Respiratory acidosis

Disease Description (Causes and Symptoms)

• Definition summary: Respiratory acidosis is a condition in which the blood becomes acidic because the partial pressure of arterial carbon dioxide (PaCO2) rises due to reduced respiration (ventilation). Usually, pH < 7.35 and PaCO2 > 45 mmHg are observed.
• Pathophysiology: Decreased ventilation → CO2 accumulation → increased blood H+ and decreased pH. In acute cases, the kidneys cannot compensate, so the increase in HCO3− is minimal (acute compensation: HCO3− increases by approximately 1 mmol/L for every 10 mmHg increase in PaCO2), whereas in chronic cases, HCO3− increases more substantially due to renal metabolic compensation (chronic compensation: HCO3− increases by approximately 3–4 mmol/L for every 10 mmHg increase in PaCO2).
• Main causes:
  • Lung diseases: acute pulmonary edema, pneumonia, asthma attacks, chronic obstructive pulmonary disease (COPD), emphysema, bronchitis, etc.
  • Respiratory muscle·chest wall problems: myasthenia gravis, chest trauma, diaphragmatic paralysis
  • Central nervous system depression: anesthetics·analgesics·sedatives (e.g., opioids), central nervous system injury (medulla oblongata injury)
  • Airway obstruction: foreign body, severe secretions, sleep apnea, obesity hypoventilation syndrome
  • Incorrect ventilator settings
• Main symptoms:
  • Acute: shortness of breath, headache, anxiety·agitation, changes in consciousness (stupor·coma), skin flushing, sweating, muscle tremors·seizures
  • Chronic: insomnia, decreased memory·concentration, daytime sleepiness, personality changes, some degree of muscle weakness

Treatment Methods

• Goals: Secure the airway and restore effective ventilation, correct the underlying cause, and stabilize acid-base balance
• Emergency·initial treatment
  • Secure the airway (remove foreign bodies in cases of airway obstruction); provide oxygen if necessary
  • In cases of severe respiratory failure or decreased consciousness, mechanical ventilation (noninvasive positive-pressure ventilation (NIV; BiPAP) or intubation followed by a ventilator)
  • Tracheostomy may be considered when long-term mechanical ventilation is required
• Medications/treatment by disease
  • Obstructive airway diseases (asthma·COPD): inhaled beta2 agonists, anticholinergics, and steroids if necessary
  • Infectious causes: appropriate antibiotics
  • Medications causing adverse effects (such as opioids): discontinue or adjust the dosage
• Precautions for oxygen therapy
  • Oxygen administration is necessary in acute hypoxemia
  • In patients with chronic CO2 retention (such as COPD), excessive oxygen administration can cause respiratory depression and worsening of PaCO2; therefore, start with a low concentration (approximately targeting SpO2 88–92%) and monitor
  • For patients with chronic respiratory acidosis, long-term oxygen therapy is generally recommended at a low flow rate (e.g., 1–2 L/min) (follow the individual prescription)
• Observation and monitoring
  • Repeated arterial blood gas (ABG) tests, oxygen saturation (SpO2), respiratory rate·consciousness
  • During mechanical ventilation, take care not to correct PaCO2 too rapidly (sudden changes can affect cerebral blood flow and acid-base balance)
• Lifestyle management
  • No smoking, regular use of medications·inhalers, weight management, and evaluation for sleep apnea; consider CPAP/BiPAP if necessary
  • Exercise caution when using sedatives·opioids and consult the attending physician

Checkpoints Before an Outpatient Visit (Including Example Questions)

• Items to prepare (for an outpatient or emergency visit)
  • A list of currently used medications (including prescriptions·OTC medications·sleeping pills·analgesics)
  • Previous test results (recent ABG, chest X-ray/CT, pulmonary function tests) and the hospital name/date
  • Settings of oxygen·CPAP/BiPAP equipment normally in use
  • The time of symptom onset and progression (episodic·gradual, aggravating factors), and the severity of shortness of breath (at rest vs during activity)
  • Findings suggestive of infection, such as fever·sputum color·blood-streaked sputum
• Information useful to record for the outpatient visit
  • Recent weight changes, whether apnea occurs during sleep, and the usual degree of daytime sleepiness (ESS, etc.)
  • Whether changes in consciousness occurred during an emergency, and whether there were any recent falls or chest trauma
• Example questions (to prepare yourself)
  • When did the symptoms begin, and under what circumstances did they worsen?
  • Are you taking any sedatives or opioids?

General Example Questions to Ask the Doctor

• What do you think is the cause of this condition? Are any additional tests needed?
• What are my current PaCO2 and pH levels, and what are the target values?
• What are the adverse effects of the medications (inhalers·analgesics·sedatives), and how can they be adjusted?
• What should my target oxygen saturation (SpO2) range and oxygen flow rate be at home?
• What lifestyle changes and preventive measures can help prevent recurrence?

Disease-Specific Example Questions

• How do you determine whether my case is acute or chronic? (Differences in treatment according to the distinction between acute and chronic)
• Chronic hypercapnia is suspected in my case; do I need home NIV (home BiPAP) or long-term oxygen therapy?

(Recommendation to visit the emergency room if necessary: If you have severe shortness of breath, rapidly progressing decreased consciousness, cyanosis, or persistent oxygen-refractory hypoxemia, visit the emergency room immediately)