45. Case 1 (Les 16)
• An 83 year-old woman with dementia is sent to the ER
from her skilled nurse facility after she was found
tachypnic and hypoxic. On arrival, she is in distress. Vital
signs: T=38.3⁰C, HR=115, BP=135/86, RR=35, O2 sat = 75%
on room air. Her breaths are rapid and shallow.
• ABG: pH=7.53, PaCO2=26, PaO2=41
• What is the most likely cause of hypoxemia?
Step 1: Check
A-a gradient
Step 2: Estimate
normal A-a
gradient
PAO2 = [FiO2(Pi – PH2O)] – (PaCO2/RQ)
PAO2 = 150 – (26/0.8) ≈ 118mmHg
A-a gradient = PAO2 – PaO2 = 118 – 41 = 77mmHg
Normal A-a grad = (Age/4) + 4
Normal A-a grad = (83/4) + 4 ≈ 25mmHg
Most likely diagnosis:
Pneumonia and/or
aspiration pneumonitis
46. Case 2 (Les 16)
• A 56 year-old man with a history of CAD, HTN, and 60 pack
years of smoking, presents to the ER with a productive
cough and dyspnea for 3 days. On exam, his RR=28 and O2
sat = 81% on room air. His breaths are shallow and with
pursed lips.
• ABG: pH=7.31, PaCO2=60, PaO2=57
• What is the most likely cause of hypoxemia?
Step 1: Check
A-a gradient
PAO2 = [FiO2(Pi – PH2O)] – (PaCO2/RQ)
PAO2 = 150 – (60/0.8) = 75mmHg
A-a gradient = PAO2 – PaO2 = 75 – 57 = 18mmHg
Step 2: Estimate
normal A-a
gradient
Normal A-a grad = (Age/4) + 4
Normal A-a grad = (56/4) + 4 = 18mmHg
Most likely diagnosis:
COPD exacerbation
47. Case 3 (Les 17)
• An 80 y/o man with COPD, presents to the ER with
progressive dyspnea and cough for 3 days. He appears
acutely uncomfortable, and is sitting up, leaning forward
with his hands on his knees. Vitals: T=36.9, HR=104,
BP=135/80, RR=30, O2 sat = 95% on Venturi mask set at
30%.
• ABG: pH=7.28, PaCO2=80, PaO2=80
• What is the most likely cause of hypoxemia?
Step 1: Check
A-a gradient
PAO2 = [FiO2(Pi – PH2O)] – (PaCO2/RQ)
PAO2 = [0.3(760-47)] – (80/0.8) ≈ 114mmHg
A-a gradient = PAO2 – PaO2 = 114 – 80 = 34mmHg
Step 2: Estimate
normal A-a
gradient
Normal A-a grad = (Age/4) + 4 + 50 (FiO2 – 0.21)
Normal A-a grad = (80/4) + 4 + 50 (0.30 – 0.21)
Normal A-a grad ≈ 29mmHg
Most likely diagnosis:
COPD exacerbation
48. Case 4 (Les 17)
• A 64 y/o man with a history of CAD, presents to the ER
with sudden onset of dyspnea 1 hour ago. He is in
moderate respiratory distress, with rapid, shallow breaths.
Vitals: T=36.2, HR=115, BP=95/40, RR=30, O2 sat = 100 on
6L via nasal cannula.
• ABG: pH=7.54, PaCO2=28, PaO2=143
• What is the most likely cause of hypoxemia?
Step 1: Check
A-a gradient
Step 2: Estimate
normal A-a
gradient
PAO2 = [FiO2(Pi – PH2O)] – (PaCO2/RQ)
PAO2 = [0.45 (760-47)] – (28/0.8) ≈ 286mmHg
A-a gradient = PAO2 – PaO2 = 286 – 143 =143mmHg
Normal A-a grad = (Age/4) + 4 + 50 (FiO2 – 0.21)
Normal A-a grad = (64/4) + 4 + 50 (0.45 – 0.21)
Normal A-a grad ≈ 32mmHg
Most likely diagnosis:
Pulmonary embolism, or
Acute coronary syndrome with
secondary pulmonary edema
55. Case 5 (Les 17)
• A 44 y/o man with a history of IV drug use is brought to
the ER by friends after he was found confused wandering
outside his house. He is currently complaining of shortness
of breath and “feeling real bad”. On exam, he appears
acutely ill, and is in severe respiratory distress. Vitals:
T=39.2, HR=125, BP=84/45, RR=44, O2 sat = 75% on room
air. He has diffuse bilateral crackles, a 3/6 systolic murmur
throughout the precordium, and flat JVP.
• ABG: pH=7.39, PaCO2=26, PaO2=48 (on room air);
pH=7.37, PaCO2=27, PaO2=230 (on 15L via Non-rebreather)
• What is the most likely cause of hypoxemia?
