MODULE 7: WATER ELECTROLYTE & ACID BASE DISTURBANCES

Q1: Define dehydration and classify different types

Answer:Dehydration is the condition where the body loses more fluid than it takes in, leading to an imbalance in water and electrolytes.

Classification of Dehydration:

1. Based on Sodium Content:

• Isotonic Dehydration: Equal loss of water and sodium

  • Normal serum sodium (135-145 mEq/L)
  • Common in diarrhea, vomiting

• Hypertonic Dehydration: Water loss > sodium loss

  • Elevated serum sodium (>145 mEq/L)
  • Common in diabetes insipidus, fever

• Hypotonic Dehydration: Sodium loss > water loss

  • Low serum sodium (<135 mEq/L)
  • Common in diuretic use, adrenal insufficiency

2. Based on Degree:

• Mild: 3-5% body weight loss
• Moderate: 6-9% body weight loss
• Severe: >10% body weight loss

3. Based on Volume Loss:

• Mild: <2 L fluid loss
• Moderate: 2-5 L fluid loss
• Severe: >5 L fluid loss

Q2: What are the clinical signs and symptoms of dehydration?

Answer:Clinical Signs of Dehydration:

Mild Dehydration:

• Thirst
• Dry mucous membranes
• Decreased skin turgor
• Dark yellow urine
• Decreased urine output (<0.5 mL/kg/hr)

Moderate Dehydration:

• Sunken eyes
• Sunken fontanelle (infants)
• Cool and clammy skin
• Tachycardia
• Orthostatic hypotension
• Decreased tear production

Severe Dehydration:

• Lethargy or altered mental status
• Absent tears
• Very dry mucous membranes
• Poor skin turgor
• Hypotension
• Tachycardia
• Oliguria or anuria
• Sunken eyes and cheeks

Q3: Calculate fluid requirements for different age groups

Answer:Fluid Requirements Calculation:

Holliday-Segar Method (Maintenance Fluids):

Infants and Children:

• 1st 10 kg: 100 mL/kg/day
• 2nd 10 kg: 50 mL/kg/day

• 20 kg: 20 mL/kg/day

Example:

• 25 kg child: (10×100) + (10×50) + (5×20) = 1000 + 500 + 100 = 1600 mL/day

Adults:

• 25-35 mL/kg/day or
• 1.5-2.5 L/day for average 70 kg adult

Replacement Fluids (Based on deficit):

• Mild deficit: 50 mL/kg
• Moderate deficit: 100 mL/kg
• Severe deficit: 150 mL/kg

Q4: What is hyperkalemia? Causes and management

Answer:Hyperkalemia is serum potassium level >5.5 mEq/L.

Causes:

1. Increased Potassium Intake:

   • Potassium supplements
   • Salt substitutes
   • IV potassium administration

2. Decreased Potassium Excretion:

   • Renal failure
   • Addison's disease
   • Medications (spironolactone, ACE inhibitors)

3. Shift from Intracellular to Extracellular:

   • Acidosis
   • Tissue breakdown (rhabdomyolysis, burns)
   • Insulin deficiency
   • Beta-blockers

Management:

1. ECG Changes Present:

   • Calcium gluconate 10% (10 mL IV over 10 minutes)
   • Insulin + glucose (10 units regular insulin + 50 mL 50% glucose)
   • Sodium bicarbonate (if acidotic)
   • Beta-agonists (salbutamol nebulization)

2. ECG Changes Absent:

   • Kayexalate 15-30 g orally
   • Diuretics (if renal function adequate)
   • Dialysis (if severe)

3. Severe Cases:

   • Hemodialysis
   • Peritoneal dialysis

Q5: What is hypokalemia? Causes and management

Answer:Hypokalemia is serum potassium level ❤️.5 mEq/L.

Causes:

1. Decreased Intake:

   • Starvation
   • Poor diet

2. Increased Losses:

   • Diarrhea
   • Vomiting
   • Diuretic therapy
   • Renal tubular acidosis
   • Cushing's syndrome

3. Shift to Intracellular:

   • Alkalosis
   • Insulin therapy
   • Beta-agonists

Management:

1. Mild Hypokalemia (3.0-3.5 mEq/L):

   • Oral potassium chloride 20-40 mEq/day
   • Dietary potassium supplementation

2. Moderate Hypokalemia (2.5-3.0 mEq/L):

   • Oral potassium chloride 40-80 mEq/day
   • Monitor serum potassium

3. Severe Hypokalemia (<2.5 mEq/L):

   • IV potassium chloride 10-20 mEq/hour
   • Maximum concentration: 40 mEq/L in peripheral line
   • Maximum rate: 10 mEq/hour (peripheral)
   • Maximum rate: 20 mEq/hour (central)

Precautions:

• Monitor ECG continuously
• Check serum magnesium (correct if low)
• Avoid IV bolus administration

Q6: Explain acid-base balance and pH regulation

Answer:Acid-Base Balance refers to the regulation of hydrogen ion concentration in body fluids to maintain pH within normal range.

