How many cases of Major Depression are actually undiagnosed cases of Hypoventilation?

Hypoventilation refers to inadequate ventilation. Hypoventilation may cause respiratory acidosis. Hypoventilation May also cause hypercapnic encephalopathy and altered mood and mental status.

Respiratory acidosis is primary increase in carbon dioxide partial pressure (Pco2) with or without compensatory increase in bicarbonate (HCO3); pH is usually low but may be near normal. Cause is a decrease in respiratory rate and/or volume (hypoventilation), typically due to central nervous system, pulmonary, or iatrogenic conditions. Respiratory acidosis can be acute or chronic; the chronic form is asymptomatic, but the acute, or worsening, form causes headache, confusion, and drowsiness. Signs include tremor, myoclonic jerks, and asterixis. Diagnosis is clinical and with arterial blood gas and serum electrolyte measurements. The cause is treated; oxygen (O2) and mechanical ventilation are often required.

Symptoms and signs depend on the rate and degree of Pco2 increase. CO2 rapidly diffuses across the blood-brain barrier. Symptoms and signs are a result of high CO2 concentrations and low pH in the CNS and any accompanying hypoxemia.

Causes are usually obvious from history and examination. https://www.merckmanuals.com/en-ca/professional/endocrine-and-metabolic-disorders/acid-base-regulation-and-disorders/respiratory-acidosis?query=respiratory%20alkalosis

The chronic form of respiratory acidosis is asymptomatic. It is very likely that Paula, when well, has chronic respiratory acidosis. Examining her respiratory rate at rest will suggest this; her respiratory rate is very depressed at rest, yet she is not aware of it and neither is anyone else. Paula also uses tremendous effort to exhale, using her accessory abdominals to squeeze air out by pushing down. Paula is not aware of this either, or rather, is not aware that this is abnormal and an indication of having difficulty breathing.

So Paula definitely has difficulty breathing and is not aware of it and does not report it as it feels normal to her and causes no distress. This suggests that her body has accommodated to her depressed breathing rate. Paula compensates by increasing her tidal volume as much as she can; this is why spirometry does not detect her chronic respiratory acidosis. Her spirometry is normal but her respiratory rate is very depressed.

Doctors seem not to remember that breathing requires 2 parts, the lung and the ventilatory apparatus. This is why it is necessary to investigate lung function AND respiratory rate. Tidal volume AND respiratory rate.

Paula’s lungs are normal. Her tidal volume is large. Her lung function is great. BUT her respiratory rate and her respiratory effort are very abnormal. A worsening of her lung function OR of her respiratory rate OR her respiratory effort will produce the acute, or worsening, form of respiratory acidosis, which causes headache, confusion, and/or drowsiness.

Symptoms and signs depend on the rate and degree of Pco2 increase. CO2 rapidly diffuses across the blood-brain barrier. Symptoms and signs are a result of high CO2 concentrations and low pH in the CNS and any accompanying hypoxemia.

What is the “confusion” [caused by worsening] respiratory acidosis like?

 Neurological symptoms correlate best with the degree of CO2 retention. Acute moderate hypercapnia, 5 to 10% CO2 in the expired air, leads to arousal and excitability, whereas higher CO2 concentrations, >35% in the expired air, are anesthetic. Patients with chronic pulmonary disorders may exhibit lethargy, confusion, memory loss and stupor.  Hypercapnic Encephalopathy Roger F Butterworth. Basic Neurochemistry: Molecular, Cellular and Medical Aspects. 6th edition. https://www.ncbi.nlm.nih.gov/books/NBK28164/

Paula had a mix of these symptoms. She looked stuporous but was actually internally very agitated. She did not look confused, yet she lost her autobiographical memory and could only offer stereotypic replies when spoken to. She had rapid thoughts yet forgot them almost instantly. She could barely speak more of two words because she ran out of breathe [and did not recognize that she was running out of breathe because her breathing was so slow].

The neurologic manifestations of acid-base disturbances, abnormal electrolyte concentrations, and acute endocrinopathies are protean and typically determined by the acuity of the underlying derangement. Detailed history and physical examination may guide appropriate laboratory testing and lead to prompt and accurate diagnosis. Neurologic manifestations of primary and secondary systemic disorders are frequently encountered in all subspecialties of medicine.  Neurol Clinic. 2010 Feb;28(1):1-16. doi: 10.1016/j.ncl.2009.09.002. Neurologic presentations of acid-base imbalance, electrolyte abnormalities, and endocrine emergencies Alan H Yee 1Alejandro A Rabinstein

to be continued…..

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