56. Case 5 (Les 17)
• ABG: pH=7.39, PaCO2=26, PaO2=48 (on room air);
• pH=7.37, PaCO2=27, PaO2=230 (on 15L via Non-rebreather)
Step 1: Check
A-a gradient
Step 1: Check
A-a gradient
PAO2 = [FiO2(Pi – PH2O)] – (PaCO2/RQ)
PAO2 = 150 – (26/0.8) ≈ 118mmHg
A-a gradient = PAO2 – PaO2 = 118 – 48 =70mmHg
Step 2: Estimate
normal A-a
gradient
Step 2: Estimate
normal A-a
gradient
Normal A-a grad = (Age/4) + 4
Normal A-a grad = (44/4) + 4 = 15mmHg
Normal A-a grad = (Age/4) + 4 + 50 (FiO2 – 0.21)
Normal A-a grad = (44/4) + 4 + 50 (0.85 – 0.21)
Normal A-a grad ≈ 47mmHg
PAO2 = [FiO2(Pi – PH2O)] – (PaCO2/RQ)
PAO2 = [0.85 (760-47)] – (27/0.8) ≈ 572mmHg
A-a gradient = PAO2 – PaO2 = 572 – 230 =342mmHg
57. Case 5 (Les 17)
• A 44 y/o man with a history of IV drug use is brought to
the ER by friends after he was found confused wandering
outside his house. He is currently complaining of shortness
of breath and “feeling real bad”. On exam, he appears
acutely ill, and is in severe respiratory distress. Vitals:
T=39.2, HR=125, BP=84/45, RR=44, O2 sat = 75% on room
air. He has diffuse bilateral crackles, a 3/6 systolic murmur
throughout the precordium, and flat JVP.
• ABG: pH=7.39, PaCO2=26, PaO2=48 (on room air);
pH=7.37, PaCO2=27, PaO2=230 (on 15L via Non-rebreather)
• What is the most likely cause of hypoxemia?
Most likely diagnosis:
Severe sepsis + acute lung injury
secondary to pneumonia and/or
endocarditis
61. Case 6 (Les 4)
• A 24 y/o man is found unresponsive on the floor soiled
with vomit. He was seen 4 hours prior, and appeared well
at that time.
• ABG: pH=7.34, PaCO2=65, HCO3=34
• Acid-base disorders?
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
pH < 7.35 → Acidemia
PCO2 > 40 → Respiratory Acidosis
Is HCO3 ↑ by 1mmol/l for each 10mmHg
PCO2 is above 40mmHg?
Therefore, a 2nd disorder is present.
HCO3 is higher than predicted.
2nd disorder: Metabolic alkalosis
No
62. Case 7 (Les 6)
• A 75 y/o woman presents with fever and profuse diarrhea
for 2 days. Vital signs: T=38.5, HR=130, BP=78/30.
• ABG: pH=7.29, PaCO2=30, HCO3=14
• Lab values: Na=128, K=3.2, Cl=94
• Acid-base disorders?
pH < 7.35 → Acidemia
PCO2 < 40 → Metabolic Acidosis
PCO2 ≈ 1.5 (HCO3) + 8 = 29
Appropriate compensation
AG = Na – (Cl + HCO3) = 20
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
Elevated Gap Metabolic Acidosis
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟖
𝟏𝟎
= 0.8 < 1.0
Normal Gap Metabolic Acidosis
63. Case 8 (Les 6)
• A 48 y/o alcoholic man is found unconscious in his
apartment, soiled with vomit. He was last seen leaving a
party 6 hours prior.
• ABG: pH=7.17, PaCO2=65, HCO3=22
• Lab values: Na=136, K=3.4, Cl=98, Alb=1.6
• Acid-base disorders?
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
pH < 7.35 → Acidemia
PCO2 > 40 → Respiratory Acidosis
Is HCO3 ↑ by 1 for each 10 PCO2 > 40? No
HCO3 ↓ than expected → Met. Acidosis
AG = 136 – (98 + 22) = 16
AGadjusted = AGmeas + 2.5(4 - Alb) = 22
↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟎
𝟐
= 5 > 2 Met. Alk
Respiratory Acidosis + Elevated Gap Metabolic Acidosis
+ Metabolic Alkalosis
64. Case 9 (Les 7)
• A 61 y/o morbidly obese man with COPD and CHF has an
ABG and metabolic panel checked during routine
pulmonary function tests.
• ABG: pH=7.41, PaCO2=55, HCO3=34
• Electrolytes: Na=134, K=3.4, Cl=92.
• Acid-base disorders?
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
Normal
PCO2 > 40 → Respiratory Acidosis
Normal pH → Opposite 1st disorder
→ Metabolic Alkalosis
AG = 134 – (92 + 34) = 8
↑ AG Metabolic Acidosis is not present
65. Case 10 (Les 7)
• A 14 y/o girl with bulimia is brought to the ER after being
found unresponsive at home with an empty pill bottle
nearby.
