Arm abduction > 90 degrees can push the head of the humerus into the axillary neurovascular bundle so keep arms less than 90 degrees. Pressure point padding may reduce the risk of skin and soft tissue damage but there are no studies showing a reduction in peripheral neuropathies in the perioperative period [Barash]
In transitioning to the supine position, ventilation becomes a function of abdominal and diaphragmatic movement, with less contribution from the rib cage / chest wall than when upright. Compared to other surgical positions, the supine position produces the least amount of hemodynamic and ventilatory changes. The “lawn chair position,” a slight variation of supine positioning in which the knees are slightly flexed, may be better tolerated in MAC procedures. The lawn chair position relaxes the abdominal musculature and thus improves closing conditions, and also enhances venous return from the legs [Miller]
Complications of the supine position include pressure alopecia (for long procedures), backache, and tissue ischemia [Warner MA. Positioning in Anesthesia and Surgery, 3rd ed: 39-46, 1997]
If a patient is placed in Trendelenburg position, shoulder braces should not be used as the risk of compressive injury to the brachial plexus is significant. Complications of the Trendelenburg position include increased intracranial and intraocular pressure, as well as increased facial/laryngeal edema which can lead to post-operative airway obstruction (consider using the air leak test in these patients). FRC and pulmonary compliance are reduced by the dislocated viscera.
The effects of the Trendelenburg (TREND) position and passive straight leg raising (PLR) on cardiopulmonary performance in 18 anesthetized patients undergoing myocardial revascularization were studied with a two-dimensional transesophageal echocardiography probe and a thermodilution right ventricular ejection fraction (RVEF) pulmonary artery catheter. The TREND position (at 20 degrees) and PLR (at 60 degrees) were studied in relation to the level-supine position in random order. At 3 min, the TREND caused significant (p less than .05) decreases in heart rate (62 +/- 9 to 58 +/- 10 [SD] beat/min) and RVEF (0.48 +/- 0.11 to 0.44 +/- 0.10), and significant increases in mean arterial pressure (77 +/- 11 to 82 +/- 11 mm Hg), mean pulmonary artery pressure (16 +/- 4.3 to 19 +/- 5.5 mm Hg), wedge pressure (11 +/- 4 to 13 +/- 4 mm Hg), cardiac index (CI) (2.36 +/- 0.79 to 2.52 +/- 0.93 L/min.m2), right ventricular end-systolic volume index (44 +/- 21 to 58 +/- 21 ml/m2), right ventricular end-diastolic volume index (83 +/- 24 to 102 +/- 22 ml/m2), and shunt fraction (0.16 +/- 0.06 to 0.19 +/- 0.06). CVP and left ventricular areas did not change significantly. PLR had similar effects as the TREND position, except CI did not change significantly. Thus, the TREND and PLR resulted in minor hemodynamic improvement with right ventricular dilation, decreased RVEF, and impaired oxygenation in the anesthetized cardiac surgical patient [Reich, Konstadt, Raissi et. al. CCM 17(4) 313, 1989].
Hips are flexed 80-100 degrees and legs abducted 30-45 degrees. Knees are flexed until parallel with the torso
Movement of abdominal contents (in particular when patients have an abdominal mass) can obstruct venous return to the heart. Loss of lordosis can lead to back pain [Martin JT. Positioning in Anesthesia and Surgery, 3rd ed: 47-70, 1997]. Arm boards are recommended to keep the fingers away from the break in the table, which has in the past caused significant crush injuries. Common peroneal nerve injury is most common with this position, accounting for 40-78% of nerve injuries in this position – risk factors include low BMI, prolonged duration, and recent cigarette use [Warner et. al. Anesthesiology 81: 6, 1994], with other studies confirming that duration > 2 hrs as a significant risk factor [Warner et. al. Anesthesiology 93: 938, 2000]. Compartment syndrome risk is approximately 1:9000. In one study, no patients suffered a motor injury and most sensory deficits/neuropathies resolved within 6 months [Warner et. al. Anesthesiology 93: 938, 2000]. In another, the incidence of motor deficit was only 1:3608 [Warner et. al. Anesthesiology 81: 6, 1994]
The risk of compartment syndrome is higher in lithotomy (1:8720) and lateral decubitus (1:9711) than it is in supine (1:92,441) – of the 13 patients in Warner’s study who developed compartment syndrome with no pre-existing cause, the duration of surgery ranged from 3.2 to 15.7 h (avg. 7.2 h, in contrast, the average duration of procedures for all patients during the 10 year study period was 2.7h) [Warner et. al. Anesthesiology 94: 705, 2001]
Lateral decubitus is associated with pulmonary compromise due to movement of abdominal contents as well as the mediastinum, which enhance airway movement to the non-dependent lung while increasing blood flow to the dependent lung, thereby adversely affecting ventilation-perfusion matching
Placing someone in lateral decubitus may require additional support for the head. The dependent eye should be checked for external compression and both eyes should be taped prior to positioning. A chest roll (NOT an “axillary roll”) is placed caudal to the axilla, ensuring that the thorax is supported by the chest wall and not the actual axilla. The dependent arm is perpendicular to the body – consider checking pulses periodically (lost pulse = arm compression vs. general hypotension). A kidney rest placed under the dependent iliac crest and prevent compression of the vena cava.
