الفهرس 
Endocrine-Metabolic diseaseOnly 14 pages are availabe for public view
 |  | from | 116 |  |  |
| | | from | 116 | | |
Abstract
The prevalence of overweight and obesity is increasing worldwide. Obesity is defined as a body mass index of 30 or greater. Obesity and overweight have many causes, including genetic, metabolic, behavioral and environmental.
Obesity has significant health implications, such as hypertension, hyperlipidemia, diabetes mellitus, increased risk for coronary artery disease, obstructive sleep apnea (OSA), obesity hypoventilation syndrome (OHS), pulmonary hypertension and cor pulmonal, and acute hypercapnic respiratory failure. The risk is related to the magnitude of BMI; e.g., BMI 25-29.9 kg/m2 carries a low risk and BMI ≥40 kg/m2 corresponds to very high risk.
The morbidly obese have severe alterations in respiratory mechanics, such as decreased chest wall and lung compliance, and decreased functional residual capacity (FRC).
Obesity is a major risk factor for OSA. A neck circumference > 17 inches for men and > 16 inches for women, which is correlated with obesity, has also been highly correlated with OSA.
Obesity hypoventilation syndrome (OHS) is characterized by obesity, daytime hypercapnia, and sleep-disordered breathing in the absence of significant lung or respiratory muscle disease. Obesity impairs ventilatory mechanics, increases the work of breathing and carbon dioxide production, results in respiratory muscle dysfunction, and reduces ventilatory response to hypercapnia. Sleep-disordered breathing is present in most patients with the OHS. When noninvasive ventilation can be successfully introduced, hypoventilation can usually be corrected. Weight loss is the desirable long-term treatment for the OHS.
Many obese patients are already CPAP-dependent due to OSA or OHS preoperatively. These patients are at extremely high risk for postoperative worsening of their respiratory depression, exacerbated by the administration of opioids and sedatives, and by the disruption of their REM sleep pattern. Upper abdominal surgery may increase postoperative atelectasis due to total collapse of lung zones with low ventilation relative to perfusion (low ventilation/perfusion ratio) when high inspiratory fraction of O2 is used.
The alteration of pulmonary function may persist for 2 weeks or more postoperatively, resulting in a high incidence of complications, such as atelectasis, retention of pulmonary secretions, and other pulmonary complications.
Preparation should be made for the possibility of difficult mask ventilation or difficult intubation. During laryngoscopy, the patient must be in the optimal sniffing position or ramped position before induction of anesthesia. Awake fibro-optic intubation should be considered.
Tracheal intubation and positive pressure ventilation are mandatory in the morbidly obese patient. The addition of PEEP improves oxygenation but at the expense of cardiac output.
Postoperatively, obese patients should be positioned in the semisitting or lateral position to improve ventilation and prevent pharyngeal obstruction. CPAP should be ready in case upper airway obstruction develops.
CPAP or BiPAP has been used with success to improve postoperative pulmonary atelectasis, restoring FRC, preventing upper airway collapse, supporting ventilation by increasing lung compliance and decreasing work of breathing, and increasing transmural pressure, thus re-expanding collapsed alveoli.
The application of NIV can return FRC to preoperative levels, with immediately improved arterial oxygenation. Furthermore, with NIV, endotracheal intubation can be often avoided, with decreased morbidity and mortality, primarily by decreasing the incidence of respiratory system infectious complications. Good selection of the patient, interface, ventilator type is a crucial issue for success of NIV therapy.
The sophistication and variety of interfaces reflects how problematic this aspect of NIV can be. Currently available interfaces include nasal, oronasal and facial masks, mouthpieces and helmets. There is no consensus on the optimal interface to use in delivering NIV.
Management of the obese patient is challenging. Optimal planning should be done pre-, intra-, and postoperatively in order to achieve an optimal outcome.