• ABG: pH=7.39, PaCO2=22, HCO3=13
• Electrolytes: Na=139, K=3.1, Cl=88
• Acid-base disorders?
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
Normal
PCO2 < 40 → Respiratory Alkalosis
Normal pH → Opposite 1st disorder
→ Metabolic Acidosis
AG = 139 – (88 + 13) = 38
↑ AG Metabolic Acidosis
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟐𝟔
𝟏𝟏
= 2.2 > 2 Met. Alk
Respiratory Alkalosis + Elevated Gap Metabolic Acidosis
+ Metabolic Alkalosis
66. Case 11 (Les 7)
• A 32 y/o pregnant woman comes to the ER with 4 days of
“non-stop” vomiting. Vitals on admission: T=37.0, HR= 145,
BP = 78/42.
• ABG: pH=7.41, PaCO2=42, HCO3=26
• Electrolytes: Na=146, K=3.2, Cl=92
• Acid-base disorders?
pH, PCO2, HCO3 normal
ABG normal
67. Case 11 (Les 7)
• A 32 y/o pregnant woman comes to the ER with 4 days of
“non-stop” vomiting. Vitals on admission: T=37.0, HR= 145,
BP = 78/42.
• ABG: pH=7.41, PaCO2=42, HCO3=26
• Electrolytes: Na=146, K=3.2, Cl=92
• Acid-base disorders?
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
Normal
Normal
AG = 146 – (92 + 26) = 28
↑ AG Metabolic Acidosis
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟔
−𝟐
= -8 Met. Alk
Elevated Gap Metabolic Acidosis + Metabolic Alkalosis
68. Case 12 (Les 13)
• A 75 y/o woman is sent to the ER from her nursing home
with fever and dyspnea. Vitals: T=39.0, HR=122, BP=95/40,
RR=35, O2 sat = 84% on 6L via face mask. Exam notable for
crackles and decreased breath sounds at right lung base.
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
• What is the most likely diagnosis?
69. Case 12 (Les 13)
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 < 40 → Respiratory Alkalosis
pH > 7.45 → Alkalemia
Is HCO3 ↓ by 2 for each 10 PCO2 < 40?
HCO3 lower than expected → Met. Acid
AG = 148 – (110 + 17) = 21
AGadjusted = AGmeas + 2.5 (4 - Alb) = 24
↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟐
𝟕
= 1.7
Step 6: Differential
diagnosis
Respiratory Alkalosis ?
71. Case 12 (Les 13)
• A 75 y/o woman is sent to the ER from her nursing home
with fever and dyspnea. Vitals: T=39.0, HR=122, BP=95/40,
RR=35, O2 sat = 84% on 6L via face mask. Exam notable for
crackles and decreased breath sounds at right lung base.
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
• Chest X-ray: Right lower lobe consolidation
72. Case 12 (Les 13)
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 < 40 → Respiratory Alkalosis
pH > 7.45 → Alkalemia
Is HCO3 ↓ by 2 for each 10 PCO2 < 40?
HCO3 lower than expected → Met. Acid
AG = 148 – (110 + 17) = 21
AGadjusted = AGmeas + 2.5 (4 - Alb) = 24
↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟐
𝟕
= 1.7
Step 6: Differential
diagnosis
Resp. Alk. → Hypoxemia → RLL pneumonia
Met. Aci. ?
73.
74. Case 12 (Les 13)
• A 75 y/o woman is sent to the ER from her nursing home
with fever and dyspnea. Vitals: T=39.0, HR=122, BP=95/40,
RR=35, O2 sat = 84% on 6L via face mask. Exam notable for
crackles and decreased breath sounds at right lung base.
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
• Chest X-ray: Right lower lobe consolidation
• Lactate=5.2, Ketones: negative
75.
76. Case 12 (Les 13)
• A 75 y/o woman is sent to the ER from her nursing home
with fever and dyspnea. Vitals: T=39.0, HR=122, BP=95/40,
RR=35, O2 sat = 84% on 6L via face mask. Exam notable for
crackles and decreased breath sounds at right lung base.
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
• Chest X-ray: Right lower lobe consolidation
• Lactate=5.2, Ketones: negative
77.
78. Case 12 (Les 13)
• ABG: pH=7.47, PaCO2=25, HCO3=17
• Lab values: Na=148, K=3.2, Cl=110, Alb=2.7
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 < 40 → Respiratory Alkalosis
pH > 7.45 → Alkalemia
Is HCO3 ↓ by 2 for each 10 PCO2 < 40?
