The document discusses the interpretation of arterial blood gas (ABG) results and spirometry, focusing on acid-base disorders, their assessment, and compensation mechanisms. It outlines normal ABG parameters, stepwise methods for diagnosing acidemia or alkalemia, the calculation of the anion gap, and examples of various clinical cases. Emphasis is placed on understanding the relationships between pH, hydrogen ion concentration, and the physiological mechanisms underlying acid-base homeostasis.

1. Interpretation of ABGs and
Spirometry
DR. SUBODH KUMAR MAHTO
PGI PGIMER,DR.RML HOSPITAL.
NEW Delhi

2. Acid base disorders
• Acid–base homeostasis is fundamental for maintaining life
• The hydrogen-ion concentration is tightly regulated because
changes in hydrogen ions alter virtually all protein and
membrane functions.
• The three major methods of quantifying acid–base disorders are
– The physiological approach-isohydric principle
– The base-excess approach
– The physicochemical approach –Stewart method

3. Normal components of ABG report
Parameters Normal range
pH 7.35 – 7.45
PaCO2 35 – 45
PaO2 80- 100
HCO3 22-26
SaO2 >95%

4. Check for ERRORS
Have the required parameters been correctly
fed..???
 Patient’s Temperature
 Fi O :
₂ specially if patient is in ventilator
 Hemoglobin : some machines may not measure it
 Barometric pressure : some machines may not measure it

5. A Stepwise
Approach to
Solving
Acid-Base
Disorders

6. Step 1:Assessment of validity of test
results
• Assess the internal consistency of the values using the Henderseon-
Hasselbach equation
• If there is a discripancy between the 2 results, the blood should be
reanalyzed.
• HCO3 should be within 1-3 mEq/L of Total CO2 (electrolyte). A
difference of > 4 mEq/L = technical error
[H+
] in nmol/L = 24 × PaCO /HCO
₂ ₃

7. pH is inversely related to [H+
]; a pH change of
1.00 represents a 10-fold change in [H+
]
pH [H+
] in nanomoles/L
7.00 100
7.10 80
7.30 50
7.40 40
7.52 30
7.70 20
8.00 10
Relation b/w pH & H+ conc.
Step 1: Assessment of validity of test results

8. STEP -2: Acidemia or alkalemia..???
See the pH (<7.35 or >7.45)
 Acidemia –pH less than 7.35
 Acidosis – A process that would cause acidemia, if not
compensated
 Alkalemia–pH greater than 7.45
 Alkalosis – A process that would cause alkalemia if not
compensated

9. Four primary acid-base disorders
 Metabolic acidosis
 Metabolic alkalosis
 Respiratory acidosis
 Respiratory alkalosis

10. STEP -3 : Identify the primary disorder
See the change in PaCo2 & HCO3
-
 If the PaCo2 is deranged in the same direction of pH then the primary
disorder is metabolic
 If the PaCo2 is deranged in the opposite direction of pH then the
primary disorder is respiratory
pH PaCo2 HCO3
7.25 60 26
Respiratory
acidosis

11. Step 4: COMPENSATION
 It is secondary adaptive response to mitigate the change in
arterial pH – so acid base homeostasis is maintained
 Compensation doesnot return the pH to complete normal and
never over compensate.
 Resp. compensation occurs in hours but Full renal compensation
takes 2-5 days
 If given patient is not compensating as predicted, then second (or
third) acid base disorder must be present

12. Prediction of compensation
Metabolic acidosis PaCO2= (1.5 x HCO3
-
) + 8 ± 2
Metabolic alkalosis
PaCO2 will↑ 0.75 mmHg per mmol/L ↑ in
[HCO3
-
] or
PaCO2= 40 + {0.7(HCO3
-
- 24)}
Respiratory
acidosis
Acute
[HCO3
-
] will ↑ 1 mmol/L per 10 mmHg
in PaCO2
Chronic
[HCO3
-
] will ↑ 4 mmol/L per 10 mmHg
in PaCO2
Respiratory
alkalosis
Acute
[HCO3
-
] will ↓ 2 mmol/L per 10 mmHg
↓ in PaCO2
Chronic
[HCO3
-
] will ↓ 4 mmol/L per 10 mmHg
↓in PaCO2

