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Two-thirds of health-related occupational exposures to blood-borne infections are associated with hollow-bore needles, over a third occurring after the procedure but during or after disposal [1]. Recent European legislation means that the use of safety needles and iv cannulae will soon become mandatory [2].

Most safety cannulae previously evaluated [3–6] have involved modifications to the usual cannulation mechanism, such that the operator’s technique requires altering. The Vasofix® Safety cannula (B. Braun Medical Ltd, Sheffield, UK) has a self-activated clip that shields the needle’s tip when retracted, allowing the cannula to be inserted in exactly the same way as for standard cannulation (Fig. 3). We conducted a randomised, controlled study comparing the Vasofix® Safety and standard Venflon™ (BD, Oxford, UK) cannulae.

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Figure 3.  Vasofix® Safety intravenous cannula (a) before insertion and (b) the needle’s tip once withdrawn from the cannula with the safety mechanism activated.

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After Research Ethics Committee approval and informed consent, 105 adults presenting for elective surgery were randomly assigned to undergo peripheral venous cannulation using a 22-G Vasofix® (n = 62) or Venflon™ (n = 43). Visual analogue scales were used to assess ease of cannulation, flashback of blood; sticking of the needle within the cannula; threading of the cannula into the vein; spillage of blood; and injection through the port once sited. We had no data indicating ease of cannulation to inform a power calculation, although a calculation based on VAS for pain, using data from previous studies [3–6], suggested a sample size of 150 patients per group. Data were compared using Mann–Whitney Fisher’s exact test as appropriate, a value of p < 0.05 denoting statistical significance.

The study was stopped after 105 patients had been recruited, because the manufacturer of the Vasofix introduced an improved design based on feedback from users, such that the type of cannula we had been studying was no longer the one marketed. Insertions were by 23 anaesthetists, with varying previous experience of the Vasofix. The Vasofix was more difficult to site than the Venflon, with slower flashback, more sticking of the needle within the cannula, and more difficulty threading the cannula, though there were no differences in blood spillage, ease of injection through the port, or overall pain of insertion (Fig. 4). There were no failures of the Vasofix safety mechanism and no needlestick injuries.

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Figure 4.  Visual analogue scales (VAS; mm) for characteristics of the Vasofix® Safety and Venflon™ intravenous cannulae: (a) ease of insertion; (b) flashback of blood; (c) sticking of the needle within the cannula; (d) threading of the cannula into the vein; (e) spillage of blood during insertion; (f) ease of injection through the port; (g) pain on insertion. In all cases except pain on injection (g) a VAS of 100 mm represents the ideal cannula; for pain on insertion a VAS of 0 mm represents no pain and 100 mm represents the worst pain imaginable. The horizontal line represents median; the box the IQR, and the whiskers the range. p = 0.0001 for (a–d).

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Since our study was not blinded we cannot exclude a bias against the Vasofix, and the participating anaesthetists were overall more experienced with the Venflon than with the Vasofix. However, even those with over 100 previous insertions were assigning lower scores to the Vasofix. Further, we only studied a single size, 22 G, and cannot extrapolate our findings to larger sizes. We stopped our study before the target number of participants was reached, but felt that proceeding with an obsolete model would provide little extra useful information. Communication with the manufacturer indicates that both the sticking and the flashback have been specifically addressed in the new version, along with improvements in the design of the needle’s tip (B. Braun, personal communication).

Our study demonstrates the risk that new devices introduced to solve a particular problem may merely exchange it for another [7, 8]. It also highlights the need for new equipment to be fully evaluated before their wholesale adoption [9], and the importance of manufacturers’ supporting such studies and willingness to adapt their products accordingly.

Acknowledgement

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We are grateful to B. Braun for supplying the Vasofix cannulae and photographs.

References

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  2. Acknowledgement
  3. References