HCO3 lower than expected → Met. Acid
AG = 148 – (110 + 17) = 21
AGadjusted = AGmeas + 2.5 (4 - Alb) = 24
↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟐
𝟕
= 1.7
Step 6: Differential
diagnosis
Resp. Alk. → Hypoxemia → RLL pneumonia
Met. Aci. → Lactic acidosis
Severe sepsis secondary to RLL pneumonia complicated by lactic acidosis
83. Case 13 (Les 13)
• A 32 y/o woman with schizophrenia is found unconscious
on the floor of her garage. Vitals: T=37.3, HR=120,
BP=104/56, RR=6, O2 sat 88% on room air.
• ABG: pH=6.96, PaCO2=60, HCO3=13
• Lab values: Na=132, K=3.4, Cl=95, Alb=1.9, Glucose=4.1
• What is the most likely diagnosis?
84. Case 13 (Les 13)
• ABG: pH=6.96, PaCO2=60, HCO3=13
• Lab values: Na=132, K=3.4, Cl=95, Alb=1.9, Glucose=4.1
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 > 40 → Respiratory Acidosis
pH < 7.35 → Acidemia
Is HCO3 ↑ by 1 for each 10 PCO2 > 40?
HCO3 lower than expected → Met. Acid
AG = 132 – (95 + 13) = 24
AGadjusted = AGmeas + 2.5 (4 - Alb) = 29
↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟕
𝟏𝟐
= 1.42
Step 6: Differential
diagnosis
Diff Dx of ↑AG acidosis < Resp. Acid
Met. Aci. → Lactic acidosis
85.
86. Case 13 (Les 13)
• A 32 y/o woman with schizophrenia is found unconscious
on the floor of her garage. Vitals: T=37.3, HR=120,
BP=104/56, RR=6, O2 sat 88% on room air.
• ABG: pH=6.96, PaCO2=60, HCO3=13
• Lab values: Na=132, K=3.4, Cl=95, Alb=1.9, Glucose=4.1
• Lactate=2.1, Ketones: negative
87.
88. Case 13 (Les 13)
• A 32 y/o woman with schizophrenia is found unconscious
on the floor of her garage. Vitals: T=37.3, HR=120,
BP=104/56, RR=6, O2 sat 88% on room air.
• ABG: pH=6.96, PaCO2=60, HCO3=13
• Lab values: Na=132, K=3.4, Cl=95, Alb=1.9, Glucose=4.1
• Lactate=2.1, Ketones: negative
• Urea=8.6, Creatinine=141
89.
90. Case 13 (Les 13)
• A 32 y/o woman with schizophrenia is found unconscious
on the floor of her garage. Vitals: T=37.3, HR=120,
BP=104/56, RR=6, O2 sat 88% on room air.
• ABG: pH=6.96, PaCO2=60, HCO3=13
• Lab values: Na=132, K=3.4, Cl=95, Alb=1.9, Glucose=4.1
• Lactate=2.1, Ketones: negative
• Urea=8.6, Creatinine=141
• Serum osmolarity=310 mOsm/l
• Serum Osmcalculated = 2[Na] + [Urea] + [Glu] = 277
→ Osmolal gap = 310 – 277 = 33
91.
92. Case 13 (Les 13)
• A 32 y/o woman with schizophrenia is found unconscious
on the floor of her garage. Vitals: T=37.3, HR=120,
BP=104/56, RR=6, O2 sat 88% on room air.
• ABG: pH=6.96, PaCO2=60, HCO3=13
• Lab values: Na=132, K=3.4, Cl=95, Alb=1.9, Glucose=4.1
• Lactate=2.1, Ketones: negative
• Urea=8.6, Creatinine=141
• Serum osmolarity=310 mOsm/l
• Serum Osmcalculated = 2[Na] + [Urea] + [Glu] = 277
→ Osmolal gap = 310 – 277 = 33
• Ethanol: not detected, urine tox screen: + opiates
Presumed ingestion of a toxic alcohol (e.g methanol,
ethylene glycol) in combination with a narcotic. Cannot r/o
coingestion with additional respiratory depressants
95. Case 14 (Les 13)
• A 56 y/o morbidly obese man with diabetes and
hypertension presents to pulmonary clinic after referral
from primary medical doctor for asymptomatic hypoxia.
He has no history of smoking. Vitals: HR=85, BP=152/86,
RR=16, O2 sat = 90% on room air, BMI=45. Difficult to
auscultate heart and lung sounds. Neuro exam normal.
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
• What is the most likely diagnosis?
96. Case 14 (Les 13)
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 > 40 → Respiratory Acidosis
pH < 7.35 → Acidemia
Is HCO3 ↑ by 4 for each 10 PCO2 > 40?
HCO3 lower than expected → Met. Acid
AG = 134 – (100 + 26) = 8
AGadjusted = AGmeas + 2.5 (4 - Alb) = 9
Nor AG
Met Aci
Step 6: Differential
diagnosis
Respiratory Acidosis ?
97.
