Positioning injuries as seen by the anaesthetist

M. Bund

10.1.1 Division of labour between surgeon and anaesthetist

Shared responsibility

The positioning of the patient on the operating table and monitoring the correct position is a shared task for surgeon and anaesthetist. The shared responsibility and distribution of labour is stipulated in the agreements between the Professional Federation of German Anaesthetists and the Professional Federation of Surgeons or of Orthopaedic Specialists [8-10].

Accordingly, the anaesthetist is responsible for positioning the patient to put him under anaesthetic and for the phase through to starting the actual surgical positioning [74]. The patient is arranged in the operating position once all anaesthesia measures have been completed. This is defined in the responsibility of the surgeon according to the requirements of the specific operation. He monitors the initial positioning of the patient on the operating table and is also responsible for intraoperative repositioning.

During the operation, the anaesthetist is responsible for the positioning of those parts of the body which he must have under his control for the anaesthetic procedure, i.e. primarily the head and the extremities required for monitoring and infusions [11]. He uses suitable measures to secure these areas so as to prevent injuries even when the covering over the patient hinders constant visual control or the position has to be changed during the operation. The anaesthetist must warn the surgeon urgently if a positioning required for a surgical position makes it difficult to monitor the patient or even jeopardises sustaining the vital functions. The same applies if there is a risk of positioning injuries from malpositioning, unintentional changes in position during the operation or from the direct intervention of the surgeons. The benefits and risks of certain positioning are to be weighed up critically. Basically, the positioning of the patient should come as close as possible to the physiologically neutral position of the joints.

The phase of immediate postoperative monitoring through to releasing the patient from the recovery room then sees the anaesthetist with responsibility for positioning again. According to the interdisciplinary agreement, this includes transferring the patient to another bed after the end of the operation, »... unless special circumstances require the surgeon's involvement in patient transfer« [9]. It is also possible for hospitals to reach their own agreements, for example with the fundamental involvement of a surgeon in patient transfer [68].

Preoperative information and documentation

An essential issue in the anaesthetist's visit to the patient before the operation is to detect potential hazards and risks for the patient and take measures to avoid them. This also includes the risk of positioning injuries. Case history, clinical examination and X-rays can draw attention to anatomic anomalies or pathological change, such as ar-throsis, cervical rib, endoprostheses or »shunt« arm. These findings are documented and their relevance discussed with the surgeon. If cervical ribs are known, the arms will not be moved out from the body because of the risk of plexus injuries [65]. In the case of neurological deficits or previous conditions, the preoperative status should be examined and documented by a neurologist. Special risks may entail giving the patient specific information about positioning injuries. Otherwise the general reference printed in the information form is adequate, to the effect that it is possible but rare for injuries to the nerves to occur with dysaesthesia and paralysis from pressure or tension in the position required for the operation.

The anaesthetist must document the kind of operative positioning on the anaesthesia protocol. A detailed description and the documentation of routine measures to control the position is not necessary in the case of standard positioning (Federal Supreme Court in its judgement pronounced on 24.01.1984, MedR 1985 p. 221/222). The situation is different if it is necessary to deviate from the standard. It is also advisable to keep a record of any discrepancies between the surgeon's explicit requirement for a certain positioning and the anaesthetist's objections. Increasingly stringent requirements in legal practice also entail stricter requirements for documentation.

During the operation, observant monitoring with repeated controls of the relevant parts of the body can help to detect or prevent unintentional changes in position and new possibilities of injuries (pressure points, incorrect joint positions, etc.).

10.1.2 Occurrence of positioning injuries

10.1.2.1 Frequency

Cases of »anaesthesia paralysis« were already reported more than 100 years ago, which soon transpired to be cases of injuries occurring during and not through anaesthesia [16].

