The presence of excessive subcutaneous tissue decreases the visibility of peripheral veins. Portable ultrasound equipment may be required for identification and cannulation of peripheral veins. In some patients it may be difficult to identify peripheral access, and central venous cannulation may be necessary. The presence of reliable venous access facilitates care in the postoperative period. In diabetic obese patients, the presence of a multiport central venous catheter facilitates blood glucose and other laboratory sampling.44,45
A detailed history, physical examination, and focused investigations help to rule out the extent and severity of the cardiovascular physiologic changes reported in obese patients. The severity of hypertension and its control with medications, if any, should be noted. Ischemic heart disease, when present, must be stable and if extensive may require further preoperative assessment. Evaluation should also include an assessment for pulmonary hypertension and signs of right- or left-sided cardiac failure. Signs of cardiac failure include increased jugular pressure, additional heart sounds, pulmonary crackles, hepatomegaly, and peripheral edema. Symptoms of pulmonary hypertension include exertional dyspnea, fatigue, and syncope, which reflect the inability to increase cardiac output during activity. Identification of tricuspid regurgitation with echocardiography is most definitive confirmation of pulmonary hypertension. A chest radiograph must be done to rule out cardiomegaly. An electrocardiogram (ECG) helps (especially in the presence of advanced right ventricular failure) to demonstrate signs of right ventricular hypertrophy, such as tall precordial R waves, right axis deviation, and right ventricular strain. Special expertise is required in the interpretation of the ECG because of excessive overlying adipose tissue and epicardial fat that may interfere with the voltage of the QRS and other waves. The ECG also demonstrates the presence of arrhythmias and axis deviation.29,46 Mild to moderate pulmonary hypertension warrants avoidance of hypoxemia, nitrous oxide, and other drugs that may further aggravate pulmonary vasoconstriction.47,48
Echocardiography helps to evaluate cardiac function in detail with respect to the ejection fraction, septal motility, valvular dysfunction, and any other functional problems. Thus, consultation with a cardiologist must be obtained when necessary for accurate diagnosis and institution of proper preoperative therapy. This may require postponing the procedure and also help in planning intraoperative invasive monitoring (e.g., transesophageal echocardiography with or without pulmonary artery catheterization).
History taking must include evaluation for the presence of OSA, OHS, upper airway obstruction, and dyspnea. One should check for the presence of snoring, apnea during sleep, frequent arousals, daytime sleepiness, and fatigue. Results from a formal sleep study are useful to ascertain objectively the presence or absence of OSA or OHS.15,49
Pulmonary function tests may be necessary to note effects on lung capacities and airflow mechanics. Arterial blood gases indicate whether the patient is retaining carbon dioxide or has hypoxemia. The presence of polycythemia suggests long-standing hypoxemia. A chest radiograph evaluates the anatomic status of the lung and cardiac structures.
Other Pertinent Concerns
Certain patients who are scheduled for repeat bariatric surgery or have had bariatric surgery in the past may have some common long-term nutritional deficiencies that may include vitamin B12, iron, calcium, thiamine, vitamin K, and zinc. Therefore, it becomes important prior to surgery to assess electrolyte and coagulation status. Chronic vitamin K deficiency (deficiency of clotting factors II, VII, IX, and X) can lead to an increase in prothrombin time with a normal partial thromboplastin time.50 For elective surgery, vitamin K analogues such as phytonadione can be used to correct the coagulopathy within 6 to 24 hours. For emergency operations, fresh-frozen plasma may be required. As mentioned earlier, obese patients are at increased risk for developing DVT. For this reason, miniheparinization, elastic stockings, pneumoboots, and frequent leg lifts are advocated. Type 2 diabetes mellitus is common in obese patients and should be confirmed with a fasting blood glucose level and a check for the presence of ketones in blood and urine. Diabetes mellitus may worsen the risk of GERD.51
Perioperative Drug Use
Obese patients often are on medications to control their blood pressure and blood glucose levels. Antihypertensives should be continued preoperatively (with a sip of water). Oral hypoglycemic drugs should be withheld and blood glucose controlled with insulin, using a sliding scale. Some bariatric patients may be on weight-reducing medications including herbal remedies. These should be reviewed for possible unwanted systemic effects and drug interactions.
