Interpreting Blood Gases, Practical and easy approach
-
Upload
muhammad-asim-rana -
Category
Education
-
view
8.347 -
download
1
Transcript of Interpreting Blood Gases, Practical and easy approach
![Page 1: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/1.jpg)
Interpreting ABGs
Practical Approach
Muhammad Asim RanaBSc, MBBS, MRCP, SF-CCM, FCCP, EDIC
Department of Adult Critical Care MedicineKSMC, Riyadh
![Page 2: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/2.jpg)
Venous Arterial
![Page 3: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/3.jpg)
Arterial Blood Gases
• Written in following manner:
pH/PaCO2/PaO2/HCO3
– pH = arterial blood pH
– PaCO2 = arterial pressure of CO2
– PaO2 = arterial pressure of O2
– HCO3 = serum bicarbonate concentration
![Page 4: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/4.jpg)
Part 1
Acid-Base Disorders
![Page 5: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/5.jpg)
Acid-Base
• Acidosis or alkalosis:
– any disorder that causes an alteration in pH
• Acidemia or alkalemia:
– alteration in blood pH; may be result of one or more disorders.
![Page 6: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/6.jpg)
Some important concepts
• The determinants of extracellular fluid pH indicate that tight control of the pH requires a fairly constant PCO2/HCO3 ratio.
• Thus, a change in one of the determinants (PCO2 or HCO3) must be accompanied by a proportional change in the other determinant to keep the PCO2/HCO3 ratio (and the pH) constant.
![Page 7: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/7.jpg)
Some important concepts
• Thus, an increase in PCO2 (respiratory acidosis) must be accompanied by an increase in HCO3 (metabolic alkalosis) to keep the pH constant.
• This is how the control system for acid-base balance operates.
• A respiratory disorder (change in PCO2) always initiates a complementary metabolic response (that alters the HCO3), and vice-versa
![Page 8: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/8.jpg)
Primary Disorder Primary Change Compensatory Change*
Respiratory acidosis Increased PCO2 Increased HCO3
Respiratory alkalosis Decreased PCO2 Decreased HCO3
Metabolic acidosis Decreased HCO3 Decreased PCO2
Metabolic alkalosis Increased HCO3 Increased PCO2
Primary Acid-Base Disorders and Associated Compensatory Changes
[H+] = 24 × PCO2/HCO3
* Compensatory changes keep the PCO2/HCO3 ratio constant.
![Page 9: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/9.jpg)
Check if data is consistent{H} = 24 [ PaCO2/HCO3]{H} = (7.8 – pH) x 100
Each 0.01 unit change in pH {H} will change by 1mEq/L{H} = 40+(delta pH) (1mEq/L)/0.01
pH-------------- {H} 7.3---------------507.2---------------637.1---------------807.0--------------1006.9--------------1256.8--------------160
![Page 10: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/10.jpg)
Check if data is consistent
{H} = 24 [PaCO2/HCO3]{H} = (7.8 – pH) x 100
• The {H} in extracellular fluid normally varies less than 10 nEq/L
• The values of {H} should be within 10 for both calculations !
• If it is beyond or more than 10 the blood gas analysis is not interpretable.
• The reasons may include improper caliberation or others
![Page 11: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/11.jpg)
Here are some examples• Written in following manner:
pH/PaCO2/PaO2/HCO3
• 7.8/36.6/76.4/55.4
• 7.7/35.5/80.3/50.6
• 7.54/53.1/63.7/44.6
24 x 36.6/55.4 = 15.857.8-7.8 x 100 = 0
The data is inconsistent
24 x 35.5/50.6 = 16.8 7.8-7.7 x 100 = 10
The data is inconsistent
24x53.1/44.6 = 28.577.8-7.54 x 100 = 26
The data is consistent
![Page 12: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/12.jpg)
Case Study
• A 13 years old female presented in ER with pain abdomen and drowsiness.
• Blood gas revealed
• 6.87/20.6/88/3.7
• Na 140.4, K 4.41, Cl 102
![Page 13: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/13.jpg)
Step-wise Approach
1. Acedemia or Alkalemia
2. Metabolic or Respiratory (Primary Pathology)
3. For metabolic is it anion gap or non anion gap.
4. For AG acidosis, are there other disturbances.
5. Resp compensation for the metabolic disturbances.
6. For respiratory disturbances is it acute or chronic.
![Page 14: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/14.jpg)
Step 1: Acidemic or Alkalemic?
