The purpose of this study is to assess the utility of the ExSpiron Respiratory Variation Monitor in patients undergoing an interventional procedure with anesthesia. The primary outcome measure will be the average minute ventilation of the patient during the procedure. This study will also examine the correlation between clinical interventions such as drug administrations or airway maneuvers with data from the monitor. Additionally the study may provide information about the ability of this new monitoring system to prevent hypoxemia during these procedures and to consider its utility, compared with capnography, to detect hypopnea.
Background Assessing the adequacy of ventilation during Monitored Anesthesia Care (MAC) and sedation is difficult. Agents used to provide procedural sedation can depress ventilatory drive and can interfere with airway patency, making it much more likely that the patient will hypoventilate and experience partial or complete obstruction to ventilation. \[It is actually clinically easier to administer general anesthesia and insert an airway management device such as an endotracheal tube or a laryngeal mask airway , however given the superior recovery profile following sedation vs. general anesthesia, it is usually preferable to administer sedation, if the procedure can be performed with its use.\] The American Society of Anesthesiologists maintains a database of closed malpractice claims which allows analysis of patterns of injury. A study considering claims from MAC/sedation cases found that 40% of the MAC claims resulted in death or brain damage, that 25% of the claims that were associated with oversedation/hypoventilation occurred in the endoscopy suite, and that 44% of the oversedation cases could have been prevented by better monitoring.1 A study comparing claims from remote locations (such as endoscopy) with operating rooms, found that 50% of remote location claims involving monitored anesthesia care, the proportion of claims for death was increased in remote location claims \[54 vs. 29% (operating room claims)\], respiratory damaging events were more common in remote location claims (44 vs. 20%), with inadequate oxygenation/ventilation the most common specific event (21 vs. 3% in operating room claims), and that remote location claims were more often judged as being preventable by better monitoring (32 vs. 8% for operating room claims).2
Upper endoscopy procedures, such as upper GI endoscopy and endoscopic retrograde cholangiopancreatography (ERCP), are particularly challenging where the anesthesiologist has limited access to the patient's head and is working in darkened rooms. Indeed investigators have found it very difficult to find a combination of propofol and short acting opioid that allows instrumentation of the esophagus without "intolerable ventilatory depression".3 Trying to assess ventilation by observing chest excursion or listening to ventilation with a stethoscope under these conditions can be difficult and can be done only periodically. Side-stream nasal cannula end-tidal capnography offers a possible solution, but the cannula can become dislodged and the proceduralist's endoscope often interferes with its function. End-tidal capnography in the non-intubated patient is very insensitive to changes in minute ventilation. At best, this technology can usually assess only the presence or absence of ventilation: there is limited ability to judge the adequacy of ventilation or to quantify it.4
The Study Device The ExSpiron Respiratory Volume Monitor (Respiratory Motion, Inc., Waltham MA) has FDA 501(k) clearance to be used for patient care. It consists of a proprietary PadSet that is placed on the chest in the mid-axillary line and connected to a free standing monitor. This monitor measures and analyzes the changes in thoracic electrical impedance that occur during the respiratory duty cycle. It is able to quantify respiratory rate and also determine tidal volume and minute ventilation as well as graphically display changes in lung volumes. It has been shown to accurately measure the effect of interventions (medications, airway maneuvers) in endoscopy patients.5 Preliminary work has determined optimal lead placement demonstrated excellent correlation to spirometry with an R value of 0.94-0.98 and excellent accuracy and precision.6
Preliminary work cited below has shown that the monitor provides information about the effect of medications and airway maneuvers on breathing patterns that is not available with routine monitoring. This study seeks to extend that knowledge by investigating whether using this information in real-time results in different respiratory measurements compared to patients with routine monitoring.
