Table 2

Summary of included studies

Reference	Study design/participants	Intervention	ETCO₂ criteria	Outcomes	Results	Quality assessment*
Burton et al 29	Prospective observational 58 adults (only adults ≥18 years old included in analysis, median age: 38 years old)	Propofol, etomidate, midazolam, ketamine (doses not defined) Supplementary oxygen: 2 L/min (all patients) Monitoring: pulse oximetry, heart rate, cardiac rhythm, RR and interval BP, ETCO₂ continuously	ETCO₂ change of ≥10 mm Hg from presedation baseline or intrasedation ETCO₂ ≤30 mm Hg or ≥50 mm Hg	▸ Accuracy of capnography in detecting acute respiratory events (SpO₂ <92%; increases in supplemental oxygen; use of bag-valve mask or oral/nasal airway; airway alignment manoeuvres; physical or verbal stimulation; reversal agent administration)	Diagnostic OR: 4.83† 14/19 experienced changes in ETCO₂ before hypoxia	18 (low quality); moderate risk of bias
Deitch et al 27	RCT 110 adults (≥18 years old; median age: 37 years old)	1–1.5 mg/kg intravenous propofol with additional 0.5 mg/kg boluses Procedure: abscess drainage (n=69); fracture/joint reduction (n=35) Supplementary oxygen: 3 L/min (56/110 patients) Monitoring: pulse oximetry, pulse rate, BP, ETCO₂ continuously	ETCO₂ ≥50 mm Hg, or ≥10% increase or decrease from baseline or loss of waveform	▸ Accuracy of capnography in detecting hypoxia (SpO₂ <93% for >15 s) ▸ Ability of physicians to recognise RD (blinded vs unblinded capnography)	Diagnostic OR: 1.21 9/25 experienced changes in ETCO₂ before hypoxia; 27/52 RD detected by ETCO₂ only; 1/27 physicians identified RD according to ETCO₂	25 (high quality); Low risk of bias
Deitch et al 25	RCT 132 adults (≥18 years old; median age: 34 years old)	0.05 mg/kg morphine or 0.5 μg/kg fentanyl intravenously and then 1 mg/kg propofol with 0.5 mg/kg boluses Procedure: abscess drainage; fracture/joint reduction Supplementary oxygen: 3 L/min (all patients) Monitoring: pulse oximetry, pulse rate, BP, ETCO₂ every 5 s	ETCO₂ ≥50 mm Hg, or ≥10% increase or decrease from baseline or loss of waveform ≥15 s	▸ Does the addition of capnography to standard monitoring reduce hypoxia (SpO₂ <93% for >15 s) ▸ Ability of capnography to detect RD	Diagnostic OR: 154.72 Hypoxia: 17/68 (capnography) vs 27/64 (blinded capnography) 44/44 changes in ETCO₂ before hypoxia; 32/76 RD detected by ETCO₂ only; 5/38 interventions based on ETCO₂	28 (high quality); low risk of bias
Deitch et al 28	Prospective observational 117 adults (≥18 years old, mean age: 34.5 years old)	1 mg/kg propofol with additional 0.5 mg/kg boluses until desired level of sedation was achieved Supplementary oxygen: 15 L/min (in 59/117) Monitoring: pulse oximetry, pulse rate, BP, ETCO₂ every 5 s	ETCO₂ ≥50 mm Hg or ≥10% increase or decrease from baseline or loss of waveform ≥15 s	▸ Accuracy of capnography in detecting hypoxia (SpO₂ <93% for >15 s) ▸ Ability of capnography to detect RD	Diagnostic OR: 9.32 28/58 experienced RD identified by ETCO₂ but did not develop hypoxia; 35/58 experienced hypoxia after RD; 29/35 experienced changes in ETCO₂ before hypoxia; 16/31 interventions based on ETCO₂	24 (moderate quality); high risk of bias
Miner et al 26	Prospective observational 74 adults (≥18 years old, mean age: 37.6 years old)	Methohexital/propofol/etomidate or fentanyl and midazolam (doses not defined) Supplementary oxygen: not given routinely (47/74 as part of airway management; concentration not stated) Monitoring: pulse oximetry, heart rate, BP, RR, ETCO₂ every 2 min (+ modified version of the OAA/S scale)	ETCO₂ >50 mm Hg or absent ETCO₂ waveform or ETCO₂ change from baseline >10 mm Hg	▸ Ability of capnography to detect RD vs pulse oximetry	Diagnostic OR: 7.31 33/74 experienced RD 33/33 detected by ETCO₂, 11/33 detected by pulse oximetry; 9/11 interventions based on ETCO₂	24 (moderate quality); low risk of bias
Miner et al 30	Prospective observational 108 adults (≥18 years old, mean age: 40.9 years old)	Methohexital/propofol/etomidate or fentanyl and midazolam (doses not given) Supplementary oxygen: 87/108 (as part of airway management; dose not stated) Monitoring: pulse oximetry, heart rate, BP, ETCO₂ continuously (+ EEG to calculate BIS score)	ETCO₂ change from baseline >10 mm Hg or absent ETCO₂ waveform	▸ Capnography vs pulse oximetry in detecting RD	Diagnostic OR: 3.99 44/108 experienced RD 41/44 detected by ETCO₂, 14/44 detected by pulse oximetry	26 (high quality); low risk of bias
Sivilotti et al 6	RCT 63 adults (≥18 years old, mean age: 39 years old)	0.3 mg/kg ketamine or 1.5 μg/kg fentanyl intravenously, 0.4 mg/kg propofol intravenously 2 min later and then 0.1 mg/kg boluses every 30 s Supplementary oxygen: if patients developed oxygen desaturation (number of patients and dose not stated) Monitoring: continuous pulse oximetry, ECG and BP, ETCO₂	ETCO₂ >50 mm Hg or a rise or fall of >10 mm Hg from presedation baseline or loss of waveform for >30 s or recurrent losses of waveform	▸ Accuracy of capnography in detecting hypoxia (SpO₂ <92%) ▸ Hypoventilation; Oxygen desaturation (SpO₂ <92%)	Diagnostic OR: 7.56 21/36 developed hypoxia and had ETCO₂ changes but only 2/36 experienced changes in ETCO₂ before hypoxia	18 (low quality); moderate risk of bias

*Quality assessment includes the Downs and Black Study Quality Score and the risk of bias according to the Cochrane Risk of Bias tool.13 ,15
†Diagnostic OR: the diagnostic accuracy of capnography to detect an adverse event was calculated as an OR for each study.
RD, respiratory depression.