Arterial blood gas analysis in intensive care uint.ppt

lecture focus on arterial blood gas analysis

1. ABG analysis & Acid-Base Disorders
January 2018

2. Outline
1.Discuss simple steps in analyzing ABGs
2.Calculate the anion gap
3.Calculate the delta gap
4.Differentials for specific acid-base disorders

3. Steps for ABG analysis
1.What is the pH? Acidemia or Alkalemia?
2.What is the primary disorder present?
3.Is there appropriate compensation?
4.Is the compensation acute or chronic?
5.Is there an anion gap?
6.If there is a AG check the delta gap?
7.What is the differential for the clinical processes?

4. Normal Values
Variable Normal Range
pH 7.35 -7.45
pCO2 35-45 mmhg ( 4.5-6kpa)
Bicarbonate 22-26
Anion gap 10-14
Albumin 4

5. Step 1:
Look at the pH: is the blood acidemicor alkalemic?
EXAMPLE :
65yo M with CKD presenting with nausea, diarrhea
and acute respiratory distress
ABG :ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.1
ACIDMEIA OR ALKALEMIA ????

6. EXAMPLE ONE
ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl 97/ HCO3 7/BUN 119/
Cr 5.1
Answer PH = 7.23 , HCO3 7
Acidemia

7. Step 2: What is the primary disorder?
Whatdisorder is
present?
pH pCO2 or HCO3
Respiratory Acidosis pH low pCO2 high
MetabolicAcidosis pH low HCO3 low
Respiratory Alkalosis pH high pCO2 low
Metabolic Alkalosis pH high HCO3 high

8. EXAMPLE
ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl97/ HCO3 7/BUN 119/ Cr 5.
PH is low , CO2 is Low
PH and PCO2 are going in same directions then its most
likely primary metabolic will check to see if there is a
mixed disoder.

9. Step 3-4: Is there appropriate
compensation? Is it chronic or acute?
Respiratory Acidosis
Acute: for every 10 increase in pCO2 -> HCO3 increases by 1and
there is a decrease of 0.08 in pH MEMORIZE
Chronic: for every 10 increase in pCO2 -> HCO3 increases by 4
and there is a decrease of 0.03 in pH
Respiratory Alkalosis
Acute: for every 10 decrease in pCO2 -> HCO3 decreases by 2 and
there is a increase of 0.08 in PH MEMORIZE
Chronic: for every 10 decrease in pCO2 -> HCO3 decreases by 5
and there is a increase of 0.03 in PH

10. Step 3-4: Is there appropriate
compensation? Is it acute or chronic ?
Metabolic Acidosis
Winter’s formula: pCO2 = 1.5[HCO3] + 8 ±2 MEMORIZE
If serum pCO2 > expected pCO2 -> additional respiratory
acidosis
Metabolic Alkalosis
For every 10 increase in HCO3 -> pCO2 increases by 6

11. EXAMPLE
ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl 97/ HCO3 7/BUN 119/ Cr 5.
Winter’s formula : 17= 1.5 (7) +8 = 18.5
So correct compensation so there is only one
disorder Primary metabolic

12. Step 5: Calculate the anion gap
AG = Na –Cl–HCO3 (normal 12 ±2)
AG corrected = AG + 2.5[4 –albumin]
If there is an anion Gap then calculate the
Delta/delta gap (step 6). Only need to calculate
delta gap (excess anion gap) when there is an anion
gap to determine additional hidden metabolic
disorders (nongapmetabolic acidosis or metabolic
alkalosis)
If there is no anion gap then start analyzing for
non-anion acidosis

13. EXAMPLE
Calculate Anion gap
ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl97/ HCO3 7/BUN 119/ Cr 5/ Albumin
4.
AG = Na –Cl–HCO3 (normal 12 ±2)
123 –97 –7 = 19
No need to correct for albumin as it is 4

14. Step 6: Calculate the different needed
formulas
Delta gap = (actual AG –12) + HCO3
Adjusted HCO3 should be 24 (+_ 6) {18-30}
If delta gap > 30 -> additional metabolic alkalosis
If delta gap < 18 -> additional non-gap metabolic
acidosis
If delta gap 18 –30 -> no additional metabolic
disorders

15. EXAMPLE : Delta Gap
ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl97/ HCO3 7/BUN 119/ Cr 5/ Albumin
4.
Delta gap = (actual AG –12) + HCO3
(19-12) +7 = 14
Delta gap < 18 -> additional non-gap
metabolic acidosis
So Metabolic acidosis anion and non anion
gap

16. Metobolic acidosis: Anion gap acidosis

17. EXAMPLE: WHY ANION GAP?
65yo M with CKD presenting with nausea, diarrhea and
acute respiratory distress
ABG :ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl97/ HCO3 7/BUN 119/ Cr 5.1
So for our patient for anion gap portion its due to
BUN of 119 UREMIA
But would still check lactic acid

18. Nongap metabolic acidosis
Causes ofnongapmetabolic acidosis -DURHAM
Diarrhea, ileostomy,colostomy, enteric fistulas
Ureteraldiversions or pancreatic fistulas
RTA type I or IV, early renal failure
Hyperailmentation,hydrochloric acid administration
Acetazolamide, Addison’s
Miscellaneous –post-hypocapnia, toulene, sevelamer, cholestyramineingestion
For non-gap metabolic acidosis, calculate the urine anion gap
UAG= UNA+ UK–UCL
If UAG>0: renal problem
If UAG<0: nonrenalproblem (most commonly GI)

19. EXAMPLE : NON ANION GAP ACIDOSIS
65yo M with CKD presenting with nausea, diarrhea and
acute respiratory distress
ABG :ABG 7.23/17/235 on 50% VM
BMP Na 123/ Cl97/ HCO3 7/BUN 119/ Cr 5.1
Most likely due to the diarrhea

20. Metabolic alkalosis
Calculate the urinary chloride to differentiate saline
responsive vssaline resistant
Must be off diuretics in order to interpret urine chloride
Saline responsive UCL<10 Saline-resistant UCL >10
Vomiting If hypertensive:Cushings, Conn’s, RAS,
renal failure with alkali administartion
NG suction If not hypertensive: severe hypokalemia,
hypomagnesemia,Bartter’s, Gittelman’s,
licorice ingestion
Over-diuresis Exogenous corticosteroidadministration
Post-hypercapnia

21. Respiratory Alkalosis
Causes of Respiratory Alkalosis
Anxiety, pain, fever
Hypoxia, CHF
Lung disease with or without hypoxia –pulmonary embolus, reactive
airway, pneumonia
CNS diseases
Drug use –salicylates, catecholamines, progesterone
Pregnancy
Sepsis, hypotension
Hepatic encephalopathy, liver failure
Mechanical ventilation
Hypothyroidism
High altitude

22. Respiratory Acidosis
Causes of respiratory acidosis
CNS depression –sedatives, narcotics, CVA
Neuromusculardisorders –acute or chronic
Acute airway obstruction –foreign body, tumor, reactive airway
Severe pneumonia,pulmonary edema, pleural effusion
Chest cavity problems –hemothorax, pneumothorax,flail chest
Chronic lung disease –obstructive or restrictive
Centralhypoventilation, OSA

23. Steps for ABG analysis
1.What is the pH? Acidemic or Alkalemic?
2.What is the primary disorder present?
3.Is there appropriate compensation?
4.Is the compensation acute or chronic?
5.Is there an anion gap?
6.If there is a AG, what is the delta gap?
7.What is the differential for the clinical processes?