This lecture on acid base disorders explains acidemia and alkalemia, associated causes, signs and symptoms, differential diagnosis, management and related aspects.
Outline of Lecture
Acid Base Disorders
Introduction
What is acidemia?
pH < 7.35
What is Alkalemia?
pH > 7.45
What is an anion gap?
Difference between the sum of the concentrations of the principal cations (sodium and potassium) and of the principal anions (chloride and bicarbonate) is known as the ‘anion gap’
What is the normal anion gap?
12 +/- 2
How do you calculate the anion gap?
(Na+ + K+) – (Cl– + HCO3–)
The ABG
pH 7.35 – 7.45
PCO2 35-45 mmHg
PO2 80-100 mmHg
O2 Saturation 95-100%
Acidemia
Anion gap Acidosis “MUDPILES”
M ethanol
U remia
D iabetic Ketoacidosis, Ketoacidosis
P araldehyde
I ron, Isoniazid (INH)
L actic Acidosis
E thanol, Ethylene glycol
S alicylates
Signs and Symptoms
Gap Acidosis
Confusion disorientation
History of drug use
Fruity breath
Kussmaul’s breathing
Tinnitus
Hypotension
Laboratory Workup
Urea, Creatinine, LFT’s
Lactate level
Ketones
Ethanol level
Salicylate level
Osmolal gap
UA
Osmolar Gap
Normal (< 25mOsm/kg)
Uremic Acidosis
Lactic Acidosis
Ketoacidosis
Salicylates
Increased (>25mOsm/kg)
Ethylene Glycol
Look for Oxalate crystals in the Urine
Methanol Intoxication
Visual Changes
Treatment
Treat underlying condition
Remember:
Methanol
Ethanol
Ethylene Glycol
Salicylates
Can Be Removed via Dialysis
Non gap Acidosis “HARDUPS”
H yperalimentation
A cetazolamide, amphotericin
R TA
D iarrhea
U reteral Diversions
P ancreatic fistula
S aline resuscitation
Non Gap Acidosis
Is There Intestinal Fluid Loss?
IF YES THINK ABOUT
Ileostomy
Diarrhea
Enteric Fistula
Non Gap Acidosis
Is there Intestinal Fluid Loss?
IF NO: What is the urine pH?
if > 5.5
Type I RTA
if < 5.5, then CHECK Potassium
if K is low = RTA type II
if K is High = RTA type IV
What if there is a low gap?
What is the cause?
P araproteinemias, Multiple myeloma
L ithium intoxication
E xcessive Calcium and Magnesium
A lbumin is low (hypoalbuminemia)
B romism
Metabolic Alkalosis Chloride responsive
Volume Contraction:
NG suction
Vomitting
Diuretics
Post Hypercapnia
Hypokalemia
Hypomagnesemia
Carbenicillin, Penicillin
Metabolic Alkalosis Chloride Unresponsive
Adrenal Disorders
Glucocorticoids Excess
Mineralcorticoid Excess
Exogenous Steroids
Alkali Ingestion
Licorice
Bartter’s Syndrome
Metabolic Alkalosis Signs and Symptoms
Muscle cramps
Weakness
Hypoxia
Arrhythmias
Treatment
Volume repletion
Correct Electrolytes
Spironolactone
Treat Underlying process
Respiratory Acidosis
Differential Diagnosis
Pulmonary Disease
Pneumothorax
Effusion
COPD
ARDS
Pulmonary embolism
Inappropriate Ventilator setting
Musculoskeletal Disease
Guillain Barre Syndrome
Myasthenia gravis
CNS
Sedatives
Trauma
Infection
Neoplasm
Treatment
ADEQUATE VENTILATION
Respiratory Alkalosis
Differential Diagnosis
Pulmonary Disease
Pulmonary Edema
Pneumonia
Pulmonary embolism
Inappropriate Vent settings
CNS
Increased Respiratory drive
Infection
CVA
Trauma
Anxiety
Drugs
Salicylates
Catecholamines
Sepsis
Fever
Pregnancy
Liver Disease
Anemia
Carbon monoxide poisoning
Treatment
TREAT UNDERLYING CAUSE
APPROACH TO ACID BASE
Approach to Acid Base
1. Is the patient acidemic(<7.35) or alkalemic(>7.45)
2.
3. Confirm pH is appropriate for (H+)
(H+) = 24 x pCO2 / HCO3
pH 7.1 7.2 7.3 7.4 7.5 7.6
H+ 78 62 50 40 32 25
4. Calculate the Anion Gap
Calculate the Anion Gap:
(normal is 12 +/- 2)
If AG is >20 then primary metab gap acidosis is present regardless of pH
5. Mixed Acid – Base Disorders
Compensated Appropriately
met acidosis expected pCO2 = 1.5(HCO3) + 8
met alkalosis expected pCO2 = .9(HCO3) + 9
Acute resp acid each increase in pCO2 of 1,
pH should decrease by .008
Acute resp alk each decrease in pCO2 of 1,
pH should increase by .008
Chronic resp acid each increase in pCO2 of 1,
pH should decrease by .003
Chronic resp alk each decrease in pCO2 of 1,
pH should increase by .003
6. The Triple Disorder
Calculate the Delta Gap
If AG acidosis is present: to determine if other underlying condition is present
Take the change in AG= (AG – 12)
Add to HCO3–
i.e. (AG – 12) + Serum HCO3–
if < 23 = non gap acidosis
if > 30 = metabolic alkalosis
Diabetic Ketoacidosis
Symptoms of Ketoacidosis
Nausea / Vomiting
Frequent urination
Thirst — excessive
Abdominal pain
SOB
Drowsiness
Stupor
Unresponsiveness
Signs of Ketoacidosis
Hypotension
Tachycardia
“fruity” breath
Kussmaul’s respirations
Orthostasis
Laboratory Abnormalities of Ketoacidosis
Glucose >16.6 mmol/L
Serum Bicarbonate <15 mEq/L
pH < 7.30
Anion gap acidosis
Electrolyte abnormalities
increased potassium
Diabetic Ketoacidosis
Treatment
VOLUME up to 5 – 6 liters
over 2 hours
add 5% dextrose when BG < 250 (why?)
INSULIN
10 units bolus then
5-10 units per hour IV continuous infusion
CORRECT ELECTROLYTE ABNORMALITIES
Hyperkalemia
Treatment
BICARBONATE
When to administer?
When do you stop the Insulin Infusion?
8-12 hours after anion gap resolved and ketonuria cleared
EXAMPLES
Case study No. 1
Case study No. 2