Normal Values:

• pH: 7.35-7.45
• PaCO2: 35-45 mmHg
• HCO3-: 22-26 mEq/L
• Base Excess: -2 to +2 mEq/L

Buffer Systems:

1. Bicarbonate System (Primary):

   • CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
   • Henderson-Hasselbalch equation

2. Phosphate System:

   • HPO4- + H+ ↔ H2PO4-

3. Protein System:

   • Hemoglobin acts as buffer
   • Plasma proteins

Compensation Mechanisms:

1. Respiratory Compensation:

   • Adjust ventilation to modify CO2
   • Immediate response (minutes)

2. Renal Compensation:

   • Adjust bicarbonate reabsorption
   • Slow response (hours to days)

Q7: What is metabolic acidosis? Causes and management

Answer:Metabolic Acidosis is characterized by:

• Low pH (<7.35)
• Low HCO3- (<22 mEq/L)
• Compensatory low PaCO2

Causes (Based on Anion Gap):

Normal Anion Gap (8-12 mEq/L):

• Diarrhea
• Renal tubular acidosis
• Ureterosigmoidostomy
• Pancreatic fistula
• Acetazolamide therapy

High Anion Gap (>12 mEq/L):

• MUDPILES:
  • Methanol
  • Uremia
  • Diabetic ketoacidosis
  • Paraldehyde
  • Isoniazid/Iron
  • Lactic acidosis
  • Ethylene glycol Salicylates

Management:

1. Treat Underlying Cause

2. Sodium Bicarbonate Therapy:

   • Indications: pH <7.1, HCO3 <10 mEq/L
   • Dose: HCO3 deficit = 0.3 × weight (kg) × (desired HCO3 - actual HCO3)
   • Give 1/2 to 2/3 of calculated dose initially
   • Monitor pH, HCO3, sodium

3. Supportive Care:

   • Maintain adequate ventilation
   • Monitor cardiac function
   • Correct associated electrolyte abnormalities

Q8: What is metabolic alkalosis? Causes and management

Answer:Metabolic Alkalosis is characterized by:

• High pH (>7.45)
• High HCO3- (>26 mEq/L)
• Compensatory high PaCO2

Causes (Based on Chloride Responsiveness):

Chloride Responsive (Urine Cl <20 mEq/L):

• Vomiting
• Nasogastric suction
• Diuretic therapy
• Post-hypercapnic state
• Volume depletion

Chloride Resistant (Urine Cl >20 mEq/L):

• Primary hyperaldosteronism
• Cushing's syndrome
• Licorice ingestion
• Bartter syndrome
• Gitelman syndrome

Management:

1. Chloride Responsive Alkalosis:

   • Normal saline infusion (0.9% NaCl)
   • Volume expansion
   • Correct hypokalemia

2. Chloride Resistant Alkalosis:

   • Treat underlying cause
   • Potassium chloride supplementation
   • Spironolactone if hyperaldosteronism

3. Severe Alkalosis (pH >7.6):

   • Hydrochloric acid 0.1-0.2 M IV
   • Acetazolamide 250-500 mg IV/PO
   • Ammonium chloride PO

Q9: Calculate anion gap and interpret results

Answer:Anion Gap = Na+ - (Cl- + HCO3-) Normal Range: 8-12 mEq/L

Formula with Potassium: Anion Gap = (Na+ + K+) - (Cl- + HCO3-) Normal Range: 12-16 mEq/L

Clinical Significance:

Increased Anion Gap (>12 mEq/L):

• Metabolic acidosis due to:
  • Organic acids accumulation
  • Inorganic acids accumulation
  • Unmeasured anions

Decreased Anion Gap (<8 mEq/L):

• Hypoalbuminemia (albumin normal anion)
• Multiple myeloma (cationic proteins)
• Lithium intoxication
• Bromide intoxication

Correction for Hypoalbuminemia:

• Corrected AG = Measured AG + 2.5 × (4 - albumin g/dL)
• Normal albumin: 4 g/dL
• Each 1 g/dL decrease in albumin decreases AG by 2.5 mEq/L

Example Calculation:

• Na+: 140 mEq/L
• Cl-: 105 mEq/L
• HCO3-: 20 mEq/L
• AG = 140 - (105 + 20) = 15 mEq/L (increased)

Q10: What is respiratory acidosis? Causes and management

Answer:Respiratory Acidosis is characterized by:

• Low pH (<7.35)
• High PaCO2 (>45 mmHg)
• Compensatory high HCO3-

Causes:

