Interpretation of Arterial Blood Gases
Traditional Vs Modern

By

Gamal Rabie Agmy , MD , FCCP

Professor of Chest Disease...
Handerson Hasselbach
Equation
•
•
•
•
•
•

PH= pKa+ Log HCO3/PaCo2
PH= Log HCO3/PaCo2
PH=  HCO3
PH=  HCO3
 PH=  PaCo...
Co2+H2o=H2co3=Hco3- + H+

Hprotein=H+ + Protein-
Normal Values
• PH
7.35-7.45
• HCO3 22-26 mEq/L
• PaCo2 35-45 mmHg
• PaO2 97 mmHg
• BE/BD +2 to -2
• Haemoglobin 15 gram
•...
Definition of Respiratory Failure

Respiratory failure is a syndrome of
inadequate gas exchange due to
dysfunction of one ...
Types of Respiratory Failure
Type 1 (Hypoxemic ): * PO2 < 60 mmHg on room air.
Type 2 (Hypercapnic / Ventilatory): *PCO2 >...
FIO2

Ventilation
without
perfusion
(deadspace
ventilation)

Hypoventilation

Diffusion
abnormality
Normal
Perfusion
with...
Brainstem

Airway

Lung

Spinal cord
Nerve root

Nerve

Pleura

Chest wall

Neuromuscular
junction
Respiratory
muscle

Sit...
Types of RF:
• Type 1:
A-Acute
B-Chronic
C-Acute on top of chronic

• Type 2:
A-Acute
B-Chronic
C-Acute on top of chronic
Types of RF:
• Type 1:
PaO2<60 mm Hg
PaCo235-45 mmHg

• Type 2:
PaO2<60 mm Hg
PaCo2>50 mmHg
Types of RF:
Type 1:
• Acute:
Pao2<60mmHg
PaCo235-45mmHg

HCO3 Normal
PH > 7.45

• Chronic:
Pao2<60mmHg
HCO3 <22mEq/L

Pa...
Types of RF:
Type 2:
• Acute:
Pao2<60mmHg
PaCo2>50 mmHg

HCO3 Normal
PH<7.35

• Chronic:
Pao2<60mmHg
HCO3 >26 mEq/L

PaCo2...
M acidosis
Uncompensated
Partially compensated
Compensated
Uncompensated
*PH < 7.35
*PaCo2 normal
*HCO3 < 22 ml eq/L
Partially compensated
*PH< 7.35
*PaCo2 < 36 mmHg
*HCO3 < 22 ml eq/L
Compensated
PH 7.35-7.40
PaCo2 < 35 mmHg
HCO3 < 22 mleq/L
M alkalosis
Uncompensated
Partially compensated
Compensated
Uncompensated
PH > 7.45
PaCo2 normal
HCO3 >26 ml Eq/L
Partially compensated
PH >7.45
PaCo2 > 45 mmHg
HCO3 > 26 ml Eq/L
Compensated
PH 7.40-7.45
PaCo2 > 45 mmHg
HCO3 > 26 mlEq/L
Combined acidosis:
PH<7.35 PaCO2>50 HCO3<22

Combined alkalosis:
PH >7.45 PaCo2<35 HCO3>26
Blood Gas Analysis &
Acid-Base Disorders
Professor Gamal Rabie Agmy, MD, FCCP
Professor of Chest Diseases , Assiut
Univers...
Blood Gas Analysis
Arterial blood
Sea level (101.3kPa, 760mmHg)
Quiet
Anti-coagulate blood
Inspire air (Whether O2 su...
Why Order an ABG?
•
•
•
•

Aids in establishing a diagnosis
Helps guide treatment plan
Aids in ventilator management
Impro...
Clinical Significance
To evaluate oxygen status
To evaluate ventilation
To evaluate acid-base disorder
How to evaluate oxygen status?
PaO2:
Partial pressure of oxygen in Arterial
blood .
Normal: 95-98 mmHg (12.6-13 kPa)
Estim...
Hypoxaemia
Mild: 80-60mmHg
Medorate: 60-40mmHg
Severe: <40mmHg
Respiratory Failure
PaO2<60mmHg  respiratory failure
Notice: sea level, quiet, inspire air
rule off other causes (Congeni...
Classification of Respiratory Failure
PaCO2: The carbon dioxide partial
pressure
of arterial blood
Normal: 35-45mmHg (4.7-...
Classification of Respiratory Failure

PaO2 (mmHg)
PaCO2 (mmHg)

Type Ⅰ
<60
≤35-45

TypeⅡ
<60
>50
Other Parameters
SaO2: Saturation of arterial blood
oxygen
Normal: 0.95-0.98
Significance: a parameter to evaluate
hypoxae...
2

SaO %

PO2

Oxygen dissociation curve
PH

2,3DPG

temperature

CO2

ODC to right deviation

Oxygenated hemoglobin release oxygen
to tissue, prevent hypoxia of t...
PA-aO2: Difference of alveoli-arterial
blood oxygenic partial pressure.
Normal: 15-20mmHg (<30mmHg in the
old)
Significanc...
PvO2: Partial pressure of oxygen in
mixed venous blood.
Normal: 35-45mmHg
mean: 40mmHg
Significance: Pa-vO2 is to reflect ...
CaO2: The content of the oxygen of the
arterial blood.
Normal: 19-21mmol/L
Significance: a comprehensive
parameter to eval...
Parameters in acid-basic disorder evaluation

PH: negative logarithm of
Hydrogen ion concentration.
Normal: 7.35-7.45
mean...
HCO3- (bicarbonate):
SB (standard bicarbonate)
AB (actual bicarbonate)
SB: the contents of HCO3- of serum of arterial
bloo...
AB and SB are parameters to reflect
metabolism, regulated by kidney.
Difference of AB-SB can reflect the
respiratory aff...
Buffer bases(BB):
is the total of buffer negative ion of
blood.
BB: HCO3hemoglobin
plasma proteins
HPO42- (phosphate)
Norm...
Bases excess (BE):
the acid or bases used to regulate
blood PH 7.4 . ( in 38℃,PaCO2
40mmHg, SaO2 100%)
Normal: 0±2.3 mmol/...
Total plasma CO2 (T-CO2):
total content of the CO2 .
Normal: HCO3- >95%
Logistics
• When to order an arterial line -– Need for continuous BP monitoring
– Need for multiple ABGs
– COP measurement...
Acid Base Balance
• The body produces acids daily
– 15,000 mmol CO2
– 50-100 mEq Nonvolatile acids

• The lungs and kidney...
Acid Base Balance
• Assessment of status via bicarbonatecarbon dioxide buffer system
– CO2 + H2O <--> H2CO3 <--> HCO3- + H...
The Terms
• ACIDS
– Acidemia
– Acidosis
• Respiratory
CO2
• Metabolic
HCO3