98. Case 14 (Les 13)
• A 56 y/o morbidly obese man with diabetes and
hypertension presents to pulmonary clinic after referral
from primary medical doctor for asymptomatic hypoxia.
He has no history of smoking. Vitals: HR=85, BP=152/86,
RR=16, O2 sat = 90% on room air, BMI=45. Difficult to
auscultate heart and lung sounds.
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
• Neuro exam normal.
• Chest X-ray: normal.
99. Case 14 (Les 13)
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 > 40 → Respiratory Acidosis
pH < 7.35 → Acidemia
Is HCO3 ↑ by 4 for each 10 PCO2 > 40?
HCO3 lower than expected → Met. Acid
AG = 134 – (100 + 26) = 8
AGadjusted = AGmeas + 2.5 (4 - Alb) = 9
Nor AG
Met Aci
Step 6: Differential
diagnosis
Respiratory Acidosis: OHS
Normal AG Metabolic Acidosis ?
100.
101. Case 14 (Les 13)
• A 56 y/o morbidly obese man with diabetes and
hypertension presents to pulmonary clinic after referral
from primary medical doctor for asymptomatic hypoxia.
He has no history of smoking. Vitals: HR=85, BP=152/86,
RR=16, O2 sat = 90% on room air, BMI=45. Difficult to
auscultate heart and lung sounds.
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
• Neuro exam normal.
• Chest X-ray: normal.
• Urea=6.4, Creatinine=150
102.
103. Case 14 (Les 13)
• A 56 y/o morbidly obese man with diabetes and
hypertension presents to pulmonary clinic after referral
from primary medical doctor for asymptomatic hypoxia.
He has no history of smoking. Vitals: HR=85, BP=152/86,
RR=16, O2 sat = 90% on room air, BMI=45. Difficult to
auscultate heart and lung sounds.
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
• Neuro exam normal. Chest X-ray: normal.
• Urea=6.4, Creatinine=150
• Urine pH=5.0
• Urine electrolytes: Na=60, K=10, Cl=15
UAG = Na + K – Cl = 60 + 10 – 15 = 55
104.
105. Case 14 (Les 13)
• ABG: pH=7.22, PaCO2=65, HCO3=26
• Lab values: Na=134, K=5.8, Cl=100, Alb=3.6, Glucose=10.7
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 > 40 → Respiratory Acidosis
pH < 7.35 → Acidemia
Is HCO3 ↑ by 4 for each 10 PCO2 > 40?
HCO3 lower than expected → Met. Acid
AG = 134 – (100 + 26) = 8
AGadjusted = AGmeas + 2.5 (4 - Alb) = 9
Nor AG
Met Aci
Step 6: Differential
diagnosis
Respiratory Acidosis → OHS
Normal AG Metabolic Acidosis → Type 4 RTA
Chronic respiratory acidosis from obesity hypoventilation syndrome
combine with coincidental type 4 RTA
116. Case 15 (Les 13)
• A 60 y/o alcoholic is found down in an alley soiled with
vomit. He is comatose in the ER with vitals: T=39.2,
HR=130, BP=74/36, RR=8, O2 sat = 80% on room air
• ABG: pH=7.37, PaCO2=65, HCO3=36
• Lab values: Na=125, K=3.2, Cl=75, Alb=1.5
• What is the most likely diagnosis?
121. Case 15 (Les 13)
• A 60 y/o alcoholic is found down in an alley soiled with
vomit. He is comatose in the ER with vitals: T=39.2,
HR=130, BP=74/36, RR=8, O2 sat = 80% on room air
• ABG: pH=7.37, PaCO2=65, HCO3=36
• Lab values: Na=125, K=3.2, Cl=75, Alb=1.5
• Lactate=4.3, Ketones: positive
122.
123. Case 15 (Les 13)
• A 60 y/o alcoholic is found down in an alley soiled with
vomit. He is comatose in the ER with vitals: T=39.2,
HR=130, BP=74/36, RR=8, O2 sat = 80% on room air
• ABG: pH=7.37, PaCO2=65, HCO3=36
• Lab values: Na=125, K=3.2, Cl=75, Alb=1.5
• Lactate=4.3, Ketones: positive
• Urea=15.3, Creatinine=150, Glucose=3.4
• Ethanol=390
• Urine toxin screen: negative
126. Case 15 (Les 13)
• A 60 y/o alcoholic is found down in an alley soiled with
vomit. He is comatose in the ER with vitals: T=39.2,
HR=130, BP=74/36, RR=8, O2 sat = 80% on room air
• ABG: pH=7.37, PaCO2=65, HCO3=36
• Lab values: Na=125, K=3.2, Cl=75, Alb=1.5, Glucose=3.4
• Lactate=4.3, Ketones: positive
• Urea=15.3, Creatinine=150
• Ethanol=390
• Urine toxin screen: negative
• Chest X-ray: Right middle lobe consolidation
Respiratory depression from acute alcoholic intoxication,
combined with a metabolic alkalosis from vomiting and
dehydration, a lactic acidosis secondary to septic shock possibly
due to aspiration pneumonia, and an alcoholic ketoacidosis
131. Case 16 (Les 14)
• A 56 y/o woman with severe COPD presents with sudden
onset of shortness of breath for 3 hours. Vitals: T=37.2,
HR=115, BP=112/66, RR=35, O2 sat 90% on room air. She is
in visible respiratory distress. Her lung sounds are clear.
