Pre-habilitation or prehab is the idea of using traditional rehabilitation strategies to prepare an individual for surgery or other serious medical intervention such as chemotherapy for cancer. The premise is that by improving the individual's health and functional status prior to the stressful event, the individual will have better outcomes from the intervention. The best pre-habilitation plans will set tangible goals such as improvements in holistic measurements of function such as the 6-minute walk test (6M WT), weight loss of a certain amount, normalization of abnormal lab values such as blood glucose or abnormal liver enzymes, or improvement in respiratory function. All of these changes are associated with different surgical outcomes such as reduced complication rates, shorter length of stay, and lower rates of reoperation depending on the intervention. This is why many surgeries-particularly orthopedic-often have BMI maximums and will refer patients for evaluation by weight loss specialist prior to surgery. In some cases, individuals will even be referred for bariatric surgery prior to orthopedic surgery.
Given the benefits of weight loss on reducing visceral and liver fat, some bariatric surgery centers require weight loss prior to surgery. This is also a common requirement by insurance plans, although this is likely to demonstrate that the patients can remain dedicated to a postoperative nutrition/exercise plan. One meta-analysis assessing weight loss before bariatric surgery from the patient's weight loss weight preoperatively had about 5% greater weight loss postoperatively. They also determined that for bariatric procedures, preoperative weight loss does decrease time of the operation room by approximately 20 minutes, although there were no other associated benefits found in this meta-analysis in terms of differences and complication rates despite shorter operative time. This study was conducted mostly to ensure that the required preoperative weight loss at least was not causing harm, as theoretically if this weight loss is accomplished through restrictive dieting to the point of developing nutritional deficiencies, this could theoretically lead to harm with poor tolerating of stress in the operating room and postoperative complications. As other research has shown that even "modest" weight loss of approximately 10% excess body weight could improve hypertension, diabetes, and obstructive sleep apnea symptoms (all of which worsen operative outcomes), a well tailored, multimodal, prehabilitation plan would likely result in better outcomes for bariatric and other kinds of surgery.
In 1 published review of prior studies about patients with obesity undergoing prehabilitation prior to bariatric and non-bariatric surgeries, the authors identified inverse relationship between fitness and 30-day medical complications, particularly if referrals for these programs based off of the presence of comorbidities instead of simply BMI. The only instances in which preoperative weight loss were associated with worse outcomes occurred when this weight loss was achieved through bariatric surgery prior to orthopedic surgeries. In these cases, it is plausible that the malabsorptive state created by bariatric surgery that underlies part of the mechanism of weight loss leads to insufficient nutrient absorption which is necessary for recovery from major surgery. In these cases, readmission and surgical revisions were higher in groups who had had bariatric surgery before joint replacement.
Excluding these studies, weight loss through other means at the very worst had no benefit-in these unsuccessful interventions, the theme was that typically interventions were fairly bland-some consisted only of counseling at the initial consultation on exercise and diet or were plagued by poor compliance and high dropout rates. Alternatively, many studies showed significant positive benefits of preoperative weight loss-some more intensive programs such as weekly meetings with a physician, nutritionist, personal trainer, and psychologist showed improvements in length of stay, complications such as poor wound healing and infection, reoperation, and mortality. Programs that were exclusively exercise-based showed sporadic benefit, but diet-only based interventions such as a very low calorie and ketogenic diet resulted in significantly greater weight loss with improvements in length of stay and wound complications postoperatively.
As part of this multimodal preoperative prehabilitation program, screening for sleep disorders (particularly obstructive sleep apnea) is warranted as patients with obesity are at significantly high risk of OSA, and the presence of OSA is undeniably associated with surgical complications. Moreover, as noted in other discussions (see: post XXX), OSA effectively short-circuit's the benefits of sleep while also adding worsening hypertension and diabetes due to the body's reaction to periods of poor oxygenation and activation of the "fight or flight" response.
Overall, programs designed for preoperative weight loss should undoubtedly be multimodal with both a focus on functional improvements in endurance and exercise tolerance, and weight loss-particularly visceral/liver fat as this will be associated with decreases in blood pressure and blood sugar. Dietary interventions should be overseen by a nutritional professional to ensure caloric restriction maintaining adequate protein and vitamin/mineral intake. Finally, these programs are only as effective as the participation level of the individuals. Therefore, great strides should be made for increasing engagement and adherence to the program through frequent touch-points with prehabilitation team members, reward systems, and even monetary buy-in.