# Respiratory Quiz #4 Flashcards

1
Q

Identify factors that determine exchange rates of gases across membranes

A

Fick’s Law combined with the diffusion rate determined from Graham’s Law (solubility) provides the means for calculating the exchange rates of gasses

2
Q

Define Fick’s Law

A

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

3
Q

Identify two factors which determine the concentration of a gas in a solution using Henry’s Law

A
• partial pressure X solubility coefficient = concentration of gas
• both are directly proportional
• concentration can be incr by incr pp or solubility
4
Q

Compare solubility coefficients for oxygen, carbon dioxide, carbon monoxide and nitrogen

A
• 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
5
Q

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

A
• 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
6
Q

Identify the mechanism responsible for most carriage of oxygen in the plasma

A

most oxygen is carried by hemoglobin, some is dissolved and carried in plasma

7
Q

Describe the effect of increasing FiO2 from 100 to 600 mmHg on oxygen carrying capacity

A

increases o2 carrying capacity very little

8
Q

Identify the average capillary exposure/transit time

A
• 0.7 seconds average, normal is 0.3

* =>0.4 sec grace period

9
Q

Identify the normal time period required for diffusion to occur

A

normal oxygenation occurs in 0.3 seconds

10
Q

Describe the effect of lower alveolar PO2 on diffusion and arterial PO

A

will decrease diffusion, lower po2=lower endpoint, less of a partial pressure gradient means slower diffusion and lower endpoint

11
Q

Compare arterial and tissue PO2 and the effect on diffusion

A

arterial =95mmHg, tissue=40mmHg, oxygen diffuses (loads) into the cell (by concentration gradient)

12
Q

Discuss the mechanism of diffusion of carbon dioxide across alveolar space

A

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

13
Q

Discuss the mechanism of diffusion of oxygen across the alveolar septa

A

=>simple diffusion based on partial pressure gradient and concentration gradient

14
Q

Define Graham’s Law

A
• 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
15
Q

Compare the diffusion capacity of oxygen relative to carbon dioxide, nitrous oxide, carbon monoxide and nitrogen

A
• Nitrous oxide 14.0, oxygen is 1, co2 is 20.5

* hypoxic mixture, diffusion hypoxia if not on a 100% o2 after nitrous use

16
Q

Describe the two major elements of diffusion capacity and their components

A
• 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
17
Q

List four conditions that decrease diffusing capacity

A

• thickening of the barrier, decreased surface area, decreased uptake by erythrocytes, VQ mismatch

18
Q

Calculate the amount of oxygen dissolved in the plasma given a PO2 25

A

• 0.003 x po2 (Henry’s law)

19
Q

Identify the maximum amount of oxygen which may combine with a gram of hemoglobin

A

• 1.34 mL/gram

20
Q

Identify the determinant of the equilibrium point of reaction that determines the amount of oxygen that binds to hemoglobin in the red blood cell

A

the po2

21
Q

Calculate oxygen content of the blood given hemoglobin concentration and oxygen saturation

A
• 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
22
Q

Define P50 for hemoglobin saturation

A

• is the point on the curve where 50% saturation occurs

23
Q

Calculate the oxygen carrying capacity for varying hemoglobin concentrations and PO2

A

.

24
Q

Describe the structure of hemoglobin in relationship to its oxygen carrying capacity

A

4 linked polypeptide chains (globin) attached to a protoporphyrin (heme), chains bind with o2 or carbon monoxide

25
Q

Calculate delivery of oxygen given PaO2 and mixed venous PO2(comparable to tissue PO2)

A

.

26
Q

Describe rationale for monitoring SVO2

A

represents balance of oxygen delivery and oxygen demand

27
Q

List five determinants of SVO2

A
• hgb concentration,
• hgb saturation,
• cardiac output,
• o2 consumption,
• o2 utilization
28
Q

List six clinical conditions that may decrease SVO2

A
• cardiac output,
• o2 saturation/ventilation/shunt,
• V/Q, tissue metabolism,
• anemia/hypovolemia,
• fever,
• shivering,
• siezures,
• pain,
• exercise,
• hyperthyroidism
29
Q

List five factors that may alter P50 and how the oxygen-hemoglobin saturation curve is affected

A
• this point may move left or right and represents changes in loading and unloading conditions
• temperature, pH, pco2, dpg levels, type of hgb
30
Q

Define the Bohr Effect as it relates to shifts in the oxyhemoglobin dissociation curve and oxygen loading/unloading

A

rightward shift means more unloading at lower pH for acidotic tissues, coincides with high pco2 => Bohr effect

31
Q

List four clinical conditions shifting the oxyhemoglobin dissociation curve to the left

A
• DECR: in H+(alkalotic),temp, pco2, 2,3-bpg

* less unloading of o2 at a given po2 in a tissue capillary

32
Q

List four clinical conditions shifting the oxyhemoglobin dissociation curve to the right

A
• INCR: in H+ (acidotic)concentration, pco2 (bohr effect), temp, 2,3-bpg
• “RIGHTS”
33
Q

Describe the effect of carbon monoxide poisoning on oxygen carrying capacity and the oxygen dissociation curve

A

interfers with o2 transport by combining with Hg to form carboxyhemoglobin, Hb and pop normal but o2 decr, shifts left

34
Q

Discuss mechanisms for dealing with carbon monoxide poisoning

A

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)

35
Q

Discuss the pathophysiology of methemoglobinemia and clinical considerations

A

.

36
Q

Describe P50 considerations of abberant hemoglobin’s

A

.

37
Q

List six anesthetic considerations for patients with sickle cell

A

avoid hypoxia and academia (fio2 > 0.5), avoid hypovolemia, avoid hypothermia, transfuse to pcv 30%, no tourniquets

38
Q

Describe how carbon dioxide is transported in the arterial and venous blood

A

.

39
Q

Calculate the amount of CO2 dissolved in the blood given a PCO2

A

.

40
Q

Compare the CO2 carrying capacity of reduced hemoglobin compared to oxyhemoglobin

A

.

41
Q

Define the Haldane Effect in relationship to the ability of hemoglobin to carry CO2

A
• 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
42
Q

Define “Chloride Shift” as it relates to RBC electrical neutrality and carbonic acid

A
• allows excess bicarb ions to diffuse out of cell in exchange for chloride ions
• more bicarb ions leave RBC than H+ ions
43
Q

Compare the carboxyhemoglobin dissociation curve to the oxyhemoglobin dissociation curve

A

• normally the “curve” is nearly a straight line, shift right for greater levels of oxyhemoglobin, shift left for greater levels of deoxyhemoglobin