Respiratory Quiz #4 Flashcards
Identify factors that determine exchange rates of gases across membranes
Fick’s Law combined with the diffusion rate determined from Graham’s Law (solubility) provides the means for calculating the exchange rates of gasses
Define Fick’s Law
the net diffusion rate of a gas across a fluid membrane is proportional to
• the difference in PARTIAL PRESSURE, the AREA of the membrane, inversely proportional to the THICKNESS of the membrane
• =>summarizes all the laws, if incr fio2 you will have more diffusion, area of membrane is important, if only 1 lung will have lower diffusion rates, inversely related to thickness of membrane bc more to cross, diffusion is limited
• => Fick’s law isn’t about giving you specific numbers, it tells you who you will have a hard time oxygenating
Identify two factors which determine the concentration of a gas in a solution using Henry’s Law
- partial pressure X solubility coefficient = concentration of gas
- both are directly proportional
- concentration can be incr by incr pp or solubility
Compare solubility coefficients for oxygen, carbon dioxide, carbon monoxide and nitrogen
- o2 - 0.024, carbon dioxide - 0.57(most soluble), carbon monoxide - 0.018, nitrogen - 0.012, helium - 0.008 (least soluble)
- =>if a bubble of carbon dioxide is trapped during open heart surgery it won’t embolize, it gets absorbed, not much of embolic effect at all
Using Henry’s Law, calculate the amount of oxygen dissolved in blood for PO2 of 50, 100,and 600 mmHg 10, CGAS = K X PGAS K=0.003
- 0.003x50=0.15, 0.003x100=0.3, 0.003x600=1.8 mL O2/100mL blood
- =>Ex: so for every 100mL of blood you would have 0.3mL of o2
Identify the mechanism responsible for most carriage of oxygen in the plasma
most oxygen is carried by hemoglobin, some is dissolved and carried in plasma
Describe the effect of increasing FiO2 from 100 to 600 mmHg on oxygen carrying capacity
increases o2 carrying capacity very little
Identify the average capillary exposure/transit time
- 0.7 seconds average, normal is 0.3
* =>0.4 sec grace period
Identify the normal time period required for diffusion to occur
normal oxygenation occurs in 0.3 seconds
Describe the effect of lower alveolar PO2 on diffusion and arterial PO
will decrease diffusion, lower po2=lower endpoint, less of a partial pressure gradient means slower diffusion and lower endpoint
Compare arterial and tissue PO2 and the effect on diffusion
arterial =95mmHg, tissue=40mmHg, oxygen diffuses (loads) into the cell (by concentration gradient)
Discuss the mechanism of diffusion of carbon dioxide across alveolar space
venous pco2= 46mmHg, alveolar pco2= 40mmHg, carbon dioxide crosses the alveolar septa by simple diffusion (by concentration gradient), much lower pp gradient, crosses readily bc of high solubility
Discuss the mechanism of diffusion of oxygen across the alveolar septa
=>simple diffusion based on partial pressure gradient and concentration gradient
Define Graham’s Law
- when gases are dissolved in liquids the relative rate of diffusion of a given gas is proportional to its solubility and inversely proportional to the square root of its molecular mass
- ex: process that occurs in the alveoli of the lungs
- =>larger the molecule the slower the diffusion
Compare the diffusion capacity of oxygen relative to carbon dioxide, nitrous oxide, carbon monoxide and nitrogen
- Nitrous oxide 14.0, oxygen is 1, co2 is 20.5
* hypoxic mixture, diffusion hypoxia if not on a 100% o2 after nitrous use
Describe the two major elements of diffusion capacity and their components
- membrane capacity - affected by factors involving movement of gas between alveoli and blood
- =>membrane affected by vq mismatch also
- reaction time with hemoglobin - affected by factors involving movement into capillary and uptake by RBC
- =>if low hct, that would decrease diffusion
List four conditions that decrease diffusing capacity
• thickening of the barrier, decreased surface area, decreased uptake by erythrocytes, VQ mismatch
Calculate the amount of oxygen dissolved in the plasma given a PO2 25
• 0.003 x po2 (Henry’s law)
Identify the maximum amount of oxygen which may combine with a gram of hemoglobin
• 1.34 mL/gram
Identify the determinant of the equilibrium point of reaction that determines the amount of oxygen that binds to hemoglobin in the red blood cell
the po2
Calculate oxygen content of the blood given hemoglobin concentration and oxygen saturation
- proportion of hemoglobin that is bound to oxygen is the percent saturation,
- %Hb saturation = o2 bound to Hb/o2 capacity of Hb
- ex: 1.34 x 15x0.98 = 19.7 mL/100mL
Define P50 for hemoglobin saturation
• is the point on the curve where 50% saturation occurs
Calculate the oxygen carrying capacity for varying hemoglobin concentrations and PO2
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Describe the structure of hemoglobin in relationship to its oxygen carrying capacity
4 linked polypeptide chains (globin) attached to a protoporphyrin (heme), chains bind with o2 or carbon monoxide
Calculate delivery of oxygen given PaO2 and mixed venous PO2(comparable to tissue PO2)
.
