Intrathoracic phrenic pacing: A 10-year experience in France

Diaphragm pacing and independent breathing in individuals with severe Pompe disease

Introduction

Pompe disease is an inherited disease characterized by a deficit in acid-α-glucosidase (GAA), an enzyme which degrades lysosomal glycogen. The phrenic-diaphragm motor system is affected preferentially, and respiratory failure often occurs despite GAA enzyme replacement therapy. We hypothesized that the continued use of diaphragm pacing (DP) might improve ventilator-dependent subjects' respiratory outcomes and increase ventilator-free time tolerance.

Methods

Six patients (3 pediatric) underwent clinical DP implantation and started diaphragm conditioning, which involved progressively longer periods of daily, low intensity stimulation. Longitudinal respiratory breathing pattern, diaphragm electromyography, and pulmonary function tests were completed when possible, to assess feasibility of use, as well as diaphragm and ventilatory responses to conditioning.

Results

All subjects were eventually able to undergo full-time conditioning via DP and increase their maximal tolerated time off-ventilator, when compared to pre-implant function. Over time, 3 of 6 subjects also demonstrated increased or stable minute ventilation throughout the day, without positive-pressure ventilation assistance.

Discussion

Respiratory insufficiency is one of the main causes of death in patients with Pompe disease. Our results indicate that DP in Pompe disease was feasible, led to few adverse events and stabilized breathing for up to 7 years.

Diaphragm Pacing: A Safety, Appropriateness, Financial Neutrality, and Efficacy Analysis of Treating Chronic Respiratory Insufficiency

OBJECTIVES

This study aimed to evaluate the safety and applicability of treating chronic respiratory insufficiency with diaphragm pacing relative to mechanical ventilation.

MATERIALS AND METHODS

A literature review and analysis were conducted using the safety, appropriateness, financial neutrality, and efficacy principles.

RESULTS

Although mechanical ventilation is clearly indicated in acute respiratory failure, diaphragm pacing improves life expectancy, increases quality of life, and reduces complications in patients with chronic respiratory insufficiency.

CONCLUSION

Diaphragm pacing should be given more consideration in appropriately selected patients with chronic respiratory insufficiency.

Diaphragm pacing using the minimally invasive cervical approach

CONTEXT

The implantation of commercially available phrenic nerve/diaphragm pacers has been available for more than 40 years and has enabled thousands of patients in over 40 countries to achieve freedom from invasive mechanical ventilation.

OBJECTIVE

The cervical approach to implantation of these pacers is described, as are the pros and cons of using this technique compared to intrathoracic and sub-diaphragmatic.

METHODS

Study design was a retrospective review of 1,522 subjects from the Avery Biomedical Devices (ABD) database who were implanted with the Avery diaphragm pacer. Long term statistics from patients implanted with diaphragm pacers are presented as well.

RESULTS

17% of cervically placed electrodes required at least one replacement compared to 18% of electrodes placed thoracically. Devices implanted cervically show no significant difference in their longevity than those implanted using the thoracic approach (P value of 0.9382 using Two-Sample t-Test). The mean longevity for both approaches was found to be 6.4 years. The majority of electrodes implanted have never required replacement. A majority of CCHS patients were implanted using the thoracic approach and only find it necessary to use the device during sleeping hours. Most of the cervically implanted patients are found to be older at the time of implantation and implanted for diagnoses that require longer daily use of the device.

CONCLUSION

The cervical approach for the implantation of phrenic nerve/diaphragm pacers is the most minimally invasive, but underutilized, technique that allows for the use of local or monitored anesthesia, does not require entering any body cavities, and keeps incision size small.

Phrenic nerve stimulation for the treatment of central sleep apnea in patients with heart failure

Objective

Central sleep apnea (CSA) is associated with increased morbidity and mortality in patients with heart failure (HF). We aimed to explore the effectiveness of phrenic nerve stimulation (PNS) on CSA in patients with HF.

Methods

This was a prospective and non-randomized study. The stimulation lead was inserted into the right brachiocephalic vein and attached to a proprietary neurostimulator. Monitoring was conducted during the implantation process, and all individuals underwent two-night polysomnography.

Results

A total of nine subjects with HF and CSA were enrolled in our center. There was a significant decrease in the apnea–hypopnea index (41 ± 18 vs 29 ± 25, p = 0.02) and an increase in mean arterial oxygen saturation (SaO2) (93% ± 1% vs 95% ± 2%, p = 0.03) after PNS treatment. We did not observe any significant differences of oxygen desaturation index (ODI) and SaO2 < 90% (T90) following PNS. Unilateral phrenic nerve stimulation might also categorically improve the severity of sleep apnea.

Conclusion

In our non-randomized study, PNS may serve as a therapeutic approach for CSA in patients with HF.

Randomized Clinical Study of Temporary Transvenous Phrenic Nerve Stimulation in Difficult-to-Wean Patients

