Technical recommendations for measurements of sensory threshold and compliance have been published in adults, and the general principles apply to practice in children [3]. However, sensory threshold assessment requires an adequate cooperation for the report of the sensations and feelings by the subject. Children younger than 7–8 years may not be able to relate adequately their sensations during the procedure. Explanation on equipment and sequence of the procedure must be given to the child and the parents. Because psychological state modulation results in changed sensation at a given stimulus in healthy adult subjects [4], environment and sequence of the barostat study should be as quiet as possible in order to minimize the external influences and standardize the procedure.

For rectal sensitivity studies in children, most authors do not clean extensively the colon but rather suggest to the child to go to the bathroom before the study. For study compliance in children with constipation, cleansing of the rectum with enema should be conducted the day before the barostat study. Because meal may interfere with colonic and gastric tone, a 4–6-h fasting period prior to the study is recommended. All medications affecting pain or gastrointestinal motility should be discontinued at least 48 h prior to the barostat procedure.

For rectal studies, the patient lies in the left lateral position and the catheter is gently inserted into the rectum. For gastric studies, the catheter is inserted by mouth. The catheter is secured with a tape and 5–10 min is allowed for adaptation before beginning the procedure. The barostat bag is then slowly inflated with 30 mL of air and the pressure is allowed to equilibrate for 3 min. The average bag pressure during the last 15 s defines the individual operating pressure (IOP) also called the minimal distending pressure (MDP) which is the minimum pressure required to overcome mechanical forces and inflate the bag with 30 mL of air.

Various distension protocols have been described [3]. In children, the ascending method of limits (AML) without [5–7] or with [8–13] tracking has been the most applied. In the AML, the barostat is programmed to deliver phasic intermittent stimuli starting at the IOP progressively increased in 2–4 mmHg steps lasting 60 s followed by 60 s deflation. When the first sensation of pain is reported, the study can be stopped (the sensory threshold is determined) or can be prolonged (tracking) by subsequent distensions randomly adjusted up or down depending on the response of the previous distension (if the subject reports pain, the next distension will be decreased or kept the same; if the subject reports no pain, the next distension will be increased or kept the same). The threshold is determined by averaging the pressures at which pain had been indicated after a series of measures (usually three) (Fig. 13.2). A four- to five-point scale [6, 10] is used as a verbal descriptor for sensation felt during the barostat procedure. The AML is vulnerable to psychological biases (fear of pain) because the stimuli are predictable to the subject. The tracking technique is believed to be more reliable because it is less vulnerable to psychological bias (the stimuli is unpredictable) and because there are multiple determinations of the threshold. On the other hand, the tracking technique necessitates delivering multiple painful stimuli that can be less acceptable in children. However, the tracking method has been used successfully without any adverse event by several pediatric groups [8–13]. Of note the majority of children tested report that the pain sensation felt during the barostat is notably lower than the pain felt in the real life.