Positioning injuries are said to occur about 50 times per 10,000 anaesthetics, including nerve lesions in 6 to 12 of 10,000 anaesthetics [19]. Other studies [25, 53] also describe the frequency of nerve injuries during an anaesthetic at approx. 0.1% (31/30,000 anaesthetics). In decreasing order, these affected the brachial plexus (11 times), ulnar nerve (8 times), radial nerve (7 times) and peroneal nerve (5 times) [25]. But the specific use of electrophysiological examinations reveals a far higher incidence of postopera-

tive nerve injuries; in the case of heart surgery, the incidence of sensibility or motor neuropathy in the ulnar nerve is said to reach up to 38% [32, 75]. But a considerable share of preexisting dysfunctions (up to 30%) must be taken into account, together with the possibility of other injury mechanisms (circulatory problems, microembo-lism) [75]. A follow-up study of peripheral nerve lesions of iatrogenic cause revealed 226 of 267 cases of nerve injuries (85.4%) in the context of surgical procedures [31]. But in this study, most of the cases had been caused directly by the surgical procedure, with positioning injuries only ascertained in 14 cases.

10.1.2.2 Kind of injuries

The range of positioning injuries extends from harmless surface abrasions through to severe, possibly incapacitating lesions. Isolated lethal cases have occurred, for example following positioning injuries with compartment syndrome in both lower legs with rhabdomyolysis and subsequent multiple organ failure [45]. Structures at risk from positioning injuries are the skin and surface soft tissues, joints and ligaments, brachial plexus and peripheral nerves, blood vessels and the eyes.

Skin and soft tissues

Long immobilisation on the operating table can cause pressure sores in the skin and subcutaneous tissues. Exposed areas such as the heels or buttocks are especially at risk. Patients with poor trophic status or circulation e.g. in the case of diabetes mellitus or arteriosclerosis and older patients are affected more frequently. Local pressure effects are usually also accompanied by more serious factors, particularly poor perfusion resulting from longer phases of hypotension or from cooling down. Together with generous padding of exposed areas (silicon gel and foam pads or padded cuffs for the extremities), formable silicon gel mats with a large support area can be used for risk patients, or multiple water mats where the support surfaces are replaced periodically, to avoid pressure necrosis. Warming mats can help to prevent drops in temperature over the operating table. Indeed, maintaining the patient's normal body temperature is an important measure to counteract peripheral circulation problems and thus pressure injuries to the skin. The influence of hypothermia and hypotension is also illustrated by the occurrence of skin ulcers at the back of the head of HLM patients (heart-lung machine) whose head was not placed on a positioning cushion [39].

Mechanical injuries to the soft tissues or muscles during surgical procedures can be caused by the operating tables and instrument tables or brackets. Soft tissues can get caught between the operating table and attached fittings if the table has to be adjusted during the operation. This can happen for example if the positioning is changed to make it easier to close the wound or if the legs are posi tioned horizontally from the lithotomy position. However, design features of modern operating tables prevent such complications to a great extent.

Joints and ligaments

Enforced movements to the relaxed body of the patient deprived of protective reflexes and pain reactions can cause injuries to the joints and ligaments. This applies in particular in the case of degenerative or traumatic conditions. In isolated cases it may be appropriate to test the required positioning while the patient is still awake to ask the patient whether the positioning is tolerable. Extremities spread out from the body should always be secured on holders to prevent them from falling. Any changes in position are carried out carefully with an adequate number of experienced helpers.

Nerves

Injuries to the nerves are caused by direct compression, by tension or pressure in unphysiological positions of the joints, and in isolated cases also if tourniquets are applied for too long [61]. In the case of tension and pressure injuries, inadequate blood circulation in the nerves (ischaemia of the vasa nervorum) plays a major role [24]. Blunt application of force which does not destroy the nerve structure will usually see good recovery of the sensory and motor deficits if the pressure injury or ischaemia was only short lived [75]. Exposed nerves of the upper and lower extremities and the brachial plexus are particularly at risk.

If a nerve lesion is ascertained after the operation, other possible causes should be examined as well as positioning injuries, such as direct injuries from the operation, pressure injuries from haematomas or oedemas and anatomic anomalies which can favour injuries. Patients with various conditions will be predisposed to neuropathies, e.g. alcohol abuse, diabetes mellitus, uraemia, vitamin deficiency, malignant tumours [71, 75, 79]. Two-sided postoperative reduction in the velocity of nerve conduction in particular will probably reveal (subclinical) neuropathy already existing before the operation [23].

