Description of the condition
A central venous catheter (CVC) is a catheter which is inserted into a large central vein, with the tip of the catheter ideally placed within the superior vena cava (Schuster 2000). This enables the administration of medications and fluids, as well as the collection of blood specimens to avoid unnecessary venipunctures. The use of long term CVCs for the management of chronic medical conditions in infants and children has greatly improved the quality and safety of care provision. Long term CVCs are typically inserted when the administration of intravenous medication or nutritional support is required over a considerable time period. Hypertonic medications such as vesicant chemotherapy drugs, certain antibiotics, other supportive drugs and parenteral nutrition are not able to be safely administered through peripheral venous catheters. For children with cancer and other chronic medical conditions who require such medications, this safety issue is overcome by the insertion of a CVC which commonly remains in place for the duration of treatment (Gonzalez 2012). There are three types of long term CVCs: tunnelled catheters; implanted ports; and peripherally inserted central catheters (PICC). A tunnelled CVC is surgically inserted under the skin, with the catheter lumen(s) typically exiting from the chest or neck. An implanted port is also surgically implanted, but is placed entirely under the skin. The port reservoir is accessed with a needle through the skin. A PICC line is inserted into a central vein through the arm and thus is a narrower catheter.
Adverse events associated with CVCs may cause complications in up to 46% of children (Athale 2012). Adverse events include mechanical failure, infections and thrombotic complications, all of which can effect patient morbidity and mortality (Baskin 2009; Fratino 2005; Stocco 2012; Wong 2012). Mechanical failure is often attributed to catheter occlusion. Over time, it is common for a fibrin sheath to develop at the tip of the catheter. This may prevent aspiration of blood from the catheter and cause resistance when infusing fluids. An intraluminal clot can also occur, totally occluding the catheter. Occlusion can result in the need for the catheter to be removed (and replaced), interrupting and delaying treatment of the underlying disease (Shah 2007). Occlusions of CVCs are estimated to occur in 14% to 36% of patients within one to two years of catheter insertion (Fratino 2005) or at an incidence rate of 1.35 per 1000 catheter days (95% confidence interval (CI) 1.1 to 1.63) (Revel-Rilk 2010). Incidence rates of blood stream infection associated with CVCs differ depending upon the type of catheter, with rates reported between 1.40 per 1000 catheter days (95% CI 1.06 to 1.82) and 0.46 per 1000 catheter days (95% CI 0.29 to 0.69). Thrombotic complications are the rarest adverse events reported in children, with a lower incidence rate of 0.08 per 1000 catheter days (95% CI 0.04 to 0.16) (Fratino 2005).
Description of the intervention
A flush refers to solution being injected to clean the catheter of blood or fibrin buildup. This is commonly used when the catheter is accessed, between administration of medications, or before and after collection of blood specimens. A positive pressure lock is used when the catheter will not be accessed for a period of time, and refers to the technique used to ensure blood does not flow back into the catheter after it is flushed, which may otherwise clot and cause occlusion. Tunnelled CVCs and PICC lines are typically flushed and locked weekly, while implanted ports are flushed and locked every 4 to 6 weeks. A typical intervention for tunnelled catheters in children is to use between 1 ml to 3 ml (depending on the volume of the catheter) of 10 units/ml of heparin for a 24 hour to 7 day lock. For implanted ports, 5 mls of 100 units/ml is typically used for a 30 day lock (Davis 2013). However, there is debate regarding the effectiveness of heparin to prevent occlusion over such time periods, given its short half life (Young 2008). The evidence to support the use of heparin to prevent occlusion in adult CVCs is inconclusive and there is growing evidence to support the use of 0.9% sodium chloride to lock CVCs, particularly in the paediatric population (Bertoglio 2012; Lee 2005).
How the intervention might work
Heparin is used to prevent occlusion because of its anti-coagulant properties which are believed to prevent thrombus forming in the catheter. Alternatively 0.9% sodium chloride, when used with pulsatile flushing techniques and a positive pressure lock or positive displacement device, may be as effective in preventing thrombus formation in catheters - eliminating the need for heparin to be used.
Why it is important to do this review
Practices vary among institutions because of the lack of evidence regarding best practice to prevent occlusion of CVCs. The use of heparin is not risk free and in certain instances may actually cause harm including heparin-induced thrombocytopenia (HIT) (Barclay 2012). The mechanism of haemostasis in children is different when compared to adults, particularly in infants and very young children (Monagle 2010). Additionally, treatments for diseases such as cancer involve the use of medications which can affect coagulation; thus the use of heparin to prevent CVC occlusion should be judicious and evidence-based. While the risks of adverse effects from the use of heparin may be regarded as less than the potential occlusion of a catheter and subsequent replacement, it is important to ensure interventions are based on evidence.
There have been several trials (Goosens 2013; Schallom 2012; Schilling 2006), a systematic review (Mitchell 2009), and a Cochrane review protocol to review the use of heparin versus 0.9% sodium chloride to prevent occlusions in CVCs in the adult population (Lopez-Briz 2010). As evidence from adult studies is not directly transferable to paediatrics, a systematic review focused on infants and children is required.