Arterial Blood Gas Interpritation

1
Arterial Blood Gas Interpritation

• Mark Bromley
• PGY-2

2
Why ABGs?

• Important clinical info
• Quick other labs (i.e. faster than a CBC)
• Fun to interpret

3
Why Not?

• ABG analysis is not without drawbacks.
• It is painful!
• Complications
• Local hematoma
• Arterial dissection and thrombosis (rarely)
• Technically difficult, particularly in children
  and elderly patients, and several attempts may be
  required.

4
Normal ABG parameters

• pH 7.40
• PCO2 40 mmHg
• HCO3 24 mmol/l
• Anion Gap lt 12

5
3 Processes

• Ventilation (CO2)
• Oxygenation (02)
• Acid-Base

6
4 Equations 3 Physiologic Processes

• Equation Physiologic Process
• 1) PaCO2 equation ------------------------------
  ------- Alveolar ventilation
• 2) Alveolar gas equation -----------------------
  ------ Oxygenation
• 3) Oxygen content equation ----------------------
  --- Oxygenation
• 4) Henderson-Hasselbalch equation --------------
  Acid-base balance

7
PaCO2 Equation
VCO2 CO2 production VA VE VD VE minute
(total) ventilation VD dead space
ventilation 0.863 converts units to mm Hg

• VCO2 x 0.863
• PaCO2 -----------------
• VA

PaCO2 reflects ratio of metabolic CO2 production
to alveolar ventilation
8
VCO2
(0.863)

PaCO2
Ventilation
9
PaCO2 Blood
Alveolar Ventilation gt45 mm Hg -------
Hypercapnia ----- Hypoventilation 35 - 45 mm Hg
- Eucapnia ---------- Normal ventilation lt35 mm
Hg ------- Hypocapnia ------- Hyperventilation
10
CO2 production
PaCO2
Alveolar Ventilation
11
Hypercapnea

• The only physiologic reason for elevated PaCO2 is
  inadequate alveolar ventilation (VA) for the
  bodys CO2 production (VCO2)
• Hypercapnia can arise from insufficient total
  ventilation, increased dead space, or a
  combination of the two

12
Case

• 54 yr female presents with acute SOB
• Post colon resection for a malignant bowel
  obstruction
• Shortly after returning home from hospital she
  experienced sudden chest pain worse with
  inspiration.

13
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.40
pO2 80 Na 136 mEq/L
pCO2 20 mm Hg Cl- 106 mEq/L
HCO3- 15 mEq\L
14
Pulmonary Embolus
CO2 production
PaCO2
(? ? ventilation) (?dead space)
15
Alveolar Gas Equation
PAO2 PIO2 - 1.2 (PaCO2)
Alveolar O2 P Inspired O2 Arterial CO2
PIO2 FIO2 (PB 47 mm Hg)
PIO2 Inspired O2 (Barometric Pressure 47
mm Hg)
water vapor pressure at normal body temperature
16

• This describes the factors that influence O2 in
  the alveoli
• Almost always,
• Alveolar O2 is higher than Arterial O2

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Alveolar O2 P Inspired O2 Arterial CO2
PIO2 Inspired O2 (Barometric Pressure 47mm
Hg)

• Thus, when PAO2 ?, PaO2 ?

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Why do I care?

• If everything else is constant
• as ?PaCO2 both PAO2 and PaO2 will decrease
• (hypercapnia causes hypoxemia)
• as ?FIO2 both PAO2 and PaO2 will decrease
• (suffocation causes hypoxemia)
• as ?PB (e.g., with altitude) both PAO2 and PaO2
  will decrease
• (mountain climbing causes hypoxemia)

19
P(A-a)O2 the A-a gradient

• P(A-a)O2 is the alveolar-arterial difference in
  pO2
• It results from gravity-related blood flow
  changes within the lungs (normal
  ventilation-perfusion imbalance)
• PAO2 is always calculated
• PaO2 is always measured

