resurging with OTC calcium supplements

— Refeeding alkalosis: rare; usually refeeding causes phosphate and K⁺ shifts rather than alkalosis

— Renal tubular acidosis type 1 and 2 — hypokalemia WITH acidosis

— DKA — hypokalemia (total body) with acidosis

— Insulin/β-agonist–induced shift — transient, no acid-base derangement

— Renal artery stenosis early phase, before alkalosis develops

— Diuretic use with concurrent metabolic acidosis from other cause

— Severe hypoalbuminemia → normal anion gap appears "low," masking gap acidosis layered onto alkalosis

— Lithium, bromide elevations → falsely measured Cl⁻

Board pearl: In a patient with hypokalemia, always check pH and HCO₃⁻ before reflexively replacing K⁺ — the acid-base status reframes the differential entirely (RTA vs alkalosis vs DKA vs shift).

Key distinction: Use the delta-delta ratio (Δ anion gap / Δ HCO₃⁻) to detect occult metabolic alkalosis hidden within a high-anion-gap acidosis. Ratio >2 suggests concurrent alkalosis.

Mixed acid-base disorders presenting with elevated HCO₃⁻:

Conditions mistaken for metabolic alkalosis:

Causes of hypokalemia without alkalosis (to rule out when K⁺ low but pH normal):

Causes of HTN + hypokalemia without alkalosis:

Pseudo-alkalosis traps:

Secondary Prevention, Discharge Meds, Long-Term Plan

— Switch from thiazide → K⁺-sparing combination (HCTZ/triamterene, HCTZ/amiloride) for HTN if recurrent hypokalemia/alkalosis

— Add spironolactone 12.5–25 mg to loop diuretic regimens in CHF (RALES/EMPHASIS-HF benefit)

— Daily oral KCl 20–40 mEq maintenance if persistent K⁺ <4.0

— Reassess diuretic indication every visit — many elderly patients can be deprescribed

— Treat root cause: antiemetic regimen, GI workup for obstruction, intensive outpatient eating disorder program

— Bulimia: SSRI (fluoxetine 60 mg), CBT, nutritional counseling

— Avoid bupropion (seizure risk) in bulimia

— Unilateral adenoma: post-adrenalectomy monitoring of BP, K⁺, renin, aldosterone — many patients remain on antihypertensive

— Bilateral hyperplasia: lifelong spironolactone or eplerenone; monitor K⁺ q3–6 months, especially with ACEi/ARB co-therapy

— Lifelong oral KCl + Mg supplementation; indomethacin in Bartter

— Liberal salt intake; avoid additional diuretics

— Amiloride 5–20 mg/day or triamterene; sodium restriction; lifelong therapy

— Primary aldosteronism carries higher CV risk than essential HTN at equivalent BP — aggressive lipid, glucose, BP control

— Statin per ASCVD risk; ACEi/ARB for proteinuria, diabetes

Step 3 management: When discharging a CHF patient with diuretic-induced alkalosis, the discharge medication list should add spironolactone 25 mg daily and KCl 20 mEq daily, with BMP scheduled in 1 week — this combination addresses alkalosis, hypokalemia, and CHF mortality simultaneously.

Diuretic-induced alkalosis (most common chronic scenario):

Vomiting / NG / eating disorders:

Primary aldosteronism:

Bartter/Gitelman:

Liddle syndrome:

Cardiovascular risk reduction:

Follow-Up, Monitoring, Rehab, Counseling

— BMP in 3–7 days after starting/changing K⁺-sparing diuretic or KCl repletion

— Repeat ABG/VBG only if symptomatic or HCO₃⁻ was severe — most outpatients monitored by BMP alone

— Primary care visit within 1–2 weeks for medication reconciliation

— Serum K⁺: goal 4.0–4.5 in patients on diuretics; q3 months once stable

— Serum Mg²⁺: annually or with persistent hypokalemia

— HCO₃⁻ and Cl⁻: trend on routine BMP; HCO₃⁻ <30 = adequate control

— Blood pressure home monitoring for mineralocorticoid disorders

— Aldosterone, renin: at 6–12 months post-adrenalectomy to confirm cure

— Dietary K⁺: bananas, potatoes, oranges, leafy greens, beans — sufficient for mild deficits

— Sodium restriction (<2 g/day) for primary aldosteronism, Liddle, secondary hyperaldosteronism

— Liberal sodium for Bartter/Gitelman

— Avoid licorice candy, chewing tobacco, herbal supplements with glycyrrhizin

— Hydration during exercise/heat especially for CF, Gitelman

— Multidisciplinary team: nutrition, psychiatry, primary care

— Weight-restoration program, family-based therapy for adolescents

— Routine dental care for erosion management

— Spironolactone side effects: gynecomastia, menstrual irregularity, hyperkalemia — switch to eplerenone if intolerable

— KCl: take with food, full glass of water, avoid lying down 30 min

— Amiloride: monitor for hyperkalemia, especially with ACEi/ARB

Board pearl: Patients on spironolactone plus ACEi/ARB plus NSAID have markedly elevated hyperkalemia risk — a Step 3 favorite for asking about medication review pitfalls in CHF or aldosteronism follow-up.

