A commentary on Prone Position Plexopathy during the COVID-19 pandemic

^a Peripheral Nerve Injury Unit, Royal National Orthopaedic Hospital, Stanmore, UK
^b Centre for Nerve Engineering, UCL, London, UK

Corresponding author email: [email protected]

Published 10 May 2020

The COVID-19 pandemic has led to a large cohort of patients across the country requiring prolonged ventilation. Many of these are being managed for long periods of time in a prone position. There are many risks of proning patients, including those of injury sustained inadvertently due to the positioning. Methods to avoid pressure sores and ocular damage are well understood¹. Concerns regarding injury to the brachial plexus have created some discussion. In recent weeks our national nerve injury unit has received numerous queries regarding the rationale for the proning posture and how best to assess and manage patients, who upon regaining consciousness, have altered upper limb neurology or a Prone Position Plexopathy (PPP).

The UK guidelines² recommend an alternating ‘swimmers position’ for the upper limbs when positioning an unconscious patient; the rationale for this is not well documented. However, the literature shows that there is little variance within the guidelines across countries,^3-5. The one arm abducted one adducted - ‘swimmers position’ is one which we have avoided using in operating theatres; favouring both arms down or both arms slightly abducted with the head well supported in the anatomic neutral position⁶. Asymmetrical arm positions risk a traction injury to the plexus on the side of the adducted arm if the head is excessively laterally flexed away from that side.

Ergonomically the situation in critical care is different to that of theatre. The head cannot easily be placed facing anatomically forward (into the bed) and is thus rotated. The rotation advised within the swimmers position (with face towards the abducted arm) means that lateral flexion away from the adducted arm is bio-mechanically impossible. Anatomically this opens up the neural foramen on the adducted side; theoretically relieving local pressure on the emerging nerve roots.

Applying the principles of tissue biomechanics and injury mechanisms (which are well understood from animal work and cadaveric studies) we understand that the major causes of injury in closed nerve injury are compression and traction. In our clinical practice we often see plexus injuries in those who have maintained a prolonged recumbent posture. The reasons for this include: intoxication, inability to rise from the ground following a fall, physical entrapment or unconsciousness. Once again these patients are dissimilar to the presentation of those in the critical care setting; often demonstrating multiple end stage complications such as compartment syndrome, rabdomyolysis, skin necrosis and dehydration.

The principles of direct nerve injury are best understood as damage to different anatomical regions of the brachial plexus. The supra-clavicular, retro-clavicular and infra-clavicular areas of the plexus are prone to injury in differing positions. Combining this knowledge with the bio-mechanical risk of injury from traction/compression allows the formulation of recommendations to avoid such injuries when placing and maintaining patients in a prone posture (Figure 1).

Figure 1. Recommendations taken from the Royal National Orthopaedic, Peripheral Nerve injury Unit by the authors⁷.

In summary, when positioned prone with the head rotated it is important that the cervical spine is kept in neural or slightly flexed and never extended⁸. Care must also be taken to maintain neutral alignment of the cervical spine (not laterally flex) when repositioning from one rotation to the other^9,10.

In the ‘swimmers position’ the arms must not be abducted more than 70°¹¹ and should be kept anterior to the sagittal plane¹²  with the scapulae shrugged¹³ cranially to avoid caudal traction of the shoulder girdle. The elbows and forearms should be slightly flexed and pronated so as to not create a stretching force along the the median and ulnar nerves^14,15.

In addition, pressure palsies are well recognised in other anatomic areas: ischium area (sciatic), the lateral knee/fibula neck (CPN) the medial epicondyle (ulnar) and parotid area (facial nerve). For patients who are spending extended times in critical care the addition of padding to protect the local nerve anatomy may be worth considering.

Differentiation between ‘normal’/expected post critical care weakness and PPP can be difficult. In addition, neurologic dysfunction following a period within critical care can have a number of differing causes¹⁶. Direct viral neuropathy¹⁷ is rare but should be considered in neuropathies which extend to multiple sites and differing anatomic locations. It is known that other Corona viruses have been documented to be neurotrophic and neuropathic¹⁷. There is no specific evidence that this is the case with COVID-19, although the symptoms of loss of smell and taste are thought to be mediated by this mechanism¹⁸.

Management

It is impossible to eliminate the risk of nerve injury. The incidence of brachial plexus injury related to prone positioning during the COVID-19 pandemic may never be fully known. Cases will arise and many orthopaedic teams will be called to assess such patients and advise on management. The following protocol for assessment and guidelines for referral are suggested (Figure 2).

Figure 2. Suggested protocol for assessment and onwards referral for PPP.

Once patients are extubated and gain capacity, it is recommended that a neurologic screening assessment (of the presence of upper limb neuropathic pain, paraesthesia/anaesthesia/dysthesia and motor loss) is performed, (Figure 3). It is likely that those with conduction block (neurapraxia) will resolve spontaneously with no long term issues. Signs that the injury is majority conduction block would be a patchy distribution where sensation and sympathetics are intact, alongside incomplete motor involvement. In this scenario there will be no neuropathic pain. A proportion of patients will have persistent symptoms which do not resolve within 3 weeks. Far from being a benign pathology, compression related nerve injuries, if not treated, have a significant risk of long term morbidity¹⁹. It is therefore important that patients who do not recover function within 3 weeks of the symptoms being identified are referred to a centre for nerve injury (Figure 2). Any patients who report the presence of neuropathic pain or a total loss of function of one nerve branch (no sympathetics, sensation or motor) require urgent treatment.

Figure 3. Suggested clinical examination screening tool.

References

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