Noninvasive Ventilation for Preoxygenation during Emergency Intubation

Introduction

Anyone working in Emergency Medicine will have been present when a critically ill patient needs tracheal intubation in the Resuscitation Room. Depending on your local set-up, this may have been performed by the emergency medicine team or colleagues from anaesthetics or intensive care. It’s a high-stakes procedure where the patient’s physiology is already compromised, and we then potentially compromise it even further by the use of drugs for sedation and paralysis and the change from negative pressure to positive pressure ventilation. It makes sense that we would do everything we can to make this as safe as possible and prevent adverse events whenever we can.

What is usual care?

Setting up for a rapid sequence induction of anaesthesia hasn’t changed much over the twenty-five years I have been practising medicine. In fact, it’s not a million miles from the ‘Thio-Sux-Tube’ I was taught when I first learned anaesthesia.

It’s important to note that many would also not include cricoid pressure as a routine manoeuvre in their practice.

What did this trial do?

One significant danger during tracheal intubation is hypoxemia, which is estimated to occur in 10-20% of intubations^​1​​. If unchecked hypoxia which can lead to significant morbidity and even to cardiac arrest. To avoid hypoxia standard teaching is to preoxygenate the patient as much as possible, essentially creating a resevoir of oxygen in the lungs by displacing as much nitrogen as possible and replacing it with an oxygen rich mixture. How this is done varies and interestingly seems to have custom and practice influences with different health systems favouring different devices. At the least complex level an oxygen mask is traditionally used to mitigate this risk, but this method has limitations.

In the UK, we typically use a Mapleson C circuit, which allows spontaneous ventilation and PEEP. Other systems favour a bag-valve-mask with or without a PEEP valve. More recently, the use of a noninvasive ventilation (NIV) circuit, effectively providing a period of CPAP or BiPAP prior to intubation, has been suggested as an alternative. NIV may provide better oxygenation by delivering a higher fraction of inspired oxygen (FiO2), provide positive pressure ventilation and increased alveolar recruitment.

Critical Care Reviews

The world of critical care has to be on its toes at this time of year, when the Critical Care Reviews conference (lead by the fantastic Rob McSweeny) jontly presents new trials alongside their journal publication.

This year is no different, with the publication in the NEJM of the fabulously acronymised “PRagmatic trial Examining OXygenation prior to Intubation (PREOXI)“, which aimed to compare the effectiveness of these two preoxygenation methods. There has been some healthy competition between medical education sites to publish and comment, but the prize surely goes to Scott Weingart for recording this fabulous podcast with the authors before the embargo was lifted! We strongly recommend you give this a listen before considering a change in your practice.

The Paper – Noninvasive Ventilation for Preoxygenation during Emergency Intubation^​2​

Abstract

Background – Among critically ill adults undergoing tracheal intubation, hypoxemia increases the risk of cardiac arrest and death. The effect of preoxygenation with noninvasive ventilation, as compared with preoxygenation with an oxygen mask, on the incidence of hypoxemia during tracheal intubation is uncertain.

Methods – In a multicenter, randomized trial conducted at 24 emergency departments and intensive care units in the United States, we randomly assigned critically ill adults (age, ≥18 years) undergoing tracheal intubation to receive preoxygenation with either noninvasive ventilation or an oxygen mask. The primary outcome was hypoxemia during intubation, defined by an oxygen saturation of less than 85% during the interval between induction of anesthesia and 2 minutes after tracheal intubation.

Results – Among the 1301 patients enrolled, hypoxemia occurred in 57 of 624 patients (9.1%) in the noninvasive-ventilation group and in 118 of 637 patients (18.5%) in the oxygen-mask group (difference, −9.4 percentage points; 95% confidence interval [CI], −13.2 to −5.6; P<0.001). Cardiac arrest occurred in 1 patient (0.2%) in the noninvasive-ventilation group and in 7 patients (1.1%) in the oxygen-mask group (difference, −0.9 percentage points; 95% CI, −1.8 to −0.1). Aspiration occurred in 6 patients (0.9%) in the noninvasive-ventilation group and in 9 patients (1.4%) in the oxygen-mask group (difference, −0.4 percentage points; 95% CI, −1.6 to 0.7).

Conclusions – Among critically ill adults undergoing tracheal intubation, preoxygenation with noninvasive ventilation resulted in a lower incidence of hypoxemia during intubation than preoxygenation with an oxygen mask. (Funded by the U.S. Department of Defense; PREOXI ClinicalTrials.gov number, NCT05267652.)

Noninvasive Ventilation for Preoxygenation during Emergency Intubation. Gibbs K, Semler M, Driver B.
N Engl J Med(2024)

.

What type of study is this?

This was a multicentre, randomized controlled trial (RCT) carried out in 24 emergency departments and intensive care units across the United States (7 Emergency Departments and 17 Intensive Care Units). The trial was pragmatic and unblinded, with adult patients randomly assigned to receive either non invasive ventilation or an oxygen mask for preoxygenation before tracheal intubation. The primary aim was to evaluate the incidence of hypoxemia during the procedure.

Tell me about the patients

The study involved 1301 critically ill adults, all aged 18 or older, who required tracheal intubation with sedation. Exclusions included patients who were pregnant, prisoners, those already receiving positive-pressure ventilation, those with apnea or hypopnea, and cases where immediate intubation was necessary. The median age of participants was 61 years, and nearly half had hypoxemic respiratory failure. The intubations took place predominantly in ICUs (73.2%) and the rest in emergency departments. A significant portion of the patients had severe chronic and acute conditions, such as sepsis, pneumonia, and gastrointestinal bleeding.

