Download Mixed alkalosis

dr. Husnil Kadri, M.Kes
Biochemistry Departement
Medical Faculty Of Andalas University
Padang
Arterial Blood Gases
•
•
•
•
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
Logistics
• When to order an arterial line -– Need for continuous BP monitoring
– Need for multiple ABGs
• Where to place – (with antikoagulant)
– A. Radial
– A. Femoral
– A. Brachial
– A. Dorsalis Pedis
– A. Axillary
The Components
Desired Ranges:
– pH ; 7.35 - 7.45
– PaCO2 ; 35-45 mmHg
– PaO2 ; 80-100 mmHg
– HCO3 ; 21-27
– O2sat ; 95-100%
– Base Excess ; +/-2 mEq/L
Arterial Blood Gases
• Reflect oxygenation, gas exchange, and acidbase balance
• PaO2 is the partial pressure of oxygen
dissolved in arterial blood
• SaO2 is the amount of oxygen bound to
hemoglobin
Base Excess
Definition: The amount of a strong acid (like
HCl) needed to bring blood to 7.40.
• Assumes 100% oxygenation, 37oC, and pCO2 of 40.
Normal = 0
Used to calculate the metabolic component of
an acid-base disturbance.
Base Excess calculations
Calculated the same way, in practice, as SID:
Buffer Base (SID) = HCO3- + AHCO3 calculated by pH & pCO2 (blood gas machine)
A- calculated using pH & hemoglobin (whole blood)
OR A- calculated using albumin & phos (plasma)
BE = Buffer Base – “expected buffer base”
(expected if pH = 7.4 and pCO2 = 40)
Indicators of hypoxaemia and hypoxia
Arterial blood gases
PO2
SO2
pH
PCO2
Lab Findings
80-100 mm Hg (normal)
60-80 mm Hg (mild hypoxemia)
40-60 mm Hg (moderate hypoxemia)
<40 mm Hg (severe hypoxemia)
95%-97% (normal)
<90% (may indicate hypoxemia)
7.35-7.45 (normal)
<7.35 (acidemia)
>7.45 (alkalemia)
35-45 mm Hg (normal)
>45 mm Hg (hypoventilation)
<35 mm Hg (hyperventilation)
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Is it Respiratory or Metabolic?
1. Respiratory
Acidosis
•
Increased pCO2
>50
2. Respiratory
Alkalosis
•
Decreased
pCO2<30
3. Metabolic Acidosis
•
4. Metabolic Alkalosis
•
Decreased HCO3
<18
Increased HCO3
>30
Compensated or Uncompensated—what does
this mean?
1. Evaluate pH—is it normal? Yes
2. Next evaluate pCO2 & HCO3
•
pH normal + increased pCO2 + increased HCO3 =
compensated respiratory acidosis
•
pH normal + decreased HCO3 + decreased pCO2
= compensated metabolic acidosis
Compensated vs. Uncompensated
1. Is pH normal? No
2. Acidotic vs. Alkalotic
3. Respiratory vs. Metabolic
• pH<7.30 + pCO2>50 + normal HCO3 =
uncompensated respiratory acidosis
• pH<7.30 + HCO3<18 + normal pCO2 =
uncompensated metabolic acidosis
• pH>7.50 + pCO2<30 + normal HCO3 =
uncompensated respiratory alkalosis
• pH>7.50 + HCO3>30 + normal pCO2 =
uncompensated metabolic alkalosis
Causes of Acidosis
• Respiratory
– Hypoventilation
– Impaired gas
exchange
• Metabolic
– Ketoacidosis
• Diabetes
– Renal Tubular
Acidosis
• Renal Failure
– Lactic Acidosis
• Decreased
perfusion
• Severe
hypoxemia
Causes of Alkalosis
• Respiratory
– Hyperventilation
due to:
• Hypoxemia
• Metabolic
acidosis
• Neurologic
–Lesions
–Trauma
–Infection
• Metabolic
– Hypokalemia
– Gastric suction or
vomiting
– Hypochloremia
Mixed Metabolic Acidosis and Chronic
Respiratory Alkalosis
Examples:
• Sepsis
