Chlorhexidine contamination of equipment used in central neuraxial anaesthesia has been implicated in causing adhesive arachnoiditis. We measured the extent of chlorhexidine splash during pouring into a gallipot (antiseptic skin preparation container) from heights of 5 cm, 10 cm, 15 cm and 20 cm. Twenty experiments were performed at each height. Measurements made up to a horizontal distance of 40 cm radius from the gallipot showed a median (IQR [range]) maximum spread of splash droplets ≥ 2 mm diameter of 26.2 (10.2–36.4 [0–40]) cm. The 40-cm radius measurement area was divided into 5-cm-wide zones to assess spread. At pouring heights of 15 cm and 20 cm, all zones were contaminated. These results demonstrate that pouring chlorhexidine into a gallipot generates significant splash, and we recommend that this should be avoided near equipment used for neuraxial anaesthesia.
Avoidance of infection-related complications following neuraxial anaesthesia is of paramount importance . Cleaning the entry site with an antiseptic solution forms an important part of aseptic technique. Chlorhexidine is a commonly used antiseptic agent that is recommended by various medical bodies [2, 3]. However, there is considerable controversy regarding the use of chlorhexidine because of the purported risk of chronic adhesive arachnoiditis and its debilitating long-term consequences [4, 5].
There is particular concern about the potential for chlorhexidine contamination of central neuraxial anaesthesia equipment. After a medicolegal hearing concerning a case of arachnoiditis subsequent to spinal anaesthesia, the judge concluded that contamination of the anaesthesia equipment by as little as 0.1 ml chlorhexidine could have been responsible; a multi-million pound settlement was made in favour of the plaintiff [4, 5]. In this case, it was suggested that chlorhexidine poured into a container kept on the sterile area might have contaminated the spinal anaesthesia equipment .
Although there is debate about the minimum volume and concentration of chlorhexidine that may cause arachnoiditis, it is prudent to avoid contamination wherever possible . We designed this study to assess the spread of chlorhexidine splash occurring during pouring into a gallipot container from a neuraxial anaesthesia pack, using a standardised equipment set-up.
An empty chlorhexidine bottle (Ecolab Ltd, Leeds, UK) was fixed to a mounting system (Fig. 1a) of adjustable height. The bottle, with its cap removed, was tilted downwards at an angle of 25° from horizontal. An 80-ml rectangular gallipot (Basic Universal Set 199.20; Vygon, Écouen, France) used to hold antiseptic solution, with maximum dimensions 74 mm × 63 mm × 28 mm, was placed directly under the spout of the bottle (diameter 24 mm), with the long axis of the gallipot in line with the long axis of the bottle.
A funnel (Fig. 1b) was inserted into a small hole made near the base of the bottle, through which a solution of 0.5% chlorhexidine with 70% alcohol (Ecolab Ltd) could be introduced; 600 ml chlorhexidine was coloured red with 12 ml carmoisine E122 dye with ethanol (Ecolab Ltd). The residual volume of the bottle below the spout was primed with chlorhexidine (Fig. 1, arrow).
For each experiment, an A0 size sheet of white paper (1189 mm × 841 mm) was placed beneath the apparatus. The bottle was fixed at a height measured from the lowest point of the mouth of the bottle to the base of the gallipot (Fig. 1c); 40 ml chlorhexidine was poured into the funnel over 5 s in order to half-fill the gallipot. Five seconds after the end of pouring, a cup was hung underneath the spout of the bottle to stop any further flow. Experiments were performed at bottle heights of 5 cm, 10 cm, 15 cm and 20 cm and were repeated 20 times at each height.
Each sheet was photographed with a digital camera (EOS 600D; Canon, Tokyo, Japan). Using digital image editing software (Photoshop CS4; Adobe, San Jose, CA, USA), 1-cm-wide concentric measurement rings centred on the gallipot were added up to a radius of 40 cm (Fig. 2). For each experiment, the maximum distance of splash droplets ≥ 2 mm diameter was recorded up to the limit of 40 cm. Concentric zones of 5 cm width were analysed for the frequency of splash droplets ≥ 2 mm diameter.
A total of 80 experiments were performed at the four measurement heights. The maximum recorded splash distance at each individual height is shown in Fig. 3. Combining data from all heights, the median (IQR [range]) of the maximum recorded splash distance from the centre of the gallipot was 26.2 (10.2–36.4 [0–40]) cm.
