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Procedural Skills (SLO6)
Question 91 of 127
You have been asked to perform arterial cannulation on a patient who is being transferred to ITU. Regarding arterial cannulation, which of the following statements is NOT true?
Answer:
- Indications include: Continuous BP monitoring in perioperative or critically ill patients and evaluation of variations in the arterial pressure waveform to predict fluid responsiveness.
- A modified Allen's test should be performed before radial artery cannulation is initiated. This procedure is a simple bedside test designed to evaluate for adequate collateral circulation to the palmar arches of the hand.
- The radial artery is the most commonly used, followed by the femoral artery.
- Contraindications include: Active Raynaud's syndrome (particularly sampling at the radial site).
Arterial Cannulation
Procedural Skills (SLO6)
Last Updated: 29th June 2023
Indications
- Continuous BP monitoring in perioperative or critically ill patients
- Inability to use non-invasive BP monitoring e.g. patient with severe burns, morbid obesity
- Evaluation of variations in the arterial pressure waveform to predict fluid responsiveness
- Intravascular access for frequent blood sampling
- Intra-arterial access for frequent arterial blood gas sampling
Contraindications
- Absolute
- An abnormal modified Allen's test
- Local infection, thrombus, or distorted anatomy at the puncture site (e.g. previous surgical interventions, congenital or acquired malformations, burns, aneurysm, stent)
- Arteriovenous fistula or vascular graft at the puncture site
- Severe peripheral vascular disease of the artery selected for sampling
- Active Raynaud's syndrome (particularly sampling at the radial site)
- Relative
- Anticoagulants or coagulopathy
- Use of thrombolytic agents
- Thrombocytopaenia
- History of Raynaud's disease
- Evidence of poor peripheral perfusion
Clinical anatomy
- The initial step in selection of a catheterisation site is the location of a palpable arterial pulse. The most favored site for arterial cannulation is the radial artery because it is easily accessible and there is collateral blood flow from the ulnar artery. Other possible sites include the ulnar, dorsalis pedis, posterior tibial, axillary, and femoral arteries.
- The radial artery originates in the cubital fossa from the brachial artery. It traverses the lateral aspect of the forearm and gives rise to the palmar arches that provide vascular flow for the hand. At the wrist, the radial artery sits proximal and medial to the radial styloid process and just lateral to the flexor carpi radialis tendon. For the radial artery, the initial puncture site should be as distal as possible. A common location is over the radial pulse at the proximal flexor crease of the wrist. In any case, the puncture site should be at least 1 cm proximal to the styloid process so as to keep from puncturing the retinaculum flexorum and the small superficial branch of the radial artery.
Modified Allen's test
- A modified Allen's test should be performed before radial artery cannulation is initiated. This procedure is a simple bedside test designed to evaluate for adequate collateral circulation to the palmar arches of the hand. In most patients, the palmar arches are supplied by both the radial artery and the ulnar artery. This collateral circulation allows perfusion of the hand should either of these vessels be injured.
- To perform this test, the examiner elevates the hand and asks the patient to make a fist for 30 seconds. With the patient’s hand in a fist, the examiner applies simultaneous pressure to the ulnar and radial arteries so as to occlude them. The patient is then asked to lower the arm and open the hand, which should appear blanched as a consequence of the occlusion of the radial and ulnar arteries.
- Next, the pressure over the ulnar artery is released (while occlusion is maintained on the radial artery), and the circulation should be observed returning to the hand i.e. it will flush pink, usually within six seconds, indicating that the ulnar artery is patent.
- Although the timing of return of circulation to the palm varies considerably, the test is generally considered abnormal if ten seconds or more elapses before color returns to the hand. An alternative puncture site should be considered if the result is abnormal.
Complications
- Pain
- Bruising
- Swelling
- Haematoma
- Bleeding
- Infection (local or systemic)
- Damage to local structures
- Vascular complications:
- Vasospasm
- Thromboembolism
- Air embolism
- Dissection
- Pseudoaneurysm
- Arteriovenous fistula formation
- Accidental intra-arterial injection of medications
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
