Risk Factors for Surgical Complications in Ventral Hernia Repair

Risk for early complications following ventral hernia repair rises with an increase in hernia aperture size. The direct relationship between hernia size and frequency and severity of surgical complications shown in the present material has not previously been described. This correlation was strong, indicating that hernia aperture size is of great importance in the preoperative risk evaluation of patients. The odds ratio of 1.01 means that the odds for a surgical complication increases by 1% for each mm increase in aperture size. This analysis shows a proportional relationship between hernia aperture size and Clavien complication class, thus telling us that there is no obvious cut-off size. One possible reason why this correlation has not previously been described is that most reports have come from retrospective studies where the size of the hernia aperture was unknown. When assessing a patient for ventral hernia repair, one must take into account hernia size, though it must be emphasised that not all ventral hernia patients need surgery and that most hernias increase in size with time [14]. Early incisional hernias grow rapidly and often involve the whole length of the incision if not repaired in time. Around 50% of incisional hernias manifest within the first 12 months [15]. Late hernias are less well described and are presumed to be result of failure of collagen in the scar [16]. Intraoperative measurement was used as determinant of the hernia aperture size. In a previous study of abdominal rectus diastasis, clinical assessment corresponded more precisely to the intraoperative measurement of the hernia than a CT scan [11]. Thus, a preoperative clinical assessment is considered to correspond to the calculated risk estimates in the present study. However, the clinician should be aware that the time span between clinical assessment or a CT scan and the time of surgery may allow for an increase in the hernia size. The fact that hernia size manifests as the solely most important risk factor for early surgical complications challenges two cornerstones in hernia treatment: watchful waiting [17] and delay of surgery in attempt to reduce weight [18]. Both these concepts must be held against the risk of an increasing hernia size. Since the natural course of early appearing incisional hernias often means extension to the entire previous incision, a prompt repair might be advocated even in patients with moderate symptoms. Watchful waiting may still be justified with a small asymptomatic hernia and high comorbidity. However, with increasing hernia size a choice must be made whether or not to apply lifelong conservative treatment. Watchful waiting concept is partly a reaction to the fact that recurrence rates with long-term follow-up is quite high and also that morbidity and mortality rates after incisional hernia repair are troublesome [19]. The same is true for obesity where a high BMI affects recurrence rates, increases infection rates and also adds a considerable risk if an emergency intervention may become necessary. Furthermore, it is well known that physical training is often embarrassed by spatial effects of the hernia per se.

To assess the most appropriate treatment principle, knowledge of the natural course of ventral hernia is important. A small incisional hernia occurring early post-laparotomy should be repaired while it is still small. These hernias almost always expand over time and extend to the entire incision leading to substantial comorbidity [14]. Current analysis states the importance of timing and suggests that prompt intervention in some cases is beneficial. Watchful waiting studies have sometimes prioritised analysing risk of acute intervention, thus neglected the risk of a more complex repair at the time of intervention [14, 20].

There are reports in the literature [21] indicating concomitant bowel surgery to be a risk factor for surgical complication. In the present study, concomitant bowel surgery manifested as a risk factor in the univariate but not in the multivariate analysis.

When performing concomitant bowel surgery, it is of utmost importance that the surgical team is experienced and well prepared. A meticulous adherence to hygienical principles: changing of gloves and instruments as well as re-sterilising the abdominal skin before inserting the mesh and use of modern large pore biomaterials of polypropylene or PVDF are principles routinely exerted by the authors. When assessing risk for adverse event in the individual case, it is necessary to take into account that concomitant surgical procedures might increase the risk for complication. However, performing the two procedures on different occasions can also increase post-operative morbidity since there will be two episodes of general anaesthesia and two post-operative courses. The reason for choosing an onlay procedure was not registered in the database. If an onlay repair is considered the most appropriate method for a specific patient, then maybe seroma should not be regarded as a complication, but rather an expected consequence of surgery.

Advanced age, several comorbidities and obesity have been associated with a higher risk for complication in previous studies [21]. In the present study, age was a risk factor for surgical complication in the multivariate analysis, but an association between obesity and complication could not be demonstrated. In the univariate analysis, obesity was associated with an increased risk, as was ASA physical score ≥3 (indication comorbidities, although not specifying which). There is a possibility that the study did not include enough patients to be able to demonstrate an existing difference regarding these variables in a multivariate analysis.

Describing risk in ventral hernia repair is a complex matter. Hernia size is associated with risk in the present study. There are, however, other important determinants, for instance, loss of domain, which was not included in our register [22]. Such analyses require special assessment of imaging material that is demanding on resources, but may be motivated in future randomised trials. Variables to be included in a register must be chosen with care [23]. If too many parameters are included or are too complicated to fill in, compliance and completeness of registration may be hampered.

Comparison of SSO rates between studies is difficult due to the fact that no adjustment of complexity is possible due to the lack of validated risk factors. Present material constitutes tertiary referral centre cases and thus expected to have a higher incidence of post-operative complications. One explanation for the relatively low complication rate (20%) in the present material, if one consider the patient selection, may have been the mandatory cessation of smoking prior to surgery practised at the two participating units [24]. For evaluation of hernia site complications, longer follow-up than 3 months is necessary. This is in order to see complications such as recurrence, pseudo-hernia and mesh migration. In contrast to earlier recommendations, synthetic material was used in cases with concomitant bowel surgery. No obvious increase in risk for SSO was detected by this practice. Modern management of complex ventral hernia repair requires a dedicated team that, after multimodal assessment and optimisation of identifiable health problems, can tailor the surgical approach to match the patient’s function and physical activity. The onlay technique is a valuable method when repairing a complex ventral hernia where other techniques are not feasible or inferior due to complicated anatomical conditions. In a previous study, we found that functional outcome in terms of abdominal wall muscle strength does not differ between the techniques used for reconstruction [25], although cases operated with onlay repair were more often re-repairs. In complicated cases, the higher risk for SSO and seroma associated with the onlay technique may be considered acceptable. Such cases include major concomitant bowel surgery where maximal distance between mesh and viscera is desirable, re-recurrence where previous mesh insertion obliterates the sublay space, and cases with anticipated dense adhesions which make the IPOM position unsuitable. The presence of excessive scar tissue and previously implanted mesh has a substantial impact on tissue remodelling and repair, and predispose to healing disturbances that increase the risk for surgical complications [26].

The most common severe complication in our study was respiratory failure. None of the respiratory failures reported were induced by sepsis. The respiratory failures reported were considered due to physiological shifts related to reduction in large hernias where the return of hernia contents into the abdominal cavity increased the respiratory demands considerably, even though the patient had worn a tight abdominal binder for several months prior to surgery. We propose that there appears to be an association between large hernia aperture and respiratory failure leading to unplanned ICU care. The aperture size should always be assessed as part of the preoperative management of the ventral hernia patient. In cases where the hernia is large, preoperative investigation and optimisation of the patient’s respiratory function are essential in order to reduce the risk for respiratory complications. In summary, according to the present findings, the larger the hernia, the greater the risk for early surgical complications, including significant complications such as respiratory decompensation. As hernias often grow in size over time, delaying repair may result in a larger hernia to repair and therefore greater risk for complications. Thus, the risks of waiting for improvements in a patient’s condition, such as waiting for weight loss, should be balanced against the risks related to possible growth in the hernia over time.