Acute Respiratory Acidosis:

• Acute respiratory failure
• Drug overdose (opioids, sedatives)
• Chest wall trauma
• Pneumothorax
• Pulmonary embolism
• Severe asthma attack

Chronic Respiratory Acidosis:

• COPD
• Obesity hypoventilation syndrome
• Neuromuscular diseases
• Chest wall deformities

Management:

1. Improve Ventilation:

   • Airway management
   • Bronchodilators (if COPD/asthma)
   • Mechanical ventilation

2. Treat Underlying Cause:

   • Pneumonia → Antibiotics
   • Pneumothorax → Chest tube
   • Drug overdose → Antagonists

3. Mechanical Ventilation:

   • Monitor PaCO2 and pH
   • Avoid overcorrection
   • Use controlled ventilation initially

Compensation:

• Acute: HCO3 increases 1 mEq/L for every 10 mmHg PaCO2 increase
• Chronic: HCO3 increases 4 mEq/L for every 10 mmHg PaCO2 increase

Q11: What is respiratory alkalosis? Causes and management

Answer:Respiratory Alkalosis is characterized by:

• High pH (>7.45)
• Low PaCO2 (<35 mmHg)
• Compensatory low HCO3-

Causes:

Central Stimulation:

• Anxiety/hyperventilation
• Pain
• Fever
• Sepsis
• CNS disorders (stroke, tumor)
• Drugs (salicylates, progesterone)

Peripheral Stimulation:

• High altitude
• Pulmonary embolism
• Pneumonia
• Asthma
• CHF

Management:

1. Treat Underlying Cause:

   • Psychological support/anxiolytics
   • Pain management
   • Antibiotics for infection
   • Oxygen for hypoxemia

2. Breathing Techniques:

   • Rebreathing into paper bag
   • Slow breathing exercises
   • Controlled ventilation

3. Medications:

   • Anxiolytics if panic disorder
   • Beta-blockers for anxiety

Compensation:

• Acute: HCO3 decreases 2 mEq/L for every 10 mmHg PaCO2 decrease
• Chronic: HCO3 decreases 5 mEq/L for every 10 mmHg PaCO2 decrease

Q12: Calculate fluid deficit and replacement therapy

Answer:Fluid Deficit Calculation:

Percentage Method:

• Mild dehydration: 5% body weight
• Moderate dehydration: 10% body weight
• Severe dehydration: 15% body weight

Example: 70 kg adult with 10% dehydration

• Fluid deficit = 70 kg × 0.10 = 7 L

Replacement Therapy:

Phase 1: Resuscitation (First 1-2 hours)

• Give 20-30 mL/kg of isotonic fluid
• Monitor vital signs, urine output
• Adults: 1-2 L rapidly

Phase 2: Correction (Next 24 hours)

• Replace remaining deficit over 24-48 hours
• Add maintenance fluids
• Monitor electrolytes

Phase 3: Maintenance

• Continue maintenance fluids
• Replace ongoing losses

Fluid Choice:

• Isotonic dehydration: 0.9% NaCl or Ringer's lactate
• Hypertonic dehydration: 0.45% NaCl
• Hypotonic dehydration: 0.9% NaCl

Monitoring:

• Weight changes
• Urine output (>0.5 mL/kg/hr)
• Vital signs
• Electrolyte levels

Q13: What are the different types of IV fluids?

Answer:Classification of IV Fluids:

1. Crystalloids:

Isotonic Crystalloids:

• 0.9% Sodium Chloride (Normal Saline):

  • Na+: 154 mEq/L
  • Cl-: 154 mEq/L
  • Uses: Volume expansion, resuscitation

• Ringer's Lactate:

  • Na+: 130 mEq/L, K+: 4 mEq/L, Ca2+: 3 mEq/L
  • Lactate: 28 mEq/L
  • Uses: Volume expansion, surgery

• Plasma-Lyte (Balanced Salt Solution):

  • Similar to plasma electrolyte composition
  • Uses: General purpose resuscitation

Hypotonic Crystalloids:

• 0.45% Sodium Chloride (Half Normal Saline):

  • Na+: 77 mEq/L
  • Uses: Hypertonic dehydration

• D5W (5% Dextrose in Water):

  • Free water administration
  • Uses: Hypernatremia, maintenance

Hypertonic Crystalloids:

• 3% Sodium Chloride:
  • Na+: 513 mEq/L
  • Uses: Severe hyponatremia, cerebral edema

2. Colloids:

• Albumin (5%, 25%)
• Hespan (Hetastarch)
• Dextran (40, 70)

3. Parenteral Nutrition:

• Dextrose solutions: D5W, D10W, D20W
• Amino acid solutions
• Lipid emulsions

Q14: How to manage hypernatremia?