• ABG: pH=7.50, PaCO2=48, HCO3=36
• Lab values: Na=138, K=3.2, Cl=92, Alb=3.8, Glucose=7.2
• Urea=11.8, Creatinine=106
• What is the most likely diagnosis?
133. Case 16 (Les 14)
• A 56 y/o woman with severe COPD presents with sudden
onset of shortness of breath for 3 hours. Vitals: T=37.2,
HR=115, BP=112/66, RR=35, O2 sat 90% on room air. She is
in visible respiratory distress. Her lung sounds are clear.
• ABG: pH=7.50, PaCO2=48, HCO3=36
• Lab values: Na=138, K=3.2, Cl=92, Alb=3.8, Glucose=7.2
• Urea=11.8, Creatinine=106
• HCO3 (2 weeks ago): 36
Post-hypocapnic metabolic alkalosis ?
Acute respiratory alkalosis superimposed on
chronic respiratory acidosis
135. Case 16 (Les 14)
• A 56 y/o woman with severe COPD presents with sudden
onset of shortness of breath for 3 hours. Vitals: T=37.2,
HR=115, BP=112/66, RR=35, O2 sat 90% on room air. She is
in visible respiratory distress. Her lung sounds are clear.
• ABG: pH=7.50, PaCO2=48, HCO3=36
• Lab values: Na=138, K=3.2, Cl=92, Alb=3.8, Glucose=7.2
• Urea=11.8, Creatinine=106
• HCO3 (2 weeks ago): 36
• Chest X-ray: Hyperinflated lungs, no other abnormality
Acute respiratory alkalosis superimposed on
chronic respiratory acidosis
136.
137.
138. Case 16 (Les 14)
• A 56 y/o woman with severe COPD presents with sudden
onset of shortness of breath for 3 hours. Vitals: T=37.2,
HR=115, BP=112/66, RR=35, O2 sat 90% on room air. She is
in visible respiratory distress. Her lung sounds are clear.
• ABG: pH=7.50, PaCO2=48, HCO3=36
• Lab values: Na=138, K=3.2, Cl=92, Alb=3.8, Glucose=7.2
• Urea=11.8, Creatinine=106
• HCO3 (2 weeks ago): 36
• Chest X-ray: Hyperinflated lungs, no other abnormality
Acute respiratory alkalosis superimposed on chronic
respiratory acidosis. Most likely etiology is acute pulmonary
embolism superimposed on chronic CO2 retention from COPD
149. Algorithm of ABG Analysis
ABG Analysis
1. Check pH
Oxygenation
Differential Diagnosis → Final summative diagnosis
2. Check PaCO2
3. Check saturation gap If AG ↑
Acid-Base Disorders
3. Check compensation
4. Check Anion Gap
5. Check Delta Ratio
1. Check A-a gradient
2. Compare with
normal/expected
A-a gradient
150. Case 17 (Les 20)
• A 92 y/o woman is sent to the ER from her nursing home
after she developed fever and dyspnea several hours ago.
On the arrival to the ER: T=39.2, HR=125, BP=76/48,
RR=30, SpO2=85% on room air. She is in respiratory distress
and incoherent. Exam otherwise notable for decreased
breath sounds at the right lung base. JVP is flat, and her
extremities are warm.
• ABG: pH=7.46, PaCO2=25, HCO3=17, PaO2=47, SaO2=83%
• Lab values: Na=130, K=5.6, Cl=93, Alb=2.5
• What is the most likely diagnosis?
152. Case 17 (Les 20)
• ABG: pH=7.46, PaCO2=25, HCO3=17, PaO2=47, SaO2=83%
• Lab values: Na=130, K=5.6, Cl=93, Alb=2.5
Step 1: Check pH
Step 2: Check PCO2
Step 3: Evaluate
compensation
Step 4: Calculate
anion gap
Step 5: Calculate
delta ratio
PCO2 < 40 → Respiratory Alkalosis
pH > 7.45 → Alkalemia
Is HCO3 ↓ by 2 for each 10 PCO2 < 40?
HCO3 lower than expected → Met. Acid
AG = 130 – (93 + 17) = 20
AGadjusted = AGmeas + 2.5 (4 - Alb) = 24
↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟏𝟐
𝟕
= 1.7
153. Case 17 (Les 20)
Differential Diagnosis
Elevated A-a grad
Hypoxemia
154.