Brachial plexus. After leaving the intervertebral foramina of the cervical spine, the brachial plexus runs through the scalene gap and narrow space between the clavicle and first rib to the axilla. The humerus head provides a fixation point here. Injuries are caused either from pressure with further narrowing of the physiological constrictions, or from positioning causing an enlargement of the distance between the named fixation points and thus stretching the plexus. The stretch mechanism impairs circulation to the nerve fibres. Depending on how long the inadequate circulation lasts, hypaesthesia and paraesthesia can be observed, and even irreversible functional loss if ischaemia lasts for several hours [45]. Possible injury mechanisms include [12]:

4 shoulder supports fitted too far in the medial direction, jamming the plexus between clavicle and first rib,

4 relapse of the shoulder girdle in the anaesthetised, relaxed patient, bringing the clavicle against the first rib,

4 hyperextension of the cervical spine with the head turned to the other side.

Abduction and outer rotation of the upper arm can make the humerus head act as a hypomochlion and stretch the plexus in the axilla. Stretching injuries of the brachial plexus can also occur after a sternotomy with use of thorax clamps, and primarily affects the lower roots [23].

People with various anomalies (cervical rib, scalene syndrome, costoclavicular syndrome, hyperabduction syndrome) in the upper thorax outlet (thoracic outlet syndrome) are particularly at risk from injuries to the brachial plexus. Compression of the vessel nerve bundle is common for these anomalies [55].

It is important above all to prevent a relapse of the shoulders, abduction of the upper arm exceeding 90°, extreme outer rotation of the upper arm, dorsal extension and excessive distal tension of the arm.

Ulnar nerve. The ulnar nerve is at risk because of its anatomically exposed position in the medial epicondyle of the humerus and also to a lesser extent at the wrist. The nerve runs in the flat groove of the sulcus of the ulnar nerve at the medial epicondyle of the humerus with inadequate cover from connective tissues or muscles to provide sufficient protection from pressure [31]. Extreme flexion of the elbow and/or pronation of the lower arm increases the exposure and risk of compression for the ulnar nerve [3, 63]. The olecranon offers a certain protection with the lower arm in supination, but up to now there has been no evidence of supination positioning resulting in a lesser incidence of pressure injuries [63]. Injuries were also reported caused by unfavourable cables or infusion leads running in the area of the medial condyle and from blood pressure cuffs pulled too far in the distal direction over the elbow from too frequent blood pressure measurements [79].

During the operation, the elbow must be padded from below to prevent pressure lesions. Ekerot recommends careful padding, and positioning with stretched elbow and supinated lower arm, particularly for anatomic anomalies of the ulnar nerve with habitual luxation [27]. Positioning with pronation position of the hand should be avoided, together with greater flexion in the elbow and adduction close to the patient's body.

Radial nerve. The radial nerve runs in a spiral around the humerus. In the proximal section it is at risk if the inside of the upper arm is pressed against the edges of the ope rating table or rails. The arm must not hang down over the edge of the table! In the middle to distal part of the upper arm, lateral brackets or instrument tables pressing against the upper arm or instrument tables can compress the radial nerve. Stirrups, retractors and the edges of the table must be checked for an adequate distance to the patient's body. The wrist can be injured if fixation cuffs are pulled too tight [22].

Median nerve. Intraoperative injuries to the median nerve are rare and usually caused by a direct surgical trauma (e.g. in the area of the carpal tunnel). As far as anaesthesia is concerned, injuries are most likely from paravenous injections in the elbow [12], which is one reason why anaesthetists usually prefer distal access to the vessels. The arm must not be fixed in the area of the elbow with blood pressure cuffs or similar.

Nerves of the lower extremities. Bending and outer rotation in the hips can stretch the sciatic nerve. In the proximal calf, the peroneal nerve is at risk from its exposed position beneath the fibular head, and in the medial calf the saphenous nerve below the medial condyle of the tibia is at risk from compression [65].

Vessels

Complications occur from massive compression to blood vessels in exposed places or if extreme positioning kinks the blood vessels. In the prone position, congestion in the veins of the lower extremities is possible from compression of the inferior vena cava if positioning pads are put too far in the cranial direction, or the arterial circulation in the legs can be affected if positioning aids are put too far in the distal direction in the groin. Patients with peripheral occlusive vascular disease are at risk from ischaemia if the lower extremities are positioned up high and/or bent (lithotomy position). Capillary injuries caused by long-lasting tissue hypoxia can cause a reperfusion oedema after reperfusion with development of a compartment syndrome [46]. Compartment syndrome caused by positioning has been described for the lower leg, lower arm and shoulder [45]. The symptoms can also occur several hours after the operation [36, 45].

