Some Key Side Effects of General Anesthetic Agents:

• CNS depression
• depression of body temperature regulating centers (hypothalamus)
  
• increased cerebral blood flow
• respiratory depression
• hypotension
• vasodilation
• myocardial depression
• muscular relaxation

Effects of Anesthesia on the Respiratory System

During breathing, a volume of air is inhaled through the airways (nose/mouth>trachea>bronchi>bronchioles) into millions of tiny gas exchange sacs (the alveoli) deep within the lungs.  Oxygen (O2) diffuses into the blood cells from the capillaries of the alveoli where it is circulated to the body's cells.  At the same time, carbon dioxide (CO2), a waste product, is released back into the lungs from the veins.  CO2 is a main stimulus for respiration.  As the amount of CO2 in the cells increases, the body is triggered to breath to rid the CO2 and intake fresh oxygen that the body's cells require.  An excessive prolonged buildup of CO2 can be toxic to the body primarily because it takes up room in the cells for oxygen. 

General anesthetics cause depression of the respiratory center in the brain reducing the ability for patients to breath on their own.  Therefore, anesthetic machines are used to breath for patients and they must produce enough gas exchange (ventilation) to keep the patient alive.  Ventilation is expressed as the volume of gas inhaled/exhaled during a breath (tidal volume) x the breathing rate.  Respiration has two phases: inhalation (oxygenation) measured by pulse oximetry and exhalation measured by capnography.  These parameters, along with anesthetic agent concentration, must be monitored closely to ensure proper ventilation.

►click here to watch About.com health video about how the lungs work

Effects of Anesthesia on the Circulatory System

Proper functioning of the heart and blood vessels is necessary to pump oxygen-rich blood through arteries, arterioles, and capillaries to be utilized by the cells within the body's tissues.   On its way back to the heart, the oxygen-poor blood travels through a system of veins.  Carbon dioxide, a waste product, is removed from the blood and replaced with fresh oxygen that has been inhaled through the lungs.

Anesthetic agents depress the heart muscle and vasculature, decreasing cardiac output and blood pressure.  Fluid requirements are increased because of fluid loss due to breathing dry, cold oxygen, hemorrhage or exposure of moist viscera to room air (e.g. during surgery).  Several measures can be taken to control heart rate, blood pressure and minimize the effects of dehydration, including the administration of certain drugs and intravenous fluids, adjusting the depth of anesthesia, etc.  Patients must be monitored closely to ensure the heart is beating properly.  A disruption in the flow of blood through the circulatory system could cause a lack of oxygen perfusion that could result in tissue and organ damage.

Effects of Anesthesia on Thermoregulation

Cells and tissues function and communicate well at a normal body temperature.  Patients frequently become hypothermic during anesthesia because of inhalation of cold gasses, exposure of body cavities to the room air (e.g. during surgery), and loss of normal thermoregulatory mechanisms and behaviors.  Hypothermia leads to depression of all physiologic functions (including respiration and cardiac function) and slows the metabolism of anesthetics resulting in prolonged recovery times.  Heat loss is prevented by minimizing anesthetic times, insulating cold surfaces with blankets and supplementing heat with water-driven heating pads, pre-warmed fluids and/or warm air blowers (BEHR Huggers).

Process for Anesthetic Procedures

• Patient is evaluated (e.g. history, physical examination, evaluation of labwork)
  
• Vitals are taken
• Preanesthetic bloodwork is performed
• IV Catheter
• Preanesthetic medications may be administered
• Patient is induced with injectable anesthetic
• Tube (endotracheal tube) is inserted in windpipe
• Hooked up to gas anesthetic and oxygen
• Monitoring equipment is connected
• Procedure performed and vitals closely monitored
• Anesthesia is turned down prior to awaking
• Anesthesia is turned off
• Medication administered to relieve pain
• Patients closely evaluated until fully awake