Following the procedure, check the patient's hand, and assess and document the temperature, colour, swelling and any signs of bleeding. Avoid taking blood pressure measurement manually on the arm where the arterial cannula was removed for 12–24 hours to minimize bleeding or haematoma formation. Medical staff must be informed immediately if the hand or forearm becomes discoloured or swollen, or if the patient complains of pain in the limb. In the event of any complication, careful documentation is essential; consider a request for medical photography of the affected area.

If the arterial device is inserted under emergency conditions and asepsis has been compromised, O'Grady et al. ([362]) recommend that the cannula should be replaced within 24 hours. Colonization and infection of arterial devices are rare (Minnaganti and Cunha [317]) and are usually related to duration of cannulation. However, arterial cannulas do represent a potential source of bloodstream infection that is often underappreciated (O'Horo et al. [363]).

Historically, arterial cannulas were associated with a significantly lower risk of local cannula‐related infection when compared to short‐term peripheral venous cannulas that had been left in situ for the equivalent length of time. Despite a common risk of catheter colonization, serious soft tissue infections are very rare, which may be related to exposure to high vascular pressures and subsequent local turbulence experienced in arterial cannulas (Koh et al. [247], O'Grady et al. [362], RCN [381]). Additionally, if the puncture site is well stabilized and treated with asepsis and all samples are obtained using aseptic technique, this will further minimize the risk of soft tissue infection (Marini and Wheeler [295]). However, more recent studies have begun to challenge this assertion and suggest that the infection risks of arterial cannulas are actually comparable to those of central venous catheters (Gowardman et al. [183], O'Horo et al. [363]). The site of arterial cannulation has relevance in preventing possible infection, and it is advisable to avoid the femoral site, when feasible (O'Horo et al. [363]). Regular observation of the arterial cannula insertion site is imperative to identify signs of inflammation, which may predispose patients to cannula‐related infection. Leaving cannulas in situ for more than 4 days increases the risk of infection (O'Grady et al. [362], O'Horo et al. [363]).

There is the potential for administration sets attached to the arterial device to provide pathways for micro‐organisms into the bloodstream, exposing the patient to catheter‐related bloodstream infections (CRBSIs). Current practices related to changing the administration sets of arterial devices are based on the Saving Lives guidelines for infections in central venous devices (DH [117]); they advocate changing sets every 72 hours (Loveday et al. [278]). There are no specific recommendations set out by any British governing body for when to change administration sets in peripheral artery devices. In a systematic review (mainly of Canadian and American studies), it was clearly found that practices around routinely changing arterial administration sets ranged from 24 to 96 hours (Daud et al. [104]). There is some evidence to suggest that changing the administration set between 24 and 72 hours is associated with less risk of infection among critically ill patients but there is not enough evidence to suggest a definitive lifetime of the sets (Daud et al. [104]).

Hypovolaemia can occur as a result of severe haemorrhage, which can be caused by (a) accidental disconnection of tubing from the cannula or from one of the connections within the system or (b) dislodgement of the cannula.

The flow from an 18 G cannula can result in blood loss of 250 mL per minute (Bersten et al. [31]). Unconscious or delirious patients and children are at particular risk. The risk can be minimized by clearly labelling the arterial cannula (Zideman and Morgan [482]), ensuring that arterial tubing and sets are predominantly red in colour, and ensuring that alarm settings on the monitor are turned on and audible (Adam et al. [1]). Further ways of reducing the risk of this complication occurring include the use of Luer‐Lok connections, ensuring visibility of the cannula, appropriate nurse–patient ratios, and adequate training and competency of nurses caring for patients with arterial cannulas.

The cannula may become dislodged, particularly if the patient is diaphoretic, in which case dressings tend to lift. Securing the cannula using an appropriate cannula‐securing device may be useful. Inform the patient about the danger of dislodging the cannula and the amount of movement that is preferred. Staff must also take care when moving the patient, and avoid putting stress on the arm and connections. Ideally, non‐invasive blood pressure readings should not be taken on the same arm as the arterial cannula. Marini and Wheeler ([295]) recommend attempting a minimum of once‐daily sphygmomanometry in order to confirm cannula pressure, especially in patients whose vasopressors are titrated to these pressures, and particularly in those patients who are elderly, are hypertensive or have underlying vascular disease.

Accidental intra‐arterial injection of drugs intended for administration through a central or peripheral venous device may cause distal ischaemia and necrosis, sometimes resulting in permanent functional damage (Marieb and Hoehn [294], Teplitz [436], Tinker and Zapol [442]). Drugs such as calcium channel blockers and vasopressors are particularly harmful if injected intra‐arterially (Marini and Wheeler [295]). Careful and appropriate labelling and appropriate staff training can minimize this risk. In the event of accidental injection of any drug, stop administering the drug and immediately report the incident to medical staff and the senior nurse. The nurse should then attempt to withdraw blood from the three‐way tap in order to aspirate any of the drug. Then assess the limb pulse, colour and temperature hourly, or more frequently if required, and complete an accident form and/or other relevant documentation.

Radial artery catheterization is considered a relatively safe procedure with an incidence of permanent ischaemic complications of only 0.09% (Chim et al. [75], Scheer et al. [403]). However, it is believed that many cases of hand ischaemia go unreported and hence it remains difficult to estimate its true incidence (Brezezinski et al. [49]). Local damage to the artery is the most common complication of arterial cannulation (Marieb and Hoehn [294]). Cannulation for as little as 6 hours has been associated with arterial wall scarring (Brezezinski et al. [49]). Regular close inspection and assessment of the limb and areas distal to the cannula must be carried out as there is a risk of thrombosis and embolism. Arterial catheter‐related ischaemia can present as:

To minimize such risks, cannulation of the non‐dominant hand should be attempted whenever possible (Wallach [460]).

The medical team should be informed if any of the above are discovered (Adam et al. [1]). If a distal embolism is suspected, the cannula may have to be removed and limb warming attempted in order to avoid permanent damage (see Box 17.11). The risk of ischaemia distal to the cannula is increased when it is associated with low cardiac output, shock, sepsis or prolonged cannulation (Bersten et al. [31], Gamby and Bennett [167]).