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
Methodology
- 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
Statistics
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.
Results
- 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])
Conclusions/Discussions
- 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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