Intubating a critically ill patient is a high-risk, high-pressure moment. When someone’s oxygen levels are severely compromised, every second counts. That’s when preoxygenation plays a pivotal role. It extends safe apnoeic time and helps minimise the potential adverse risks of intubation, particularly in high-risk populations such as patients with obesity or limited physiological reserve. Conventional methods including non-rebreathing masks and bag-valve masks are sometimes just insufficient. Luckily, novel techniques such as non-invasive ventilation (NIV) and high-flow nasal cannula (HFNC) offer promising alternatives.

NIV: Positive Pressure, Positive Results

Enter the PREOXI trial, a large-scale multi-centre RCT with 1,301 critically ill patients recruited from 24 EDs and ICUs in the U.S.. This trial showed that preoxygenating with BiPAP (bilevel positive airway pressure) reduces hypoxaemia rates nearly in half, down to 9% compared to 19% using a standard oxygen mask, and without bumping up aspiration risk. (1) 

Another study in ICU supports the use of the pressure support (PS) mode with PEEP, showing it performs better than non-rebreathing masks at keeping the arterial O2 level up. (2) However, another RCT failed to show any major difference in organ protection when NIV was used. (3)

HFNC: The Hands-Free Hero

HFNC is like the “hands-free” preoxygenation gadget.(8) It delivers oxygen continuously during apneic phase, even during laryngoscopy, and doesn't need to be removed mid-procedure. (4, 5, 7, 8) 

Multiple RCTs in ICU found that HFNC holds its own against non-rebreathing and bag-valve masks, offering similar lowest oxygen saturations during intubation (4, 5, 6, 7, 8), maintaining O2 during the apneic phase (7), and lowering the odds of scary complications like deep desaturation, shock, or cardiac arrest. (4, 8)

A meta-analysis also gave HFNC a high-five for being non-inferior to the standard care, even showing shorter ICU stays and fewer cases of severe hypoxaemia. (9)

NIV vs HFNC: The Showdown

So, which one is better: NIV or HFNC?

The FLORALI-2 trial, a multi-centre randomised open-label trial in 28 ICUs in France, tried to settle the score. Spoiler alert: it’s not that simple.

In patients with acute hypoxaemic respiratory failure, both approaches performed similarly in terms of preventing severe desats or complications. (10)

But secondary analyses suggest NIV may have an edge in patients with moderate-to-severe hypoxaemia thanks to its combo of high FiO₂ and PEEP that keeps those alveoli open and ready for action. (11) 

Digging deeper, a subgroup analysis of the same trial showed that in obese patients, NIV didn’t really outperform HFNC. (12) A network meta-analysis also found NIV reduced desaturation more effectively than conventional methods and HFNC. (13) For HFNC, open mouths during respiratory distress might also reduce its PEEP-like benefit. (14)

In the end, both NIV and HFNC seem better than the traditional methods, and neither appears to be better or worse on mortality. (13) A systematic review suggests NIV probably reduces hypoxaemia more reliably than HFNC, and might even lead to fewer serious adverse events. (15)

The Dream Team? Combining HFNC and NIV

Why choose one when you can have both? In OPTINIV trial, patients got both HFNC and NIV (with PS and PEEP), and they had better oxygen saturation than those with NIV alone, without more complications or ICU deaths. (16)

What is holding us back?

Our emergency clinicians are still hesitant to use NIV or HFNC for some reasons.

1. Availability of Equipment

Many emergency departments just don’t have the right equipment. That said, some conventional mechanical ventilators used for mechanical ventilation after intubation can provide NIV too. One case series showed that patients stayed safe and hypoxia-free using NIV delivered by a portable machine. (17) HFNC can be readily initiated with a dedicated device.

2. Aspiration Anxiety

There is a worry that NIV could up the risk of aspiration. Evidence from both a systematic review and the PREOXI trial showed no evidence of an increased risk of aspiration with NIPPV compared with alternative preoxygenation methods (1, 15)

Final Take

NIV and HFNC have emerged as game-changers of optimising preoxygenation before intubation. Whether used alone or together, they help us make the whole intubation process a little less risky. Hope that they become the initial tools for preoxygenation in every emergency department.