Arterial and Venous Blood Gas Values

                Arterial Blood Gas         Mixed Venous

Assay              Normal Range         Assay     Normal Range

pH                  7.35-7.45            pH        7.32-7.36
PaCO2               35-45 mmHg           PvCO2     46 mmHg
PaO2                80-100 mmHg          PvO2      40 mmHg
O2 Sat              95-99 %              SvO2      60-80%
CO                  0-1.5 %
Base Excess         + 2%
CO2 Content         21-27 
HCO3                20-26 meq/L

Disease States Related to Arterial Blood Gases

Respiratory acidosis

chronic causes

     Causes of respiratory acidosis include:

          Chronic obstructive pulmonary disease (COPD)
          Oxygen excess in COPD
          Drugs
               Barbiturates
               Anesthetics
               Narcotics
               Sedatives
          Extreme ventilation-perfusion mismatch
          Exhaustion
          Neuromuscular disorders
          Poliomyelitis
          Amyotrophic lateral sclerosis
          Guillain-Barre syndrome
          Electrolyte deficiencies (K+, P04 - )
          Myasthenia gravis
          Inadequate mechanical ventilation
          Neurologic disorders
          Excessive CO2 production
          Total parenteral nutrition
          Sepsis
          Severe burns
          NaHCO3 administration

Respiratory alkalosis may result from a variety of acute and chronic causes. It disrupts the body's acid-base balance by depleting the normal blood concentration of carbonic acid.

     Causes of respiratory alkalosis include:

            Hypoxemia (moderate to severe)
            Overzealous mechanical ventilation
            Restrictive lung disorders
            Fibrosis
            Ascites
            Scoliosis and thoracic cage deformities
            Third trimester of pregnancy
            Pneumonia
            Adult respiratory distress syndrome (ARDS)
            Congestive heart failure
            Emboli in pulmonary circulation
            Neurologic origin
            Fever
            Anxiety
            Cerebrospinal fluid acidosis
            Trauma
            Severe pain
            Shock/decreased cardiac output

Metabolic acidosis may be the result of either the accumulation of some fixed acid in the blood or the loss of normal blood base. The potential causes of metabolic acidosis can be separated into two groups: (1) those associated with the accumulation of fixed acids and therefore with a high anion gap, and (2) those associated with the loss of base and a normal anion gap.

     Causes of high anion gap metabolic acidosis:

          Aspirin overdose
          Wood alcohol  (methanol)
          Ethylene glycol
          Paraldehyde
          Toluene
          Azotemic renal failure
          Lactic acidosis
          Hypoxia
          Liver failure
          Starvation
          Alcoholism (ethanol)
          Diabetes

     Causes of normal anion gap metabolic acidosis:

          Renal tubular acidosis
          Enteric drainage tubes
          Diarrhea
          Urinary diversion
          Carbonic anhydrase inhibitors
          Early renal disease
          Dilution acidosis
          Biliary or pancreatic fistulas
          Acidifying salts
          Sulfur, hydrogen sulfide, drugs

Metabolic alkalosis is very common in acute illness. It may be caused by an abnormal loss of fixed acid from the body or by the abnormal accumulation or production of blood base. Most often the loss of acid caused by either renal H+ excretion or loss of HCl from the stomach, is accompanied by the concurrent production of blood bicarbonate.

     Causes of metabolic alkalosis:

          Hypokalemia
          Ingestion of large amounts of alkali or licorice
          Gastric fluid loss
          Vomiting
          Nasogastric drainage
          Hyperaldosteronism secondary to nonadrenal factors
          Bartter's syndrome
          Inadequate renal perfusion
          Diuretics
          Bicarbonate administration
          Sodium bicarbonate overcorrection
          Blood transfusions
          Adrenocortical hypersecretion
          Steroids
          Eucapnic ventilation posthypercapnia

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