Acute post-discharge follow-up:

Chronic monitoring parameters:

Lifestyle counseling:

Eating disorder rehab:

Pharmacy counseling:

Ethical, Legal, Patient Safety Considerations

— Ethically sensitive — patient may deny use; non-confrontational disclosure combined with urine diuretic screen is appropriate

— Document findings objectively; do not threaten or shame; refer to eating disorder team

— Confidentiality vs family disclosure: respect adult autonomy unless safety threat; involve adolescents' parents per state law

— Severe eating disorders with refusal of treatment may meet criteria for involuntary psychiatric hold if imminent risk (K⁺ <2.5, arrhythmia)

— Assess decisional capacity carefully — alkalosis-induced confusion can impair capacity transiently; reassess after correction

— HCl infusion carries small but real risk of central line complications and extravasation — explicit consent and second-physician verification of central placement before initiation

— Adrenalectomy consent must include risk of contralateral adrenal insufficiency, BP non-cure (~50%), and need for lifelong steroids if bilateral

— Genetic testing for Bartter/Gitelman/Liddle: pre-test counseling about implications for family, insurance under GINA

— Hospital-to-home: failure to stop NG suction–era PPI or hold home diuretic at discharge is a top cause of recurrence

— Medication reconciliation at discharge: explicitly review whether home diuretic should resume and at what dose

— 7-day post-discharge BMP prevents readmission for hypokalemia/alkalosis

— Skilled nursing facility handoff: communicate K⁺ goal, spironolactone dose, and BMP schedule in writing

— KCl IV is a high-alert medication — never IV push; verify concentration and rate; use smart pumps

— Never give concentrated KCl on ward without dilution — sentinel event

CCS pearl: On a CCS discharge, explicitly order "BMP in 7 days, follow up with PCP in 1–2 weeks" — the scorer credits the structured transition-of-care plan.

Surreptitious diuretic and laxative abuse:

Mandatory reporting and capacity:

Informed consent edge cases:

Transition-of-care risks (Step 3 staple):

Patient safety:

High-Yield Associations and Rapid-Fire Facts

Board pearl: Chronic hypokalemia (K⁺ <3.0 for weeks) itself causes alkalosis by stimulating renal H⁺ secretion via H⁺/K⁺-ATPase upregulation in α-intercalated cells — fixing the K⁺ fixes the alkalosis.

Vomiting alkalosis paradox: Initial urine Na⁺ HIGH (bicarbonaturia obligates Na⁺), but urine Cl⁻ LOW — use Cl⁻, not Na⁺, to assess volume.

Diuretic timing: Active diuretic = urine Cl⁻ HIGH; held >24h = urine Cl⁻ LOW. Same drug, opposite urine chloride.

Gitelman = hypocalciuria + hypomagnesemia + adult onset. Bartter = hypercalciuria + neonatal/childhood onset.

Liddle responds to amiloride, NOT spironolactone (defect is at ENaC, downstream of MR).

Licorice ingestion (glycyrrhizic acid) inhibits 11β-HSD2 → cortisol acts on MR → "apparent mineralocorticoid excess." Stop licorice, alkalosis resolves over weeks.

Post-hypercapnic alkalosis: Rapid lowering of PaCO₂ in chronic CO₂ retainer exposes elevated HCO₃⁻; treat with acetazolamide.

Pyloric stenosis: hypochloremic, hypokalemic, paradoxical aciduria (kidneys exchange K⁺ then H⁺ for Na⁺ to preserve volume).

Milk-alkali syndrome: Hypercalcemia + alkalosis + AKI — think OTC calcium + bicarbonate.

CF "pseudo-Bartter": Chloride loss in sweat → hypochloremic alkalosis, especially infants in summer.

Refractory hypokalemia → check Mg²⁺. Hypomagnesemia prevents K⁺ retention via ROMK channel disinhibition.

Ionized hypocalcemia in alkalosis causes Chvostek/Trousseau even with normal total Ca²⁺.

Aldosterone:renin ratio (ARR) >20 with aldosterone >15 ng/dL = screen positive for primary aldosteronism.

Glucocorticoid-remediable aldosteronism (GRA): AD, family history of early stroke, treated with low-dose dexamethasone.

Acetazolamide is first-line for volume-overloaded patients with alkalosis (CHF, COPD on diuretics).

