Peripheral intravenous cannulation is the most common minimally invasive procedure performed on hospitalised patients (Keleekai et al, 2016; Cooke et al, 2018), of whom up to 70% are estimated to require the procedure (Rickard et al, 2012). In many situations, such as an emergency, the insertion of a peripheral cannula will save a patient's life (Carr et al, 2016). More generally, peripheral cannulas are used for procedures ranging from the administration of injections and the delivery of nutrients and substances, such as blood and its products, to haemodialysis—they are familiar to health professionals in their daily practice (Farrelly and Stitelman, 2016; Smith and Schoch, 2016; Tokizawa et al, 2017). In the UK alone, one in three hospitalised patients have peripheral cannulas in situ (Boyd et al, 2011), costing about £29 million of the £4.5 billion that the NHS spends annually on clinical products in acute care (Guerrero, 2019).
Due to its proximity to the skin's surface and its diameter, the antecubital cephalic vein is commonly used in emergencies and in situations where vein access is difficult due to patient characteristics and medical conditions (Di Carlo and Biffi, 2012; Gonzalez and Cassaro, 2018). Examples of individuals in whom vascular access may be difficult include (Forsberg and Engström, 2018):
In children, in addition to physiological factors such as vein fragility and vein suitability, psychological factors, eg needle phobia, may contribute to failure to insert a venous cannula (Cook, 2016; Piredda et al, 2017; Orenius et al, 2018). Carr et al (2016) suggested that a number of factors, such as age and gender, can result in failure to insert a cannula on first attempt.
Failure rates on first attempt to insert a peripheral cannula range from 12% to 40% in adults and 24% to 64% in children (Sabri et al, 2013; Cooke et al, 2018). Goff et al (2013) and Cooke et al (2018) reported that in 23–28% of children aged between 2 days and 18 years four or more attempts may be required to insert a cannula. This places a great deal of strain on the child, their family and health professionals involved, especially in the case of non-cooperative children. In addition, failure to insert a peripheral cannula may have physical consequences for the patient, eg pain, tissue damage and infection (Piper et al, 2018). According to Witting (2012), infiltration and inflammation of the area will be visible in many cases where venous access has failed. This points to the importance of ensuring that the cannula is correctly placed on first attempt.
Techniques currently employed to improve vein access in both standard and emergency situations include venous visualisation techniques (transillumination through the use of normal light, infrared or sonography), and venodilation techniques (eg the use of gravity, fist clenching, vein tap and milking, tourniquet application, the use of local vasodilators such as nitroglycerin, applying topical heat, and stimulating the surface veins by striking them) (Sabri et al, 2013).
A number of studies have discussed the effect of applying heat locally to facilitate the insertion of a cannula. Warming techniques include the immersion of the hands in warm water for a few minutes, using digital moist heat application pads and applying heat using warming gloves before inserting the cannula (Kiger et al, 2014; Robinson-Reilly, 2017; Tasavori et al, 2017; Tokizawa et al, 2017; Yamagami et al, 2017; Sharp et al, 2018; Yamagami et al, 2018). Local application of heat expands the veins and reduces the contractile effect of the alpha-2 adrenergic. Research has shown that temperatures of between 39°C and 42ºC produce favourable vascular expansion (Yamagami et al, 2018).
The application of heat is widely used to improve peripheral cannulation. In a study undertaken in the USA, nurses used topical heat in up to 73% of cases to improve vein access in adult patients (Kiger et al, 2014). However, in almost all previous studies to investigate the effect of warming on facilitating cannula placement identified by the authors in a literature search, there were confounding variables, such as the skill of the operator, the visibility of veins, and vasoconstriction due to pain and anxiety subsequent to previous attempts to cannulate (Biyik Bayram and Caliskan, 2016; Robinson-Reilly, 2017). More research is needed to clarify the issue.
This study aimed to determine the effect of local warming on the antecubital cephalic vein diameter of adults.
Materials and methods
The present study was a prospective, non-randomised trial that was performed in the radiology department of a hospital affiliated with Guilan University of Medical Sciences. It involved 55 healthy participants recruited using convenience sampling, comprising university students (n=17) and nurses (n=38). All participants completed an informed consent form.
Sample
Student participants were recruited at two colleges affiliated with the Guilan University of Medical Sciences through a repeated process of invitation. Eligibility criteria for participation included:
The study initially involved 17 students; semester exams precluded greater numbers from volunteering. The remaining participants (n=38) were therefore recruited from among nurses working at the same centre by applying the same eligibility criteria.
