Fluid, Electrolyte, and Acid-Base Imbalances – Core Vocabulary

Body Water, Homeostasis, and Functions

• Water ≈ 60 % of adult male body weight, 50 % female, 70 % infant (↓ to ≈45 % in elderly women) Key: Blue- facts Red- Headers

• Central to homeostasis; acts as:

  • Medium for metabolic reactions

  • Transport system (blood, lymph, secretions)

  • Lubricant & cushion for joints, organs, CSF

  • Facilitator of movement (muscle, GI, lungs)

• Input must equal output (≈2500\,\text{mL·day}^{-1}):

  • Sources: liquids (1200 mL), solid foods (1000 mL), cell metabolism (300 mL)

  • Losses: urine (1400 mL), feces (200 mL), lungs (400 mL), skin (500 mL)

Fluid Compartments and Typical Volumes

• Intracellular Fluid (ICF): Most of the intracellular fluid is pottassium

  • ≈28\text{ L} (40 % body weight adult male)

• Extracellular Fluid (ECF): subdivided into. Most of the fluid made up of extracellular fluid is sodium

  • Intravascular fluid (IVF/plasma) ≈4–5 %

  • Interstitial fluid (ISF) ≈10–15 %

  • Cerebrospinal fluid (CSF)

  • Transcellular fluids (synovial, pericardial, pleural, ocular, GI secretions)

• Total water ≈43\text{ L} (60 % adult male)

Regulation of Water & Electrolytes

• Thirst → osmoreceptors (hypothalamus) trigger intake - this is what makes ypur brain say “hey you are thirsty”

• Antidiuretic Hormone (ADH) → ↑ water re-absorption in renal distal tubules & collecting ducts Makes you pee less and hold onto fluids (diabeetes insipidous for example)

• Aldosterone → ↑ Na^+ & water re-absorption. does the sodium balancing in the kidneys

• Atrial & B-type Natriuretic Peptides (ANP, BNP/T-type) → ↑ Na^+/water excretion, inhibit RAAS, vasodilate

Movement of Water Between Compartments

• Governed by filtration & osmosis across semipermeable capillary membranes

• Hydrostatic pressure (pushing) vs. Osmotic/oncotic pressure (pulling). Osmosis to keep things even by balancing the sodium content/ diffusion is the substance that is moving

  • Water flows from \text{low\ solute}\;\to\;\text{high\ solute} concentration

• Normal starling forces example (arteriolar end):

  • P_{hydro}^{IVF}=30\,\text{mmHg} outward

  • \pi_{oncotic}^{IVF}=25\,\text{mmHg} inward

Fluid Excess Intracential Intracential fluid

• Definition: excess ISF → visible swelling, possible weight gain

• Clinical forms: localized (injury, allergic), generalized (anasarca), pulmonary, cerebral, ascites

Etiologies

• ↑ Capillary hydrostatic pressure (HTN, hypervolemia, CHF, pregnancy) → forces fluid out

• ↓ Plasma oncotic pressure (loss of albumin via malnutrition, nephrosis, burns)

• ↑ Capillary permeability (inflammation, infection, toxins, large burns)

• Lymphatic obstruction (tumor, surgical removal, radiation) → protein-rich localized edema

Consequences

• Pitting edema (indent persists)

• Functional impairment: ↓ joint ROM, ↓ vital capacity, impaired diastolic filling

• Pain (pressure on nerves; organ capsule stretch)

• ↓ arterial circulation → ischemia, skin breakdown, ulcers, infection; dental fitting issues

• Drug trapping in ISF (↓ therapeutic effect)

Fluid Deficit — Dehydration

• Caused by ↓ intake, ↑ loss, or both; severe in infants & elderly

Common Causes

• Vomiting/diarrhea, excessive sweating, diabetic ketoacidosis (osmotic diuresis), limited access to water, concentrated infant formula

Manifestations

• Dry mucosa, ↓ skin turgor, sunken eyes & fontanelles (infant)

• Rapid weak pulse, ↓ BP, orthostatic hypotension

• ↑ hematocrit, ↑/variable electrolytes, high urine specific gravity with low volume

