ABG interpretation Flashcards
1
Q
What is a simple acid base disorder?
A
When there is only one primary disorder
2
Q
What are examples of simple acid base disorder?
A
Respiratory or metabolic disorders
3
Q
What should be assessed with simple acid base disorders?
A
acuteness
4
Q
What is mixed acid base disorder?
A
When there are two or more primary disorders present at the same time
5
Q
What should be assessed with mixed base disorder?
A
- Compensation
- Appropriate compensation
6
Q
Define acidemia.
A
Lower than normal arterial blood pH
7
Q
Define alkalemia.
A
Higher than normal arterial blood pH
8
Q
Define acidosis.
A
- A process that tends to acidify body fluids and may lead to acidemia.
- Could result from metabolic or respiratory dysfunction or compensatory response
9
Q
Define alkalosis.
A
- A process that tends to alkalinize body fluids and may lead to alkalemia.
- Could result from metabolic or respiratory dysfunction or compensatory response
10
Q
What acidosis and alkalosis may or may not be associated with?
A
with abnormal pH in the same direction…
11
Q
Define metabolic acidosis.
A
HCO3 <24 or Anion Gap >12
12
Q
Define metabolic alkalosis.
A
HCO3 >24
13
Q
Define respiratory alkalosis.
A
PCO2 <40 or PCO2 less than expected for primary metabolic abnormali
14
Q
Define respiratory acidosis.
A
PCO2 >40 or PCO2 higher than expected for primary metabolic abnormality
15
Q
Define high anion gap.
A
> 12-20 always indicates primary metabolic acidosis
16
Q
Anion gap greater than 12 __________ indicates primary metabolic acidosis
A
always
17
Q
We do not compensate for abnormality of one system with compensation by the _______
A
same system
18
Q
Compensatory response never brings the pH back to _________
A
Normal
19
Q
Compensation: How does arterial pH normalize?
A
Tends to return ratio of HCO3 to PCO2 back toward normal and therefore normalize the arterial pH
20
Q
Compensation: Is pH returned to normal?
A
Does not return pH to normal except in primary respiratory alkalosis of chronic duration
21
Q
Compensation: What is required for compensation to work?
A
Requires normal function of kidneys and lungs
22
Q
What does lack of appropriate compensation suggest?
A
second primary disorder
23
Q
What does compensatory response create?
A
second lab abnormality
24
Q
Appropriate degree of compensation can be ________
A
predicted
25
How much of volatile acids are produced daily?
12,000 to 15,000 mEq of volatile acids are produced daily by the body and excreted as CO2 by lungs
26
How much non volatile acids are produced daily?
1 mEq/kg/day of non-volatile acids (sulfuric and phosphoric acids) are produced daily by the body and excreted by the kidneys
27
What determines the pH of fluid?
determined by the amount of acid produced, the buffering capacity and the acid excretion by the lungs and kidneys
28
What are the most important buffers in the body? (3)
hemoglobin, plasma proteins and bicarbonate
29
What is the acute compensation for respiratory acidosis?
10mmHg increase in PCO2 leads to 1mEq/L increase in HCO3
30
What is the chronic compensation for respiratory acidosis?
10mmHg increase in PCO2 lead to 3-3.5mEq/L increase in HCO3
31
What is the acute compensation for respiratory alkalosis?
10mmHg decrease in PCO2 leads to 2mEq/L decrease in HCO3
32
What is the chronic compensation for respiratory alkalosis?
10mmHg decrease in PCO2 leads to 4-5mEq/L decrease in HCO3
33
What is the compensation for metabolic acidosis?
PCO2 = Last 2 digits of pH
34
What is the compensation for metabolic alkalosis?
1 mEq/L increase in HCO3 leads to 0.6-0.7mmHg increase in PCO2
35
What is the acid base equation for changes in pH in acute respiratory acidosis and acute respiratory alkalosis?
= [0.08 x (PaCO2 - 40)] ÷ 10
36
What is the acid base equation for Change in pH in chronic respiratory acidosis and chronic respiratory alkalosis?
