Hypoventilation patterns during bronchoscopic sedation and their clinical relevance based on capnographic and respiratory impedance analysis

  • Yu-Lun Lo
  • Hau-Tieng Wu
  • Yu-Ting Lin
  • Han-Pin Kuo
  • Ting-Yu LinEmail author
Original Research


Capnography involves the measurement of end-tidal CO2 (EtCO2) values to detect hypoventilation in patients undergoing sedation. In a previous study, we reported that initiating a flexible bronchoscopy (FB) examination only after detecting signs of hypoventilation could reduce the risk of hypoxemia without compromising the tolerance of the patient for this type of intervention. We hypothesize that hypoventilation status could be determined with greater precision by combining thoracic impedance-based respiratory signals, RESP, and EtCO2 signals obtained from a nasal-oral cannula. Retrospective analysis was conducted on RESP and EtCO2 waveforms obtained from patients during the induction of sedation using propofol for bronchoscopic examination in a previous study. EtCO2 waveforms associated with hypoventilation were then compared with RESP patterns, patient variables, and sedation outcomes. Signals suitable for analysis were obtained from 44 subjects, 42 of whom presented indications of hypoventilation, as determined by EtCO2 waveforms. Two subtypes of hypoventilation were identified by RESP: central-predominant (n = 22, flat line RESP pattern) and non-central-predominant (n = 20, RESP pattern indicative of respiratory effort with upper airway collapse). Compared to cases of non-central-predominant hypoventilation, those presenting central-predominant hypoventilation during induction were associated with a lower propofol dose (40.2 ± 18.3 vs. 60.8 ± 26.1 mg, p = 0.009), a lower effect site concentration of propofol (2.02 ± 0.33 vs. 2.38 ± 0.44 µg/ml, p = 0.01), more rapid induction (146.1 ± 105.5 vs. 260.9 ± 156.2 s, p = 0.01), and lower total propofol dosage (96.6 ± 41.7 vs. 130.6 ± 53.4 mg, p = 0.04). Hypoventilation status (as revealed by EtCO2 levels) could be further classified by RESP into central-predominant or non-central-predominant types. It appears that patients with central-predominant hypoventilation are more sensitive to propofol during the induction of sedation. RESP values could be used to tailor sedation management specifically to individual patients.


Propofol Hypoventilation Impedance measurement End-tidal CO2 Procedure sedation Bronchoscopy 



This study was supported by Chang-Gung Memorial Hospital (Grant No. CMRPG3E2241).

Compliance with ethical standards

Conflict of interest

We declare no conflicts of interest.


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Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Department of Thoracic MedicineChang Gung Memorial Hospital, Chang Gung University, College of MedicineTaipeiTaiwan
  2. 2.Department of Mathematics and Department of Statistical ScienceDuke UniversityDurhamUSA
  3. 3.Mathematics DivisionNational Center for Theoretical SciencesTaipeiTaiwan
  4. 4.Department of AnesthesiologyTaipei-Veterans General HospitalTaipeiTaiwan

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