ABG, Fluids and Electrolytes

Target range for pH

7.35-7.45

Target range for PaCO2

35-45mmHg

Target range for PaO2

70-100mmHg

Target range for SaO2

93-98%

Target range for HCO3

22-26mmol/L

Steps for interpreting ABG results

1. Evaluate oxygenation

2. Evaulate pH

3. Evaulate PaCO2

4. Evaluaten HCO3

5. Match PaCO2 or HCO3 with pH

6. Assess for complete, partial, uncomplete compensation

What is acidosis

• pH is below 7.35

• Caused by excess acid or loss of bases

What is alkalosis?

• pH is above 7.45

• Caused by excess bases or loss of acid

How does the body maintain pH homeostasis?

Through the buffer system

• Renal compensation: changes bicarb level, slower acting = 1 day

• Respiratory compensation: changes CO2 level, faster acting = minutes

Respiratory acidosis

pH less than 7.35 caused by respiratory system

Causes of respiratory acidosis

Buildup of CO2 in the blood leading to excess H+

• Sedatory drugs

• Lung diseases

• TBI

• Rib fracture

Signs and symptoms of respiratory acidosis

• Headache,

• blurred vision,

• SOB,

• lethargy,

• muscle twitching,

• convulsions.

Respiratory Alkalosis

pH greater than 7.45 caused by respiratory system

Causes of respiratory alkalosis

Anything that increases breathing rate and depth

• Anxiety

• Head injuries

• Excessive mechanical ventilation

• Responding to high metabolic rates e.g. sepsis/fever

Sign and symptoms of respiratory alkalosis

• Dizziness

• Tingling

• Confusion

• Convulsions

• Coma

Metabolic alkalosis

pH greater than 7.45 caused by the kidneys/body

Causes of metabolic alkalosis

• Severe vomitting (acid loss from stomach)

• Loop diuretics (acid secreted in urine)

• Hyperaldosteronism (kidneys reabsorb sodium but lose H+ and K+)

• Overtreatment with bicarbonate

Symptoms of metabolic alkalosis

• cramps

• Tetany

• tachycardia

• convulsions

• hyperactive reflexes

Metabolic acidosis

pH less than 7.35 caused by the kidneys and body

Causes of metabolic acidosis

1. Build up of acid

   • Renal failure e.g. can’t filter

2. Loss of bicarbonate

   • Severe diahorrea

3. Body making too much acid

   • Diabetic ketoacidosis: breakdown of fats/proteins to make acid

   • Excess lactic acid production

Signs and symptoms of metabolic acidosis

• N+V

• Anorexia

• Arrythmias

• Hypotension

• Kussmaul respirations (fast, deep breathing)

What is ICF

Intracellular fluid

• 2/3 off all body fluid

• K+ most common electrolyte

What is ECF

Extracellular fluid

• 1/3 of all body fluids

• Na+ most common electrolyte

• Contains:

  • Interstitual fluid within tissues surrounding cells

  • Plasma

What are hypotonic solutions

More diluted than blood plasma so fluid foes into cells to expand ICF and increasing total body fluid e.g. 0.45% NS

What are the uses of hypotonic solutions

• Increase total fluid

• Diabetic ketoacidosis (cells need more water due to glucose surplus)

• Gastric fluid loss e.g. V+D

What are isotonic solutions

Expand ECF only. Replenish cells from fluid loss without changing their shape e.g. 0.9% NS

What are the uses of isotonic solutions

• Burns

• Blood loss

• Dehydration

• Sepsis

• Anaphylaxis

• Surgery

What are hypertonic solutions

More concentrated than blood plasma causing flood to leave cells, shrinking cells and decreasing ICF levels e.g. dextrose 5% or 3% NS

What are the uses of hypertonic solutions

• Hyponatraemia

• Cerebral oedema

• Hypovolaemia

• Metabolic acidosis

Mechanisms of fluid intake

• Drink

• Food

• Cellular respiration

Mechanisms of fluid output

• urine

• sweat

• feces

• evaporation off skin and lungs

Mechanisms of fluid regulation

1. Thirst mechanism:

   • Triggered when osmolarity of ECF is too high, increase H2O intake

2. Anti-diuretic hormone:

   • Increase in ADH reduces water output in urine by causing water reuptake into blood (water reabsorption)

