To the Editor:—
Moderate intravenous sedation is routinely administered for diagnostic and interventional procedures to alleviate patient discomfort and anxiety. Oxygen desaturation is a common problem for anesthesiologists providing moderate sedation to patients undergoing upper endoscopy (esophagogastroduodenoscopy, endoscopic retrograde cholangiopancreatography, or bronchoscopy). During these procedures, patients typically receive intravenous propofol for sedation while supplemental oxygen is administered via nasal cannulae. The nasal cannula often becomes an ineffective tool for providing supplemental oxygen when the patient’s mouth is open and the endoscopy probe is in place. We would like to report a technique that is simple and effective for increasing oxygenation in patients receiving moderate intravenous sedation as described above.
After the patient assumes the lateral decubitus or prone position, we place a clear plastic sheet over the patient’s face and tape it to the patient’s head (fig. 1). The nasal cannula is thus effectively converted into a face tent. This technique creates an oxygen reservoir that provides an inspiratory fraction of oxygen of 40–60% with oxygen flows of 4 l/min. After preoxygenation using this technique for a few minutes, we usually titrate intravenous propofol to achieve moderate-to-deep sedation while maintaining spontaneous respiration without oxygen desaturation. We monitor the patient’s respirations with capnography or a pediatric precordial stethoscope placed over the trachea. If the patient becomes apneic because of airway obstruction or oversedation, we still have an average of 2 to 3 min to manipulate the airway before oxygen desaturation occurs.
We make a 12”× 12” or larger plastic sheet using any clean, clear plastic bag (nasal cannula bags, specimen bags, or breathing circuit bags) or the plastic cover from the upper body warming blanket kit. After explaining to the patient that by applying this plastic sheet we will be increasing their oxygen supply, even the most anxious patients are receptive. One concern is that a plastic sheet could increase “dead space” resulting in rebreathing of carbon dioxide and hypercarbia. We routinely monitor rebreathing of carbon dioxide using capnography for prolonged cases or whenever it is available. By maintaining the plastic sheet in a tent-like position covering only the upper two thirds of the head or using oxygen flow greater than 4 l/min, we can avoid rebreathing of carbon dioxide and hypercarbia. There is minimal (0–3 mmHg) carbon dioxide rebreathing with this face tent. During manipulation of the endoscopy probe, we lift the plastic sheet slightly to avoid dragging it into the mouth.
Although there are commercially available masks for bronchoscopy, this technique uses plastic sheets that are ubiquitous and available at no additional cost. We also use this technique for patients undergoing colonoscopy in the lateral decubitus position, rectal procedures in the jackknife position or pain management procedures in the prone position.
* UMDNJ-Robert Wood Johnson Medical School, New Brunswick, New Jersey. email@example.com