Advantages include excellent surgical exposure, decreased blood loss, superior access the airway, reduced facial swelling, and improved ventilation (especially in obese patients). Sitting patients are, however, prone to hypotension – consider alternating between other positions. In neurosurgical patients (p-fossa), excessive neck flexion can impede both arterial and venous blood flow, kink the ETT, and put significant pressure on the tongue (which could potentially require tracheostomy). Always leave at least two fingerbreadths distance between the chin and the sternum. Sitting patients (especially neurosurgical) are also at risk for venous air embolisms, which cause arrhythmias, desaturation, pulmonary hypertension, arrest, and even stroke or MI in PFO patients. Ultrasound may help in detection
Mandates frequent eye checking just like the lateral position. Keep in mind that in certain patients, lateral rotation of the neck can compromise arterial flow to the brain. Horseshoe headrests are ideal in that they allow reasonable access to the airway in these patients. Thorax is supported by rolls/bolsters and OR tables are generally designed to relieve abdominal compression and maintain pulmonary function. Breasts should be placed medial to the bolsters. Prone positioning is not ideal for obese patients, whose pulmonary function is reduced and who cannot be easily repositioned if needed – consider alternative positions if possible
For prone patients, Backofen and Schauble found that even after careful positioning, being prone caused an increase in SVR and PVR as well as a decrease in SV and CI (MAP stayed the same), and recommended that patients in precarious cardiovascular states receive invasive monitoring before being placed prone [Backofen et al Anesth Analg 64: 194, 1985 (abstract)]. Kaneko et. al. found that the lungs of prone patients were entirely West Zone 3 conditions [Kaneko et. al. J Applied Physio 21: 767, 1966]. Consider goggles on all prone patients – blindness is more common in prone patients and is associated with A) long procedures B) blood loss C) hypotension D) < 8 mg/dL and E) neurovascular or bypass procedures.
Overall incidence of peripheral nerve injury is 0.11% [Blitt et. al. APSF 9: 17 1994]. In terms of claims filed, ulnar neuropathy is the most common (28%), followed by brachial plexus (20%), lumbosacral (16%), and spinal cord (13%), however ulnar neuropathies are decreasing, with current proportion dropping to ~ 17% (1990’s), as spinal cord injuries now make up almost 27%. Note that the ASA practice advisory, published in 2000 [Anesthesiology 92: 1168, 2000], was based on expert opinion and not science
Upper Extremity Positioning
Should be kept at < 90 degrees abduction, and the forearm should be either supinated or neutral to keep pressure away from the spiral groove of the humerus and the ulnar nerve.
Note that ulnar neuropathies develop in medical and surgical patients [Warner et. al. Anesth 92: 613, 2000]. Non-surgical contributing factors include A) Male B) BMI > 38 C) prolonged post-operative bed rest [Warner et. al. Anesth 81: 1332, 1994]. Furthermore, many patients who develop postoperative ulnar neuropathies are found to have contralateral nerve dysfunction as well [Alvine et. al. J Bone Joint Surg Am 69: 255, 1987], suggesting that these patients may actually be predisposed to injury. Lastly, many patients who develop an ulnar neuropathy do not complain about symptoms until 48 hours after their surgical procedure [Warner et. al. Anesth 81: 1332, 1994; Alvine et. al. J Bone Joint Surg Am 69: 255, 1987]. Interestingly, a prospective study of ulnar injuries showed that none occurred in the first two postoperative days [Warner et. al. Anesth 90: 54, 1999]
For nerve deficits in general – if the deficit is sensory, assure the patient that the deficit will almost certainly resolve within 5 days and follow up with them by phone (if function abnormal, obtain formal neurologic consultation). A motor deficit is more important, less common, and requires immediate neurologic consultation.
Brachial Plexus Injury
Often presents as an ulnar nerve sensory deficit, most commonly associated with abduction > 90 degrees, lateral rotation of the head, sternal retraction, or trauma to the nerves themselves. In non-cardiac surgery, the incidence is only 0.02% [Cooper et. al. Clin Orth Relat Res 228: 33, 1988].
Treatment of Nerve Injuries
Always seek neurologic consultation. Sensory injuries usually resolve, whereas motor injuries are more severe and mandate EMG (can help determine if it was present preoperatively, as denervation signs take ~ 3 weeks to develop). Reversible motor nerve injuries usually take 3-12 months to recover and require physical therapy to prevent atrophy and contractures in the interim
Pulses and capillary refill are unreliable indicators of CS (i.e., you can still get a compartment syndrome despite having pulses and refill. Overall risk is 1:9000 and is no different in the lithotomy (legs) and lateral (arms) positions. Ferrohemate is a byproduct of CS which can lead to ARF. Additionally, the dead tissue from CS is predisposed to infection and can lead to lung injury and possibly acute lung injury. [Barash]
Perioperative eye injuries occurred in 0.056% of 60,000 cases [Roth et. al. Anesthesiology 85: 1020, 1996]. Corneal abrasions are the most common and should be treated with antibiotic ointment – a prospective study of 671 patients suggested that vision worsens in 4.2% of patients postoperatively, but that it almost always resolves by 2 months [Warner et. al. Anesthesiology 96: 855, 2002]. Blindness is more rare, with incidences between 1:50-100,000 for non-ocular/cardiac/spine surgery, and closer to 0.1% for bypass or prone spine surgery [Kalyani et. al. Ann Thor Surg 78: 34, 2004; Roth et. al. Anesthesiology 85: 1020, 1996; Roth et. al. Anesthesiology 95: 575, 2001; Warner ME et. al. Anesth Analg 93: 1417, 2001; Nuttall GA et. al. Anesth Analg 93: 1410, 2001]. Etiology is usually ischemic optic neuropathy, which is caused by prolonged hypotension, duration of surgery, blood loss, anemia, and pressure secondary to prone positioning. Note, however, that 44% of patients with ION in the ASA Postoperative Visual Loss Registry eventually recovered their vision [Lee ASA Newsletter 67: 7, 2003].