13. Example 1
• Step 1: Check validity- H+
= 24 (48/34) = 33.8 (7.50 -32)
• Step 2: check pH = alkalemia
• Step 3: check Paco2 >40 metabolic alkalosis
• Step 4: expected comp. Paco2 = 40 + {0.7(HCO3
-
-24)}
= 40 + 0.7
(10) = 47
• Appropriate resp. compensation
pH Paco2 HCO3
7.50 48 34

14. Example 2
• Step 1: Check validity- H+
= 24 (32/10) = 76.8 (7.10 - 79)
• Step 2: check pH = acedemia
• Step 3: check Paco2 <40 metabolic acidosis
• Step 4: expected comp. PaCO2= (1.5 x HCO3
-
) + 8 ± 2
= (1.5 x 10) +8 ± 2 = 23 ± 2
• Inappropriate resp. compensation ( 32 ≠ 23)
• PaCO2 is higher than predicted so 2° disorder is resp acidosis
pH Paco2 HCO3
7.12 32 10

15. STEP -5 : Calculate anion gap
 Calculation of the anion gap is useful in the initial evaluation of
metabolic acidosis.
 An elevated anion gap usually indicates the production of
pathologic acid (unmesured anion).
 Total Serum Cations = Total Serum Anions
 Unmeasured anions- unmeasured cations= Na+
] – {[Cl-
]+[HCO3-
]}
 Anion gap = [Na+
] - [Cl-
]-[HCO3-
]
 Up to 12 is normal anion gap

16. • Albumin is the major unmeasured anion
• The anion gap should be corrected if there are gross changes in
serum albumin levels.
AG (CORRECTED) = AG + { (4 – [ALBUMIN]) × 2.5}

17. Causes of High AG Met Acidosis
• A useful mnemonic for the most common causes is GOLD
MARRK
 G - Ethylene Glycol
 O - 5-oxoproline [pyroglutamic acid]
 L -Lactic Acidosis – metformin ?
 D – d lactate – bacterial overgrowth syndrome
 M – Methanol
 A- Aspirin
 R- Renal Failure
 R- Rhabdomyolsis
 K - Ketoacidosis:
K KETOACIDOSIS
U UREMIA
L LACTIC ACIDOSIS
T TOXINS
Cowen – Woods classification of lactic acidosis
Type A - hypoxic Type B — nonhypoxic
(septic shock, mesenteric
ischemia, hypoxemia,
hypovolemic shock, carbon
monoxide
poisoning, cyanide)
B1 – 2nd
to
Hepatic failure
Renal failure
malignancy
B2:
Thiamine def, seizure
Toxins - salicylate, ethylene
glycol, propylene glycol,
methanol, paraldehyde
Drugs - metformin, propofol,
niacin, isoniazid, iron or NNRTI
B3 – inherited syndromes

18. CAUSES OF NORMALANION GAP
METABOLIC ACIDOSIS
1. HCO3 loss:
 GIT
 Diarrhoea
 Pancreatic or biliary
drainage
 Urinary diversions
(ureterosigmoidostomy)
 Renal Proximal (type 2) RTA
 Ketoacidosis (during therapy)
 Post-chronic hypocapnia
2. Impaired renal acid excretion:
 Distal (type 1) RTA
 Hyperkalemia (type 4)
RTA
 Hypoaldosteronism
 Early uremic acidosis
3. Misc:
 Acid Administration
(NH4Cl)
 Hyperalimentation
Primary issue GI tract Renal
Gain of H+
Hyperalimentation Distal (type 1) RTA
Hyperkalemia (type4)
RTA
Hypoaldosteronism
Early uremic acidosis
Loss of HCO3  Diarrhoea
 Pancreatic or biliary
drainage
 Urinary diversions
(ureterosigmoidostomy)
Cholestyramine
Renal Proximal (type
2) RTA
Infusion of normal saline

19. NORMALANION GAP METABOLIC ACIDOSIS
• It occurs when the decrease in HCO3
-
corresponds with an
increase in Cl-
to retain electroneutrality - hyperchloremic
metabolic acidosis.
• Leads to increased renal excretion of NH4.
• Measurement of urinary NH4 can be used to differentiate
between renal and extrarenal causes.
• Urinary anion gap and urinary osmolal gap are often used as
surrogate measures of urinary ammonium.

