Examinations & Procedures - Part 2: Arterial Blood Gas

2. Mannikins

2.3. Arterial Blood Gas

You are FY2 in Emergency Department. Mr Ronald Smith aged-66, has been brought in by ambulance. He is complaining of cough and shortness of breath. Talk to the patient, collect Arterial Blood Gas sample and discuss the management with him.

Arterial Blood Gas

Arterial blood gas (ABG) sampling is a medical procedure that involves taking a small sample of arterial blood to measure blood oxygenation and acid-base balance.

Indications

Arterial blood gas (ABG) sampling is a medical test used to measure the levels of gases, such as oxygen and carbon dioxide, in the arterial blood. It is usually done in the hospital or clinical setting and may be indicated for the following reasons:

Respiratory distress: ABG sampling is often used to evaluate patients with respiratory distress, such as those with chronic obstructive pulmonary disease (COPD), asthma, or acute respiratory distress syndrome (ARDS).
Acid-base imbalances: ABG sampling can help diagnose and monitor acid-base imbalances, such as metabolic acidosis, respiratory acidosis, and metabolic alkalosis.
Monitoring critically ill patients: ABG sampling can help monitor critically ill patients in the intensive care unit (ICU), such as those on mechanical ventilation or receiving supplemental oxygen.
Assessing oxygenation status: ABG sampling can assess a patient's oxygenation status and help guide treatment, such as adjusting oxygen therapy or ventilation.
Monitoring the effectiveness of therapy: ABG sampling can help assess the effectiveness of therapy for respiratory or metabolic disorders, such as oxygen therapy, mechanical ventilation, or medications that affect acid-base balance.
Evaluating shock: ABG sampling can help evaluate patients in shock, a life-threatening condition that can result in decreased tissue perfusion and inadequate oxygenation.

It is important to note that ABG sampling is an invasive procedure and should only be performed by trained medical professionals when medically necessary.

Steps of the procedure

The following are the general steps involved in ABG sampling:

Obtain informed consent: Explain the procedure to the patient and obtain their informed consent.
Prepare the equipment: Gather the necessary equipment, including sterile gloves, a syringe, a heparinized capillary tube, a needle, a heparinized saline flush, alcohol swabs, and a gauze pad.
Choose the puncture site: Typically, the radial artery in the wrist is the most common puncture site. Other potential puncture sites include the femoral artery in the groin or the brachial artery in the elbow.
Clean the puncture site: Clean the puncture site with an alcohol swab and allow it to dry.
Anesthetize the area: Apply a topical anesthetic, such as lidocaine, to the puncture site.
Insert the needle: Insert the needle into the artery and draw back the plunger to collect the arterial blood sample.
Transfer the blood to a heparinized syringe: Transfer the blood sample to a heparinized syringe to prevent clotting.
Cap the syringe: Cap the syringe and mix it well to prevent clotting.
Analyze the sample: Send the sample to the laboratory for analysis, which typically involves measuring the blood pH, oxygen and carbon dioxide levels, and bicarbonate concentration.
Monitor the patient: Monitor the patient for any complications, such as bleeding or hematoma formation, at the puncture site.

It is important to note that ABG sampling is an invasive procedure that carries risks, including bleeding, hematoma formation, and infection. As such, it should only be performed by trained medical professionals who have been trained in the proper techniques.

Post procedure care

Post-procedure care after ABG sampling involves monitoring the patient for any potential complications and taking appropriate steps to manage them. The following are some general post-procedure care steps:

Apply pressure: After the procedure, apply firm pressure to the puncture site for at least 5 minutes to prevent bleeding and hematoma formation.
Monitor vital signs: Monitor the patient's vital signs, such as blood pressure, pulse rate, and oxygen saturation levels, to ensure they remain stable.
Observe the puncture site: Check the puncture site frequently for any signs of bleeding, swelling, or hematoma formation. If any of these occur, apply pressure to the site and notify the healthcare provider.
Provide pain relief: If the patient experiences pain at the puncture site, provide pain relief medication as prescribed by the healthcare provider.
Assess for signs of infection: Watch for signs of infection at the puncture site, such as redness, warmth, swelling, or drainage. If these symptoms occur, notify the healthcare provider.
Provide instructions to the patient: Educate the patient on signs and symptoms to watch out for and the importance of following up with their healthcare provider if they experience any complications.
Dispose of the equipment: Dispose of the used equipment safely and according to hospital protocol.

It is important to note that post-procedure care may vary depending on the patient's individual needs and the healthcare provider's specific instructions.

Complications

Arterial blood gas (ABG) sampling is generally a safe procedure when performed by trained medical professionals. However, as with any invasive procedure, there are potential risks and complications that can occur. The following are some possible complications of ABG sampling:

Bleeding: Bleeding can occur at the puncture site and can range from mild to severe. The risk of bleeding is higher for patients who have bleeding disorders or are taking blood-thinning medications.
Hematoma: Hematoma is a collection of blood outside of the blood vessels that can form at the puncture site. It can cause pain, swelling, and discoloration.
Infection: Infection can occur at the puncture site and can range from mild to severe. Patients who are immunocompromised or have underlying medical conditions that increase their risk of infection are at higher risk.
Arterial occlusion: Arterial occlusion occurs when the artery becomes blocked, either by a blood clot or other material. It can cause pain, numbness, and other neurological symptoms.
Nerve damage: Nerve damage can occur if the needle used to puncture the artery accidentally damages a nerve. This can cause pain, numbness, or weakness in the affected area.
Hypoxemia: Hypoxemia is a condition in which the blood has low oxygen levels. It can occur if the ABG sample is not properly handled or analyzed, leading to inaccurate results and inappropriate treatment.
Vasovagal reaction: A vasovagal reaction is a type of fainting episode that can occur in response to the stress of the procedure.

It is important to note that while these complications are possible, they are relatively rare. Healthcare professionals take precautions to minimize these risks and closely monitor patients during and after the procedure.

Allen's test and its procedure

The Allen's test is a medical test used to assess the patency of the ulnar artery in the hand. The test is performed by a healthcare provider and involves applying pressure to both the radial and ulnar arteries in the wrist to occlude blood flow. The patient is then asked to make a fist while the pressure on the ulnar artery is released, allowing blood to flow into the hand through the ulnar artery. The time it takes for the hand to return to its normal color indicates the adequacy of blood flow through the ulnar artery.

The Allen's test is typically performed prior to arterial puncture, such as for arterial blood gas sampling or during arterial line placement, to ensure that adequate collateral circulation is present in the hand in case of arterial occlusion. If the test indicates inadequate collateral circulation, the healthcare provider may choose to use a different site for arterial puncture to minimize the risk of ischemia or other complications.

The normal time it should take to reperfuse the hand after performing the Allen's test is typically less than 5 seconds. This indicates adequate collateral circulation through the ulnar artery. However, the time to reperfuse can vary depending on the individual and other factors such as the presence of arterial disease or previous vascular surgery. If the hand takes longer than 5 seconds to reperfuse, or if there is no reperfusion at all, this suggests inadequate collateral circulation through the ulnar artery and may indicate the need to choose a different site for arterial puncture.

Examinations & Procedures - Part 2