Linking To And Excerpting From PulmCrit’s “Bilevel Sequence Intubation (BSI) – The new standard”

Posted on May 14, 2025 by Tom Wade MD

In addition to today’s resource, please see and review:

Today I review, link to, and excerpt from PulmCrit’s “Bilevel Sequence Intubation (BSI) – The new standard”.  by .

All that follows is from the above resource.

introduction

Bilevel Sequence Intubation (BSI) refers to initiation of noninvasive bilevel positive pressure ventilation with a backup rate prior to intubation (either using a BiPAP machine or a full-featured mechanical ventilator). BSI is distinct from traditional rapid sequence intubation (RSI), since BSI involves the delivery of machine-initiated, pressure-controlled breaths following administration of sedation and paralytics.

I’ve been using BSI for about a decade for optimization of the sickest patients, prior to intubation. It’s safe and highly effective. The PREOXI trial recently demonstrated that BSI is beneficial among all subsets of critically ill patients (even patients on room air). PREOXI is a high-quality, pragmatic RCT that will change practice. The trial has already been reviewed (e.g., EMCrit, First10EM). When you read the study, please bear in mind that, due to the Hawthorne effect, the control group did an outstanding job of pre-oxygenation – so implementing protocolized BSI in real-world ICUs would cause greater benefit than seen in the PREOXI trial.

I wrote about BSI in 2015 here. That post is reasonably good, and maybe worth looking at for folks who aren’t familiar with BSI. However, I’ve learned more about BSI over the past decade, so it’s time for a fresh post on the nuances of this technique.

getting started: benefits of BSI

The primary benefits of BSI are:

  1. Administration of 100% FiO2 for several minutes with a pressure-reinforced mask seal (if there is a mask leak, pressurized leak compensation from the ventilator will cause oxygen to leak out of the mask – rather than allowing the patient to suck air into the mask).
  2. Recruitment of lung tissue using positive pressure.
  3. Prevention of de-recruitment during sedation/paralysis.
  4. Early identification of hemodynamic instability induced by positive pressure ventilation (allowing for vasopressor initiation prior to intubation).
  5. Early identification of patients who are difficult to bag-mask ventilate.

key concept: CO2 clearance from mechanical breaths is probably irrelevant

You might be wondering why I didn’t list CO2 clearance above. It’s because it probably doesn’t matter.

Apnea causes the pCO2 to rise about 2-3 mm per minute. Anyone who has done an apnea test to confirm brain death will recognize that pCO2 rises slowly (in order to achieve a pCO2 rise of >20 mm consistently, a 10-minute apnea test is required).

In BSI, the duration of time when the machine is providing breaths is about one minute, which might equate to a pCO2 rise of ~2-3 mm. Providing gentle breaths during this minute might provide about 25-50% of a normal minute ventilation, so mechanical breaths might blunt the rise of pCO2 by 25-50% (leading to an absolute pCO2 improvement of ~1-2 mm).

Hypercapnia is generally very well tolerated, so the degree of pCO2 rise required to cause clinical harm is usually high. This renders the tiny pCO2 gains provided by mechanical breaths (~1-2 mm) wholly irrelevant.

OK… so why provide any machine breaths at all? A few reasons:

  • Machine breaths may improve recruitment and oxygenation (e.g., by increasing the mean airway pressure, and providing spikes in airway pressure that help pop open atelectatic alveoli).
  • This is what has been demonstrated to work in the PREOXI trial.
  • Providing machine breaths confirms that the patient can be successfully bag-mask ventilated (more on this below).

early evaluation of whether the patient can be bag-mask ventilated 

Most patients will maintain a patent airway during BSI (with ongoing tidal volumes recorded on the machine) – which is reassuring. This indicates that if laryngoscopy fails, the patient can be re-oxygenated with bag-mask ventilation.