= [0.03 x (PaCO2 - 40)] ÷ 10
37
What is the acid base equation for expected PCO2 in primary metabolic acidosis?
= [HCO3 x 1.5] + 8 +/-2
38
Define anion.
a negatively charged ion
39
What is a normal albumin range?
3.4 to 5.4 g/dL
40
What is the anion gap formula?
AG = (Na+) – (Cl- + HCO3-) = 12 +/- 2
41
What does the anion gap measure?
Estimates unmeasured anions
42
What is the normal anion gap?
8-12
43
When may the anion gap be underestimated?
Hypoalbuminemia, Albumin is a negatively charged protein and its loss from serum results in retention of other negatively charged ions, e.g. chloride and bicarbonate
44
What is the corrected anion gap formula?
AG + 2.5 x (normal albumin g/dL – albumin g/dL)
45
When is urinary anion gap used?
Useful in differential diagnosis of non-gap acidosis
46
What is the urinary anion gap formula?
Na+ + K+ - Cl-
47
What is a negative anion gap?
Cl- >> Na+ + K+
| -suggests appropriate urinary ammonia excretion and GI loss of HCO3
48
What is a positive anion gap?
Cl- << Na+ + K+
| -suggests renal tubular acidosis with distal acidification defect and inadequate ammonia excretion in urine
49
What is causes of metabolic acidosis? (3)
- Caused by excess acid production which overwhelms renal capacity to excrete acids (e.g. DKA, shock)
- Loss of alkali (e.g. bicarbonate loss in diarrhea)
- Renal failure
50
What is the action of tissues and RBCs in metabolic acidosis?
act to increase the serum bicarbonate by exchanging intracellular Na+ and K+ for extracellular hydrogen ions, resulting in increased serum K+ and bicarbonate
51
How does increased pulmonary ventilation attempt to compensate for metabolic acidosis?
Increased pulmonary ventilation leads to decreased PaCO2 and change in pH toward normal
52
What does an HCO3 <10 or Anion Gap >12 always suggest?
primary metabolic acidosis
53
What are the characteristics of acidosis (low pH)? (3)
- Lowering extracellular pH by rising concentration of hydrogen ions
- Fall in bicarbonate concentration
- Elevation in PCO2
54
What cardiac response occur with acidosis (low pH)?
- Decreases force of cardiac contractions
| - Decreases vascular response to catecholamines
55
What effect does acidosis (low pH) have on medications?
Decreases response of certain medications
56
What are causes of anion gap associated with metabolic acidosis? (8)
```
Aspirin (Salicylate)
Methanol
Uremia
DKA
Paraldehyde
INH
Lactic acidosis
Ethylene glycol
```
57
What are causes of non anion gap associated with metabolic acidosis? (6)
```
Hyperalimentation
Acetazolamide
Renal tubular acidosis
Diarrhea
Ureterosigmoidostomy
Pancreatic fistula
```
58
What are characteristics of alkalosis (high pH)?
- Elevation of the pH of the extracellular fluid
- Lowering hydrogen ion concentration
- Elevation in plasma bicarbonate
- Reduction in PCO2
59
What does alkalosis (high pH) impair?
- Impairs oxygenation
- Impairs muscular function
- Impairs neurologic function
60
What are causes of metabolic alkalosis? (3)
- Gain of bicarbonate by abnormal renal absorption
- Volume contraction (low urine chloride)
- Mineralocorticoid excess (high urine chloride)
61
What are some causes of volume contraction associated with metabolic alkalosis?
- Vomiting: Loss of H+
- Diuretics: Depletion of -Severe hypokalemia
- Renal failure
62
What are causes of urinary chloride <20 meg/L associated with metabolic alkalosis? (7)
- Vomiting/NGT suction
- Chloride wasting diarrhea
- Colonic villous adenoma
- Diuretic therapy
- Post hypercapnia
- Poorly reabsorbed anions
- Glucose refeeding
63
What are causes of urinary chloride >20 meg/L associated with metabolic alkalosis? (7)
- Primary hyperaldosteronism (Conn’s Syndrome)
- Cushing’s syndrome
- Exogenous steroids/Licorice
- Adrenal 11 or 17 hydroxylase defects
- Liddle/Bartter syndromes
- K and Mg deficiency
- Milk alkali syndrome
64
What is adrenal hyperplasia?