Circulatory problems caused by positioning for certain syndromes can be ascertained by provocation tests. In the case of thoracic outlet syndrome, a backwards tilt of the head while turning the chin sideways to the affected side (Adson's manoeuvre) not only causes sensibility problems but also compression of the subclavian artery with diminished radial pulse [55]. Similar symptoms can b e triggered by raising the arm ab ove the horizontal in the case of hyperabduction syndrome. This would prohibit any »over-head« positioning of the patient's arm. But these tests are not performed during routine preoperative examinations, nor are they demanded by law because of the rarity of thoracic outlet syndrome, for example [68]. If during an operation doubts occur with regard to circulation of the extremities, pulse oximetry at the corresponding extremity can provide initial indications of circulatory problems.

Depending on cuff pressure and length of time used, tourniquets can conceal the risk of ischaemic injuries to the tissue (nerve lesions, myasthenia, rhabdomyolysis, compartment syndrome). Arterial vascular occlusions occur, the frequency of deep vein thrombosis is not increased [6, 28]. Cuff pressure of 100-150 mmHg above the systolic blood pressure is considered adequate, and the tourniquet time should not exceed 2 h [76].

»Shunt« arms are wrapped up well in cotton wool, l oosely fixed and protected with arm positioning rails against exerted pressures.

Eyes

Lacking eyelid closure at the same time as a decrease in lacrimation while under anaesthetic can cause erosion of the cornea. Lacking eyelid closure increases the risk of direct injuries to the cornea, e.g. from face masks, fingernails, catheters or adhesive drapes. High persistent pressure on the orbita and bulbus can cause a fatal reduction in vision through to irreversible loss of sight. Irreversible loss of sight has been observed after being exposed to pressure for just 10 min in the prone position [22]. This is caused by ischaemia of the optic nerve and retina as a result of compression. Hypotension and anaemia can cause the ischaemic injuries and loss of sight [14]. The blood flow through the optic nerve and choroid is essentially passive from the arterial blood pressure, with only very slight autoregulation mechanisms [67]. According to Wolfe [78], unexpected bradyarrhythmia can be a warning sign of increased intraocular pressure.

Although impaired vision has been described for various positionings, specific significance is attributed to the prone position with the use of headrests. In rare cases, the use of face masks with a hard bead can cause pressure injuries to the optic nerve when the mask is unsuitably held. To avoid injuries of this kind, while under anaesthetic the patient's eyelids are closed without any pressure on the eyeball and complete orbital region. If the eyes cannot be seen during the operation, the eyelids must always be held closed with a plaster.

In the case of loss of vision after heart surgery, consideration must always also be given to the possibility of an embolism with occlusion of the central retinal artery [77].

Head and neck

The patient's head is positioned on a pillow or head ring so that the cervical spine is in the middle position. When the patient is relaxed, turning the head suddenly to the side can cause pain in the muscles and joints after the operation and even cause irritation to the branches of the cervical plexus. Turning the head with an extreme movement can stretch the brachial plexus on the contralateral side. In the case of bone disease in the cervical spine, the posture assumed by the patient while still awake is retained. Special care is required when operating a patient with a cervical fracture. These patients are brought into the operating theatre with a halo extension. They are intuba-ted with fibre-optic intubation in bed without changing the position of the head and cervical spine.

A strong turn of the cervical spine interrupts the flow of blood in the arteries to the brain. Turning the head 90° to the side must be expected to completely interrupt the flow of blood in the contralateral vertebral artery [66]. In the case of stenosis of the carotid artery, interference with the collateral flow can cause deleterious ischemia in the brain stem and cerebellum [61]. Venous drainage is also best with the head in the middle position.

In the supine position, the eyes are free. The only routine measure entails ensuring that the eyes are closed to prevent them from drying out.

Suitable devices must be provided to neutralise any tension or pressure on the tubus, e.g. from respiratory tubes or measuring sensors.

Arms

In the supine position, the arms can be basically positioned at the body, spread out on an arm support or one arm is raised on the anaesthesia stirrup. All kinds of arm positioning require special protection for the brachial plexus, for the radial nerve in its progress along the humerus and for the ulnar nerve in the medial elbow. Principle mechanisms causing injuries have already been discussed (7 see Sect. 10.1.2.2, Nerves).

