Kristy Maracle
Posted Date
Apr 7, 2022, 12:34 PM
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Respiratory acidosis is caused by a depression of the respiratory center due to pulmonary or neuromuscular disorders and may be acute or chronic. It is the direct result of the generation of CO2 at a rate that exceeds the capacity of the lungs to secrete it. Respiratory acidosis is characterized by a pH < 7.35 and a PaCO2 level >45 mm Hg. In acute cases, bicarbonate levels (HCO3) may increase by 1 mEq/l for every 10 mm Hg increased in PaCO2 due to metabolic compensation Pulmonary conditions associated with this derangement include asthma, COPD, and ARDS. Neuromuscular associated diseases include multiple sclerosis (MS), myasthenia gravis (MG), CVA, traumatic brain injury, encephalopathy, and sedatives/anesthesia. Obesity hypoventilation syndrome is also a common cause of respiratory acidosis. Clinical manifestations include dyspnea, confusion, psychosis, headache, irritability, anxiety, and when severe, seizures. Treatment includes managing the underlying cause, the administration of sodium bicarbonate if mixed respiratory /metabolic acidosis. Reversal agents including Narcan for suspected overdose, and bronchodilators. Acetazolamide is sometimes used in post-hypercapnic metabolic alkalosis. Additionally, diuretics should be discontinued, when possible, to avoid hypokalemia and worsening symptoms. The use of alkali remains controversial (Tinawi, 2021).
An example of ABG’s suggesting respiratory acidosis would include a patient in an MG crisis with recent nausea and vomiting that is requiring mechanical ventilation with the following results: Ph 7.22, PaCO2 68 mmHg, HCO3 35 mEq/l, and PaO2 50 (Tinawi, 2021). Respiratory acidosis results in hypercapnia due to dead space ventilation. Ventilator management would include modifications to the ventilator circuit to include connecting the Y-piece directly to the endotracheal tube to decrease dead space in the circuit, prolonging the end-inspiratory pressure pause from 0.1 to 0.7 to increase clearance of CO2, and titrating PEEP to promote lung recruitment and decrease work or breathing (Tiruvoipati, Gupta, Pilcher, & Bailey, 2020).
Respiratory alkalosis is characterized by a Ph > 7.45 and a PaCO2 < 35 mm Hg and is most commonly associated with hyperventilation. It may be acute or chronic and can be seen in normal pregnancy, exercise, and in people living at high altitudes. It is common in critically ill patients. It may also be caused by hypoxemia with PaO2 < 60 mm Hg linked with hyperventilation, CNS stimulation, pulmonary disorders, anxiety, medications/salicylate overdose, and hormones. Clinical manifestations include tachypnea, confusion, atrial and ventricular tachyarrhythmias, lightheadedness, and paresthesia of the upper extremities and around the mouth. Treatment includes sedation, paralytics, correction of electrolyte imbalances, acetazolamide if related to high altitude sickness, and isotonic saline to decrease HCo3 if elevated due to compensation (Tinawi, 2021). An example of an ABG reflecting respiratory alkalosis is a patient having a prolonged panic attack with the following levels: Ph 7.61, PaCO2 30 mm Hg, HCO3 16 mEq/l, PaO2 66. Mechanical ventilation management for respiratory alkalosis includes avoiding the use of volume control and reducing minute ventilation or tidal volume (Dang & Sasson, 2021).
Environmental and nutritional recommendations to avoid respiratory acid-base imbalances include avoiding allergic/environmental/emotional triggers/nutritional, taking bronchodilators/inhaled corticoid steroids, and antihistamines as directed, and voiding the use of sedatives/muscle relaxers if possible.
References
Dang, B., & Sasson, C.S. (2021). Assessment of respiratory alkalosis. BMJ Best Practice. Retrieved on April 4, 2022, from
https://bestpractice.bmj/topics/en.gb/463
Tinawi, M. (2021). Respiratory acid-base disorders: Respiratory acidosis and respiratory alkalosis. Archives of Clinical Biomedical
Research, 5: 158-168. https://doi:10.26502/acbr.50170157
Tiruvaipati, R., Gupta, S., Pilcher, D. & Bailey, M. (2020). Management of hypercapnia in critically ill mechanically ventilated patients: A
narrative review of literature. Journal of the Intensive Care Society, 21(4), 327-333. https://doi.org/10.1177/1751143720915666
