An Emergency Difficult Airway Predictor Would be From HEAVEN

31 Jan
January 31, 2018

Background: Predicting an anatomically and/or physiologically challenging airway is not a straightforward task by any stretch of the imagination.  There are some existing difficult-airway prediction tools available (i.e. LEMON = Look externally, Evaluate 3-3-2 rule, Mallampati score, Obstruction, Neck mobility), but many of them were derived in an elective surgery setting and may not be as applicable to emergency airway management.  Additionally, these prediction models only focus on anatomical challenges and ignore physiologic ones. Several components of the LEMON approach require an awake, cooperative patient. The authors of this paper derived a tool, called the HEAVEN criteria (Hypoxemia, Extremes of size, Anatomic abnormalities, Vomit/blood/fluid, Exsanguination, Neck mobility issues) to address this clinical need.

What They Did:

  • Validation of the HEAVEN criteria for difficult airway prediction in emergency RSI
  • Retrospective analysis of a large air medical registry

Outcomes:

  • Intubation success
  • First-attempt success
  • First attempt success without desaturation

Inclusion:

  • Any patient requiring RSI to facilitate ETT placement

Exclusion:

  • None listed in the paper

Results:

  • Approximately 2400 patients undergoing air medical RSI included
    • Overall First attempt Intubation Success Rate = 92%
    • Overall Intubation Success Rate = 97%
    • 1363 (56.3%) of patients had at least one HEAVEN criteria identified
  • The Specific Sensitivity, Specificity, PPV, and NPV of the HEAVEN criteria for first attempt success without desaturation are listed below:

  • Sensitivity and specificity evaluate a clinical test while predictive values are useful when considering the value of the test to a clinician. In this case sensitivity helps rule out a difficult airway while specificity helps rule in a difficult airway.  Therefore  as the number of criteria increase, so does the specificity or probability of a difficult airway.  The predictive values however are not that great. Even at 5+ criteria our PPV is only 57%, meaning this criteria will fail at identifying a difficult airway in almost 1 in 2 patients (Not that useful).
  • First attempt success lower with each additional HEAVEN criteria with an inverse relationship observed between HEAVEN criteria and intubation success
  • First attempt success without desaturation is lower with each additional HEAVEN criteria with an inverse relationship observed between HEAVEN criteria and intubation success

Strengths:

  • Large cohort of patients
  • All medical providers with training in airway management (i.e. Helicopter Advanced Resuscitation Training (HeART) Program)
  • Use of Apneic oxygenation and graduated escalation of preoxgenation from NRB to BVM as needed by patients
  • Confirmation of ETT placement was with waveform capnography

Limitations:

  • Retrospective analysis of pre-hospital population
  • Many of the variables evaluated at time of laryngoscopy instead of prior to attempted intubation making this tool limited in predicting airway difficulty
  • Medical provider teams consist of flight nurse and paramedics in austere environments. This may limit generalizability to physicians in emergency departments
  • Providers only used CMAC laryngoscope, but no other types of blades available
  • After patient disposition a complete electronic medical record requiring up to 245 data elements was filled out for each patient. This retrospective nature of data collection is based on recollection and may be flawed (i.e. self – reported recollection of desaturation numbers)
  • Majority of patients were trauma patients (63%) which limits generalizability to other patient groups
  • Only a small group of patients had a high number of HEAVEN criteria present. This limits the ability to make sub group comparisons at higher numbers of criteria
  • HEAVEN score was not compared to standard practice, so its unclear if this score would perform better or worse than clinician gestalt

Discussion:

  • Etomidate (75%) and Succinylcholine (80%) were the RSI medications of choice for most intubations
  • Vomit/blood/fluid (38%) and Neck mobility (25%) were the two most common HEAVEN criteria present

Author Conclusion: “The HEAVEN criteria seem to be a useful tool to predict difficult airways in emergency RSI.”

Clinical Take Home Point: At this time the HEAVEN criteria cannot be recommended as an assessment of difficult airways prior to intubation in the emergency department, as the data is retrospective, in the pre-hospital setting, and the impact on airway management success has not been determined.

References:

  1. Kuzmack E et al. A Novel Difficult-Airway Prediction Tool for Emergency Airway Management: Validation of the HEAVEN Criteria in a Large Air Medical Cohort. JEM 2018. PMID: 29331494

Post Peer Reviewed By: Anand Swaminathan (@EMSwami)

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Salim Rezaie

Emergency Physician at Greater San Antonio Emergency Physicians (GSEP)
Creator & Founder of R.E.B.E.L. EM
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4 replies
  1. David says:

    Where did you get the information that only CMAC was used? We utilize direct laryngoscopy with standard Miller and Macintosh blades as well. It is the decision of the individual clinician to determine whether DL or VL is most appropriate for a specific patient.

    You also need to recognize that the majority of the intubations that we do are not in ‘austere’ environments but rather in the ED itself. We opt for this controlled environment over the helicopter anytime there is the option. You’d be surprised how unwilling many physicians are to initubate and initiate mechanical ventilation, especially in the types of smaller community hospitals that we typically pick-up from. And yes, these are most often ABEM certified physicians.

    Reply
    • Salim Rezaie says:

      Hello David,
      Appreciate your comment. In the study, under protocol, it says, “During the study period, providers had access to the CMAC laryngoscope (KARL STORZ Endoscopy-America, El Segundo, CA), which allows for either direct or video-assisted laryngoscopy.” Appreciate you clarifying the environments as this was not clear in the paper itself.

      Salim

      Reply
  2. Matt says:

    It would be nice for them to reproduce study with with DL and VL at random. As we all know depending on the provider, patient, and context the two devices can make a world of difference in first pass success.

    Reply

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