Respiratory Alkalosis
Respiratory Alkalosis
David Ray Velez, MD
Table of Contents
Definition
Definition: An Acid-Base Disorder with Alkalosis (Elevated pH) Due to Excessive Respiratory Elimination of pCO2
Arterial Blood Gas (ABG) Analysis
- General Levels in a Primary Respiratory Alkalosis:
- pH > 7.45
- pCO2 < 35 mmHg
- *See Arterial Blood Gas (ABG) Analysis
Causes
Hyperventilation – The Primary Mechanism of All Causes of Respiratory Alkalosis
Central Causes
- Traumatic Brain Injury (TBI)
- Psychogenic – Anxiety, Pain, Fear, or Stress
- Stroke (CVA)
- Salicylate Intoxication (Early Stages)
Pulmonary Causes
- Pulmonary Embolism (PE)
- Pneumonia
- Pulmonary Edema
- Asthma
- Hypoxemia
Can Be Induced by Excessive Ventilation When Mechanically Ventilated
Physiologic Changes of Alkalosis
Pulmonary Changes
- Inhibition of Respiratory Drive and Decreased Respiratory Rate
- Left-Shift of the Oxygen-Hemoglobin Dissociation Curve (Increased Affinity)
Cardiovascular Changes
- Increased Risk of Arrhythmia
- Increased Systemic Vascular Resistance (SVR) and Arterial Vasoconstriction
Hematologic Changes
- Minimal Effects on Coagulation
Renal Changes
- Increased Bicarbonate Secretion
Electrolyte Changes
- Hypokalemia – From Intracellular Shifts
- Hypocalcemia – From Increased Calcium Binding to Albumin
Neurologic Changes
- Cerebral Vasoconstriction and Decreased Intracranial Pressure (ICP)
- Decreased Cerebral Blood Flow
- Lightheadedness and Confusion
Acuity/Compensation
Respiratory Acid-Base Disorders are Compensated by Renal Changes in Bicarbonate Reabsorption (Slow Process Over Days-Weeks)
Acuity/Compensation
- Acute Respiratory Alkalosis – High pH Changes are Seen with Minimal Compensation
- Chronic Respiratory Alkalosis – pH More Normalized Due to Renal Compensation Over Days-Weeks with Decreased Reabsorption of Bicarbonate
Expected Change in Bicarbonate
- Acute Respiratory Alkalosis: HCO3 = 24 – 2 x (40 – pCO2) / 10
- Chronic Respiratory Alkalosis: HCO3 = 24 – 5 x (40 – pCO2) / 10
- Mnemonic: “1-2-3-4-5 Rule”
- Expected Change in HCO3 (mEq/L) for Every 10 mmHg Change in pCO2 Due to Respiratory Acid-Base Disorders
| Acute | Chronic | |
| Respiratory Acidosis (↑ CO2) | ↑ 1 | ↑ 4 |
| Respiratory Alkalosis (↓ CO2) | ↓ 2 | ↓ 5 |
Treatment
Treatment
- Primarily Managed by Treatment of the Underlying Cause