The first step in preoperative evaluation involves eliciting an obesity focused history. Onset of weight gain has to be enquired. In majority of patients weight gain has a late onset secondary to a change in life events or stressful life events. These events commonly include change in marital status, change in occupation, severe illness, pregnancy, menopause, restricted mobility etc. Early onset obesity is identified by a history of childhood or adolescent obesity. Early onset of obesity is a predictor of severe obesity in adulthood [4]. Predisposing genetic background need to be assessed by enquiring for obesity in parents and/or siblings. Parental obesity more than doubles the risk of adult obesity [4].

Dietary intake has to be assessed in all patients. Eating disorders such binge eating disorder, bulimia, or night-eating syndrome etc need to be looked for. The calorie/protein intake of the patient should be assessed. Common preexisting nutritional deficiencies need to be looked for and corrected. A physical activity history is also to be assessed.

Determining a patient’s motivation is also an important part of the initial evaluation. Firstly this involves assessment of the appropriateness of the patient’s goals and expectations. An assessment of time availability and constraints, stressful life events, psychiatric status etc helps understand the likelihood of lifestyle change. Assessment of psychological and psychiatric history is to be routinely performed to confirm the patient’s ability to incorporate nutritional and behavioral changes before and after bariatric surgery [6–8]. Physical examination in addition to a routine examination should look for stigmata of syndromes associated with obesity like dysmorphism, hypogonadism, purple abdominal striae etc. A system wise evaluation is covered in the subsequent sections.

Obesity is associated with several cardiac co-morbidities including hypertension, arrhythmias, coronary artery disease, cardiac failure, cardiomyopathy etc [9]. Every patient should be evaluated with a cardiac specific history, history of coronary risk factors and a physical examination. General evaluation requires a 12-lead electrocardiogram (ECG) and echocardiogram. In case stress testing is deemed necessary a dobutamine stress echocardiogram is performed since exercise induced echocardiogram is usually not possible in obese patients [10]. Cardiac computed tomography angiogram can be used as a method to evaluate the coronary vasculature in patients prior to invasive imaging procedures. Invasive cardiac interventions if needed are performed based on the assessment and advice of a cardiologist.

The routine recommendation for hypertension is adequate control of blood pressure before the procedure [10]. In patients with cardiac disease close collaboration with the patient’s cardiologist during the preoperative workup, intraoperatively and postoperatively is needed for optimal management. In patients who have undergone cardiac stenting antiplatelet therapy in the perioperative period often presents a controversy for the surgeons. Specific to bariatric surgery, it is recommended that patients with bare metal or drug eluting stents should not undergo surgery within the first year of stent placement. If, as determined by a cardiologist, the patient requires dual therapy longer than 1 year after stent placement, recommendation is to remain on antiplatelet therapy and this should not be discontinued.

Obesity is a hypercoagulable state [11]. This leads to an increased risk of venous thromboembolism (VTE) in morbidly obese patients undergoing bariatric surgery. Venous thromboembolic events are a leading cause for mortality after bariatric surgery. The reported incidence of symptomatic VTE is <1 % for laparoscopic bariatric surgery. However common predisposing factors cited for an increased risk of VTE in obese patients are elderly patients, prior deep venous thrombosis (DVT), hypercoagulable states, superobesity, documented obesity hypoventilation and/or pulmonary hypertension. It is generally recommended that patients undergoing weight loss surgery receive VTE chemoprophylaxis in adjunct to mechanical methods during the perioperative period [12]. Details regarding peri-operative DVT prophylaxis after bariatric surgery have been discussed in detail in Chap. 19. Routine screening for deep venous thrombosis prior to bariatric surgery is controversial but may be advisable in high risk patients as outlined before. Also patients with suspicious limb findings or findings suggestive of venous insufficiency should be investigated for a preexisting thrombus. The preferred method for evaluation is venous duplex ultrasound. This study has a sensitivity and specificity of 97 % and 94 %, respectively, of diagnosing a lower extremity DVT [13].

Obesity related impairment of respiratory function is caused by deposition of fatty tissue in and around the upper airways by reducing oropharyngeal patency (resulting in obstructive sleep apnoae [OSA]) and increased adipose tissue resulting in mechanical restriction of adequate ventilation by reducing diaphragmatic excursion and chest wall expansion (resulting in obesity hypoventilation syndrome [OHS]). Obesity is also a risk factor for airway disease and there is a 50 % higher incidence of severe asthma in obese patients when compared to normal controls [14, 15]. Details regarding OSA and OHS have been discussed in detail in Chap. 21.