Rationale: Diaphragm dysfunction is frequently observed in critically ill patients with difficult weaning from mechanical ventilation. Objectives: To evaluate the effects of temporary transvenous diaphragm neurostimulation on weaning outcome and maximal inspiratory pressure. Methods: Multicenter, open-label, randomized, controlled study. Patients aged ⩾18 years on invasive mechanical ventilation for ⩾4 days and having failed at least two weaning attempts received temporary transvenous diaphragm neurostimulation using a multielectrode stimulating central venous catheter (bilateral phrenic stimulation) and standard of care (treatment) (n = 57) or standard of care (control) (n = 55). In seven patients, the catheter could not be inserted, and in seven others, pacing therapy could not be delivered; consequently, data were available for 43 patients. The primary outcome was the proportion of patients successfully weaned. Other endpoints were mechanical ventilation duration, 30-day survival, maximal inspiratory pressure, diaphragm-thickening fraction, adverse events, and stimulation-related pain. Measurements and Main Results: The incidences of successful weaning were 82% (treatment) and 74% (control) (absolute difference [95% confidence interval (CI)], 7% [-10 to 25]), P = 0.59. Mechanical ventilation duration (mean ± SD) was 12.7 ± 9.9 days and 14.1 ± 10.8 days, respectively, P = 0.50; maximal inspiratory pressure increased by 16.6 cm H₂O and 4.8 cm H₂O, respectively (difference [95% CI], 11.8 [5 to 19]), P = 0.001; and right hemidiaphragm thickening fraction during unassisted spontaneous breathing was +17% and -14%, respectively, P = 0.006, without correlation with changes in maximal inspiratory pressure. Serious adverse event frequency was similar in both groups. Median stimulation-related pain in the treatment group was 0 (no pain). Conclusions: Temporary transvenous diaphragm neurostimulation did not increase the proportion of successful weaning from mechanical ventilation. It was associated with a significant increase in maximal inspiratory pressure, suggesting reversal of the course of diaphragm dysfunction. Clinical trial registered with www.clinicaltrials.gov (NCT03096639) and the European Database on Medical Devices (CIV-17-06-020004).

The terminal segment of the human phrenic nerve as a novel implantation site for diaphragm pacing electrodes: Anatomical and clinical description

BACKGROUND

Diaphragm pacing allows certain ventilator-dependent patients to achieve weaning from mechanical ventilation. The reference method consists in implanting intrathoracic contact electrodes around the phrenic nerve during video-assisted thoracic surgery, which involves time-consuming phrenic nerve dissection with a risk of nerve damage. Identifying a phrenic segment suitable for dissection-free implantation of electrodes would constitute progress.

STUDY DESIGN

This study characterizes a free terminal phrenic segment never fully described before. We conducted a cadaver study (n = 14) and a clinical observational study during thoracic procedures (n = 54).

RESULTS

A free terminal phrenic segment was observed on both sides in 100% of cases, "jumping" from the pericardium to the diaphragm and measuring 60 mm [95% confidence interval; 48-63] and 72.5 mm [65-82] (right left, respectively; p = 0.0038; cadaver study). This segment rolled up on itself at end-expiration and became unravelled and elongated with diaphragm descent (clinical study). Three categories of fat pads were defined (type 1: pericardiophrenic bundle free of surrounding fat; type 2: single fatty fringe leaving the phrenic nerve visible until diaphragmatic entry; type 3: multiple fatty fringes masking the site of penetration of the phrenic nerve) that depended on body mass index (p = 0.001, clinical study). Hematoxylin-eosin and toluidine blue staining (cadaver study) showed that all of the phrenic fibers in the distal, pre-branching part of the terminal segment were contained within a single epineurium containing a variable number of fascicles (right: 1 [95%CI 0.65-4.01]; left 5 [3.37-7.63]; p = 0.03).

CONCLUSION

Diaphragm pacing through periphrenic electrodes positioned on the terminal phrenic segment should be tested.

Minimally Invasive Plication of the Diaphragm: A Single-Center Prospective Study

OBJECTIVE

Plication of the diaphragm is a life-changing procedure for patients affected by diaphragm paralysis. Traditionally, this procedure is performed through a thoracotomy. Access to the diaphragm via this incision is poor and the indications for surgery are limited to patients who can actually sustain such an invasive approach and associated morbidities. A minimally invasive approach was developed to improve the surgical management of diaphragm paralysis.

METHODS

Patients underwent minimally invasive diaphragm plication either by video-assisted or robotic surgery through a 3-port technique with CO₂ insufflation. Patients were followed at the routine 6-week clinic and also by telephone consultation 6 to 12 months postoperatively. Data were collected on postoperative complications, postoperative pain or numbness, symptomatic improvement, and change to quality of life following surgery.

RESULTS

Forty-eight patients underwent 49 minimally invasive diaphragm plication. Median postoperative length of hospital stay was 4 days (range: 2 to 34 days) and there were no cases of mortality. Mean reduction in Medical Research Council dyspnea score per patient was 2.2 points (mode: 3 points). Twenty-eight patients (77.8%) reported a significant symptomatic improvement enabling improvements in quality of life, and 97.2% (n = 35) were satisfied with the surgical outcome.

CONCLUSIONS

Minimally invasive diaphragm plication is a safe procedure associated with prompt postoperative recovery. It is effective at reducing debilitating dyspnea and improving quality of life.

Diaphragm pacing improves respiratory mechanics in acute cervical spinal cord injury

BACKGROUND

Cervical spinal cord injury (CSCI) is devastating with ventilator-associated pneumonia being a main driver of morbidity and mortality. Laparoscopic diaphragm pacing implantation (DPS) has been used for earlier liberation from mechanical ventilation. We hypothesized that DPS would improve respiratory mechanics and facilitate liberation.

METHODS

We performed a retrospective review of acute CSCI patients between January 2005 and May 2017. Routine demographics were collected. Patients underwent propensity score matching based on age, Injury Severity Score, ventilator days, hospital length of stay, and need for tracheostomy. Patients with complete respiratory mechanics data were analyzed and compared. Those who did not have DPS (NO DPS) had spontaneous tidal volume (Vt) recorded at time of intensive care unit admission, at day 7, and at day 14, and patients who had DPS had spontaneous Vt recorded before and after DPS. Time to ventilator liberation and changes in size of spontaneous Vt for patients while on the ventilator were analyzed. Bivariate and multivariate logistic and linear regression statistics were performed using STATA v10.

