Blood gas is an important diagnostic tool that provides rapid information about a patient's respiration, oxygenation, and acid-base status. Correct sampling and interpretation are crucial for the assessment and treatment of acutely ill patients.

Blood gas analysis is one of the most central diagnostic tests in emergency medicine and intensive care. For healthcare professionals, blood gas provides quick and precise information about the patient's respiration, oxygenation, electrolytes, and acid-base status.

At Akuttundervisning, we have been teaching blood gas sampling and interpretation to healthcare professionals for years, and our courses are an important part of professional development for medical personnel working in demanding situations.
This article provides a professional overview of what blood gas is, when it is used, how the sample is taken, and how the results are interpreted in practice.

What is Blood Gas?

Blood gas is a blood test that analyzes gas exchange and acid-base balance in the blood, usually based on arterial blood. The most important parameters include:

• pH – expression of acidity
• pO₂ – partial pressure of oxygen freely dissolved in the blood (We use PaO2 specifically for arterial blood)
• SO₂ – Saturation of oxygen bound to hemoglobin (We use SaO2 specifically for arterial blood)
• We use PaCO2 specifically for arterial blood
• HCO₃ – bicarbonate level
• BE: Base Excess: metabolic base excess

These values collectively provide insight into how the lungs, circulatory system, and metabolism function in concert.

When is Blood Gas Relevant?

Blood gas is used in a variety of clinical situations where rapid assessment is crucial:

• Acute respiratory failure
• Suspicion of metabolic acidosis or alkalosis
• Monitoring of patients with COPD or other lung diseases
• Monitoring of intensive care patients
• Evaluation of ventilatory support such as mechanical ventilation or NIV - Non-invasive ventilation.
• In cases of poisoning
  

Blood gas is particularly useful because it provides real-time information that can immediately influence treatment choices.

Arterial Blood Gas – The Gold Standard

The most precise form of blood gas is arterial blood gas, which is usually taken from the radial artery at the wrist. This method provides accurate information about oxygenation (PaO₂ and SaO₂), which cannot be obtained from venous samples.
Before sampling, it is recommended to assess the circulation in the hand, often using Allen's test. This ensures that the patient has adequate blood supply via the ulnar artery on the little finger side should complications arise.

Avoid taking blood gas over infected skin and assess the patient's coagulation status before proceeding.

Practical Execution of Blood Gas Sampling

Correct technique is crucial to ensure reliable results. The blood gas procedure should be performed systematically:

• Prepare equipment, including a heparinized syringe
• Correctly identify the patient and perform hand hygiene
• Identify the artery by palpation
• Thoroughly disinfect the skin with chlorhexidine alcohol
• Stabilize the wrist in slight dorsiflexion (bending backward)
• Pull back the plunger of the blood gas syringe so that there is at least 0.5 mL of air in the syringe.
• Insert the needle at a 30–45 degree angle
• Allow the syringe to fill spontaneously due to arterial pressure (at least 0.5 mL, preferably more)
• Remove the needle and compress the puncture site for a few minutes.

It is important to work calmly and precisely, as arterial sampling can be painful for the patient.

Pre-analytical Factors

The quality of blood gas results largely depends on correct sample handling:

• Air bubbles must be removed immediately
• The sample must be gently mixed with heparin (invert the blood gas syringe 5-10 times)
• Analysis should be performed as quickly as possible
• The sample must be correctly labeled

Errors in this phase can lead to misleading results, especially for PaO₂ and PaCO₂.

Interpretation of Blood Gas

Understanding blood gas requires a structured approach. A common method is to analyze the values in the following order:

• PaO₂ and SaO2 – oxygenation
  Provides information about the blood's oxygenation.
  
• pH – is it acidemia or alkalemia?
  Normal pH is between 7.35 and 7.45. A lower pH means acidemia, while a higher pH means alkalemia. The underlying processes that affect pH and thus determine whether one has acidemia or alkalemia are called acidoses and alkaloses. Often, several acidoses and alkaloses are present simultaneously. The patient's pH depends on how many acidoses and alkaloses are present and how severe they are.
  
• pCO₂ – respiratory component
  Elevated pCO₂ indicates hypoventilation (respiratory acidosis), while low pCO₂ indicates hyperventilation (respiratory alkalosis).
  
• HCO₃ and Base Excess (BE) – metabolic component
  Changes in bicarbonate and base excess reflect metabolic disturbances.
  

By combining these parameters, both primary and compensated acid-base disturbances can be identified.

Common Clinical Conditions

Blood gas is often used to identify and monitor various conditions:

• Respiratory acidosis = High pCO2: For example, in COPD exacerbation or hypoventilation due to overdose.
• Respiratory alkalosis = low pCO2: Seen in hyperventilation, for example due to pulmonary embolism, pain, fever, or anxiety.
• Metabolic acidosis = low bicarbonate and base excess: Seen, for example, in sepsis or diabetic ketoacidosis.
• Metabolic alkalosis = high bicarbonate or base excess: Seen, for example, in prolonged vomiting or diuretic use.
  

Correct interpretation of blood gas can be crucial for rapid and targeted treatment.

Venous Blood Gas as an Alternative

Venous blood gas is a less invasive and painful alternative to arterial blood gas. It provides relatively good information about pH and pCO₂, but is not suitable for assessing oxygenation.
In many situations, venous blood gas can be more than sufficient as a screening tool, especially when arterial sampling is challenging.

Complications and Patient Safety

Although blood gas is a common procedure, there is a risk of complications:

• Pain and discomfort
• Hematoma/bleeding
• Infection
• Arterial spasm
• Good training and correct technique are crucial to reduce risk. Compression after sampling is particularly important to prevent bleeding.
• Competence and training
  

At Akuttundervisning, blood gas is an important part of training for healthcare professionals. Emphasis is placed on both theoretical understanding and practical skills. Being able to correctly take and interpret blood gas is a critical competence in acute situations.
Simulation, practical training, and structured education contribute to increased confidence and improved patient care.

Want more information? See how to take arterial blood gas here:

Summary: 

For healthcare professionals, mastering both sampling and interpretation of blood gas is crucial. Through systematic training and practical experience, high quality can be ensured, errors reduced, and better clinical decisions made.
Akuttundervisning works to strengthen this competence so that healthcare professionals are better equipped to handle complex and acute situations where blood gas plays a central role.

See all our courses here: https://akuttundervisning.no/kurs/

The content of this article is for informational purposes only and should not be considered medical advice. Before performing medical procedures, you must have undergone proper training, education, and certification. The article may contain errors, and we do not assume responsibility for patient treatment or outcomes. Always consult with qualified healthcare professionals for medical advice and training. The use of this article does not replace professional medical training and certification. Please note that important steps such as obtaining patient consent, hand hygiene, ensuring you have the correct patient, and other critical aspects of patient care are not necessarily shown in the article. The purpose of this article may be to show a specific part of a procedure or patient encounter.