Respiratory Acidosis
Based on Theodore (2020), respiratory acidosis is a disruption in acid-base balance usually due to alveolar hypoventilation that can be acute or chronic. It is characterized by an increased PaCO2 >45 mmHg (hypercapnia) and a reduction in pH (pH <7.35). In contrast, respiratory alkalosis is usually due to alveolar hyperventilation, decreasing PaCO2 (hypocapnia), and increased pH. However, it can also be acute or chronic. In acute respiratory alkalosis, the PaCO2 level is below the lower limit of normal (<35 mmHg), and the serum pH is appropriately alkalemic (>7.45). In an ABG sample, based on Emmett & Palmer (2020), the normal range for pH: 7.35-7.45; bicarbonate (HCO3) concentration: 21-27 mEq/L; and PCO2: 35-45 mmHg.
Examples:
- ABG report shows a pH=7.32, PaCO2=70 mmHg, and HCO3=30 mEq/L. The patient is acidemic and has a high PaCO2, consistent with respiratory acidosis.
- ABG report reveals pH=7.47, PaCO2=28 mmHg, HCO3=20 mEq/L. The patient is alkalotic and has a low PaCO2 consistent with respiratory alkalosis.
According to DuBose (2018), if not correctly adjusted and managed, mechanical ventilation may result in respiratory acidosis, mainly if CO2 production rises (fever, agitation, sepsis, or overfeeding) or alveolar ventilation falls because of worsening pulmonary function. High levels of positive end-expiratory pressure (PEEP) with reduced cardiac output may force hypercapnia due to significant increases in alveolar dead space. Permissive hypercapnia may minimize intrinsic PEEP in acute lung injury/acute respiratory distress syndrome and severe obstructive lung disease. The respiratory acidosis associated with permissive hypercapnia may require administration of NaHCO3 to increase the arterial pH to ∼7.15–7.20, but rapid correction of the acidemia to a normal arterial pH is harmful. Therefore, the initial treatment should focus on lowering the PaCO2 gradually, aiming to restore the PaCO2 to baseline levels and provide sufficient Cl− and K+ to enhance the renal excretion of HCO3. Pharmacologic therapy (such as bronchodilators like beta-agonists and anticholinergic drugs) can also help improve ventilation.
Theodore (2020) also wrote that respiratory alkalosis develops when the lungs are stimulated to remove more carbon dioxide produced metabolically in the tissues. The stimulus to increase respiratory drive is controlled by central and peripheral factors. Thus, respiratory alkalosis is typically encountered in anxiety, panic, pain, fever, psychosis, and hyperventilation syndrome. Respiratory alkalosis is typically managed by treating the underlying cause (e.g., anxiolytic, pain control) and using maneuvers to reduce alveolar ventilation (e.g., sedation, reducing the respiratory rate and/or tidal volume when on mechanical ventilation).
The supportive care of mechanically ventilated patients includes sedation, analgesia, delirium management, hemodynamic monitoring, nutritional support, glucose control, VAP measures, VTE prophylaxis, G.I. prophylaxis, venous or arterial access, and temperature management (Hyzy & McSparron, 2021).
References
DuBose, T.D. (2018). Acidosis and alkalosis. In Jameson, J.L., Kasper, D.L., Longo, D.L., Fauci, A.S., Hauser, S.L. & Loscalzo, J. (Eds). Harrison’s Principles of Internal Medicine (20th Ed, Vol., Part 1, Chap. 51, pp. 368-370). McGraw-Hill Education.
Hyzy, R.C. & McSparron, J.I. (October 08, 2021). Overview of initiating invasive mechanical ventilation in adults in the intensive care unit. UpToDate. https://www.uptodate.com/contents/overview-of-initiating-invasive-mechanical-ventilation-in-adults-in-the-intensive-care-unit?search=invasive%20mechanical%20ventilation&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H2938860842
Theodore, A.C. (September 29, 2020). Arterial blood gases. UpToDate. https://www.uptodate.com/contents/arterial-blood-gases?search=respiratory%20alkalosis%20treatment&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H620442291
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