The resting membrane potential (RMP) of myocytes is determined by the Na+/K+-ATPase, which pumps 3 Na+ out for every 2K+ pumped and an open potassium channel that allows K to move outside the cell, down its concentration gradient. Both these events produce a negative intracellular change and a negative RMP. Since the potassium channel is the open at rest, changes in the internal or external K concentration may change the RMP according to the equation:
Historically, the incidence of paraplegia following thoracic aortic aneurysm (TAA) surgery was on the order of 40%, although more recent estimates are below 20% for open TAA surgery and 8% for thoracic endovascular aneurysm repair (TEVAR). Possible mechanisms of injury include: (1) Decrease in spinal cord perfusion pressure during use of the aortic cross-clamp, (2) Increase in intrathecal pressure (ITP) transmitted from elevated ICP and hypercarbia, (3) Ligation of collateral vessels, (4) Thrombosis, (5) Hematoma, (6) Repefusing injury causing cord edema, (7) Predisposing conditions (peripheral vascular disease, diabetes, prior aortic surgery).
Due to the physiologic changes associated with ECT, the list of contraindications includes recent MI, heart failure, recent stroke, elevated ICP, aneurysm/AVM at risk of rupture, pheochromocytoma, severe HTN, and cervical spine instability, most of which are only relative.
Carcinoid tumors are slow growing neuroendocrine cells that usually originate from primitive stem cells in the GI tract (67%), usually in the small intestine, rectum/appendix, and stomach, but may also be found in the lung, pancreas, and, rarely, gonads. They release a variety of mediators, including serotonin (abdominal cramps, diarrhea, bronchospasm), kallekrein (which converts kininogen to bradykinin, causing flushing), and histamine (vasodilation, bronchospasm). Other mediators include dopamine, prostaglandins, neurotensin, corticotrophin, and substance P. These mediators are usually metabolized by the liver before they reach the rest of the body, so by the time symptoms appear, hepatic metastases are likely. Pulmonary or ovarian carcinoid tumors also release mediators into the circulation that bypass hepatic metabolism. Carcinoid is the #1 tumor of the appendix, peaking in the 4th to 5th decade, primarily in women.
Meconium aspiration syndrome (MAS) is defined as respiratory distress in a newborn infant born through meconium-stained fluid whose symptoms cannot otherwise be explained. MAS occurs in approximately 2-10% of infants born through meconium-stained fluid. The incidence as a function of gestational age takes on a U-shaped curve, with a nadir at 31 weeks and greater incidence before and after that time. Other risk factors include being black, South Asian, post-mature, and small-for-gestational-age.
The use of a tourniquet in orthopedic surgery or other procedures provides the benefits of producing a bloodless field, reducing blood loss, and decreasing time of surgery. At the same time, prolonged tourniquet use can cause hemostasis, acidosis, and hypoxia, factors known to increase the chances of sickling in patients with sickle cell disease and rarely trait.
There is a sharp debate on whether the Perioperative Surgical Home (PSH) should represent the future of our profession. It has been estimated that two-thirds of all hospital costs are directly related to surgical care. In US, this amounts to approximately $180 billion per year on inpatient surgical procedures in nonfederal hospitals alone. According to the Institute for Healthcare Improvement, the “Triple Aim" for health care is to (1) Improve the patient experience, (2) Improving the health of the population, and (3) Reducing health care costs.