Adrenal 11 or 17 hydroxylase defects
65
What is liddle's syndrome?
Genetic disorder inherited in an autosomal dominant manner that is characterized by early, and frequently severe, high blood pressure associated with low plasma renin activity, metabolic alkalosis, low blood potassium, and normal to low levels of aldosterone
66
What is bartter syndrome?
Rare inherited defect in the thick ascending limb of the loop of Henle characterized by hypokalemia, alkalosis, and normal to low blood pressure.
67
What are the types of respiratory acidosis?
Acute or chronic elevation in PCO2
68
What is the characteristics of acute respiratory acidosis?
- Hydrogen ions buffered by organic tissue buffers
| - A 10mmHg increase in PCO2 leads to a decrease in pH of 0.08
69
What is the characteristics of chronic respiratory acidosis?
- Renal production and reabsorption of bicarbonate
- Chloride decreases to balance charges
- A 10mmHg increase in PCO2 leads to an decrease of pH of 0.03
70
What are the criteria for respiratory acidosis?
- Elevation of PCO2 above normal causing drop in pH
- Caused by a ventilation abnormality
- Lower CO2 elimination than production
71
What are causes of respiratory acidosis? (5)
- CNS depression
- Pleural disease
- COPD and ARDS
- Musculoskeletal disorders
- Compensatory for metabolic alkalosis
72
What does low PCO2 trigger?
bicarbonate loss
73
What electrolyte abnormality is associated with alkalosis?
Mild hypokalemia
74
What does chloride retention with respiratory acidosis promote?
Chloride retention to offset loss of bicarbonate negative charge
75
Respiratory alkalosis: What is acute response associated with?
Acute response independent of renal bicarbonate wasting
76
Respiratory alkalosis: What is chronic response associated with?
Chronic compensation driven by renal bicarbonate wasting
77
What are causes of respiratory alkalosis? (6)
- Intracerebral hemorrhage
- Drugs
- Decreased lung compliance
- Anxiety
- Cirrhosis of the liver
- Sepsis
78
What are some drugs associated with respiratory alkalosis?
- Salicylates
| - Progesterone
79
Interpretation tips: What do you need to intrepret an ABD with? (Tip 1)
Do not interpret ABG for acid base diagnosis without examining electrolytes
80
Interpretation tips: What does CO2 out side of normal range represent?
CO2 out of the normal range represents an acid base disorder
81
Interpretation tips: What does a high CO2 indicate?
metabolic acidosis and/or bicarbonate retention as compensation for respiratory acidosis
82
Interpretation tips: What does a low CO2 indicate?
metabolic alkalosis and/or bicarbonate excretion as compensation for respiratory alkalosis
83
Interpretation tips: What does a normal CO2 indicate?
double or triple acid base abnormalities
84
Interpretation tips: What is the pH in single acid base disorders? (Tip 2)
Single acid base disorders do not lead to normal blood pH
85
Interpretation tips: What does a truly normal pH suggest?
double or triple base abnormalities
86
What do simplified rules help predict? (Tip 3)
pH and bicarbonate
| for a given change in PCO2
87
Expected change in pH and HCO3 for every ______ change in PCO2
10 mmHg
88
What is the expected change in pH and HCO3- with acute respiratory acidosis?
pH decrease by 0.07=HCO3- increase by 1
89
What is the expected change in pH and HCO3- with acute respiratory alkalosis?
pH increase by 0.08=HCO3- decrease by 2
90
What is the expected change in pH and HCO3- with chronic respiratory acidosis?
pH decrease by 0.03=HCO3- increase by 3-4
91
What is the expected change in pH and HCO3- with chronic respiratory alkalosis?
pH increase by 0.03=HCO3- decrease by 5
92
What is true about the PCO2 and pH with maximally compensated metabolic acidosis? (Tip 4)
In maximally compensated metabolic acidosis the PCO2 should be the same as the last two digits of the arterial pH
93
What formula that represents the change in pH and PCO2 in maximally compensated metabolic acidosis?
