Clinical diagnosis
Case 319
【Progress】
She received mechanical ventilation. However, severe mycobacterium damaged a whole lung. Regrettably, she passed away five days after.
【Discussion】
CO2 narcosis is in a condition that consciousness level drops associated with PCO2 elevation. Normal PCO2 level of arterial blood gas analysis is nearly 40 mmHg. When it rises to 60 mmHg or greater, CO2 narcosis of headache associated with, consciousness level decrease begins (1, 3). When left untreated, it leads severe respiratory failure and death. The etiology of narcosis is believed that PCO2 elevation induces vasodilation of brain blood vessels whose blood volume increase and intracranial pressure increase, leading headache and dropping consciousness (1, 2).
PCO2 elevation is caused by lowering potency of PO2-CO2 exchange whose reasons are categorized into functional alveolar volume loss, pulmonary capillary loss and weakened respiratory mechanism (1-4). Functional alveolar volume loss includes COPD, tuberculosis, non-tuberculosis mycobacterium and acute respiratory distress syndrome (ARDS). Pulmonary capillary loss includes pulmonary embolism, and pulmonary hypertension. Mechanical (neuromuscular) hypofunction includes Guillain-Barre, myasthenia gravis, amyotrophic lateral sclerosis, and drugs or toxins weakening respiratory muscle (heroin) and/or repressing respiratory center (globe fish toxin).
The most encountered CO2 narcosis occurs during O2 inhalation in COPD patients whose symptoms are consciousness disorder and whose arterial blood gas analysis reveals high PCO2 elevation. That is called oxygen-induced hypercapnia in COPD (5).
It is believed that CO2 narcosis in COPD arises in situation where CO2 sensitive respiratory center in medulla oblongata is paralytic to CO2 because of persistent PCO2 elevation, does not work to stimulate respiration, and further, chemoreceptors situated at bifurcation of carotid arteries sensitive PO2 do not work to stimulate respiration because O2 inhalation via O2 mask is served to continue (1, 2, 5). Respiratory momentum does not work, inducing PO2 elevation and PCO2 elevation which dilate vessels to brain, leading brain pressure elevation and drop of consciousness.
In our case, she was suffering from non-tuberculosis mycobacterium after menopausal which no infected to other person but it expanded to her/his own lung if left untreated. Chest CT depicted marked bronchiectasis at right middle lobe and left lingula, ground glass opacity and small nodules at both upper lobes, indicative of advanced non tuberculosis mycobacterium. O2 inhalation via mask induces paralysis of chemoreceptors at carotid artery bifurcation, and chronic pulmonary failure of PCO2 elevation induces to paralysis of respiratory center at medulla oblongata. She underwent mechanical ventilation but in vain, died several days after admission to our hospital.
【Summary】
We presented a seventy-five-year-old female transported by ambulance car for respiratory failure. Arterial blood gas analysis revealed PCO2 73.3mmHg, PO2 149mmHg, implying CO2 narcosis and chest CT depicted advanced non-tuberculosis mycobacterium. It is borne in mind that consciousness disorder often encountered in CO2 narcosis is caused by that CO2 induces dilatation of brain vessels, leading intracranial high pressure. Treatment is mechanical ventilation. Despite O2 inhalation and PO2 elevation, respiration does not proceed but represses in CO2 narcosis probably because of two factors; one factor, respiratory center, medulla oblongata usually sensitive to CO2 elevation falls in insensitive to CO2 probably due to persistent high PCO2: another factor, chemoreceptor sensitive to O2 level falls into insensitive to O2 inhalation.
【References】
1.Williams MH, Shim CS. Ventilatory failure. Etiology and clinical forms. Am J Med. 1970 Apr;48(4):477-83.
2.Yoon S, et al. pCO(2) and pH regulation of cerebral blood flow. Front Physiol. 2012;3:365.
3.Kamil F, Pinzon I, Foreman MG. Sex and race factors in early-onset COPD. Curr Opin Pulm Med. 2013 Mar;19(2):140-4.
4.Centers for Disease Control and Prevention (CDC). Chronic obstructive pulmonary disease among adults--United States, 2011. MMWR Morb Mortal Wkly Rep. 2012 Nov 23;61(46):938-43
5.Abdo WF, et al. Oxygen-induced hypercapnia in COPD: myths and facts. Crit Care. 2012; 16(5): 323.Published online 2012 Oct 29. doi: 10.1186/cc11475
2023.12.12