• BASES
– Alkalemia
– Alkalosis
• Respirator...
Respiratory Acidosis
• ph, CO2, Ventilation
• Causes
– CNS depression
– Pleural disease
– COPD/ARDS
– Musculoskeletal d...
Respiratory Acidosis
• Acute vs Chronic
– Acute - little kidney involvement. Buffering
via titration via Hb for example
• ...
Respiratory Alkalosis
• pH, CO2, Ventilation
•  CO2   HCO3 (Cl to balance charges 
hyperchloremia)
• Causes
–
–
–
...
Respiratory Alkalosis
• Acute vs. Chronic
– Acute - HCO3 by 2 mEq/L for every
10mmHg  in PCO2
– Chronic - Ratio increase...
Metabolic Acidosis
• pH, HCO3
• 12-24 hours for complete activation of
respiratory compensation
• PCO2 by 1.2mmHg for e...
The Causes
• Metabolic Gap
Acidosis
–
–
–
–
–
–
–
–

M - Methanol
U - Uremia
D - DKA
P - Paraldehyde
I - INH
L - Lactic Ac...
Metabolic Alkalosis
• pH, HCO3
• PCO2 by 0.7 for every 1mEq/L  in HCO3
• Causes
–
–
–
–
–

Vomiting
Diuretics
Chronic ...
Mixed Acid-Base Disorders
• Patients may have two or more acidbase disorders at one time
• Delta Gap
Delta HCO3 = HCO3 + C...
The Steps
•
•
•
•

Start with the pH
Note the PCO2
Calculate anion gap
Determine compensation
Sample Problem #1
• An ill-appearing alcoholic male presents
with nausea and vomiting.
– ABG – 7.25 / 34 / 85 / 16
– Na- 1...
Sample Problem #1
• Anion Gap = 137 - (90 +16) =31
 anion gap metabolic acidosis
• Winters Formula = 1.5(16) + 8  2
= 32...
Sample Problem #2
• 22 year old female presents for
attempted overdose. She has taken an
unknown amount of Midol containin...
Sample Problem #2
• ABG - 7.47 / 19 / 123 / 14
• Na- 145 / K- 3.6 / Cl- 109 / HCO3- 14
• ASA level - 38.2 mg/dL
Sample Problem #2
• Anion Gap = 145 - (109 + 14) = 22
 anion gap metabolic acidosis
• Winters Formula = 1.5 (14) + 8  2
...
Sample Problem #3
• 47 year old male experienced crush
injury at construction site.
• ABG - 7.3 / 32 / 96 / 15
• Na- 135 /...
Sample Problem #3
• Anion Gap = 135 - (98 + 15) = 22
 anion gap metabolic acidosis
• Winters Formula = 1.5 (15) + 8  2
=...
Sample Problem #4
• 1 month old male presents with
projectile emesis x 2 days.
• ABG - 7.49 / 40 / 98 / 30
• Na- 140 / K- ...
Sample Problem #4
• Metabolic Alkalosis, hypochloremic
• Winters Formula = 1.5 (30) + 8  2
= 53  2
 uncompensated
ABG Analysis, Introduction
• pH, PaCO2, PaO2 are measured directly
by special electrodes contained in a
device made for th...
QA in Blood Gas Analysis
• ABG lab must be able to assure
accurate and reliable results
• The above is accomplished by app...
Pre-analytic Error
• All factors that cause variance in lab results
prior to the sample arriving in the ABG lab.
• 4 facto...
Calibration
• Purpose is assure consistency
• Def.: the systemic standardization of the
graduation of a quantitative measu...
Calibration (cont’d)
• A “one-point calibration” is an
adjustment of the electronic response of
an electrode to a single s...
Quality Control
• Refers to a system that documents the
accuracy and reliability of the blood gas
measurements and is esse...
QC (cont’d)
• Documentation of QC is usu. on LevyJennings Chart which shows measured
results on the y axis versus time of
...
QC (cont’d)
• A properly functioning electrode that
repeatedly analyzes a known value will
produce results within a rel. s...
QC (cont’d)
• Random errors indicates a value outside of 2
SD of the mean: a single random error has
minor signif., but if...
QC (cont’d)
• Causes of systematic error (cont’d)
- inconsistent calibration
technique
- change in QC
standard storage or ...
QC Levels
• Level 1 simulates a patient
hypoventilating
• Level 2 simulates a patient with normal
ventilatory status
• Lev...
HCO3- (bicarbonate):
SB (standard bicarbonate)
AB (actual bicarbonate)
SB: the contents of HCO3- of serum of arterial
bloo...
AB and SB are parameters to reflect
metabolism, regulated by kidney.
Difference of AB-SB can reflect the
respiratory aff...
8 Sequential Rules:
• Rule #1
– Must know the pH; pH determines whether the
primary disorder is an acidosis or an alkalosi...
Are the data consistent?
• The Henderson Equation:

H   24 


PaCO
HCO

2


3
Convert

+]
[H

to pH:

• Subtract calculated [H+] from 80; this gives
the last two digits of a pH beginning with 7
– exam...
Relationship between

+]
[H

& pH
Relationship between
+

+]
[H
+

& pH

pH

[H ]

pH

[H ]

7.80
7.75
7.70
7.65
7.60
7.55
7.50
7.45
7.40
7.35

16
18
20
22
...
Simple Acid-Base Disorders:
T y p e o f D iso rd er
M etab o lic A cid o sis
M etab o lic A lk alo sis
A cu te R esp irato...
Simple Acid-Base Disorders:
T y p e o f D iso rd er
M etab o lic A cid o sis
M etab o lic A lk alo sis
A cu te R esp irato...
Simple Acid-Base Disorders:
T y p e o f D iso rd er

pH

P a C O 2 [H C O 3 ]

M etab o lic A cid o sis
M etab o lic A lk ...
Simple Acid-Base Disorders:
T y p e o f D iso rd er
T y p e o f D iso rd er

pH
pH

P a C O 2 [H C O 3 ]
P a C O 2 [H C O ...
Simple Acid-Base Disorders:
T y p e o f D iso rd er

pH

P a C O 2 [H C O 3 ]

M etab o lic A cid o sis
M etab o lic A lk ...
Simple Acid-Base Disorders:
T y p e o f D iso rd er

pH

P a C O 2 [H C O 3 ]

M etab o lic A cid o sis
M etab o lic A lk ...
Simple Acid-Base Disorders:
T y p e o f D iso rd er

pH

P a C O 2 [H C O 3 ]

M etab o lic A cid o sis
M etab o lic A lk ...
Simple Acid-Base Disorders:
T y p e o f D iso rd er

pH

P a C O 2 [H C O 3 ]

M etab o lic A cid o sis
M etab o lic A lk ...
Simple Acid-Base Disorders:
T y p e o f D iso rd er

pH

P a C O 2 [H C O 3 ]