Describe rationale for monitoring SVO2
represents balance of oxygen delivery and oxygen demand
List five determinants of SVO2
- hgb concentration,
- hgb saturation,
- cardiac output,
- o2 consumption,
- o2 utilization
List six clinical conditions that may decrease SVO2
- cardiac output,
- o2 saturation/ventilation/shunt,
- V/Q, tissue metabolism,
- anemia/hypovolemia,
- fever,
- shivering,
- siezures,
- pain,
- exercise,
- hyperthyroidism
List five factors that may alter P50 and how the oxygen-hemoglobin saturation curve is affected
- this point may move left or right and represents changes in loading and unloading conditions
- temperature, pH, pco2, dpg levels, type of hgb
Define the Bohr Effect as it relates to shifts in the oxyhemoglobin dissociation curve and oxygen loading/unloading
rightward shift means more unloading at lower pH for acidotic tissues, coincides with high pco2 => Bohr effect
List four clinical conditions shifting the oxyhemoglobin dissociation curve to the left
- DECR: in H+(alkalotic),temp, pco2, 2,3-bpg
* less unloading of o2 at a given po2 in a tissue capillary
List four clinical conditions shifting the oxyhemoglobin dissociation curve to the right
- INCR: in H+ (acidotic)concentration, pco2 (bohr effect), temp, 2,3-bpg
- “RIGHTS”
Describe the effect of carbon monoxide poisoning on oxygen carrying capacity and the oxygen dissociation curve
interfers with o2 transport by combining with Hg to form carboxyhemoglobin, Hb and pop normal but o2 decr, shifts left
Discuss mechanisms for dealing with carbon monoxide poisoning
may still have normal o2 levels, incr the foil to promote elimination of carbon monoxide ( dear 1/2 life from 4 hrs to <1 hr)
Discuss the pathophysiology of methemoglobinemia and clinical considerations
.
Describe P50 considerations of abberant hemoglobin’s
.
List six anesthetic considerations for patients with sickle cell
avoid hypoxia and academia (fio2 > 0.5), avoid hypovolemia, avoid hypothermia, transfuse to pcv 30%, no tourniquets
Describe how carbon dioxide is transported in the arterial and venous blood
.
Calculate the amount of CO2 dissolved in the blood given a PCO2
.
Compare the CO2 carrying capacity of reduced hemoglobin compared to oxyhemoglobin
.
Define the Haldane Effect in relationship to the ability of hemoglobin to carry CO2
- fall in hemoglobin saturation increases buffering (more H+ capacity) and increases carbon dioxide carriage
- o2 diffuses out of the blood into the cells, more co2 loads into blood, blood carries more co2 to lungs for elimination
Define “Chloride Shift” as it relates to RBC electrical neutrality and carbonic acid
- allows excess bicarb ions to diffuse out of cell in exchange for chloride ions
- more bicarb ions leave RBC than H+ ions
Compare the carboxyhemoglobin dissociation curve to the oxyhemoglobin dissociation curve
• normally the “curve” is nearly a straight line, shift right for greater levels of oxyhemoglobin, shift left for greater levels of deoxyhemoglobin