• Fatigue, dizziness, confusion → LOC

• Tachypnea

Compensation

• ↑ thirst & HR, cutaneous vasoconstriction, oliguria with concentrated urine

Third-Spacing

• Fluid trapped in cavity/ISF (burns: ↑ ISF osmotic pressure; sepsis: ↑ capillary permeability). Non-functional until reabsorbed Third spacing can occur hours after injury

Major Electrolyte Distribution (typical, mEq·L⁻¹)

• [Na^+]{ICF}\approx10 vs [Na^+]{plasma}\approx142

• [K^+]{ICF}\approx160 vs [K^+]{plasma}\approx4

• [Ca^{2+}]_{plasma}\approx5 (ionized) — largely extracellular

• [Mg^{2+}]{ICF}\approx35,\ [Mg^{2+}]{plasma}\approx3

• Bicarbonate [HCO3^-]{plasma}\approx27; Chloride [Cl^-]{plasma}\approx103; Phosphate [HPO4^{2-}]_{ICF}\aHyponatremia

Sodium Imbalances

Hyponatremia (Sodium level 135-145) Hyponatremia is below 135

• Loss via sweating, vomiting, diarrhea; diuretics + low-salt diet; endocrine (↓ aldosterone, adrenal insuff., ↑ ADH), excessive water intake/IV D5W, renal losses (osmotic diuresis)

• This can also be casued by increased water intake (drinking gallons and gallons of water)

• Effects:

  • Cellular swelling → fatigue, cramps, nausea

  • ↓ ECF osmotic pressure → hypovolemia, ↓ BP

  • Cerebral edema → headache, confusion, seizures

  • Charlie horse or cramps

Hypernatremia (Sodium level 135-145) Hypernatremia is above 145

• Etiology: ↓ ADH (diabetes insipidus), lack of thirst, watery diarrhea, prolonged tachypnea, excessive Na^+ intake (tube feeding, hypertonic IV) w/ inadequate water

• Excessive consumption of salt or not drinking water

• Effects: thirst, dry tongue, rough mucosa, edema, agitation, ↑ BP

Potassium Imbalances (life-threatening cardiac effects)

Hypokalemia (Potassium level 3.5-5 mEq/L) hypo less than 3.5mEq

• Causes: diarrhea, loop/thiazide diuretics, hyperaldosteronism/Cushing, insufficient intake, insulin treatment of DKA

• Manifestations:

  • Cardiac dysrhythmias → cardiac arrest (flattened T-wave, U-wave) always effects the ehart

  • Neuromuscular: muscle weakness, paresthesias, ↓ GI motility, shallow respirations, polyuria (↓ ADH response)

Hyperkalemia (Potassium level 3.5-5 mEq/L) Hyperkalemia is more potassium that 5

• Causes: renal failure, K^+-sparing diuretics, hypoaldosteronism, extensive tissue damage/burns, acidosis (H^+/K^+ shift)

• Manifestations:

  • ECG changes (tall peaked T or exagerated T wave, widened QRS) → VT/VF, arrest

  • Muscle weakness → paralysis, respiratory failure

  • Paresthesias, nausea, oliguria

• Relationship: acidosis drives K^+ extracellularly (and vice-versa)

Calcium Imbalances

Hypocalcemia (9-10.5 mg/dL) hypo less than 9

• Etiologies: hypoparathyroidism, malabsorption/vit D deficit, ↓ albumin, alkalosis, renal failure ( the parathyroid is the ontroler of the calcium)

• Can be casued with the removal of the thyroid when Dr takes parathyroid glands

• Effects: ↑ neuromuscular excitability → tetany (Chvostek & Trousseau signs), muscle twitch, paresthesias; weak heart contractions → dysrhythmia, ↓ BP

• Trousseaus signs when the arm flexes alone with blood pressure cuff or Chyosteks sign when you flip the cheek and the face twitches

Hypercalcemia (Calcium level 9-10.5 mg/dL) hyper is more than 10.5

• Causes: hyperparathyroidism, malignancy (bone tumors), immobility, excess vit D/Ca intake, milk-alkali syndrome (when the bones release excess calcium, high calcium levels may indicate cancer)