Data collection protocol
Data collection was carried out in two phases. In the first phase, the researcher (AH) contacted people who had agreed to participate by telephone. During this contact, the information required was requested from the volunteers and recorded in the registration form; this included demographic information and details related to the eligibility criteria. If participants were eligible to take part, they were provided with the time and place where the intervention would take place.
During the second phase, participants read and signed an informed consent form, after which they completed the data collection form, which recorded all the study variables, bar the diameter of the cephalic vein. Each volunteer was then given detailed information about the intervention and the measurements to be recorded. One radiologist entered the measurements on each participant's registration form. To prevent any error in data registration, all the information, including measurement of each volunteer's cephalic vein diameter, was simultaneously entered in a data sheet.
Heating device
Before undertaking the study, the authors reviewed a number of articles on the use of heat to facilitate venous access (Fink et al, 2009; Sasaki et al, 2014) and postulated that a limitation of previous studies may have been the lack of an easy method to deliver heat at a constant temperature, which may have affected the results. To resolve the problem, a heating device was developed by the researchers with the assistance of a dedicated technical team. The device generates heat using an urban electricity source, powered by an AC adapter. It produces heat through a few internal delicate elements, which are designed to ensure that the temperature does not exceed 42ºC.
Tokizawa et al (2017) showed that it is safe to deliver a thermal stimulus of 40ºC ± 2ºC to the skin for 15 minutes. In addition to the internal elements, the device has one thermal sensor on the inside and another on the outside. The first sensor measures and displays the amount of heat generated by the device and the second acts as a safety mechanism, cutting off the flow of electricity when there is malfunction to prevent the skin burning. In addition to the measures described above to prevent harm to participants, the researcher was present at each intervention throughout the procedure.
The heating device has the following specifications:
After the heating device had been manufactured, field tests were undertaken to ensure that it conformed to the standards laid down by Guilan University's office for medical equipment and supplies, that it met local safety criteria and also the specifications of the Iranian Patent Office. These bodies were satisfied with the operation of the device and subsequently approved its registration.
Working phase
The goals and phases of the research were explained to participants and their informed written consent was obtained. They were then asked to refrain from using stimulants such as cigarettes, tea and coffee for at least 2 hours before the ultrasound was performed. Initial ultrasonography was undertaken on the forearm area and the right-hand cubital area of each volunteer by a qualified radiologist. The heat device was subsequently applied over the area, which was heated to 42ºC for 10 minutes. The second ultrasound of the target area was similarly immediately followed by the application of heat, which was undertaken by the same specialist who had performed the first ultrasound.
The main researcher (AH) was present alongside each volunteer at each stage: he asked questions about any symptoms of burning and also examined the heated area to check for signs of possible burning. The data were recorded on the registration form.
Data analysis
The statistical software package SPSSv19 was used to analyse the data. To describe the data, statistical indices such as number, minimum, maximum, mean and standard deviation were used. To analyse the hypotheses, the Mann-Whitney and Spearman statistical tests were used. The level of significance was 0.05.
Ethical considerations
The proposal was approved by Research Ethics Committee of Guilan University of Medical Sciences (reference number 2930043002) before the study was undertaken, and all the steps of the research were registered with the Iranian Registry of Clinical Trials under IRCT201405281048N4 (further information at www.irct.ir). All participants were adults and enrolled to participate voluntarily.
The intervention was non-invasive—both in its application of the heating device and measurement steps—and precautionary measures, ie the device safety mechanism and having the researcher present throughout, were put in place to avoid injury to participants. The objectives of the study and information about the research method used were explained to the volunteers. They signed the informed consent sheet and participated in the research without payment.