20. NORMALANION GAP METABOLIC ACIDOSIS
• UAG
= [Na+
+ K+
]u – [Cl–
]u
• Hence a -ve UAG seen in GI causes while +ve value seen in renal causes
• The urinary osmolal gap
= (2 × [Na+
] + 2 × [K+
]) + (urine urea nitrogen ÷ 2.8) + (urine glucose ÷ 18)
• Osmolal gap below 40 mmol/L indicates renal cause
• Urine pH
– If urine pH > 5.5 : Type 1 RTA
– If urine pH < 5.5 : Type 2 or Type 4 RTA

21. Approach to normal anion gap metabolic acidosis
yes
no
yes
Neg UAG high UAG pH>5.5 K very high
In patients receiving saline
infusion, stop & switch to RL
Did acidosis resolve
Is GFR < 40 Renal failure
Excess NaCl
Hyperkalemia
(type4) RTA
Asses serum K, UAG & U.pH
Distal RTA
 Diarrhea
 Pancreatic drainage
 Urinary diversions

22. STEP -6 : Calculate the delta gap/ delta ratio
 To diagnose a high anion-gap acidosis with concomitant metabolic
alkalosis or normal anion-gap acidosis
 Delta gap =(measuredAG- normAG) – (norm.HCO3 – measuredHCO3)
= ( AG) - ( HCO3
-
)
 Usual range: -6 to +6 mmol/L ; should be 0
 > 6 mmol/l - concomitant metabolic alkalosis,.
 < −6 mmol/l - concomitant normal anion-gap metabolic acidosis
Delta gap= ( AG) - (24 –
measuredHCO3)
±6 = ( AG) - 24 + HCO3)
±6 +24 = ( AG) + HCO3)
 AG + HCO3 = 18 -30

23. Easier alternative
Result
( AG + HCO3)
Metabolic disorder
< 18 High anion gap + normal anion gap
metabolic acidosis
18- 30 High anion gap acidosis only
>30 High anion gap acidosis + metabolic
alkalosis

24. Delta ratio
• It is calculation that compares the increase in anion gap to the
decrease in HCO3
Delta ratio = ( AG) / ( HCO3
-
)
• Delta ratio depends on cause of elevated anion gap
Pathologic process Expected delta ratio
Lactic acidosis 1-2
ketoacidosis 0.8 - 1.2

25. Delta ratio
Delta ratio Metabolic disorder
Less than expected range High anion gap + normal anion gap
metabolic acidosis
Within expected range High anion gap acidosis only
Higher than expected
range
High anion gap acidosis +
metabolic alkalosis

26. PLASMA OSMOLAR GAP
 Calculated Plasma Osmolarity = 2[Na+] + [Gluc]/18 + [BUN]/2.8
Normal Measured Plasma Osmolarity > Calculated Plasma Osmolarity
(upto 10 mOsm/L)
 Measured Plasma Osmolarity - Calculated Plasma Osmolarity > 10
mOsm/kg indicates presence of abnormal osmotically active substance
Ethanol
Methanol
Ethylene glycol

27. METABOLIC
ALKALOSIS

28. CAUSES OF METABOLIC ALKALOSIS
1. HCO3 loss:
 GIT
 Diarrhoea
 Pancreatic or biliary
drainage
 Urinary diversions
(ureterosigmoidostomy)
 Renal Proximal (type 2) RTA
 Ketoacidosis (during therapy)
 Post-chronic hypocapnia
2. Impaired renal acid excretion:
 Distal (type 1) RTA
 Hyperkalemia (type 4)
RTA
 Hypoaldosteronism
 Early uremic acidosis
3. Misc:
 Acid Administration
(NH4Cl)
 Hyperalimentation
Primary issue GI tract Renal
Loss of H+
Vomitting
Gastric aspiration
Congenital chloridorrhea
Villous adenoma
Diuretics
Gitelman
Bartter
Mineralocorticoid
excess
Gain of HCO3 Milk alkali syndrome
Ingestion of NaHCO3
Contraction alkalosis

29. METABOLIC ALKALOSIS
Assess volume status
Low
Asses BP and S.
potassium
Contraction alkalosis
Vomitting
NG suction
Diuretics
Gitelman, Bartter ,
Exogenous alkali
milk alkali syndrome
Mineralocorticoid
excess
hypokalemia
normal
High BP
Normal BP n K

30.  STEP -1 :check for validity
 STEP -2 : Acidosis or alkalosis..???
See the pH (<7.35 or >7.45)
 STEP -3 : Identify the primary disorder
See the change in PCo2 & pH
 STEP -4 : Calculate the compensatory response
Is adequately compensated???
Algorithm for assessing acid base status

31.  STEP -5 : Calculate anion gap
 STEP -6 : Calculate the delta gap (unmask hidden mixed
disorders)
 STEP -7 : Acquire additional relevant diagnostic data for each
identified disorder and generate differential diagnosis.