The intervention group

In the intervention group, patients received non-invasive ventilation using a tight-fitting mask, either from a conventional ventilator with NIV mode or a separate NIV machine. The operators selected the type of ventilator and the mode, although best practice recommendations were given.

• Preoxygenation for at least 3 minutes if possible
• Fraction of inspired oxygen (FiO₂) of 100%
• Expiratory pressure of at least 5cm of water
• Inspiratory pressure of at least 10cm of water
• Respiratory rate of at least ten breaths per minute.
• Ventilation could happen after induction at the operator’s discretion.
• Supplemental oxygen given by nasal cannula or high-flow nasal cannula at the operator’s discretion

The control group

Patients were given additional supplemental oxygen using a ‘non-rebreather’ mask or a bag-mask device without any manual ventilation before the induction of anaesthesia.

• Preoxygenation for at least 3 minutes if possible
• Administer supplemental oxygen through the oxygen mask from the start of preoxygenation until initiation of laryngoscopy at the highest flow rate possible (>15 litres per minute)
• Ventilation could happen after induction at the operator’s discretion.
• Supplemental oxygen given by nasal cannula or high-flow nasal cannula at the operator’s discretion

(Rant – ‘Non-Rebreather’ Mask)

Bear with me for a moment… Please, please can we call the ‘non-rebreather’ mask an oxygen bag with reservoir. The reservoir makes the main difference, not the three flappy green bits. Thanks.

What were the measured outcomes in this study?

The primary outcome measured was hypoxemia during intubation, defined as an oxygen saturation of less than 85% between the induction of anaesthesia and two minutes after tracheal intubation. Secondary outcomes included the lowest oxygen saturation during the same period, and exploratory outcomes examined hemodynamic events like hypotension, the use of vasopressors, and cardiac arrest. Safety outcomes focused on aspiration incidents and other complications.

What are the main results?

• Hypoxemia: Occurred in 9.1% of the NIV group compared to 18.5% in the oxygen-mask group.
• Cardiac arrest: 0.2% in the NIV group versus 1.1% in the oxygen-mask group.
• Aspiration: 0.9% in the NIV group and 1.4% in the oxygen-mask group.
• Lowest oxygen saturation: Median was 99% in the NIV group and 97% in the oxygen-mask group.
• Oxygen saturation below 80%: 6.2% in the NIV group versus 13.2% in the oxygen-mask group.

This trial’s strength lies in its robust sample size and multicenter design, enhancing the generalisability of the findings. The randomized controlled structure and intention-to-treat analysis provide a solid basis for the results.

However, there are some limitations:

• Unblinded Design: The trial’s unblinded nature might introduce bias, although independent observers mitigated this risk.
• Exclusions: Patients already receiving positive-pressure ventilation were excluded, potentially limiting the applicability of findings to this group.
• Urgency of Intubation: Approximately 20% of eligible patients were excluded due to the urgency of their intubation, which may not reflect everyday clinical practice where rapid decisions are often necessary.

Should we change practice based on this study?

The findings suggest a clear benefit of non-invasive ventilation over traditional oxygen masks in reducing hypoxemia during emergency intubation, which is associated with lower risks of severe outcomes like cardiac arrest. Given these results, there is a strong case for considering non-invasive ventilation as the preferred method for preoxygenation in critically ill adults. However, clinicians should weigh the benefits against practical constraints, such as the availability of equipment and the time required for setup.

In the UK many clinicians preoxygenate with a device other than a hudson mask and so we don’t know from this paper whether there is an advantage over a BVM, BVM + PEEP valve, or Mapleson C circuit. All of which are commonly used in critical, emergency and prehospital care, and which may have some of the same impact as NIV. This would arguably do much the same as non-invasive ventilation, although as it wasn’t tested in this trial we don’t really know, but what this study does tell us is that the use of hudson mask is not optimal for many patients.

There is also a useful reminder in this study that my 20-year-old practice of not ventilating a patient during the apnoeic period prior to intubation is outdated and unnecessary. We have previously covered this on the blog and would recommend gentle ventilation during the apnoeic period.

Do we do this for everyone?

This paper makes a strong argument that if you are using a simple face mask for preoxygenation, you need to reconsider and probably change that. The question would then be whether you need to do it for everyone or just those who are really at risk. I think there are two main arguments for doing it routinely.

• If you always do it, you get better at it, and your team gets better at it.
• You cannot always predict which patients will be difficult and/or become hypoxic.

However, there is an argument that only the patients with some degree of hypoxemia before intubation had any benefit.

That said, this is one of those times when I think, “Why not?”. You’ll be using the machine anyway, and the more you do this, the easier it will become (particularly when you really need it). It’s similar to when I offer colleagues the ultrasound machine when they put in an arterial line, to which they say ‘I’ll use it if I have trouble’. To which I gently ask, “Why wait until then?”

The other caveat is in prehospital care, where the setup to achieve non invasive ventilation and prehospital emergency anaesthesia may be rather complex and, in many cases, unachievable with a specific NIV machine.

And to reiterate our point from earlier we don’t know whether alternative methods of delivering PEEP/BiPAP (BVM/Mapleson C) are as effective, but they are likely to be as good as non-invasive ventilation, or at least better than a standard oxygen mask.

Summary

This study demonstrates that preoxygenation with noninvasive ventilation significantly reduces the risk of hypoxemia during tracheal intubation compared to traditional oxygen masks. Whether it is better than alternative methods remains to be seen, but we would certainly look forward to more trials in this area.