M etab o lic A cid o sis







M etab o...
Simple Acid-Base Disorders:
• The compensatory variable always changes
in the SAME DIRECTION as the
primarily deranged var...
8 Sequential Rules:
• Rule #4:
– must know if compensation is appropriate
– compensation never overshoots
• Must have know...
Rules of Compensation:
• Metabolic Acidosis
– PaCO2 should fall by 1 to 1.5 mm Hg x the fall
in plasma [HCO3]

• Metabolic...
Rules of Compensation:
• Acute Respiratory Acidosis
– Plasma [HCO3] should rise by ~1mmole/l for
each 10 mm Hg increment i...
Rules of Compensation:
• Acute Respiratory Alkalosis
– Plasma [HCO3] should fall by ~1-3 mmole/l for
each 10 mm Hg decreme...
Case #1:
• A 24 years old with chronic renal failure
presents to ER with history of increasing
azotemia, weakness, and let...
Case #1:
• Steps 1&2: must know pH, PaCO2, HCO3
• pH=7.37, PaCO2=22, and HCO3=12
• Step 3: are the available data consiste...
Case #1:
• [H+]=44, equates to pH~7.36; data are thus
consistent
• What is the primary disorder?
• “_________Acidosis”
• W...
Is compensation appropriate?
• HCO3 is decreased by 12 mmoles/l
• PaCO2 should decrease by 1 to 1.5 times the
fall in HCO3...
8 Sequential Rules:
• Rule #5:
– If the data are consistent with a simple disorder,
it does not guarantee that a simple di...
Case #2:
• A 16 year old male with sickle cell anemia,
hemochromatosis, & subsequent cirrhosis,
presents with a several da...
Case #3:
• 16 yo male with sickle cell anemia, hemochromatosis, & subsequent cirrhosis, and
several days of emesis. In the...
Case #3:
•
•
•
•

What baseline information is available?
pH=7.55, PaCO2=66
„lytes: Na+=166, K+=3.0, Cl-=90, HCO3=56
Are t...
Case #3:
•
•
•
•
•

[H+]~28, equates to pH~7.55; consistent
What is the primary abnormality?
“_________ Alkalosis”
PaCO2e...
Case #3:
• Metabolic Alkalosis
– PaCO2 should rise by .25 to 1 mm Hg x the rise
in plasma [HCO3]

• HCO3 ed by 32; PaCO2 ...
Case #3:
•
•
•
•
•
•

Could there be a concealed lactic acidosis?
What is the anion gap?
Na+- (Cl- + HCO3), normally 12-14...
8 Sequential Rules:
• Rule #7: Always calculate the anion gap
• Often it is the only sign of an occult
metabolic acidosis
...
Causes of  Anion Gap Acidosis:
• Endogenous acidosis
– Uremia (uncleared organic acids)
– Ketoacidosis, Lactic acidosis (...
Causes of normal Anion Gap Acidosis:
•
•
•
•
•

Diarrhea
Isotonic saline infusion
Renal tubular acidosis
Acetazolamide
Ure...
Anion Gap:
• Based on the concept of electroneutrality; the
assumption that the sum of all available cations=
the sum of a...
Anion Gap:
• Na+-(Cl-+HCO3)=UA-UC
• Serum albumin contributes ~1/2 of the total anion
equivalency of the “UA” pool. Assumi...
Case #3:
• A 3 year old is brought to the pedes ER at
~3am, stuporous and tachypneic. History is
remarkable for his parent...
Case #4:
• Available data: pH=7.53, PaCO2=12;
Na+=140, K+=3.0, Cl-=106, HCO3=10
• Are the data internally consistent?

H ...
Case #4:
•
•
•
•

[H+]~29, so pH~7.51; data consistent
What is the primary disturbance?
“__________ Alkalosis”
Which varia...
Case #4:
• Is compensation appropriate?
• Acute respiratory alkalosis
– Plasma [HCO3] should fall by ~1-3 mmole/l for
each...
Case #4:
• What is the anion gap?
• 140 - (106 + 10) = 24; elevated anion gap
consistent with metabolic acidosis
• What is...
Case #5:
• A 5 year old with Bartter‟s Syndrome is
brought to clinic, where she collapses. She
has recently been febrile, ...
Case #5:
• Are the data consistent?

H   24 


PaCO
HCO

2

3

• [H+]=122, pH~6.9; data are consistent
Case #5:
• What is the primary disturbance?
• “_________ Acidosis”
• Which variable (PaCO2, HCO3) is deranged
in a directi...
Case #5:
• Acute Respiratory Acidosis
– Plasma [HCO3] should rise by ~1mmole/l for
each 10 mm Hg increment in PaCO2

• Sin...
Case #5:
• Combined Respiratory Acidosis and
Metabolic Acidosis; are there other
disorders present?
• What about the dx of...
Case #5:
• Anion gap is 39, or 25-27 greater than
normal
• Typically, increases in anion gap correlate
with decreases in H...
Case #5:
• Therefore, starting HCO3 was ~41 mmol/l,
consistent with expected chronic metabolic
alkalosis. This metabolic a...
8 Sequential Rules; Rule #8
• Rule #8: Mixed Acid-Base Disorders
• Coexistant metabolic acidosis and
metabolic alkalosis m...
Case #6:
• A 3 year old toddler is brought to the ER at
3 am after being found unarousable on his
bedroom floor, with urin...
Case #6:
• Initial lab studies (lytes, ABG & urine tox
screen) are sent. Initial dextrostick is >800.
• Initial available ...
Case #6:
•
•
•
•
•
•
•

What is the primary disturbance?
________ Acidosis
Metabolic Acidosis
Is compensation appropriate?...
Case #6:
• What is our differential thus far?
– Anion gap vs. non-anion gap metabolic acidosis
– DKA, lactic acidosis, ren...
Case #6:
• What is the calculated serum osmolality,
and does an osmolal gap exist?
• 2(Na) + BUN/2.8 + Glucose/18
– Calcul...
Case #6:
Methanol, ethylene glycol
ethyl alcohol, isopropyl alcohol

Anion gap metabolic acidosis

Osmolal gap
Gap-Gap
*AG excess/HCO3 deficit=
(Measured AG-12)/ (24-measured HCO3)
*Ratio <1 in presence of high AG acidosis
means coex...
Interpretation of arterial  blood gases:Traditional versus Modern
Interpretation of arterial  blood gases:Traditional versus Modern
Interpretation of arterial  blood gases:Traditional versus Modern
Interpretation of arterial  blood gases:Traditional versus Modern
Interpretation of arterial  blood gases:Traditional versus Modern
Interpretation of arterial  blood gases:Traditional versus Modern
Interpretation of arterial  blood gases:Traditional versus Modern
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Interpretation of arterial blood gases:Traditional versus Modern

