An observational study will be conducted in 20 hospitalized surgical patients routinely managed with opioids for anesthesia and post-operative pain control. Trachea Sound Sensor measurements and reference respiratory measurements will be recorded and analyzed to develop diagnostic algorithms that produce a risk-index score that detects/predicts progression from mild hypoventilation, to moderate hypoventilation, to severe hypoventilation due to opioids and other medications that cause respiratory depression.

Our current Trachea Sound Sensor (TSS) has a wired Sony commercial microphone integrated into a commercial pediatric stethoscope, coupled to the skin surface over the trachea at the sternal notch. The Trachea Sound Sensor will measure and record the sounds of air moving within the proximal trachea during inhalation and exhalation. The microphone signal will be converted into an accurate measurement of the patient's respiratory rate and tidal volume (during inhalation & exhalation) over time, to determine the minute ventilation trend, breathing patterns, apnea episodes, and degree of snoring (due to partial upper airway obstruction).

A commercial respiratory facemask and two pneumotachs (gas flow sensors) will also be used to accurately and continuously measure the patient's respiratory rate and tidal volume (during inhalation & exhalation) to determine the minute ventilation trend, breathing patterns, and apnea episodes.

TSS data and reference respiratory data will be collected prior to surgery with the patient breathing normally (baseline), in the Operating Room (OR) during the induction and maintenance of anesthesia, in the Post Anesthesia Care Unit (PACU), and on the general nursing floors of Thomas Jefferson University Hospital (TJUH).

The sounds of air flowing through the proximal trachea will be correlated with the reference breathing measurements using signal processing methods to optimize the measurement accuracy of RR, TV, breathing pattern, apnea episodes, and degree of snoring. A commercial accelerometer may be coupled to the skin surface of the neck (with tape) to measure body position and activity level. The TSS and vital sign trend data will be analyzed to produce a Risk-Index Score every 30 seconds with alerts and alarms that warn the patient and caregivers about progressive Opioid Induced Respiratory Depression (OIRD).

RTM's Trachea Sound Sensor (TSS) and data acquisition system will be used to measure and record the sounds of air movement within the trachea during inhalation/exhalation prior to surgery (baseline), and during management with opioid medications in the operating room (OR), post-anesthesia care unit (PACU), intensive care unit (ICU), and/or general nursing floor.

The TSS will be adhered to the skin of the neck (within the sternal notch) to measure and record the sounds of air flowing through the proximal trachea during inhalation and exhalation. A commercial miniature accelerometer sensor may also be adhered to the skin of the neck and used to measure and record the patient's body position and activity level.

In addition, research staff will intermittently measure and record each patient's respiratory rate (RR) and tidal volume (TV) prior to surgery (baseline), during anesthesia (OR), during anesthesia recovery (PACU), and during post-operative care (ICU or nursing floor) using a commercial research facemask and respiratory flow sensors (pneumotachs) hardwired to a data acquisition system and personnel computer (PC). One commercial pneumotach will accurately measure the patient's tidal volume during inhalation, and another commercial pneumotach will accurately measure the patient's tidal volume during exhalation.

The concentration of oxygen in the inspired air delivered into the facemask will be tightly controlled, according to a physician's order and standard-of-care methods. The facemask and commercial ventilation measurement system was designed and tested in collaboration with Nick Rudolph from the company Hans Rudolph, Inc.

Capnography will also be used to continuously measure and record the concentration of carbon dioxide within the facemask's air during inhalation and exhalation, using end-tidal measurements to estimate the concentration carbon dioxide in the alveoli and arterial blood. Hemoglobin oxygen saturation will be continuously measured and recorded using a commercial pulse oximeter and finger probe.

In some of the study subjects, blood will be intermittently sampled from a radial artery catheter (previously inserted for clinical care) or a peripheral venous catheter and used to measure the levels of pH, oxygen, carbon dioxide, lactate and other analytes using a point-of- care meter. Blood may be sampled more frequently before and after an opioid bolus or a change in opioid dose. Blood will not be sampled from some of the study subjects because a radial artery/venous catheter were not available or functional for blood sample acquisition.

Trend data will be used to develop a diagnostic algorithm with a risk-index score that detects/predicts progression from mild hypoventilation, to moderate hypoventilation, to severe hypoventilation due to opioids

Inclusion Criteria:

• Patients scheduled for inpatient surgery at Thomas Jefferson University Hospital that would routinely receive opioids for their clinical care.
• Age 18 to 80 years.
• Body Mass Index < 35.
• Stable lung function, oxygenation, and ventilation prior to the surgical procedure.
• Stable cardiac, vascular, renal, hepatic, neurologic, gastrointestinal, or muscular function prior to the surgical procedure

Exclusion Criteria:

• Patients scheduled for inpatient surgery at TJUH that would not routinely receive opioids for their clinical care.
• Age < 18 and > 80 years.
• Body Mass Index > 35.
• History of difficult airway management or difficult endotracheal intubation
• History of severe seep apnea, requiring oxygen therapy, or CPAP management at home.
• Unstable pulmonary, cardiac, vascular, renal, hepatic, immune, neurologic, gastrointestinal, or muscular function prior to the surgical procedure.
• Excessive facial hair that may prevent a tight seal around the respiratory facemask.
• Pregnancy
• Patients that decline to participate

All patients scheduled for inpatient surgery at Thomas Jefferson University Hospital that would routinely receive opioids for their clinical care.