Two commonly used weight-loss drugs are sibutramine and orlistat. Sibutramine inhibits the reuptake of norepinephrine, serotonin, and dopamine, thereby causing anorexia. It causes transient dose-related increases in both systemic and diastolic blood pressure by a mean of 2 to 4 mmHg and induces a small increase in heart rate of 3 to 5 beats per minute. Orlistat is a product of Streptomyces toxytricini, which inhibits mammalian lipase. It blocks the digestion and absorption of dietary fat by binding lipases in the gastrointestinal tract. It causes fat malabsorption and decreases in serum concentration of fat-soluble vitamins (A, D, E, and K). In some cases, orlistat has been reported to result in aggravated hypertension.52–54 Warfarin's anticoagulant effect may also be increased because orlistat decreases the absorption of vitamin K.
Perioperative antibiotic prophylaxis is important to minimize the risk of wound infection. The published rate of wound infection after gastric procedures in the morbidly obese is approximately twice that in lean patients. Nguyen and colleagues found that open Roux-en-Y gastric bypass has approximately a tenfold incidence of wound infection as compared to the laparoscopic approach.55 However, practitioners recommend antibiotic prophylaxis for the laparoscopic approach as well.56 Antibiotics should be administered no more than 45 minutes prior to the incision and repeated every 2 hours in protracted cases. Prophylaxis for DVT with haparin and compression devices is instituted just before surgery and continued until at least 12 hours postoperatively unless the patient has other significant medical problems that require prolonged anticoagulation.
Preoperative Airway Assessment
Obese patients are more difficult to mask, ventilate, and intubate. This is because of their size, the presence of a shorter neck that has a widened circumference, the presence of excessive pharyngeal tissue, and a tongue that has a large base.15 It is imperative that every obese patient be carefully examined for the feasibility of mask ventilation and intubation, including aspiration risk. In the absence of significant reflux and hiatal hernia, most patients may be passively ventilated prior to intubation by mask, if required. This is important to know preoperatively because endotracheal intubation may take longer than anticipated, so mask ventilation becomes necessary. Although histories and reviews of medical records are necessary, one must remember that they may be misleading if the patient has gained significant amounts of weight. If the patient was difficult to ventilate by mask or difficult to intubate on a prior occasion, unless there has been a major weight loss with an improvement in the airway, the patient should be assumed to be difficult for airway care unless proven otherwise. Obese patients may have limited neck movement and mouth opening, making intubation difficult. Voyagis and colleagues looked at Mallampati class, mouth opening, and risks of intubation.57 They found that a disproportionately large base of tongue predisposes a patient to difficult intubation. Those with a neck circumference of 42 cm are more likely to be difficult to intubate unless an increased mouth opening and tongue size compensate for this feature.58,59 The presence of effortless breathing and patent nostrils should be noted. The presence of OSA and body size greater that 175% ideal body weight often suggests the possibility of a difficult airway. In two studies done in a series of morbidly obese patients undergoing abdominal surgery, the incidence of difficulty with the airway after general anesthesia was 13% and 24%, and the incidence of patients requiring awake intubation was 8%.39,60 The authors felt that this was due to several factors: the presence of a short thick neck, the close relationship of a short neck and OSA, and excess pharyngeal tissue in the lateral walls of the larynx. Brodsky and associates61 studied 100 morbidly obese patients to identify factors that complicate direct laryngoscopy and tracheal intubation. Preoperatively they recorded height, weight, neck circumference, width of mouth opening, sternomental distance, thyromental distance, and Mallampati score. They also scored the laryngoscopic view and the number of attempts at tracheal intubation. They found that neither obesity nor BMI was correlated with difficult intubation. Large neck and Mallampati score were the only two predictors of potential intubation problems. Patients with increased neck circumference required intervention by a fiberoptic bronchoscope to establish an airway. Also, patients with a Mallampati score greater than or equal to 3 had increased difficulty with tracheal intubation. Other routine assessments, such as jaw and neck mobility, dental status, patency of nostrils, and inspection of oropharynx, should be done prior to implementation of an anesthesia care plan for obese patients.