Initial Assessment of the Percutaneous Electrical Phrenic Nerve Stimulation System in Patients on Mechanical Ventilation.

OBJECTIVES: Maintaining diaphragm work using electrical stimulation during mechanical ventilation has been proposed to attenuate ventilator-induced diaphragm dysfunction. This study assessed the safety and feasibility of temporary percutaneous electrical phrenic nerve stimulation on user-specified inspiratory breaths while on mechanical ventilation. DESIGN: Two-center, nonblinded, nonrandomized study. SETTING: Hospital ICU. PATIENTS: Twelve patients mechanically ventilated from 48 hours to an expected 7 days. INTERVENTIONS: Leads were inserted to lie close to the phrenic nerve in the neck region using ultrasound guidance. Two initial patients had left-sided placement only with remaining patients undergoing bilateral lead placement. Percutaneous electrical phrenic nerve stimulation was used for six 2-hour sessions at 8-hour intervals over 48 hours. MEASUREMENTS AND MAIN RESULTS: Data collected included lead deployment success, nerve conduction, ventilation variables, work of breathing, electrical stimulation variables, stimulation breath synchrony, and diaphragm thickness measured by ultrasound at baseline, 24, and 48 hours. Primary endpoints included ability to capture the left and/or right phrenic nerves and maintenance of work of breathing within defined limits for 80% of stimulated breaths. Lead insertion was successful in 21 of 22 attempts (95.5%). Analysis of 36,059 stimulated breaths from 10 patients with attempted bilateral lead placement demonstrated a mean inspiratory lag for phrenic nerve stimulation of 23.7 ms (p < 0.001 vs null hypothesis of <88ms). Work of breathing was maintained between 0.2 and 2.0 joules/L 96.8% of the time, exceeding the 80% target. Mean diaphragm thickness increased from baseline by 7.8% at 24 hours (p = 0.022) and 15.0% at 48 hours (p = 0.0001) for patients receiving bilateral stimulation after excluding one patient with pleural effusion. No serious device/procedure-related adverse events were reported. CONCLUSIONS: The present study demonstrated the ability to safely and successfully place percutaneous electrical phrenic nerve stimulation leads in patients on mechanical ventilation and the feasibility of using this approach to synchronize electrical stimulation with inspiration while maintaining work of breathing within defined limits.

Use of a novel "Split" ventilation system in bench and porcine modeling of acute respiratory distress syndrome.

Split ventilation (using a single ventilator to ventilate multiple patients) is technically feasible. However, connecting two patients with acute respiratory distress syndrome (ARDS) and differing lung mechanics to a single ventilator is concerning. This study aimed to: (1) determine functionality of a split ventilation system in benchtop tests, (2) determine whether standard ventilation would be superior to split ventilation in a porcine model of ARDS and (3) assess usability of a split ventilation system with minimal specific training. The functionality of a split ventilation system was assessed using test lungs. The usability of the system was assessed in simulated clinical scenarios. The feasibility of the system to provide modified lung protective ventilation was assessed in a porcine model of ARDS (n = 30). In bench testing a split ventilation system independently ventilated two test lungs under conditions of varying compliance and resistance. In usability tests, a high proportion of naïve operators could assemble and use the system. In the porcine model, modified lung protective ventilation was feasible with split ventilation and produced similar respiratory mechanics, gas exchange and biomarkers of lung injury when compared to standard ventilation. Split ventilation can provide some elements of lung protective ventilation and is feasible in bench testing and an in vivo model of ARDS.

Acute respiratory distress syndrome: underrecognition by clinicians.

BACKGROUND: Previous reports suggest that acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is underdiagnosed in both adult and pediatric clinical practice. Underrecognition of this condition may be a barrier to instituting a low tidal volume ventilation strategy. This study aimed to determine the accuracy of clinical diagnoses of ARDS in daily practice using the American European Consensus Conference (AECC) criteria as a criterion standard and to investigate whether clinical recognition of ARDS altered ventilator management. METHODS: This retrospective study included intensive care unit (ICU) patients who died and underwent postmortem examination. Two independent reviewers assigned each patient to those with ALI/ARDS or no ALI. For those who met AECC criteria for ARDS, all patient records were reviewed for the presence of a documented diagnosis of the condition. The accuracy of the clinicians in diagnosing ALI/ARDS was determined, and ventilator settings between the clinically "diagnosed" and "non-diagnosed" groups were compared. The diagnostic accuracy in predetermined subgroups (those with diffuse alveolar damage, with ≥3 affected chest x-ray quadrants, with diagnosis≥3 days, with pulmonary vs extrapulmonary cause) was also examined. RESULTS: Of 98 consecutive ICU patients who died and underwent autopsy, 51 met the inclusion criteria. Sixteen of 51 patients (31.3%) who had ALI/ARDS according to the AECC criteria had this recorded in their clinical notes. Those with histologic evidence of ALI/ARDS (diffuse alveolar damage) and with a more severe chest x-ray pattern or who satisfied the criteria for a number of consecutive days were no more likely to have a clinical diagnosis of ALI/ARDS recorded. However, those with a pulmonary cause of ALI/ARDS were more likely to have a diagnosis recorded. Tidal volumes, positive end-expiratory pressure, and mean airway pressure were higher in those with a clinical diagnosis of ARDS. CONCLUSIONS: Acute respiratory distress syndrome is underrecognized by clinicians in ICU, and recognition does not result in lower tidal volume ventilation. Significant barriers remain to the recognition of ALI/ARDS and application of an evidence-based ventilator strategy.