METABOLICACIDOSIS

III-D2 Rodriguez, Jan Gayl – Sahagun, Marie Janice

SALIENT FEATURES

OBJECTIVE SUBJECTIVE

• 45 Y/O FEMALE

• HIGH GRADE FEVER (39oC)• CHILLS

• MYALGIA

• DIARRHEA

• BP : 84/52• PR : 118 BEATS PER MINUTE

• RR : 42 CYCLES PER MINUTE, LABORED

• DIABETES MELLITUS

• NO MEDICATIONS/ ALCOHOL

• DRY MUCOUS MEMBRANES

• FLAT NECK VEINS

• NO EDEMA

• FIRM, MILDLY TENDER, DISTENDED ABDOMEN

• HYPERACTIVE BOWEL SOUNDS

SALIENT FEATURES

OBJECTIVE(LAB DATA)

ACTUAL NORMAL

Hemoglobin 15.5 g/dL 12-16 g/dL

Hematocrit 48 % 37-48%

WBC count 22.8x103 4.5-11 x103

Segmenters 66 % 50-70% Bands 23 % 0-5%

Serum Na 138 meq/L

135-145 mEq/L

Serum K 4.2 meq/L

3.5-5.0 mEq/L

Serum Cl 108 meq/L

95-108 meq/L

ACTUAL NORMAL

SerumCreatinine

2.4 mg/dl 0.35-0.9 mg/dl

Lactate 3.0 meq/L 0.5-1.3 mEq/L

pH 7.39 7.34-7.44

pCO2

17.0 mmHg

35-45 mmHg

Glucose 342.0 mg/dL

65-110 mg/dL

Ketones None None

BUN 28.0 mg/dL

7-21 mg/dL

HCO3

10.0 meq/L

22-26 mEq/L

WHAT IS THE ACID BASE DISTURBANCE PRESENT IN THIS

CASE?

Respiratory acidosis

Respiratory alkalosis

Metabolic alkalosis

Metabolic acidosis

Patient Normal values

pH 7.38 – 7.44

H+ 40 meq/L

pCO2 35 – 45 mmHg

HCO3 21 – 30 meq/L

METABOLIC ACIDOSIS

METABOLIC ACIDOSIS

• Infection Increased plasma lactate: 3.0 meq/L

• Severe diarrhea Decreased serum bicarbonate: 10 meq/L

• Increased serum chloride: 108 meq/L• Kussmaul respiration• Decreased PCO2 : 17 mmHg (compensated)• Normal blood pH: 7.39 (compensated)

ALGORITHM FOR THE DIAGNOSIS OF THE ACID BASE

DISORDER

1. Establish database

2. Identify the main disorder:

3. Evaluate compensation (using the formulas)

4. Determine the anion gap (AG, normal = 12). 

* If the AG is >20 = metabolic acidosis

* If there is an AG, 

Calculate the gap-gap (delta-gap) = patient’s anion gap – 12 (normal anion gap). 

Calculate the delta HCO3 = normal HCO3 (use 25) – the patient's HCO3. 

delta-gap ÷ delta HCO3 should normally be between 1-2

If < 1 = combined non-gap and gap acidosis  

If > 2 suggests = metabolic alkalosis.

RULE OF THUMB IN BEDSIDE INTERPRETATION OF ACID BASE

DISORDER

Metabolic acidosis

• PaCO2 should fall by 1.0 to 1.5 X the fall in

plasma HCO3- concentration

• pCO2 should rarely be < 20 mmHg.

• Bicarbonate deficit (mEq/L) = [0.5 x BW(kg)] x (24 - HCO3)

Metabolic alkalosis • PsCO2 should rise by 0.25 to 1.0 X the rise in

plasma HCO3- concentration

RULE OF THUMB

Acute respiratory acidosis • Plasma HCO3

- concentration should rise by about

1 mmole per liter for each 10 mm Hg increment in PaCO2 ( 3 mmoles per liter).

• Acute change pH/pCO2 = 0.008

Chronic respiratory acidosis • Plasma HCO3

- concentration should rise by about 4

mmoles per liter for each 10 mm Hg increment in PaCO2 ( 4 mmoles per liter).

• Chronic change pH/pCO2 = 0.003

RULE OF THUMB

Acute respiratory alkalosis • Plasma HCO3

- concentration should fall by about

1 to 3 mmoles per liter for each 10 mm Hg decrement in the PaCO2, usually not to less than

18 mmoles per liter

• Acute change pH/pCO2 = 0.008

Chronic respiratory alkalosis • Plasma HCO3

- concentration should fall by about 2

to 5 mmoles per liter per 10 mm Hg decrement in PaCO2 but usually not to less than 14 mmoles per

liter.

• Chronic change pH/pCO2 = 0.003

RULE OF THUMB

HOW DO YOU COMPUTE FOR THE

ANION GAP?

WHAT IS ITS SIGNIFICANCE?

COMPUTE FOR THE ANION GAP OF

THIS PATIENT

ANION GAP COMPUTATION

• Anion Gap

represents the difference between the concentration of the major plasma cation (Na+) and the major plasma anions (Cl- and HCO3

-)

• Formula

AG = [Na+] – ([Cl-] + [HCO3-])

SIGNIFICANCE OF AG• Nonvolatile acid added to body fluids ↑ [H+], ↓ pH, ↓

[HCO3-] ↑ Anion Concentration

• Change in Anion- provides convenient way to analyze and help

determine the cause of metabolic acidosis• NV 10-12 mmol/L• Normal AG

- Anion of nonvolatile acid Cl-

• High AG- Anion of nonvolatile acid Lactate, β-

hydroxybutyrate

Calculation of AG is a useful way to identify thecause of a metabolic acidosis

AG COMPUTATION (Case)

AG = [Na+] – ([Cl-] + [HCO3-])

= [138] – ([108) + [10])

= 20 meq/L (High AG)

ANION GAP

Normal Anion Gap

• Loss of bicarbonate

• Addition of HCl

• Renal Tubular Dysfunction

High Anion Gap

• Overproduction of organic acids

• Failure of the kidneys to maintain bicarbonate levels

Normal Anion Gap

• Diarrhea

• Renal Tubular Acidosis

• Carbonic Anhydrase Inhibition

High Anion Gap

• Lactic Acidosis

• Ketoacidosis

• Drug and Toxin Induced

• Advanced Renal Failure

Prediction of Compensatory Responses on Simple Acid Base Disturbances

• Acid-Base Nomogram– Shaded areas show 95% confidence limits for

normal compensation – Finding acid-base values within the shaded

areas does not rule out a mixed disturbance– Not a substitute for computation

Prediction of Compensatory Responses on Simple Acid Base Disturbances

• Acid-Base Nomogram– pH 7.39

– HCO3 10 mEq/L

– PCO2 17 mmHg

TREATMENT

• Antibiotic

• IVF/Vasopressors