Case studies: Gas Transfer
Name: ______Date:______
1. Your patient is a 55 year-old BM with a history of COPD. His Hematocrit is 50 and his Hb is 17 gram/dL. HbCO is 2.8%. On RA, you get the following ABG on 760 Pb.
PH / PaC02 / HC03 / Pa027.38 / 49 / 28 / 45
a. Calculate his PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x .209 - (49/.8) =
PAO2 = 142.6 - 61.2 =
PA02 = 87.76 torr
b. Calculate his CaO2
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (17 x 1.34 x .80) + (45 x .003)
CaO2 = (22.78 x .80) + .135
CaO2 = 18.35
c. Calculate his a/A ratio
PaO2/PAO2 =
45/87.76 =
.51 or 51%
d. What level of PaO2 should this patient have as a baseline?
This patient is breathing off an hypoxic drive because his PacO2 is chronically high [ I know this because his pH is WNL because it has gone on long enough to compensate –or get used to the hypercapnia. Because he has a hypoxic drive, we need only correct him to 55-65 torr to fix his hypoxemia.
e. If possible, correct his 02 derangement
Current Fi02 = Desired Fi02
Current Pa02 = Desired Pa02
.21 = X
45 torr = 60 torr
45X = .21(60)
X = .28
We need to move his Fi02 from .21 to .28% and the predicted Pa02 will be 60 torr
f. Which of the 5 types of Hypoxia [if any] is the most likely cause of his 02 derangement?
Hypoxemic Hypoxia
2. Your patient is a 64 LAF year-old who is s/p hip surgery. She is in traction and on the V/Q scan you see that she has large areas of decreased diffusion in the LLL due to an emboli. Her Hematocrit/Hemoglobin is 36 / 12 gr/dL. HbCO is 0.7%. On 50% Venturi mask, she has the following ABG on 760 Pb
PH / PaC02 / HC03 / Pa027.44 / 35 / 23 / 43
a. Calculate her PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x .50 - (35/.8) =
PAO2 = (713 x .5) – 43.75
PAO2 = 142.6 - 61.2 =
PA02 = 312.75 torr
b. Calculate her CaO2
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (12 x 1.34 x .80) + (43 x .003)
CaO2 = (22.78 x .85) +(.129)
CaO2 = (12.864) + (.129)
CaO2 = 12.993
c. Calculate her a/A ratio
PaO2/PAO2 =
43/312.75 =
.137 or 14%
c. What level of PaO2 should this patient have as a baseline?
She doesn’t retain C02 so she most likely has normal lungs and has a 80-100 torr Pa02 as a baseline
e. If possible, correct her O2 derangement
We can’t; the a/A ratio of less than 17% means there is refractory hypoxemia
f. Which of the 5 types of Hypoxia (if any) is the most likely cause of his O2 derangement?
Hypoxemic hypoxemia includes diffusion defects
3. Your patient is a 34 year-old WM who has suffered a GSW (gun shot wound) to the chest. There is severe blood loss Hb is 8 gr/dL. HbCO is 0.9%. SaO2 is 98%. The HR is 145 and the pulse is thready. The patient is being bagged with 100% at a rate of 12 bpm with good bilateral breath sounds and you get the following ABG on 760 Pb
PH / PaC02 / HC03 / P027.37 / 41 / 23 / 455
a. Calculate his PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x 1 - (41/.8) =
PAO2 = (713 x 1) – 51.25
PAO2 = 713 - 51.25 =
PA02 = 661.75 torr
b. Calculate his CaO2
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (8 x 1.34 x .98 ) + (455 x .003)
CaO2 = (22.78 x .98) +(.129)
CaO2 = (12.864) + (.129)
CaO2 = 11.87
b. Calculate his a/A ratio
PaO2/PAO2 =
455/661.75 =
.687 or 69%
c. What level of PaO2 should this patient have as a baseline?
We can assume this patient was healthy so 80-100 torr is a reasonable baseline Pa02
e. If possible, correct his O2 derangement
Current Fi02 = Desired Fi02
Current Pa02 = Desired Pa02
1 = X
455 torr = 80 torr
455X = .21(80)
X = .1758
Reduce the Fi02 to RA because this patient doesn’t need 02 as much as he needs to be bagged and to get surgery and transfusions
f. Which of the 5 types of Hypoxia (if any) is the most likely cause of his 02 derangement?
He is bleeding so he has anemic hypoxia & if his CO is affected he might also have circulatory hypoxia
4. Your patient is a 24 year-old BF with sickle cell. She has diffuse crackles in the bases of her lungs. Her Hb is 10 gram/dL, HbCO is o.8%, SaO2 is 99% and on 3 lpm nasal cannula you get the following ABG on 760 torr Pb.
PH / PaC02 / HC03 / P027.34 / 44 / 23 / 120
a. Calculate her PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x .33 - (44/.8) =
PAO2 = (713 x .33) – 55
PAO2 =235.29 - 51.25 =
PA02 = 184.04 torr
b. Calculate her CaO2
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (10 x 1.34 x .99 ) + (120 x .003)
CaO2 = (13.4 x .99) +(.36)
CaO2 = (13.266) + (.36)
CaO2 = 13.626
c. Calculate her a/A ratio
PaO2/PAO2 =
120/184.24 =
.651 or 65%
d. What level of PaO2 should this patient have as a baseline?
