Blood gases and electrolytes analysis


Electrolytes are charged particles (ions) dissolved in different fluid compartments (intravascular, interstitial and intracellular) of the body and perform a variety of functions in the human body.The clinical important electrolytes are: sodium, potassium, calcium, hydrogen and bicarbonate.Because hydrogen and bicarbonate ions mainly contribute to the pH balance, they are discussed separately.In this article, sodium, potassium and calcium are taken into account. Sodium is primarily an extracellular ion, potassium mainly occurs intracellularly and calcium performs a variety of functions.


Sodium is the most important extracellular cation. Sodium balance generally defines water balance.

Functions of Sodium

  • Na+ is the most abundant electrolyte in body transmission and nerve impulse conduction
  • Responsible for vascular fluid osmolality
  • Regulation of Body fluid level
  • Sodium moves into cells and potassium moves out of cells (sodium pump)
  • Supports the control of the acid – base balance by combining Cl-or HCO3-to regulate the balance

Abnormalities of Sodium

Hyponatremia: Loss of excess sodium or gain of H2O

Causes of Hyponatremia

  • Prolonged diuretic therapy
  • Insufficient Na intake
  • GI losses – suctioning, laxatives, vomiting
  • Administration of hypotonic fluids
  • Alcoholism

Hypernatremia: happens with excessive H2O loss or excessive Na retention. If not treated, can lead to death

Causes of Hypernatremia

  • Vomiting/diarrhea
  • Inadequate AntiDiuretic Hormone
  • Major burns


In body cells, potassium is the most abundant cation. About 97% of the intracellular fluid is contains potassium. Normal extracellular K+ is 3.5-5.3mEq / L. A K+ serum level below 2.5 or above 7.0 can cause heart arrest.

Functions of potassium

  • Essential for normal membrane excitability of nerve impulses
  • Promotes conduction and transmission of nerve impulses
  • Muscle contraction
  • Favors enzyme action
  • Assist in the maintenance of acid-base
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Abnormalities of potassium


Causes of Hypokalemia

  • Prolonged diuretic therapy
  • Inadequate intake
  • Gastric suctioning, laxative use, vomiting
  • Excess insulin
  • Hepatic disease
  • The low concentration of potassium has a dramatic effect on the excitable function of the muscle and nerve membrane. Levels <3 create distinctive neuromuscular symptoms


Causes of Hyperkalemia

  • Shock, severe hemolysis, lysis of the tumor, burns (cell release)
  • Renal failure (Decrease excretion)
  • Endocrine diseases with deficiency of mineralocorticoids
  • Diuretics ” potassium sparing “
  • Acidosis (K exits cells in exchange for H)
  • Artifactual hemolysis of blood specimens; K leak in chilled or unprocessed specimens

Symptoms of Hyperkalemia

  • Greater than 5.0, EKG changes, decreased pH
  • Acts as myocardial depressant; decreased heart rate, cardiac output
  • Symptoms: muscle weakness, nausea, lethargy, arrhythmias, characteristic ECG changes, cardiac arrest, GI hyperactivity
  • levels > 7.5 produce symptoms and levels > 10 are lethal


The most important extracellular anion (118–132 meq / l in serum)

Function of Chlorine

  • Important in water distribution, osmotic pressure and balance of anion
  • Cl- : regulates osmotic pressure and assists in regulating acid-base balance. Maintains serum osmolality along with Na+
  • Helps to maintain acid/base balance
  • Combines sodium, hydrochloric acid, potassium and calcium with other ions for homeostasis
  • Closely tied to Na+
  • Reduced levels are usually due to GI losses
  • Found in ECF
  • Changes osmolality of the serum
  • Along with Na+ causes water retention
  • Assists with regulation of acid-base balance
  • Cl-combines with hydrogen ion in the stomach to form hydrochloric acid

Abnormalities of Chloride


Causes of Hypochloremia

  • Fluid volume expansion (dilution)
  • Renal diseases (reabsorption failure)
  • Metabolic acidosis with increased “unmeasured anions” (e.g. DKA)
  • GI loss (protracted vomiting)
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Causes of Hyperchloremia

  • Dehydration
  • Renal tubular acidosis, acute renal failure
  • Bicarbonate loss (diarrhea)
  • Mineralocorticoid excess (Cushing’s syndrome and hyperaldosteronism)
  • Diabetes insipidus


Ca2 +: usually in combination with phosphorus to form bone and teeth mineral salts, promotes nerve impulse and muscle contraction / relaxation.

Abnormalities of Calcium


Causes of hypocalcemia

  • Abnormalities of the parathyroid gland
  • Inadequate intake
  • Excessive losses.

Symptoms of hypocalcemia

  • Can cause skeletal and neuromuscular abnormalities
  • Impairs clotting mechanisms
  • Affects membrane permeability
  • Diagnostic findings: EKG changes, Serum Ca++levels < 8.5 mg/dL, Prolonged PT and PTT


  • Increased serum levels of Ca++
  • Symptoms are directly related to degree of elevation
  • Clients with metastatic cancer are especially at risk

Causes of Hypercalcemia

  • Excessive intake
  • Excessive use of antacids with phosphate-binding
  • Prolonged immobility
  • Excessive vitamin D intake
  • Thiazide diuretics
  • Cancer
  • Thyrotoxicosis


  • Mg2+ plays role in carbohydrate and protein metabolism, storage and use of intracellular energy and neural transmission
  • Important in the functioning of the heart, nerves, and muscles at a glance
  • Hyponatremia (sodium deficit < 130 mEq/L)
  • Hypernatremia (sodium excess >145 mEq/L)
  • Hypokalemia (potassium deficit <3.5mEq/L)
  • Hyperkalemia (potassium excess >5.1mEq/L)
  • Chloride imbalance (<98 mEq/L or >107 mEq/L)
  • Magnesium imbalance (<1.5mEq/L or >2.5mEq/L)


  • Blood gas analysis may be carried out in a main laboratory, in an ER or OR lab or using POC devices.
  • Provides accurate measurement of PO2, PCO2, pH, hemoglobin saturation, bicarbonate and hematocrit (some analyzers also offer electrolytes, lactate, glucose, Hgb, CO-Hgb, met- and sulfHgb).
  • Arterial blood, drawn in appropriate equipment and transported quickly (10 – 15 min) on ice to the lab.
  • Check ulnar artery patency before withdrawing blood from radial artery.
  • “Arterialized capillary blood” (warmed heel or earlobe) may be acceptable in some Cases.
  • Specimen is accompanied by history with FIO2 and clinical status of patient, and patient temperature (all are important for interpretation and are included in the returned report).
  • Erroneous results from room temp specimens and specimens with air bubbles or improper capping.

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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