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Interpretation of arterial blood gases:Traditional versus Modern

  1. 1. Interpretation of Arterial Blood Gases Traditional Vs Modern By Gamal Rabie Agmy , MD , FCCP Professor of Chest Diseases ,Assiut University
  2. 2. Handerson Hasselbach Equation • • • • • • PH= pKa+ Log HCO3/PaCo2 PH= Log HCO3/PaCo2 PH=  HCO3 PH=  HCO3  PH=  PaCo2 PH=  PaCo2
  3. 3. Co2+H2o=H2co3=Hco3- + H+ Hprotein=H+ + Protein-
  4. 4. Normal Values • PH 7.35-7.45 • HCO3 22-26 mEq/L • PaCo2 35-45 mmHg • PaO2 97 mmHg • BE/BD +2 to -2 • Haemoglobin 15 gram • A-a O2 gradient N < 15 A-a O2 gradient OLDER PERSONS – 2.5 +0.25*AGE – eg. AGE 60, 2.5+15=17.5 – eg. AGE 80, 2.5+20=22.5
  5. 5. Definition of Respiratory Failure Respiratory failure is a syndrome of inadequate gas exchange due to dysfunction of one or more essential components of the respiratory system
  6. 6. Types of Respiratory Failure Type 1 (Hypoxemic ): * PO2 < 60 mmHg on room air. Type 2 (Hypercapnic / Ventilatory): *PCO2 > 50 mmHg Type 3 (Peri-operative): *This is generally a subset of type 1 failure but is sometimes considered separately because it is so common. Type 4 (Shock): * secondary to cardiovascular instability.
  7. 7. FIO2 Ventilation without perfusion (deadspace ventilation) Hypoventilation Diffusion abnormality Normal Perfusion without ventilation (shunting)
  8. 8. Brainstem Airway Lung Spinal cord Nerve root Nerve Pleura Chest wall Neuromuscular junction Respiratory muscle Sites at which disease may cause ventilatory disturbance
  9. 9. Types of RF: • Type 1: A-Acute B-Chronic C-Acute on top of chronic • Type 2: A-Acute B-Chronic C-Acute on top of chronic
  10. 10. Types of RF: • Type 1: PaO2<60 mm Hg PaCo235-45 mmHg • Type 2: PaO2<60 mm Hg PaCo2>50 mmHg
  11. 11. Types of RF: Type 1: • Acute: Pao2<60mmHg PaCo235-45mmHg HCO3 Normal PH > 7.45 • Chronic: Pao2<60mmHg HCO3 <22mEq/L PaCo235-45mmHg PH=7.40-7.45 • Acute on top of chronic: Pao2<60mmHg PaCo235-45mmHg HCO3 <22mEq/L PH > 7.45
  12. 12. Types of RF: Type 2: • Acute: Pao2<60mmHg PaCo2>50 mmHg HCO3 Normal PH<7.35 • Chronic: Pao2<60mmHg HCO3 >26 mEq/L PaCo2 >50 mmHg PH=7.35-7.40 • Acute on top of chronic: Pao2<60mmHg PaCo2 >50 mmHg HCO3 >26 mEq/L PH<7.35
  13. 13. M acidosis Uncompensated Partially compensated Compensated
  14. 14. Uncompensated *PH < 7.35 *PaCo2 normal *HCO3 < 22 ml eq/L
  15. 15. Partially compensated *PH< 7.35 *PaCo2 < 36 mmHg *HCO3 < 22 ml eq/L
  16. 16. Compensated PH 7.35-7.40 PaCo2 < 35 mmHg HCO3 < 22 mleq/L
  17. 17. M alkalosis Uncompensated Partially compensated Compensated
  18. 18. Uncompensated PH > 7.45 PaCo2 normal HCO3 >26 ml Eq/L
  19. 19. Partially compensated PH >7.45 PaCo2 > 45 mmHg HCO3 > 26 ml Eq/L
  20. 20. Compensated PH 7.40-7.45 PaCo2 > 45 mmHg HCO3 > 26 mlEq/L
  21. 21. Combined acidosis: PH<7.35 PaCO2>50 HCO3<22 Combined alkalosis: PH >7.45 PaCo2<35 HCO3>26
  22. 22. Blood Gas Analysis & Acid-Base Disorders Professor Gamal Rabie Agmy, MD, FCCP Professor of Chest Diseases , Assiut University
  23. 23. Blood Gas Analysis Arterial blood Sea level (101.3kPa, 760mmHg) Quiet Anti-coagulate blood Inspire air (Whether O2 supply)
  24. 24. Why Order an ABG? • • • • Aids in establishing a diagnosis Helps guide treatment plan Aids in ventilator management Improvement in acid/base management allows for optimal function of medications • Acid/base status may alter electrolyte levels critical to patient status/care
  25. 25. Clinical Significance To evaluate oxygen status To evaluate ventilation To evaluate acid-base disorder
  26. 26. How to evaluate oxygen status? PaO2: Partial pressure of oxygen in Arterial blood . Normal: 95-98 mmHg (12.6-13 kPa) Estimate formula of age: PaO2=100mmHg-(age×0.33) ±5mmHg
  27. 27. Hypoxaemia Mild: 80-60mmHg Medorate: 60-40mmHg Severe: <40mmHg
  28. 28. Respiratory Failure PaO2<60mmHg  respiratory failure Notice: sea level, quiet, inspire air rule off other causes (Congenital cyanotic heart disease and abnormal types of Hg)
  29. 29. Classification of Respiratory Failure PaCO2: The carbon dioxide partial pressure of arterial blood Normal: 35-45mmHg (4.7-6.0kPa) mean: 40mmHg
  30. 30. Classification of Respiratory Failure PaO2 (mmHg) PaCO2 (mmHg) Type Ⅰ <60 ≤35-45 TypeⅡ <60 >50
  31. 31. Other Parameters SaO2: Saturation of arterial blood oxygen Normal: 0.95-0.98 Significance: a parameter to evaluate hypoxaemia, but not sensitive ODC ( Dissociation curve of oxygenated hemoglobin): “S” shape
  32. 32. 2 SaO % PO2 Oxygen dissociation curve
  33. 33. PH 2,3DPG temperature CO2 ODC to right deviation Oxygenated hemoglobin release oxygen to tissue, prevent hypoxia of the tissue. But absorbed oxygen of hemoglobin is decreased from the alveoli. Bohr effect: movement of ODC place is induced by PH.
  34. 34. PA-aO2: Difference of alveoli-arterial blood oxygenic partial pressure. Normal: 15-20mmHg (<30mmHg in the old) Significance: a sensitive parameter in gas exchange
  35. 35. PvO2: Partial pressure of oxygen in mixed venous blood. Normal: 35-45mmHg mean: 40mmHg Significance: Pa-vO2 is to reflect the tissue absorbing oxygen.
  36. 36. CaO2: The content of the oxygen of the arterial blood. Normal: 19-21mmol/L Significance: a comprehensive parameter to evaluate arterial oxygen.
  37. 37. Parameters in acid-basic disorder evaluation PH: negative logarithm of Hydrogen ion concentration. Normal: 7.35-7.45 mean: 7.4 〔HCO3- 〕 PH=Pka+log =6.1+log 0.03PaCO2 20 1
  38. 38. HCO3- (bicarbonate): SB (standard bicarbonate) AB (actual bicarbonate) SB: the contents of HCO3- of serum of arterial blood in 37℃, PaCO2 40mmHg, SaO2 100%. Normal: 22-26 mmol/L mean: 24mmol/L AB: The contents of HCO3- in actual condition. In normal person: AB=SB
  39. 39. AB and SB are parameters to reflect metabolism, regulated by kidney. Difference of AB-SB can reflect the respiratory affection on serum HCO3- . Respiratory acidosis: AB>SB Respiratory alkalosis: AB<SB Metabolic acidosis: AB=SB<Normal Metabolic alkalosis: AB=SB>Normal