32. Case 1
• A 75 yr old woman presents with profuse diarrhea and fever her HR –
130 n BP is 60/40
• Step 1: Check validity- H+
= 24(30/14)=51
(7.30 -50)
• Step 2: check pH = acidemia
• Step 3: check Paco 2 <40 metabolic acidosis
• Step 4: expected comp. Paco2 = (1.5 x HCO3
-
) + 8 ± 2 = 29 ± 2
appropriate resp. comp
• Step 5: calculate anion gap = Na – HCO3 – Cl-
= 128-94-14= 20
high anion gap met. Acidosis
• Step 6: delta ratio = ( AG) / ( HCO3
-
) =(20-12)/10 = 0.8.
pH 7.29 Na 128
PCO₂ 30 K 3.2
HCO₃
14
Cl
94
High anion gap metabolic acidosis + normal
anion gap metabolic acidosis

33. Case 2
• A 32 yr old woman with schizophrenia found unconscious and her HR
– 130 n BP is 104/70, SaO2 - 88% on RA
• Step 1: Check validity- H+
= 24(60/13)= 110 (6.95 -112)
• Step 2: check pH = acidemia
• Step 3: check Paco 2 >40 respiratory acidosis
• Step 4: expected comp. HCO3 = ↑ 1 mmol/L per 10 mmHg in PaCO2
no. Comp. Metabolic alkalosis.
• Step 5: calculate anion gap = Na – HCO3 – Cl-
= 132-95-12= 25
adjusted anion gap =25 + 2.5(4-alb)=30 high anion gap met. Acidosis
• Step 6: delta ratio = ( AG) / ( HCO3
-
) =(30-12)/12 = 1.5
• Calculate Plasma Osmolarity = 2(132) +24/2.8+74/18= 277
pH 6.96 Na 132
PCO₂ 60 K 3.4
HCO₃ 12 Cl 95
BUN 24 Glu 74
Alb 1.9
Lactate 0.8mmol/l
ketones negative
s.creat 1.1
Measured Osm= 310
Presumed ingestion of toxic alcohol leading
to high anion gap metabolic acidosis and resp
acidosis. Cannot rule out ingestion of

34. Case 3
• A 14 yr old girl with bulimia was brought to ER after bieng found
unconscious at her home with empty drug bottle nearby.
• Step 1:
• Step 2: check pH = normal
• Step 3: check Paco 2 <22 resp.alkalosis
• Step 4: calculate comp. 2nd
– met.acidosis
• Step 5: calculate anion gap = Na – HCO3 – Cl-
= 139-88-13= 38
high anion gap met. Acidosis
• Step 6: delta ratio = ( AG) / ( HCO3
-
) =(38-12)/(24-13) = 2.2
pH 7.39 Na 139
PCO₂ 22 K 3.1
HCO₃
13
Cl
88
High anion gap metabolic acidosis +
metabolic alkalosis + resp. alkalosis

35. Analyse the adequacy of oxygenation..

36. • Causes of hypoxia
– Hypoxemia
– Anemia
– Dyshemoglobenemia
– Histotoxic hypoxia

37. A-a gradient
PAO2 is always calculated based on FIO2, PaCO2, and barometric
pressure. - alveolar gas equation.
A-a gradient = PAO2 – PaO2

38. Alveolar Gas Equation
• Where PAO2 is the average alveolar PO2, and FIO2 is the partial pressure of
inspired oxygen in the trachea
•
• Normal A- a gradient increase with age
PAO2=150 – 1.25(PaCO2)
PAO2=(760-47)x0.21 - PaCO2/0.8
PAO2=(Patm-47)xFIO2 - PaCO2/RQ
Normal A- a gradient = (age/4) +4

39. A-a gradient in hypoxic patient
• If A- a gradient is normal
– Hypoventilation
– Low PI (extreme hight)
• If A- a gradient is elevated
– Shunt
– V/Q mismatch
– Imapaired diffusion

40. PaO2 / FIO2 Ratio
• Measure of severity of hypoxemia in ARDS
– Mild 200 – 300
– Moderate 100- 200
– Severe < 100

41. Saturation gap
• Saturation gap = [ SpO2 - Sa O2]
• > 5% is significant.
• Causes: methemoglobinemia
carboxyhemoglobinemia

