General complications, risks with anaesthetics
The risks of general, non-surgical complications during and after the procedure are significantly higher than for people with normal body weight. The reason for this lies in the lingering effects of morbid obesity on a wide variety of organ systems. In this context, the key factors include the degree of obesity, the type of fat, the severity and duration of concomitant diseases and the patient's age.
Under the general anaesthesia required by the surgical therapy, the organism must withstand the high state of stress to which it is subjected.
Risks to the cardiovascular system
Due to the increased volume of blood circulation, an extremely overweight patient's heart must perform extra work. This also increases the oxygen demand of the cardiac muscle. This leads in turn to enlargement of the cardiac muscle, especially of the left ventricle, and reduced functional capacity. With each additional increase in weight, the heart's pumping capacity is further diminished. Even in the total absence of apparent symptoms, therefore, the anaesthetist should consider the morbidly obese patient as having a weakened heart, i.e. one where the cardiac muscle capacity is potentially very small.
The stress associated with all the various facets of an operation triggers changes identical to those associated with physical exertion. For example, administration of the pneumoperitoneum (CO2 insufflation in the abdominal cavity) can cause cardiac output to drop off. This is why all morbidly obese patients have their cardiac output tested (stress ECG) prior to undergoing the operation.
The incidence of high blood pressure itself and the mortality rate associated with existing high blood pressure conditions are higher for obese patients. For this reason, blood pressure must be normalised prior to an operation. Even with normal blood pressure, no diabetes and moderate cholesterol levels, morbidly obese patients exhibit an increased susceptibility to cardiovascular disease. This results in an increased risk of sudden cardiac death or cardiac infarction. The success rate of reanimation in cases of cardiac arrest in the phase following the operation is relatively low. This can be attributed to rapid oxygen desaturation caused by mechanically insufficient heart massage, which is often limited by the patient's physical condition.
Cardiovascular risks must be carefully assessed and known dysfunctions must be treated seriously. Under optimum management, post-operative cardiac complications such as cardiac infarction or related dysrhythmia are extremely rare.
Risks for the lungs
An overweight patient's oxygen demand and carbon dioxide production are greater and increase faster under physical stress than do those of patients with normal body weight. This means that, in order to avoid generating an excess of carbon dioxide, an increased level of respiratory activity is required. The excess body mass supported by the thoracic cage and the mass of fat in the abdominal cavity reduce the elasticity of the thoracic wall. In addition, the elasticity of the lungs themselves is also reduced, thus resulting in a reduction of the functional lung volume. Shallow, rapid breathing is symptomatic of this condition. Modest physical stress causes a tremendous increase in oxygen demand, which points to an ineffective respiratory musculature that requires more oxygen because it must overcome the reduced elasticity of the thoracic cage. The functional capacity of the lungs is small, moderate stress can lead to respiratory failure.
The anatomy of the upper respiratory tract by intubation (insertion of the breathing tube into the trachea) as well as the special conditions related to artificial respiration with high pressures represent a challenge for the anaesthesiologist. When administering the pneumoperitoneum (introduction of gas to expand the abdominal cavity for minimally invasive surgery), oxygen saturation levels can drop off sharply.
The occurrence of post-operative respiratory insufficiency (respiratory failure after the operation with elevated CO2, reduced O2) can be effectively minimised through a combination of appropriate respiratory gymnastics before and after the operation together with inhalation therapy.
Established lung diseases such as sleep apnoea syndrome complicate matters further. Here again, proper diagnosis and therapy must be applied in weighing the operation's risks versus its benefits. Thus, the sleep apnoea patient's condition improves under CPAP therapy (continuous artificial respiratory assistance with positive air pressure), allowing him to be operated on. This leads in turn to successful weight reduction, which eventually frees him from the need to use the CPAP device.
The risk of aspiration (the intake of gastric fluid into the lungs) is increased with morbidly obese patients. This risk can be minimised through removal of gastric fluid (via mechanical aspiration) and proper placement of the patient along with appropriate supply and drain tube procedures for anaesthetics. Aspiration can cause pneumonia, accompanied by decompensation of pulmonary function.
Pulmonary complications also include pulmonary embolism, which occurs at a higher rate. Blood clots from deep within the venous system (leg veins, pelvic veins) find their way into the pulmonary circulation where, depending on their size, they block pulmonary arteries of various diameters. When it obstructs central pulmonary vessels, embolism can cause death. Smaller peripheral pulmonary embolisms probably go unnoticed much of the time or develop only minor symptoms. In order to minimise risk of pulmonary embolism, potential prophylactic methods are employed: Standing up on the day of the operation, wearing compression stockings to promote flow of the venous bloodstream from the legs and taking high-dosage prophylactic medication (low molecular weight heparin). The latter continues on an out-patient basis for 3 weeks following the operation.