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hypoxemia
RPM I
29
Medical
Graduate
05/08/2010

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Term
what is the alveolar gas equation? what can it be simplfied to? what is it calculating?
Definition
PAO2 = (.21)(760-47) - PaCO2/R which can be simplified to PAO2 = 150-40/.8 under normal circumstances. it is calculating the level of O2 that is in the alveoli, available to diffusion into the pulmonary vein (function of the arterial blood gas). (a fudge factor for computing PaCO2/R is 1.2xPCO2)
Term
how is the alveolar gas equation used?
Definition
a pt comes in, is hypoxic, do you put them on 50% O2, and get an ABG. therefore you can plug in .5 for the FIO2, 760 for the atm, and PCO2 from the ABG. the alveolar O2 pressure will then be = .5(760-47) - 1.2 (PCO2 from ABG)
Term
what is the AA gradient?
Definition
the PAO2 (from the alveolar gas equation) minus the pa02 (from the ABG), which will tell you if the lungs are adequately loading the blood with O2
Term
what do you need to check on a hypoxic pt who has a good pulse ox?
Definition
Hb levels
Term
if a pt is breathing fast, what might their body be trying to do in terms of pH balance?
Definition
blow off CO2, which will make their blood less acidic. less acidic blood allows Hb to retain O2 better
Term
what causes a respiratory acidosis?
Definition
not breathing in the appropriate amount of O2, not breathing out the appropriate amount of CO2
Term
what causes a metabolic acidosis? what may this result in?
Definition
if a pt is diabetic, glucose levels rise and cause the blood to become more acidic. this may result in respiratory compensation (respiratory alkalosis)
Term
what can cause metabolic alkalosis?
Definition
vomiting
Term
what is normal body pH?
Definition
7.4
Term
what is acidemia?
Definition
any pH < 7.4
Term
what is alkalemia?
Definition
any pH > 7.4
Term
what are signs of likely respiratory acidosis?
Definition
increased CO2 levels, increased HCO3- levels (CO2 binds w/water = bicarb)
Term
what are signs of likely metabolic acidosis?
Definition
decreased bicarb b/c metabolic acids are producing H+ ions and decreased CO2 b/c body is compensating
Term
what are signs of likely respiratory alkalosis?
Definition
decreased CO2 (definition of hyperventilation)
Term
what are signs of likely metabolic alkalosis?
Definition
increased bicarbonate levels - appropriate bicarb ingestion/retention/iatrogenic
Term
what is winters formula? what is it used for?
Definition
winters formula: PaCO2 = (1.5)(HCO3-)+8+/-2. this gives you the expected CO2, so if the CO2 from the ABG is higher, you would look for resp acidosis/if it is lower, you would look for metabolic acidosis
Term
what are ancillary functions of the lung?
Definition
endocrine (angiotensin I -> II), thermoregulation
Term
how can lung overcompliance lead to pneumothorax?
Definition
they can take air in easily, but do not have the recoil to correctly expel it - the excess air eventually pops an alveolus and air gets between the visceral and parietal pleura
Term
what is pulmonary respiration?
Definition
# of breaths per unit time
Term
what can help pts with sleep apnea?
Definition
continuous positive airway pressure - keeps lungs from deflating too far
Term
when is a BiPAP used?
Definition
when an elderly pt who may not be able to regain lung strength after being intubated needs airway pressure nonetheless. this is a mask that can provide continuous positive airway pressure and positive end expiratory pressure as well as monitor and adjust said pressure.
Term
how do higher acid levels affect Hb?
Definition
Hb will drop O2 easier. (more alkolotic: Hb will hold O2 tighter)
Term
what is the haldane effect?
Definition
hypercarbic - O2 comes off easier (more acidic)
Term
how does 2,3-BPG affect Hb? where does it come from?
Definition
2,3-BPG causes Hb to drop O2. it comes from anerobic glycolysis in the cells, and enhances O2 levels there.
Term
how does a pulse oximeter work?
Definition
unsaturated Hb absorbs red light, while oxygenated Hb reflects it - the pulse oximeter quantifies this. however, you still need to know Hb levels to determine total body oxygen level
Term
what happens in emphysema?
Definition
lungs are overcompliant - do not exhale well and trap air
Term
henderson hasselbach equation:
Definition
blow off CO2, pH goes up/increase CO2, pH goes down
Term
if you have appropriate breathing, what do you need to match it?
Definition
appropriate Hb, CO
Term
how do you calculate alveolar ventilation?
Definition
subtract known volume of the upper airway (trachea, carina & bronchi), somewhere between 200-150 mL = dead space, from the tidal volume multiply by the frequency
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