**5. RAO: prevention/therapy**

Radial artery occlusion (RAO) is common and is seen in up to 10% of patients early after the procedure, although the more recent trials (after 2018) showed an RAO rate of less than 3.7% [18].

Multiple preventive techniques have been described including importance of anticoagulation, proper sizing of the radial artery to sheath/guide, patent hemostasis, prophylactic ulnar compression and shorten duration of compression [18]. A meta-analysis that included 31,345 patients and 66 studies concluded that high dose heparin (5000 IU) administration decreased the risk of RAO by 64%, and reducing compression times decreased this risk by 72% [19]. A recent study of high dose (100 IU/kg body weight) versus (50 IU/kg/body weight) lowered RAO [20]. That is why it has been recommended to administer at 5000 U or 50 or higher IU/kg body weight unfractionated heparin for all procedures with radial artery access [18, 21]. Importance of having sheath to radial artery diameter < 1.0 is considered best for reducing RAO [18, 21], pushing industry to provide sheaths with thinner walls or sheathless guide systems. The 6.5 F sheathless Eaucath appeared to have lower RAO compared to thin walled 6F sheath, 0.0% vs. 2.0%, p 0.031 with sample size of 600 randomized patients [22]. Although thinner, the RAP and BEAT (Radial Artery Patency and Bleeding, Efficacy, Adverse evenT) trial found thin walled 6French (F) sheath failed noninferiority to 5F sheath, (3.7% vs. 1.7%, pnon-inferiority = 0.150) [23]. Even a difference of 0.24 mm (5F standard with 2.22 mm vs. thin-walled 6F with 2.44 mm) may have lower RAO, implying smaller is better. Reduction of RAO rates have been reported after subcutaneous injection of nitroglycerin at the radial access site before the procedure (5% vs. 14%, P = 0.04) and the use of intraarterial nitroglycerin after the procedure (8% vs. 12%, p = 0.006) [24]. Maintaining radial artery patency during hemostasis is proven to reduce RAO rates, or patent hemostasis [18, 21]. This can be achieved by periodically monitoring oximetryplethysmography after the procedure to ensure radial flow [25] Pneumatic radial compression based on the patient's mean arterial pressure and concomitant ulnar compression to increase radial flow have also been shown to be beneficial [26].