155. Case 17 (Les 20)
• A 92 y/o woman is sent to the ER from her nursing home
after she developed fever and dyspnea several hours ago.
On the arrival to the ER: T=39.2, HR=125, BP=76/48,
RR=30, SpO2=85% on room air. She is in respiratory distress
and incoherent. Exam otherwise notable for decreased
breath sounds at the right lung base. JVP is flat, and her
extremities are warm.
• ABG: pH=7.46, PaCO2=25, HCO3=17, PaO2=47, SaO2=83%
• Lab values: Na=130, K=5.6, Cl=93, Alb=2.5
• Chest X-ray: Right lower and middle lung consolidation
156.
157. Case 17 (Les 20)
Differential Diagnosis
Elevated A-a grad
Hypoxemia
Fever + SOB + ↑RR
→ Pneumonia, PE, sepsis + ARDS
Respiratory
Alkalosis
159. Case 17 (Les 20)
Differential Diagnosis
Elevated A-a grad
Hypoxemia
Fever + SOB + ↑RR
→ Pneumonia, PE, sepsis + ARDS
Respiratory
Alkalosis
Hypoxemia
↑ AG Metabolic
Acidosis
Check lactate & ketones?
Lactate=5.5. Ketones: negative
→ Lactic Acidosis
160.
161. Case 17 (Les 20)
• A 92 y/o woman is sent to the ER from her nursing home
after she developed fever and dyspnea several hours ago.
On the arrival to the ER: T=39.2, HR=125, BP=76/48,
RR=30, SpO2=85% on room air. She is in respiratory distress
and incoherent. Exam otherwise notable for decreased
breath sounds at the right lung base. JVP is flat, and her
extremities are warm.
• ABG: pH=7.46, PaCO2=25, HCO3=17, PaO2=47, SaO2=83%
• Lab values: Na=130, K=5.6, Cl=93, Alb=2.5
• Chest X-ray: Right lower and middle lung consolidation
• Lactate=5.5. Ketones: negative
162. Case 17 (Les 20)
Differential Diagnosis
Elevated A-a grad
Hypoxemia
Fever + SOB + ↑RR
→ Pneumonia, PE, sepsis + ARDS
Respiratory
Alkalosis
Hypoxemia
↑ AG Metabolic
Acidosis
Lactate=5.5. Ketones: negative
→ Lactic Acidosis
→ Systemic hypoperfusion + sepsis
→ Septic shock
Septic shock, secondary to pneumonia (health care
associated), complicated by hypoxemia and lactic acidosis
Health care associated pneumonia, complicated by septic
shock, hypoxemia, and lactic acidosis
163. Case 18 (Les 20)
• A 45 y/o man is found unconscious in a park. On arrival to
the ER: T=36.4, HR=115, BP=80/48, RR=6, SpO2=75% on
room air. He is disheveled and comatose. Aside from the
vital sign abnormalities, and non-visible JVP, pulmonary
and cardiac exams are normal. Extremities are cold andn
mildly cyanotic.
• ABG: pH=7.03, PaCO2=70, HCO3=18, PaO2=46, SaO2=77%
• Lab values: Na=125, K=2.6, Cl=83, Alb=2.0
• What is the most likely diagnosis?
166. Case 18 (Les 20)
Differential Diagnosis
Normal A-a grad
Hypoxemia
Hypoventilation
Respiratory
Acidosis
COPD/asthma, OHS, drugs
167. Case 18 (Les 20)
• A 45 y/o man is found unconscious in a park. On arrival to
the ER: T=36.4, HR=115, BP=80/48, RR=6, SpO2=75% on
room air. He is disheveled and comatose. Aside from the
vital sign abnormalities, and non-visible JVP, pulmonary
and cardiac exams are normal. Extremities are cold andn
mildly cyanotic.
• ABG: pH=7.03, PaCO2=70, HCO3=18, PaO2=46, SaO2=77%
• Lab values: Na=125, K=2.6, Cl=83, Alb=2.0
• Urine tox screen: + opiates, + benzos
• Ethanol = 350mg/dl
• Salicylate, acetaminophen: negative
168. Case 18 (Les 20)
Differential Diagnosis
Normal A-a grad
Hypoxemia
Hypoventilation
Respiratory
Acidosis
COPD/asthma, OHS, drugs → Drugs ?
Opiates, benzodiazepines, ethanol
↑ AG Metabolic
Acidosis
Check lactate & ketones?
169. Case 18 (Les 20)
• A 45 y/o man is found unconscious in a park. On arrival to
the ER: T=36.4, HR=115, BP=80/48, RR=6, SpO2=75% on
room air. He is disheveled and comatose. Aside from the
vital sign abnormalities, and non-visible JVP, pulmonary
and cardiac exams are normal. Extremities are cold andn
mildly cyanotic.
