Acid Base and Hyponatremia

enzyme functions, protein structures, cellular metabolism, physiological processes

Improper balance of acids and bases can negatively affect

Volatile acid

An acid that can be converted to gas and breathed out (Carbonic → CO2)

Nonvolatile acid

An acid that is fixed or produced in the body that must be metabolized and excreted by the kidneys (lactic, sulfuric, phosphoric, acetoacetic acid)

Physiological/chemical buffers, Respiratory, Renal

What are the 3 lines of defense against pH changes?

Bicarb, hemoglobin, phosphate, plasma proteins

What are the buffer systems in the body?

7.35-7.45

Normal blood pH

4.5-8

Normal urine pH

HA, hypotension, hyperkalemia, warm flushed skin, N/V/D, confusion, Kussmaul Respirations (DKA), chest pain, palpitations, AMS, hypoxia, weight gain

Symptoms of a metabolic acidosis

CBC, CMP, UA, ABG, tox screen, renal U/S

Diagnostics for Metabolic acidosis

Too much acid is produced, not enough acid is cleared, loss of bicarb

Pathophys for metabolic acidosis

Na - (Cl + bicarb) = 4-12 (NORMALLY)

*What is the formula for Anion Gap

determines if the lungs are responding appropriately, predicts the compensation

*What is Winter’s formula used for?

Helps determine if the metabolic acidosis is mixed

What is Delta Gap used for?

DKA (acetoacetic acid and beta-hydroxybutyric acid), lactic acidosis (most common in hospitalized patients), Uremic acidosis (CKD - stage 5)

*Endogenous etiologies of Anion Gap Metabolic Acidosis

ASA OD, methanol poisoning (wood EtOH → formic acid), Ethylene glycol (antifreeze), toluene (hippuric acid)

*Exogenous etiologies of Anion Gap Metabolic Acidosis

IV fluids, K (if under 3.3), IV insulin (if K is over 3.3), IV bicarb (if pH under 6.9), phosphates if low

*Treatment plan for DKA

Treat the underlying, IV Na-Bicarb (pH under 7.1, bicarb under 6)

*Treatment plan for Lactic acidosis

Judicious IV bicarb, fluids, glucose (CNS issues)

*Treatment plan for ASA OD

IV/IM thiamine, dextrose, saline, phosphate, Mg PRN

*Treatment plan for alcoholic anion gap metabolic acidosis

Fomepizole w/wo dialysis

*Treatment plan for methanol intoxication

diarrhea, Renal tubular acidosis (RTA)

*Major causes of normal anion gap metabolic acidosis/hyperchloremic

Kidneys cannot acidify urine; hypokalemia, renal stones, bone loss; link to autoimmune disease (Sjogren’s, SLE)

Tell me about Type I RTA

treat the underlying cause, bicarb replacement, K, citrate (prevent stones)

Treatment plan for Type I RTA

Unable to reabsorb bicarb; hypokalemia, low uric acid, phosphate, protein; glucosuria, proteinuria, bone disease; Linked to Fanconi syndrome, carbonic anhydrase, drugs toxins

Tell me about Type II RTA (leaky tubule)

Remove offending agents, high dose bicarb, K, phosphate, vitamin D

Treatment plan for Type II RTA (leaky tubule)

Decreased aldosterone causes impaired renal excretion (hyperchloremia, hyperkalemic) Common with DM, CKD, hypoaldosteronism, NSAIDs, ACEi/ARB, diuretics

Tell me about Type IV RTA (hyperkalemic distal - most common)

Treat the underlying, bicarb replacement, K restriction, loop/thiazides, K-binder

Treatment plan for Type IV RTA

High level of HCO3 in the blood either due to a loss of acid (excessive vomiting, NG tube), gain of alkali, failure of kidney to excrete bicarb

Etiology of metabolic alkalosis - diagnosed based on serum/urine Cl and volume status

N/V, HA, muscle cramps, tremors, tingling, weakness, seizures, dysrhythmias, tetany, delirium, restlessness, stupor, hypoventilation, hypotension (if there’s fluid loss), decreased respirations (hold CO2)

Signs and Symptoms for metabolic alkalosis - usually pop up at over 50

ABGs, hyperkalemia, hypercalcemia, Urine Cl (under 20 saline responsive, over 40 saline unresponsive)

Diagnostics for Metabolic alkalosis

Chloride loss from the stomach (common), Diuretics (thiazides, metolazone, loop), Chloride-depleting diarrhea (rare), impaired chloride-linked sodium transport, recovery from chronic hypercapnia, gastrocystoplasty, cystic fibrosis, severe K deficiency

Causes of Chloride-Depletion Metabolic Alkalosis

Cortosteroid induced!!

