An elderly man with type 2 diabetes mellitus and ischemic pain in the lower extremity is scheduled for femoral-to-popliteal bypass surgery. He has a history of hypertension and coronary artery disease with symptoms of stable angina and can walk only half a block before pain in his legs forces him to stop. He has a 50-pack-a-year smoking history but stopped 2 years ago. His medications include atenolol, atorvastatin, and hydrochlorothiazide. The nurse in the preoperative holding area obtains the following vital signs: temperature 36.8°C (98.2°F), blood pressure 168/100 mm Hg, heart rate 78 bpm, oxygen saturation by pulse oximeter 96% while breathing room air, pain 5/10 in the right lower leg. What anesthetic agents will you choose and why? Does the choice of anesthetic make a difference?
For centuries, humankind has relied on natural medicines and physical methods to control surgical pain. Historical texts describe the sedative effects of cannabis, henbane, mandrake, and opium poppy. Physical methods such as cold, nerve compression, carotid artery occlusion, and cerebral concussion were also employed, with variable effect. Although surgery was performed under ether anesthesia as early as 1842, the first public demonstration of surgical general anesthesia in 1846 is generally accepted as the start of the modern era of anesthesia. For the first time physicians had a reliable means to keep their patients from experiencing pain during surgical procedures.
The neurophysiologic state produced by general anesthetics is characterized by five primary effects: unconsciousness, amnesia, analgesia, inhibition of autonomic reflexes, and skeletal muscle relaxation. None of the currently available anesthetic agents when used alone can achieve all five of these desired effects well. In addition, an ideal anesthetic drug should induce rapid, smooth loss of consciousness, be rapidly reversible upon discontinuation, and possess a wide margin of safety.
The modern practice of anesthesiology relies on the use of combinations of intravenous and inhaled drugs (balanced anesthesia techniques) to take advantage of the favorable properties of each agent while minimizing their adverse effects. The choice of anesthetic technique is determined by the type of diagnostic, therapeutic, or surgical intervention to be performed. For minor superficial surgery or for invasive diagnostic procedures, oral or parenteral sedatives can be used in combination with local anesthetics, so-called monitored anesthesia care techniques (see Box: Sedation & Monitored Anesthesia Care, and Chapter 26). These techniques provide profound analgesia, with retention of the patient’s ability to maintain a patent airway and to respond to verbal commands. For more extensive surgical procedures, anesthesia may begin with preoperative benzodiazepines, be induced with an intravenous agent (eg, thiopental or propofol), and be maintained with a combination of inhaled (eg, volatile agents, nitrous oxide) or intravenous drugs (eg, propofol, opioid analgesics), or both.
MECHANISM OF GENERAL ANESTHETIC ACTION
General anesthetics have been in clinical use for more than 160 years but their mechanism of action ...