The frequency of contamination in different 5-cm-wide zones is shown in Fig. 4. At a pouring height of 5 cm, contamination occurred in only one zone in three experiments; the zone was different in each of these three experiments.
Chlorhexidine splash was recorded at all the pouring heights studied, with spread at pouring heights of 15 cm and 20 cm that was up to the 40-cm maximum radius that was analysed in the photographs. Even at the lowest pouring height of 5 cm, splash was recorded at a distance of 10.2 cm.
These results demonstrate that pouring chlorhexidine into a gallipot is likely to contaminate neuraxial anaesthesia equipment in the vicinity. For example, in our hospital, regional anaesthesia trolleys have surface dimensions of 45 cm × 45 cm. This study recorded splash up to 40 cm away from the gallipot, suggesting that equipment placed anywhere on such trolleys would be at risk of contamination.
It is known that measurable volumes of chlorhexidine are neurotoxic, as shown by a recent case of accidental injection of 8 ml chlorhexidine 0.5% into the epidural space [5, 7]. However, the minimum volume of chlorhexidine that may cause chronic arachnoiditis is not known. The ruling in the recent medicolegal case concerning arachnoiditis subsequent to spinal anaesthesia speculated that a contamination volume as small as 0.1 ml chlorhexidine might have been responsible [4, 5]. We believe that while the minimum volume of safe contamination is unknown, one should aim for zero contamination of neuraxial anaesthesia equipment in view of the severe morbidity associated with chronic arachnoiditis.
Considering our evidence, to prevent any contamination chlorhexidine should not be poured into a gallipot kept on the same tray as the equipment for neuraxial anaesthesia. Alternative methods of applying antiseptic solutions should be employed; for example, the neuraxial anaesthesia tray may be kept unopened or covered until the antiseptic solution has been prepared and applied to the patient's back. Pouring may be avoided altogether if pre-soaked antiseptic sponge applicators (swabsticks) or sprays are used. However, these applications may entail their own risks of contamination. Antiseptic solutions may drip and contaminate the operator's gloves . A recent case report describes adhesive arachnoiditis following spinal anaesthesia in which chlorhexidine was applied with a swabstick . Antiseptic sprays may result in aerosol contamination, or miss an area thereby compromising sterility . These risks need to be evaluated, with appropriate measures taken to reduce them.
Chlorhexidine was chosen for this study because it is a commonly used antiseptic and because it has been implicated in chronic arachnoiditis [4-8, 10]. However, it is possible that other antiseptic agents may also be implicated in neurotoxicity. For example, an in-vitro study demonstrated that both povidine-iodine and chlorhexidine were toxic to human neuronal cells . It is likely that other antiseptic agents have similar splash distances to that shown for chlorhexidine in our study, and it would be prudent to use similar precautions for any agent.
This study did not measure splash beyond 40 cm. The interquartile range of the measurements made at a 20-cm pouring height was narrower than those at other heights (Fig. 3), suggesting that the maximum spread lies beyond the 40-cm limit of our recording. Furthermore, only splash drops having a diameter ≥ 2 mm were analysed because of technical limitations to the study. The results that we present therefore underestimate the overall frequency of contamination.
Our study was carried out in a controlled and simulated setting. It may not, therefore, have fully replicated the hand movements or the various angles at which the bottle may be held during actual pouring by a practitioner. We chose to do a simulated study instead of using human subjects as it would have been impossible to blind subjects to the fact that splash was being measured. Without blinding, it is quite possible that the subject under observation would have been extraordinarily careful when pouring, leading to splash recordings that did not represent those found in actual clinical practice. Due to the complexities involved, we did not measure the total area occupied by the recorded splash droplets. This information, combined with knowledge of the total area occupied by the neuraxial anaesthesia equipment, would have enabled us to calculate the probability of equipment contamination.
In conclusion, the results of our study demonstrate that pouring chlorhexidine into a gallipot generates splash that spreads considerable distances. We therefore recommend that antiseptic solutions are not poured into gallipots located adjacent to equipment to be used for neuraxial anaesthesia. Covering the regional anaesthesia tray until after the back has been prepared with antiseptic should minimise the risk of contamination, and thereby help prevent devastating antiseptic-induced neurological morbidity.
No external funding and no competing interests declared.