RESULTS

Between July 2011 and May 2017, 37 patients that had DPS were matched to 34 who did not (NO DPS). Following DPS, there was a statistically significant increase in spontaneous Vt compared with NO DPS (+88 mL vs. -13 mL; 95% confidence interval, 46-131 mL vs. -78 to 51 mL, respectively; p = 0.004). Median time to liberation after DPS was significantly shorter (10 days vs. 29 days; 95% CI, 6.5-13.6 days vs. 23.1-35.3 days; p < 0.001). Liberation prior to hospital discharge was not different between the two groups. The DPS placement was found to be associated with a statistically significant decrease in days to liberation and an increase in spontaneous Vt in multivariate linear regression models.

CONCLUSION

The DPS implantation in acute CSCI patients produces significant improvements in spontaneous Vt and reduces time to liberation from mechanical ventilation. Prospective comparative studies are needed to define the clinical benefits and potential cost savings of DPS implantation.

LEVEL OF EVIDENCE

Therapeutic IV.

Thirty-Six-Month Follow-up of Diaphragm Pacing with Phrenic Nerve Stimulation for Ventilator Dependence in Traumatic Tetraplegia: The Way Forward for Spinal Cord Injury Rehabilitation in a Developing Country

Respiratory failure and chronic ventilator dependence in tetraplegics following cervical injuries located high on the spine (C1-C3) constitute significant challenges in the rehabilitation of patients given the occurrence of repeated hospitalizations and an ever-increasing financial burden. A 30-year-old man presented with posttraumatic tetraplegia following an unstable injury at the C1-C2 level with cord compression; he was managed by posterior stabilization and decompression followed by ventilator dependence and no rehabilitation until 6 months postinjury. We implanted phrenic nerve stimulator electrodes bilaterally for indirect diaphragm pacing by an implantable pulse generator that allowed for weaning from mechanical ventilation and spontaneous ventilator-free breathing at 20 weeks post-implantation and which facilitated post-tetraplegia rehabilitation. At 36 months after implantation, the patient is ventilator- free without any procedure-related complications or respiratory infections. Diaphragm pacing with phrenic nerve stimulation may be a way forward for ventilator-dependent tetraplegics in developing countries to pursue effective rehabilitation and improved quality of life.

Respiratory Monitoring Based on Tracheal Sounds: Continuous Time-Frequency Processing of the Phonospirogram Combined with Phonocardiogram-Derived Respiration

Patients with central respiratory paralysis can benefit from diaphragm pacing to restore respiratory function. However, it would be important to develop a continuous respiratory monitoring method to alert on apnea occurrence, in order to improve the efficiency and safety of the pacing system. In this study, we present a preliminary validation of an acoustic apnea detection method on healthy subjects data. Thirteen healthy participants performed one session of two 2-min recordings, including a voluntary respiratory pause. The recordings were post-processed by combining temporal and frequency detection domains, and a new method was proposed—Phonocardiogram-Derived Respiration (PDR). The detection results were compared to synchronized pneumotachograph, electrocardiogram (ECG), and abdominal strap (plethysmograph) signals. The proposed method reached an apnea detection rate of 92.3%, with 99.36% specificity, 85.27% sensitivity, and 91.49% accuracy. PDR method showed a good correlation of 0.77 with ECG-Derived Respiration (EDR). The comparison of R-R intervals and S-S intervals also indicated a good correlation of 0.89. The performance of this respiratory detection algorithm meets the minimal requirements to make it usable in a real situation. Noises from the participant by speaking or from the environment had little influence on the detection result, as well as body position. The high correlation between PDR and EDR indicates the feasibility of monitoring respiration with PDR.

Breathing detection from tracheal sounds in both temporal and frequency domains in the context of phrenic nerve stimulation

Electrical stimulation of the phrenic nerves via implanted devices allows to counteract some disadvantages of mechanical ventilation in patients with high tetraplegia or Ondine's syndrome. Existing devices do not allow to monitor breathing or to adapt the electroventilation to patients' actual needs. A reliable breathing monitor with an inbuilt alarm function would improve patient safety. In our study, a real-time acoustic breathing detection method is proposed as a possible solution to improve implanted phrenic stimulation. A new algorithm to process tracheal sounds has been developed. It combines breathing detection in both temporal and frequency domains. The algorithm has been applied on recordings from 18 healthy participants. The obtained average sensitivity, specificity and accuracy of the detection are: 99.31%, 96.84% and 98.02%, respectively. These preliminary results show a first positive proof of the interest of such an approach. Additional experiments are needed, including longer recordings from individuals with tetraplegia or Ondine Syndrome in various environments to go further in the validation.

Phrenic Nerve Stimulation for the Treatment of Central Sleep Apnea: A Pooled Cohort Analysis

STUDY OBJECTIVES

Early evidence with transvenous phrenic nerve stimulation (PNS) demonstrates improved disease severity and quality of life (QOL) in patients with central sleep apnea (CSA). The goal of this analysis is to evaluate the complete prospective experience with PNS in order to better characterize its efficacy and safety, including in patients with concomitant heart failure (HF).

METHODS

Using pooled individual data from the pilot (n = 57) and pivotal (n = 151) studies of the remedē System in patients with predominant moderate to severe CSA, we evaluated 12-month safety and 6- and 12-month effectiveness based on polysomnography data, QOL, and cardiac function.