• Effects: ↓ neuromuscular activity (weakness, lethargy), GI upset, polyuria (ADH resistance), renal stones, ↑ cardiac contractility & dysrhythmias

Magnesium (useful in L&D)

• Hypomagnesemia: malnutrition, alcoholism, diuretics, DKA, hyperthyroid → ↑ neuromuscular irritability, cardiac dysrhythmia (up to 65% of ICU patients)

• Hypermagnesemia: renal failure → CNS depression, hyporeflexia (can be caused by medications) Causes diarrhea

Phosphate 3-4.5 mg/dL

• Functions: bone/teeth, ATP, buffer, cell membrane; inverse with Ca^{2+}

• Hypophosphatemia: malabsorption, diarrhea, antacids

• Hyperphosphatemia: renal failure

• super close with calcium they work hand in hand to make bones

Chloride 98-106 mEq/L

• Major ECF anion; parallels Na^+

• Hypochloremia usually with alkalosis (early vomiting → loss of HCl, chloride shift: HCO_3^- exits RBC to plasma)

• Hyperchloremia: excess NaCl intake → metabolic acidosis possibility

• Chloride follows sodium follows the same basis as hypo and hypernatremia

Acid–Base Balance Basics

• Normal serum pH 7.35\text{–}7.45; death < 6.8 or > 7.8 -blood

• Normal CO2 35-45 -respiratory

• Bicarb HCO3- normal 22-26 - kidney function

• Respiratory rate effects PH level faster than kidneys however the kidneys are more effective

• 3 lines of defense:

  • Buffers (instantaneous)

  • Respiratory (minutes) alters CO2 → H2CO_3

  • Renal (hours–days) excrete H^+, regenerate HCO_3^-$$ (most powerful)

Classification of Imbalances

• Respiratory Acidosis (↑ PCO₂) : hypoventilation, COPD, drugs, airway obstruction- when the Co2 level is high common with COPD patients

• Respiratory Alkalosis (↓ PCO₂) : hyperventilation (anxiety, pain, fever, ASA OD), brain stem lesion- when the Co2 levels are low most common in anxiety (when the cartoons do the paper bag)

• Metabolic Acidosis (↓ HCO₃⁻) : diarrhea, DKA, shock/lactic, renal failure - most common with diarrhea

• Metabolic Alkalosis (↑ HCO₃⁻) : vomiting/NG suction, hypokalemia, antacid excess -most common with vomitting

• Alkolosis is when the PH goes to >7.45

• Acidosis is when PH goes <7.35

Compensation & Decompensation

• Compensation seeks to restore 20:1 ratio, may normalize pH but underlying values abnormal

• Decompensation when buffering/respiratory/renal limits exceeded → life-threatening

Representative Lab Patterns (Table 2-8)

• Example compensated respiratory acidosis: ↑ PCO₂, ↑ HCO₃⁻, pH ≈7.38

Clinical Effects

• Acidosis: CNS depression → headache, lethargy → coma; Kussmaul respirations; acidic urine

• Alkalosis: CNS irritability → restlessness, tetany, seizures; hypokalemia often accompanies

Treatment Principles

• Correct underlying etiology (e.g., insulin for DKA, antidote for salicylates, adjust ventilation)

• Replace or remove fluids/electrolytes cautiously to avoid rapid shifts

• Bicarbonate infusion for severe metabolic acidosis

• Modify diet (electrolyte content, protein, fluid)

• Dialysis or mechanical ventilation where indicated

Things mentioned specifically in class

• fluid loss happens with Urine, sweat, feces, and intake happens excatly how it sounds when you drink or IV

• Hypotonic water moving in, isotonic means equal not a lot of shifting, Hypertonic is when the fluid is leaving the cell. Things are always trying to shift to find a balance or homeostasis

• Normak ranges sodium 135-145, calcium 9-10.5, potassium- 3.5-5, magnesium- 1.3-2.1, chloride- 98-106, phosphurus- 3-4.5 chloride- 95-105