Fluids, Electrolytes, Acid-Base Disorders, and Nutrition Support

Box 1. Adverse Effects of Severe Acidemia (pH 7.25 or less)

Impaired cardiac output

Increased metabolic demands

Peripheral ischemia (centralization of blood)

Insulin resistance and hyperglycemia

Increased pulmonary vascular resistance

Decreased ATP synthesis

Hypotension

Increased protein breakdown

Increased risk of arrhythmias

Hyperkalemia

Decreased catecholamine responsiveness

Diaphragmatic fatigue/dyspnea

Obtundation/coma

Hyperventilation

Box 2.Adverse Effects of Severe Alkalemia (pH of 7.55 or greater)

Arteriolar constriction

Hypokalemia

Hypotension

Hypophosphatemia

Increased risk of arrhythmias

Hypocalcemia/tetany

Decreased coronary blood flow/decreased angina threshold

Organic acid production

Seizures

Hypoventilation/hypercapnia/hypoxemia

Lethargy, delirium, stupor

Use of base excess

Reflects the amount of base needed in vitro to return the plasma pH to 7.40 at standard conditions

(Pco2 40 mm Hg, body temperature 37°C)

Base excess reflects the metabolic component to interpreting the ABG. Despite its simplicity,

it has limitations (J Trauma Acute Care Surg 2012;73:27-32). Crystalloid resuscitation (leading

to hyperchloremic acidosis), exogenous bicarbonate (HCO3) administration, ethanol ingestion,

and acetate/HCO3 buffer in hemodialysis or CRRT solutions can lead to erroneous base excess

calculations and errors in interpretation (J Trauma Acute Care Surg 2012;73:27-32).

Compensatory response to acid-base disorders

Primary Disorder

Serum Bicarbonate

(mEq/L)

Anticipated Pco2 (mm Hg)

Metabolic acidosis

< 22

(1.5 × HCO3) + 8 (± 2)

Metabolic alkalosis

> 26

(0.7 × HCO3) + 20