Abnormalities in Acid-Base Balance, Exams of History

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ABNORMALITIES IN

ACID-BASE BALANCE

• Many critical illnesses can disturb acid-base balance.
• Acid-base disturbances may indicate an underlying

disease or organ damage.

• Accurate interpretation of acid-base disturbances requires

the following:

 Arterial blood gases.  Plasma electrolytes.  Knowledge of the compensatory physiologic mechanisms.

Abnormalities in Acid-Base Balance

(Appel & Downs. 2008. Understanding acid-base balance)

Abnormalities in Acid-Base Balance

Acidosis Alkalosis

HCO3 − PCO ↑↑ PCO 2

Respiratory

↓↓ HCO 3-

Metabolic

↓↓ PCO 2

Respiratory

↑↑ HCO 3-

Metabolic

• Acid-base disorders are classified by changes in pH, PCO 2

and HCO 3 -

• There are 4 primary acid-base disorders:

 Respiratory acidosis: ↑ PCO 2  Respiratory alkalosis: ↓ PCO 2  Metabolic acidosis: ↓ [HCO 3 - ]  Metabolic alkalosis: ↑ [HCO 3 - ]

• The body normally attempts to correct the primary acid-

base disturbances by a secondary or compensatory

response trying to restore pH towards normal.

 The kidneys compensate for primary respiratory disorders.  The lungs compensate for primary metabolic disorders.

Fundamentals in Acid-Base Disorders

(Dooley & Sisson. Acid-base disorders)

• Respiratory acidosis = ↓ pH + ↑ PCO

 Due to alveolar hypoventilation.

Respiratory Acidosis

Causes of respiratory acidosis

Alveolar hypoventilation

Depression of respiratory center Opioid ingestion Head injury

Lung disease COPD Pneumonia Pulmonary edema

• Respiratory alkalosis = ↑ pH + ↓ PCO

 Due to alveolar hyperventilation.

Respiratory Alkalosis

Causes of respiratory alkalosis

Alveolar hyperventilation

Mechanical hyperventilation

Anxiety

Metabolic acidosis = ↓pH due to ↓ [HCO 3 - ]

 Due to acid gain.

 Due to loss of HCO 3

Metabolic Acidosis

Causes of metabolic acidosis

↑ body acids

↑ acid production Lactic acidosis Diabetic ketoacidosis Salicylate poisoning Starvation

↓ a cid elimination Renal failure

↑ HCO3 loss

Through kidneys (RTA)

Through GIT (diarrhea) (Appel & Downs. 2008. Understanding acid-base balance; Dooley & Sisson. Acid-base disorders)

Primary Disturbance Compensatory Mechanism

Respiratory Acidosis Increase HCO

Respiratory Alkalosis Decrease HCO

Metabolic Acidosis Decrease PCO

Metabolic Alkalosis Increase PCO

Compensatory Mechanisms

Summary of Primary Acid-Base Disorders

pH PCO2 (mmHg) HCO3 (mEq/L)

Normal 7.35-7.45 35-45 22-

Respiratory acidosis

Decrease Increase Increase

Respiratory alkalosis

Increase Decrease Decrease

Metabolic acidosis

Decrease Decrease Decrease

Metabolic alkalosis

Increase Increase Increase

Simple Acid-Base Disturbances

• A patient known to have COPD presented with 3-day

history of fever, SOB, and cough productive of yellowish

sputum. His ABGs showed:

• pH = 7.
• PCO2 = 80 mmHg.
• HCO3- = 34 mEq/L.

Case study 1

• A 2-year old child who is lethargic and dehydrated has a

3-day history of vomiting. His ABGs showed:

• pH = 7.
• PCO2 = 44 mmHg
• HCO3- = 37 mEq/l

Case study 3

• A 20-year old student suffered a panic attack while

awaiting an exam. Her ABGs showed:

• pH = 7.
• PCO2 = 24 mmHg.
• HCO3 = 23 mEq/L.

Case study 4