From the Guidelines
Respiratory acidosis is a life-threatening condition that occurs when the lungs cannot remove enough carbon dioxide from the body, causing blood pH to drop below 7.35, and it is crucial to address the underlying cause and manage it promptly to prevent serious complications. Gas exchange disorders involve imbalances in the body's acid-base status, primarily affecting the respiratory and metabolic systems. Respiratory acidosis occurs when carbon dioxide accumulates in the body due to hypoventilation, causing blood pH to drop below 7.35 with elevated PCO2 levels above 45 mmHg, as explained in the BTS guideline for oxygen use in adults in healthcare and emergency settings 1. This can result from conditions like COPD, severe asthma, or drug-induced respiratory depression.
Key Points to Consider
- Treatment focuses on addressing the underlying cause, which may include bronchodilators for obstructive diseases, mechanical ventilation for respiratory failure, or naloxone for opioid overdose.
- The body compensates for these imbalances through opposing mechanisms - the lungs adjust breathing rates while the kidneys modify bicarbonate retention or excretion.
- Understanding these processes is crucial because acid-base disturbances can significantly impact oxygen delivery to tissues, enzyme function, and electrolyte balance, potentially leading to serious complications if not properly managed.
- According to the official ERS/ATS clinical practice guidelines, bilevel NIV may be considered in COPD patients with an acute exacerbation to prevent acute respiratory acidosis, prevent endotracheal intubation, or as an alternative to invasive ventilation 1.
- The BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults suggests that allowing permissive hypercapnia may result in cerebral vasodilation and a rise in intracranial pressure, and may also compromise myocardial contractility, but attempts to raise pH to >7.2 may compound hyperinflation and barotrauma 1.
Management Strategies
- In ARDS, a low Vt strategy improves survival, and in airflow obstruction, prolonging the expiratory time reduces dynamic hyperinflation (gas-trapping) 1.
- In AECOPD, attempts to rapidly restore pO2 and pCO2 to normal are unnecessary, and it is suggested that the higher the pre-morbid pCO2, the higher the target pCO2 should be 1.
- Any metabolic causes of acidosis should be treated separately, and lung recruitment strategies should be considered when there is persisting hypoxia and/or evidence of premature small airway closure in dependent lung tissue 1.
From the Research
Gas Exchanges and Respiratory Acidosis
- Respiratory acidosis, or primary hypercapnia, is the acid-base disorder that results from an increase in arterial partial pressure of carbon dioxide 2.
- This condition can occur acutely or chronically, with acute respiratory acidosis resulting from sudden respiratory failure, and chronic respiratory acidosis resulting from numerous processes, including increased carbon dioxide production, alveolar hypoventilation, and abnormalities of the chest wall and respiratory muscles 2.
- The symptoms, signs, and physiologic consequences of respiratory acidosis are numerous, with principal effects on the central nervous and cardiovascular systems 2.
Treatment of Respiratory Acidosis
- Treatment for respiratory acidosis may include invasive or noninvasive ventilatory support and specific medical therapies directed at the underlying pathophysiology 2.
- Non-invasive ventilation (NIV) and high-flow oxygen therapy (HFOT) are two common treatments used to manage respiratory acidosis, with NIV being the best strategy of oxygenation in patients with acute-on-chronic respiratory failure and respiratory acidosis 3.
- HFOT, on the other hand, may be considered as a first-line strategy of oxygenation in patients with de novo acute respiratory failure, due to its good tolerance and physiological characteristics, including delivery of high FiO2 and positive end expiratory pressure (PEEP) effect 3.
Management of Severe Acute Exacerbations of COPD
- Patients with chronic obstructive pulmonary disease (COPD) may experience an acute worsening of respiratory symptoms, defined as a COPD exacerbation (AECOPD) 4.
- Treatments for AECOPD aim to minimize the negative impact of the current exacerbation and to prevent subsequent events, such as relapse or readmission to hospital, and may include inhaled bronchodilators, steroids, and antibiotics, as well as non-pharmacological treatments like oxygen, HFNC oxygen therapy, NIV, and pulmonary rehabilitation (PR) 4.
- Early rehabilitation, if associated with standard treatment of patients, is recommended due to its feasibility and safety 4.
Diagnosis and Management of Severe Respiratory Acidosis
- Respiratory acidosis is characterized by a primary increase in whole-body carbon dioxide stores caused by a positive carbon dioxide balance, and requires prompt recognition and expert management 5.
- The diagnosis and management of respiratory acidosis involve the assessment of arterial and venous blood gas analyses, and the recognition of a primary respiratory arrest in contrast to primary circulatory arrest when managing a patient who requires resuscitation from "cardiorespiratory arrest" 5.
- Oxygen therapy and NIV have been increasingly used to treat hypoxemic and hypercapnic respiratory failure in patients with progressive COPD, aiming to improve both prognosis and quality of life 6.