20
P(A-a)O2 the A-a gradient

• Normal P(A-a)O2 ranges from _at_ 5 to 25 mm Hg ORA
• (it increases with age)
• A higher than normal P(A-a)O2 means the lungs are
  not transferring oxygen properly from alveoli
  into the pulmonary capillaries
• An ?P(A-a)O2 signifies a problem within the lungs
  
• Exception right to left cardiac shunts

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NON-RESPIRATORY P(A-a)O2Cardiac right to left
shunt Increased Decreased PIO2 NormalLow
mixed venous oxygen content Increased RESPIRATO
RYPulmonary right to left shunt IncreasedVenti
lation-perfusion imbalance IncreasedDiffusion
barrier IncreasedHypoventilation (increased
PaCO2) Normal Unlikely to be clinically
significant unless there is right to left
shunting or ventilation-perfusion imbalance
22
Ventilation-Perfusion imbalance

• A normal amount of ventilation-perfusion (V-Q)
  imbalance accounts for the normal P(A-a)O2
• By far the most common cause of low PaO2 is an
  abnormal degree of ventilation-perfusion
  imbalance within the millions of
  alveolar-capillary units
• Virtually all lung disease lowers PaO2 via V-Q
  imbalance
• i.e. asthma, pneumonia, atelectasis, pulm edema,
  COPD
• Diffusion barrier is seldom a major cause of low
  PaO2
• (it can lead to a low PaO2 during exercise)

23
Case VQ Mis-Match
24
Case

• 34 Male presents with HA
• Working out of town sleeping in the shop
• Awoken at 2-3am by an alarm but went back to
  sleep
• Found by his foreman at about 9am
• Drove back to Calgary but had difficulty staying
  awake

25
GAS
Arterial Blood Gas Serum Chemistries Other Tests
pH 7.40 O2 sat 97
pO2 80 mm Hg
pCO2 38 mm Hg
HCO3- 24 mEq\L
26
How much oxygen is in the blood?PaO2 vs. SaO2
vs. CaO2

• OXYGEN PRESSURE PaO2
• PaO2 reflects only free oxygen molecules
  dissolved in plasma and not those bound to
  hemoglobin
• PaO2 cannot tell us how much oxygen is in the
  blood
• OXYGEN SATURATION SaO2
• The percentage of all the available heme binding
  sites saturated with oxygen is the hemoglobin
  oxygen saturation (in arterial blood, the SaO2)
• How much hemoglobin is there?
• OXYGEN CONTENT CaO2
• CaO2 is the only value that incorporates the
  hemoglobin content (units ml O2/dl)
• Oxygen content can be measured directly or
  calculated by the oxygen content equation
• CaO2 (Hb x 1.34 x SaO2) (.003 x PaO2)

27

• Is pO2 the best measure of oxygenation in this
  case?

28
Case Continued

• returned a few hours later with mental confusion
• this time both SaO2 and COHb were measured

Arterial Blood Gas Serum Chemistries Other Tests
pH 7.36 O2 sat 97
pO2 79 mm Hg
pCO2 31 mm Hg
SaO2 53
COHb 46
HCO3- 24 mEq\L
29

• CO has a double-whammy effect
• decreases SaO2 by the amount of COHb present
• shifts the O2-dissociation curve to the left,
  retarding unloading of oxygen to the tissues
• CO does not affect PaO2, only SaO2
• To detect CO poisoning, SaO2 and/or COHb must be
  measured
• In the presence of excess CO, SaO2 will be lower
  than expected from the PaO2

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Carbon Monoxide

• CO is colorless, odorless gas, a product of
  combustion all smokers have excess CO in their
  blood, typically 5-10
• CO binds 200x more avidly to hemoglobin than O2,
  effectively displacing O2 from the heme binding
  sites
• CO is a major cause of poisoning deaths
  world-wide
• Normal COHb in the blood is 1-2, from
  metabolism and small amount of ambient CO
• (higher in smokers and traffic-congested areas)