Chest radiographs are ordered frequently as part of a routine preoperative evaluation. Spirometry has value in diagnosing obstructive lung disease and can be ordered if this is present or suspected. A reduction in the expiratory reserve volume (ERV) is the most commonly identified abnormality on spirometry in patients with obesity.

The definitive diagnosis of obstructive sleep apnea (OSA) is made with an overnight polysomnography (PSG). However an overnight PSG is expensive and inconvenient to use in all patients. The Epworth Sleepiness Score, the Berlin Questionnaire and the STOP-BANG Questionnaire are clinical screening tools designed to quickly assess if a patient should be assessed further for OSA by PSG. A PSG assesses the Apnoea/Hypnoea index (AHI). In general, an AHI of less than 5 is normal, 5–15 is mild sleep apnea, >15 is moderate sleep apnea and >30 severe sleep apnea. Obesity hypoventilation syndrome (OHS) manifests with daytime hypercapnia with PaCO₂ >44 mmHg or 6 kPa, elevated hematocrit, with sleep disordered breathing and needs an arterial blood gas analysis in addition to a PSG for diagnosis. Screening tests for deranged arterial blood gases can be done by pulse oximetry and serum bicarbonate levels. A room air saturation of <94 % is suspicious of a paO₂ <70 mmHg and a serum bicarbonate of >27 mEq/L is suspicious of elevated paCO₂ levels. If these tests are suggestive of derangement they should be followed by arterial blood gas analysis. Patients with moderate to severe apnea/OHS should be optimized with preoperative incentive spirometry and continuous positive airway pressure (CPAP) or bi-level positive airway pressure (Bi-PAP). Details regarding the perioperative management of OSA after bariatric surgery have been discussed in detail in Chap. 21.

Smoking is a common entity which significantly impacts pulmonary function. It has been identified as an independent factor associated with a greater incidence of acute respiratory failure after bariatric surgery and also shown to be an independent predictor of increased hospital length of stay [16]. Therefore smoking cessation at least for 3 weeks is an essential component of the preoperative assessment to prevent further morbidities.

Obesity has been found to be associated with type 2 diabetes mellitus (T2DM) and hypothyroidism [17, 18]. Glycemic control in T2 DM should be assessed preoperatively by performing hemoglobin A1c (Hb A1c) levels in addition to fasting and postprandial glucose levels. Poor glycemic control is associated with lower rates of type 2 DM remission [19]. C-peptide levels need to assessed in patients with T2DM to know to measure beta cell function. Directly measuring insulin levels may be fallacious in those who are receiving insulin therapy. WJ Lee et al reported that a fasting C-peptide levels more than or equal to 3 nmol/l is the best prognostic marker of good remission after bariatric surgery [20]. He also reported that low C-peptide levels <1 nmol/l in severely obese T2DM indicated partial beta cell failure and predicted a markedly reduced chance of resolution of T2DM [21].

Hypothyroidism is a known cause of obesity; however, de novo thyroid dysfunction such as subclinical hypothyroidism is associated with obesity [18]. In some patients, the TSH level has been shown to return to normal levels after significant weight loss, however the outcome is not universal.

Obesity is a risk factor for gastroesophageal reflux disease, erosive esophagitis, and esophageal adenocarcinoma [22]. The rationale for performing an UGI endoscopy before bariatric surgery is to detect and treat UGI lesions that might cause symptoms or complications in the postoperative period or to detect lesions that may need a change in bariatric procedure performed. While some institutions routinely evaluate patients with preoperative UGI endoscopy prior to bariatric surgery, some suggest symptom-directed UGI endoscopy as in the general population [23]. In places where gastric and other upper gastrointestinal cancers are more prevalent, routine screening OGD is a must for all patients especially in procedures which exclude the stomach. It is also necessary in all patients undergoing revision surgery. Routine screening for H. pylori and eradication is indicated in high prevalence areas. Patients with normal findings or mild mucosal inflammatory lesions (mild to moderate esophagitis, gastritis, or duodenitis) or mild anatomical abnormalities (lax lower esophageal sphincter, small hiatal hernias) proceed with surgery as previously planned [24]. Patients with severe erosive gastritis or duodenitis or gastroduodenal ulcers require treatment with proton pump inhibitors for 4 weeks with reassessment to confirm mucosal healing [24]. Gastroesophageal reflux disease associated with hiatal hernias and Barrett’s esophagus found preoperatively may require a change in planned bariatric procedure [24].