Preoxygenation strategies for endotracheal intubation in resource-limited settings: reframing the basics

Abstract

Endotracheal Intubation (ETI) is a common procedure in the emergency department and intensive care units (ICUs). In contrast to elective surgical patients, critically ill patients often face acute hypoxemic events related to underlying pulmonary pathology, elevated metabolic demands, impaired respiratory drive, obesity, or an inability to protect the airway from aspiration. Nearly half of emergency intubations were complicated by major adverse events, most commonly cardiovascular collapse, severe hypoxemia, and even cardiac arrest [1]. Critically ill patients with acute hypoxemic respiratory failure (AHRF) are particularly vulnerable to rapid oxygen desaturation during ETI due to intrapulmonary shunting and restrained functional residual capacity (FRC), which limit the effectiveness of conventional preoxygenation. These patients cannot tolerate prolonged apnea, resulting in frequent oxygen desaturation during laryngoscopy, immediately after intubation, or even following ventilator connection. Preoxygenation strategies incorporating positive end-expiratory pressure (PEEP), such as noninvasive positive pressure ventilation (NIPPV), can enhance alveolar recruitment, preserve FRC, and optimize oxygen storage. In resource-limited settings (LRS), where advanced backup equipment and staffing may be unavailable, ETI remains one of the major challenges for physicians in Emergency Departments and ICUs.

Preoxygenation is essential to increasing oxygen reserves, prolonging the safe apnea time during ETI, and reducing hypoxemia-related complications. However, traditional preoxygenation using a non-rebreather mask or bag-mask ventilation (BVM) with 100% oxygen is often inadequate in critically ill patients due to low flow rates and lack of PEEP.

Recent evidence supports that both HFNC and NIPPV are effective preoxygenation strategies in patients with AHRF. A recent network meta-analysis by Pitre et al. [2], which included 15 randomized trials and over 3400 patients, found that HFNC and NIPPV were superior to facemask oxygenation in reducing the incidence of peri-intubation hypoxemia. Importantly, NIPPV reduced the risk of hypoxemia compared with HFNC (relative risk [RR] 0.73, 95% CI 0.55–0.98) and facemask oxygen (RR 0.51, 95% CI 0.39–0.65). HFNC also demonstrated superiority over the facemask (RR 0.69, 95% CI 0.54–0.88), likely due to its ability to deliver high and stable oxygen flow during apnoeic oxygenation, wash out pharyngeal dead space, and improve FRC. Additionally, NIPPV might reduce the risk of serious adverse events compared with HFNC (RR 0.32, 95% CI 0.11–0.91) and probably does so compared to facemasks (RR 0.30, 95% CI 0.12–0.77). These findings reinforce prior individual trial results, highlighting the efficacy and safety of NIPPV, especially in patients with moderate-to-severe AHRF. Furthermore, the strategy combined NIPPV and HFNC effectively maintained oxygen saturation during laryngoscopy in severe AHRF patients. Similarly, in the PREOXI trial, the benefit of NIPPV was more evident in the subgroups of patients with AHRF, pre-intubation FiO₂ >70%, or body mass index ≥ 30 kg/m² [3]. These findings support the use of HFNC as an effective strategy for mild hypoxemia, whereas NIPPV is beneficial for moderate to severe hypoxemia, and a combination of multiple modalities is necessary for more severe patients [2].

Challenges and practical solutions in Low-Resource settings

Although advanced preoxygenation modalities such as HFNC and NIPPV have proven clinical benefits, these are often unavailable in LRS. In such contexts, clinicians must individualize preoxygenation strategies based on available devices and patient-specific factors.

