Acid Base Part Balance Intensive care unit

Acid base balance

1. ACID-BASE
DISORDERS

2. REVIEW
WHAT ARE THE FOUR PRIMARY TYPES OF ACID BASE DISORDERS
RESPIRATORY ACIDOSIS
RESPIRATORY ALKALOSIS
METABOLIC ACIDOSIS
METABOLIC ALKALOSIS

3. REVIEW
WHAT ARE THE TWO COMPUNDS MOST COMMONLY MANIPULATED
TO COMPENSATE FOR AN ACID -BASE DISORDER?
CO
2
BICARB (HCO
3
-
)

4. REVIEW
DISORDER PRIMARY CHANGE COMPENSATORY
RESPONSE
Respiratory Acidosis
Respiratory Alkalosis
Increased PaCO
2
Decreased PaCO
2
Increased HCO
3
-
Decrease HCO
3
-
Metabolic Acidosis
Metabolic Alkalosis
Decreased HCO
3
-
Increased HCO
3
-
Decreased PaCO
2
Increased PaCO
2

5. REVIEW
WHY DO WE CARE SO MUCH ABOUT ACID -BASE DISTURBANCES?
(hint-why is pH so important?)
Biological processes require a very narrow pH to function correctly

6. RESPIRATORY ACIDOSIS
WHAT IS THE PRIMARY PROBLEM?
Increased PaCO
2(typically >45mmHg)
Increased CO
2is caused by decreased alveolar ventilation or
increased CO
2production:

7. CAUSES OF RESPIRATORY ACIDOSIS
ALVEOLAR
HYPOVENTILATION
CNS Depression
Neuromuscular Disorders
Pleural Effusion or Pneumothorax
Airway Obstruction
Asthma, foreign body,
laryngospasm, COPD, Tumor, OSA
Pneumonia
Aspiration
Pulmonary Edema
Ventilator Malfunction
INCREASED CO
2
PRODUCTION
Shivering
Malignant Hyperthermia
Prolonged Seizure
Thyroid storm
Extensive burns

8. Respiratory Acidosis Compensation
Compensation varies depending on whether it is ACUTE versus CHRONIC
Resp. Acidosis
ACUTE: Limited compensation available
Hgb can act as a buffer
Exchange of potassium and H
+
ions
Minimal increased renal retention of Bicarb
CHRONIC
Significant renal compensation with Bicarb retention in about 24h, with peak effect in 3-
5 days
***Special consideration for the anesthetist: patients with chronically elevated CO
2
should be ventilated to their “Normal” pCO
2

9. Respiratory Acidosis Compensation

10. METABOLIC ACIDOSIS
WHAT IS THE PRIMARY PROCESS CAUSING METABOLIC ACIDOSIS?
Decreased Bicarb (HCO
3
-
) –usually <21mEq/L
Occurs via 3 primary processes
Consumption of bicarb
Excess Wasting
Rapid dilution of plasma via non-barb containing fluid (Like Normal Saline)

11. CALCULATE THE ANION GAP FIRST!
Anion Gap= Major cations –major anions= 12mEq/L (range 7-14)
Equation:
Electrical Neutrality must exist!
Erroneously low AG can occur in the setting of low albumin (as in
chronic liver disease).
For every 1g/dL decrease in albumin AG decreases by 2.5mEq/L

12. Causes of Metabolic Acidosis
Increased Anion Gap
Increased Production of Acid
Ketoacidosis, renal failure (GFR
<20mL/min), lactic acidosis
(hypoxemia, hypoperfusion or
cyanide poisoning)
Toxins
Salicylate, methanol, ethylene
glycol, etc
Rhabdomyolosis
Normal Anion Gap
GI loss of bicarb:
Diarrhea, biliary/bowel/pancreatic
fistulas, etc
Renal loss of bicarb
Renal tubular acidosis (defect in
secretion of H+), carbonic
anhydrase inhibitor,
hypoaldosteronism
Dilutional
**large volume NaCl administration
TPN

13. Trick to remember High AG
Metabolic Acidosis

14. Metabolic Acidosis Compensation
Winter’s Formula:

15. Anesthesia and Acidosis
Increase the availability of opioids
Increased depressant effects of most sedatives
Increased risk of aspiration if airway reflexes are not intact
Difficult to control hypotension
Increased risk of arrhythmia with Halothane if acidemia is present
Acidosis is often accompanied by hyperkalemia AVOID
succinylcholine

16. RESPIRATORY
ALKALOSIS
PRIMARY PROCESS THAT CAUSES RESPIRATORY
ALKALOSIS:
Decreased pCO
2–typically via increased
hyperventilation
Causes
Pain, anxiety, ischemia, stroke, infection, fever,
progesterone (pregnancy), asthma, anemia,
ventilator induced

17. RESPIRATORY ALKALOSIS
COMPENSATION

18. METABOLIC ALKALOSIS
Primary process is an increase in plasma bicarb
Chloride Sensitive
GI
Vomiting, NGT
Renal
**Diuretics (furosemide, thiazides,
etc)
Post hypercapnic
Cystic Fibrosis
Chloride Resistant
Severe Hypokalemia
Licorice Ingestion
Hyperaldosteronism
Other
Massive Transfusion

19. Anesthesia and Alkalosis
Prolonged opioid induced respiratory depression
Severe respiratory alkalosis can lead to decreased cerebral blood
flow
Alkalemia often is accompanied by hypokalemia increased risk
of arrhythmias
Possible potentiation of nondepolarizing NMBs

21. Strategies to Diagnose Acid Base
Disturbances

22. Another strategy:

23. References
1.Barash. Clinical Anesthesia: https://ovidsp-dc2-ovid-
com.proxy.library.vanderbilt.edu/sp-4.02.1a/ovidweb.cgi
2.Morgan and Mikhail. Clinical Anesthesiology. https://accessmedicine-mhmedical-
com.proxy.library.vanderbilt.edu/content.aspx?bookid=564&sectionid=42800584#57
239135
3.http://www.ucdenver.edu/academics/colleges/medicalschool/departments/medi
cine/intmed/imrp/CURRICULUM/Documents/Evaluation%20of%20Acid%20Base%20D
isorders.pdf