Metabolic Alkalosis – Definition, etiology and treatment - John Ingram, CCP

John Ingram, CCP gives an excellent review on metabolic alkalosis and how it is treated in the critical care unit. John describes the etiology, clinical significance of and also the degree to which this finding is understood and treated. 

Introduction to Metabolic Alkalosis

Metabolic alkalosis is a biochemical disturbance characterized by an increase in arterial blood pH above 7.45, primarily due to an increase in plasma bicarbonate or a loss of hydrogen ions. This condition is pivotal in clinical settings as it impacts various physiological processes and can complicate the management of patients undergoing procedures like cardiopulmonary bypass and ECMO.

Detailed Etiology

The causes of metabolic alkalosis can be broadly categorized based on their origin:

• Gastrointestinal Losses: Conditions such as prolonged vomiting or excessive gastric suction can lead to significant losses of gastric acid, which is rich in hydrogen ions.
• Renal Causes: Excessive use of certain diuretics can lead to increased renal excretion of hydrogen ions. Additionally, conditions like Conn's syndrome that involve excessive aldosterone production also contribute by promoting renal reabsorption of sodium and water, which leads to hydrogen ion loss.
• Increased Bicarbonate: This can occur through excessive intake of bicarbonate through diet or medications or through endogenous overproduction in certain metabolic disorders.
• Intracellular Shifts: Hypokalemia can cause potassium to move out of cells, compensating by moving hydrogen ions into cells, which reduces extracellular hydrogen ion concentration, leading to alkalosis.

Clinical Manifestations

The effects of metabolic alkalosis range from subtle physiological changes to severe, life-threatening conditions. One critical aspect is the leftward shift of the oxygen-hemoglobin dissociation curve, which impairs oxygen delivery to tissues. This phenomenon can lead to:

• Neuromuscular excitability
• Arrhythmias
• Decreased myocardial contractility
• Confusion and other neuropsychiatric symptoms

Diagnostic Approach

Diagnosis involves a thorough assessment including:

• Arterial Blood Gases: Elevated blood pH and bicarbonate levels are key indicators.
• Serum Electrolytes: Imbalances in potassium, chloride, and calcium can provide clues to the underlying cause.
• Clinical History: Understanding the patient's medical history, medication use, and symptoms are crucial for identifying potential causes.

Management Strategies

The management of metabolic alkalosis involves:

• Addressing Underlying Causes: Whether it's adjusting medication, managing fluid losses, or treating associated medical conditions.
• Fluid and Electrolyte Replenishment: Essential for restoring balance, especially in cases caused by dehydration or diuretics.
• Acid Administration: In severe cases, careful administration of acids like hydrochloric acid may be necessary.
• Continuous Monitoring: Vital signs, blood gases, and electrolytes must be monitored closely, especially in severe cases requiring intensive care.

Special Considerations for Perfusionists

Perfusionists must be vigilant about metabolic alkalosis during procedures such as cardiopulmonary bypass and ECMO because:

• Impact on Equipment Performance: Alkalotic blood can affect the operation and outcomes of extracorporeal circulation systems.
• Patient Safety: Managing pH levels is critical to ensuring oxygen delivery and preventing complications like hypoxia and arrhythmias.

Conclusion

Understanding and managing metabolic alkalosis is critical for perfusionists and other healthcare professionals involved in the care of patients undergoing complex medical procedures. This condition requires an integrated approach to treatment, combining rapid diagnostic assessments with targeted therapeutic interventions to ensure the best patient outcomes.