Math Flashcards
(22 cards)
What does the A-a gradient and a/A ratio asses
efficiency of gas exchange across alveolar membrane
low A-a gradient/ratio indicates what
V/Q mismatch, diffusion defect or shunt
hypoventilation produces what gradients/ratios
normal
what does the alveolar/arterial O2 tension gradient
estimate degree of hypoxemia and physiological shunt
when is the alveolar/arterial O2 tension gradient increased
when hypoxemia is due to V/Q mismatch, diffusion, shunt or aging
on room air what should the Alveolar/Arterial O2 tension gradient be
less than 4mmhg for every 10 years of age
on 100% O2 what should the alveolar/arterial O2 tension gradient be
with every 50mmhg difference in P(A-a) there is a 2% shunt, and the normal changes with O2 level
what does the a/A ratio indicate
efficiency of O2 transport
what does low a/A ratio indicate
v/q mismatch, diffusion, or shunt
what is normal a/A value
80%
what does the shunt equation calculate
calculates portion of output not taking part in gas exchange
in terms of a shunt what is normal mild shunting significant shunting severe shunting
normal = less than 10%
mild = 10-20%
significant shunting = 20-30%
severe shunting = greater than 30%
what can cause anatomic shunt
congenital heart disease, vascular lung tumors, fistulas
what can cause physiological shunt or capillary shunt
atelectasis, alveolar fluid, venous admixture (causes hypoventilation, uneven distribution of ventilation, diffusion defects)
what can cause increase in peak/plateau combined
increased tidal volume endotracheal intubation pulmonary edema pleural effusion pneumothorax decreased pulmonary compliance
what can cause an increase in peak but unchanged plateau
increased inspiratory gas flow rate increased airway resistance kinked ET tube secretions bronchospasm airway compression foreign body aspiration
pressure is greater under what circumstances
under any kind of airway resistance (edema, mucus, constriction, stiffness)
what is the normal adult compliance on room air
100mL/cmH2O
what is the normal adult compliance on a ventilator
50mL/cmH2O
peak measures
both airway resistance and stiffness
plateau measures
only stiffness
pressure and compliance are related how
inversely related
