"Primum non nocere" (first of all do no harm). Hippocrates 400BC Surgeon and anaesthetist are jointly responsible for positioning the patient. Patient positioning depends on the following factors : 1. Patient : CVS and RS compromised, obesity 2. Surgical : Provide surgical access and minimize bleeding 3. Anaesthetic : Prevent aspiration and optimize respiration and venous return PROBLEMS 1. Cardiovascular Postural hypotension occurs as venous return is greatly influenced by gravity in the anaesthetized patient, being more marked with sympathetic block. e.g. spinal blockade, vasodilators, prolonged immobilization. Blood pressure should be measured within 5 minutes of changing position. Air embolism may occur when the site of surgery is above the level of the heart. 2. Respiratory Difficulty in maintaining the airway Limited access to the airway (e.g. prone position) Endobronchial intubation should be excluded after change of position. Embarrassment of ventilation by upward displacement and splinting of the diaphragm (e.g. head low position) Hypoxaemia due to airway closure, reduction of FRC and increased ventilation I perfusion mismatch (e.g. head low position) 3. Gastro intestinal Increased tendency to regurgitation as GA reduces tone in the crico-pharyngeal sphincter. Prevention of regurgitation is therefore dependent on the competence of the lower oesophageal sphincter, which may also reduce during anaesthesia. 4. Pressure effects Eyes, ears, blood vessels, breasts, genitals may be injured. 5. Nerve damage 7.1 Occurs due to stretching (brachia! plexus) or localized compression against a bony prominence causing demyelination (ulnar, common peroneal)
Strain on ligaments and joints Joints should not be subjected to a range of passive movement under anaesthesia which would not be tolerated in the awake state especially in the elderly where movements are restricted. Backache occurs due to muscle relaxation particularly under regional anaesthesia. DORSAL DECUBITUS (SUPINE) POSITION (Decubitus refers to the part of the body in contact with the table) Problems Pressure point injuries : head, heels, sacrum, elbows and nerve injuries • Brachia! plexus injuries are most likely if the head is extended and turned away from an arm abducted> 90°, both arms are abducted, externally rotated, or lies below the horizontal plane. • Radial nerve compression occurs due to a vertical screen pressing the nerve against the humerus causing wrist drop. • Ulnar nerve is compressed as it passes behind the medial epicondyle causing a sensory loss over the fifth finger. 1. SUPINE HORIZONTAL The horizontal position is poorly tolerated in the awake patient. A pillow placed under the knees to flex the hips and knees increases comfort. 2. TRENDELENBURG (head low) Figure 7.1 Trendelenburg position • Arterial hypoxaemia due to reduction in FRC, airway closure, and embarrassment of ventilation is a special problem in the obese and elderly. • Increased airway pressures may occur specially with IPPV with LMA. • Increased venous return may overload the heart in cardiac disease e.g.mitral stenosis, left ventricular dysfunction. To increase venous return in hypovolaemia only the legs should be elevated. Congestion in the head and neck may cause cerebral oedema. • Increased risk of regurgitation • Brachia! plexus is at risk due to over-abduction of the arm. Shoulder braces over the acromio-clavicular joint prevent compression.
Precautions • Always restore to the horizontal position before reversing the relaxant and establishing adequacy of ventilation. • Increase the Fi02 for the obese and the elderly. 3. REVERSE TRENDELENBURG (head high) Problems • Hypotension due to reduced venous return (gravity dependent) • Cerebral perfusion pressure will be less than the measured blood pressure by 2 mm Hg for every 2.5 cm elevation of head above the horizontal. • Aspiration of blood or vornitus • Air embolism (see page 19.15) Gall bladder bridge may cause hypotension due to interference with venous return. Precautions • Be careful with sympathetic blockade, hypovolaemia and cardiac disease. • Monitor for air embolism. 4. LITHOTOMY POSITION Padded support Ensure sacral support Figure 7.2 Lithotomy position Both legs should be flexed at the hips and knees, and simultaneously elevated. They should be lowered together at end of surgery to avoid strain on the lumbar spine. Overstretching should be avoided to prevent sciatic nerve damage.
Problems • Increased venous return may compromise cardiac patients. • Ventilation is restricted due to compression by thighs especially in the obese. • Tendency to regurgitate (avoid inducing anaesthesia in lithotomy position) • Bleeding may not be visible to the anaesthetist at the head end of the patient. • Concealed hypovolaemia causing hypotension when the legs are lowered • Backache due to strain on the sacro-iliac joints and hips LATERAL DECUBITUS POSITION Figure 7.3 The lateral position showing upper ann in position and axillary roll which supports the chest to free the axilla STANDARD LATERAL POSITION FOR RENAL SURGERY Aex the downside thigh and knee, while the upper leg is kept extended in line with the body to maintain alignment of cervical and thoracic spines. Place pillows under the head and between the legs. Kidney bridge should be situated just below the costal margin. LATERAL JACK KNIFE POSITION FOR RENAL SURGERY The down side iliac crest should be over the table hinge to allow stretching of the up-side flank. Venous pooling occurs in the legs. Figure 7.4 Jack knife position
LATERAL POSITION FOR THORACIC SURGERY Figure 7.5 Lateral position for thoracic surgery • Risk of pressure damage o Lateral peroneal nerve as it lies superficial to the neck of the fibula o Supra scapular nerves over the shoulder o Eyes and ears o Neuro-vascular bundle compressed in the downside axi!la reduces blood flow to the lower arm particularly in the obese. • Limited access to the airway • V/Q mismatch especially during IPPV due to better ventilation in the upper more compliant under perfused lung and reduced in the over-perfused dependent lung. Precautions Maintain the airway with an ETI or LMA. Monitor BP and pulse after the bridge is raised as it interferes with venous return. VENTRAL DECUBITUS (PRONE) POSITION Avoid overextension of shoulder Avoid facial trauma} -m m+ t t Support&--···· Figure 7.6 The standard prone position STANDARD PRONE POSITION Pelvis and shoulders should be elevated on pillows so that the abdomen hangs free to permit respiration. Arms placed by the side of the body protects the brachial plexus. The head, neck and limbs should be supported with padding for breasts and genitals.
KNEE CHEST POSITION ("seated prone") This position is most commonly used for spinal surgery (laminectomy, scoliosis correction) Figure 7.7 Knee chest position ("Seated prone") Problems of the Prone Position • Compression of the abdomen which occurs in the obese patient leads to : o Inferior vena caval compression which causes : increased venous engorgement specially in the spinal canal and increased venous bleeding which interferes with surgery hypotension due to reduced venous return o Embarrassment of respiration • No access to the airway during surgery • High risk of regurgitation • Pressure on nerves, eyes, ears, breasts, genitals • Neck injury (avoid by keeping the head in the sagittal plane in arthritic patients) Precautions • Maintain the airway with a cuffed tracheal tube. • IPPV is advisable for all but the shortest operations. • Be careful to support the head, neck and limbs while turning. • Check pressure points, airway, ears and eyes after positioning. • Place pads at all sites of compression against the table or supports. • Keep eyes closed with plaster to prevent corneal abrasions and avoid compression by the catheter mount. • Check for rotation of the neck which can cause strain on ligaments, and compression of the neck veins causing increased intracranial pressure. • Check BP, pulse, and ETT placement after changing posture or raising the bridge.