Automated Insufflation

Automated insufflation devices are now widely utilised across Europe and the US, despite the additional equipment costs. Advocates suggest that insufflating carbon dioxide at controlled flow rates and pressures is convenient for the operator, and improves distension and patient compliance.

Early experience comparing a crudely modified laparoscopic insufflator to manual bulb insufflation of room air showed equivocal effects on luminal distension (Ristvedt et al. 2003). More recently, two

Enema Bags Used Hospitals
Fig. 5.4. Standard enema bag containing approximately 3 L of carbon dioxide for manual insufflation

studies (Yee et al. 2002; Iafrate et al. 2004) compared specifically designed automated CO2 insufflation devices with manual insufflation of room air. The first showed a modest improvement in distension using automated insufflation, particularly in the left colon (Yee et al. 2002). The second showed the insufflation methods were equivocal for luminal distension but that examination times were significantly longer (although less ileal reflux was encountered) using the automated device (Iafrate et al. 2004). These data might suggest that only a modest benefit, if any, is derived from using an automated device. However, one significant advantage of automated insufflation is that administration has been specifically designed for use with carbon dioxide. As discussed below, there is good evidence from the colonoscopic and barium enema literature that demonstrates greater patient comfort when using carbon dioxide compared to air, because of its relatively rapid absorption by the colonic mucosa (GRAnT et al. 1986; ChuRch and DElAnEy 2003). Recent evidence also suggests that automated insufflation produces significantly better distension when compared to manual insufflation of carbon dioxide, again particularly in the left colon (BuRling et al. 2005; RogAllA et al. 2004a).

At the time of writing, the authors are aware of only one commercially available device specifically designed for colonic insufflation (Fig. 5.5, Protocol colon insufflation system, E-Z-EM Inc, Westbury, NY, USA). This system electronically controls the flow rate of carbon dioxide increasing over time in a step wise fashion from 1 to 3 L/min to prevent spasm (1 L/min for the first 0.5 L, 2 L/min from 0.5 to 1.0 L, and then 3.0 L/min thereafter). The total volume of gas administered is displayed continuously and, if intracolonic pressure (measured at the rectal catheter tip) increases beyond the limit set by the user (up to a maximum of 25 mm Hg), the system automatically shuts down to prevent further insufflation and so reduces the risk of colonic perforation. In the latest version, insufflation automatically ceases when a total of 4 L of gas have been administered and then for every 2 L administered beyond this. To recommence insufflation, the operator needs to manually override this additional safety feature by pressing the start button.

The company's recommended technique is to insufflate the patient in the supine position. The pressure limit is set at 15 mm Hg initially, increasing to 25 mm Hg depending upon patient tolerance. Three litres of carbon dioxide are instilled (again dependent on patient tolerance), at which point the

Fig. 5.5. Automated colonic insufflator, connected to a thin rectal catheter, displaying the intraluminal rectal pressure and total volume of carbon dioxide administered

Fig. 5.5. Automated colonic insufflator, connected to a thin rectal catheter, displaying the intraluminal rectal pressure and total volume of carbon dioxide administered patient is asked if they feel gas on the right side of their abdomen - if not, insufflation is continued until they do, or until they feel uncomfortable. A CT scout is then performed to confirm adequate distension prior to data acquisition. For the prone acquisition, propping up the patient's chest with a pillow or foam wedge helps to optimise distension of the transverse colon. The authors use a slightly modified technique (described below), setting the pressure limit at 25 mm Hg initially and pausing insufflation if the patient becomes uncomfortable. In our experience, the volume of gas administered during automated insufflation varies widely between patients (for example between 2.6 and 8.0 L with a median of approximately 4 L). Larger volumes are occasionally necessary, mostly due to anal incontinence, small bowel reflux and colonic redundancy, but are paradoxically associated with significantly poorer distension. Clearly these individuals are a challenging group to distend optimally and although the total volume of insufflated gas is a useful guide to the eventual adequacy of distension, practitioners should not limit their insufflation merely according to the volume insufflated. Interestingly, we have found no demonstrable learning curve using the automated device, suggesting that once familiar with the device's controls, practitioners can independently achieve satisfactory results despite little prior experience.

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