Clinician Review: Arterial Blood Gases

........ This article is a review on the basics of Arterial Blood Gases- ABG interpretation. A nurse can use this as a review for the clinical practice setting, and also a review for certification. It's important to note that in testing the values will not be provided; Nurse or healthcare professional will need to memorize and know the lab values. This is also true for electrolyte labs and cardiac enzymes, etc.. In the case of ABGs the nurse simply needs to identify the different types. Identify if the patient is in respiratory acidosis, respiratory alkalosis, metabolic acidosis, or metabolic alkalosis. Anticipate 2-3 questions on this topic for medical surgical certification exam. Sometimes the clue is in the question. Once you know the values, this could be easy points for you on the test.

According to Physopedia:

Arterial Blood Gases

Blood Gas Analyzer

Arterial blood gases (ABG's) is a blood test that is used to give an indication of ventilation, gas exchange, and acid-base status and is taken from an arterial blood supply[1]. The arterial blood gas test is one of the most common tests performed on patients in intensive care units. At other levels of care,?pulse oximetry?plus transcutaneous carbon dioxide measurement is a less invasive alternative method of obtaining similar information.[2]

To perform this test, blood is collected from a specific artery, usually the wrist's radial artery. This blood sample allows an accurate determination of the amount of oxygen that passes from the lungs to the blood. This test is the one most commonly performed to diagnose cases of?respiratory failure[3].

Arterial blood gas test results can show if:

• Lungs are getting enough oxygen.
• Lungs are removing enough carbon dioxide.
• Kidneys are working properly.[2]

Uses

ABGs are very useful for detecting conditions that cause respiratory failure. Including:?Lung Failure;?Acute respiratory distress syndrome (ARDS);?Sepsis; Diabetic?ketoacidosis?(DKA);?Cystic fibrosis;?Pneumonia;?Emphysema;?Hypovolemic shock;?Acute heart failure;?Cardiac arrest;?Kidney Failure;?Septic Shock;?Trauma; Chronic vomiting;?Uncontrolled diabetes;?Asthma?;?Chronic Obstructive Pulmonary Disease (COPD); Hemorrhage; Drug Overdose; Metabolic Disease; Chemical Poisoning; To check if lung condition treatments are working.[4]

Here are some Examples:

Quiz

?A) A 40-year-old male is brought to the ED after taking 20 Percocet tablets. He is confused with pale skin and a tremor in both hands. Vital signs are a blood pressure of 92/60 mm Hg; heart rate of 116; respirations of 8/min (clue). ABG results: pH 7.21; PaCO2 57 mm Hg; HCO3 26 mEq/L; PaO2 89. What is the patient showing?

(a)??Metabolic alkalosis

(b)??Metabolic acidosis

(c)??Respiratory alkalosis

(d)??Respiratory acidosis

B) An asymptomatic(clue) patient with a pH of 7.37, PaCO2 43 mm Hg, and HCO3 24 mEq/L would demonstrate:

(a)??Respiratory acidosis

(b)??Respiratory alkalosis

(c)??Metabolic acidosis

(d)??A normal ABG

C) The presentation of a patient with metabolic acidosis shows:

(The answer is either C or D)-the ph is what determines if it acidic or alkalosis.

(a)??An increase in pH, a decrease in PaCO2, and a decrease in HCO3

(b)??An increase in pH, PaCO2, and HCO3

(c)??A decrease in pH and HCO3; and PaCO2 in the normal range

(d)??A decrease in pH, an increase in PaCO2, and an increase in HCO3

?D) A patient presents with an elevated pH an elevated HCO3 and normal PaCO2. (Clue: Remember the ph is what determines acid or alkalosis). The answer is either B or D.

The patient has:

(a)??Metabolic acidosis

(b)??Metabolic alkalosis

(c)??Respiratory acidosis

(d)??Respiratory alkalosis

E) ?A patient with a pH of 7.32, PaCO2 47 mm Hg, and HCO3 26 mEq/L would demonstrate:

(a)??Metabolic acidosis

(b)??Metabolic alkalosis

(c)??Respiratory acidosis

(d)??Respiratory alkalosis

F) ?A patient with a pH of 7.32, PaCO2 40 mm Hg, and HCO3 19 mEq/L would demonstrate:

(a)??Metabolic acidosis

(b)??Metabolic alkalosis

(c)??Respiratory acidosis

(d)??Respiratory alkalosis

CAUSES OF ACID-BASE DISTRUBANCES

Causes of Respiratory Acidosis

• COPD
• Severe asthma
• Obstructive sleep apnea
• Chest wall disorders – kyphoscoliosis, flail chest, ankylosing spondylitis
• Obesity
• Sedative/narcotic overdose
• Neuromuscular disease – myasthenia gravis, ALS, Guillain-Barré Syndrome
• CNS depression – encephalitis, trauma

Causes of Respiratory Alkalosis

• Hyperventilation
• Fever
• Anxiety
• Hypoxemia
• Pregnancy

Causes of Metabolic Acidosis

• Increased acid production – generally increased anion gap
• Ketoacidosis
• Lactic acidosis
• Ingestions – aspirin, methanol, ethylene glycol
• Loss of bicarbonate – generally normal anion gap
• Diarrhea
• Intestinal tube drainage
• Carbonic anhydrase inhibitor
• Renal tubular acidosis Type 2
• Decreased renal acid secretion
• Chronic kidney disease
• Renal tubular acidosis Type 1 and 4

Causes of Metabolic Alkalosis

• Renal hydrogen loss
• Diuretics
• Primary mineralocorticoids excess
• Gastrointestinal hydrogen loss
• Chronic diarrhea
• Vomiting
• NG suctioning
• Contraction alkalosis
• Diuresis
• Sweat loss in cystic fibrosis
• Vomiting/NG suction in achlorhydria
• Intracellular shift of hydrogen
• Low serum potassium
• Alkali administration

REFERENCES :

CEUfast Course: ABG Interpretation www.ceufast.com

Thanks for reading a review on the basics of ABG. It's a guide to simply identify clinical problem based on lab values, and will help in answering questions in prep for certification exam. Test your knowledge and take quiz above and provide answers in the comment section.

By Gina DesRosiers, RN, BSN, CMSRN, Travel RN with PRN Healthcare in the Maryland area. PRN Healthcare has contract nursing jobs in all 50 states in all specialties. For referral, contact my Recruiter, Hailey Albright, 1-888-439-8585.