Not a C02 retainer so we can assume 80-100 torr as baseline; we might want to keep her on the high side of normal to prevent more damage to the RBC which bend in low Sa02
e. If possible, correct her O2 derangement
Current Fi02 = Desired Fi02
Current Pa02 = Desired Pa02
.33 = X
120 torr = 100 torr
120X = .33(100)
X = .28
We can reduce her FiO2 to 28%
f. Which of the 5 types of Hypoxia (if any) is the most likely cause of his 02 derangement?
Anemic Hypoxia
5. Your patient is a 27 y/o WM who is a firefighter suffering from smoke inhalation. His BBS are clear and he is c/o dyspnea. His Hb is 11 g/dL, HbCO is 15%. His SpO2 is 100%. His pulse is 92 bpm. He is on a non-rebreather. The hospital is at sea level. His ABG is as follows:
pH / PaC02 / HC03- / Pa027.41 / 36 / 22 / 70
a. Calculate his PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x 1 - (36/.8) =
PAO2 = (713 x 1) – 45
PAO2 =713 - 45 =
PA02 = 668 torr
b. Calculate his CaO2.
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (11 x 1.34 x .85 ) + (70 x .003)
CaO2 = (14.74 x .85) +(.21)
CaO2 = (12.529) + (.21)
CaO2 = 12.739
b. Calculate his a/A ratio
PaO2/PAO2 =
70/668 =
.104 or 10%
c. What level of PaO2 should this patient have as a baseline?
We can assume this patient was healthy so 80-100 torr is a reasonable baseline Pa02
d. How can we treat this patient?
Continue 100% via NRB, Hyperbaric chamber if necessary
f. Which of the 5 types of Hypoxia (if any) is the most likely cause of his O2 derangement?
Anemic Hypxoia – Due to Carbon Monoxide
6. Your patient is a 19 y/o LAF that was from rescued from the fire that the previous patient had attended. She has been severely burned over 60% of her body. Her Hr is 109 bpm, with a strong pulse via femoral artery. Her Hb is 10 g/dL. She is breathing rapidly and shallowly. Upon auscultation her BBS are crackles and coarse. SPO2 is 83% on 100% via NRB . HbCO is 10%. Her ABG drawn from the femoral artery is:
pH / PaC02 / HC03- / Pa027.29 / 47 / 22 / 68
a. Calculate her PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x 1 - (47/.8) =
PAO2 = (713 x 1) – 58.75
PAO2 =713 - 58.75 =
PA02 = 654.25 torr
b. Calculate her CaO2
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (10 x 1.34 x .73 ) + (68 x .003)
CaO2 = (13.4 x .73) +(.204)
CaO2 = (9.782) + (.204)
CaO2 = 9.986 vol %
c. Calculate her a/A ratio
PaO2/PAO2 =
68/654.25 =
.103 or 10%
d. What level of PaO2 should this patient have as a baseline?
We can assume this patient was healthy so 80-100 torr is a reasonable baseline Pa02
e. If possible, correct her O2 derangement.
We can’t; the a/A ratio of less than 17% means there is refractory hypoxemia
f. Which of the 5 types of Hypoxia (if any) is the most likely cause of his 02 derangement?
Anemic Hypoxia due Carbon Monoxide poisoning, and eventually Hypermetabolic hypoxia due to the severity of her burns.
7. Your patient is a 72 y/o WM with a hx of CHF. He is c/o dyspnea and is very sluggish. Hr is 62 bpm, BP is 110/65, his pulse is weak. His Hb is 10 g/dL, HbCO is 2%, SaO2 is 92% and he is on 4 lpm oxygen. The hospital is located at sea level. An ABG is drawn and reads:
pH / PaC02 / HC03- / Pa027.46 / 56 / 38 / 44
a. Calculate his PAO2
PAO2 = [Pb –PH2O] x FiO2 – (PaCO2/.8) =
PAO2 = [760-47] x .37 - (56/.8) =
PAO2 = (713 x .37) – 70 =
PAO2 = 263.81 - 70 =
PA02 = 193.81 torr
b. Calculate his CaO2.
CaO2 = (Hb x 1.34 x SaO2) + (PaO2 x .003)
CaO2 = (10 x 1.34 x .92 ) + (44 x .003)
CaO2 = (13.4 x .92) +(.132)
CaO2 = (12.328) + (.132)
CaO2 = 12.46
c. Calculate his a/A ratio
PaO2/PAO2 =
44/165.29 =
.227 or 23%
d. What level of PaO2 should this patient have as a baseline?
This patient is breathing off an hypoxic drive because his PacO2 is chronically high [ I know this because his pH is WNL because it has gone on long enough to compensate –or get used to the hypercapnia. Because he has a hypoxic drive, we need only correct him to 55-65 torr
e. If possible, correct her O2 derangement.
Current Fi02 = Desired Fi02
Current Pa02 = Desired Pa02
.37 = X
44 torr = 58 torr
44X = .37(58)
X = 0.487
We can increase his FiO2 to 49%
f. Which of the 5 types of Hypoxia (if any) is the most likely cause of his O2 derangement?
Hypoxemic Hypoxia,
It can also be due to circulatory hypoxia b/c of his heart condition.