Author: Len Belotti, DO, MBS

Editor: Silas Smith, MD

Background

  • NRBs consist of one unidirectional inspiration valve and two unidirectional expiration valves.
  • The oxygen source is connected under the inspiration valve, with an attached reservoir bag that typically holds ~1L O₂.
  • Reservoir bags must be cycled with an O₂ flow greater than the patient’s minute ventilation and inspiratory flow volume for adequate oxygen delivery.
  • CO₂ rebreathing dramatically increases if the flow of O₂ is lower than the patient’s minute ventilation (respiratory rate x tidal volume), leading to CO₂ retention.
  • NRBs do not provide positive pressure.
  • There is not a reliable way to measure FiO₂ from an NRB, due to potential seal leaks, CO₂ rebreathing, and other factors.
  • As a result, adequate oxygen delivery is difficult to confirm, and titration of oxygen concentration is limited.

Physiology

  • Work of breathing (WOB) is the energy required to overcome the respiratory system’s elastic and resistive elements to move gas into and out of the lung.
  • In hypoxia:

    • Pulmonary vasculature vasoconstricts to match ventilation and perfusion.
    • Other vessels—especially coronary and cerebral—dilate.
    • This response is regulated by carotid bodies, which are sensitive to rising CO₂ levels.
  • At rest, approximately 2% of total oxygen consumption is used by respiratory muscles, primarily the diaphragm.
  • With increased WOB:

    • More oxygen is consumed to support respiration (the “oxygen cost of breathing”).
    • Additional muscle recruitment further decreases available oxygen for other organs.
  • In sepsis:

    • Compensatory increase in respiratory rate occurs in response to metabolic demand, acidosis, and lactate production – independent of pulmonary infection.
    • Tachypnea is associated with inflammatory mediator-induced damage to alveolar capillary membranes, leading to:

      • Decreased lung compliance
      • Compromised oxygen uptake
      • Impaired carbon dioxide elimination

Data and Trials

  • In patients in respiratory distress first treated with an NRB prior to intubation, as compared with those that were not:

    • 30-day mortality and duration of mechanical ventilation were increased.
    • The most significant mortality increase (35.5%) occurred in patients with prolonged NRB use >2 hours pre-intubation.
  • In acute hypoxemic respiratory failure without hypercapnia, HFNC vs. NRB improved oxygenation and Lowered intubation rates (by 9% to 20%)
  • In moderate COVID pneumonia, HFNC vs. NRB:

    • Improved progression-free survival without escalation of oxygen delivery
    • Provided better oxygenation
    • Led to more rapid de-escalation of oxygen therapy
    • Resulted in greater patient satisfaction
  • In hypostatic pneumonia, HFNC vs. NRB:
    • Better oxygenation
    • Reduced hypercarbia
    • Reduced inflammatory markers (WBC, procalcitonin, CRP)
    • Improved symptomatic dyspnea
    • Reduced adverse events (abdominal distention, facial dermatitis, etc.)
  • In radiation pneumonia with respiratory failure, HFNC vs. NRB:

    • Improved oxygenation faster
    • Reduced need for intubation within 72 hours
  • In patients <2 years with bronchiolitis, HFNC vs. NRB:

    • Improved oxygenation
    • Reduced respiratory rates
    • Reduced duration of oxygen therapy and hospitalization
  • In cardiac surgery patients, HFNC vs. NRB:

    • Substantially improved severe and refractory hypoxemia
  • In preoxygenation for intubation, NRB vs. BVM:

    • NRB achieved an expired O₂ fraction of 64% vs 89% BVM on first exhaled breath
    • Decreased peri-intubation desaturations and severe hypoxemic events
  • Post-extubation:
    • HFNC rather than NRB immediately post-extubation demonstrated better oxygenation, reduced desaturations, reduced rates of reintubation, and improved patient comfort.

Management Issues and Recommendations

  • NRBs may be used to temporize acute respiratory decompensation and hypoxia, but they are not definitive therapy.
  • If used, NRB O₂ flow rates must exceed the patient’s minute ventilation and peak inspiratory flow.
  • NRB oxygen delivery is cold and dry, requiring patient energy expenditure to heat and humidify.

    • This increases insensible losses and causes discomfort.
  • NRBs:

    • Cannot accurately measure or titrate FiO₂
    • Lack positive pressure or PEEP
    • Provide inferior and/or insufficient flow rates
  • Ongoing NRB use to maintain saturations suggests:

    • Substantial ongoing oxygen consumption and/or deficit
    • Presence of pulmonary or cardiac compromise
    • Need for advanced respiratory therapies
  • Ongoing tachypnea, NRB use, or increasing O₂ demand should trigger consideration of modalities delivering direct or indirect PEEP to reduce WOB and fatigue, and evaluation for critical care resources
  • In sepsis and similar conditions, both NIV and HFNC mitigate respiratory drivers and reduce respiratory effort
  • A definitive oxygenation and ventilation modality should be established prior to admission:

    • Patients should not be transported to a floor setting on a NRB
    • Acceptable options include:

      • HFNC
      • BiPAP/CPAP
      • Intubation with mechanical ventilation, as appropriate

Further Reading:

  1. Abe Y, et al. Tokai J Exp Clin Med. 2010;35(4):144–7. PMID: 21319045
  2. Brotfain E, et al. Isr Med Assoc J. 2014;16(11):718–22. PMID: 25558703
  3. Coudroy R, et al. Thorax. 2020;75(9):805–7. PMID: 32522764
  4. Frat JP, et al. N Engl J Med. 2015;372(23):2185–96. PMID: 25981908
  5. Groombridge CJ, et al. Anaesthesia. 2017;72(5):580–4. PMID: 28295147
  6. Herren T, et al. J Med Case Rep. 2017;11(1):204. PMID: 28750686
  7. Li CJ, et al. Am J Med Sci. 2021;361(4):436–44. PMID: 33622528
  8. Maggiore SM, et al. Am J Respir Crit Care Med. 2014;190(3):282–8. PMID: 25003980
  9. Mauri T, et al. Anesthesiology. 2021;135(6):1066–75. PMID: 34644374
  10. Michiels C. Am J Pathol. 2004;164(6):1875–82. PMID: 15161623
  11. Miguel-Montanes R, et al. Crit Care Med. 2015;43(3):574–83. PMID: 25479117
  12. Muneer S, et al. J Med Sci. 2018;4(1):28–30.
  13. Nazir N, Saxena A. Afr J Thorac Crit Care Med. 2022;28(1). PMID: 35692457
  14. Roberts JK, et al. Ann Am Thorac Soc. 2015;12(6):952–5. PMID: 26075558
  15. Song Y, et al. J Int Med Res. 2021;49(6):3000605211022279. PMID: 34111998
  16. Thompson WT. MCV/Q. 1965;1(1):48–9.
  17. Türe E, et al. Signa Vitae. 2020;16(1):47–53.
  18. Vourc’h M, et al. J Cardiothorac Vasc Anesth. 2020;34(1):157–65. PMID: 31230964
  19. Xing D, et al. Technol Health Care. 2022;30(4):869–80. PMID: 35001901
  20. Zakynthinos S, Roussos C. In: Gutierrez G, Vincent JL (eds). Tissue Oxygen Utilization. Springer-Verlag; 1991:171–84.