Use of an arterial cannula is indicated:

Use of an arterial cannula is contraindicated in patients with:

The radial artery originates from the brachial artery at the neck of the radius and passes along the lateral aspect of the forearm (Jenkins and Tortora [230]). The radial artery gives off multiple fasciocutaneous perforators until it reaches the wrist, where it forms the deep palmar arch. It contributes to the main artery of the thumb and index finger (Wallach [460]). The radial pulse can be felt by gently palpating the radial artery against the underlying muscle and bone (Drake et al. [132]). Cannulation of the radial artery is the most common placement of arterial cannulas (Brezezinski et al. [49], Mignini et al. [316]) and is performed in most acute care settings. The hand has a good collateral blood supply as the radial artery is near the skin surface; this artery is also readily accessible and easily secured, and the patient is disturbed less than when other sites are used (Adam et al. [1], Brezezinski et al. [49], Wallach [460]). Ideally, the cannula should not be positioned close to any intravenous cannulas as this may compromise blood flow around the adjoining structures.

The dorsalis pedis originates from the anterior tibial artery and arises at the anterior aspect of the ankle joint (Irwin and Rippe [224]). The dorsalis pedis route for arterial cannulation is no more or less risky than radial cannulation; it is more technically difficult, but it provides a safe and easily available alternative when radial arteries are not accessible (Chen et al. [71]).

Blood pressure measured from the dorsalis pedis and radial artery typically has higher systolic and lower diastolic pressures than centrally measured blood pressure (due to distal amplification), although the mean blood pressure is identical and clinically interchangeable (Mignini et al. [316]). Antiembolic stockings must be adapted to avoid any pressure on the device itself (which may dampen the waveform trace or cause a pressure sore) and also to leave the insertion site visible (Koyfman et al. [248]).

The femoral artery may be cannulated if it is not possible to cannulate a peripheral artery. This is particularly useful if the patient is haemodynamically compromised as it can be palpated with relative ease even when there is only a weak pulse (Adam et al. [1]). Lower extremity insertion sites, such as the femoral artery, will increase the risk of infection and should be avoided if possible in favour of the radial artery (O'Horo et al. [363]). Femoral catheters should be positioned at a 45° angle, as there is an increased risk of catheter fracture (Ho et al. [214]). This is a particularly serious risk as there is no collateral blood supply to the leg and lower limb, and as such arterial fracture may have major long‐term consequences for the patient (Chim et al. [75]).

The brachial artery is the major artery of the arm and divides into the radial and ulnar branches (Irwin and Rippe [224]). A cannula inserted at the antecubital fossa into the brachial artery may risk cannula fracture in conscious patients due to arm flexion. Its placement may also be uncomfortable and cause inconvenience as the patient will be asked to reduce their arm flexion.

The ulnar artery, along with the radial artery, forms the blood supply to the forearm and hand (Irwin and Rippe [224]). It is often avoided as it is usually the dominant artery of the hand, providing the most collateral circulation. Cannulation of the ulnar artery is also technically challenging because of its deeper and more painful course, and its size associates it with more risk of bleeding on removal than the radial artery (Brezezinski et al. [49]). For these reasons the ulnar artery is an unfavourable peripheral site and generally avoided.