• Acidemic : PH < 7.35
• Alkalemic: PH > 7.45
An acid-base abnormality is present if either the PaCO2 or the pH is outside the normal range. (A normal pH or PaCO2 does not exclude the presence of an acid-base abnormality)
![Page 15: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/15.jpg)
Type of disturbance
pH 6.87
Acidemia
![Page 16: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/16.jpg)
Primary Acid-Base Disorders
• A change in either the PCO2 or the HCO3 will cause a change in the [H+] of extracellular fluid.
• When a change in PCO2 is responsible for a change in [H+], the condition is called a respiratory acid-base disorder– an increase in PCO2 is a respiratory acidosis– a decrease in PCO2 is a respiratory alkalosis.
• When a change in HCO3 is responsible for a change in [H+], the condition is called a metabolic acid-base disorder– a decrease in HCO3 is a metabolic acidosis– an increase in HCO3 is a metabolic alkalosis.
![Page 17: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/17.jpg)
Step 2: Primary disturbance metabolic or Respiratory
If the pH and PaCO2 are both abnormal, compare the directional change. If both change in the same direction (both increase or decrease), the primary acid-base disorder is metabolic, and if both change in opposite directions, the primary acid-base disorder is respiratory.
If either the pH or PaCO2 is normal, there is a mixed metabolic and respiratory acid-base disorder (one is an acidosis and the other is an alkalosis). • If the pH is normal, the direction of change in PaCO2
identifies the respiratory disorder• If the PaCO2 is normal, the direction of change in the pH
identifies the metabolic disorder.
![Page 18: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/18.jpg)
Type of disturbance
pH 6.87
Acidemia
Metabolic
pH: 6.8PaCO2: 14.5
![Page 19: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/19.jpg)
Step 3 : What is the Anion Gap
• Anion gap measures the difference between Anions(-) and Cations(+) present in blood
• AG = Na – (Cl + HCO3)
• Normal Anion gap is 12 mEq/L
![Page 20: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/20.jpg)
Anion Gap
Unmeasured Anions Unmeasured Cations
Proteins 15 mEq Calcium 5 mEq
Organic acid 5 mEq Potassium 4.5 mEq
Phosphate 2 mEq Magnesium 1.5 mEq
Sulfates 1 mEq
Total 23 mEq Total 11 mEq
Difference : 23 – 11 = 12
![Page 21: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/21.jpg)
Extra for the experts
• Albumin carries negative charge .
• Hypo-albuminemia causes falsely low AG.
• To correct for that
• AG adjusted = AG Observed + 0.25 × (4.5 – pt’s alb)
Other causes of low AG Paraproteinemia,
Bromism, lithium toxicity,
Profound hypocalcemia, hypomagnesemia
hyponatremia
![Page 22: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/22.jpg)
Extra for the experts
• In metabolic alkalosis AG can be high but it could be due to unmeasured anions, specifically the albumin.
![Page 23: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/23.jpg)
Type of disturbance
pH 7.10
Acidemia
Metabolic
High AG
Anion Gap?Na = 140.4
Cl = 104
HCO3 = 3.7
AG = 140.4 - 104 - 3.7 = 32.3
![Page 24: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/24.jpg)
Causes Of Anion Gap Acidosis
• Methanol• Uremia• DKA• Paraldehyde• INH• Iron• Lactic Acidosis• Ethanol• Ethylene Glycol• Salicylic Acid
MUDPILES
![Page 25: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/25.jpg)
Step 4: Is there other metabolic disturbances coexisting with AG Acidosis
• In the presence of high AG metabolic acidosis, it is possible that patient may have another metabolic acid base disorder.
• A normal AG metabolic acidosis or a metabolic alkalosis
• This can be discovered by comparing the AG excess to the HCO3 deficit.
![Page 26: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/26.jpg)
Step 4: Is there other metabolic disturbances coexisting with AG Acidosis
• Delta Anion Gap or ΔAG: • Difference between measured and normal AG
– ΔAG = AG - 12
• Delta HCO3 or ΔHCO3:– Difference between measured and normal HCO3
– ΔHCO3 = 24 – Measured HCO3
Delta Anion Gap or ΔAG is sometimes simply called Δgap
![Page 27: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/27.jpg)
Step 4: Is there other metabolic disturbances coexisting with AG Acidosis
• If the disturbance is pure AG Acidosis• Δ AG/Δ HCO3 = unity or 1
• In our example • HCO3= 3.7 so • ΔHCO3 = 24 – 3.7 = 20.3• Now Δ AG • AG = 32.3 so• Δ AG = 32.3 – 12 = 20.3• Δ AG /ΔHCO3 = 20.3/20.3 = 1.0
So this patient has pure high AG metabolic acidosis
![Page 28: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/28.jpg)
Remember !