Arms at the body. To relieve the brachial plexus, the clavicle is raised from the first rib with a stationary pad under the shoulder when the arm is positioned at the body. This is particularly important for example if tension is applied to the arms with strips of sticky plaster when the cervical vertebrae are blocked, because otherwise there is a risk of the plexus getting caught between the clavicle and first rib.

If the upper arm protrudes beyond the edge of the table, there is a risk of pressure injuries to the radial nerve. Not even a pad between the arm and operating table will withstand the pressure if an assistant leans against it! Further in the distal direction, the radial nerve can be compressed on the outside of the humerus and injured if the upper arm is jammed between the thorax and various holders fastened to the operating table.

The ulnar nerve is at risk from the pressure of the edge of the table in the area of the medial epicondyle of the humerus, particularly if the arm is not fixed adequately, for example just at the wrist. The risk is increased by flexion in the elbow and pronation of the lower arm, for example when positioning and fixing the lower arms at the body. These risks are frequently caused by the arm not having enough space next to the body on the operating table. They can be avoided by widening the table with a metal or plastic support device and laying the arm in a padded cuff (Aschemann arm positioning support, see Figs. 8.15 and 8.16). A rare cause for pressure injuries to the ulnar nerve can come from infusion leads or cables along the inside of the arm.

Spreading the arms out away from the body. If the arms are spread out away from the body, the brachial plexus can be inj ured by overstretching the arm in the shoulder joint, because the humerus head acts as a hypomochlion on the nerve bundles of the brachial plexus. In fact, abduction of the upper arm through more than 90° is the most frequently mentioned kind of positioning mistake causing plexus injuries [48]. But even keeping to an angle under 90° in the shoulder joint cannot always prevent intraoperative injuries to the plexus, because with the patient relaxed under the anaesthetic, the shoulder can fall back onto the table surface and clamp the plexus between the clavicle and first rib.

Effective prophylaxis consists of raising the arm above the level of the shoulder joint and padding under the shoulder, thus enlarging the distance between the clavicle and the first rib. The arm is extended from the body on a padded support. The upper arm is slightly rotated inwards in the shoulder joint and abducted by maximum 90°, the elbow is slightly bent (about 150°) and the back of the hand is pronated. Turning the head slightly to the side of the extended arm also takes the tension from the brachial plexus.

Even if the arm is correctly extended at first, during the operation it is not rare for critical changes to take place if the position of this arm is changed because of space requirements at the operating table or an assistant leaning against it. It is therefore vital for the arm to be fixed to the arm rest by suitable means such as a tape or non-compressive plaster so that it cannot fall down, because if the relaxed arm falls down, this can cause luxation of the shoulder and/or acute overstretching of the brachial plexus with a loss of functions. The arm itself, in particular the medial elbow, must not rest on the edge of the arm support.

Raising one arm. Pads must be used at the raised arm to prevent pressure injuries from the metal structure [65]. No tension must be exerted to the shoulder joint and brachial plexus.

Spinal column

About 30% of all patients claim »backache« after an operation, regardless of the anaesthetic procedure [38]. This is caused primarily by negating the lordosis in the lumbar spine and coccyx on the hard operating table so that the ligaments are stretched. Patients with »backache« should be allowed to dictate their own position on the operating table, indicating the painful area and using positioning cushions to improve the situation.

On the other hand, hyperlordosis of the lumbar spine as is common practice for some abdominal, gynaecological and urological operations, can also cause postoperative discomfort. Particularly in the case of predisposed patients with degenerative change in the spinal column, there is evidence of postoperative injuries to the vertebral joints caused by subluxation, microfractures and haema-tomas [40]. In the case of a patient with stenosis of the vertebral canal, hyperlordosis during an extended urol-ogical operation caused spinal infarction at L2/3 [4].

Lower extremities

As far as possible, the hips and knees are arranged in a physiological position, i.e. with a slight bend. The legs must not be crossed.

At the fibular head, the exposed peroneal nerve is at risk from support structures for drapes or operating tables and from incorrectly positioned tourniquets. In particular when the table is tilted, attention must be paid to a compression-free area. The Achilles tendon and heel must not protrude beyond the operating table and are secured from pressure.

