Abdominal Functional Electrical Stimulation Training and Its Effect on Mechanical Insufflation-Exsufflation

Respiratory infections are a leading cause of morbidity and mortality for the tetraplegic population. They are often caused by the build up of secretions in the lungs as a result of being unable to generate an effective cough. This inability to cough leads to many tetraplegic people requiring some type of intervention to aid the removal of secretions. Manually assisted coughing or routine suctioning through the patient's tracheostomy tube are commonly used. Both of these techniques are associated with problems: (i) Tracheostomy suctioning is uncomfortable and often misses the left bronchus, one of the contributing factors to 80% of pneumonia occurring in the left lung of the spinal cord injured population. (ii) A manually assisted cough is a safe and effective procedure but needs to be provided by a trained care giver with associated resource implications for the local health care provider. An alternative method to help clear secretions and improve ventilation is Mechanical Insufflation-Exsufflation (MI-E) where a combination of positive and negative pressure is applied to the user's airway in order to induce a cough. A number of studies have shown that MI-E is more effective at removing secretions and reducing respiratory infections than conventional suctioning and manually assisted cough techniques, with the advantage that secretions are removed from both bronchi. MI-E has also been shown to significantly reduce the length of ICU stay and reduce the rates of reintubation.

Individuals with tetraplegia have reduced exhaled tidal volume (VT) and reduced Cough Peak Flow (CPF) (maximum air flow rate during a cough. The CPF value can be used to assess the risk of respiratory infection, with a CPF < 160 L/min associated with no functional cough and a high risk of infection and a CPF of <270 L/min suggesting that a person will not be able to adequately clear secretions from their airway. The use of MI-E is therefore suggested for anyone with a CPF of <270 L/min.

Functional Electrical Stimulation (FES) is a technique which can be used to make paralysed muscles contract. The most effective contraction is observed when train of electrical pulses are applied close to the motor point of a paralysed muscle. When FES is applied to the abdominal muscles it is called Abdominal Functional Electrical Stimulation (AFES). AFES has previously been used to increase the VT and CPF of tetraplegic patients in a number of studies.

MI-E is routinely combined with manually assisted coughing in order to loosen lung secretions and to increase the user's CPF. In the same way as a manually assisted cough, AFES leads to increased abdominal movement, resulting in larger CPF. During recent studies the investigators have observed that the use of AFES with acute tetraplegic patients appears to be associated with an increased need for secretion clearance, indicating that AFES aids the loosening of lung secretions. Although the abdominal movement achieved with AFES is typically significantly smaller than that achieved with a manually assisted cough, it may have beneficial effects in combination with MI-E. In addition, AFES has the advantage that it can be applied consistently and requires less involvement of the caregiver.

The investigators hypothesise that (i) maximal respiratory improvements due to an AFES training programme will be achieved after more than 3 weeks of training, and (ii) that the combined use of AFES with MI-E may improve the respiratory function and ability to clear secretions of tetraplegic patients, resulting in a reduction in the number of respiratory infections in this group.