A 64-year-old female with a history of COPD and obstructive sleep apnea was admitted to the hospital for suspected methicillin-resistant Staphylococcus aureus cellulitis. The patient was started on intravenous vancomycin. She refused to use the hospital CPAP machine during the night. At 6:00 AM the phlebotomist found the patient unresponsive and the rapid response team was called. The patient had a Glasgow coma score of 5. Her vital signs were normal except for an O2 saturation of 85% on room air. ABG showed: pH of 7.01, PO2 of 55, PCO2 of 90, and HCO3 of 30.
1. What is the acid-base abnormality?
2. What is the cause of this abnormality?
3. What would you do for the patient?
The patient has acute noncompensated respiratory acidosis.
The patient had acute hypercapnic respiratory failure secondary to worsening apnea most likely secondary to not using the CPAP machine.
The patient needs emergent intubation. Noninvasive ventilation is not appropriate in this case because of her poor mental status and severe acidosis.
High Anion Gap Metabolic Acidosis
High anion gap metabolic acidosis (HAGMA) is simply caused by adding acid to the serum. The excessive hydrogen ions will be buffered by bicarbonate, so bicarbonate concentration will decrease. Chloride concentration will stay the same because the loss of bicarbonate will be replaced by the negatively charged anion part of the added acid. The low bicarbonate and the normal chloride concentrations will result in a high anion gap.
The most clinically important acids that cause HAGMA and their etiologies are shown in Table 6-1. A simplified algorithm to HAGMA is shown in Figure 6-1.
Table 6-1. Etiologies of HAGMA |Favorite Table|Download (.pdf)
Table 6-1. Etiologies of HAGMA
|Lactic acid → shock, drugs (metformin, salicylates, INH, methanol, ethylene glycol, propofol, linezolide, stavudine, didanosine), seizure, liver failure, malignancy, cyanide poisoning, and carbon monoxide poisoning|
|Ketones → diabetes, starvation, ethanol|
|Salicylates → salicylate toxicities|
|Glycolic and oxalic acids → ethylene glycol toxicity|
|Formic acid → methanol toxicity|
|Pyroglutamic acid → acetaminophen|
|Phosphoric acid, sulfuric acid, and other acids → advanced chronic kidney disease|
|D-Lactic acidosis → after small bowel resection|
Approach to high anion gap metabolic acidosis.
Advanced chronic kidney disease (CKD) is commonly associated with HAGMA when GFR decreases to less than 20 mL/min. Metabolic acidosis promotes protein catabolism and worsens bone disease in this group. Acidosis is effectively corrected by hemodialysis. Patients not on hemodialysis may need sodium bicarbonate to keep serum bicarbonate above ...