In patients with no or mild AHRF, combining an oxygen mask at a flush rate (fully opening a standard oxygen flowmeter beyond 15 L/min) with a nasal cannula at 15 L/min may increase the FiO₂ and help maintain apneic oxygenation after mask removal. The nasal oxygenation approach may be a widely applicable technique for apneic oxygenation when HFNC is unavailable. In critically ill patients who sustained moderate-to-severe AHRF or risk factors for reduced oxygen reserves (e.g., obesity, pleural effusion, and intra-abdominal hypertension), preoxygenation methods that provide PEEP, such as NIPPV or continuous positive airway pressure (CPAP), should be used to improve FRC and enhance alveolar recruitment [3]. If NIPPV is unfeasible, BMV with a PEEP valve is a practical, low-cost alternative for preoxygenation. PEEP valves are generally available in most ICU emergency kits. This BMV approach was demonstrated by the PREVENT trial, which showed that using BMV peri-intubation reduced the incidence of severe hypoxemia without increasing the risk of aspiration [4]. Furthermore, the Mapleson C circuit with 100% oxygen may offer similar benefits to BMV with a PEEP valve. It allows clinicians to feel the patient’s respiratory effort, rate, and lung compliance, enabling better control of tidal volumes than self-inflating bags [5], as illustrated in Fig. 1. However, these circuits are limited by insufficient delivered flow in patients with high inspiratory demand or mask leak, leading to dilution with ambient air and reduced FiO₂. Adequate staff training is essential, as these techniques are often unfamiliar outside of anesthesiology practice (Supplement material in Table S1). Routine use of BMV with a PEEP valve or a Mapleson C circuit after induction and prior to laryngoscopy as well as in cases of failed or prolonged intubation, is vital to prevent severe hypoxemia, or other life-threatening events. Maintaining spontaneous ventilation during EIT should be considered in patients who are anticipated to have a difficult airway or require prolonged intubation. Additionally, strategic triage and targeted allocation of available equipment, such as reserving limited NIPPV-capable ventilators or HFNC devices for the most critical patients, may significantly influence outcomes. Finally, leveraging low-cost tools and contextual expertise can bridge the gap in preoxygenation quality across settings.

Fig. 1

Preoxygenation strategies using available devices in low-resource settings. BMV: bag-mask ventilation; CPAP: continuous positive airway pressure; ETI: endotracheal intubation; FiO₂: fraction of inspired oxygen; HFNC: high-flow nasal cannula; IAH: intra-abdominal hypertension; IBW: ideal body weight; MV: mechanical ventilation; NIV: noninvasive ventilation; NRM: non-rebreather mask; P/F: PaO₂/FiO₂ ratio; PEEP: positive end-expiratory pressure; RR: respiratory rate; S/F: SpO₂/FiO₂ ratio; VCV: volume-controlled ventilation; VT: tidal volume

Full size image

Future studies should focus on validating simplified, cost-effective devices, such as flush rate nasal cannulas, basic CPAP systems, BVM with PEEP valves, and Mapleson C circuits as practical alternatives to advanced equipment in LRS. The development of standardized, low-complexity preoxygenation protocols and context-specific training modules will be essential to enhance patient safety where HFNC and NIPPV are not routinely available.

Optimal preoxygenation strategies for ETI in LRS require both protocol adaptation and clinical resourcefulness. An individualized approach using the most feasible combination of techniques should be based on fundamental principles, which include maximizing inspired oxygen fraction, ensuring adequate preoxygenation duration, and preserving FRC. Simple interventions such as flush rate oxygen delivery via standard devices, upright patient positioning, and manual application of PEEP using BMV can approximate the effect of advanced devices. Clinicians can tailor the approach to each patient in each context, which is essential to optimizing preoxygenation and apneic oxygenation, thereby enhancing peri-intubation safety.

No datasets were generated or analysed during the current study.

AHRF:

Acute hypoxemic respiratory failure

BMV:

Bag-mask ventilation

CPAP:

Continuous positive airway pressure

ETI:

Endotracheal intubation

FiO₂:

Fraction of inspired oxygen

FRC:

Functional residual capacity

HFNC:

High-flow nasal cannula

ICU:

Intensive care unit

LRS:

Low-resource settings

NIPPV:

Noninvasive positive pressure ventilation

PEEP:

Positive end-expiratory pressure

P/F:

PaO₂/FiO₂ ratio

RR:

Respiratory rate

S/F:

SpO₂/FiO₂ ratio

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Authors and Affiliations

1. Faculty of Medicine, University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh City, Vietnam

   Dai Quang Huynh

2. Department of Intensive Care Medicine, Cho Ray Hospital, 201B Nguyen Chi Thanh Street, Ward 12, District 5, Ho Chi Minh City, Vietnam

   Ngan Hoang Kim Trieu & Thao Thi Ngoc Pham

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2. Ngan Hoang Kim TrieuView author publications

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All authors contributed equally to the conceptualization and writing of the manuscript. All authors approved the final version.

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Huynh, D.Q., Trieu, N.H.K. & Pham, T.T.N. Preoxygenation strategies for endotracheal intubation in resource-limited settings: reframing the basics. Crit Care 29, 259 (2025). https://doi.org/10.1186/s13054-025-05508-2

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• Received: 19 April 2025

• Accepted: 15 June 2025

• Published: 23 June 2025

• DOI: https://doi.org/10.1186/s13054-025-05508-2

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