Rarely during BSI, as paralysis and sedation take effect the airway will occlude (in the final ~20-30 seconds prior to laryngoscopy). Practitioners should anticipate potential airway occlusion during this period and attempt to keep the airway open using a jaw thrust. Nonetheless, airway occlusion will sometimes occur.  This should be managed as follows:

  1. Don’t panic. The airway occlusion has trapped positive-pressure oxygen in the patient’s lungs – so they won’t desaturate rapidly. Just wait until the patient is fully relaxed and proceed with intubation.
  2. If the first intubation attempt fails, then re-oxygenation should be performed with the use of an airway adjunct (e.g., bag mask ventilation with an oral airway, or laryngeal mask airway).

early identification of hemodynamic instability 

Bilevel positive pressure ventilation is often initiated ~5-15 minutes before intubation. This provides some time to evaluate how the patient responds hemodynamically to increased intrathoracic pressure. Some patients will experience hypotension during this period of time, allowing for immediate initiation of a vasopressor infusion.

Early identification of tenuous hemodynamics prior to intubation is useful, because this allows for hemodynamic stabilization before administration of sedation and full conversion to positive-pressure ventilation.

nuts & bolts: how to optimize BSI performance 

Based on the above concepts, we can set the ventilator in a rational fashion:

try to maximize the expiratory pressure (aka ePAP, aka PEEP)

  • A key principle here is that we are fundamentally trying to maximize the ePAP.
  • Expiratory pressure is probably providing the bulk of the benefit of BSI:
    • ePAP is the primary driver of mean airway pressure and recruitment.
    • ePAP is the primary factor that affects preload, allowing for early assessment of hemodynamic deterioration.
  • In order to maximize the ePAP while providing some degree of ventilation, it might be reasonable to set the ePAP at 4-5 cm below the iPAP.

try to keep the inspiratory pressure (iPAP) at a safe level

  • Excessive iPAP may increase the risk of gastric insufflation and aspiration. Most literature suggests that keeping iPAP below ~20 cm is safe, but this precise cutoff remains poorly defined. (34992795)
  • Overall, a range of 10-18 cm iPAP seems reasonable for most patients (selected based on assessments of the risk of aspiration, as compared to benefits from improved recruitment).
  • For patients with refractory hypoxemia, higher settings may occasionally be reasonable (e.g., iPAP of 25 cm).  The use of higher iPAP may be especially reasonable for patients who have a nasogastric tube placed to suction (which may help to reduce the risk of gastric insufflation).

examples of how this would work:

  • [1] Conservative setting (e.g., increased concern for aspiration): 10 cm iPAP / 5 cm ePAP.
    • The PREOXI trial required at least 10 cm of iPAP and 5 cm of EPAP. Thus, pressures below this shouldn’t generally be utilized.
  • [2] Generic setting: 15 cm iPAP / 10 cm ePAP.
  • [3] Severe hypoxemia setting: 18 cm iPAP / 14 cm ePAP.
  • [4] Maximally aggressive for refractory hypoxemia: 25 cm iPAP / 21 cm ePAP.

machine respiratory rate:

  • Patients are often tachypneic prior to intubation (e.g., respiratory rate 25-35).  It’s often reasonable to set the machine’s respiratory rate slightly below the patient’s native respiratory rate (so the ventilator doesn’t trigger while the patient is still awake). A rate of ~20 breaths/minute is often reasonable.
  • The PREOXI trial required a respiratory rate of ≧10 breaths/minute, so the respiratory rate should not be lowered below 10 breaths/minute.
  • As the patient’s breathing slows following sedation and paralysis, the machine will seamlessly start providing breaths.

  • BSI (bilevel sequence intubation) has been shown to avoid hypoxemia and peri-intubation cardiac arrest. Adoption of this as standard care will improve patient safety and cognitively off-load practitioners (so that they can focus on other aspects of airway management).
  • Carbon dioxide clearance by machine-triggered breaths is miniscule and unlikely to contribute to the benefits of BSI.
  • The primary benefits of BSI are likely the administration of 100% FiO2 and positive mean airway pressure that maintains recruitment. Consequently, maximization of ePAP (i.e., PEEP) makes sense.
  • Inspiratory positive airway pressure (iPAP) is limited to below roughly ~20 cm, to reduce the risk of aspiration.
  • Ventilator settings may be determined based on a balance of the risk of hypoxemia versus the risk of aspiration:

more information on PREOXI: 

 

 

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