Chapter 14 Progressive Preoperative Pneumoperitoneum for Hernias with Loss of Abdominal Domain
1 Clinical Anatomy
1 Features/Characteristics of the Defect
Definition of Loss of Abdominal Domain
There is no consensus in the literature on the definition of loss of abdominal domain. Determination of this condition is subjective and typically refers to massive hernias with a significant amount of intestinal contents that have herniated through the abdominal wall into a hernia sac that forms a secondary abdominal cavity. On physical exam, the inability to reduce the herniated contents below the level of the fascia when the patient is lying supine should raise suspicion of the diagnosis. Although the surgeon can often make the assumption that a patient has loss of domain on physical exam, we utilize computed tomography (CT) to determine the true nature of the hernia.
2 Measuring Loss of Domain
We define a loss of abdominal domain on CT scan as greater than 50% of the intestinal contents lying outside the native abdominal cavity in the hernia sac. This may be more accurately defined when the ratio of the volume of the hernia sac to the volume of the abdominal cavity is ≥0.5.
A sagittal reconstruction of the CT scan is used to measure the length of the hernia sac from the top to the bottom of the sac. The length of the abdominal cavity is measured from the top of the diaphragm to the inferior aspect of the symphysis pubis (Fig. 14-1, A).
Axial reconstructions are used to measure the width of the hernia sac and abdominal cavity at their widest point. The height of the hernia sac is measured from an imaginary line drawn across the hernial orifice to the apex of the hernia sac at its tallest portion. The height of the abdominal cavity is measured from the anterior portion of the fourth lumbar space to an imaginary line drawn across the hernial orifice (see Fig. 14-1, B).
Using the formula to measure the volume of an ellipsoid (V = 4/3 × π × r1 × r2 × r3), the hernia sac and abdominal cavity volumes can be measured and compared. To simplify the ellipsoid volume equation, multiply the length, height, and width measurements of the cavities times a factor of 0.52 (V = 0.52 × L × H × W). Loss of domain exists when the ratio of the volume of the hernia sac to the volume of the abdominal cavity is ≥0.5.
Physiology of Hernias with Loss of Abdominal Domain
In patients with loss of abdominal domain, the bowels reside outside the abdominal cavity. As intraabdominal pressure decreases to approach atmospheric pressure, abdominal viscera become edematous and their vasculature becomes engorged. This makes simple hernia reduction nearly impossible. In addition, respiratory function is altered secondary to the loss of diaphragmatic support, and anterior spinal support fails, leading to lordosis.
4 Physiology of Progressive Preoperative Pneumoperitoneum
The immediate reintroduction of viscera and abdominal reconstruction in patients with loss of domain can result in a significant increase in intraabdominal pressure, which can lead to abdominal compartment syndrome and its resultant ill effects. Progressive preoperative pneumoperitoneum (PPP) attenuates the adverse physiologic effects associated with ventral hernia repair in patients with a loss of abdominal domain.
Insufflation of the abdominal cavity acts as an intraperitoneal pneumatic tissue expander and lengthens the abdominal wall musculature, increasing the volume of the abdominal cavity. This allows for adequate accommodation for the herniated contents.
The pneumoperitoneum also dissects throughout the intraperitoneal cavity providing a pneumatic lysis of adhesions aided by gravity as the bowels are suspended by their adhesions within the hernia sac.
Physiologically, PPP slowly creates a chronic abdominal compartment syndrome. With decreased diaphragmatic excursion, the patient is forced to overcome the inherent decreased inspiratory capacity. Additionally the adverse cardiovascular effects of acute abdominal compartment syndrome are attenuated by the slow introduction of intraperitoneal air.
2 Preoperative Considerations
1 Physical Examination
The physical exam alone is often helpful in determining whether a patient has loss of domain. With the patient lying supine on the examination table, the surgeon should attempt to reduce the herniated contents below the fascia. If the hernia does not reduce because of the amount of herniated contents, the patient likely has loss of domain
The abdominal wall should be examined for elasticity. Although some massive hernias may be irreducible, the patient’s abdominal wall musculature may have such laxity and elasticity that it could accommodate the herniated contents easily at the time of surgery. This finding would obviate the need for PPP because single stage repair may be feasible.
The quality of the skin should be examined to determine if any adjunctive maneuvers will be required to obtain safe skin closure at the time of hernia repair.
Wide thin scars, ulcerated skin, thin subcutaneous tissue with tense and immobile skin, and large pannus flaps should all raise concern over skin closure. Consultation with a plastic surgeon may help determine the need for preoperative tissue expanders, panniculectomy, or complex skin closure at the time of hernia repair.
2 Computed Axial Tomography
As previously described, the volume of the hernia sac and abdominal cavity are calculated and compared. A volume ratio of the hernia sac to the abdominal cavity of ≥0.5 should raise the suspicion of loss of abdominal domain.
Other attributes of the abdominal wall should be examined on CT because they may determine the utility or futility of preoperative pneumoperitoneum.
In our experience, patients with small defects and a significant amount of herniated contents benefit the most from preoperative pneumoperitoneum.
Patients with round-shaped abdominal cavities and thick, robust rectus abdominis and oblique muscles may experience less muscle lengthening with preoperative pneumoperitoneum compared to those with a more ellipsoid appearance to the abdominal wall and thin atrophic musculature.
Patients with “open book” abdomens, such as those with significant loss of abdominal wall substance (missing abdominal wall musculature) and hernia defects that span the entire abdominal wall, may not benefit anatomically from preoperative pneumoperitoneum because there may not be enough abdominal wall musculature to stretch. The physiologic benefits may still be realized however.