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SaO2 and CaO2 test your understanding
Below are blood gas results from four pairs of
patients. For each letter pair, state which
patient, (1) or (2), is more hypoxemic. Units
for hemoglobin content (Hb) are gm and for PaO2
mm Hg. a) (1) Hb 150, PaO2 100, pH 7.40, COHb
20 (2) Hb 120, PaO2 100, pH 7.40, COHb
0 b) (1) Hb 150, PaO2 90, pH 7.20, COHb
5 (2) Hb 150, PaO2 50, pH 7.40, COHb 0
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SaO2 and CaO2 test your understandingAnswers
a) (1) CaO2 .78 x 15 x 1.34 15.7 ml
O2/dl (2) CaO2 .98 x 12 x 1.34 15.8 ml
O2/dl The oxygen contents are almost identical,
and therefore neither patient is more hypoxemic.
However, patient (1), with 20 CO, is more
hypoxic than patient (2) because of the
left-shift of the O2- dissociation curve caused
by the CO b) (1) CaO2 .87 x 15 x 1.34 17.5
ml O2/dl (2) CaO2 .85 x 15 x 1.34 17.1 ml
O2/dl A PaO2 of 90 mm Hg with pH of 7.20 gives an
SaO2 of _at_ 92 subtracting 5 COHb from this
value gives a true SaO2 of 87, used in the CaO2
calculation of patient (1). A PaO2 of 50 mm Hg
with normal pH gives an SaO2 of 85. Thus
patient (2) is slightly more hypoxemic.
33
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34
Acid-Base

• Normal serum pH is between 7.36-7.44
• A pH outside 6.8 7.8 is incompatible with life
• pH is maintained by 3 systems
• Physiologic buffers
• Lungs
• Kidneys
• Disorders in any of these systems leads to
  alterations in blood pH

35

• Methanol poisoning example

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Physiologic Buffers

• 1) Bicarbonate-carbonic acid
• H HCO3- ? H2CO3 ? H2O CO2
• 2) Blood protein buffers
• Hemoglobin
• 3) Bone
• Reservoir of bicarb and phosphate

37
Lungs

• ? pH sensed by peripheral and central
  chemoreceptors
• Peripherally (carotid bodies)
• Centrally (medulla oblongata)
• ? pH
• Increased minute ventilation
• Lowers PaCO2
• ? pH
• Decreased ventilatory effort
• Increases PaCO2

38
Kidneys

• Not involved in acute compensation
• After 6hrs of Alkalemia
• Excretion of HCO3-
• Retention of H
• 6-12hrs Acidosis
• Excretion of H
• Retention of HCO3-

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Terminology

• Acidemia blood pH lt 7.35
• Acidosis a physiologic process that, occurring
  alone, tends to cause acidemia
• e.g. metabolic acidosis from decreased
  perfusion (lactic acidosis) respiratory acidosis
  from hypoventilation
• If the patient also has an alkalosis at the same
  time, the resulting blood pH may be low, normal
  or high

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Terminology

• Alkalemia blood pH gt 7.45
• Alkalosis a primary physiologic process that,
  occurring alone, tends to cause alkalemia
• i.e. metabolic alkalosis from excessive
  diuretic therapy respiratory alkalosis from
  acute hyperventilation
• If the patient also has an acidosis at the same
  time, the resulting blood pH may be high, normal
  or low.

41
Terminology

• Primary acid-base disorder One of the four
  acid-base disturbances that is manifested by an
  initial change in HCO3- or PaCO2.
• Compensation The change in HCO3- or PaCO2 that
  results from the primary event. Compensatory
  changes are not classified by the terms used for
  the four primary acid-base disturbances.
• i.e. a patient who hyperventilates (lowers PaCO2)
  solely as compensation for MAc does not have a
  RAlk, the latter being a primary disorder that,
  alone, would lead to alkalemia. In simple,
  uncomplicated MAc the patient will never develop
  alkalemia.