RESULTS

Among 208 combined patients (June 2010 to May 2015), a remedē device implant was successful in 197 patients (95%), 50/57 pilot study patients (88%) and 147/151 pivotal trial patients (97%). The pooled cohort included patients with CSA of various etiologies, and 141 (68%) had concomitant HF. PNS reduced apnea-hypopnea index (AHI) at 6 months by a median of -22.6 episodes/h (25th and 75th percentile; -38.6 and -8.4, respectively) (median 58% reduction from baseline, P < .001). Improvement in sleep variables was maintained through 12 months of follow-up. In patients with HF and ejection fraction ≤ 45%, PNS was associated with improvement in systolic function from 27.0% (23.3, 36.0) to 31.1% (24.0, 41.5) at 12 months (P = .003). In the entire cohort, improvement in QOL was concordant with amelioration of sleep measures.

CONCLUSIONS

Transvenous PNS significantly improves CSA severity, sleep quality, ventricular function, and QOL regardless of HF status. Improvements, which are independent of patient compliance, are sustained at 1 year and are associated with acceptable safety.

Electrical connectors for neural implants: design, state of the art and future challenges of an underestimated component

Technological advances in electrically active implantable devices have increased the complexity of hardware design. In particular, the increasing number of stimulation and recording channels requires innovative approaches for connectors that interface electrodes with the implant circuitry.

OBJECTIVE

This work aims to provide a common theoretical ground for implantable connector development with a focus on neural applications.

APPROACH

Aspects and experiences from several disciplines are compiled from an engineering perspective to discuss the state of the art of connector solutions. Whenever available, we also present general design guidelines.

MAIN RESULTS

Degradation mechanisms, material stability and design rules in terms of biocompatibility and biostability are introduced. Considering contact physics, we address the design and characterization of the contact zone and review contaminants, wear and contact degradation. For high-channel counts and body-like environments, insulation can be even more crucial than the electrical connection itself. Therefore, we also introduce the requirements for electrical insulation to prevent signal loss and distortion and discuss its impact on the practical implementation.

SIGNIFICANCE

A final review is dedicated to the state of the art connector concepts, their mechanical setup, electrical performance and the interface to other implant components. We conclude with an outlook for possible approaches for the future generations of implants.

Use of diaphragm pacing in the management of acute cervical spinal cord injury

BACKGROUND

Cervical spinal cord injury (CSCI) is devastating. Respiratory failure, ventilator-associated pneumonia (VAP), sepsis, and death frequently occur. Case reports of diaphragm pacing system (DPS) have suggested earlier liberation from mechanical ventilation in acute CSCI patients. We hypothesized DPS implantation would decrease VAP and facilitate liberation from ventilation.

METHODS

We performed a retrospective review of patients with acute CSCI managed at a single Level 1 trauma center between January 2005 and May 2017. Routine demographics were collected. Patients underwent propensity matching based on age, injury severity score, ventilator days, hospital length of stay, and need for tracheostomy. Outcome measures included hospital length of stay, intensive care unit length of stay, ventilator days (vent days), incidence of VAP, and mortality. Bivariate and multivariate logistic and linear regression statistics were performed using STATA Version 10.

RESULTS

Between July 2011 and May 2017, all patients with acute CSCI were evaluated for DPS implantation. Forty patients who had laparoscopic DPS implantation (DPS) were matched to 61 who did not (NO DPS). Median time to liberation after DPS implantation was 7 days. Hospital length of stay and mortality were significantly lower on bivariate analysis in DPS patients. Diaphragm pacing system placement was not found to be associated with statistically significant differences in these outcomes on risk-adjusted multivariate models that included admission year.

CONCLUSIONS

Diaphragm pacing system implantation in patients with acute CSCI can be one part of a comprehensive critical care program to improve outcomes. However, the association of DPS with the marked improved mortality seen on bivariate analysis may be due solely to improvements in critical care throughout the study period. Further studies to define the benefits of DPS implantation are needed.

LEVEL OF EVIDENCE

Therapeutic, level IV.

Perioperative anesthetic management of children with congenital central hypoventilation syndrome and rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation undergoing thoracoscopic phrenic nerve-diaphragm pacemaker implantation

BACKGROUND

Congenital Central Hypoventilation Syndrome and Rapid-Onset Obesity with Hypothalamic dysfunction, Hypoventilation, and Autonomic Dysregulation are rare neurocristopathies characterized by autonomic dysregulation including bradyarrhythmias, abnormal temperature control, and most significantly, abnormal control of breathing leading to tracheostomy and ventilator dependence as life support. Surgical advancements have made phrenic nerve-diaphragm pacemakers available, to eliminate the tether to a mechanical ventilator for 12-15 hours each day. The thoracoscopic approach to implantation has allowed for a less invasive approach which may have implications for pain control and recovery time. However, thoracoscopic implantation of these devices presents several challenges to the anesthesiologist in these complex ventilator-dependent patients, including, but not limited to, sequential lung isolation, prevention of hypothermia, and management of arrhythmias. Postoperative challenges may also include strategies to treat hemodynamic instability, managing the ventilator following lung derecruitment, and providing adequate pain control.

AIMS

We aimed to describe the anesthetic management of Congenital Central Hypoventilation Syndrome and Rapid-Onset Obesity with Hypothalamic dysfunction, Hypoventilation, and Autonomic Dysregulation patients undergoing thoracoscopic phrenic nerve-diaphragm pacemaker implantation and the nature and incidence of perioperative complications.

METHODS

A retrospective chart review was performed of 14 children with Congenital Central Hypoventilation Syndrome and Rapid-Onset Obesity with Hypothalamic dysfunction, Hypoventilation, and Autonomic Dysregulation undergoing phrenic nerve-diaphragm pacemaker implantation at a single academic pediatric hospital between 2009 and 2017. Demographic information, intraoperative management, and perioperative complications were analyzed from patient records.

