ReviewIntramuscular diaphragmatic stimulation for patients with traumatic high cervical injuries and ventilator dependent respiratory failure: A systematic review of safety and effectiveness
Introduction
Spinal cord injury is a serious condition primarily affecting young adults resulting in significant disability or death. Worldwide, the prevalence of spinal cord injury is estimated to be between 3.6 and 195.4 per million [1]. The majority of such cases are traumatic in nature with road traffic accidents, falls, and recreational activities being the most common mechanism of injury.
Approximately 20% of spinal cord injuries occur between the levels of C1 and C4. Patients with such injuries are at high risk of respiratory complications, and invariably require mechanical ventilation at hospital discharge [2]. The mainstay of treatment for patients with ventilator-dependant spinal cord injury is positive pressure mechanical ventilation. Due to the nature of these ventilator devices, the ability to cough is impaired, increasing the risk of respiratory tract infections. Although regular suction of secretions helps avoid these complications, this can be intrusive and disruptive for patients. Therefore, ventilated patients have increased mortality and decreased independence compared to patients with similar injuries who are not ventilated [3].
In selected patients with ventilator-dependent spinal cord injury, phrenic nerve stimulation, also known as diaphragmatic pacing, is an alternative to standard mechanical ventilation. Regular electrical pulses applied directly to the nerve via implanted phrenic nerve stimulators cause contraction of the diaphragm, resulting in the intake of air.
Each phrenic nerve is formed by the cervical rootlets from the C3 to C5 spinal cord segments. For successful diaphragmatic pacing, it is imperative that the phrenic motor neurons are viable. Patients with mid cervical injuries often have damaged phrenic motor neurons. However, in patients with upper cervical spinal cord injuries, the somatic neuromuscular and mechanical function of the respiratory apparatus below the level of injury usually remain intact and are amenable to electrical stimulation to restore function [4]. Therefore patients with injuries cephalad to the C3–C5 spinal cord segments are ideal candidates.
Diaphragmatic pacing offers the ability to limit some of the changes in respiratory physiology seen in chronic spinal cord injury. Over time, ventilator-dependent spinal cord injury can result in a decrease in total lung capacity. There exists an inverse relationship between forced vital capacity and higher levels of injury [5]. Although it has been thought that the loss of gas containing alveoli causes the changes in pressure volume curves, one study suggested that lung distensibility is related to changes in elasticity of lung tissue [6].
Early phrenic nerve stimulators all used electrodes placed in direct contact with the phrenic nerve through an open cervical or thoracic approach. These implant procedures are invasive, requiring mobilisation of nerves that may result in their injury [7]. Recently, intramuscular diaphragmatic stimulation using an abdominal laparoscopic approach has been proposed instead, in an effort to reduce the risk of phrenic nerve injury.
The timing of diaphragmatic pacing is contentious. Typically, implantation is avoided in the acute setting due to safety concerns associated with surgery in unstable patients. However, animal studies suggest that a significant amount of phrenic motor neurones are lost during the first 24 h post-injury, resulting in persistent phrenic nerve axonal degenerations and denervation at the diaphragm neuromuscular junction [8]. Provided the phrenic motor neurons are viable, the clinical corollary is that early surgery may be more effective.
The aim of this study was to systematically review the safety and effectiveness of intramuscular diaphragmatic stimulators in the treatment of patients with traumatic high cervical injuries resulting in long-term ventilator dependence. Particular emphasis was placed on the timing of insertion of such stimulators.
Section snippets
Methods
The review protocol was registered on the PROSPERO international prospective register of systematic reviews. The Preferred Reporting Items For Systematic Reviews and Meta-Analyses (PRISMA) Statement was used in the preparation of this manuscript.
Results
A total of 145 retrieved articles were located on the initial search, and two further articles were retrieved from reference lists for further analysis (Fig. 1). We excluded 131 articles on the basis of their title and abstract as they did not feature adult patients with traumatic high cervical injury or patients did not undergo intramuscular diaphragmatic stimulation. Full text screening of the remaining articles led to the exclusion of a further four articles. In all, 12 eligible articles
Discussion
In this systematic review, we have demonstrated that evidence for the use of intramuscular diaphragmatic stimulation in patients with traumatic high cervical injuries and ventilator dependent respiratory failure is presently limited. Nonetheless, the technique appears to a safe and effective alternative to conventional phrenic nerve stimulation. Moreover, earlier implantation of such devices in selected patients does not appear to be associated with greater surgical risk, and may be more
Conclusions
In conclusion, although the evidence is presently limited, intramuscular diaphragmatic stimulation for patients with traumatic high cervical injuries and ventilator dependent respiratory failure appears to be both safe and effective. Following traumatic cervical spinal cord injury, early laparoscopic diaphragm motor point mapping can immediately identify patients with intact phrenic nerves and enable implantation of diaphragmatic pacemakers. This may have the advantage of shortening the
Authors’ contribution
BG, AW and HJM were involved with the study design, data acquisition, data analysis, and data interpretation. KT, MHW and MK were involved with the study design, and data interpretation. All authors were involved with drafting and critical revision of the manuscript.
Funding
The authors report no specific funding for this study.
Conflict of interest statement
The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
References (34)
Phrenic nerve stimulation in patients with spinal cord injury
Respir Physiol Neurobiol
(2009)- et al.
Diaphragmatic pacing stimulation in spinal cord injury: anesthetic and perioperative management
Clinics
(2012) - et al.
A preliminary feasibility study of different implantable pulse generators technologies for diaphragm pacing system
Neuromodulation
(2005) - et al.
Mapping the phrenic nerve motor point: the key to a successful laparoscopic diaphragm pacing system in the first human series
Surgery
(2004) - et al.
Phrenic nerve pacing via intramuscular diaphragm electrodes in tetraplegic subjects
Chest
(2005) - et al.
Electrophrenic respiration by radiofrequency induction
J Thorac Cardiovasc Surg
(1966) - et al.
Late neurologic recovery after traumatic spinal cord injury
Arch Phys Med Rehabil
(2004) - et al.
Incidence of traumatic spinal cord injury worldwide: a systematic review
Eur Spine J
(2014) - et al.
Characterizing the need for mechanical ventilation following cervical spinal cord injury with neurologic deficit
J Trauma
(2005) - et al.
Overview of the national spinal cord injury statistical center database
J Spinal Cord Med
(2002)