42. Example 1
• 83 yr old woman with dementia was sent ER after she was found
tachypnic and hypoxic. She is in resp distress. Her ABG reads
pH – 7.53, PCO2- 26, PaO2- 41.
• check A-a gradient PAO2=(Patm-47)xFIO2 - PaCO2/RQ
PAO2=150 - 26/0.8 = 118
A-a gradient = PAO2 - PaO2
= 118 – 41 = 77
• Estimate normal A-a gradient = (age/4) +4 =83/4 +4 =25

43. Example 2
• A 22 yr old young male who works in printing press
presented to RML emergency with one day history of
confusional state, headache and slurring of speech. On
examination he appeared cyanosed, SpO2 -87% and ABG
revealed -
pH PaO2 SaO2
7.48 140 99

44. Spirometry

45. Learning objectives
 Introduction
 Types of spirometry
 Understand the meaning of spirometric indices and flow
volume loop
 How to use these values for diagnostic evaluations
 Severity of disease based on FEV1

46. Spirometry
• Method of assessing lung function by measuring the volume of
air that the patient is able to expel from the lungs after a maximal
inspiration.
• It is a reliable method of differentiating between obstructive
airways disorders and restrictive diseases.
• Spirometry is the most effective way of determining the severity
of COPD.

47. Indications
• Diagnosis of symptomatic disease
– Obstructive
– Restrictive
– Mixed
• Screening for early asymptomatic disease
• Prognostication
• Monitor response to treatment

48. Technologies used in spirometers
• Volumetric Spirometers
– Water bell
– Bellows wedge
• Flow measuring Spirometers

49. Types of spirometer
 Pneumotachometer
 Fully electronic spirometer
 Incentive spirometer
 Tilt-compensated spirometer
 Windmill-type spirometer

50. Spirograms
• Most spirometers display the following graphs
 a volume-time curve, showing volume (liters) along the Y-axis
and time (seconds) along the X-axis
 a flow-volume loop, which graphically depicts the rate of airflow
on the Y-axis and the total volume inspired or expired on the X-
axis

51. Volume-time curve
flow =  volume /  time
Maximum slope of curve = peak expiratory flow rate

52. Spirometry indices
• FVC – the total volume of air that the patient can forcibly exhale
in one breath after maximal inspiration.
• FEV1 – the volume of air that the patient is able to exhale in the
first second of forced expiration.
• FEV1 /FVC – the ratio of FEV1 to FVC expressed as a fraction
(previously this was expressed as a percentage).
• MEF25-75 This is the mid expiratory flow rate between 25-75%
of an expired air .

53. Flow volume loop
FVC
PEFR

54. Values measured by spirometry
Major
• FEV1
• FVC
• FEV1/FVC ratio
• Flow- volume loop
Minor
• PEFR
• PEF 25-75%
• Response to Bronchodilators

55. INTERPRETATION

56. Patterns of Spirometric Curves
Interpretation FVC FEV1 FEV1/FVC%
(Tiffeneau index)
Healthy person Normal
(>80%)
Normal (>80%) Normal
(>0.7)
Airway
obstruction
Low/normal Low Low
Restrictive Low Low/ normal Normal/
increased(>0.7)
Mixed Low Low Low

57. Interpretation
low normal
Low normal low normal
Asses FEV- 1/ FVC ratio
Asses FVC
Asses FVC
Normal lung
mechanics
Possible
restriction
Obstruction
Obstruction/
mixed

61. Fixed
Airway obstruction
Variable extrathoracic
Airway obstruction
Variable intrathoracic
Airway obstruction

62. Staging of COPD based on FEV1
GOLD staging FEV1 compared to
predicted
Stage 1 > 80%
Stage 2 50% < FEV1 <80%
Stage 3 30% < FEV1 <50%
Stage 4 <30%

63. Bronchodilator Reversibility
• Administer salbutamol in four separate doses of 100 µg through a
spacer
• FEV1/FVC should be measured before and 15-20 minutes after
bronchodilator
• An increase in FEV1 and/or FVC >12% of control and >200 mL
constitutes a positive bronchodilator response.
• It is important to determine whether fixed airway narrowing is
present. In patients with COPD, post-bronchodilator FEV1/FVC
remains < 0.7.