RESULTS

Twelve of 14 patients (86%) underwent an inhalational induction via tracheostomy. Lung isolation was achieved via fiberoptic guidance of a single lumen endotracheal tube sequentially into the right or left mainstem bronchi for 12 patients (86%). Double lumen endotracheal tubes were utilized in two patients (7%) and bronchial blockers in two patients (7%) for lung isolation. Anesthesia was maintained using a balanced technique of volatile agents (sevoflurane/isoflurane) and opioids (fentanyl). Bradyarrhythmias developed in six patients (43%) during surgery, 5 (36%) responded to anticholinergics and one patient (7%) required backup cardiac pacing using a previously implanted bipolar cardiac pacemaker. Intraoperative hypothermia (<35.5°C) was present in five patients (36%) despite the use of warming devices. Hypercarbia (>50 mm Hg) during lung isolation was present in eight patients (57%) and hemoglobin desaturation (<90%) in four patients (29%). Postoperatively, oxygen desaturation was a common complication with nine patients (64%) requiring supplemental oxygen administration via mechanical ventilator or manual bag ventilation. Opioids via patient-controlled analgesia devices (12 patients, 86%) or intermittent injection (two patients, 14%) were administered to all patients for postoperative pain control. Phrenic nerve-diaphragm pacemaker placement was successful thoracoscopically in all patients with no perioperative mortality.

CONCLUSION

The main anesthetic challenges in patients with Congenital Central Hypoventilation Syndrome and Rapid-Onset Obesity with Hypothalamic dysfunction, Hypoventilation, and Autonomic Dysregulation include hemodynamic instability, the propensity to develop hypothermia, hypercarbia/hypoxemia, and the need to perform bilateral sequential lung isolation requisite to the thoracoscopic implantation technique. Most anesthetic agents can be used safely in these patients; however, adequate knowledge of the susceptibility to complications, coupled with adequate preparation and understanding of the innate disease characteristics, are necessary to treat anticipated complications.

Phrenic nerve stimulation to treat patients with central sleep apnoea and heart failure

AIMS

The presence of central sleep apnoea (CSA) is associated with poor prognosis in patients with heart failure (HF). The aim of this analysis was to evaluate if using phrenic nerve stimulation to treat CSA in patients with CSA and HF was associated with changes in HF-specific metrics.

METHODS AND RESULTS

All patients randomized in the remedē System Pivotal Trial and identified at baseline with HF were included (n = 96). Effectiveness data from treatment and former control groups were pooled based on months since therapy activation. Changes from baseline to 6 and 12 months in sleep metrics, Epworth Sleepiness Scale, patient global assessment health-related quality of life, Minnesota Living with Heart Failure Questionnaire (MLHFQ), and echocardiographic parameters are reported. HF hospitalization, cardiovascular death, and the composite of HF hospitalization or cardiovascular death within 6 months are reported by the original randomized group assignment for safety assessment. Sleep metrics and quality of life improved from baseline to 6 and 12 months. At 12 months, MLHFQ scores changed by -6.8 ± 20.0 (P = 0.005). The 6-month rate of HF hospitalization was 4.7% in treatment patients (standard error = 3.3) and 17.0% in control patients (standard error = 5.5) (P = 0.065). Reported adverse events were as expected for a transvenous implantable system.

CONCLUSIONS

Phrenic nerve stimulation reduces CSA severity in patients with HF. In parallel, this CSA treatment was associated with benefits on HF quality of life.

Management of phrenic nerve palsy following cardiac surgery

Phrenic nerve palsy (PNP) is a potential complication of cardiac surgery. It may prolong ventilation and hospitalization and result in significant morbidity and mortality. The diagnosis and management of PNP following cardiac surgery is reviewed.

Reinnervation of the diaphragm by the inferior laryngeal nerve to the phrenic nerve in ventilator-dependent tetraplegic patients with C3-5 damage

The aim of this study was to evaluate the feasibility of unilateral diaphragmatic reinnervation in humans by the inferior laryngeal nerve. This pilot study included chronically ventilated tetraplegic patients with destruction of phrenic nerve motoneurons. Five patients were included. They all had a high level of tetraplegia, with phrenic nerve motor neuron destruction. They were highly dependent on ventilation, without any possibility of weaning. They did not have other chronic pathologies, especially laryngeal disease. They all had diaphragmatic explorations to diagnose the destruction of the motoneurons of the phrenic nerves and nasoendoscopy to be sure that they did not have laryngeal or pharyngeal disease. Then, surgical anastomosis of the right phrenic nerve was performed with the inferior laryngeal nerve, by a cervical approach. A laryngeal reinnervation was performed at the same time, using the ansa hypoglossi. One patient was excluded because of a functional phrenic nerve and one patient died 6 months after the surgery of a cardiac arrest. The remaining three patients were evaluated after the anastomosis every 6 months. They did not present any swallowing or vocal alterations. In these three patients, the diaphragmatic explorations showed that there was a recovery of the diaphragmatic electromyogram of the right and left hemidiaphragms after 1 year. Two patients had surgical diaphragmatic explorations for diaphragmatic pacing 18-24 months after the reinnervation with excellent results. At 36 months, none of the patients could restore their automatic ventilation. In conclusion, this study demonstrated that diaphragmatic reinnervation by the inferior laryngeal nerve is effective, without any vocal or swallowing complications.

Phrenic pacing compared with mechanical ventilation

STUDY DESIGN

Comparable case series.

OBJECTIVES

High-cervical spinal cord injury (SCI) may disrupt the ability to breathe sufficiently. To restore respiration a phrenic nerve pacer can be implanted. The aims of this study were to describe the use of phrenic nerve pacing in tetraplegics in Denmark and compare the users with a population of ventilator dependent tetraplegics.

