**2.5 Patient's health conditions**

It is reported that the physiological and psychological conditions of the individuals exert an effect on their venous structure [12, 14]. It is elucidated that certain chronic diseases may cause the deterioration and hardening of the vascular structure, rendering the catheter placement process difficult. Cancer, diabetes mellitus, and vascular diseases are among the conditions that render vein access difficult [7, 13, 14]. Intravenous chemotherapy treatment or surgical procedure/ dissection of the lymph nodes associated with breast cancer reduces the visibility and palpability of the veins. Furthermore, circulation problems, which are among the advanced complications of diabetes mellitus, and conditions such as coronary artery disease and the associated medical treatments, may directly cause the deterioration of the vein structure [7, 8, 12, 17]. Loon et al. (2019) reported that diabetes mellitus and chemotherapy treatment were associated with forced catheter intervention [13]. Piredda and colleagues (2019), as well as Carr and colleagues (2016), stated that the treatments of diabetes, venous disease, and cancer are closely associated with the difficult catheter intervention as they cause the reduction of blood vessel diameter [7, 17].

Dehydration is another risk factor for difficult catheter insertion as it causes the blood volume to decrease and the venous pressure to decrease, thereby rendering the detection of veins and consequently catheter insertion difficult. Dehydration is reported to lead to repeated catheter interventions [22]. However, in the study conducted by Sharp et al. (2018), a decrease of 0.57 mm in the diameter of the median cubital vein and 0.33 mm in the diameter of the cephalic vein was observed after oral rehydration. This could be related to the fact that drinking water may stimulate the sympathetic nervous system, which would then decrease the vessel diameter [23].

Emotional conditions of the individuals may also affect catheter intervention. Anxiety may lead to peripheral vasoconstriction, thereby increasing the difficulty of cannulation [24]. Having the patient lie in the during catheterization, using the muscle tensing technique, informing the patient regarding the procedure, and gaining the patient's confidence are a few factors that may reduce anxiety in the patients prior to the procedure, enabling better cannulation [25].