• If Δ AG /ΔHCO3 < 1.0
• The decrease in the HCO3 is greater than the increase in the AG and the ratio falls below 1
• It means there is accumulation of other acid which does not affect the AG but causes a fall in HCO3 i.e. NON-AG Metabolic Acidosis
![Page 29: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/29.jpg)
Remember !
• If Δ AG /ΔHCO3 > 1.0
• When alkali is added in the presence of high AG acidosis, the decrease in serum HCO3 is less than the increase in the AG and the ratio goes above 1
• Therefore, in the presence of high AG metabolic acidosis a gap-gap ratio of greater than 1 indicates co-existence of – metabolic alkalosis
![Page 30: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/30.jpg)
Concept of corrected HCO3
• Add rgap to measured HCO3
– If new value becomes normal (22-26)
– There is no other metabolic problems
– If it still stays < 22, then there is concomitant metabolic acidosis, non AG metabolic acidosis
– If it goes > 26, then there is concomitant metabolic alkalosis
![Page 31: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/31.jpg)
Revision
rgap + HCO3 = N (Only one disorder i.e.↑AG Met Acid)
rgap + HCO3 = >N (↑AG Met Acid + Meta Alk)
rgap + HCO3 = <N (↑AG Met Acid + Nor AG Meta Acid)
![Page 32: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/32.jpg)
Let us apply on our case
• Corrected HCO3 = HCO3 + Δ AG
• Corrected HCO3 = 3.7 + 20.3 = 24
• Perfect !!
![Page 33: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/33.jpg)
In ↑AG metabolic acidosis
Extend your search further
To pin point the diagnosis
![Page 34: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/34.jpg)
In case of high AG acidosis
• Always calculate Osmolar gap:
• Osm gap = measured Osm – Calc Osm
• Calc Osm =
(2 x Na+) + (glucose/18) + (BUN/2.8)
Normal Osm gap < 10 mOsm/kg
• In areas where alcohol is common
• Calc Osm = (2 x Na+) + (glucose/18) +(BUN/2.8) + (EtOH/4.6)
![Page 35: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/35.jpg)
In case of high AG acidosis
↑AG acidosis but N osmolar gap
• DKA
• Uremia
• Lactic acidosis
• Salisylates
↑AG acidosis and ↑osmolar gap
• Ethanol
• Methanol
• Ehylene Glycol
![Page 36: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/36.jpg)
Causes of non-Anion Gap Acidosis
• Hyper Alimentation
• Acetazolamide
• Renal Tubular Acidosis
• Diarrhea
• Ureterosigmoidostomy
• Pancreatic Fistula
• Primary Hyperparathyroidism
HARD-UP
![Page 37: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/37.jpg)
Compensatory responses
• Compensatory responses are secondary responses designed to limit the change in [H+] produced by the primary acid-base disorder, and this is accomplished by changing the other component of the PaCO2/HCO3 ratio in the same direction.
![Page 38: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/38.jpg)
Secondary Responses
• If the primary problem is an increase in PaCO2 (respiratory acidosis)
– The secondary response will involve an increase in HCO3, and this will limit the change in [H+] produced by the increase in PaCO2.
• Secondary responses should not be called “compensatory responses” because they do not completely correct the change in [H+] produced by the primary acid-base disorder
![Page 39: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/39.jpg)
Secondary/Compensatory responses
• If there is a primary metabolic acidosis or alkalosis, use the measured HCO3 to identify the expected PaCO2.
• If the measured and expected PaCO2 are equivalent, the condition is fully compensated.
• If the measured PaCO2 is higher than the expected PaCO2, there is a superimposed respiratory acidosis.
• If the measured PCO2 is less than the expected PCO2, there is a superimposed respiratory alkalosis.
Metabolic AcidosisExp PaCO2 = 1.5 x HCO3 + 8 ± 2
Metabolic AlkalosisExp PaCO2 = 0.7 x HCO3 + 21 ± 2
![Page 40: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/40.jpg)
Let’s see our case
pH 7.10
Acidemia
Metabolic
High AG
Compensated or ????