SETTING

Clinics for Spinal Cord Injuries, and Respiratory Centre East, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.

METHODS

Nine tetraplegic individuals who had implantation of a phrenic nerve pacer and 16 home mechanical ventilator dependent tetraplegics met the inclusion criteria. Data were retrieved from medical records and a structured follow-up interview with seven individuals from each group.

RESULTS

No significant differences were found when comparing age at injury, time since injury, length of hospitalization, incidence of pneumonia, number of pneumonia hospitalizations, number of tracheal suctions, speech quality and activities of daily living or quality of life. On the Short Form Health Survey (SF36) mental health summary the median for both users of phrenic nerve pacing and users of mechanical ventilation was one s.d. above the mean of a standard population.

CONCLUSIONS

Nine people have had a phrenic nerve pacer implanted. They do not significantly differ from a group of home mechanical ventilator dependent tetraplegics on a number of performance measures, but both groups seem to have better quality of life than a standard population.

Corrective effect of diaphragm pacing on the decrease in cardiac output induced by positive pressure mechanical ventilation in anesthetized sheep

Positive pressure ventilation (PPV) is a fundamental life support measure, but it decreases cardiac output (CO). Diaphragmatic contractions produce negative intrathoracic and positive abdominal pressures, promoting splanchnic venous return. We hypothesized that: 1) diaphragm pacing alone could produce adequate ventilation without decreasing CO; 2) diaphragm pacing on top of PPV could improve CO. Of 11 anesthetized and mechanically ventilated ewes (39.6±5.9kg), 3 were discarded from analysis because of hemodynamic instability during the experiment, and 8 retained for analysis. Phrenic stimulation electrodes were inserted in the diaphragm (implanted phrenic nerve stimulation, iPS). CO was measured by the thermodilution technique (pulmonary artery catheter). CO during end-expiratory apnea served as reference. Median CO was 9.77 [6.25-11.25] lmin^-1 during end-expiratory apnea, 8.25 [5.06-9.25] lmin^-1 during "PPV" (-15%) (p<0.05), 9.19 [5.60-10.19] lmin^-1 during "PPV-iPS" (NS vs apnea) and 9.37 [6.12-10.48] lmin^-1 during "iPS" (NS vs. apnea). iPS-driven ventilation was comparable to its PPV counterpart (median 92% [74-97], NS). Diaphragm pacing alone can produce adequate ventilation without reducing CO. Superimposed onto PPV, diaphragm pacing can reduce the PPV-induced decrease in CO.

Evaluating the evidence: is phrenic nerve stimulation a safe and effective tool for decreasing ventilator dependence in patients with high cervical spinal cord injuries and central hypoventilation?

INTRODUCTION

Case reports, case series and case control studies have looked at the use of phrenic nerve stimulators in the setting of high spinal cord injuries and central hypoventilation syndromes dating back to the 1980s. We evaluated the evidence related to this topic by performing a systematic review of the published literature.

METHODS

Search terms "phrenic nerve stimulation," "phrenic nerve and spinal cord injury," and "phrenic nerve and central hypoventilation" were entered into standard search engines in a systematic fashion. Articles were reviewed by two study authors and graded independently for class of evidence according to published guidelines. The published evidence was reviewed, and the overall body of evidence was evaluated using the grading of recommendations, assesment, development and evaluations (GRADE) criteria Balshem et al. (J Clin Epidemiol 64:401-406, 2011).

RESULTS

Our initial search yielded 420 articles. There were no class I, II, or III studies. There were 18 relevant class IV articles. There were no discrepancies among article ratings (i.e., kappa = 1). A meta-analysis could not be performed due to the low quality of the available evidence. The overall quality of the body of evidence was evaluated using GRADE criteria and fell within the "very poor" category.

CONCLUSION

The quality of the published literature for phrenic nerve stimulation is poor. Our review of the literature suggests that phrenic nerve stimulation is a safe and effective option for decreasing ventilator dependence in high spinal cord injuries and central hypoventilation; however, we are left with critical questions that provide crucial directions for future studies.

Diaphragm pacing: the state of the art

Diaphragm pacing (DP) is an orphan surgical procedure that may be proposed in strictly selected ventilator-dependent patients to get an active diaphragm contraction. The goal is to wean from mechanical ventilation (MV) and restore permanent efficient breathing. The two validated indications, despite the lack of randomised control trials, concern patients with high-level spinal cord injuries (SCI) and central hypoventilation syndromes (CHS). To date, two different techniques exist. The first, intrathoracic diaphragm pacing (IT-DP), based on a radiofrequency method, in which the electrodes are directly placed around the phrenic nerve. The second, intraperitoneal diaphragm pacing (IP-DP) uses intradiaphragmatic electrodes implanted through laparoscopy. In both techniques, the phrenic nerves must be intact and diaphragm reconditioning is always required after implantation. No perioperative mortality has been reported and ventilator-weaning rate is about 72% to 96% in both techniques. Improvement of quality of life, by restoring a more physiological breathing, has been almost constant in patients that could be weaned. Failure or delay in recovery of effective diaphragm contractions could be due to irreversible amyotrophy or chest wall damage. Recent works have evaluated the interest of IP-DP in amyotrophic lateral sclerosis (ALS). After some short series were reported in the literature, the only multicentric randomized study including 74 ALS patients was prematurely stopped because of excessive mortality in paced patients. Then, another trial analysed the place of IP-DP in peripheral diaphragm dysfunction but, given the multiple biases, the published results cannot validate that indication. Reviewing all available literature as in our experience, shows that DP is an effective method to wean selected patients dependent on ventilator and improve their daily life. Other potential indications will have to be evaluated by randomised control trials.