10.1.3.1 Struma position

In patients with arthrotic conditions, extreme extension of the cervical spine, as required for example to expose the goitre, can cause pain and blockages. The head must never be allowed to »float freely« in extension.

Together with hyperextension of the cervical spine, the main risk in this position consists of the poor access and restricted possibilities for controlling the tracheal tubus and eyes because of the vicinity of the operating site and sterile covered operating area [65]. An eye ointment should therefore be administered as prophylaxis and both eyes covered.

10.1.3.2 Extension table

The extension table is required for reposition and osteo-synthesis of fractures to the femur head and per/subtro-chanteric fractures of the femur. A brace is positioned at the perineum to support the pelvis. In male patients, com pression of the genitals must be avoided [65]. Image converters are used to check reposition and osteosynthesis. Care must be taken to ensure that adjustment of the C-arm does not clamp or cause pressure injuries to any parts of the patient's body.

10.1.3.3 Lithotomy position

The lithotomy position with raised legs bent at the hips and knees causes considerable changes to respiration and circulation. Movement of the diaphragm is limited. Raising the legs results in autotransfusion of up to 600 ml of blood with a corresponding increase in the intrathoracic blood volume [41]. This change in position must be brought about with particular care in patients with cardiac insufficiency. Similarly, moving the patient back out of this position results in a sudden drop in volume with a decrease in venous return and consecutive fall in blood pressure. This risk of hypotension is increased even further in spinal or peridural anaesthesia because the sympathetic nervous system is blocked.

The lithotomy position poses problems for nerve supply and circulation of the lower extremities, with descriptions of injuries to the sciatic nerve and compartment syndrome on both sides [61]. The sciatic nerve is stretched by bending and outer rotation in the hips. The leg support can cause pressure to the lateral peroneal nerve (caught between the support and head of the fibula) and compression of the medial saphenous nerve (caught between the support and tibia) [65]. This is why the largest possible contact surface and padding is important. The bend in the hips must be produced carefully and adjusted to the existing mobility of the patient.

Extreme flexion in the hips can prevent venous drainage, cause stasis and finally thrombosis. At an angle >90°, this can result in arterial vascular compression through to occlusion of the inguinal vessels. The leg support can cause compression in the back of the knee and to the calf. Patients with peripheral arterial vascular disease are at risk from ischaemia from the raised position and kinking of the lower extremities. Stretching injuries to the sciatic nerve are aggravated further by inadequate blood flow. Ischaemia of the lower extremities on both sides with compartment syndrome in the calves has been described after a gynaecological operation lasting several hours in the lithotomy position [43].

With the arms positioned at the body, there is a risk of injuring the patient's fingers when the legs are returned to their normal position after the operation.

10.1.3.4 Head-down position

The so-called Trendelenburg position is used for example for laparoscopic procedures and urological operations, as well as for treating shock.

The head-down position should not be so extreme that shoulder supports have to be used to prevent the pa tient sliding down. The pressure on the costoclavicular space then poses a risk of injuries to the plexus. Otherwise in positioning terms, there are no major differences to the neutral supine position.

But the Trendelenburg position does have a major effect on respiration (cranial displacement of the diaphragm, diminished functional residual capacity and long compliance) and circulation (increase in cardiac filling pressure, increase in cardiac output, but in the case of left ventricular failure also the risk of a lung oedema caused by positioning) [22, 42]. There is also an increase in intracranial pressure [36] and there are reports about possible retinal detachment in the context of the Trendelenburg position [36].

To prevent any drop in blood pressure, the patient should be returned to the neutral position slowly and after correcting any hypovolaemia.

10.1.4 Lateral position

The patient is turned into the side position in a co-ordinated procedure with several helpers, ensuring that the head, shoulders, pelvis and legs are all turned along the axis. Bearing supports are then put in place.

Head

The head is supported with pads so that the cervical spine forms a straight line with the thoracic spine (neutral position). Extension and flexion are avoided because too great a deviation from the neutral position poses the same risks for cervical spine, brachial plexus and cerebral circulation as already described for the supine position. The head padding must not bend or crush the lower ear. The eyes must be freely accessible and protected from pressure caused by padding, cables, tubes and the assistant's elbows. Stretching of the cervical sympathetic chain can cause Horner's syndrome [35].

