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Blood Gas Interpretation Review for Pandemic. Blood Gases. Important diagnostic tool Reveals: 1. acid-base balance 2. oxygenation status **arterial gases only** 3. abnormalities of ventilation. Acid- base balance. The body is designed for optimum performance at a specific pH level - PowerPoint PPT Presentation
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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
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Step 3…
• Evaluate HCO3 (metabolic)
22 24 26
Acid Normal Base
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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