Results
All 55 subjects completed the study. There was no attrition and no adverse events were reported, such as burning of skin. The majority (64%) of subjects were women. Participants' characteristics were as follows:
The data showed that the application of heat changed the cephalic vein diameter by 0.43 ± 0.4 mm (confidence interval (CI), 0.88 to 0.04). The difference in vein diameter was statistically significant (P <0.05) (Table 1). However, the difference in cephalic vein diameter changes between men and women was not significant (P =0.570) (Table 2).
| Variable | Minimum–maximum (mm) | Mean (mm) | P |
|---|---|---|---|
| Vein diameter (before) | 1–7 | 3.78±1.22 | P<0.05 |
| Vein diameter (after) | 2–8 | 4.21±1.28 | Significant |
| Gender | Mean (±SD) | P |
|---|---|---|
| Men | 0.46 (0.42) | P=0.57 |
| Women | 0.42 (0.33) | Not significant |
The results showed that, although the change in cephalic vein size has a negative correlation with age and BMI, this was not statistically significant (P >0.05) (Table 3).
| Variable | Correlation | P |
|---|---|---|
| Age | -0.2 | P=0.18 |
| Body mass index | -0.08 | P=0.49 |
Discussion
Applying heat to achieve vasodilation is a known technique, and health professionals have adopted a range of methods to apply heat to improve peripheral cannulation (Fink et al, 2009; Kiger et al, 2014; Biyik Bayram and Caliskan, 2016). However, there is a limited number of studies to assess how the application of heat affects vein diameter. The results of the authors' study indicate that local warming can increase cephalic vein diameter in the antecubital area by about 0.43 mm.
A experimental study undertaken with a group of adult patients receiving chemotherapy showed that applying heat increased the success rate on first attempt cannulation by about 27.5%% and reduced the time needed for cannula insertion by about 39% (Biyik Bayram and Caliskan, 2016). According to the results of a recent study (Yamagami et al, 2017), heat application increased cephalic vein diameter by at least 2 mm in the intervention group compared with the controls.
In the authors' study, the relationship between heat-induced venodilation and gender was not found to be statistically significant. Although there was a negative relationship between age and venodilation in this study, this was not statistically significant. The authors were unable to find any research on the application of heat to improve venous access that concurrently explored the relationship between age and the extent of diameter change. However, the relationship between vein flexibility and the non-responsiveness of veins in older people to local stimuli, such as heat, has been mentioned (Gabriel, 2017). Indeed, the lack of any recorded relationship in previous research between age and change in vein diameter could be due to the fact that participants in these studies were children or young adults; they did not include older adults.
The results of the authors' study showed that BMI did not influence the effect of heating on cephalic vein diameter change. Tasavori et al (2017) analysed the effect of warming on vein cannula insertion among overweight people, concluding that local warming can increasing the visibility and palpability of peripheral veins, helping to reduce the number of attempts needed and the duration of cannula insertion. Regarding the lack of a relationship between BMI and change in vein diameter, this result may have been due to the small sample size in the authors' study.
In the authors' research, a tool was used to apply dry heat to the intended vein. The decision to use dry heat was based on the results of Fink et al's (2009) study, which found that the use of dry heat increased the success rate of vein cannula insertion by about 2.7 times on first attempt compared with the use of moist heat. The research presented here showed that the application of heat locally affected the diameter of veins, which may facilitate cannula placement.
The results of the authors' study also showed no significant relationship between gender and change in cephalic vein diameter following the application of heat. This would suggest that local warming has an equal effect on increasing vein diameter in both men and women. However, the authors were unable to find any previous studies exploring the relationship between gender and change in vein diameter due to the use of heat, so further research is required.
The studies on the application of heat to facilitate venodilation found by the authors as part of a literature search investigated the variation in the success rate of inserting vein cannulas following the application of heat packs, but they did not explore the skill of the nurse undertaking the procedure as a variable (Fink et al, 2009; Kiger et al, 2014; Biyik Bayram et al, 2016).
Other researchers (Lund et al, 2012; Herrmann-Werner et al, 2013), however, found that the skill of the practitioner can have a profound effect on the success rate of cannulation. Further studies in which heating devices are applied at a constant, controlled temperature in real situations and in which the skill of the practitioners is also evaluated are therefore warranted.
Limitations
The results of the study reported here should be considered with caution. The major limitation of this research is the non-random sampling method used to select volunteers, who were healthy and in whom the results differed from those reported in patient groups. In additional, since participants were in the 20–40 year age range, the results may not be generalised to younger or older groups for whom vein cannula insertion poses a range of difficulties.
Conclusion
The results of this research showed that the application of heat increases the diameter of the cephalic vein in the antecubital area. It also showed no relationship between the variables gender and BMI and the increase in vein diameter. The results also indicate that applying heat using a simple technique and tools similar to the intervention used in the authors' research can assist to make vein cannula insertion easier.
It could therefore be suggested that local warming could be used to improve venous cannulation in circumstances when vein cannula insertion may be difficult.