This is an early phase, proof-of-concept clinical trial assessing the safety and feasibility of non-invasive spinal cord stimulation to prevent respiratory muscle atrophy in mechanically ventilated ARDS patients. The investigators will recruit 10 elective surgery patients (surgery cohort) and 10 ARDS patients (ARDS cohort) for this study. A non-invasive, alpha-prototype Restore Technology stimulator using hydrogel surface electrodes will be used to stimulate the spinal cord at the cervical or thoracic level.

Stimulation will be conducted in closed-loop fashion at the start of inspiratory cycle. Signal from a chest belt will be used to synchronize stimulation with ventilator and prevent interference with ventilator (see Protection of Human Subjects). Prior to treatment stimulation, mapping will be conducted at 1 Hz with electrodes placed in locations identified to be optimal in the surgery cohort. Assessment of evoked EMG responses from respiratory muscles will be conducted. Once this electrode configuration is confirmed as effective (capable of evoking EMG activity), stimulation with this configuration will be applied for treatment.

Inclusion Criteria:

1. Male or female 18-85 years;
2. Intubated with confirmed diagnosis of ARDS (by Berlin Criteria: acute onset within one week of known insult, bilateral airspace opacities not fully explained by pleural effusions, atelectasis, and/or nodules, respiratory failure not explained by heart failure or fluid overload, PaO2/FiO2 ratio < 300); or identified as a patient admitted to the intensive care unit (ICU) after non-cardiac surgery;
3. Able to provide informed consent or available next of kin able to provide informed consent;
4. Have intact chest/lung, upper and lower extremity anatomy;
5. The neuromuscular connections between the spinal cord, diaphragm, and intercostal muscles are intact;
6. Enrollment of subject within 48 hours of intubation;
7. Able to induce evoked response of diaphragm muscle by spinal cord TES.

Exclusion Criteria:

1. Phrenic nerve or diaphragm pacer;
2. History of seizure disorder or on anti-epileptic medication for the treatment of seizures;
3. Compromised skin in back (neck, upper and lower back);
4. Pregnancy;
5. Implanted devices: cardiac pacemakers, implanted defibrillators, implanted neurostimulators, phrenic nerve pacers;
6. BMI greater than or equal to 35;
7. Pharmacological paralysis/neuromuscular blockade*.