Shoulders and arms

The lateral position endangers the brachial plexus when the weight of the upper body rests on the lower axle. To relieve the shoulder and vessel nerve bundle, a roll is placed in the caudal direction from the axilla under the upper chest. This support roll must fulfil the following requirements [45]:

4 It must be so thick that the thorax is raised from the operating table to such an extent that the lower shoulder is relieved. Easily compressible materials are therefore not suitable. 4 The roll must be so wide that the contact pressure is distributed across several ribs. 4 The complete anterior-posterior depth of the thorax must be supported.

4 The roll must not be positioned too high under the axilla because it can then compress the vessel nerve bundle. A position in the distal direction from the sixth rib has a negative effect on respiratory excursion. The shoulder is pulled forwards with the lower arm to move the clavicle away from the first rib.

If the lateral position is extended beyond 90° towards the prone position, the lower arm should be positioned backwards parallel to the body. It is helpful to check the radial pulse after positioning.

The upper arm is spread out on a support in accordance with the function. The arm is to be positioned in such a way that it is spread out horizontally from the body, certainly not at an acute angle to the head. Tension in particular can cause injuries to the brachial plexus. The operating site must never be exposed by force from tension to the arm.

Pelvis and legs

The operating table must be bent for kidney operations in such a way that the pivotal point is on the level of the iliac blade. A higher pivotal point in the side or lower ribs increases intra-abdominal pressure and restricts respiration. Even a case of obstruction of the inferior vena cava has been described [36]. The joints are arranged in a neutral position (slight bend). The lower leg must be protected from the pressure of the upper leg by suitable positioning and padding, e.g. cushions between the two knees. Pads must prevent the head of the fibula and thus the peroneal nerve from being squashed against the operating table. Belts, plasters etc. must not hinder the blood flow.

10.1.5 Prone position

Numerous orthopaedic, neurosurgical and trauma surgery procedures are performed in the prone position as a matter of routine. Together with the problems resulting from changing the patient's position, the main interest is focussed on positioning of the head and arms with free mobility for thorax and abdomen.

Changing the position

Changing the position of the anaesthetised patient from the supine to the prone position is a critical phase. Successful procedures without complications depend on the quality and number of experienced helpers. When the patient is relaxed under anaesthetic, the natural protective functions of the muscles and ligaments do not apply, so that in particular the head, vertebral column and joints of the extremities are at risk. Specific anaesthesia-related complications include the unintended disconnection or dislocation of the tube and infusion leads, and interruption of the monitoring system.

In practice, the anaesthetist stands at the patient's head during repositioning and secures the head and en-dotracheal tube. Any monitor and infusion leads which are not vital are disconnected. But there must not be a longer interruption in the monitoring procedure. The tube is also briefly disconnected from the respirator to reliably prevent dislocation under tension. A controlled, step-by-step procedure is vital. In the case of patients with instable circulation or respiration, the fundamental question of feasibility should be discussed with the surgeon before starting to change the patient's position. In the case of injuries to the cervical spine, the surgeon is responsible for the patient's head and corresponding positioning.

Head

Longer low positioning of the head below the heart can cause blepharoedema or swelling in the face, and possibly also an increase in brain pressure. The neck must remain free so as not to prevent venous drainage from the head. Pressure on the carotid sinus can cause cardiac irregularity and a drop in blood pressure. Turning the head sideways from the median position can impair the blood flow in the vessels supplying the brain [66]. This matters when impending carotid stenosis makes it necessary to establish a collateral circulation using the circulus arteriosus Willisii.

When positioning the head in U-shaped headrests, foam blocks with C-shaped cut-outs or gel pillows for the prone position, the eyeballs must be reliably protected from pressure to prevent impaired vision or even loss of vision. Eye ointment can be administered and the eyelids closed with plasters to prevent erosion to the cornea. Correct positioning of the eyes free of pressure must be checked from time to time by inspecting and palpating the complete orbita. Nor should there by any infusion leads, tubes and cables anywhere near the eyes.

In addition to being fixed by plaster to the patient's head, the tubus is secured so as to prevent extubation from tension on the tubus and tubes even if the plaster works loose from saliva flowing out of the patient's mouth. It must be possible to detect any changes in the position of the headrests or any twisting of the head out of the support or headrest.