Winter’s formula
-Expected PaCO2 = [1.5 x serum CO2] + (8 +/-2)
94
What is the first step in the ABG interpretation?
- Is there acidemia or alkalemia?
| - Is the abnormality respiratory or metabolic?
95
What is the second step in the ABG interpretation?
Is there appropriate compensation for the primary disturbance?
96
What is the third step in the ABG interpretation?
Anion gap if metabolic acidosis exists, follow by osmolal gap
97
What is the fourth step in the ABG interpretation?
Delta anion gap
98
What is the delta anion gap?
A calculation that compares the increase in the anion gap to the decrease in HCO3
99
Step 1: What is the pH?
- Acidemia <7.40
| - Alkalemia >7.40
100
Step 2: How do u calculate the anion gap.
Anion Gap = Na – (Cl + HCO3)
101
What does AGMA mean?
Anion gap metabolic acidosis
102
What does NAGMA mean?
Non-anion gap metabolic acidosis
103
Step 3: What is the expected PCO2?
1.5(HCO3) + 8 (+/-2)
104
Step 4: What is the delta gap formula?
Delta HCO3 = HCO3 + Change in anion gap
105
What is the delta gap for a Non-anion gap metabolic acidosis?
<24
106
What is the delta gap for an anion gap metabolic alkalosis?
>24
107
Practice 1: 33 year old diabetic male with polydipsia, tachypnea, nausea and vomiting, markedly dehydrated with a fruity smell on his breath
Laboratory studies:
Na = 128; K = 4.5; Cl = 90; CO2 = 4; BUN = 43; Creat = 2; Gluc = 800
ABG = 7.0/14/90/4/95%
What is the acid base disturbance and what is the cause?
- How is the pH? Acidemia (pH <7.40)
- Is there an anion gap? 128 – (90+4) = 34 (12 +/-2)
- Is there respiratory compensation? Expected PCO2 1.5(4)+8=14
- What is the delta gap? 4+(34-12)=26
Interpretation:
- Anion gap metabolic acidosis
- Appropriate respiratory compensation
- Diabetic ketoacidosis
108
Practice 2: 56 year old female with history of COPD presents with dyspnea, cough, wheezing and she is now hypotensive and has had diarrhea for the past 7 days
```
Na = 139; K = 4.0; Cl = 110; CO2 = 10; BUN = 20; Creat = 1.5; Gluc = 120
ABG = 7.22/30/65/10/90%
```
What is the acid base disturbance and what is the cause?
- How is the pH? Acidemia (pH <7.40)
- Is there an anion gap? 139 – (110+10) = 19
- Is there respiratory compensation? Expected PCO2 1.5(10)+8=23 -- No
- What is the delta gap? 10+(19-12)=17
Interpretation: Triple disorder
- Anion gap metabolic acidosis (Hypotension causing lactic acidosis)
- Respiratory acidosis (COPD exacerbation)
- Non gap metabolic acidosis (Diarrhea with bicarbonate loss)
109
Practice 3: An acutely ill 50 year old woman with a history of vomiting for four days is brought to the ED. Exam shows profound lethargy.
Pulse 120bpm; RR 12bpm; BP 80/50mmHg
Na = 140; K = 3.3; Cl = 85
ABG = pH = 7.4; PCO2 = 43; HCO3 = 25
Most likely acid base disorder is:
A.) Metabolic acidosis
B.) Metabolic alkalosis
C.) Respiratory acidosis and metabolic alkalosis
D.) Respiratory alkalosis
E.) Metabolic acidosis and metabolic alkalosis
E.) Metabolic acidosis and metabolic alkalosis
-pH = neutral. Acidosis and alkalosis
-Anion gap. (140-(85+25)=30)
-Respiratory compensation
(Expected PCO2: (1.5 x 25)+8=45.5)
-Delta gap
(Change in bicarbonate 25+(30-12)=43)
