A comparative evaluation of capnometry versus pulse oximetry during procedural sedation and analgesia on room air

Abstract

Objective:Important questions remain regarding how best to monitor patients during procedural sedation and analgesia (PSA). Capnometry can detect hypoventilation and apnea, yet it is rarely used in emergency patients. Even the routine practice of performing preoxygenation in low-risk patients is controversial, as supplementary oxygen can delay the detection of respiratory depression by pulse oximetry. The purpose of this study was to determine whether the capnometer or the pulse oximeter would first detect respiratory events in adults breathing room air.Methods:During a randomized clinical trial comparing fentanyl with low-dose ketamine for PSA with titrated propofol, patients were monitored using pulse oximetry and continuous oral–nasal sampled capnography. Supplemental oxygen was administered only for oxygen desaturation. Sedating physicians identified prespecified respiratory events, including hypoventilation (end-tidal carbon dioxide > 50 mm Hg, rise of 10 mm Hg from baseline or loss of waveform) and oxygen desaturation (pulse oximetry < 92%). These events and their timing were corroborated by memory data retrieved from the monitors.Results:Of 63 patients enrolled, 57% (36) developed brief oxygen desaturation at some point during the sedation. All responded to oxygen, stimulation or interruption of propofol. Measurements of end-tidal carbon dioxide varied substantially between and within patients before study intervention. Hypoventilation (19 patients, 30%) was only weakly associated with oxygen desaturation (crude odds ratio 1.4 [95% confidence interval 0.47 to 4.3]), and preceded oxygen desaturation in none of the 12 patients in whom both events occurred (median lag 1:50 m:ss [interquartile range 0:01 to 3:24 m:ss]).Conclusion:During PSA in adults breathing room air, desaturation detectable by pulse oximeter usually occurs before overt changes in capnometry are identified.

End-tidal capnometry during emergency department procedural sedation and analgesia: a randomized, controlled study

“…The clinical significance of transient hypoventilation, however, is questionable in that it denotes patients at risk of hypoxia rather than clinically important RD. [9] Although it did not occur in our study, premature diagnosis of RD may, in fact, be deleterious to patients might be unnecessarily subjected to bag valve mask ventilation, insufflating their stomachs with air, and increasing their chances of aspiration. [10] This might be especially true in the case of ultra short acting agents, where momentary apnea (safe in the presence of adequate pre-oxygenation) is likely to correct itself spontaneously as the effect of the drug wears off.…”

“…Other investigators, however, have failed to show a benefi t to patients when comparing ETC with PO for detecting RD. [9,20] With regard to ETC preventing hypoxia, Deitch et al [13][14][15] found hypoxia in 25% of patients monitored by ETC, compared with 42% of those where the sedationist was blinded to the ETC reading [difference of 17% (95%CI 1.3-33)]. They also noted that all cases of hypoxia were identified by ETC before onset (100% sensitivity) although 32/132 ETC monitored patients exhibited respiratory depression without going on to hypoxia [64% specifi city (95%CI 53%-73%)].…”

“…[1,[4][5][6][7][8] Other investigators, using different methods and definitions, found PO to reveal respiratory depression before ETC. [9] The use of combined PO and ETC has been strongly recommended. [10] The clinical use of ETC has not yet to be determined, as the level of RD at which adverse events are more likely has not yet to be determined.…”

“…[10] The clinical use of ETC has not yet to be determined, as the level of RD at which adverse events are more likely has not yet to be determined. [9] Furthermore, variability in ETC readings at baseline has been noted. Sivilotti et al [9] found fluctuations in ETC readings even before drug administration and also considerable variation between participating physicians in the way they intervened in ETC changes.…”

Myths, fallacies and practical pearls in GI lab

“…Fortunately, room air Pulse oximetry is quite sensitive in the detection of the onset of sedation-associated hypoventilation. It is a myth that capnometry offers any advantage over room air Pulse oximetry [5,6] . Supplemental oxygen prevents or delays oxygen desaturation resulting from hypoventilation induced by sedation.…”