• Addition of respiratory alkalosis to metabolic
acidosis further decreases HCO3- but pH may
remain normal
• Lactic acidosis plus respiratory alkalosis due
to severe liver disease, pulmonary emboli, or
sepsis
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Mixed Metabolic Alkalosis and Chronic
Respiratory Acidosis
Examples:
• Patient with COPD receiving glucocorticoids or
diuretics
• pCO2 and HCO3- are increased by both
conditions, but pH is neutralized
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Mixed Alkalosis, Severe
Example:
• Postoperative patient with severe hemorrhage
stimulating hyperventilation [respiratory
alkalosis] plus massive transfusion and
nasogastric drainage [metabolic alkalosis]
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Mixed Chronic Respiratory Acidosis
and Acute Metabolic Acidosis
Examples:
• COPD [chronic respiratory acidosis] with
severe diarrhoea [metabolic acidosis]. pH is
too low for pCO2 of 55 mmHg in chronic
respiratory acidosis, indicating low pH due to
mixed acidosis, but HCO3- effect is offset
17
Mixed Metabolic Acidosis and
Metabolic Alkalosis
Examples:
• Gastroenteritis with vomiting [metabolic
alkalosis] and diarrhoea [metabolic acidosis
due to loss of HCO3-]; surprisingly normal
findings with marked volume depletion
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Serum Values in Acid-Base Disturbances
Condition
Na+
Cl-
HCO3- pCO2
mmol/L
mmol/L
mmol/L mmHg
Normal
140
105
25
40
7.40
Metabolic acidosis
140
115
15
31
7.30
Chronic respiratory alkalosis
136
102
25
40
7.44
Mixed metabolic acidosis and 136
chronic respiratory alkalosis
140
Metabolic alkalosis
108
14
24
7.39
92
36
48
7.49
100-102 28
50
7.37
90
67
7.40
Chronic respiratory acidosis
140
Mixed metabolic alkalosis and 140
chronic respiratory acidosis
40
pH
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Serum Values in Acid-Base Disturbances
Condition
Na+
Cl-
HCO3- pCO2
pH
mmol/L
mmol/L
mmol/L
mmHg
Normal
136-145 100-106 24-26
35-45
7.35-7.45
Metabolic alkalosis
139
89
35
47
7.49
Respiratory alkalosis
136
102
20
30
7.44
Mixed alkalosis, mild
139
92
32
39
7.53
Mixed alkalosis, severe
139
92
32
30
7.63
Mixed chronic respiratory
acidosis and acute
metabolic acidosis
Mixed metabolic acidosis
and metabolic alkalosis
136
102
22
55
7.22
140
103
25
40
7.40
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Summary of Pure and Mixed Acid-Base
Disorders
Decreased
pH
Normal pH Increased
pH
 pCO2
Respiratory acidosis
with or without
incompletely
compensated
metabolic alkalosis or
coexisting metabolic
acidosis
Respiratory
acidosis and
compensated
metabolic alkalosis
Metabolic alkalosis
with incompletely
compensated
respiratory acidosis
or coexisting
respiratory acidosis
Normal
pCO2
Metabolic acidosis
Normal
Metabolic alkalosis
Source: Adapted from Friedman HH. Problem-oriented medical
diagnosis, 3rd ed. Boston: Little, Brown. 1983
21
References
• Anisman, S. Base Excess & Strong Ion Theories. ppt.
2003.
• Klee, V. Arterial Blood Gas Analysis.ppt. 2012.
• Perkins, J. ABG Interpretation. ppt. 2012.
• Rashid, FA. Respiratory Mechanisms in Acid-Base
Homeostasis.ppt. 2005.