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24 Cards in this Set
- Front
- Back
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What does capnography rely on?
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infrared absorption(function of molecular weight)
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How does infrared absorption interpret the N20 in the presence of CO2?
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amount of N2O is artificially higher due to CO2 having the same molecular weight
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What is the cause of a sudden drop but not to 0 of the CO2 waveform?
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leakage or partial obstruction of the airway
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what is the cause of an exponential decrease of the CO2 waveform?
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increased alveolar dead space such as PE or cardiac arrest
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What does a gradual increase of the CO2 waveform indicate?
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decreased minute ventilation, prolapse of the expiratory valve
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What is the cause of a sudden increase in CO2 on the CO2 waveform?
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release of a tourniquet(sudden increase in CO2)
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in general what do peripheral and central chemoreceptors modulate?
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peripheral: ventilatory response to arterial hypoxemia(paO2<60mm Hg, they do not respond to low O2 content); central: response to pH and pCO2(CO2 actually cross the BBB and then in the CSF, H+ is formed and acidosis occurs)
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What is the afferent and efferent limb of the carotid and aortic bodies response to hypoxemia?
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afferent CN IX
efferent CN X |
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where is the chemosensitive area in the brainstem that controls ventilation located?
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medulla
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How does CO2 rise during apnea?
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6mm Hg the 1st minute and 3mm Hg for each minute thereafter
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what is the ventilatory response to increased CO2?
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increased tidal volume and increased RR
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Where is hypoxic ventilatory drive primarily regulated?
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carotid bodies
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what is the slope of the carbon dioxide response curve?
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0.5-0.7 liters/min/mmHg(when CO2>100 slope is 2 L/m/mmHg)
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When does carbon dioxide act as a ventilatory depressant?
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PaCO2>100mmHg
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What causes a left shift of the CO2 response curve(increased sensitivity to CO2)?
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arterial hypoxemia, metabolic acidemia, central causes(increased ICP, anxiety, fear, cirrhosis), drugs(doxepram, strychnine, picrotoxin(analeptics)
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what is the x and y axis of the CO2 response curve?
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X-PaCO2, Y-alveolar ventilation
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What causes a right shift of the CO2 response curve(decrease sensitivity to CO2)?
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aminophylline, salicylates, catecholamines, physiologic changes(metabolic alkalemia, denervation of peripheral chemoreceptors, normal sleep, drugs, hypothermia)
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What causes a down and to the right shift of the CO2 response curve?
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high doses of opioids, potent anesthetics(with increasing dose curve becomes more horizontal-not responsive to CO2, greatest to least ventilatory depression is enflurane>halothane>isoflurane), neuromuscular blockade
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How does 0.1MAC affect the ventilatory response to hypercarbia versus hypoxemia?
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greater effect on the ventilatory response to hypoxemia than hypercarbia
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What are the physiologic effects of hypoventilation-hypercarbia?
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A RIPE: acidosis, arrhythmias, right shift of oxy-hemoglobin curve, intracerebral steal, PA pressure increase, Epi-norepi release
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what are the physiologic effects of hyperventilation-hypocarbia?
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AVCO: apnea, alkalosis, airway constriction, V/Q mismatch, cardiac output, CBF, coronary blood flow and calcium all decrease, oxyhemoglobin curve shifted to the left
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How is CO2 carried in the blood?
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carbaminohemoglobin, bicarb, hydrated carbonic acid, dissolved in solution
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what is the haldane effect?
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affinity of hemoglobin for CO2 increases with deoxygenation
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why is endobronchial intubation not detected by capnography?
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CO2 is more than 20x more diffusible than O2, as shunt increases the PaO2 progressively decreases but PaCO2 does not increase until the shunt is >50%
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