Winter’s Formula :Expected PaCO2 = (1.5 x HCO3) + 8 ± 2
Applying Winter’s Formula :Expected PaCO2 = (1.5 x 3.7) + 8 ± 2 = 13.5-15.5
So in our case it is :Metabolic acidemia is compensated
![Page 41: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/41.jpg)
Mixed Disorders
• If either the pH or PaCO2 is normal, there is a mixed metabolic and respiratory acid-base disorder
– (one is an acidosis and the other is an alkalosis).
• If the pH is normal, the direction of change in PaCO2 identifies the respiratory disorder, and if the PaCO2 is normal, the direction of change in the pH identifies the metabolic disorder.
![Page 42: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/42.jpg)
Mixed Disorders
• If there is a respiratory acidosis or alkalosis, use the PaCO2 to calculate the expected pH for respiratory acidosis or for respiratory alkalosis.
• Compare the measured pH to the expected pH to determine if the condition is acute, partially compensated, or fully compensated.
![Page 43: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/43.jpg)
Mixed Disorders
• For respiratory acidosis
– If the measured pH is lower than the expected pH for the acute, uncompensated condition, there is a superimposed metabolic acidosis
– If the measured pH is higher than the expected pH for the chronic, compensated condition, there is a superimposed metabolic alkalosis.
![Page 44: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/44.jpg)
• For respiratory alkalosis
– If the measured pH is higher than the expected pH for the acute, uncompensated condition, there is a superimposed metabolic alkalosis
– If the measured pH is below the expected pH for the chronic, compensated condition, there is a superimposed metabolic acidosis.
Mixed Disorders
![Page 45: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/45.jpg)
Formulae for secondary responsesPredicting Timing by pH change
Acute Respiratory AcidosisFall in pH or Δ pH = 0.008 x ΔPaCO2
Expected pH = 7.40 – [0.008 x ( PaCO2 – 40)]Chronic Respiratory AcidosisFall in pH or Δ pH = 0.003 x ΔPaCO2
Expected pH = 7.40 – [0.003 x ( PaCO2 – 40)]Acute Respiratory AlkalosisRise in pH or ΔpH = 0.008 x ΔPaCO2
Expected pH = 7.40 + [0.008 x ( 40 - PaCO2 )]Chronic Respiratory AlkalosisRise in pH or Δ pH = 0.003 x ΔPaCO2
Expected pH = 7.40 + [0.003 x ( 40 - PaCO2 )]
![Page 46: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/46.jpg)
Predicting Timing by response
![Page 47: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/47.jpg)
Another way to cram compensatory responses
• Metabolic Acidosis HCO3 ↓----------------PaCO2 ↓
• PaCO2 ↓ by 1.3 for each 1 mEq ↓in HCO3
• Metabolic Alkalosis ↑in HCO3------------------ PaCO2 ↑
• PaCO2 ↑ by 0.7 for each 1 mEq ↑in HCO3
• Acute Respiratory Acidosis ↑in PaCO2---- -HCO3 ↑
• HCO3 ↑ by 1 mEq for each 10 mmHg ↑in PaCO2
• Acute Respiratory Alkalosis ↓in PaCO2----- HCO3 ↓
• HCO3 ↓ by 2 mEq for each 10 mmHg ↓in PaCO2
• Chronic Respiratory Acidosis ↑in PaCO2 ---HCO3 ↑
• HCO3 ↑ by 3.5 mEq for each 10 mmHg ↑in PaCO2
• Chronic Respiratory Alkalosis ↓in PaCO2---HCO3 ↓
• HCO3 ↓ by 5mEq for each 10 mmHg ↓in PaCO2
![Page 48: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/48.jpg)
Causes Of metabolic Alkalosis
• Volume contraction
– (Vomiting, diuresis, ascities)
• Hypokalemia
• Alkali ingestion
• Excess gluco-mineralocorticosteroids
• Bartter’s Syndrome
![Page 49: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/49.jpg)
Let’s Solve PH 7.02/PaCO219/HCO32.8, Na 141, Cl 111
Acedmia
AG=141-111-3=27
Corrected HCO3=3 + (15) = 18
AdditionalNon AG acidosis
PaCO2 = 1.5 × 3 + 8 ± 2= 12.5 ± 2
Resp Acidosis
Metabolic
Status
Met/ Resp
Anion Gap Other disorder?
Compensation??
![Page 50: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/50.jpg)
7.50/21.9/88.7/20.3/98.2%
Alkalemia
Acute Respiratory Alk
Exp HCO3=24+0.2x40-21.9= 27.6
Respiratory
Status
Met/ Resp
Acute/Chronic
Compensation??
