Acidosis Flashcards
What is the definition of metabolic acidosis?
Metabolic acidosis is caused by the presence of a metabolic
acid, which lowers the pH to less than 7.35
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372-373.
What is the definition of respiratory acidosis?
Respiratory acidosis occurs when alveolar ventilation decreases
enough that the PaCO2 rises, leading to a pH less than 7.35
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372.
What are the major cardiac effects of acidosis and at
what pH does this occur?
Acidosis decreases myocardial contractility. The effects are
usually not clinically evident until the pH is less than 7.2 when
the ability of the heart to respond to catecholamines is
decreased. It is more evident, however, in patients with
impaired left ventricular function, those on beta-blockers, or
patients under general anesthesia.
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 370-371.
A patient is suffering from an exacerbation of chronic
ventilatory failure and exhibits severe acidosis. You
are about to intubate the patient and place him on
the ventilator. Should the acidosis be corrected
urgently or slowly? Why?
Chronic respiratory acidosis should not be corrected too rapidly
because the lungs are able to eliminate CO2 much more quickly
than the kidneys can eliminate bicarbonate. If the CO2 is
eliminated too quickly, the patient will suffer from a metabolic
alkalosis that can lead to neuromuscular irritability and CNS
excitation that can lead to seizures.
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372.
What is the most likely cause of respiratory
depression in the perioperative period?
Drug-induced depression of ventilation due to opioids or general
anesthetics
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372.
What are the primary causes of respiratory acidosis?
The primary causes of respiratory acidosis can be divided into
two categories: those due to alveolar hypoventilation and those
due to increased CO2 production. Factors that impair CO2
elimination such as pulmonary diseases, neuromuscular
disorders, chest wall abnormalities, and obtundation can
potentially result in alveolar hypoventilation. Factors such as
intense shivering, malignant hyperthermia, prolonged seizure
activity, thyroid storm, and extensive burns result in an increase
in CO2 production.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 1149.
A patient with metabolic acidosis has a sodium of
148 mEq/L, a chloride of 103 mEq/L, and a
bicarbonate level of 19 mEq/L. Is this a normal
anion gap acidosis or a high anion gap acidosis?
The formula for the anion gap is: [Na+] - ([Cl-] + [HCO3-]). In
this instance, the anion gap is 26 mEq/L. The normal anion gap
is 7 to 12 mEq/L, so this is a high anion gap acidosis.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 1150-1152.
What are the two major classifications of metabolic
acidosis?
Normal anion gap acidosis and high anion gap acidosis
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372-373.
What systemic abnormalities may occur with
acidosis?
Severe acidosis is associated with decreased cardiac
contractility, decreased responsiveness to catecholamines,
sensitization to re-entrant tachydysrhythmias, lowered threshold
for ventricular fibrillation, hyperkalemia, hyperventilation, insulin
resistance, and inhibition of anaerobic glycolysis.
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372-373.
How does acidosis affect the oxyhemoglobin
dissociation curve?
The oxyhemoglobin dissociation curve shifts to the right in
acidosis to allow for a greater unloading of oxygen from the
hemoglobin in the tissue bed. Other factors that shift the
oxyhemoglobin dissociation curve to the right include:
increased 2,3 DPG, fever, elevated CO2, and low carbon
monoxide levels.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 1149.
How does high anion gap acidosis occur?
A high anion gap acidosis occurs when a fixed acid is
introduced into the extracellular space. As the acid dissociates,
the hydrogen ion bonds with bicarbonate to form carbonic acid.
It is the drop in bicarbonate that produces the anion gap.
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372-373.
What are the most common causes of a normal
anion gap acidosis?
Conditions that result in an increased production of nonvolatile
acids such as renal failure, ketoacidosis, nonketotic
hyperosmolar coma, and rhabdomyolysis or the ingestion of
toxins such as salicylates, methanol, paraldehyde, and ethylene
glycol can result in an acidosis with an increased anion gap.
Acidosis with a normal anion gap can be produced by increased
gastrointestinal losses of HCO3- from diarrhea, fistulas, or
ingestion of CaCl2 or MgCl2. Other factors that can produce a
normal anion gap acidosis include hypoaldosteronism, renal
tubular acidosis, carbonic anhydrase inhibitors or the
administration of large volumes of bicarbonate-free intravenous
fluids.
Butterworth JF, Mackey DC, Wasnick JD. Morgan & Mikhail’s
Clinical Anesthesiology. 5th ed. New York, NY: McGraw-Hill;
2013: 1151.
What is another name for normal anion gap acidosis?
Hyperchloremic metabolic acidosis
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372.
What are the characteristics of normal anion gap
acidosis?
Normal anion gap acidosis is due to an increase in chloride
concentration. This usually occurs in instances where
bicarbonate is lost, so the kidneys retain chloride ions to
maintain electrical neutrality.
Hines RL, Marschall KE. Anesthesia & Co-Existing Diseases.
6th ed. Philadelphia, PA: Elsevier-Saunders; 2012: 372-373.