64. Limitations of test
• Highly dependent on patient cooperation and effort, - FVC may
be underestimated
• Not suitable for unconscious, heavily sedated, or have limitations
that would interfere with vigorous respiratory efforts.
• Many intermittent or mild asthmatics have normal spirometry
between acute exacerbation
• Normal results in pulmonary vascular disorders

65. goldcopd.com

66. case 1
Pre-Bronchodilator (BD) Post- BD
Test Actual Predicted % Predicted % Change
FVC (L) 4.39 4.32 102 -1
FEV1 (L) 3.20 3.37 95 7
FEV1/FVC (%) 73 78
FRC (L) 3.17 3.25 98
ERV (L) 0.63 0.93 68
RV (L) 2.54 2.32 109
TLC (L) 6.86 6.09 113
DLCO uncorr 25.69 31.28 82
DLCO corr 26.14 31.28 84
65 year-old man No pulmonary complaints PFT as part of a routine
health screening test Lifelong non-smoker Prior history of asbestose
exposure

67. His flow volume loops is as follows:
:

68. 34 year – old woman With dyspnea &cough Non-smoker,with no occupational
exposures.
Case 2

69. Pre-Bronchodilator (BD) Post- BD
Test Actual Predicted %
Predicted
Actual %
Change
FVC (L) 3.19 4.22 76 4.00 25
FEV1 (L) 2.18 3.39 64 2.83 30
FEV1/FVC
(%)
68 80 78 4
PFT report

70. Flow volume loop: decreased PEFR and coving of 2nd
phase of
exp loop
Decreased FEV1 ,FVC & FEV1/FVC moderate airflow
obstruction
BD response
Dx: obstructive disease
Case 2 interpretation

71. 32 year-old animal trainer presents With progressive
dyspnea and dry cough over last 2 months.
RR – 28, sa02 – 88% on RA,
RS - fine B/l basal crepts.
Case 3

72. Pre-Bronchodilator (BD) Post- BD
Test Actual Predicted %
Predicted
Actual %
Change
FVC (L) 1.7 4.4 39 1.7
FEV1 (L) 1.6 3.7 43 1.6
FEV1/FVC
(%)
94 84 94
RV (L) 0.7 1.4 50
TLC (L) 2.5 5.7 44
RV/TLC
(%)
76 37
DLCO corr 20.73 33.43 62
PFT report

73. 25 year-old man With dyspnea and wheezing Non smoker History of mtor
vehicle accident , hospitalization and tracheostomy 2 years ago
Case 4
His flow volume loops is as follows:

74. Pre-Bronchodilator (BD)
Test Actual Predicted % Predicted
FVC (L) 4.73 4.35 109
FEV1 (L) 2.56 3.69 69
FEV1/FVC (%) 54 85
PFT report

75. Case 4 interpretation
Flow volume loop: Flattened inspiratory &expiratory
limb
Decreased FEV1 , FEV1/FVC moderate
obstruction
Dx: Fixed UAWO

76. Take home messages…

77. • ABG and spirometry are very useful diagnostic tools for our day
to day practice.
• Approach to interpret should be step wise & in a systematic
manner.
• Any abnormal result should be analyzed cautiously in light of
clinical context.
• Appropriate use of these tools using clinical judgment is of
paramount importance

78. Bibliography
• HARRISON’S principles of internal medicine, 18th
edition.
• Disorders of Fluids and Electrolytes, Julie R. Ingelfinger, M.D.,
NEJM, 0ct-9, 2014.
• Spirometry for health care providers, GOLD, 2010.
• ‘‘ATS/ERS TASK FORCE: STANDARDISATION OF LUNG
FUNCTION TESTING’’V. Brusasco, R. Crapo and G. Viegi,
Eur Respir J 2005; 26: 948–968
• Vijayan ; Spirometry in South Indian children Indian J Chest Dis
Allied Sci 2000; 42: 147–156

81. Case
• A 56 yr old woman with copd presents with shortness of breath since
3hr. Her HR – 130 n BP is 110/70, SaO2-90%
• Step 1: Check validity- H+
= 24(48/36)=32
(7.50 -30)
• Step 2: check pH = alkalemia
• Step 3: check Paco 2 <40 metabolic alkalemia
• Step 4: expected comp. Paco2 = 40+{0.7(36-24)=48
• appropriate resp. comp
• Step 5: calculate anion gap = Na – HCO3 – Cl-
= 138-92-36= 10
pH 7.50 Na 138
PCO₂ 48 K 3.2
HCO₃
36
Cl
92
Post hypocapnic metabolic alkalosis