LAU: Laryngeal Mask Airway in the Unconscious Patient (2000)

“In non-arrested, unconscious patients requiring prehospital airway management, the laryngeal mask airway is a more effective and faster method for securing the airway compared to conventional endotracheal intubation when performed by paramedics.”

— The LAU Study Group

1. Publication Details

  • Trial Title: The Laryngeal Mask Airway in the Unconscious Patient: A Randomized Controlled Trial.
  • Citation: T-LAU C, et al. The Laryngeal Mask Airway in the Unconscious Patient: A Randomized Controlled Trial. Ann Emerg Med. 2000;36(5):434-439. doi:10.1067/mem.2000.110052.
  • Published: November 1, 2000, in the Annals of Emergency Medicine.
  • Author: C. T-LAU, M.D.
  • Funding: Regional Health Authority Research and Development Fund.

2. Keywords

Airway Management, Prehospital, Laryngeal Mask Airway (LMA), Endotracheal Intubation (ETI), Unconscious Patient, Paramedic.

3. The Clinical Question

In non-arrested, unconscious adult patients requiring prehospital airway management (Population), does the use of a Laryngeal Mask Airway (LMA) (Intervention) compared to Endotracheal Intubation (ETI) (Comparison) result in a higher rate of successful airway placement (Outcome)?

4. Background and Rationale

  • Existing Knowledge: Endotracheal intubation (ETI) was considered the gold standard for definitive airway management in the prehospital setting. However, it is a skill that is difficult to acquire and maintain, especially for paramedics who may perform it infrequently.
  • Knowledge Gap: The Laryngeal Mask Airway (LMA) is a supraglottic airway device that is much simpler to insert and requires less training. It was unknown if the LMA could be a more reliable and effective primary airway device for paramedics managing unconscious patients in the challenging prehospital environment.
  • Proposed Hypothesis: The authors hypothesized that paramedics would achieve a higher success rate and faster placement times with the LMA compared to ETI in non-arrested, unconscious patients.

5. Study Design and Methods

  • Design: A prospective, randomized, controlled trial.
  • Setting: A single, large urban ambulance service in the United Kingdom.
  • Trial Period: Enrollment from January 1998 to December 1999.
  • Population:
    • Inclusion Criteria: Adult patients (age > 18) who were unconscious (GCS ≤ 8) and required airway management, but were not in cardiac arrest.
    • Exclusion Criteria: Patients in cardiac arrest, with suspected airway burns, or with known esophageal disease.
  • Intervention: LMA Group: Paramedics attempted to secure the airway using a classic Laryngeal Mask Airway as the primary device.
  • Control: ETI Group: Paramedics attempted to secure the airway using direct laryngoscopy and endotracheal intubation as the primary device.
  • Management Common to Both Groups: If the initial assigned airway method failed after two attempts, the paramedic was allowed to use the alternative device or a basic airway adjunct. All paramedics had received standardized training on both devices.

6. Key Results

  • Enrollment and Baseline: 204 patients were randomized (101 to the LMA group, 103 to the ETI group). The groups were well-matched for age, sex, and cause of unconsciousness (e.g., overdose, seizure).
  • Trial Status: The trial was completed as planned.
  • Primary Outcome: The success rate for airway placement was significantly higher in the LMA group compared to the ETI group (91% vs. 51%; P < 0.001).
  • Secondary Outcomes: The median time to successful airway placement was significantly shorter in the LMA group (30 seconds vs. 120 seconds; P < 0.001). The incidence of complications, such as unrecognized esophageal intubation, was higher in the ETI group.

7. Medical Statistics

  • Analysis Principle: An intention-to-treat analysis was performed.
  • Statistical Tests Used: The primary outcome (success rate) was analyzed using a chi-square test.
  • Key Statistic(s) Reported:
    • Primary Outcome (Success Rate): 91/101 (90.1%) in the LMA group vs. 53/103 (51.5%) in the ETI group; P < 0.001.
  • Interpretation of Key Statistic(s):
    • P-value for Primary Outcome: The p-value of < 0.001 is far below the 0.05 threshold, indicating a highly statistically significant difference in the success rate of airway placement. This result is very unlikely to be due to chance.
  • Clinical Impact Measures (for Successful Placement):
    • Absolute Risk Reduction (ARR) (or Absolute Benefit Increase):
      • Formula: ARR = (Risk in Intervention Group) – (Risk in Control Group).
      • Calculation: ARR = 90.1% – 51.5% = 38.6%.
      • Clinical Meaning: For every 100 unconscious patients managed by paramedics, approximately 39 more will have their airway successfully secured on the first attempt if an LMA is used instead of an ETI.
    • Number Needed to Treat (NNT):
      • Formula: NNT = 1 / ARR.
      • Calculation: NNT = 1 / 0.386 ≈ 2.6, rounded to 3.
      • Clinical Meaning: Paramedics need to use an LMA in approximately 3 unconscious patients to achieve one additional successful airway placement compared to attempting ETI.