42
Henderson without Hassel(balch)
H x HCO3-
k1 x H2CO3
k2 x CO2 x H2O
k2 x CO2 x H2O
H x HCO3-
X
X
HCO3-
H
43
Henderson without the Hassel(balch)
CO2
H
HCO3-
44
Henderson-Hasselbach

• Henderson's equation shows the relationship
  between H, HCO3-, and PCO2
• It performs the same function as the more
  Henderson-Hasselbalch Equation

45
Acid-Base Disorders

• Respiratory disorders
• Alter the serum PaCO2
• Metabolic disorders
• Alter the serum HCO3-

Thanks Marc!
46
Respiratory Disorders

• ACIDOSIS
• Hypoventilation
• Pulmonary pathology
• Airway obstruction
• Decreased respiratory drive

• ALKALOSIS
• Hyperventilation
• CNS disease
• Hypoxemia
• Anxiety
• Toxic states
• Hepatic insufficiency
• Assisted ventilation

Thanks Marc!
47
Metabolic Disorders

• ACIDOSIS
• Wide gap metabolic acidosis
• Non-AG metabolic acidosis

• ALKALOSIS
• Saline responsive
• Saline resistant

Thanks Marc!
48
Anion Gap Metabolic Acidosis

• Addition of Acids
• or
• Creation of Acids

• CAT MUDPILES
• Carbon monoxide/cyanide
• Alcohol/AKA
• Toluene
• Methanol
• Uremia
• DKA
• Paraldehyde
• INH/Iron
• Lactic Acidosis
• Ethylene glycol
• Salicylates

Thanks Marc!
49
Normal AG Metabolic Acidosis

• HARD UPS
• Hyperalimentation/Hyperventilation
• Acids/Addisons/Acetazolamide
• RTA
• Diarrhea/Dehydration/ Diuretics
• Uterosigmoidostomy
• Pancreatic fistula or drainage
• Saline (large amounts)

• Excessive loss of HCO3-
• OR
• Inability to excrete H

Thanks Marc!
50
Metabolic Alkalosis

• Saline Responsive
• Vomit ? lose HCl
• Kidneys try to hang on to H
• excrete Na instead
• Until, dehydration kicks in ? Renin/Aldo
• If we rehydrate we allow the kidneys to work

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Saline Responsive

• Vomiting/Gastric Suction
• Diuretics
• Ion-deficient baby formula
• Colonic adenomas (HCl)
• Saline shuts off Renin/Angiotensin/Aldo

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Saline Non-Responsive

• Higher up in the cascade
• Primary aldosteronism
• Exogenous steroids
• Adenocarcinoma
• Bartters Syndrome
• Cushings disease
• Ectopic ACTH

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Mixed Acid-Base Disorders

• In chronically ill respiratory patients
• In renal failure

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Metabolic Compensation for Respiratory Disorders

• Compensation PaCO2 HCO3-
• Acute Resp Acidosis 101
• Acute Resp Alkalosis 102
• Chronic Resp Acidosis 103
• Chronic Resp Alkalosis 104

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Respiratory Compensation for Metabolic Disorders

• Compensation PaCO2 HCO3-
• Metabolic Acidosis 11
• Metabolic Alkalosis 1 0.75

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The Corey Slovis approach to acid-base
abnormalities

• Thanks again Marc!

57
Slovis 6-step approach to ABG

1. Check the numbers
2. Apply the ABG rules
3. Calculate the AG
4. If Acidosis apply the rule of 15 (/- 2)
5. If Acidosis apply the delta gap (/- 4)
6. Check the osmolar gap

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Check the numbers

• Know your normal values
• Does the blood gas make sense?
• Are there any immediate hints to the diagnosis

59
The ABG rules

• 1) Is it an Acidosis or Alkalosis
• Look at the pH
• 2) Is it Respiratory or Metabolic
• Metabolic pCO2 pH ? in same direction
• Resp pCO2 pH ? in opposite direction
• 3) Is it a pure respiratory acidosis?
• ?pCO2 ?pH 11

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Calculate the AG

• Na HCO3 Cl
• Normal 5-12
• Upper limit of normal is 15

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What is the Anion Gap?
62
What is the Anion Gap?
Ca
Mg
Lactate
Hipurate
K
Acetate
HCO3-
Na
Cl-
63
What elevates the Gap?
Lactate
Hipurate
Mg
Ca
Acetate
K
HCO3-
Na
Cl-
64
What lowers the Gap?
Ca
Mg
Lactate
lithium
K
HCO3-
Na
Cl-
65

