positioning in anesthesia

Topic for the day is "what are the different positions given in anesthesia and what are the adverse effects of each?"

The specific positions given in anesthesia are as below

• supine
• prone
• sitting
• lithotomy
• lateral decubitus

The variations given to the above positions are the following

1. The lawn chair position, in which the hips and knees are slightly flexed which, reduces stress on the back, hips, and knees, and is better tolerated by patients who are awake or undergoing monitored anesthesia care. In addition, because the legs are slightly above the heart, venous drainage from the lower extremity is facilitated.
2. The frog-leg position, in which the hips and knees are flexed, and the hips are externally rotated with the soles of the feet facing each other, allows access to the perineum, medial thighs, genitalia, and rectum.
3. The Trendelenburg position  is supine head down position helps improve exposure during abdominal and laparoscopic surgery, and to prevent air emboli and facilitate cannulation during central line placement,The Trendelenburg position has significant cardiovascular and respiratory consequences -The head-down position increases central venous, intracranial, and intraocular pressures. Prolonged head-down position also can lead to swelling of the face, conjunctiva, larynx, and tongue with an increased potential for postoperative upper airway obstruction. The cephalic movement of abdominal viscera against the diaphragm also decreases functional residual capacity and pulmonary compliance. The stomach also lies above the glottis. Endotracheal intubation is often preferred to protect the airway from pulmonary aspiration related to reflux and to reduce atelectasis.
4. Reverse Trendelenburg position is supine head tilt up position  is often employed to facilitate upper abdominal surgery by shifting the abdominal contents caudad mostly used in laparoscopic surgeries. The position of the head above the heart reduces perfusion pressure to the brain and should be taken into consideration when determining optimal blood pressure.
5. The prone or ventral decubitus position  is used primarily for surgical access to the posterior fossa of the skull, the posterior spine, the buttocks and perirectal area, and the lower extremities. Both arms may be positioned to the patient's sides and tucked in the neutral position.Head is kept neutral with horse shoe headrest, surgical pillow or mayfield pins or rotated to the side if adequacy of neck mobility is available.. Extra padding under the elbow is needed to prevent compression of the ulnar nerve. The arms should not be abducted greater than 90 degrees to prevent excessive stretching of the brachial plexus. Elastic stockings and active compression devices are needed for the lower extremities to minimize pooling of the blood, especially with any flexion of the body,The dependent eye must be checked frequently for external compression. The face is not always visible, hence  Mirror systems are available to monitor eye compression  but visual confirmation that the eyes are unimpinged, by direct visualization or tactile confirmation is good.Because the abdominal wall is easily displaced, external pressure on the abdomen may elevate intra-abdominal pressure in the prone position. This elevated pressure compromises respiration and transmits elevated venous pressures to the abdominal and spine vessels, including the epidural veins which increases chances of bleeding in spinal surgery, low venous pressure is desirable to minimize bleeding and facilitate surgical exposure. External pressure on the abdomen may push the diaphragm cephalad, decreasing functional residual capacity and pulmonary compliance, and increasing peak airway pressure. Abdominal pressure also may impede venous return through compression of the inferior vena cava. For these reasons, careful attention must be paid to the ability of the abdomen to hang free and to move with respiration.To prevent tissue injury, pendulous structures (e.g., male genitalia and female breasts) should be clear of compression; the breasts should be placed medial to the bolsters.
6. The sitting position,is less common, is mostly used to approach the posterior cervical spine and the posterior fossaa has advantages over the prone position for neurosurgical and cervical spine surgeries are excellent surgical exposure, decreased blood in the operative field, and, possibly,superior access to the airway, reduced facial swelling, and improved ventilation, particularly in obese patients. A variation of the sitting position, the beach chair position is increasingly used for shoulder surgeries, including arthroscopic procedures for its  access to the shoulder from the anterior and posterior aspect, and potential for great mobility of the arm at the shoulder joint.The head may be fixed in pins for neurosurgery or taped in place with adequate support for other surgeries Excessive cervical flexion has numerous adverse consequences.it can impede arterial and venous blood flow, causing hypoperfusion or venous congestion of the brain. It may impede normal respiratory excursion. Excessive flexion also can obstruct the endotracheal tube and place significant pressure on the tongue, leading to macroglossia. Generally, maintaining at least two fingers' distance between the mandible and the sternum is recommended for a normal-sized adult, and patients should not be positioned at the extreme of their range of motion Extra caution with neck flexion is advised if transesophageal echocardiography (TEE) is used for air embolism monitoring because the esophageal probe lies between the flexed spine and the airway and endotracheal tube, adding potential for compression of laryngeal structures and the tongue.. The arms are supported to the point of slight elevation of the shoulders to avoid traction on the shoulder muscles and potential stretching of upper extremity neurovascular structures. The knees are usually slightly flexed for balance and to reduce stretching of the sciatic nerve, and the feet are supported and padded.The hemodynamic effects of  a supine patient in the sitting position are  Because of the pooling of blood into the lower body under general anesthesia  patients are particularly prone to hypotensive episodes. Elastic stockings and active leg compression devices can help maintain venous return.Because of the elevation of the surgical field above the heart, and the the dural venous sinuses are open causing risk of  venous air embolism Arrhythmia, desaturation, pulmonary hypertension, circulatory compromise, or cardiac arrest may occur if sufficient quantities are entrained. If the foramen ovale is patent, even small amounts of venous air may result in a stroke or myocardial infarction owing to paradoxical embolism.
7. Lithotomy position is frequently used during gynecologic, rectal, and urologic surgeries. The hips are flexed 80 to 100 degrees from the trunk, and the legs are abducted 30 to 45 degrees from the midline. The knees are flexed until the lower legs are parallel to the torso, and the legs are held by supports or stirrups caution for safety  of the hand must be done  to avoid crush injury to the fingers if trapped in table positioning  so the arms on armrests far from the table hinge point is recommended at all times when patients are in the lithotomy position.The lithotomy position also may cause significant physiologic changes. When the legs are elevated, preload increases, causing a transient increase in cardiac output and, to a lesser extent, cerebral venous and intracranial pressure in otherwise healthy patients. In addition, the lithotomy position causes the abdominal viscera to displace the diaphragm cephalad, reducing lung compliance and potentially resulting in a decreased tidal volume.
8. The lateral decubitus position  is used most frequently for surgery involving the thorax, retroperitoneal structures, or hip. The patient rests on the nonoperative side and is balanced with anterior and posterior support, such as bedding rolls or a deflatable beanbag, and a flexed dependent leg. The arms usually are positioned in front of the patient. The dependent arm rests on a padded arm board perpendicular to the torso. The nondependent arm is often supported over folded bedding or suspended with an armrest or foam cradle. If possible, the arm should not be abducted more than 90 degrees. The patient's head must be kept in a neutral position to prevent excessive lateral rotation of the neck and stretch injuries to the brachial plexus.To avoid compression injury to the dependent brachial plexus or vascular compression, an “axillary roll” (generally a liter bag of intravenous fluid) is frequently placed just caudal to the dependent axilla.The lateral decubitus position also is associated with pulmonary compromise. In a patient who is mechanically ventilated, the combination of the lateral weight of the mediastinum and disproportionate cephalad pressure of abdominal contents on the dependent lung favors overventilation of the nondependent lung. At the same time, pulmonary blood flow to the underventilated, dependent lung increases owing to the effect of gravity. Consequently, ventilation-perfusion matching worsens, potentially affecting gas exchange and ventilation.