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 –Overall H+ from both respiratory and metabolic factors pCO2- partial pressure of carbon dioxide in the blood –Normal range mmHg –Snapshot of adequacy of alveolar ventilation HCO3- the amount of bicarbonate in the blood –Normal range mEq/L

5 Acid – Base Balance Bicarbonate – carbonic acid buffer equation (H + )(HCO 3 ) (H 2 CO 3 ) (CO 2 )(H 2 O) It’s not that complicated! pH Acidic Neutral Alkaline

6 Acid – Base Balance Lungs Respiratory CO 2 (acid) Kidneys Metabolic HCO 3 ( base/alkaline)

7 Making sense of it… pH 7.35 – 7.45 Respiratory Metabolic CO 2 =Acidosis HCO 3 =Acidosis CO 2 =Alkalosis HCO 3 =Alkalosis

8 Interpretation: 4 steps Normal Values –pH7.35 – 7.45 –pCO 2 35 – 45 mmHg –HCO mEq/L Evaluate each component as Acid or Base

9 Step 1… Evaluate pH and determine acidosis or alkalosis Acid Normal Base Acidosis Alkalosis

10 Step 2… Evaluate pCO 2 (respiratory) Base Normal Acid

11 Step 3… Evaluate HCO 3 (metabolic) 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 pCO 2 match = respiratory –If pH and HCO 3 match = metabolic

13 pHpCO 2 HCO 3 Resp. AcidosisA (<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… pHpCO 2 HCO Respiratory Acidosis Metabolic Alkalosis Normal Respiratory Alkalosis Metabolic Acidosis AAN BNB NNN BBN ANA AAA 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 7.30A –pCO 2 60A –HCO 3 25N Uncompensated 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 7.34A –pCO 2 59A –HCO 3 28B Partially Compensated Respiratory Acidosis

18 Understanding Compensation Fully Compensated – the alternate system has adjusted enough to restore balance and normalize the pH Example –pH 7.36N (but slightly A) –pCO 2 58A –HCO 3 31B Compensated Respiratory Acidosis

19 Let’s Practice Compensation… pHpCO 2 HCO Metabolic Alkalosis partially compensated Respiratory Acidosis uncompensated Metabolic Acidosis fully compensated Respiratory Alkalosis partially compensated Respiratory Acidosis fully compensated BAB AAN NBA NAB BBA AAB Respiratory 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 CO 2 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 CO 2 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 HCO 3 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 HCO 3 while treating underlying cause –Monitor intake and output –Monitor electrolytes, especially K+ –Seizure precautions

30 Metabolic Alkalosis HCO 3 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