Answer:Hypernatremia is serum sodium >145 mEq/L.

Causes:

1. Water Loss > Sodium Loss:

   • Diabetes insipidus
   • Fever, burns
   • Diarrhea, vomiting
   • Hyperventilation

2. Sodium Gain:

   • Salt poisoning
   • Hypertonic saline administration
   • Conn's syndrome

Management:

1. Calculate Water Deficit: Water deficit = 0.6 × body weight (kg) × (1 - 140/serum Na)

2. Rate of Correction:

• Acute hypernatremia (<24 hours): Correct rapidly
• Chronic hypernatremia (>24 hours): Maximum 0.5 mEq/L/hour
• Maximum change: 12 mEq/L in 24 hours

3. Fluid Selection:

• If hypotonic fluids needed: D5W or 0.45% NaCl
• If hypertonic fluids needed: 3% NaCl

4. Treatment Algorithm:

• Severe symptoms (seizures, coma): 3% NaCl 1-2 mL/kg over 10 minutes
• Mild-moderate hypernatremia:
  • Calculate water deficit
  • Use D5W (if no glucose intolerance)
  • Target correction: 0.5 mEq/L/hour

5. Monitoring:

• Serum sodium every 2-4 hours
• Neurological status
• Fluid balance

Complications of Overcorrection:

• Cerebral edema
• Seizures
• Permanent neurological damage

Q15: How to manage hyponatremia?

Answer:Hyponatremia is serum sodium <135 mEq/L.

Causes (Based on Volume Status):

Hypovolemic Hyponatremia:

• Diuretics
• Vomiting, diarrhea
• Salt-wasting nephropathy

Euvolemic Hyponatremia:

• SIADH (Syndrome of Inappropriate ADH)
• Hypothyroidism
• Adrenal insufficiency
• Psychogenic polydipsia

Hypervolemic Hyponatremia:

• CHF
• Cirrhosis
• Nephrotic syndrome
• Renal failure

Management:

1. Severity Assessment:

• Mild: Na 130-134 mEq/L
• Moderate: Na 125-129 mEq/L
• Severe: Na <125 mEq/L

2. Symptom Assessment:

• Mild symptoms: Nausea, headache
• Moderate symptoms: Confusion, lethargy
• Severe symptoms: Seizures, coma

3. Treatment Approach:

Emergency Treatment (Severe Symptoms):

• 3% NaCl 1-2 mL/kg/hr
• Monitor serum sodium every 1-2 hours
• Stop if symptoms improve

Chronic Hyponatremia:

• Restrict fluid intake (800-1000 mL/day)
• Salt tablets if volume depleted
• Loop diuretics if volume overloaded
• Demeclocycline if SIADH

4. Correction Rate:

• Maximum correction: 8 mEq/L in 24 hours
• Maximum rate: 0.5 mEq/L/hour
• Risk of osmotic demyelination if corrected too rapidly

5. Monitoring:

• Serum sodium every 4-6 hours initially
• Neurological status
• Fluid balance

Q16: What is SIADH? Diagnosis and management

Answer:SIADH (Syndrome of Inappropriate Antidiuretic Hormone) is characterized by excessive ADH secretion leading to water retention and hyponatremia.

Diagnostic Criteria:

1. Hyponatremia: Serum Na <135 mEq/L
2. Hypo-osmolality: Serum osmolality <275 mOsm/kg
3. Inappropriately concentrated urine: Urine osmolality >100 mOsm/kg
4. Euvolemia: No signs of dehydration or edema
5. Elevated urine sodium: >40 mEq/L with normal salt intake
6. Normal thyroid and adrenal function
7. No diuretic use

Causes:

1. Malignancies: Small cell lung cancer, lymphoma
2. CNS disorders: Stroke, tumor, infection
3. Pulmonary diseases: Pneumonia, COPD
4. Medications: SSRIs, carbamazepine, vincristine
5. Postoperative state

Management:

1. Fluid Restriction:

   • First-line treatment
   • 800-1000 mL/day
   • Monitor weight and urine output

2. Salt Tablets:

   • If severe hyponatremia
   • 3-6 g/day NaCl

3. Loop Diuretics:

   • Furosemide 40-80 mg/day
   • Enhances water excretion

4. Demeclocycline:

   • 600-1200 mg/day
   • Causes nephrogenic diabetes insipidus

5. Vasopressin Antagonists:

   • Conivaptan, Tolvaptan
   • For severe cases

6. Hypertonic Saline:

   • For severe symptoms
   • 3% NaCl infusion

Monitoring:

• Serum sodium every 6-12 hours
• Serum osmolality
• Urine osmolality and sodium

---

Module 7 focuses on comprehensive understanding of fluid, electrolyte, and acid-base disorders essential for anesthesia practice.