• Our blood is neutral
• ?AG unmeasured cations
• ?AG unmeasured anions

66
Rule of 15

• HCO3 15 pCO2 and pH (last 2 digits)
• Used in acidosis
• Derived from Henderson Hasselbalch equation
• It predicts what resp compensation will do to the
  pCO2 and the pH
• If the Rule is broken then another process other
  than just resp compensation exists

67
Rule of 15

• Creates a new set point for the pCO2
• pCO2 appropriate normal compensation
• pCO2 too low superimposed primary resp
  alkalosis
• pCO2 too high superimposed primary resp
  acidosis
• Note as HCO3 falls below 10 you need to use the
  formula
• HCO3 x 1.5 8 expected pCO2

68
Examples of rule of 15

• 1) HCO320, pCO235 pH 7.35
• Pure wide gap metabolic acidosis with an
  appropriate 2ndary resp alkalosis
• 2) HCO310, pCO220 pH 7.32
• pCO2 is too low. Superimposed primary resp
  alkalosis
• 3) HCO310, pCO232 pH 7.14
• pCO2 is too high. Superimposed primary resp
  acidosis

69
Delta Gap

• Checks for hidden metabolic process
• Based on the 11 concept that
  ?AG ?HCO3
• Upper limit of AG 15
• Normal HCO3 24
• Bicarb too high metabolic alkalosis
• Bicarb too low Non-gap metabolic acidosis

70
What is the Delta Gap?

• Looks for other metabolic processes in an
  elevated AG acidosis
• What happens in an isolated AG acidosis?

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• Acid is added ? Anion H
• H HCO3- ? H2CO3 ? H2O CO2
• ? Anion H2O CO2
• ?AG ?HCO3

72

• Bicarb too high metabolic alkalosis
• Bicarb too low Non-gap metabolic acidosis

73
Examples of delta gap

• AG22 HCO317
• ?AG 7 and ?HCO3 7
• No hidden process
• AG24 HCO38
• ?AG 9 and ?HCO3 16
• Bicarb too low additional non-gap MAc
• AG28 HCO320
• ?AG 13 and ?HCO3 4
• Bicarb too high additional MAlk

74
Osmolar Gap

• 2Na BUN Glucose calculated gap
• OG Measured calculated
• Upper limit of normal is 10
• If higher consider toxic alcohols
• Remember with EtOH
• 2Na BUN Glucose 1.25 x EtOH

75
Case 1
20 F presents with lethargy, polydipsia and
polyuria
Arterial Blood Gas Lytes Urine Tests
pH 7.24 Na 130 mEq/L pH 5.0
pCO2 24 mm Hg K 4.5 mEq/L
HCO3- 10 mEq/L Cl- 94 mEq/L
Glucose 32
76
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

77
Case 2
43 F known diabetic, asymptomatic, managed with
Glyburide. FHx of HTN. No
personal Hx of HTN. OE 180/100
Arterial Blood Gas Lytes Urine Tests
pH 7.49 Na 142 mEq/L pH 6.5
pCO2 45 mm Hg K 4.5 mEq/L
HCO3- 33 mEq/L Cl- 98 mEq/L
Cr 110
BUN 14 mg/dL
78
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

79
Case 3
22 M with a Hx of nephrolithiasis.
Arterial Blood Gas Lytes Urine Tests
pH 7.29 Na 138 mEq/L pH 6.0
pCO2 32 mm Hg K 3.0 mEq/L Na 35 mEq/L
HCO3- 15 mEq/L Cl- 110 mEq/L K 45 mEq/L
Cl- 75 mEq/L
80
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

81
Case 4
Case 4a. 72 F with a brain tumor (dx in April
07), presents with an acute change in
mental status. Presently comatose with Kussmals
respirations. CT HEAD Intracerebral
Hemorrhage with shift!
Arterial Blood Gas Lytes Urine Tests
pH 7.57 Na 136 mEq/L pH 7.0
pCO2 20 mm Hg K 4.0 mEq/L
HCO3- 18 mEq/L Cl- 103 mEq/L
82
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