• ABG: pH=7.03, PaCO2=70, HCO3=18, PaO2=46, SaO2=77%
• Lab values: Na=125, K=2.6, Cl=83, Alb=2.0
• Urine tox screen: + opiates, + benzos
• Ethanol = 350mg/dl
• Salicylate, acetaminophen: negative
• Lactate=4.1. Ketones: positive, Glu=4.7
172. Case 18 (Les 20)
Final Diagnosis
1. Overdose of alcohol, opiates, and benzodiazepines,
resulting in a severe respiratory acidosis and
hypoventilation-associated hypoxemia
2. Lactic acidosis, secondary to hypoxemia, acute ethanol
intake, and hypovolemic +/- septic shock
3. Alcoholic ketoacidosis
4. Metabolic alkalosis, likely secondary to dehydration +/-
vomiting
173. Case 19 (Les 20)
• A 48 y/o man with AIDS and depression is brought to the
ER after he was found unconscious by a friend, surrounded
by empty pill bottles. On arrival, he is comatose and
cyanotic. Vitals: T=37.5, HR=105, BP=95/45, RR=30,
SpO2=87% on 10L via face mask. The remainder of the
exam is unremarkable.
• ABG: pH=7.40, PaCO2=20, HCO3=12, PaO2=370, SaO2=100%
• Lab values: Na=140, K=6.2, Cl=113, Alb=2.0
• What is the most likely diagnosis?
175. Case 19 (Les 20)
• ABG: pH=7.40, PaCO2=20, HCO3=12, PaO2=370, SaO2=100%
• Lab values: Na=140, K=6.2, Cl=113, Alb=2.0
Step 1: Check pH
Step 2: Check PCO2
& HCO3
Step 3: Calculate
anion gap
Step 4: Calculate
delta ratio
Both low → Resp. Alk + Met. Aci
Normal
AG = 140 – (113 + 12) = 15
AGadjusted = AGmeas + 2.5 (4 - Alb) = 20 ↑ AG
Met Aci
Delta Ratio =
∆ 𝑨𝑮
∆ 𝑯𝑪𝑶𝟑
=
𝟖
𝟏𝟐
= 0.7
→ Normal AG Met. Aci
176. Case 19 (Les 20)
Differential Diagnosis
Evaluated
Saturation Gap
SaO2 > SpO2 + cyanosis
→ Methemoglobinemia ?
177. Case 19 (Les 20)
• A 48 y/o man with AIDS and depression is brought to the
ER after he was found unconscious by a friend, surrounded
by empty pill bottles. On arrival, he is comatose and
cyanotic. Vitals: T=37.5, HR=105, BP=95/45, RR=30,
SpO2=87% on 10L via face mask. The remainder of the
exam is unremarkable.
• ABG: pH=7.40, PaCO2=20, HCO3=12, PaO2=370, SaO2=100%
• Lab values: Na=140, K=6.2, Cl=113, Alb=2.0
• %MetHb=35%
181. Case 19 (Les 20)
• A 48 y/o man with AIDS and depression is brought to the
ER after he was found unconscious by a friend, surrounded
by empty pill bottles. On arrival, he is comatose and
cyanotic. Vitals: T=37.5, HR=105, BP=95/45, RR=30,
SpO2=87% on 10L via face mask. The remainder of the
exam is unremarkable.
• ABG: pH=7.40, PaCO2=20, HCO3=12, PaO2=370, SaO2=100%
• Lab values: Na=140, K=6.2, Cl=113, Alb=2.0
• %MetHb=35%
• Med List: Anti-retrovirals, Bactrim, aspirin
• Salicylate=3.5mmol/l
• Urine tox screen, acetaminophen: negative
186. Case 19 (Les 20)
Differential Diagnosis
Evaluated
Saturation Gap
SaO2 > SpO2 + cyanosis
→ Methemoglobinemia → SMX ?
Respiratory
Alkalosis
Hypoxemia & Aspirin toxicity
↑ AG Metabolic
Acidosis
Lactate=5.5. Ketones: negative
→ Lactic acidosis
Normal AG
Acidosis
Renal failure
187. Case 19 (Les 20)
Final Diagnosis
1. Methemoglobinemia, secondary to presumed Bactrim
overdose
2. Lactic acidosis, secondary to aspirin overdose and/or
methemoglobinemia
3. Acute kidney injury, secondary to aspirin overdose
and/or methemoglobinemia
4. Respiratory alkalosis, secondary to aspirin overdose
and/or methemoglobinemia
188. Case 19 (Les 20)
Final Diagnosis
Overdose of aspirin and presumably Bactrim,
resulting in methemoglobinemia, lactic
acidosis, acute kidney injury, and a primary
respiratory alkalosis.
