High-Flow Nasal Cannula Versus Bag-Valve-Mask for Preoxygenation Before Intubation in Subjects With Hypoxemic Respiratory Failure

Simon. Respir Care 2016;61(9):1160-7. DOI: 10.4187/respcare.04413

Clinical Question

• In adult critically ill patients with hypoxaemic respiratory failure necessitating intubation, does high flow nasal cannula (HFNC) compared to bag-valve-mask (BVM) for both pre-oxygenation and oxygenation during intubation reduce desaturation?

Background

• The process of induction of anaesthesia and intubation has inherent risks, and these are greatest in critically ill patients
• Published data suggest up to a quarter of patients suffer a significant complication, and a quarter of these complications are due to severe hypoxia
• A variety of strategies are used to provide pre-oxygenation, including face masks with reservoir bags, non-invasive ventilation, BVM devices and HFNC devices, but trials comparing these have not demonstrated a clearly superior strategy
• More recently the PROTRACH study has been published

Design

• Single center prospective, randomised clinical trial
• Randomised by computer-generated random number sequence allocation
• Allocation concealed by opaque sequential envelopes
• Parallel assignment in 1:1 ratio
• Single blinded: Clinicians aware, study team blinded to intervention
• Sample size calculated to detect a 3% difference in minimal oxygen saturation; with a false negative rate of 20% and a false positive rate of 5%
• Intention-to-treat analysis
• Registered with clinicaltrials.gov
• Arterial blood gases collected at pre-defined time points: baseline, after 3 minutes pre-oxygenation, immediately after intubation, and 5 and 30 minutes post intubation
• Board certified intensivists performed all intubations
• Comparison between 2 groups was performed using t test for continuous data and chi-squared test for categorical data

Setting

• 11 departmental intensive care units at University Medical Center Hamburg-Eppendor
• January 2014 to November 2014

Population

• Inclusion criteria:  adult patients with hypoxic respiratory failure (PaO₂/FiO₂ < 300 mmHg) requiring intubation
• Exclusion criteria:
  • contra-indications for BVM or HFNC
  • nasopharyngeal obstruction or blockage
  • emergency endotracheal intubation
  • suspected or know difficult airway
• 773 patients screened – 40 patients enrolled
• Comparing baseline characteristics of BVM vs HFNC groups respectively
  • No significant differences in:
    • SAPS II score: 37 vs. 37
    • BMI: 27 vs. 25
    • Primary Surgical Patients: 95% vs. 75%
    • Hospitalization due to malignant or non-malignant abdominal process: 90% vs. 80%
    • Mean P/F at baseline: 205 vs. 200mm Hg
    • Mean SpO₂ at baseline: 94% vs. 96%
    • Type of oxygen therapy at baseline:
      • Low flow nasal cannula: 70% vs. 55%
      • Low Flow via Face Mask: 15% vs. 5%
      • HFNC:  5% vs. 25%
      • Noninvasive ventilation 10% vs. 15%
  • Age – significantly older in HFNC group
    • 54 yrs. vs. 63 yrs., p=0.02
• Comparing characteristics of intubation procedure in BVM vs. HFNC group
  • No significant difference in:
    • Duration of intubation; 37s vs. 30s
    • Cormack-Lehane Grade: 2 vs. 1
    • PEEP just after intubation: 8 vs. 8

Intervention

• High-Flow Nasal Cannula Device (HFNC)
  • Pre-oxygenation with FiO₂ 1.0 with oxygen flow set to 50 L/min and left in place during intubation

Control

• Bag-Valve-Mask Device (BVM)
  • Without PEEP valve
  • Pre-oxygenation oxygen flow rate 10L/min
  • No manual insufflations during apnoeic period
  • Removed immediately prior to intubation

Management common to both groups

• Preoxygenation Phase: 3 minutes followed by rapid sequence induction
• Apnoeic Phase: rapid sequence induction used sufentanil, propofol and rocuronium lasting 1 minute followed by intubation
• Intubation by direct laryngoscopy
• Initial ventilator settings: pressure control mode with an FiO₂ 1.0

Outcome

• Primary outcome: Mean lowest SpO₂ during intubation was not significantly different
  • BVM: 86% (SD ±11%)
  • HFNC: 89% (SD ±18%)
  • Absolute difference: 3% (95% CI -6.55% to +12.55%; P = 0.56)
• Secondary Outcomes
  • Pre-oxygenation
    • BVM significant improved SpO₂ from 94% at baseline to 98% (P = 0.004)
    • HFNC significantly improved SpO₂ from 95% to 99% only in a subset of patients receiving low flow oxygen prior to HFNC (P = 0.007)
  • Apnoeic Period
    • SpO₂ significantly dropped in BVM group compared to pre-oxygenated level (P = 0.001)
    • SpO₂ did not significantly drop in HFNC group compared to pre-oxygenation level (P = 0.17)
  • No difference between two groups at any predefined points for SpO₂, PaO₂/FiO₂, and PaCO₂
  • 5 subjects in each group desaturated to <80%
  • 2 cases in each group aborted during the pre-oxygenation or apnea phase due to profound hypoxia

Authors’ Conclusions

• This trial found no significant difference in SpO₂ between BVM and HFNC during intubation in adult patients with hypoxic respiratory failure

Strengths

• Randomised trial with treatment allocation being concealed – minimises selection bias
• A uniform intubation procedure with respect to duration of the intubation procedure, use of expert clinicians, medication usage and complication rates – minimising procedural co-founders
• Registered with clinicaltrials.gov

Weaknesses

• Powered to detect a 3% difference in lowest oxygen levels
  • This is not a patient centred outcome and arguably it is not a clinically relevant difference
  • As they were investigating the difference in a continuous variable only a small number of patients were required to achieve this power
  • A significantly greater number of patients would be required to investigate a dichotomous outcome, such as their secondary outcome of proportion of patients with severe hypoxia (SpO₂ <80%)
• Wide confidence intervals in primary outcome include clinically significant differences
• Single center
• Surgical population with abdominal pathology – difficult to generalise
• Patient population not equivalent on all baseline characteristics
• Statistical analysis performed assumed normal distributed data
  • However, the data is not normally distributed, SpO₂ maximum value is 100%, and a non-parametric analysis is more appropriate for this study

The Bottom Line

• This randomised controlled trial in adult critically ill patients with hypoxaemic respiratory failure necessitating intubation reported that the use of high flow nasal cannula (HFNC) compared to bag valve mask (BVM) for both pre-oxygenation and oxygenation during intubation, did not reduce desaturation during intubation
• Although this was a well-executed study, due to inappropriate statistical analysis and the small number of patients included, a generalisable conclusion cannot be made

External Links

• [article] High-Flow Nasal Cannula Versus Bag-Valve-Mask for Preoxygenation Before Intubation in Subjects With Hypoxemic Respiratory Failure
• [further reading] Correspondence to trial team
• [further reading] EMNerd: the case of the false dichotomy

Metadata

Name: Stephen Huelskamp
Date written: 28 Feb 2019
Peer-review: Duncan Chambler and David Slessor