83
Case 5
A 20-year-old man is brought to the emergency
room by his sister, who tells you he took a
bottle of pills.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.35 Na 140 mEq/L pH 5.0
pCO2 15 mm Hg K 3.5 mEq/L
HCO3- 8 mEq\L Cl- 104 mEq/L
84
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

85
Case 6
Case 6a A 57-year-old patient with a long
history of smoking presents to you in no
distress, but he tells you he develops dyspnea on
exertion. You send him for pulmonary function
tests (PFTs) and an arterial blood gas (ABG).
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.35 Na 143 mEq/L pH 5.0
pCO2 50 mm Hg Cl- 105 mEq/L
HCO3- 27 mEq\L
86
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

87
Case 6b
Case 6b The patient in Case 6a presents to the
emergency room again 1 month later in respiratory
distress. He is wheezing and his respiratory rate
is 33 breaths/minute.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.29 Na 142 mEq/L pH 5.0
pCO2 61 mm Hg Cl- 100 mEq/L
HCO3- 29 mEq\L
88
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

89
Case 7
Case 7 A 45-year-old diabetic patient presents
with obtundation.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.01 Na 138 mEq/L pH 5.0
pCO2 70 mm Hg K 5.5 mEq/L
HCO3- 18 mEq\L Cl- 97 mEq/L
90
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

91
Case 8
A 78-year-old nursing home patient has been
vomiting for several days and has rapidly
developed a fever and increasing shortness of
breath over the past several hours. Her
respiratory rate is 35 breaths/minute, and she
has consolidative signs in the right base of the
lung.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.69 Na 138 mEq/L pH 8.0
pCO2 20 mm Hg Cl- 97 mEq/L
HCO3- 28 mEq\L
92
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

93
Case 9
A 20-year-old diabetic patient presents with
nausea and vomiting for several days, and with
fever and shortness of breath that have developed
over the past 8 hours.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.59 Na 140 mEq/L pH 8.0
pCO2 25 mm Hg Cl- 95 mEq/L Ketones postive
HCO3- 24 mEq\L Glucose 34
BUN 9.3
94
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

95
Case 10
A 47-year-old man with alcoholism presents with
vomiting after binge drinking for the past 2
days. He is brought to the emergency room by his
friend, who tells you he took a large number of
diazepam pills 1 hour prior and became very
sleepy. His respiratory rate is 8 breaths/minute
and he is unresponsive.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.27 Na 135 mEq/L pH 5.0
pCO2 62 mm Hg Cl- 85 mEq/L
HCO3- 28 mEq\L BUN 7.5
96
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

97
Case 11
A 65-year-old man with chronic obstructive
pulmonary disease (COPD) and congestive heart
failure (CHF) presents with increasing shortness
of breath and wheezing for the past 4 hours. He
is currently on furosemide.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.40 Na 140 mEq/L pH 5.0
pCO2 60 mm Hg Cl- 90 mEq/L
HCO3- 37 mEq\L
98
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

99
Case 12
A 27-year-old diabetic patient presents with 1
hour of acute shortness of breath. He has been
nauseated and has had increased urination over
the past 2 days. Because of his nausea, he
decided not to take his insulin and has been
bedridden the past 2 days. In the emergency room,
you discover he has a family history of
hypercoagulable disorder.
Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.40 Na 140 mEq/L pH 5.0
pCO2 20 mm Hg Cl- 102 mEq/L Ketones positive
HCO3- 12 mEq\L Glucose 35
100
Approach

• Check the numbers
• Apply the ABG rules
• Calculate the AG
• If Acidosis apply the rule of 15 (/- 2)
• If Acidosis apply the delta gap (/- 4)
• Check the osmolar gap

101
Case 13

• You receive a 67 M with post polio lung disease
  in handover. He presents to the ER with increased
  WOB and decreased LOC. Been in the department for
  some time.

Arterial Blood Gas Serum Chemistries Urine Tests
pH 7.60
pCO2 40 mm Hg
pO2 60 mm Hg
Sat 90
HCO3- 30 mEq\L
102
Thanks!