  40. 40. Buffer bases(BB): is the total of buffer negative ion of blood. BB: HCO3hemoglobin plasma proteins HPO42- (phosphate) Normal: 45-55mmol/L mean: 50mmol/L Significance: Metabolic acidosis:  BB Metabolic alkalosis:  BB
  41. 41. Bases excess (BE): the acid or bases used to regulate blood PH 7.4 . ( in 38℃,PaCO2 40mmHg, SaO2 100%) Normal: 0±2.3 mmol/L Significance: add acid: BE(+), BB add base: BE(-), BB
  42. 42. Total plasma CO2 (T-CO2): total content of the CO2 . Normal: HCO3- >95%
  43. 43. Logistics • When to order an arterial line -– Need for continuous BP monitoring – Need for multiple ABGs – COP measurement by thermodilution method • Where to place -- the options – – – – – Radial Femoral Brachial Dorsalis Pedis Axillary
  44. 44. Acid Base Balance • The body produces acids daily – 15,000 mmol CO2 – 50-100 mEq Nonvolatile acids • The lungs and kidneys attempt to maintain balance
  45. 45. Acid Base Balance • Assessment of status via bicarbonatecarbon dioxide buffer system – CO2 + H2O <--> H2CO3 <--> HCO3- + H+ – ph = 6.10 + log ([HCO3] / [0.03 x PCO2])
  46. 46. The Terms • ACIDS – Acidemia – Acidosis • Respiratory CO2 • Metabolic HCO3 • BASES – Alkalemia – Alkalosis • Respiratory CO2 • Metabolic HCO3
  47. 47. Respiratory Acidosis • ph, CO2, Ventilation • Causes – CNS depression – Pleural disease – COPD/ARDS – Musculoskeletal disorders – Compensation for metabolic alkalosis
  48. 48. Respiratory Acidosis • Acute vs Chronic – Acute - little kidney involvement. Buffering via titration via Hb for example • pH by 0.08 for 10mmHg  in CO2 – Chronic - Renal compensation via synthesis and retention of HCO3 (Cl to balance charges  hypochloremia) • pH by 0.03 for 10mmHg in CO2
  49. 49. Respiratory Alkalosis • pH, CO2, Ventilation •  CO2   HCO3 (Cl to balance charges  hyperchloremia) • Causes – – – – – Intracerebral hemorrhage Salicylate and Progesterone drug usage Anxiety  lung compliance Cirrhosis of the liver Sepsis
  50. 50. Respiratory Alkalosis • Acute vs. Chronic – Acute - HCO3 by 2 mEq/L for every 10mmHg  in PCO2 – Chronic - Ratio increases to 4 mEq/L of HCO3 for every 10mmHg  in PCO2 – Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH
  51. 51. Metabolic Acidosis • pH, HCO3 • 12-24 hours for complete activation of respiratory compensation • PCO2 by 1.2mmHg for every 1 mEq/L HCO3 • The degree of compensation is assessed via the Winter’s Formula  PCO2 = 1.5(HCO3) +8  2
  52. 52. The Causes • Metabolic Gap Acidosis – – – – – – – – M - Methanol U - Uremia D - DKA P - Paraldehyde I - INH L - Lactic Acidosis E - Ehylene Glycol S - Salicylate • Non Gap Metabolic Acidosis – Hyperalimentation – Acetazolamide – RTA (Calculate urine anion gap) – Diarrhea – Pancreatic Fistula
  53. 53. Metabolic Alkalosis • pH, HCO3 • PCO2 by 0.7 for every 1mEq/L  in HCO3 • Causes – – – – – Vomiting Diuretics Chronic diarrhea Hypokalemia Renal Failure
  54. 54. Mixed Acid-Base Disorders • Patients may have two or more acidbase disorders at one time • Delta Gap Delta HCO3 = HCO3 + Change in anion gap Delta HCO3 >24 = metabolic alkalosis
  55. 55. The Steps • • • • Start with the pH Note the PCO2 Calculate anion gap Determine compensation
  56. 56. Sample Problem #1 • An ill-appearing alcoholic male presents with nausea and vomiting. – ABG – 7.25 / 34 / 85 / 16 – Na- 137 / K- 3.8 / Cl- 90 / HCO3- 16
  57. 57. Sample Problem #1 • Anion Gap = 137 - (90 +16) =31  anion gap metabolic acidosis • Winters Formula = 1.5(16) + 8  2 = 32  2  compensated • Delta Gap =( 31 – 12) + 16 = 35  metabolic alkalosis
  58. 58. Sample Problem #2 • 22 year old female presents for attempted overdose. She has taken an unknown amount of Midol containing aspirin, cinnamedrine, and caffeine. On exam she is experiencing respiratory distress.
  59. 59. Sample Problem #2 • ABG - 7.47 / 19 / 123 / 14 • Na- 145 / K- 3.6 / Cl- 109 / HCO3- 14 • ASA level - 38.2 mg/dL
  60. 60. Sample Problem #2 • Anion Gap = 145 - (109 + 14) = 22  anion gap metabolic acidosis • Winters Formula = 1.5 (14) + 8  2 = 29  2  uncompensated • Delta Gap = 22 - 12 = 10 10 + 14 = 24  no metabolic alkalosis
  61. 61. Sample Problem #3 • 47 year old male experienced crush injury at construction site. • ABG - 7.3 / 32 / 96 / 15 • Na- 135 / K-5 / Cl- 98 / HCO3- 15 / BUN- 38 / Cr- 1.7 • CK- 42, 346
  62. 62. Sample Problem #3 • Anion Gap = 135 - (98 + 15) = 22  anion gap metabolic acidosis • Winters Formula = 1.5 (15) + 8  2 = 30  2  compensated • Delta Gap = 22 - 10 = 12 12 + 15 = 27  mild metabolic alkalosis
  63. 63. Sample Problem #4 • 1 month old male presents with projectile emesis x 2 days. • ABG - 7.49 / 40 / 98 / 30 • Na- 140 / K- 2.9 / Cl- 92 / HCO3- 32
  64. 64. Sample Problem #4 • Metabolic Alkalosis, hypochloremic • Winters Formula = 1.5 (30) + 8  2 = 53  2  uncompensated
  65. 65. ABG Analysis, Introduction • pH, PaCO2, PaO2 are measured directly by special electrodes contained in a device made for that purpose • Other indirect measurements can be made or calculated from the above measurements i.e., HCO3-, O2 Sat. SVCC Respiratory Care Programs
  66. 66. QA in Blood Gas Analysis • ABG lab must be able to assure accurate and reliable results • The above is accomplished by applying protocols in 3 areas: - pre-analytic error - calibration - quality control SVCC Respiratory Care Programs
  67. 67. Pre-analytic Error • All factors that cause variance in lab results prior to the sample arriving in the ABG lab. • 4 factors assoc. with signif. P. E. are: - air bubbles in sample - time delay (iced sample with more than 60 min. or uniced with more than 10 min.) - blood clots in sample - small sample size where excessive anticaogulation is suspect SVCC Respiratory Care Programs
