Reply to Letter “Evaluation of Quality of Life After Incisional Hernia Repair Using Condition-specific Scales and Risk Factors”

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Thank you for the questions and engagement in our PROLOVE1 trial.
The ultimate goal of surgical intervention is to improve the quality of life (QoL) for the patient, that is, the health-related QoL. It is convenient for us surgeons to focus on the technique and actions taken to relieve the immediate disease or symptoms of the patient. Surgery on a patient may leave complaints on different issues where the outcome did not match the patient's expectations. A symptom may be tolerable to one patient, but intolerable to another.
The condition-specific instruments are designed to capture mainly the technical aspects of an intervention, which allows for detecting outcome differences regarding symptom relief, complications, recovery time, and so on.2 These outcomes may directly or indirectly affect QoL, but they are specific for the disease/intervention/condition and cannot be used for comparison of patient categories/populations with other conditions. The condition-specific instrument may more easily detect small changes related to changes of the intervention, but may fail to detect other conditions affecting the outcome. The generic QoL instrument Short Form 36 (SF-36) is thoroughly validated across different populations with a defined norm, making comparisons between patient populations and between treatment groups possible and very valid.
Incisional hernia is a complication after previous surgery. The hernia problem varies in magnitude depending on size and symptoms, and may severely affect QoL beyond the mere loss of function of the abdominal wall. Chronic pain, disfiguring body shape, impact on clothing and social activities, physical limitation, and more, are all founding dimensions of the SF-36 (and other) QoL instruments. We have also addressed these factors separately.
When our trial was designed no hernia-specific instruments were available. The HerQLes3 was published in 2012 and focuses on the impact of the abdominal wall on several dimensions of QoL, quite like the SF-12—a further reduced version of the SF-36.4
The question then remains: why use a specific instrument to assess QoL if it cannot be compared to a norm population and is not thoroughly validated? What is the concept of health-related QoL? What proportion of a patient's QoL deficit can be blamed on the specific condition (eg, abdominal wall hernia)? When the SF-36 physical dimension is scrutinized it seems very sensitive to impaired function of the legs (walking, stair climbing, etc). QoL instruments are valid on group level, but not on individual level. The SF-36 questions were distilled from 140+ questions and selected to monitor domains with large impact on the perceived QoL.5 It could have been that the incisional hernia problem did not fit the SF-36 QoL model. However, in our trial, the preoperative physical QoL was low and was restored to normal level after surgical procedure. Changes in SF-36 were significant, which implies that incisional hernia causes a substantial reduction of QoL (as measured by SF-36), which in turn is remedied by laparoscopic or open surgery.
The selection of reported risk factors was decided on in the design of the trial. The study size of the randomized controlled trial, dependent on the primary outcome bodily pain as assessed by SF-36, limits the number of risk factors possible to include in a reasonable regression analysis. Obesity is included as risk factor body mass index greater than 30 kg/m2. We originally included other comorbidities (diabetes, heart or lung conditions, steroid treatment, and antithrombotic treatment), but the American Society of Anesthesiologists physical status classification system6 assess these conditions and consequently correlated highly, making them redundant in the analysis.
The proposed risk factors were not recorded in our trial; in fact, some were part of the exclusion criteria.
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