tips and tricks

• Patients unable to walk 5 m (Hughes scale score ≥3) require intensive monitoring.
  
• Patients with autonomic dysregulation or who fail the “20/30/40” test should be monitored in ICU.
  
• Further respiratory deterioration, or with bulbar dysfunction at risk of aspiration, necessitates intubation, not noninvasive positive pressure ventilation (NIV).

Bedbound patients are more at risk of significant autonomic dysfunction, including orthostatic hypotension, dysrhythmia, and asystole. These patients should have continuous EKG monitoring, and emergency external pacing via chest pads should be readily available in patients with signs of cardioautonomic dysfunction. Bradycardia/tachycardia syndrome seen on the EKG monitor may be predictive of dysrhythmic events. The risk of autonomic complications remains even during the rehabilitation phase.

Intubation should take place earlier rather than later, and noninvasive bilevel positive airway pressure (BiPAP) ventilation, sometimes advocated as a temporizing measure, may not be safe in progressing GBS. Preferred ventilatory modes are assist control (AC) or synchronized intermittent mandatory ventilation (SIMV) with pressure support and positive end-expiratory pressure (PEEP). Of intubated patients 50% will require ventilation for more than 3 weeks. Treatment must take autonomic dysfunction into consideration, which apart from dysrhythmia can cause labile blood pressure, adynamic ileus, or bladder dysfunction. The response to commonly used medications may be excessive in these patients and vasodilators, and β blockers in particular, must be used with caution – likewise neostigmine or metoclopramide in bradycardic patients. Evidence-based specific treatments are either intravenous immunoglobulins (400 mg/kg on 5 consecutive days) or four to six plasma exchanges of 1.5–2 L each on consecutive or alternate days. Particularly younger survivors have a chance of full recovery even after very prolonged ventilation, but up to 20% of all survivors retain a long-term disability. Mortality rates are commonly cited as 5–10%, but this applies to all cases of GBS and the mortality rate may reach 20% in ventilated patients. The authors’ experience suggests that mortality may vary considerably between units and outcome data should be systematically audited.

Myasthenic Crisis

Myasthenia gravis (MG) is an autoimmune condition of the neuromuscular junction in which one of several antibodies targeting postsynaptic proteins leads to loss of function of acetylcho­line receptors (AChRs). In most patients the first muscles to be involved are the extrao­cular muscles, causing diplopia and ptosis. In some the disease remains confined to the extraocular muscles, but in most it becomes generalized and can lead to severe weakness, including ventilatory failure. There is initially no fixed weakness in myasthenia, which can mislead the inexperienced examiner into underestimating severity.

Treatment initially consists of the cholinesterase inhibitor pyridostigmine, which provides symptomatic relief. MuSK-antibody-positive MG differs from AChR-antibody-positive MG by an inferior response to cholinesterase inhibitors and often a more unpredictable course. In most cases, immunosuppressive treatment (incremental corticosteroids, with or without a steroid-sparing agent such as azathioprine) is required for sustained benefit.

Critical care teams become involved when bulbar or respiratory weakness affects airways and breathing – the “myasthenic crisis.” This most often occurs during the first year or two after presentation, or may be precipitated by infections or inappropriate medications at a later stage of the disease. Rarely, a second type of crisis (“cholinergic crisis”) occurs due to excessive anticholinesterase medication, in which weakness is accompanied by cholinergic features such as miosis, bradycardia, increased bronchial secretions, cramps, fasciculations, and diarrhea. Cholinergic crisis is never seen if the dose of pyridostigmine is kept below 360 mg daily.

The initial challenge is to recognize the impending myasthenic crisis early and put adequate protection in place. The team needs to monitor fatigability and not just initial strength, which means tests of sustained muscle contraction (e.g. the Quantitative Myasthenia Gravis Score – Barohn et al 1998). Respiratory function, cough, swallowing, oxygen saturation, and alveolar–arterial gradient need to be checked frequently. Myasthenic crises have a more erratic course than GBS, which critical care outreach needs to take into account when considering ICU admission.

Treatment principles on ICU include infection control, rehydration, and careful review of medication for drugs that may impair neuromuscular transmission. If the patient is intubated, pyridostigmine is often discontinued initially, then reintroduced gradually. Intravenous pyridostigmine is given at approximately a thirtieth of the oral dose; 60 mg pyridostigmine orally is also approximately equivalent to 0.5 mg neostigmine i.v. and 1–1.5 mg neostigmine i.m. or s.c. Immunomodulatory treatment with intravenous immunoglobulin (IVIG) or plasma exchange (PE) is used in standard doses, and high-dose steroids can be given in ventilated patients, because the potential transient exacerbation of weakness that may occur in response to initiating steroids is not a concern. Intensive respiratory therapy and initial noninvasive BiPAP may reduce ventilator days. In myasthenic crises often only a short period of ventilation is needed, meaning that there is no reason for early tracheostomy (i.e. before day 7). There is, however, a relatively high risk of reintubation especially in patients with atelectasis, and the standard predictors of extubation success used on ICU may not apply.