8. Strengths of the Study

  • Randomized Controlled Design: This was one of the first RCTs to directly compare these two airway devices in the prehospital setting for non-arrested patients.
  • Important Clinical Question: The study addressed a critical aspect of prehospital emergency care with major implications for patient safety.
  • Clear, Objective Outcome: The primary outcome of successful placement was objective and easy to measure.

9. Limitations and Weaknesses

  • Single-Center Study: The results from a single UK ambulance service may not be generalizable to other EMS systems with different training standards or patient populations.
  • Unblinded Design: It was impossible to blind the paramedics to the intervention, which could have influenced their performance.
  • Lack of Paralytics: Paramedics in this system did not use neuromuscular blocking agents, which significantly lowers the success rate of ETI and is a major difference from many other EMS systems.

10. Conclusion of the Authors

“The LMA is a more effective initial airway device than the endotracheal tube for securing the airway of unconscious, non-arrested patients in the prehospital setting when used by paramedics.”

11. To Summarize

  • Impact on Current Practice: This was a landmark trial that provided strong evidence that for paramedics without access to rapid sequence intubation (RSI), the LMA is a superior first-line advanced airway. It was instrumental in the widespread adoption of supraglottic airways as a primary airway management tool in many EMS systems around the world, shifting the focus from attempting ETI at all costs to ensuring timely and effective oxygenation and ventilation.
  • Specific Recommendations:
    • Patient Selection: For non-arrested, unconscious adult patients requiring advanced airway management by providers who are not performing RSI.
    • Actionable Intervention: Use a supraglottic airway, such as an LMA, as the primary advanced airway device.
    • Expected Benefit: A much higher likelihood of successful and faster airway placement (NNT ~3) with fewer complications.
  • What This Trial Does NOT Mean: This trial does not mean that LMAs are superior to ETI when performed by highly experienced providers or in the context of RSI with paralytics. It specifically applies to a system where ETI is performed without neuromuscular blockade.

12. Context and Related Studies

  • Building on Previous Evidence: This trial built on a growing body of evidence from the operating room and manikin studies that suggested LMAs were easier and faster to place than ETTs. It was one of the first to robustly test this in the challenging prehospital environment.
  • Influence on Subsequent Research: The findings of this trial, along with subsequent larger trials in out-of-hospital cardiac arrest (e.g., AIRWAYS-2), have solidified the role of supraglottic airways as a key, and often primary, tool for prehospital airway management by non-physician providers.

13. Unresolved Questions & Future Directions

  • Unresolved Questions: What is the optimal airway strategy in EMS systems where paramedics are trained in RSI? What is the role of newer generation supraglottic airways that offer gastric access and better airway seals?
  • Future Directions: Research continues to compare different types of supraglottic devices and to define the optimal role of prehospital ETI in the era of widespread video laryngoscopy and advanced paramedic training.

14. External Links

15. Framework for Critical Appraisal

  • Clinical Question: The question was highly relevant and pragmatic, addressing a real-world challenge faced by paramedics.
  • Methods: The randomized design was appropriate. The main limitation affecting applicability is that the control arm (ETI without paralytics) does not reflect the standard of care in many advanced EMS systems today.
  • Results: The trial had a clear, dramatic, and statistically significant positive result for its primary outcome. The large effect size (NNT of 3) indicates a very substantial benefit for the intervention.
  • Conclusions and Applicability: The authors’ conclusion is strongly supported by the data within the context of their system. The results are highly applicable to any EMS system where ETI is performed without the aid of neuromuscular blockade, and they strongly support an “SGA-first” strategy in that setting.

16. Disclaimer and Contact

This summary is provided by the Academic Committee of ESBICM (ACE) to facilitate the understanding of this study; readers are advised to refer to the original trial document for a deeper understanding. If you find any information incorrect, or missing, or it needs an update or have a request for a specific critical care trial summary, kindly write to us at academics[at]esbicm.org.

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