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