Diaphragm Pacing
The diaphragm is primarily controlled by the phrenic nerve. Diaphragm pacing involves surgically implanted electrodes onto the diaphragm that stimulates intact phrenic nerves to contract the diaphragm muscle (Madden 2016). In 2008 the Food and Drug Administration approved the use of the NeuRx Diaphragm Pacing System (DPS) for humanitarian-use for patients with SCI (Madden 2016).
Discussion
In 1972, the first tetraplegic patient underwent phrenic nerve pacing (PNP). This technology was widely used in the 1980s and 1990s, but had considerable risks from thoracotomy, phrenic nerve damage with electrode placement, and perineural fibrosis (scarring) around the phrenic nerve. Then in 2002, DiMarco and Onders described placement of electrodes into the diaphragm muscle itself, positioning the leads near the motor points of the phrenic nerve without compromising the nerve or its sheath. The diaphragm pacing system (DPS) is gaining acceptance as an alternative to mechanical ventilation in centers that are capable of implanting these systems.
To date only a few studies have examined diaphragm pacing during the acute SCI phase. Diaphragm pacing is one of the newer approved interventions for respiratory function post SCI. There are three cohort studies that have compared patients with acute and cervical SCI who received (DPS) (n = 40) and those who didn’t receive DPS (n = 61) (Kerwin et al. 2020a; Kerwin et al. 2020b; Kerwin et al. 2018). Studies showed that DPS implantation produced significant improvements in spontaneous Vt, and reduced hospital LOS, time to liberation from mechanical ventilation and hospital charges, compared with no receive DPS (Kerwin et al. 2020a; Kerwin et al. 2020b). In the case of development of VAP, the DPS patients had significantly shorter vent days compared with the No DPS patients (mean = 8.7 days less) (Kerwin et al. 2018). However, DPS implantation did not demonstrate any significant improvement in outcome measures (HLOS, ICU LOS, vent days, or VAP) when examined in multivariable linear regression models (controlling for confounders such as age, sex, race, insurance status, and injury year) (Kerwin et al. 2018). In the previous study by Kerwin et al. (2018), diaphragm pacing was found to have no significant influence on the rates of ventilator associated pneumonia. However, its efficacy as an intervention for improving respiratory outcomes needs to be further examined as there were no significant effects of diaphragm pacing on the number of days spent on a ventilator. As only one respiratory outcome and one complication were examined in this sole study, more research needs to be conducted to make conclusions about the value of diaphragm pacing for patients with acute SCI. In another retrospective case control study, Esclarin et al. (1994) reported higher rates of power wheelchair management, phonation success, patient satisfaction and hospital discharge in paced participants compared to mechanically ventilated participants. A basic cost analysis in that study suggested that costs were 50 hours per year for ventilatory management in the mechanically ventilated group (Esclarin et al. 1994). However, caution in data interpretation is warranted given small sample sizes, lack of baseline statistics between groups, potential for selection bias in participants receiving pacemakers, and overall high rate of death in the high lesion SCI population. Prospective comparison studies looking at morbidity, mortality, quality of life and costs related to phrenic and diaphragmatic pacing are lacking. There are several small level 4 studies to show that bilateral phrenic nerve pacing and bilateral diaphragmatic pacing can be used successfully for the ventilation of people with SCI (Posluszny et al. 2013; Elefteriades et al. 2002; Nakajima & Sharkey 1990).
A recent case-control retrospectively analyzed 10 patients with tracheostomy and cervical SCI and showed that those who received transcutaneous electrical diaphragmatic stimulation (TEDS) training in combination with a standard weaning protocol had a shorter duration of IMV and ICU LOS compared who received only the standard weaning protocol (Duarte et al. 2021).
Conclusion
There is level 3 evidence (from one case control study; Kerwin et al. 2018) that diaphragm pacing may not increase the risk of ventilator associated pneumonia or reduce the number of ventilator days compared to no implantation for patients acute SCI. There is level 3 evidence (from 2 case control studies: Kerwin et al. 2020a; Kerwin et al. 2020b) that DPS implantation produced significant improvements in spontaneous Vt and reduced hospital charges, hospital LOS and time to liberation from mechanical ventilation compared with those who did not receive DPS in patients with acute cervical SCI.
There is level 3 evidence (from one case control study: Esclarin et al. 1994) that suggests better power wheelchair management, phonation success, patient satisfaction and hospital discharge in phrenic paced participants compared to mechanically ventilated participants.
There is level 4 evidence (from three case series: Posluszny et al. 2013; Elefteriades et al. 2002; Nakajima & Sharkey 1990) that phrenic nerve stimulation can be used as a long-term alternative to mechanical ventilation for people with injuries at C2 or above.
There is level 3 evidence (from one case control study: Duarte et al. 2021) that patients submitted to TOT due to cervical SCI who received TEDS training in combination with a standard weaning protocol have a shorter duration of IMV and ICU LOS compared with who received only a standard weaning protocol.
