End-tidal Carbon Dioxide for Diagnosing Anaphylaxis in Patients with Severe Postinduction Hypotension

Erlich C, Lamer A, Moussa MD et al.

Anesthesiology 2022; 136:472–481

Aim of Study

To investigate whether end-tidal CO2 a reliable indicator for diagnosing anaphylaxis in patients with severe post-induction hypotension

Design and Location

Lille University Hospital, France; case-control retrospective study


  • Patient selection – French national residents undergoing non-emergent surgery.
  • Case – Confirmed anaphylaxis through biochemical assays such as tryptase and histamine levels and with a Ring and Messmer scale grade III/IV. Data taken from surgeries between 2010-2018. Total number of cases 49.
  • Control – Patient with non-anaphylaxis hypotension described by a MAP < 50 for at least 6 minutes, in the first 30 minutes after induction. Data taken from surgeries in 2017. Total number of cases 555.

Primary outcome:

  • End-tidal CO2 cut-off value predictive of anaphylaxis

Secondary outcome:

  • MAP cut-off value predictive of anaphylaxis


Ability of ETCO2 to differentiate between anaphylaxis and severe post induction hypotension qualified by:

  • Receiver operating characteristic curve, 95% CI calculated by area under curve and cut-off defined by maximisation of Youden index
  • Various regression models to adjust for confounding variables including ASA grade, patient demographics and competing predictions such as MAP and HR
  • Threshold for statistical significance set to P<0.05.


  • ETCO2 is an independent predictor of anaphylaxis
  • ETCO2 values <25mmHg significant predictor of anaphylaxis (sensitivity [95% CI], 0.92 [0.82 to 0.98]; specificity, 0.94 [0.92 to 0.99])
  • MAP values <37mmH significant predictor of anaphylaxis (sensitivity [95% CI], 0.63 [0.45 to 0.80]; specificity, 0.80 [0.66 to 0.93])


  • ETCO2 is a sensitive, specific, and independent marker of anaphylaxis in mechanically ventilated patients
  • It should be considered as one of the means of distinguishing between anaphylaxis and other potential causes of hypotension

Limitations from the study

  • Single-centre study with limited cases of anaphylaxis for this case to be generalisable to global population
  • Results only applicable to elective procedures
  • Any severe decrease in cardiac output, whatever the causes, is likely to result in profound drop in ETCO2
  • Break down of causes of post-induction hypotension not secondary to anaphylaxis not explored; therefore, unable to determine if other specific causes of hypotension could also yield low ETCO2 readings

Summary by Dr Y Salih. Journal Club Meeting 27 October 2022

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