Surgical positions
Surgical positioning is the practice of placing a patient in a particular physical position during surgery. The goal in selecting and adjusting a particular surgical position is to maintain the patient's safety while allowing access to the surgical site. Often a patient must be placed in an unnatural position to gain access to the surgical site. Positioning normally occurs after the administration of anesthesia. In addition to considerations related to the location of the surgical site, the selection of a surgical position is made after considering relevant physical and physiological factors, such as body alignment, circulation, respiratory  constraints, and the musculatory system to prevent stress on the patient. Physical traits of the patient must also be considered including size, age, weight, physical condition, and allergies. The type of anesthesia used also affects the decision. Factors influencing the choice. Pressure is the force put on the patient's body. Those forces can stem from the surgery itself, instruments, drills, gravity, attachments, and bandages. The duration and intensity of the pressure is inversely correlated. The longer the duration of the pressure, the less pressure the body can endure. However, the body can endure a large amount of pressure for  brief periods of time. The amount of pressure on the tissue is based on the size of the area of the contact: the smaller the point of pressure, the greater effect it will have on the tissue. The position of instruments can cause damage to the body if pressure is not relieved periodically. The patient's own health is also considered. Respiratory and circulatory disorders, blood pressure, the patient's weight, old age, and body temperature may affect a patient's potential for pressure. Other forces that may damage the body are the folding of the tissue, called "shear", friction  from the tissue rubbing against other tissue, and moisture on the skin that can cause it to be more vulnerable to the other forces and factors, called "maceration". Changing positions. If the patient has been immobilized, it may be important to change the patient's position periodically to prevent blood pooling, to stimulate circulation, and to relieve pressure on tissues. The patient should not be placed in unnatural positions for an extended period of time. After anesthesia, the patient's inability to react to movements may damage joints and muscle groups. Considerations should be taken not to damage these muscle  groups by, for example, moving both legs simultaneously. Risks to extremities. The most common nerve injuries during surgery occur in the upper and lower extremities. Injuries to the nerves in the arm or shoulder can result in numbness, tingling, and decreased sensory or muscular use of the arm, wrist, or hand. Many operating room injuries could be solved by simply restraining the arms and legs. Other causes of nerve or muscular damage to the extremities is caused by pressure on the body by the surgical team leaning on the patient's arms and legs. The patient's arms can be  protected from these risks by using an arm sled. Separation of the sternum during a heart procedure can also cause the first rib to put pressure on the nerves in the shoulder. The lithotomy position is also known to cause stress on the lower extremities.