Fig. 11.1
Laparoscopic implant instrument houses the diaphragm pacing electrode, which is a double helix of 14 stainless steel wires that are Teflon coated. The needle of the implant instrument enters the diaphragm muscle and a polypropylene barb allows the electrode to be fixed in place
The implanted intramuscular electrodes are connected to a four-channel, external pulse generator (EPG). This stimulator provides capacitive coupled, charge-balanced, biphasic stimulation to each subcutaneous electrode. The EPG is programmed with patient-specific parameters of pulse amplitude, pulse duration, inspiratory time, pulse rate, and respiratory rate to maximize ventilation for SCI patients or for muscle training in other patient populations. DP users simply connect and turn the device on or off. The goal for patient settings is to use the highest settings that do not cause any patient discomfort. Once implanted, the device can be utilized immediately to begin diaphragm conditioning. DP conditioning will convert the atrophied muscle fibers from fast-fatigable type 2B muscle fibers to the better functioning, slow-twitch type 1.
The initial FDA, multicenter clinical trial of DP in SCI dependent on tracheostomy and MV showed that 100% of implanted patients with stimulatable diaphragms were able to breathe for 4 consecutive hours with DP alone. Over 50% of patients utilized DP for over 24 h of continuous use. While the objective of DP in SCI is to provide primary ventilatory support off MV for several hours, a course of short-duration diaphragm conditioning sessions is needed first in order to reverse disuse atrophy of the diaphragm as would be done in ICU patients. This trial reports no pneumonia deaths because of the improvement of posterior lobe ventilation with DP as opposed to MV. Therefore, DP may be beneficial for even short-term use in ICU patients.
Posluszny et al. [5] conducted a retrospective analysis of the interventional use of DPS in 29 traumatic cervical SCI patients at 10 centers who underwent early implantation in the ICU after their injury. Of the stimulable patients undergoing DP, 72% (16 of 22) were completely free of ventilator support in an average of 10.2 days. The study concluded that DP can shorten the duration of mechanical ventilation and, in many instances, allow for complete independence from mechanical ventilation in those patients with an intact phrenic system but without control of ventilation. Also, 30% of the patients recovered their own ability to breathe and no longer needed DP, therefore identifying the use of DP as a temporary device in the ICU.
In a pilot ALS study in which 16 patients were implanted with diaphragmatic pacers, there were a total of 452 implant months of follow-up, with a mean of 28.2 months per patient [6]. This study showed that the post-DP implant diaphragm muscle thickness, as evaluated by ultrasound, was consistently greater for all patients than at pre-implant. This showed the ability of DP to overcome disuse atrophy and improve diaphragm strength. Further, an evaluation of 86 ALS patients with chronic hypoventilation and preserved bilateral phrenic nerve function showed that DPS used with or without concurrent NIV improved survival when compared to historical controls (FDA: HDE H100006).
Recently, Onders et al. [7] reported on the extended use of diaphragm pacing in patients with diaphragm dysfunction leading to symptomatic hypoventilation. In this study, 21 patients with a mean of 36 months of respiratory symptoms were implanted with diaphragmatic pacers. Thirteen patients (62%) had clinically relevant respiratory improvements, and 4 had partial improvement. Four patients were able to be completely weaned from MV. In these patients, the DP system was removed, again highlighting the possibility of a temporary DP system for weaning patients from MV in the ICU.
Development of NOTES Diaphragm Pacing in the Intensive Care Unit
For NOTES DP to be successful for temporary use in the ICU, several key points needed to be addressed: adequate visualization of the diaphragm with NOTES, utilization of NOTES in the ICU, gastrotomy closure, concern of infection with a NOTES approach to diaphragm pacing, the development of temporary diaphragm electrodes for implantation and externalization, and ability to implant the diaphragm electrodes without laparoscopic mapping and still able to provide respiratory support.
Our group at University Hospitals and Case Western Reserve University has shown the feasibility both in animals and in humans for ICU NOTES. One of the first ICU NOTES cases was a PEG rescue showing the initial feasibility of ICU access to the peritoneal cavity with closure of the gastrostomy with a PEG [8]. In subsequent clinical experience in these cases, we could easily see both diaphragms in retroflexed view through the gastrotomy. In an initial pilot (and subsequently randomized) animal trial comparing NOTES with laparoscopy to assess for simulated ICU pathology, we showed that a positive identification via NOTES was highly specific, with a strong positive predictive value [9, 10]. The diaphragm was also easily visualized in these cases. We therefore believe that diaphragm visualization can be easily done with NOTES in the ICU setting.
Diagnostic and therapeutic flexible endoscopy at the bedside is a standard ICU procedure that requires minimal support from ancillary staff. Using the same equipment, NOTES can provide access to the peritoneal cavity and could decrease the number of patients with unrecognized intra-abdominal catastrophic events. The peritoneal cavity is accessed by a transgastric route through a modified percutaneous endoscopic gastrostomy (PEG) technique, which is a common ICU procedure. It is a technically familiar procedure and uses instruments and materials that are widely available. This appears to be the most dependable method, involving a Seldinger technique in which a guidewire is placed in the gastric lumen at a standard anterior site on the abdominal wall for a PEG. The endoscope and guidewire are then brought out through the mouth, and the endoscope is reinserted alongside the guidewire. A gastrotomy is performed at the site of the guide wire with needle-knife cautery to make the initial incision, followed by endoscopic balloon dilation to enlarge the gastrotomy. The endoscope is then advanced into the peritoneal cavity for visualization and can be retroflexed to visualize both diaphragms through the gastrotomy.
The optimal gastrotomy closure for NOTES is still to be determined. However, in the ICU, the gastrotomy does not have to be closed but can be managed with the use of a PEG. PEGs are commonly placed in patients on MV to optimize nutrition. Once the NOTES abdominal exploration is complete, the gastrotomy is managed by attaching a standard-pull PEG tube to the guidewire left in place during the NOTES procedure. The PEG is withdrawn back through the gastrotomy, leaving the internal mushroom bumper in the gastric lumen. When concern that the gastrotomy has become too large is an issue, additional sutures to affix the stomach to the anterior abdominal wall can be accomplished using a T-fastener technique. Therefore, the concern of closing the gastrotomy in NOTES DP is easily addressed.
In a group of ALS patients undergoing simultaneous DP and gastrostomy, a significant improvement was seen in both 30-day mortality and 1-year survival compared with PEG alone (76% survival at 1 year with DP and PEG vs. only 23% with PEG alone) [11]. Simultaneous diaphragm pacing and PEGs showed no increase in the infection rate of the implanted transperitoneal diaphragm wires when a gastrostomy was done, even though it became a contaminated case. This large experience of DP with PEGs, and no increase in infection with long-term DP use, confirms temporary DP wires placed via NOTES should not increase the infection risk, since NOTES is only used to visualize the percutaneous implantation of the electrodes.
One major change that was performed was to change the electrode to allow for easier removal. The distal end of the newly designed temporary diaphragm electrode (TransLoc, Synapse Biomedical, Oberlin, OH) is identical to the permanent diaphragm pacing electrode used in over 1500 humans (PermaLoc, Synapse Biomedical, Oberlin, OH) except that there is no polypropylene barb affixed to the stimulus end of the electrode (Fig. 11.2). The removal of the polypropylene barb from the electrode reduces the fixation of the electrode to the diaphragm that occurs during normal tissue encapsulation. This allows easy removal with no retained foreign bodies. It has also been reported in animal studies that a similar electrode can be placed successfully with the use of NOTES visualization [12]. This would also decrease the risk of contamination because the electrode does not traverse the gastric lumen.
