Catheter-related infection is a major risk factor which can compromise vascular catheter studies.
Literature reviews provide only a small number of publications reporting implant-related infections in laboratory animals and how to prevent or manage them. However, there are a vast number of publications concerning human vascular catheter-related infection, and also many reports of animal models of implant infections showing that animals are not resistant to surgical and implant infections. As in vivo experiments become more complex and animals with vascular catheters are kept for much longer periods than in the past (i.e. weeks and months as opposed to hours or days), evidence of infection is likely to increase.
Microbial infections can originate externally, via the catheter lumen at the skin/catheter interface, and internally, via haematogenous spread from distant sites. All surgically-implanted foreign materials can potentially cause infection. Steps that can be taken to reduce infection include:
- Using a strict aseptic technique to reduce the risk of infection.
- Prophylactic antibiotics may help reduce the risk of infection, but should not be used to cover for deficiencies in aseptic technique; it is recommended that veterinary advice be sought before using antibiotics.
- Even where implantation has been performed under strict aseptic conditions, catheter infection from the animal's skin or blood borne from distant sites (e.g. wounds) is possible. A pre-operative health examination should be performed in all animals undergoing any experimental surgery to identify possible infection risks and exclude unhealthy animals from procedures.
Exit sites through skin represent a special challenge as the smooth, non-adherent surfaces of catheter tubing that are desirable for the intravascular portion will create a potential opening where it passes through the skin.
- Applying materials such as polyester meshes or velour to the catheter at the catheter exit site in the skin promotes the ingrowth of body tissue, and in this way can help to provide resistance to microbial infection.
- The use of subcutaneous flanges around catheters may also help to stabilise the skin and limit movement around the catheter exit site facilitating better sealing of skin around the catheter.
- Titanium materials also provide good biointegration at skin-to-implant interfaces and are worth considering when designing or choosing a vascular catheter.
Vascular access ports
Vascular access ports consist of an implantable chamber attached to the catheter. The chamber has a thick polymer septum which is capable of withstanding repeated punctures, and provided that specially designed (Huber) needles are used, it has a self-sealing action (Figure 2).
Puncturing the skin overlying the VAP is necessary to access the lumen. Since the septum of a VAP is very thick it gives stable support to the needle and it is possible to leave the needle in situ for many hours or days if required, provided it is suitably protected. Following needle withdrawal, no special care is required and infection rates associated with the use of VAPs are very much lower than for external catheters.
In addition to reducing infection rates and the need for protective dressings or jackets, VAPs can allow animals to be group-housed as the risk of damage to external implants is removed.
Potential problems associated with VAP implantation are dehiscence of overlying skin and displacement or inversion of the device if it is not securely anchored during surgery. Good surgical technique can help to prevent these problems and selecting small, low profile VAPs may help to prevent skin dehiscence.
Figure 1. A typical vascular access port with attached vascular catheter, suitable for use in larger laboratory animals.
Figure 2. Cross section of a vascular access port; the septum has been punctured with a right-angled Huber needle.
- Catheter locking has already been mentioned in connection with preventing thrombosis. Locking technique and solutions are also crucial in minimising infection.
- Whatever solution is used to lock a catheter, a strict aseptic technique must always be used.
- Adding antimicrobial agents to catheter lock solutions is possible but the potential influences of these substances on experimental outcome must be considered. It is inappropriate to use antibiotics reserved for clinical use in catheter locking solutions as this may give rise to bacterial populations with antibiotic resistance.
Resources and references
- Bradfield JF et al. (1992) Behavioural and physiologic effects of innaparent wound infection in rats. Laboratory Animal Science 42(6): 572-578.
- Sheretz RJ et al. (1995) Contribution of vascular catheter material to the pathogenesis of infection: the enhanced risk of silicone in vivo. Journal of Biochemical Materials Research 29: 635-645.
- Popp MB & Brennan MF (1981) Long-term vascular access in the rat: importance of asepsis. American Journal of Physiology 241 (Heart Circ Physiol 10): H606-H612.
- DaRif CA & Rush HG (1983) Management of septicaemia in rhesus monkeys with chronic indewelling venous catheters. Laboratory Animal Science 33 (1): 90-94.
- Goldmann DA & Pier GB (1993) Pathogenesis of infections related to intravascular catherisation. Clinical Microbiology Reviews 6(2): 176-192.
- Cooper GL et al. (1988) Possible role of capillary action in pathogensis of experiemtnal catheter-associated dermal tunnel infections. Journal of Clinical Microbiology 26(1): 8-12.
- Dennis MB et al. (1974) Long-term vascular access for animal studies. Journal of Applied Physiology 37(6): 978-981.
- Swindle MM et al. (2005) Vascular access port (VAP) usage in large animal species. Contemporary Topics in Laboratory Animal Science 44(3): 1-17.
- Guiding principles for preparing for and undertaking aseptic surgery: A report by the LASA Education, Training and Ethics section.
- Methods in vascular infusion biotechnology in research with rodents.
- Refining procedures for the administration of substances.
- Removal of blood from laboratory animals and birds.