Respiratory neuromodulation in patients with neurological pathologies: for whom and how?

Implanted phrenic nerve stimulation is a technique restoring spontaneous breathing in patients with respiratory control failure, leading to being dependent on mechanical ventilation. This is the case for quadriplegic patients with a high spinal cord injury level and for patients with congenital central hypoventilation syndrome. The electrophysiological diaphragm explorations permits better patient selection, confirming on the one hand a definite issue with central respiratory command and on the other hand the integrity of diaphragmatic phrenic nerves. Today there are two different phrenic stimulation techniques: the quadripolar intrathoracic stimulation and the bipolar intradiaphragmatic stimulation. Both techniques allow patients to be weaned off their mechanical ventilator, improving dramatically their quality of life. In fact, one of the systems (phrenic intradiaphragmatic stimulation) was granted social security reimbursement in 2009, and now both are reimbursed. In the future, phrenic intradiaphragmatic stimulation may find its place in the intensive care unit, for patients needing it temporarily, for example, after certain surgeries with respiratory complications as well as diaphragmatic atrophies induced by prolonged mechanical ventilation.

Video-assisted thoracoscopic implantation of a diaphragmatic pacemaker in a child with tetraplegia: indications, technique, and results

We report the case of a child with tetraplegia after cervical trauma, who subsequently underwent diaphragmatic pacemaker implantation. We reviewed the major indications for diaphragmatic pacing and the types of devices employed. We highlight the unequivocal benefit of diaphragmatic pacing in the social and educational reintegration of individuals with tetraplegia.

Sites of electrical stimulation used in neurology

Rehabilitation aims to decrease neurological impairments, in guiding plasticity. Electrical stimulation has been used for many years in rehabilitation treatment of neurological disabilities as a tool for neuromodulation inducing plasticity, although the mechanisms of its action are not well known. The applications vary, encompassing therapeutic and rehabilitative aims. The type and site of stimulation vary depending on the objectives. Some techniques are widely used in clinical practice; others are still in the research stage. They may be invasive, epidural or in direct contact with neurons; they may be noninvasive, applied transcutaneously or indirectly by current vectors. The indications vary: mobility, functionality, pain as well as pharyngeal, respiratory, and perineal function. This paper aims to summarize current data on electrical neuromodulation techniques used in neurorehabilitation, their effects and their mechanisms of action.

Diaphragm pacing failure secondary to deteriorated chest wall mechanics: When a good diaphragm does not suffice to take a good breath in

Diaphragm pacing allows certain quadriplegic patients to be weaned from mechanical ventilation. Pacing failure can result from device dysfunction, neurotransmission failure, or degraded lung mechanics (such as atelectasis). We report two cases where progressive pacing failure was attributed to deteriorated chest wall mechanics. The first patient suffered from cervical spinal cord injury at age 45, was implanted with a phrenic stimulator (intrathoracic), successfully weaned from ventilation, and permanently paced for 7 years. Pacing effectiveness then slowly declined, finally attributed to rib cage stiffening due to ankylosing spondylitis. The second patient became quadriplegic after meningitis at age 15, was implanted with a phrenic stimulator (intradiaphragmatic) and weaned. After a year hypoventilation developed without obvious cause. In relationship with complex endocrine disorders, the patient had gained 31 kg. Pacing failure was attributed to excessive mechanical inspiratory load. Rib cage mechanics abnormalities should be listed among causes of diaphragm pacing failure and it should be kept in mind that a “good diaphragm” is not sufficient to produce a “good inspiration”.

Proceedings of the fourth international conference on central hypoventilation

Central hypoventilation syndromes (CHS) are rare diseases of central autonomic respiratory control associated with autonomous nervous dysfunction. Severe central hypoventilation is the hallmark and the most life-threatening feature. CHS is a group of not-fully defined disorders. Congenital CHS (CCHS) (ORPHA661) is clinically and genetically well-characterized, with the disease-causing gene identified in 2003. CCHS presents at birth in most cases, and associated with Hirschsprung's disease (ORPHA99803) and neural crest tumours in 20% and 5% of cases, respectively. The incidence of CCHS is estimated to be 1 of 200,000 live births in France, yet remains unknown for the rest of the world. In contrast, late-onset CHS includes a group of not yet fully delineated diseases. Overlap with CCHS is likely, as a subset of patients harbours PHOX2B mutations. Another subset of patients present with associated hypothalamic dysfunction. The number of these patients is unknown (less than 60 cases reported worldwide). Treatment of CHS is palliative using advanced techniques of ventilation support during lifetime. Research is ongoing to better understand physiopathological mechanisms and identify potential treatment pathways.The Fourth International Conference on Central Hypoventilation was organised in Warsaw, Poland, April 13-15, 2012, under the patronage of the European Agency for Health and Consumers and Public Health European Agency of European Community. The conference provided a state-of-the-art update of knowledge on all the genetic, molecular, cellular, and clinical aspects of these rare diseases.

