Page 34 - The Insurance Times February 2025

If the anion gap is elevated, consider calculating the Table 2: Selected etiologies of respiratory
osmolal gap in compatible clinical situations. acidosis
o Elevation in AG is not explained by an obvious case
o Airway obstruction
(DKA, lactic acidosis, renal failure
- Upper
o Toxic ingestion is suspected
- Lower
OSM gap = measured OSM - (2[Na+] - glucose/18 -
o COPD
BUN/2.8
o The OSM gap should be < 10 o asthma
o other obstructive lung disease
Step 6: If an increased anion gap is present, assess the o CNS depression
relationship between the increase in the anion gap and the
o Sleep disordered breathing (OSA or OHS)
decrease in [HCO -].
3
o Neuromuscular impairment
Assess the ratio of the change in the anion gap ( AG ) to o Ventilatory restriction
the change in [HCO -] ( [HCO -]): AG/ [HCO -] o Increased CO2 production: shivering, rigors, seizures,
3 3 3
malignant hyperthermia, hypermetabolism, increased
This ratio should be between 1.0 and 2.0 if an uncomplicated intake of carbohydrates
anion gap metabolic acidosis is present. o Incorrect mechanical ventilation settings

If this ratio falls outside of this range, then another meta-
Table 3: Selected etiologies of respiratory
bolic disorder is present:
alkalosis
If AG/ [HCO -] < 1.0, then a concurrent non-anion
3
gap metabolic acidosis is likely to be present. o CNS stimulation: fever, pain, fear, anxiety, CVA, cere-
bral edema, brain trauma, brain tumor, CNS infection
If AG/ [HCO -] > 2.0, then a concurrent metabolic
3
alkalosis is likely to be present. o Hypoxemia or hypoxia: lung disease, profound anemia,
low FiO
2
It is important to remember what the expected "normal" o Stimulation of chest receptors: pulmonary edema, pleu-
anion gap for your patient should be, by adjusting for hy- ral effusion, pneumonia, pneumothorax, pulmonary em-
poalbuminemia (see Step 5, above.) bolus
o Drugs, hormones: salicylates, catecholamines,
Table 1: Characteristics of acid-base distur- medroxyprogesterone, progestins

bances o Pregnancy, liver disease, sepsis, hyperthyroidism
o Incorrect mechanical ventilation settings

Disorder pH Primary Compensa-
problem tion Table 4: Selected causes of metabolic al-

Metabolic in HCO - in PaCO kalosis
3 2
acidosis o Hypovolemia with Cl- depletion
o GI loss of H+
Metabolic in HCO - in PaCO
3 2 Vomiting, gastric suction, villous adenoma, di-
alkalosis
arrhea with chloride-rich fluid
Respiratory in PaCO in [HCO -]
2 3 o Renal loss H+
acidosis
Loop and thiazide diuretics, post-hypercapnia
Respiratory in PaCO in [HCO -] (especially after institution of mechanical ven-
2 3
alkalosis tilation)

The Insurance Times February 2025 31