♦ A nasogastric tube is placed after induction of anesthesia. The patient should be placed in lithotomy position, with the buttocks brought to the edge of the table and propped on a folded towel. The legs should be carefully positioned on wooden skis or leg supports with proper padding and care paid to pressure points. Both the abdomen and perineum should be prepared with antiseptic solution in standard fashion before draping both areas to allow for access to the anus and entire abdomen. Alternatively, in infants, the entire body from the upper abdomen to the feet may be prepped in total, and feet and legs placed in stockinettes (Fig. 19-1). One may then have an assistant elevate both legs during the transanal anastomosis portion of the procedure. Once the patient is prepped, a Foley catheter should be inserted into the urinary bladder. Before the incision is made, the entire table should be placed in a slight Trendelenburg position.

♦ The classic appearance of the proximal (ganglionic) bowel shows an extremely hypertrophied muscular wall, with a loss of the taenia coli (Fig. 19-2). The transition zone between aganglionic and ganglionic bowel can be made by a combination of visual inspection and a series of frozen sections. Once the presence of normal ganglion cells is identified, the bowel should be transected with a stapling device above the transition zone (ideally about 5 cm proximal or cranial to this point). This step is recommended because the level of aganglionosis can vary around the circumference of the colon, and proceeding more proximally will help to ensure that the selected bowel will have essentially normal pathology throughout. Both the proximal bowel and distal bowel are then mobilized, with the latter dissected to around 2 to 4 cm above the peritoneal reflection. Traction sutures are then placed at the end of the proximal colonic segment to facilitate the pull-through.

♦ Beginning on the distal bowel, a 2-cm segment just below the level of the peritoneal reflection should be cleared of serosa, mesentery, and pericolonic fat. The seromuscular layer is then incised by electrocautery down to the level of the submucosa. This incision is extended circumferentially using a hemostat. Dissection is carried further using a Kitner to perform blunt dissection, or in infants or neonatal patients a cotton-tipped applicator can be used effectively for this purpose (Fig. 19-3).

♦ Once established, this plane of dissection is continued distally. Upward pulling on the traction sutures of the distal rectum is necessary to provide helpful countertraction. A helpful addition is the placement of other traction sutures into each quadrant of the muscle cuff as the dissection progressively develops (Fig. 19-4). Without the application of this countertraction, the dissection becomes ineffective, and one cannot proceed distally to an adequate level. Electrocautery should be used to coagulate larger communicating vessels between the submucosa and muscular cuff. The dissection should be carried out to within 0.5 cm of the dentate line in neonates and approximately 1 cm in older children.