Acid-Base Disorders Robert Fields, DO St Joseph’s Mercy Hospital Emergency Dept.

5 Steps is all you need Check the pH Check the pH Find the primary disorder (Look at pCO2 and HCO3) Find the primary disorder (Look at pCO2 and HCO3) Calculate the anion gap (AG=Na – (HCO3 + Cl-) Calculate the anion gap (AG=Na – (HCO3 + Cl-) Calculate the excess anion gap (AGp - AGn + HCO3p = X) Calculate the excess anion gap (AGp - AGn + HCO3p = X) Winters formula pCO2 = 1.5(HCO3-) + 8 Winters formula pCO2 = 1.5(HCO3-) + 8

What do you really need to do this? ABG, with pCO2 and pH ABG, with pCO2 and pH Chem 7 with Na+, Cl-, HCO3- Chem 7 with Na+, Cl-, HCO3-

STEP 1, Check the pH Acidemia, pH < 7.35 Acidemia, pH < 7.35 Alkalemia, pH >7.45 Alkalemia, pH >7.45 Made Simpler! Acidemia Alkalemia Made Simpler! Acidemia Alkalemia Acidosis/Alkalosis vs. Acidemia/Alkalemia Acidosis/Alkalosis vs. Acidemia/Alkalemia Know the “normals” of the rest. (This is not to hard as it is printed in the computer) Know the “normals” of the rest. (This is not to hard as it is printed in the computer)

STEP 2, Find the Basic Problem Look at the pCO2 and the HCO3- Look at the pCO2 and the HCO3- Respiratory problems relate to pCO2 Respiratory problems relate to pCO2 Metabolic problems relate to HCO3- Metabolic problems relate to HCO3-

Respiratory Acidosis Causes Causes CNS depression CNS depression NMS disorders NMS disorders Pulmonary edema Pulmonary edema Ventilatory dysfunction Ventilatory dysfunction

Respiratory Alkalosis Causes Causes Anxiety Anxiety Hypoxia Hypoxia CNS stimulants CNS stimulants Pregnancy Pregnancy Sepsis Sepsis Excessive mechanical ventilation Excessive mechanical ventilation

Metabolic Alkalosis Chloride responsive Chloride responsive Vomiting Vomiting Diuretics Diuretics Dehydration Dehydration Chloride unresponsive Chloride unresponsive Excess mineral corticoid activity Excess mineral corticoid activity Cushing's, Conn’s Cushing's, Conn’s The infamous licorice ingestion The infamous licorice ingestion

STEP 3, Check the Anion Gap

What is the Anion Gap? Cations = Anions Cations = Anions Na+ + K+ etc. = HC03- + Cl- + Alb + etc Na+ + K+ etc. = HC03- + Cl- + Alb + etc Simplified Simplified Na+ = HC03- + Cl- + others Na+ = HC03- + Cl- + others We will call the others, AG (anion gap) and solve for AG. We will call the others, AG (anion gap) and solve for AG. Therefore AG = Na+ - (HCO3- + Cl-) Therefore AG = Na+ - (HCO3- + Cl-)

Increased Anion Gap Metabolic Acidosis Methanol Methanol Uremia Uremia DKA (starvation ketosis, alcohol ketosis) DKA (starvation ketosis, alcohol ketosis) Paraldehyde Paraldehyde INH, Iron INH, Iron Lactic Acidemia (type A, B, D) Lactic Acidemia (type A, B, D) Ethanol, Ethylene Glycol Ethanol, Ethylene Glycol Salicylates Salicylates

Columbia Encyclopedia:Columbia Encyclopedia: paraldehyde (pârăl'dəhīd'), nervous system depressant similar to alcohol in its effects and used as a sedative. A colorless flammable liquid with a disagreeable odor, paraldehyde produces sleep for up to 12 hr. with little or no muscle, heart, or respiratory depression. It is often given to alcoholics having delirium tremens, to induce sleep, and is also used to calm psychiatric patients. Like alcohol and other depressants it is addictive (see drug addiction and drug abuse). Paraldehyde is also used in the manufacture of synthetic resins, as a preservative, and in preparing leather. It is produced by treating acetaldehyde with a small amount of sulfuric acid.depressant sedativedrug addiction and drug abuse

Normal Anion Gap Metabolic Acidosis Gastrointestinal GastrointestinalDiarrhea Ureteral diversion Renal Loss Renal LossRTA Early renal failure Acetozolamide Aldosterone inhibitors

+ H+ Lactic Acid Production

+ H++HCO3- + H+ + HCO3- H2CO3 CO2 + H2O +

Buffering Species CO2 + H2O H2CO3 CO2 + H2O H2CO3 carbonic anyhdrase carbonic anyhdrase H2CO3 HCO3- + H+ H2CO3 HCO3- + H+

STEP 4, Check the Anion Gap Excess This is going to help you determine if there is an alkalosis or acidosis that is NOT related to the anion gap. This is going to help you determine if there is an alkalosis or acidosis that is NOT related to the anion gap. This done by doing this equation This done by doing this equation AGp – AGn + HCO3-p = X AGp – AGn + HCO3-p = X X should equal 24 if there is no additional acidosis or alkalosis. X should equal 24 if there is no additional acidosis or alkalosis.

The results of Step 4 If you calculated < 20 mmol/L If you calculated < 20 mmol/L There is a an acidosis present that is unrelated to the AG. There is a an acidosis present that is unrelated to the AG. If you calculated >30 mmol/L there is an alkalosis present. If you calculated >30 mmol/L there is an alkalosis present.