Acute Respiratory AlkalosisRise in pH or ΔpH = 0.008 x ΔPaCO2
Expected pH = 7.40 + [0.008 x ( 40 - PaCO2 )]Chronic Respiratory AlkalosisRise in pH or Δ pH = 0.003 x 40 – ΔPaCO2
Expected pH =7.40 + [0.003 x ( 40 - PaCO2 )]
ΔHCO3 = 0.2 x ΔPaCO2
Exp HCO3 = 24 + [ 0.2 x (40 – PaCO2)]
Acute Resp alkalosis with metabolic acidosis?Acute Resp alkalosis not yet compensated? PaCO2 = 0.7 x HCO3 + 21 ± 2
![Page 51: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/51.jpg)
7.23/58/96/24
Acidosis
Respiratory
Δ PH= 0.008 x (58-40)=0.08 x 1.8 = 0.144
Δ PH=0.003 x 18 = 0.054
PH=7.326PH=7.236
ChronicAcute
Compensated or? Exp HCO3 = 24 + [0.1(PaCO2-40)]
Exp HCO3 = 24 + [0.1(58-40)]Answer = 25.8
Acute resp acidosis not yet fully compensated
![Page 52: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/52.jpg)
7.35/48/69/29
Mixed Disorder
Respiratory
Δ PH= 0.008 x (48-40)=0.008 x 8 = 0.064
7.40 – 0.064 =
Δ PH= 0.003 x (48-40)=0.003 x 8 = 0.024
7.40 – 0.024 =
PH=7.37PH=7.336
ChronicAcute
Compensated or? Exp HCO3 = 24 + [0.4(PaCO2-40)]
Exp HCO3 = 24 + [0.4(48-40)]Answer = 27.2
Chronic compensated resp acidosisWith metabolic alkalosis
![Page 53: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/53.jpg)
More Examples
![Page 54: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/54.jpg)
7.27/87.4/83.5/40.1
• Acidemia• Respiratory• Acute or Chronic ?• ΔpH:
– Acute: 0.008 x ΔPaCO2 = 0.008 x 47 = 0.379 – Expected pH = 7.40 – 0.379 = 7.021– Chronic: 0.003 x ΔPaCO2 = 0.003 x 47 = 0.142– Expected pH = 7.40 – 0.142 = 7.258
• Chronic Respiratory Acidosis• Compensation:
– 3.5 x 47 / 10 = 16.59– Expected HCO3 = 24 + 16.59 = 40.59
For each 10 mmHg CO2 rise HCO3 rises by 3.5
![Page 55: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/55.jpg)
7.24/62/58/22
• Acidemia• Primary …. Respiratory acidosis as PaCO2↑• Acute or Chronic ?• ΔpH:
– Acute: 0.008 x ΔPaCO2 = 0.008 x 22= 0.176– Expected pH = 7.40 - 0.176 = 7.224– Chronic: 0.003 x ΔPaCO2 = 0.003 x 22 = 0.066– Expected pH = 7.40 + 0.066 = 7.334
• So it is Acute Respiratory Acidosis• Compensation for acute resp acidosis
– Expected ↓ in HCO3 = 22/10 = 2.2– Expected HCO3 = 24 – 2.2 = 21.8
HCO3 will fall by 1 with each 10 mmHg rise in CO2
![Page 56: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/56.jpg)
7.365/22/110/12.3
• Mixed Disorder ….. pH (N) and CO2 ↓• Respiratory alkalosis as PaCO2↓• ΔpH:
– Acute: 0.008 x ΔPaCO2 = 0.008 x 18 = 0.114 – Expected pH = 7.40 + 0.114 = 7.514– Chronic: 0.003 x ΔPaCO2 = 0.003 x 18 = 0.054– Expected pH = 7.40 + 0.054 = 7.454
• In both cases the pH should be higher than what we have !!• So there is concomitant metabolic acidosis !! • Expected HCO3 for respiratory alkalosis
– Expected HCO3 for acute 24 - 3.6 = 20.4 – Expected HCO3 for chronic 24 - 9= 15
Acute: HCO3 ↓by 2 for each 10 mmHg ↓ in CO2
Chronic: HCO3 ↓by 5 for each 10 mmHg ↓ in CO2
Although the last calculation is not required !!
![Page 57: Interpreting Blood Gases, Practical and easy approach](https://reader034.fdocuments.us/reader034/viewer/2022050613/554b5633b4c905793d8b4ae5/html5/thumbnails/57.jpg)
Thank you
See you in part 2
Oxygenation Status