1.8 - Respiratory Acidosis & Alkalosis Flashcards
What is respiratory acidosis?
- It is a ventilatory process that increases hydrogen; pH less than 7.35
- It is identified by an increase in arterial pCO2 greater than 45 mmHg
- Metabolic alkalosis seen as compensating process
What causes respiratory acidosis?
Respiratory academia occurs when a failure (either acute or chronic) in ventilation occurs. The manifestations of respiratory academia are often overshadowed by the symptoms of hypoxia the patient may be exhibiting.
What are the 5 causes for acute respiratory acidosis ?
1. CNS depression - can be caused by opiates (main cause), sedatives additive effect to opiates
2. CNS injury - brain stem injury, CVA
3. Neuromuscular disease
- Myasthenia Gravis
- Guillain-Barre’ syndrome
- Poliomyelitis
4. Airway obstruction
- Mucus/foreign body
- Severe bronchospasm of status asthmaticus
- Bronchitis
- Emphysema
5. Disorders of the chest
- Flair chest
- Pneumothorax
- Kyphoscoliosis
What are the 3 causes for chronic respiratory acidosis?
- COPD
- Obesity – Pickwickian hypoventilation syndrome
- Diaphragmatic weakness/paralysis
What are the subjective exam findings associated with respiratory acidosis (acute/chronic)?
Acute respiratory acidosis:
- Decreased level of consciousness, drowsiness to coma
- Mental changes
- Headache
- Anxiety
- Confusion
- Hallucinations
- Dyspnea
Chronic respiratory acidosis:
- CNS symptoms
- Sleep disturbances
- Memory loss
Neuromuscular changes:
- Impaired coordination
- Tremor
What causes the subjective symptoms associated with respiratory acidosis?
- The symptoms of respiratory acidosis result from changes in the cerebrospinal fluid (CSF) pH.
- A very severe hypercapnia may be well tolerated if it is accompanied by renal compensation and a relatively normal pH. Conversely, only a slight rise in pCO2 may cause extreme symptoms if it occurs acutely.
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Signs and symptoms of respiratory acidosis are also directly attributed to CO2 retention and are: bradypnea, drowsiness, confusion, papilledema and asterix.
- These are generally not seen until the CO2 is 70 mmHg or higher
What are the physical exam findings associated with respiratory acidosis (acute/chronic)?
Acute respiratory acidosis:
- Blood pressure elevation
- CNS signs
- Altered mental status or level of consciousness
- Papilledema
Chronic respiratory acidosis:
- CNS signs: none or mild tremor
- Cardiovascular: you may see signs of cor pulmonale
- Right ventricular heave
- Pulmonary diastolic murmur
- Cyanosis
- Pulmonary: signs of COPD
- Increased anterior-posterior chest diameter
- Expiratory wheeze
- Accessory respiratory muscle use
What laboratory/diagnostic tests are done to diagnose respiratory acidosis?
- ABG: pH, pCO2, pO2 and calculated HCO3
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Pulmonary Function tests
- Decreased forced expiratory volume in 1 second (FEV1)
- Increased residual volume
What is the treatment of acute respiratory acidosis based on?
- Treatment should be based on patient symptoms and degree of acidemia.
- If a patient has mild respiratory acidemia (pH 7.30-7.35) they can be observed while the causes are explored and corrected.
- A patient with moderate respiratory acidemia (7.20-7.29) is on the edge of life threatening ventricular arrhythmias.
- Patients with severe respiratory acidemia (pH 7.19 or lower) is at high risk for cessation of spontaneous respirations and ventricular arrhythmias.
How do you treat a patient with acute respiratory acidosis?
1. Assist ventilation
- Facemask for continuous positive airway pressure
- Airway intubation with mechanical ventilation
2. Reverse CNS depression if appropriate
- Naloxone (Narcan) 0.4-2 mg IV for opioid overdose
- Flumazenil (Romazicon) 0.2 mg (2 ml) IV over 30 seconds for benzodiazepine overdose (observe for seizures)
3. Reverse Airway obstruction
- Bronchodilator therapy for bronchospasm with Albuterol (Ventolin, Proventil) 180 mcg inhaled Q6H Ipratropium (Atrovent) 36 mc inhaled Q6H
- Mechanical extraction of secretions or foreign bodies
How do you treat a patient with chronic respiratory acidosis?
- Avoid respiratory depression (sedatives, O2 therapy exceeding 3L/min)
- Nocturnal continuous positive airway pressure
- Vigorous treatment of the underlying disorder
What is respiratory alkalosis?
- It is a ventilatory process that decreases hydrogen resulting in a pH greater than 7.45
- Identified by a decrease in arterial pCO2 to below 35 mmHg
- Metabolic acidosis (decreased HCO3) is the compensating process
What are the 5 causes of acute respiratory alkalosis?
1. CNS disorders:
- Anxiety, pain
- Fever
- Head trauma
2. Pulmonary diseases; decreased lung compliance
- Pulmonary edema/CHF
- Pneumonia
- Pulmonary embolism
- Asthma
- Sepsis
- Acute salicylate toxicity
3. Physiological conditions
- Pregnancy
- High altitudes
4. Drugs:
- Salicylates
- Aspirin
- Progesterone
Miscellaneous
- Hepatic failure
- Hyperthyroidism
What causes the subjective symptoms associated with respiratory alkalosis?
The rise in CSF pH that occurs with respiratory alkalosis is associated with a significant reduction in cerebral blood flow that leads to the CNS/neurological symptoms
What are the subjective signs associated with respiratory alkalosis (acute/chronic)?
Acute respiratory alkalosis:
- CNS symptoms
- Lightheadedness
- Confusion
- Neurological
- Paresthesias, especially around the mouth
- Muscular symptoms – caused by an abrupt fall in ionized calcium that can occur
- Chest tightness
- Muscle cramps
Chronic respiratory alkalosis
- Usually none because of a normal pH due to compensatory mechanisms
What are the physical signs associated with respiratory alkalosis (acute/chronic)?
Acute respiratory alkalosis:
- Hyperactive deep tendon reflexes
- Carpopedal spasm (tetany): flexed wrist/ankle with hyperextended digits (in severe cases)
Chronic respiratory alkalosis:
- Usually none