What we are doing so far ? 1. Determine the pH 1. Determine the pH 2. Finding primary disorder 2. Finding primary disorder 3. Finding AG Metabolic Acidosis if not already recognized 3. Finding AG Metabolic Acidosis if not already recognized 4. Finding Metabolic Acidosis (unrelated to the AG) and/or metabolic Alkalosis if not yet recognized. 4. Finding Metabolic Acidosis (unrelated to the AG) and/or metabolic Alkalosis if not yet recognized.

So What’s Left? Respiratory Alkalosis or Acidosis that may have gone unrecognized. Respiratory Alkalosis or Acidosis that may have gone unrecognized. Winter’s formula Winter’s formula pCO2 = 1.5 (HCO3) pCO2 = 1.5 (HCO3)

Examples

Example 1 pH, 7.50 pH, 7.50 pCO2, 20mm Hg pCO2, 20mm Hg Na+, 140 mmol/L Na+, 140 mmol/L Cl-, 103 mmol/L Cl-, 103 mmol/L HCO3-, 15 HCO3-, 15

Results Alkalemia Alkalemia Primary disorder, respiratory Primary disorder, respiratory AG is 22, Therefore metabolic acidosis with AG. A-ha! Two disorders are present. AG is 22, Therefore metabolic acidosis with AG. A-ha! Two disorders are present. Excess AG, = 25, no alkalosis or acidosis otherwise present. Excess AG, = 25, no alkalosis or acidosis otherwise present. Don’t need to do Winter’s as you can only have one respiratory problem. Don’t need to do Winter’s as you can only have one respiratory problem. Clinical correlation? Clinical correlation?

Salicylate Toxicity

Example 2 pH, 7.40 pH, 7.40 pCO2, 40mm Hg pCO2, 40mm Hg Na+, 145 mmol/L Na+, 145 mmol/L Cl-, 100 mmol/L Cl-, 100 mmol/L HCO3-, 24 HCO3-, 24

Results pH? Normal pH? Normal Primary, What Primary? Primary, What Primary? Anion Gap = 21 Anion Gap = 21 Excess anion gap = =33, A significant metabolic alkalosis is present too! Excess anion gap = =33, A significant metabolic alkalosis is present too! Winter’s ? Nothing too bad here. Winter’s ? Nothing too bad here. Clinical Correlation? Clinical Correlation?

CRI (AG acidosis) with vomiting as uremia worsened

Example 3 pH, 7.50 pH, 7.50 pCO2, 20mm Hg pCO2, 20mm Hg Na+, 145 mmol/L Na+, 145 mmol/L Cl-, 100 mmol/L Cl-, 100 mmol/L HCO3-, 15 HCO3-, 15

Example 3 Alkalemia Alkalemia Respiratory primarily Respiratory primarily Anion Gap is 30, AG MA (MUDPILES) Anion Gap is 30, AG MA (MUDPILES) Excess anion gap plus HC03 = = 33, There it is the triple threat. Excess anion gap plus HC03 = = 33, There it is the triple threat. Don’t need Winter’s, respiratory determined as primary. Don’t need Winter’s, respiratory determined as primary.

Clinical Correlation Vomiting (metabolic alkalosis) Vomiting (metabolic alkalosis) Alcoholic ketoacidosis (AG metabolic acidosis) Alcoholic ketoacidosis (AG metabolic acidosis) Pneumonia, (Respiratory alkalosis) Pneumonia, (Respiratory alkalosis)

Example 4 pH, 7.10 pH, 7.10 pCO2, 50mm Hg pCO2, 50mm Hg Na+, 145 mmol/L Na+, 145 mmol/L Cl-, 100 mmol/L Cl-, 100 mmol/L HCO3-, 15 HCO3-, 15

Example 4 Acidemia Acidemia Respiratory and Metabolic Respiratory and Metabolic Anion Gap is 30, you know the drill Anion Gap is 30, you know the drill Excess AG + HCO3 = =33, Metabolic Alkalosis. Excess AG + HCO3 = =33, Metabolic Alkalosis. Clinical Correlation? Clinical Correlation?

Clinical Correlation DKA with vomiting, followed by aspiration and unresponsive. DKA with vomiting, followed by aspiration and unresponsive.

Example 5 pH 7.25 pH 7.25 pCO2, 45 pCO2, 45 Na+, 137 Na+, 137 Cl-, 79 Cl-, 79 HCO3-, 20 HCO3-, 20

Example 5 Acidemia Acidemia Metabolic Metabolic AG=38 AG= = = 46 Winter’s ! 1.5(20) + 8 = 38 Winter’s ! 1.5(20) + 8 = 38

Clinical Correlation Borhaave’s Esophageal Rupture Borhaave’s Esophageal Rupture Anion Gap Acidosis from lactic acid and ketoacidosis Anion Gap Acidosis from lactic acid and ketoacidosis Metabolic alkalosis from profound dehydration and loss of gastric HCL into chest wall Metabolic alkalosis from profound dehydration and loss of gastric HCL into chest wall Respiratory acidosis from large pleural effusion. Respiratory acidosis from large pleural effusion.

References 1991 West J. Medicine, A Practical Approach to Acid-Base Disorders West J. Medicine, A Practical Approach to Acid-Base Disorders.