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Blood Gas Interpretation Review for Pandemic

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Blood Gas Interpretation Review for Pandemic

2

Blood Gases

• Important diagnostic tool• Reveals:

1. acid-base balance

2. oxygenation status**arterial gases only**

3. abnormalities of ventilation

3

Acid- base balance

• The body is designed for optimum performance at a specific pH level

• Cell division• Metabolism

4

Components of Acid- Base Balance• pH- measures the bloods acidity

– Normal range 7.35- 7.45– Overall H+ from both respiratory and metabolic factors

• pCO2- partial pressure of carbon dioxide in the blood– Normal range 35-45 mmHg– Snapshot of adequacy of alveolar ventilation

• HCO3- the amount of bicarbonate in the blood– Normal range 22- 26 mEq/L

5

Acid – Base Balance

Bicarbonate – carbonic acid buffer equation

(H+)(HCO3) (H2CO3) (CO2)(H2O)

It’s not that complicated!pH 1 7 14

Acidic Neutral Alkaline

6

Acid – Base Balance

• Lungs• Respiratory• CO2 (acid)

• Kidneys• Metabolic• HCO3 ( base/alkaline)

7

Making sense of it…

pH

7.35 – 7.45

Respiratory Metabolic

CO2=Acidosis HCO3=Acidosis

CO2=Alkalosis HCO3=Alkalosis

8

Interpretation: 4 steps

• Normal Values– pH 7.35 – 7.45– pCO2 35 – 45 mmHg– HCO3 22 - 26 mEq/L

• Evaluate each component as Acid or Base

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Step 1…

• Evaluate pH and determine acidosis or alkalosis

7.35 7.40 7.45

Acid Normal Base

Acidosis Alkalosis

10

Step 2…

• Evaluate pCO2 (respiratory)

35 40 45

Base Normal Acid

11

Step 3…

• Evaluate HCO3 (metabolic)

22 24 26

Acid Normal Base

12

Step 4…

• Determine which regulatory system is responsible for the imbalance by checking to see which component matches the pH.– If pH and pCO2 match = respiratory

– If pH and HCO3 match = metabolic

13

pH pCO2 HCO3

Resp. Acidosis A

(<7.35)

A

(>45)

N

(22-26)

Resp.

Alkalosis

B

(>7.45)

B

(<35)

N

(22-26)

Metabolic Acidosis

A

(<7.35)

N

(35-45)

A

(<22)

Metabolic

Alkalosis

B

(>7.45)

N

(35-45)

B

(>26)

ABG Analysis

14

Let’s practice…

pH pCO2 HCO3

7.26 55 23

7.54 43 39

7.39 41 25

7.51 29 24

7.29 40 17

7.28 61 18

Respiratory Acidosis

Metabolic Alkalosis

Normal

Respiratory Alkalosis

Metabolic Acidosis

A A N

B N B

N N N

B B N

A N A

A A A Mixed Acidosis

15

Compensation

• When an acid – base imbalance exists, over time the body attempts to compensate.

16

Understanding Compensation

• Uncompensated – the alternate system has not attempted to adjust (remains within normal range), and the pH remains abnormal

• Example

– pH 7.30 A – pCO2 60 A– HCO3 25 NUncompensated Respiratory Acidosis

17

Understanding Compensation

• Partial Compensation – the alternate system is trying to create a balanced environment and bring the pH back within normal limits, but hasn’t yet succeeded.

• Example– pH 7.34 A – pCO2 59 A– HCO3 28 B

Partially Compensated Respiratory Acidosis

18

Understanding Compensation

• Fully Compensated – the alternate system has adjusted enough to restore balance and normalize the pH

• Example

– pH 7.36 N (but slightly A)– pCO2 58 A– HCO3 31 B

Compensated Respiratory Acidosis

19

Let’s Practice Compensation…

pH pCO2 HCO3

7.51 49 40

7.29 53 22

7.37 25 18

7.35 65 28

7.46 22 20

7.34 52 27

Metabolic Alkalosis partially compensated

Respiratory Acidosis uncompensated

Metabolic Acidosis fully compensated

Respiratory Alkalosis partially compensated

Respiratory Acidosis fully compensated

B A B

A A N

N B A

N A B

B B A

A A BRespiratory Acidosis partially compensated

20

A Final Step…

• Determine level of oxygenation

(arterial samples only)• Normal = 80 – 100 mmHg• Mild hypoxemia = 60 – 80 mmHg• Moderate hypoxemia = 40 – 60 mmHg• Severe hypoxemia = less than 40 mmHg

21

Respiratory Acidosis

• Excessive CO2 retention• Causes

– Airway obstruction– Depression of respiratory drive

• Sedatives, analgesics• Head trauma

– Respiratory muscle weakness resulting from muscle disease or chest wall abnormalities

– Decreased lung surface area participating in gas exchange

22

Respiratory Acidosis

• Clues– Confusion, restlessness– Headache, dizziness– Lethargy– Dyspnea– Tachycardia– Dysrhythmias– Coma leading to death

23

Respiratory Acidosis

• Solutions– Improve ventilation

• Ensure adequate airway; positioning, suctioning

• Encourage deep breathing and coughing• Frequent repositioning• Chest physio/ postural drainage• Bronchodilators• Decrease sedation/analgesia• Oxygen therapy

24

Respiratory Alkalosis

• Excessive CO2 loss due to hyperventilation• Causes

– CNS injury: brainstem lesions, salicylate overdose, Reye’s Syndrome, hepatic encephalopathy

– Aggressive mechanical ventilation– Anxiety, fear or pain– Hypoxia – Fever– Congestive heart failure

25

Respiratory Alkalosis

• Clues– Light headedness– Confusion– Decreased concentration– Tingling fingers and toes– Syncope– Tetany

26

Respiratory Alkalosis

• Solutions– Decrease respiratory rate and depth

• Sedation/analgesia as appropriate• Rebreather mask• Paper bag• Emotional support/encourage patient to slow

breathing• Calm, soothing environment

27

Metabolic Acidosis

• Excessive HCO3 loss, or acid gain• Causes

– Diabetic ketoacidosis– Sepsis/shock– Diarrhea (fluid losses below gastric sphincter)– Renal Failure– Poison ingestion– Starvation– Dehydration

28

Metabolic Acidosis

• Clues– Stupor– Restlessness– Kussmaul’s respirations (air hunger)– Seizures– Coma leading to death

29

Metabolic Acidosis

• Solutions– Replace HCO3 while treating underlying cause– Monitor intake and output– Monitor electrolytes, especially K+– Seizure precautions

30

Metabolic Alkalosis

• HCO3 retention, or loss of extracellular acid, • Causes

– GI losses above gastric sphincter• Vomiting• Nasogastric suction

– Antacids– Diuretic therapy causing electrolyte loss

31

Metabolic Alkalosis

• Clues– Weakness, dizziness– Disorientation– Hypoventilation– Muscle twitching– Tetany

32

Metabolic Alkalosis

• Solutions– Control vomiting– Replace GI losses– Eliminate overuse of antacids– Monitor intake and output– Monitor electrolytes