Causes of Saline Non-responsive Metabolic alkalosis

Saline responsive vs. non-responsive (do a saline trial)

How do you classify Metabolic alkalosis?

IV saline, KCL (optional), treat emesis, stop/reduce diuretics, reduce/stop NG suction, PPI/H2 blockers (may help with acid loss), Acetazolamide/spironolactone to increase bicarb excretion, Dialysis (Xtreme)

Treatment plan for Saline responsive metabolic alkalosis

Surgery to remove mineralocorticoid producing tumor (primary aldosteronism), K repletion and spironolactone, O2

Treatment plan for Saline Non-responsive

Intracellular (2/3), Extracellular (1/3)

Where does water exist in the body?

Osmolarity

The total number of dissolved particles in a liter of solution (a measure of volume)

Osmolality

The number of dissolved particles in a kilogram (mass) of solvent

Tonicity

The effect of a solution on a cell volume when the cell is placed in that solution (shrink vs. swell)

diffusion

The movement of molecules of a substance through a semipermeable membrane from a high to low concentration

Osmosis

The movement of water across a semi-permeable membrane

285-295

Isotonic range

Sodium

What is the most common extracellular electrolyte and the most common electrolyte abnormality in hospitalized patients?

Sodium level (mild: 130-134, severe under 120), Serum Osmolality, Urine Osmolality (dilute if under 100, concentrated if over 300), Spot urine sodium (under 20 = nonrenal)

What labs should we look at for hyponatremia?

Pseudohyponatremia (lab error), paraproteinemia, hypertriglyceridemia

What are the causes of isotonic hyponatremia?

Hyperglycemia, mannitol usage, sorbitol w/ TURP, radiocontrast agents

What are the causes of hypertonic hyponatremia (over 295 mOsm/kg)?

treat the underlying, NO sodium

Gameplan for Isotonic hyponatremia

N/V, HA, confusion, stupor, seizures, coma, variable BP

Symptoms of isotonic and hypertonic hyponatremia

Get rid of the extra components that are pulling water out of the cells

Gameplan for hypertonic hyponatremia

Dehydration (orthostatic hypotension, decreased skin turgor, dry mucous membranes), HA, lethargy, N/V, muscle cramps; If severe - AMS, coma, death

Symptoms of a TRUE hyponatremia (low sodium with low serum osmolality)

primary polydipsia, beer potomania, tea and toast diet

Causes of a Hypotonic Hyponatremia with a low urine osmolality (so the kidneys are trying - ADH independent)

vomiting, diarrhea, burns, 3rd spacing

Causes of a Hypotonic Hyponatremia with a high urine osmolality (kidneys are not effective - look at ADH) and a low urine sodium (under 10 - kidneys are preserving the sodium)

diuretics, uncontrolled DM, cerebral salt wasting

Causes of a Hypotonic Hyponatremia with a high urine osmolality (kidneys are not effective - look at ADH) and a high urine sodium (Over 20 - kidneys are wasting sodium)

NS, MAX INCREASE IS 8-10 OVER 24 HOURS, treat the underlying

Treatment plan for chronic/mild/asymptomatic hypovolemic hypotonic hyponatremia

Raise Na FAST - 100 ml bolus of 3% NaCl over 10 min

Treatment plan for Acute (under 48 hours)/severe/symptomatic hypovolemic hypotonic hyponatremia

Osmotic demyelination syndrome (ODS or central pontine myelinolysis)

What can happen if we over correct hypovolemic hypotonic hyponatremia too quicklike

Depressed awareness, difficulty speaking and swallowing, weakness/paralysis in arms and legs, stiffness, impaired sensation, difficulty coordinating

What does ODS present with (usually 2-6 days later)

uncertain of the cause, need hypertonic saline, refractory to treatment, more aggressive treatment is needed, concurrent liver/heart disease

When to refer/admit hypovolemic hypotonic hyponatremia

HF, liver failure, nephrotic syndrome, advanced CKD

Etiology of hypervolemic hypertonic hyponatremia

Limit water intake to 1L/day, limit salt, loop diuretics, treat underlying, may require dialysis

Treatment plan for hypervolemic hypertonic hyponatremia

SIADH (diagnosis of exclusion), pyschogenic polydipsia, exercised induced

Etiology for Euvolemic hypertonic hyponatremia

Fluid restriction (corner stone - 1-1.5 L/day), Salt tablets, vaptans to block ADH, urea diurectic, hypertonic saline (3%)

Treatment plan for Euvolemic hypertonic hyponatremia