electrolytes and acid/base

Hypovolemia

Decreased intravascular volume causing hypotension and tachycardia.

Causes of Hypovolemia

Bleeding, vomiting, diarrhea, burns, diuretics.

Signs of Hypovolemia

Thirst, dry skin, low BP, weak pulse, decreased urine output.

Hypervolemia

Excess intravascular volume; common in HF and renal failure.

Causes of Hypervolemia

Renal failure, excessive IV fluids, hyperaldosteronism.

Signs of Hypervolemia

Edema, hypertension, bounding pulses, JVD.

Dehydration

Loss of free water leading to hypernatremia.

Hypovolemia vs Dehydration

Hypovolemia = volume loss; dehydration = water loss.

Hemoconcentration

Increased lab values due to plasma loss.

Hemodilution

Decreased lab values after fluid replacement.

Normal ph

7.35 -7.45

Normal PaCO2

35-45 mmHg

Normal HCO3-

22-26 mEq/L

High CO2 in blood

Causes acidity; decrease ph of blood (<7.35)

High HCO3 in blood

Causes alkalinity ; increases ph of blood (>7.45)

Shock

Failure of perfusion and oxygen delivery to tissues.

Hypovolemic Shock

Caused by blood or fluid loss.

Cardiogenic Shock

Caused by pump failure.

Distributive Shock

Caused by vasodilation (sepsis, anaphylaxis).

Clinical Shock Priority

Restore perfusion before correcting labs.

Sodium

Major ECF cation controlling osmolality and fluid balance.

Hyponatremia Serum

Na⁺ <135 mEq/L; usually excess water.

Symptoms of Hyponatremia

Headache, confusion, seizures due to cerebral edema.

SIADH

Excess ADH → water retention → dilutional hyponatremia.

SIADH Urine Findings

Low volume, high concentration.

Hypernatremia Serum

Na⁺ >145 mEq/L; usually water deficit.

Symptoms of Hypernatremia

Thirst, agitation, seizures from neuronal shrinking.

Diabetes Insipidus

ADH deficiency or resistance → excessive dilute urine.

DI Urine Findings

Large volume, low specific gravity.

Sodium Correction

Must be slow to prevent demyelination.

Water Intoxication

Rapid hyponatremia from excess free water intake.

Dilutional Hyponatremia

Common in HF and SIADH.

Sodium Reflects Water Balance

Not total body sodium.

Brain Sensitivity to Sodium

Rapid changes cause neurologic symptoms.

Clinical Sodium Rule

Treat the water problem, not just sodium.

Tonicity

Effect of a solution on cell volume.

Isotonic Fluids

Remain in ECF; expand intravascular volume.

Normal Saline (0.9%)

Isotonic; used for hypovolemia.

Lactated Ringers

Isotonic with electrolytes; mimics plasma.

Hypotonic Fluids

Cause cells to swell; used for hypernatremia.

Half-Normal Saline (0.45%)

Hypotonic; used cautiously.

Hypertonic Fluids

Draw water out of cells.

3% Saline

Treats severe hyponatremia under close monitoring.

D5W

Isotonic in bag, hypotonic in body.

Iatrogenic Injury

Harm caused by inappropriate fluid therapy.

Potassium

Major ICF cation; critical for cardiac rhythm.

Hypokalemia

K⁺ <3.5 mEq/L; causes muscle weakness and arrhythmias.

Hyperkalemia

K⁺ >5.0 mEq/L; causes life-threatening arrhythmias.

EKG Changes in Hyperkalemia

Peaked T waves, wide QRS.

EKG Changes in Hypokalemia

Flattened T waves, U waves.

Insulin and Potassium

Insulin shifts K⁺ into cells.

Acidosis and Potassium

H⁺ enters cells → K⁺ exits.

Calcium

Needed for muscle contraction, clotting, and nerve transmission.

Hypocalcemia

Causes tetany, muscle spasms, seizures.

Hypercalcemia

Causes lethargy, kidney stones, fractures.

Calcium-Phosphate Relationship

Inverse relationship.

Normal pH of blood

Normal 7.35-7.45.

Metabolic Acidosis

Low HCO₃⁻; seen in DKA, diarrhea.

Respiratory Compensation

Lungs adjust CO₂ to correct pH.

DKA Pathophysiology

Insulin deficiency → ketones → metabolic acidosis with fluid and electrolyte shifts.

Thirst Mechanism

Hypothalamic response to increased osmolality; promotes water intake.

Antidiuretic Hormone (ADH)

Hormone that increases water reabsorption in kidneys; affects sodium concentration indirectly.

Aldosterone Hormone

Increases sodium and water retention and potassium excretion; raises blood volume and pressure.

Renin

Enzyme released by kidneys in response to low perfusion; initiates RAAS.

Angiotensin II

Causes vasoconstriction and stimulates aldosterone and ADH; raises BP.

Renin-Angiotensin-Aldosterone System (RAAS)

Major regulator of blood pressure and volume; overactivation worsens HF and edema.

Sympathetic Nervous System

Decreases renal perfusion and increases sodium retention during hypovolemia.

Atrial Natriuretic Peptide (ANP)

Hormone released by atria that promotes sodium and water excretion.

Addison's Disease

Adrenal insufficiency → low aldosterone → hypovolemia, hyponatremia, hyperkalemia.

Cushing's Disease

Excess cortisol → sodium retention and fluid volume excess.

Conn's Syndrome

Hyperaldosteronism → hypertension, hypokalemia, metabolic alkalosis.

Baroreceptors

Sense changes in blood pressure and trigger compensatory mechanisms.

Kidney as Regulator

Kidneys adjust sodium, water, acid, and potassium balance.

Hormonal Backup Systems

ADH and RAAS activate when perfusion is threatened.

Clinical Volume Sensing

The body prioritizes perfusion over electrolyte balance.

Capillary Filtration

Movement of fluid out of capillaries driven by hydrostatic pressure.

Capillary Reabsorption

Movement of fluid back into capillaries driven by oncotic pressure.

Lymphatic System

Returns excess interstitial fluid to circulation; failure causes lymphedema.

Edema

Abnormal accumulation of interstitial fluid.

Pitting Edema

Indentation remains after pressure; common in HF and venous disease.

Venous Obstruction

Increases hydrostatic pressure causing dependent edema.

Hypoalbuminemia

Low albumin decreases oncotic pressure → fluid leaks into tissues.

Inflammation

Increases capillary permeability → localized edema.

Burns

Damage capillaries causing massive fluid shifts and hypovolemia.

Lymphedema

Edema caused by impaired lymphatic drainage.

Third Spacing

Fluid shifts into transcellular spaces, reducing effective circulation.

Ascites

Fluid accumulation in peritoneal cavity, often from liver disease.

Pulmonary Edema

Fluid in alveoli impairing gas exchange.

Chronic Venous Insufficiency

Leads to stasis ulcers and lower extremity edema.