Hernias are openings in the abdominal wall through which abdominal contents escape and protrude to the outside. Inguinal hernias (groin) are the most freguently encountered and probably the most dangerous when diving.
Of course, other types of hernia can occur, eg., umbilical (navel), incisional (post-operative), diaphragmatic (between the abdomen and the chest cavity), internal (a loop of intestine through an post-surgical adhesion), femoral (another type of groin hernia), and others much less frequently seen.
All hernias are dangerous, in that every one poses the threat of incarceration (entrapment), strangulation (entrapment with loss of blood supply), obstruction (blockage of the intestinal flow)and the possibility of death. That a hernia should be repaired goes without saying and an unrepaired hernia should be considered a contra-indication for diving until it is satisfactorily repaired. The diving danger has to do mainly with the effects of pressure on gas inside a loop of intestine.
Without repair, a previously asymptomatic hernia can be pushed out through the ring of the hernia and become entrapped. If this occurs with the straining and lifting of heavy tanks and gear, then the person dives to depth, the air in the trapped bowel really becomes larger due to the effects of Boyle’s law on ascent. This leads to strangulation-obstruction and a requirement for emergency surgery. Getting to a good surgical facility may not be so easily done in some of the places that we go to dive.
Theoretically this same process can occur with gas filled loops of intestine in any of the hernias described above.
Returning to diving after hernia surgery should be after complete healing of the wound and with the advice of the operating surgeon. The incision should be completely healed and there should be no other complications, such as pneumonitis or deep vein thrombosis. Weight-bearing of dive gear is a major consideration after hernia surgery.
Newer operations, such as the laparoscopic repair, should be advised on an individual basis. Generally, the wounds are much smaller and the repairs just as strong. The CO2 insufflated during the procedure should not be a factor if the postoperative period is two weeks or more since there is rapid absorption of the gas. There is also occasional collapse of the alveoli from the diaphragmatic pressure of the pneumoperitoneum (gas in the peritoneal cavity).