[Diaphragmatic palsy and dysfunction: from physiology to surgery]

The clinical presentations of diaphragm dysfunctions vary according to etiologies and unilateral or bilateral diseases. Elevation of the hemidiaphragm from peripheral origins, the most frequent situation, requires a surgical treatment only in case of major functional impact. Complete morphological and functional analyses of the neuromuscular chain and respiratory tests allow the best selection of patients to be operated. The surgical procedure may be proposed only when the diaphragm dysfunction is permanent and irreversible. Diaphragm plication for eventration through a short lateral thoracotomy, or sometimes by videothoracoscopy, is the only procedure for retensioning the hemidiaphragm. This leads to a decompression of intrathoracic organs and a repositioning of abdominal organs without effect on the hemidiaphragm active contraction. Morbidity and mortality rates after diaphragm plication are very low, more due to the patient's general condition than to surgery itself. Functional improvements after retensioning for most patients with excellent long-term results validate this procedure for symptomatic patients. In case of bilateral diseases, very few bilateral diaphragm plications have been reported. Some patients with diaphragm paralyses from central origins become permanently dependent on mechanical ventilation whereas their lungs, muscles and nerves are intact. In patients selected by rigorous neuromuscular tests, a phrenic pacing may be proposed to wean them from respirator. Two main indications have been validated: high-level tetraplegia above C3 and congenital alveolar hypoventilation from central origin. After progressive reconditioning of the diaphragm muscles following phrenic pacing at thoracic level, more than 90% of patients can be weaned from respirator within a few weeks. This weaning improves the quality of life with more physiological breathing, restored olfaction, better sleep and better speech. The positive impact of diaphragm stimulation has also been evaluated in other degenerative neurological diseases, particularly the amyotrophic lateral sclerosis. For either central or peripheral diaphragm dysfunctions, a successful surgical treatment lies on a strict preoperative selection of patients.

Partial recovery of respiratory function and diaphragm reinnervation following unilateral vagus nerve to phrenic nerve anastomosis in rabbits

Respiratory dysfunction is the leading cause of mortality following upper cervical spinal cord injury (SCI). Reinnervation of the paralyzed diaphragm via an anastomosis between phrenic nerve and a donor nerve is a potential strategy to mitigate ventilatory deficits. In this study, anastomosis of vagus nerve (VN) to phrenic nerve (PN) in rabbits was performed to assess the potential capacity of the VN to compensate for lost PN inputs. At first, we compared spontaneous discharge pattern, nerve thickness and number of motor fibers between these nerves. The PN exhibited a highly rhythmic discharge while the VN exhibited a variable frequency discharge pattern. The rabbit VN had fewer motor axons (105.3±12.1 vs. 268.1±15.4). Nerve conduction and respiratory function were measured 20 weeks after left PN transection with or without left VN-PN anastomosis. Compared to rabbits subjected to unilateral phrenicotomy without VN-PN anastomosis, diaphragm muscle action potential (AP) amplitude was improved by 292%, distal latency by 695%, peak inspiratory flow (PIF) by 22.6%, peak expiratory flow (PRF) by 36.4%, and tidal volume by 21.8% in the anastomosis group. However, PIF recovery was only 28.0%, PEF 28.2%, and tidal volume 31.2% of Control. Our results suggested that VN-PN anastomosis is a promising therapeutic strategy for partial restoration of diaphragm reinnervation, but further modification and improvements are necessary to realize the full potential of this technique.

Clinical advances in diaphragm pacing

Diaphragmatic pacing is a valuable tool that can significantly benefit certain patients with respiratory insufficiency provided they have an intact phrenic nerve and a functional diaphragm. Careful patient selection is critical to successful long-term results. The main populations that derive benefit from pacing include those with congenital or acquired central hypoventilation syndrome and more commonly those with a high cervical spinal cord injury, where the phrenic nerves remain intact. The pacing electrode of most phrenic nerve pacemakers is implanted directly on the phrenic nerve. A newer device relies on intramuscular implantation of the electrode on the diaphragm at the phrenic nerve motor point. Most patients can be successfully weaned from mechanical ventilation for a substantial time each day, if not completely. This has significant impact on quality of life and implications for healthcare costs. The potential exists for application of this technology to patients with other types of respiratory failure as investigative experience emerges. These include the chronic progressive disease, amyotrophic lateral sclerosis, or temporary scenarios in difficult-to-wean intensive care unit patients. This enabling technology should hold a place in the thoracic surgeon's armamentarium.

Diaphragm pacing in amyotrophic lateral sclerosis: a literature review

Amyotrophic lateral sclerosis (ALS) remains a rapidly progressive fatal degenerative disease of motor neurons for which there are few interventions to slow disease progression or improve quality of life. A diaphragm pacing system was approved by the U.S. Food and Drug Administration in September 2011 for ALS under a Humanitarian Device Exemption. News of this approval has been met with a combination of excitement and uncertainty by members of the ALS community. We review the currently available data on the diaphragm pacing system and its use in ALS. Diaphragm pacing appears to be reasonably safe in carefully selected patients, but flaws in the reporting on it thus far preclude conclusions regarding efficacy. Further study is needed.

Is there a case for diaphragm pacing for amyotrophic lateral sclerosis patients?

Respiratory pacing has advanced the long-term management of respiratory failure secondary to neurological disorders. It has an established role in curtailing invasive mechanical ventilation after upper motor neuron lesions such as spinal cord injury. There is increasing interest to expand the application of intramuscular diaphragm pacing to amyotrophic lateral sclerosis (ALS), a progressive and fatal neurodegenerative disease. Although diaphragm pacing has been offered to ALS patients, evidence-based data to determine its benefits remain lacking. The limited current literature indicates progression of respiratory dysfunction in ALS patients despite diaphragm pacing. The data from clinical trials are inadequate to substantiate its survival and sleep benefits. Its advantages over non-invasive mechanical ventilation have not been directly investigated. Furthermore, there are cautions for ALS patients to consider when opting for diaphragm pacing. Progressive degeneration of the phrenic motor neurons in classic ALS will interrupt the transmission of pacer signals to sustain diaphragm contractions. Pacing protocols that are safe for other neurological conditions may be detrimental for ALS, at least as suggested by transgenic animal models. Issues inherent to the device warrant expert intervention in implanted patients. At present, clinical effectiveness and long-term safety concerns about diaphragm pacing in ALS remain to be addressed.