  68. 68. Calibration • Purpose is assure consistency • Def.: the systemic standardization of the graduation of a quantitative measuring instrument • Calibrating standards for blood gas analyzers should simulate the physical properties of blood and meet manuf. specs. • When 2 standards are used ---> 2-point calibration, performed after 50 blood gases or at least every 8 hours SVCC Respiratory Care Programs
  69. 69. Calibration (cont’d) • A “one-point calibration” is an adjustment of the electronic response of an electrode to a single standard and is performed more freq. than a 2 pt. cal., ideally prior to each sample analysis SVCC Respiratory Care Programs
  70. 70. Quality Control • Refers to a system that documents the accuracy and reliability of the blood gas measurements and is essential to assure accuracy in the blood gas lab • Media available as blood gas controls include: - aqueous buffers - glycerin soltn. - human/animal serum and blood - artificial blood • A QC system must ID problems and specify SVCC Respiratory Care corrective action, document. of accept. oper. Programs
  71. 71. QC (cont’d) • Documentation of QC is usu. on LevyJennings Chart which shows measured results on the y axis versus time of measurement on the x axis • SD is used to summarize a mass of data: the difference between a number in a data set and the mean of the data set is called a deviation. A deviation shows how much a number varies from the mean SVCC Respiratory Care Programs
  72. 72. QC (cont’d) • A properly functioning electrode that repeatedly analyzes a known value will produce results within a rel. small range, e.g., a PaCO2 electrode that analyzes a 40 mmHg standard 100 times will produce results where 2/3 of the measurements are 39 - 41 mmHg and nearly all measurements fall in 38 - 42 range • 95% of the control measurements should fall within 2 SD SVCC Respiratory Care Programs
  73. 73. QC (cont’d) • Random errors indicates a value outside of 2 SD of the mean: a single random error has minor signif., but if number increased the machine and techniques must be evaluated • Systematic errors is recurrent measurable deviation from the mean • Causes of systematic errors: - contaminated standard - variations in electrode temp. SVCC Respiratory Care Programs
  74. 74. QC (cont’d) • Causes of systematic error (cont’d) - inconsistent calibration technique - change in QC standard storage or prep. - electrode problems, e.g., protein contamin., membrane malfunction, contamin. electrolyte, or electrical problems SVCC Respiratory Care Programs
  75. 75. QC Levels • Level 1 simulates a patient hypoventilating • Level 2 simulates a patient with normal ventilatory status • Level 3 simulates a patient hyperventilating SVCC Respiratory Care Programs
  76. 76. HCO3- (bicarbonate): SB (standard bicarbonate) AB (actual bicarbonate) SB: the contents of HCO3- of serum of arterial blood in 37-38℃, PaCO2 40mmHg, SaO2 100%. Normal: 22-27mmol/L mean: 24mmol/L AB: The contents of HCO3- in actual condition. In normal person: AB=SB
  77. 77. AB and SB are parameters to reflect metabolism, regulated by kidney. Difference of AB-SB can reflect the respiratory affection on serum HCO3- . Respiratory acidosis: AB>SB Respiratory alkalosis: AB<SB Metabolic acidosis: AB=SB<Normal Metabolic alkalosis: AB=SB>Normal
  78. 78. 8 Sequential Rules: • Rule #1 – Must know the pH; pH determines whether the primary disorder is an acidosis or an alkalosis • Rule #2 – Must know the PaCO2 and serum HCO3- • Rule #3 – Must be able to establish that the available data (pH, PaCO2, and HCO3-) are consistent
  79. 79. Are the data consistent? • The Henderson Equation: H   24   PaCO HCO 2  3
  80. 80. Convert +] [H to pH: • Subtract calculated [H+] from 80; this gives the last two digits of a pH beginning with 7 – example: calculated [H+] of 24 converts to pH of (80-24)~7.56 – example: calculated [H+] of 53 converts to pH of (80-53)~7.27 • Refer to table 1 in handout for more precise conversion, or if calculated [H+] exceeds 80
  81. 81. Relationship between +] [H & pH
  82. 82. Relationship between + +] [H + & pH pH [H ] pH [H ] 7.80 7.75 7.70 7.65 7.60 7.55 7.50 7.45 7.40 7.35 16 18 20 22 25 28 32 35 40 45 7.30 7.25 7.20 7.15 7.10 7.00 6.95 6.90 6.85 6.80 50 56 63 71 79 89 100 112 141 159
  83. 83. Simple Acid-Base Disorders: T y p e o f D iso rd er M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis A cu te R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis pH  P a C O 2 [H C O 3 ] 
  84. 84. Simple Acid-Base Disorders: T y p e o f D iso rd er M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis A cu te R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis pH  P a C O 2 [H C O 3 ]  
  85. 85. Simple Acid-Base Disorders: T y p e o f D iso rd er pH P a C O 2 [H C O 3 ] M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis A cu te R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis  
  86. 86. Simple Acid-Base Disorders: T y p e o f D iso rd er T y p e o f D iso rd er pH pH P a C O 2 [H C O 3 ] P a C O 2 [H C O 3 ] M etab o lic A cid o sis M etab o lic A cid o sis M etab o lic A lk alo sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis A cu te R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis A cu te R esp irato ry A lk alo sis A cu te R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis      
  87. 87. Simple Acid-Base Disorders: T y p e o f D iso rd er pH P a C O 2 [H C O 3 ] M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis   C h ro n ic R esp irato ry A cid o sis   A cu te R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis
  88. 88. Simple Acid-Base Disorders: T y p e o f D iso rd er pH P a C O 2 [H C O 3 ] M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis    C h ro n ic R esp irato ry A cid o sis    A cu te R esp irato ry A lk alo sis C h ro n ic R esp irato ry A lk alo sis
