Blood Gas Interpretation Review for Pandemic

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 2

Acid- base balance The body is designed for optimum performance at a specific pH level Cell division Metabolism 3

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 4

Acid – Base Balance Bicarbonate – carbonic acid buffer equation (H )(HCO3) (H2CO3) (CO2)(H2O) It’s not that complicated! pH 1 Acidic 7 Neutral 14 Alkaline 5

Acid – Base Balance Lungs Respiratory CO2 (acid) Kidneys Metabolic HCO3 ( base/alkaline) 6

Making sense of it pH 7.35 – 7.45 Respiratory Metabolic CO2 Acidosis HCO3 Acidosis CO2 Alkalosis HCO3 Alkalosis 7

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 8

Step 1 Evaluate pH and determine acidosis or alkalosis 7.35 7.40 7.45 Acid Acidosis Normal Base Alkalosis 9

Step 2 Evaluate pCO2 (respiratory) 35 Base 40 Normal 45 Acid 10

Step 3 Evaluate HCO3 (metabolic) 22 24 Acid Normal 26 Base 11

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 12

ABG Analysis 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) 13

Let’s practice pH pCO2 A A 7.26 B 55 N HCO3 N 23 B 7.54 43 39 7.39 41 25 7.51 29 24 N B A N B N N N A 7.29 40 17 7.28 61 18 A A A Respiratory Acidosis Metabolic Alkalosis Normal Respiratory Alkalosis Metabolic Acidosis Mixed Acidosis 14

Compensation When an acid – base imbalance exists, over time the body attempts to compensate. 15

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 N Uncompensated Respiratory Acidosis 16

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 17

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 18

Let’s Practice Compensation pH pCO2 HCO3 B A B 7.51 49 40 A A 7.29 53 N 25 7.35 65 B 7.46 A 7.34 22 B 7.37 N N B 22 A 52 A A 18 28 A 20 B B Metabolic Alkalosis partially compensated Respiratory Acidosis uncompensated Metabolic Acidosis fully compensated Respiratory Acidosis fully compensated Respiratory Alkalosis partially compensated Respiratory Acidosis partially compensated 27 19

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 20

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 21

Respiratory Acidosis Clues – Confusion, restlessness – Headache, dizziness – Lethargy – Dyspnea – Tachycardia – Dysrhythmias – Coma leading to death 22

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 23

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 24

Respiratory Alkalosis Clues – Light headedness – Confusion – Decreased concentration – Tingling fingers and toes – Syncope – Tetany 25

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 26

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 27

Metabolic Acidosis Clues – Stupor – Restlessness – Kussmaul’s respirations (air hunger) – Seizures – Coma leading to death 28

Metabolic Acidosis Solutions – Replace HCO3 while treating underlying cause – Monitor intake and output – Monitor electrolytes, especially K – Seizure precautions 29

Metabolic Alkalosis HCO3 retention, or loss of extracellular acid, Causes – GI losses above gastric sphincter Vomiting Nasogastric suction – Antacids – Diuretic therapy causing electrolyte loss 30

Metabolic Alkalosis Clues – Weakness, dizziness – Disorientation – Hypoventilation – Muscle twitching – Tetany 31

Metabolic Alkalosis Solutions – Control vomiting – Replace GI losses – Eliminate overuse of antacids – Monitor intake and output – Monitor electrolytes 32