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25 Cards in this Set
- Front
- Back
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key concept regarding the trachea
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-serves as a conduit for ventilation and clearing tracheal and bronchial secretions
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how long is the trachea?
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10-13cm
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what is unique about the right mainstem bronchus vs. the left?
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the right is in a more vertical orientation
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gas exchange between the body and atmosphere
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gas from the alveoli and fresh gas from the upper airway are periodically exchanged to reoxygenate blood and eliminate CO2
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what brings about this exchange in spontaneously breathing vs. mechanically ventillated patients?
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both are brought about by small cyclic pressure gradients created in the airways, in the spontaneously breathing patient the gradients are due to intrathoracic pressure changes, in the mechanically ventilated patient by intermittent positive pressure in the upper airway
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what is the lung volume at the end of normal exhalation called?
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FRC
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what is unique about FRC?
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its the volume at which the inward elastic recoil of the lungs approximates the outward elastic recoil of the chest
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closing capacity compared to FRC
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closing capacity is normally well below FRC, but it rises steadily with age
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what does this increase in closing capacity likely explain?
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the normal age-related decline in arterial O2 tension
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comparing PFTs in terms of reliable measures of obstruction
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both FEV1 and FVC are effort dependent, the forced midexpiratory flow (FEF 25-75%) is more effort independent, and thus may be a more reliable measure of obstruction
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changes to lung mechanics during general anesthesia
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begin shortly after induction:
-supine position decreases FRC by 1 L -induction of GA further reduces FRC by 0.5 L due to alveolar collapse and compression atelectasis from loss of inspiratory muscle tone, change in chest wall rigidity, and upqard shift of the diaphragm |
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which is more important in influencing pulmonary vascular tone, local factors or the autonomic nervous system?
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local factors
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what local factor is a powerful stimulus for pulmonary vasoconstriction?
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hypoxia
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what does hypoxia do in the systemic circulation?
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the opposite of the pulmonary circulation, vasodilates
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normal V/Q ratio
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because alveolar ventilation is normally 4 L/min, and pulmonary capillary perfusion (Q) is 5 L/min, the overall V/Q ratio is 0.8
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what is shunt?
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when desaturated, mixed venous blood from the right heart returns to the left heart without being resaturated with O2
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what is the overall effect of shunting?
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to decrease arterial O2 content
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what is the effect of GA on venous admixture?
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GA increases venous admixture 5-10%, likely due to atelectasis and airway collapse in dependent lung areas
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effect of large increases of PCO2 on O2 levels
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large increases of CO2 (>75 mmHg) readily produce hypoxia (PaO2 <60mmHg) at room air, but not at high inspired O2 concentrations
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what is the rate limiting step in the transfer of O2 from alveolar gas to blood?
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the binding of O2 to Hb
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shunt and increasing FIO2
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the greater the shunt, the less likely increasing the FIO2 will prevent hypoxemia
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oxygen-Hb dissociation curve changes and affinity for O2
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-a rightward shift in the curve lowers affinity for O2, displaces O2 from Hb and makes more available for tissues
-a leftward shift causes greater affinity for O2, reducing its availability in tissues |
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what represents the greatest fraction of CO2 in the blood?
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bicarbonate
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central regulation of PCO2
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there are chemoreceptors on the anterolateral surface of the medulla, which respond to changes in CSF [H+], as the BBB is permeable to dissolved CO2 but not bicarbonate ions
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what happens to the PaCO2/minute ventilation curve and the apneic threshold during GA?
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with increasing depth of anesthesia, the slope of the PaCO2/ minute ventilation curve decreases, and the apneic threshold increases
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