  89. 89. Simple Acid-Base Disorders: T y p e o f D iso rd er pH P a C O 2 [H C O 3 ] M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis A cu te R esp irato ry A lk alo sis   C h ro n ic R esp irato ry A lk alo sis  
  90. 90. Simple Acid-Base Disorders: T y p e o f D iso rd er pH P a C O 2 [H C O 3 ] M etab o lic A cid o sis M etab o lic A lk alo sis A cu te R esp irato ry A cid o sis C h ro n ic R esp irato ry A cid o sis A cu te R esp irato ry A lk alo sis    C h ro n ic R esp irato ry A lk alo sis   
  91. 91. Simple Acid-Base Disorders: T y p e o f D iso rd er pH P a C O 2 [H C O 3 ] M etab o lic A cid o sis    M etab o lic A lk alo sis    A cu te R esp irato ry A cid o sis    C h ro n ic R esp irato ry A cid o sis    A cu te R esp irato ry A lk alo sis    C h ro n ic R esp irato ry A lk alo sis   
  92. 92. Simple Acid-Base Disorders: • The compensatory variable always changes in the SAME DIRECTION as the primarily deranged variable • Compensation is always more pronounced in CHRONIC RESPIRATORY disorders than in acute respiratory disorders
  93. 93. 8 Sequential Rules: • Rule #4: – must know if compensation is appropriate – compensation never overshoots • Must have known “rules of thumb” to interpret appropriateness of compensation
  94. 94. Rules of Compensation: • Metabolic Acidosis – PaCO2 should fall by 1 to 1.5 mm Hg x the fall in plasma [HCO3] • Metabolic Alkalosis – PaCO2 should rise by .25 to 1 mm Hg x the rise in plasma [HCO3]
  95. 95. Rules of Compensation: • Acute Respiratory Acidosis – Plasma [HCO3] should rise by ~1mmole/l for each 10 mm Hg increment in PaCO2 • Chronic Respiratory Acidosis – Plasma [HCO3] should rise by ~4mmoles/l for each 10 mm Hg increment in PaCO2
  96. 96. Rules of Compensation: • Acute Respiratory Alkalosis – Plasma [HCO3] should fall by ~1-3 mmole/l for each 10 mm Hg decrement in PaCO2, usually not to less than 18 mmoles/l • Chronic Respiratory Alkalosis – Plasma [HCO3] should fall by ~2-5 mmole/l for each 10 mm Hg decrement in PaCO2, usually not to less than 14 mmoles/l
  97. 97. Case #1: • A 24 years old with chronic renal failure presents to ER with history of increasing azotemia, weakness, and lethargy. Exam reveals the patient to be modestly hypertensive, and tachypneic. Labs reveal BUN=100 mg, and Creatinine=8 mg.
  98. 98. Case #1: • Steps 1&2: must know pH, PaCO2, HCO3 • pH=7.37, PaCO2=22, and HCO3=12 • Step 3: are the available data consistent? H   24   PaCO HCO 2  3
  99. 99. Case #1: • [H+]=44, equates to pH~7.36; data are thus consistent • What is the primary disorder? • “_________Acidosis” • Which variable (PaCO2, HCO3) is deranged in a direction consistent with acidosis? • Primary disorder is “Metabolic Acidosis”
  100. 100. Is compensation appropriate? • HCO3 is decreased by 12 mmoles/l • PaCO2 should decrease by 1 to 1.5 times the fall in HCO3; expect PaCO2 to decrease by 12-18 mm Hg or be between 22-28 mm Hg • Since PaCO2 is 22 mm Hg, compensation is appropriate, and the data are consistent with a simple metabolic acidosis with respiratory compensation
  101. 101. 8 Sequential Rules: • Rule #5: – If the data are consistent with a simple disorder, it does not guarantee that a simple disorder exists; need to examine the patient’s history • Rule #6: – When compensatory responses do not lie within the accepted range, by definition a combined disorder exists.
  102. 102. Case #2: • A 16 year old male with sickle cell anemia, hemochromatosis, & subsequent cirrhosis, presents with a several day history of emesis. At presentation to the pedes ER, he is hypotensive, orthostatic, and confused. • What acid-base disorders might be anticipated based on the above information?
  103. 103. Case #3: • 16 yo male with sickle cell anemia, hemochromatosis, & subsequent cirrhosis, and several days of emesis. In the pedes ER, he is hypotensive, orthostatic, and confused. • Emesis-loss of H+ (HCl)-metabolic alkalosis • Orthostatic hypotension-?lactic acidosis • SCD-decreased O2 delivery-?lactic acidosis • Cirrhosis-decreased lactate metabolism
  104. 104. Case #3: • • • • What baseline information is available? pH=7.55, PaCO2=66 „lytes: Na+=166, K+=3.0, Cl-=90, HCO3=56 Are the data internally consistent? H   24   PaCO HCO 2  3
  105. 105. Case #3: • • • • • [H+]~28, equates to pH~7.55; consistent What is the primary abnormality? “_________ Alkalosis” PaCO2ed, HCO3 ed, therefore……. “Metabolic Alkalosis” presumed due to emesis • Is compensation appropriate?
  106. 106. Case #3: • Metabolic Alkalosis – PaCO2 should rise by .25 to 1 mm Hg x the rise in plasma [HCO3] • HCO3 ed by 32; PaCO2 should  by 8-32 • PaCO2 ed by 26, so compensation appears appropriate • What about multiple risk factors for lactic acidosis?
  107. 107. Case #3: • • • • • • Could there be a concealed lactic acidosis? What is the anion gap? Na+- (Cl- + HCO3), normally 12-14 Anion gap here is 166 - (90 + 56) = 20 ed anion gap implies metabolic acidosis Combined metabolic alkalosis & metabolic acidosis therefore present
  108. 108. 8 Sequential Rules: • Rule #7: Always calculate the anion gap • Often it is the only sign of an occult metabolic acidosis – acidotic patients partially treated with HCO3 – acidotic patients with emesis • May be the only sign of metabolic acidosis “concealed” by concomitant acid-base disorders
  109. 109. Causes of  Anion Gap Acidosis: • Endogenous acidosis – Uremia (uncleared organic acids) – Ketoacidosis, Lactic acidosis (increased organic acid production), Rhabdomyolosis • Exogenous acidosis – ingestions: salicylate, iron; paraldehyde use • Other Ingestions: – Methanol toxicity, Ethylene Glycol toxicity
  110. 110. Causes of normal Anion Gap Acidosis: • • • • • Diarrhea Isotonic saline infusion Renal tubular acidosis Acetazolamide Ureterocolic shunt
  111. 111. Anion Gap: • Based on the concept of electroneutrality; the assumption that the sum of all available cations= the sum of all available anions. Restated as: • Na+ + Unmeasured Cations (UC) = Cl- + HCO3 + Unmeasure Anions (UA); conventionally restated: • Na+-(Cl-+HCO3)=UA-UC=Anion Gap=12 to 14