Shoulders and arms

The shoulders should hang down to the front; the arms are also guided forwards and slightly downwards and positioned on a padded support with bent elbow. If necessary, the arms can be positioned slightly bent at the body. Elevation or extreme abduction of the arms can cause compression of the vessel nerve bundle in the area of the scalene gap or costoclavicular space. In extreme abduction, the head of the humerus can also compress the vessel nerve bundle.

Thorax and abdomen

In the prone position, the weight of the spinal column and back muscles rests on the thorax, and impairs respiration and restricts the mobility of the abdominal wall. The maximum of expandable lung sections is preserved if the thorax is supported with padding from under the jugular to the sixth rib. Padding positioned too far in the cranial direction can compress the plexus between the clavicle and first rib. [61]. The abdominal wall must always remain free, because otherwise this places extreme restrictions on the mobility of the diaphragm as a result of increased intra-abdominal pressure. There must not be any pressure on the inferior vena cava. Compression of the inferior vena cava during operations to the spinal column causes increased blood loss, because this results in bypass circulation through epidural venous plexus.

Pelvis and legs

The iliac blades act as distal support point for the body. Positioning padding located too far down under the groin causes severe restrictions in the blood flow to the legs. If in any doubt about an adequate blood supply to the lower extremities, it helps to check the pulses of the popliteal artery, posterior tibial artery and dorsalis pedis artery of the foot, and to do a plethysmograph curve at a toe.

The genitals must be checked and penis and scrotum protected from pressure injuries. The bladder catheter must be protected from getting crushed and from tension.

The legs must be positioned so that venous reflux is not impeded by gravity. Pressure bandages are obligatory, but they must be checked to ensure that they are not displaced and cannot cause any constriction. The nerves and tendons of the back of the foot are protected by padding to prevent them being squashed against the operating table.

10.1.6 Sitting/half-sitting position

The sitting position in neurosurgery entails known risks, particularly those of a drop in blood pressure and embolism, which shall not be considered in any greater detail at this point. These problems can also be encountered to a lesser extent in beach-chair positioning, which is used above all for surgery to the shoulders.

Raising the patient from the supine position must be carried out step-by-step. Skull clamp or headrests are fixed carefully and secured to prevent unintentional displacement. Tracheal tubes and respiratory tubes are fastened without any tension and secured to prevent disconnection.

The patient's head is fixed in the middle position to avoid any negative effects on the cervical spine, cervical plexus and vessels. If the head is anteflected too much so that the chin comes closer to the thorax, this can impair venous and lymphatic drainage and cause an increase in intracranial pressure. This position can also cause overstretching of the cervical medulla with a decrease in spinal perfusion. Position-induced tetraplegic injuries have been described as a consequence [21]. The bulbus of the eye must be protected from pressure and the conjunctiva protected from drying out.

Stretching the shoulder to obtain better surgical exposure can cause stretching of the brachial plexus when combined with an extension of the cervical spine and turning the head to the opposite side. A Horner's syndrome from stretching the nerve fibres in the stellate ganglion has also been described in this context [59].

Strong flexion in the hip and extension in the knee causes overstretching of the sciatic nerve [36]. In cachectic patients, the sciatic nerve can be injured directly by pressure in the absence of padding [36].

10.1.7 Final remarks

Knowledge of possible injury mechanisms and a correspondingly planned and cautious approach to positioning the patient should clearly reduce the risk of positioning injuries. Even then they cannot be avoided completely. Positioning procedures with a high risk of complications must be given due consideration, weighing up the possible advantages for the surgical procedure against the risks of injuries to the patient. After the procedure, exposed parts of the body (joints, nerves, circulatory system) must be checked critically.

After the operation, there should be an increased awareness for possible positioning injuries already in the recovery room, if the surgical or anaesthetic procedure does not explain any swelling, pain or sensibility and movement problems. This must be followed immediately by exact diagnosis and therapy where possible. If nerve injury is presumed, arrangements are made for a clinical and electrophysiological examination by a neurologist. It is not rare for anatomic anomalies or previously existent neuropathies to be ascertained in retrospect as being partly responsible for the injuries [31, 55].

Was this article helpful?

+1 0

Post a comment