HCl infusion requires central line; never peripheral.

Compensation formula: PaCO₂ rises 0.7 mmHg per 1 mEq/L ↑HCO₃⁻ (max ~55).

Board Question Stem Patterns

Step 3 management: When the stem mentions "resistant hypertension on 3 drugs with spontaneous hypokalemia," the answer is aldosterone:renin ratio — not adrenal CT first.

Stem 1 — Bulimia: Young woman, parotid swelling, dental erosions, K⁺ 2.8, HCO₃⁻ 38, urine Cl⁻ 8. → Chloride-responsive, give NS + KCl, refer eating disorder team.

Stem 2 — Pyloric stenosis: 5-week-old male, non-bilious projectile vomiting, palpable epigastric mass, HCO₃⁻ 34, Cl⁻ 88, K⁺ 3.0. → Correct fluids/electrolytes first, then pyloromyotomy.

Stem 3 — Conn syndrome: 45-year-old with resistant HTN on 3 drugs, K⁺ 2.9, HCO₃⁻ 32, urine Cl⁻ 45. → ARR; if positive, saline suppression then adrenal CT/AVS.

Stem 4 — Liddle: Family history of early HTN and stroke, K⁺ 2.7, low renin AND low aldosterone, fails spironolactone. → Switch to amiloride.

Stem 5 — Licorice: Man chewing tobacco daily, BP 170/100, K⁺ 2.8, low renin, LOW aldosterone, urinary cortisol:cortisone ratio elevated. → Stop licorice/tobacco.

Stem 6 — Gitelman: Young adult with chronic cramps, K⁺ 2.9, Mg²⁺ 1.4, HCO₃⁻ 30, normotensive, urine Ca/Cr 0.05. → Gitelman; lifelong K⁺ and Mg²⁺ replacement.

Stem 7 — Bartter: Infant with polyhydramnios history, failure to thrive, polyuria, hypercalciuria. → Bartter; KCl + indomethacin.

Stem 8 — Post-hypercapnic: COPD patient extubated 2 days ago, now pH 7.52, HCO₃⁻ 36, K⁺ 3.2, failing to wean. → Acetazolamide.

Stem 9 — CHF diuretic: Elderly woman on furosemide 80 BID, HCO₃⁻ 38, K⁺ 2.8, edema. → Add spironolactone + KCl, NOT saline.

Stem 10 — NG suction: Postop SBO with high NG output, HCO₃⁻ 40, K⁺ 2.6, urine Cl⁻ 10. → NS + KCl + PPI to reduce HCl loss.

Stem 11 — Surreptitious diuretic: Nurse with eating disorder, normotensive, K⁺ 2.8, alkalosis, urine Cl⁻ 50, no edema. → Urine diuretic screen.

Stem 12 — Severe refractory: ICU patient, pH 7.62, HCO₃⁻ 48, arrhythmia, CHF (can't tolerate saline). → HCl infusion via central line.

One-Line Recap

Metabolic alkalosis is split by spot urine chloride: <20 mEq/L is chloride-responsive (vomiting, NG suction, prior diuretics, post-hypercapnia) and corrects with saline plus KCl; >20 mEq/L is chloride-resistant (active diuretics, mineralocorticoid excess, Bartter/Gitelman/Liddle) and requires targeting the underlying driver — never saline alone.

Board pearl: The fastest path to the right answer on any metabolic alkalosis stem is urine chloride first, then volume status, then renin/aldosterone — these three data points solve >90% of board questions.

Diagnostic axis: ABG confirms primary alkalosis; spot urine Cl⁻ bisects the differential; aldosterone:renin ratio and urine Ca/Mg/diuretic screen refine the resistant arm.

Treatment axis: Chloride-responsive → 0.9% NaCl + KCl + remove insult (stop diuretic, PPI for NG losses, antiemetics). Chloride-resistant + volume overload → acetazolamide, spironolactone/eplerenone, or amiloride (Liddle). Severe (pH >7.60) → HCl infusion via central line, or hemodialysis with low-bicarbonate bath.

High-yield distinctions: Gitelman = hypocalciuria + hypomagnesemia (adult, mild); Bartter = hypercalciuria (neonatal, severe); Liddle = amiloride-responsive low-renin/low-aldosterone HTN; licorice mimics primary aldosteronism via 11β-HSD2 blockade; primary aldosteronism = high aldosterone/low renin (ARR >20).

Step 3 pearls: Always correct Mg²⁺ to fix refractory hypokalemia; check urine Cl⁻ BEFORE giving fluids; in CHF use acetazolamide + spironolactone rather than saline; HCl infusion requires central access; schedule BMP within 7 days of discharge on any K⁺-altering regimen; deprescribe diuretics in elderly when feasible to prevent recurrence.