What is Inflow and outflow pain in Peritoneal Dialysis?
Occasionally, patients complain of pain upon infusion or drainage of PD fluid. Infusion pain can result from infusion of an inappropriately cool or warm PD solution, peritoneal sensitivity to the lower than physiologic pH of PD solution (i.e., 5.2 to 6.4), visceral sensitivity to a directed jet stream of PD fluid from the PD catheter, or a malpositioning of the PD catheter against the viscera. Discomfort during drainage (“drain pain”) of PD effluent usually relates to a siphoning effect on the viscera or peritoneum and may therefore also relate to catheter positioning. The effect of constipation on expansion of intestinal diameter and resultant crowding of the viscera around the catheter should not be minimized as a cause of either fill or drain pain.
Timing and duration of the pain usually provide the diagnostic clues as to which of the aforementioned issues are causative and therefore crucial to discerning appropriate treatment. Transient pain related to inappropriate temperature can be adequately managed with proper patient instruction. Pain related to the lower pH of the PD solution is also transient in nature, given the rapid increase in the PD fluid pH to physiologic levels. The use of neutral pH PD solutions can address this issue if available. Although addition of bicarbonate to the PD solution prior to peritoneal infusion can also help reduce pain, introduction of any exogenous substance to the PD fluid theoretically may increase infection risks. Alternatively, patients can leave a small residual volume of PD fluid in the abdomen at the end of the drain phase of the exchange. This residual volume serves as a buffer to the inflowing dialysate and reduces the tugging sensation associated with the last phase of the drain. Use of “tidal” therapy with APD accomplishes the same effect. Tidal PD can also reduce nightly alarms during cycler treatment related to sluggish PD catheter outflow. However, caution should be taken to avoid too large of a residual volume so as to avoid a total IP volume that may cause clinical problems. Effective treatment of constipation should always be undertaken as a simpler means to relieve either fill or drain pain prior to considering leaving a residual volume after each exchange.