  112. 112. Anion Gap: • Na+-(Cl-+HCO3)=UA-UC • Serum albumin contributes ~1/2 of the total anion equivalency of the “UA” pool. Assuming normal electrolytes, a 1gm/dl decline in serum albumin decreases the anion gap factitiously by 3 mEq/L. Therefore an anion gap of 12 mEq/L is corrected to 17-18 mEq/L when the serum albumin is half of normal; this is an important correction factor in settings of chronic illness or malnourished patients
  113. 113. Case #3: • A 3 year old is brought to the pedes ER at ~3am, stuporous and tachypneic. History is remarkable for his parents having cleaned out their medicine cabinet earlier that day. An ABG and electrolytes have been accidentally drawn by the nurse.
  114. 114. Case #4: • Available data: pH=7.53, PaCO2=12; Na+=140, K+=3.0, Cl-=106, HCO3=10 • Are the data internally consistent? H   24   PaCO HCO 2  3
  115. 115. Case #4: • • • • [H+]~29, so pH~7.51; data consistent What is the primary disturbance? “__________ Alkalosis” Which variable (PaCO2, HCO3) is deranged in a direction consistent with alkalosis? • ed PaCO2, ed HCO3; so “Respiratory Alkalosis”
  116. 116. Case #4: • Is compensation appropriate? • Acute respiratory alkalosis – Plasma [HCO3] should fall by ~1-3 mmole/l for each 10 mm Hg decrement in PaCO2, usually not to less than 18 mmoles/l • PaCO2 ed by ~30 mm Hg; HCO3 should fall by 3-9 mmole/l; HCO3  is too great, so superimposed metabolic acidosis
  117. 117. Case #4: • What is the anion gap? • 140 - (106 + 10) = 24; elevated anion gap consistent with metabolic acidosis • What is the differential diagnosis? • Combined (true) respiratory alkalosis and metabolic acidosis seen in sepsis, or salicylate intoxication
  118. 118. Case #5: • A 5 year old with Bartter‟s Syndrome is brought to clinic, where she collapses. She has recently been febrile, but history is otherwise unremarkable. An ABG and serum electrolytes are obtained: pH=6.9, PaCO2=81; Na+=142, K+=2.8, Cl-=87, HCO3=16
  119. 119. Case #5: • Are the data consistent? H   24   PaCO HCO 2  3 • [H+]=122, pH~6.9; data are consistent
  120. 120. Case #5: • What is the primary disturbance? • “_________ Acidosis” • Which variable (PaCO2, HCO3) is deranged in a direction consistent with acidosis? • Both; pick most abnormal value-• “Respiratory Acidosis” • Is compensation appropriate?
  121. 121. Case #5: • Acute Respiratory Acidosis – Plasma [HCO3] should rise by ~1mmole/l for each 10 mm Hg increment in PaCO2 • Since HCO3 is inappropriately depressed, compensation is not appropriate, and there is a concomitant metabolic acidosis as well • What is the anion gap? • AG=39, confirms metabolic acidosis
  122. 122. Case #5: • Combined Respiratory Acidosis and Metabolic Acidosis; are there other disorders present? • What about the dx of Bartter‟s Syndrome? • Bartter‟s Syndrome characterized by hypokalemic metabolic alkalosis • Does this patient have a concealed metabolic alkalosis?
  123. 123. Case #5: • Anion gap is 39, or 25-27 greater than normal • Typically, increases in anion gap correlate with decreases in HCO3 • Assuming a 1:1 relationship, as anion gap increases by 25, HCO3 should fall by 25 • Starting HCO3 must have been 16 + 25 = 41
  124. 124. Case #5: • Therefore, starting HCO3 was ~41 mmol/l, consistent with expected chronic metabolic alkalosis. This metabolic alkalosis was “concealed” by the supervening profound metabolic and respiratory acidoses associated with her arrest event. • Final diagnosis: Metabolic alkalosis, metabolic acidosis, & respiratory acidosis
  125. 125. 8 Sequential Rules; Rule #8 • Rule #8: Mixed Acid-Base Disorders • Coexistant metabolic acidosis and metabolic alkalosis may occur. Always check the change in the anion gap vs. decrement in bicarbonate to rule out a concealed metabolic disorder.
  126. 126. Case #6: • A 3 year old toddler is brought to the ER at 3 am after being found unarousable on his bedroom floor, with urinary incontinence. EMS monitoring at the scene revealed sinus bradycardia. One amp of D50W and 5 mg of naloxone were given IV without response. Vital signs are stable; respiratory effort is regular, but tachypneic. He is acyanotic.
  127. 127. Case #6: • Initial lab studies (lytes, ABG & urine tox screen) are sent. Initial dextrostick is >800. • Initial available data are: • Na+=154, K=5.6, Cl=106, HCO3=5, BUN=6 creatinine=1.7, glucose=804, PO4=12.3, Ca++=9.8, NH4=160, serum osms=517 • pH=6.80, PaCO2=33, PaO2=298
  128. 128. Case #6: • • • • • • • What is the primary disturbance? ________ Acidosis Metabolic Acidosis Is compensation appropriate? No; PaCO2 level is inappropriately high Are other disorders present? Respiratory acidosis (due to evolving coma)
  129. 129. Case #6: • What is our differential thus far? – Anion gap vs. non-anion gap metabolic acidosis – DKA, lactic acidosis, renal failure, ingestion • The urine tox screen comes back negative – What does urine tox screen actually screen for? • The patient‟s IV falls out. He then has a seizure, is incontinent of urine, and fills the specimen bag you placed on ER arrival.
  130. 130. Case #6: • What is the calculated serum osmolality, and does an osmolal gap exist? • 2(Na) + BUN/2.8 + Glucose/18 – Calculated=355, Measured=517 • What is the most likely diagnosis? • How can this be confirmed definitively? – Review of urinalysis – Serum ethylene glycol level
  131. 131. Case #6: Methanol, ethylene glycol ethyl alcohol, isopropyl alcohol Anion gap metabolic acidosis Osmolal gap
  132. 132. Gap-Gap *AG excess/HCO3 deficit= (Measured AG-12)/ (24-measured HCO3) *Ratio <1 in presence of high AG acidosis means coexistance of normal AG metabolic acidosis *Ratio >1 in presence of high AG acidosis means coexistance of metabolic alkalosis

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