乌鸦传媒

SAN DIEGO -- Critically ill patients who underwent tracheal intubation had higher oxygen saturations and a lower incidence of severe hypoxemia with bag-mask ventilation, according to results of the PreVent trial.

In a sample of about 400 critically ill patients, those who received bag-mask ventilation in the interval between induction and laryngoscopy had a lower incidence of severe hypoxemia (oxygen saturation <80%) compared with patients who did not receive ventilation (10.9% vs 22.8%, relative risk 0.48, 95% CI 0.30-0.77), and the bag-mask ventilation group had a nadir oxygen saturation 3.9 percentage points higher, reported Jonathan Casey, MD, of Vanderbilt University Medical Center, and colleagues.

Operator-reported aspiration during intubation was more likely in the control arm than in the bag-mask ventilation group (4% vs 2.5%, P=0.41), they reported at the Society of Critical Care Medicine (SCCM) annual meeting and simultaneously in the .

"This piece of equipment, this bag-mask device, is involved in every intubation procedure because when you push these medications, if you have difficulty placing a tube or are unable to place a tube, you have to have a way to breathe for the patient," Casey told 乌鸦传媒. "The whole idea of this trial was that, instead of just using it as treatment when you're having trouble [intubating], you should use it preventatively with everyone."

In an , Patricia Kritek, MD, and Andrew Luks, MD, both of the University of Washington in Seattle, said the trial results "may not settle the question of the safety of bag-mask ventilation during rapid-sequence intubation," but they do provide "reassurance" that manual ventilation will not likely lead to clinically significant harm.

The editorialists noted that a study limitation was the possibility that the bag-mask group had a "significantly higher arterial partial pressure of oxygen than the control group and greater reserve protecting against peri-intubation hypoxemia."

"The fact the median oxygen saturation before induction was the same in the two groups (99%) does not preclude marked differences in the arterial partial pressure of oxygen," they wrote. "That is because an oxygen saturation of 100% can be associated with an arterial partial pressure of oxygen that is anywhere from 110 mm Hg to nearly 600 mm Hg, given the shape of the hemoglobin-oxygen dissociation curve."

They also cautioned that in this study, pre-oxygenation strategies were not standardized, causing more patients in the bag-mask ventilation group to receive the treatment before induction than in the control group (39.7% vs 10.9%).

However, Casey said that not controlling for pre-oxygenation could mean the effects of the intervention were actually underestimated.

For the Preventing Hypoxemia with Manual Ventilation During Endotracheal Intubation trial, Casey and colleagues collected data from seven U.S. ICUs, in which patients were randomized 1:1 to bag-mask ventilation or no ventilation in permuted blocks of 2, 4, and 6, stratified by trial site. Patients and clinicians were unblinded to their assignments.

Bag-mask ventilation during the interval from induction until the initiation of laryngoscopy was used for 199 patients and involved oxygen flow rates of ≥15 L/m; a valve attached to the expiratory port of the bag-mask device generating a positive end-expiratory pressure of 5 to 10 cm of water; an oropharyngeal airway; a two-handed mask seal with head-tilt and chin-lift maneuver; and ventilation at 10 breaths per minute with the smallest volume necessary for a visible chest rise, the authors reported.

Meanwhile the control group (202 patients) did not undergo bag-mask ventilation during this interval, unless an attempted laryngoscopy failed, it was needed to treat hypoxemia (oxygen saturation ≤ 90%), or the patient's safety was at risk.

Patients were excluded if they were pregnant or incarcerated, had urgent need for tracheal intubation, or if a clinician determined ventilation between induction and laryngoscopy was required or contraindicated, the authors reported.

In total, the trial enrolled 401 adults (average age 60) undergoing induction and tracheal intubation. Half of patients had sepsis or septic shock (50%) and close to 60% had hyperemic respiratory failure that lead to tracheal intubation.

No differences were observed between life-threatening events or mortalities across the two groups, Casey and colleagues reported.

In a subgroup analysis, patients with lower index oxygen saturation had significantly greater differences in lowest oxygen saturation across groups, although no other characteristics, such as BMI, Acute Physiology and Chronic Health Evaluation (APACHE) II scores, and operator experience, had significant effects on the primary results, the authors reported.

Study limitations included its non-blinded nature and the failure to control for pre-oxygenation strategies. The trial also did not measure the use of noninvasive ventilation during this interval, and only included ICU patients so the results may not be generalizable to other patient populations, the authors noted.

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