Hypovolaemia

Loss of water and electrolytes

Causes of hypovolaemia

• V+D

• Hemorrage

• Dehydration

• Sweating/diaphoresis

Symptoms of hypovolaemia

• Hypotension

• Dizziness

• Thirst

• Oliguria

• Tachycardia

• Hypoxia

• Confusion

Interventions for hypovolaemia

• Monitor input/output

• Monitor BP and labs

• Provide fluid replacement therapy

Complications of hypovolaemia

• Hypovolaemic shock = decrease MAP = disrupting perfusion of tissues

Hypervolaemia

Fluid overload / excess fluid

Causes of hypervolaemia

• Heart failure

• Renal failure

• Over hydration

• Burns

Symptoms of hypervolaemia

• Hypertension

• Tachycardia

• Oliguria

• Confusion

• Crackles in lungs

• Oedema

• Muscle weakness

Interventions for hypervolaemia

• Monitor labs and vitals

• Monitor input/output

• Chest xray

• Administer diuretics as per orders

Target range for sodium

135-145mmol/L

What is sodium important for

• Fluid balance

• Blood pressure / volume

• Active/passive transport

• Conduction of A.P. down neurons

Hypernatraemia

Sodium greater than 145mmol/L

Hypernatraemia signs and symptoms

• Decreased urine output

• Increased BP

• Fluid retention

• Oedema

• Thirst

• Restlessness

• Anxiety

• Confusion

Hyponatraemia

Sodium less than 135mmol/L

Types of hyponatraemia

1. Hypovolemic hyponatraemia: Decrease in fluid and sodium

2. hypervolemic hyponatraemia: Increase in water not proportional to sodium

Signs and symptoms of hypovolemic hyponatraemia

• Coma

• Tachycardia

• Lethargy

• N+V

Signs and symptoms of hypervolemic hyponatraemia

• Muscle weakness

• Headache

• Seizure

• orthostatic hypotension

• Cramps

Risk factors for sodium imbalance

• Increased sodium excretion e.g. diuretics

• Decreased sodium excretion e.g. kidney injury

• Increased sodium intake

• Inadequate sodium intake

• Fluid loss e.g. diarrhea

• Heart failure

• Kidney disease

Nursing considerations

• Administer IV NS per medical orders if hypovolaemic

• Administer diuretics per medical orders if hypervolemic

• Prevent falls from orthostatic hypotension

• limit water intake in hypervolemic hyponatraemia

Target range for potassium

3.5-5.2mmol/L

What is potassium essential for

• Pumping heart and musckles

• Controlling acid-base balance

Hyperkalemia

Potassium greater than 5.2mmol/L

Hyperkalemia signs and symptoms

• Bradycardia

• Hypotension

• Diarrhea

• Muscle weakness

• Confusion

• Tingling

Risk factors for hyperkalemia

• Acidosis

• Renal failure

• Uncontrolled diabetes

ECG changes in hyperkalemia

• Tall T-wave

• Prolonged PR interval

• ST-elevation

• loss of P wave

• Widening QRS

• Ventricular fibrillation

Hypokalemia

Potassium less than 3.5mmol/L

Hypokalemia signs and symptoms

• Muscle weakness

• Metabolic acidosis

• Confusion

• N+V

ECG changes for Hypokalemia

• ST depression

• Flatted T wave

• U wave after T wave

• Ventricular dysrthmias

• Bradycardia

Risk factors for Hypokalemia

• Diuretic use

• Vomitting

• Diahrrea

• Diaphoresis

Potassium imbalance considerations

• Monitor HR and rhythm

• Monitor RR and depth

• Monitor urine output

• Consider administration of loop diuretics (K+ sparing)

Electrolyte balance rules

1. Increased K+ = Decreased Na+

2. Decreased K+ = Increased Na+

3. Increased Mg2+ = Increased K+

4. Decreased Mg2+ = Decreased K+