[show abstract][hide abstract] ABSTRACT: Reflective forehead pulse oximeter sensors have recently been introduced into clinical practice. They reportedly have the advantage of faster response times and immunity to the effects of vasoconstriction. Of concern are reports of signal instability and erroneously low Spo(2) values with some of these new sensors. During a study of the plethysmographic wave forms from various sites (finger, ear, and forehead) it was noted that in some cases the forehead wave form became unexpectedly complex in configuration. The plethysmographic signals from 25 general anesthetic cases were obtained, which revealed the complex forehead wave form during 5 cases. We hypothesized that the complex wave form was attributable to an underlying venous signal. It was determined that the use of a pressure dressing over the sensor resulted in a return of a normal plethysmographic wave form. Further examination of the complex forehead wave form reveal a morphology consistent with a central venous trace with atrial, cuspidal, and venous waves. It is speculated that the presence of the venous signal is the source of the problems reported with the forehead sensors. It is believed that the venous wave form is a result of the method of attachment rather than the use of reflective plethysmographic sensors.
[show abstract][hide abstract] ABSTRACT: Patients with diabetes are prone to metabolic derangements because of their lack of effective insulin. Comorbid conditions, such as coronary artery disease, nephropathy, and autonomic neuropathy warrant preoperative assessment to ensure safety in the perioperative period. Preoperative evaluation must include assessment of chronic complications of diabetes. A thorough history and physical should guide preoperative testing which should be aimed at detecting correctable abnormalities and assessing the extent of end-organ disease. Surgery poses special challenges to patients with diabetes because the stress response, interruption of food intake, altered consciousness, and circulatory alterations all lead to unpredictable glucose and electrolyte levels. The management of insulin perioperatively depends on the preparation normally taken by the patient, and the glucose level on the morning of surgery. The goal is to avoid hypoglycemia and extreme hyperglycemia. Oral hypoglycemic agents should be held on the morning of surgery. Metformin should be discontinued 48 hours prior to and subsequent to surgery in order to reduce the risk of lactic acidosis. The avoidance of hypoglycemia and excessive hyperglycemia intraoperatively is best achieved with frequent monitoring of blood glucose and treating abnormalities according to patients' preoperative regimen and current condition. Maintaining blood glucose levels below 110 mg/dL reduces morbidity and mortality in critically ill patients. Measure blood glucose immediately following surgery because progression of the stress response postoperatively, in addition to possible nausea and vomiting, can complicate the patient's management. Precautions should be taken to prevent damage to peripheral nerves while diabetics are on the operating table because their nerves and limbs are already vulnerable to pressure and stretch injuries secondary to neurologic and vascular disease. With thorough and careful management, metabolic control in the perioperative period is a goal that is attainable for most patients.