It’s not time to start checking the want ads just yet, and the Singularity may not be at hand, but make no mistake, fellow pulmonologists: the computers are gunning for our jobs.
Or maybe it’s the surgeons who are tired of consulting us for “vent management,” and finding out we can’t get patients off the vent any faster than they can without our help. Anyway, some troublemakers in Germany (Dirk Schadler et al) found that among 300 patients in surgical intensive care units (SICUs), an automatically-weaning ventilator was as good as human beings using a ventilator weaning protocol at liberating patients from mechanical ventilation.
What They Did
Authors randomized 300 post-surgical patients at 3 SICUs at one hospital in Kiel, Germany after they had been on 9 hours of mechanical ventilation to one of two weaning strategies. Half were managed with standard ventilator-weaning protocols, managed by physicians and respiratory therapists. Half had a switch on their ventilators (Evita XL) flipped to enable the SmartCare software embedded into it. This software automatically adjusts the pressure support delivered in response to patient effort, aiming to keep a patient in a “comfort zone” of 15-30 breaths per minute, with expired paCO2 of < 55 mm Hg, and tidal volumes greater than 300 mL. PEEP had to be set and changed manually.
When the patient is staying in the respiratory comfort zone with a minimum of pressure support and PEEP, the clever ventilator automatically initiates a spontaneous breathing trial. If the patient passes the machine-initiated and monitored SBT, the ventilator goes “DING!“, then extubates the patient and transfers them out of the ICU (I’m making up this last part…I think).
The study’s primary endpoint was overall ventilation time in the ICU, including noninvasive ventilation (NIPPV/BiPAP), during the 28-day study period. Secondary end points were time in the respiratory “comfort zone”, numbers of alarms and vent changes, length of stay in the ICU and hospital, and mortality at 28- and 90-days.
They predefined three subgroups: cardiac surgery patients (n=132), patients with sepsis (n=44), and patients with COPD (n=41).
The study was funded in large part by a grant of 70,000 euros from Drager, the company that makes the SmartCare software.
What They Found
Overall, patients were weaned/liberated from mechanical ventilation equally quickly in both groups: a median of 31 hours in the automatic-weaning group, and 39 hours in the humans-using-weaning-protocols group (p=0.18).
In the predefined cardiac surgery subgroup (n=132), patients on the automatic-weaning vent were liberated a bit faster: 24 hours of ventilation, vs. 35 hours for controls.
In the sepsis and COPD subgroups, there was no statistically significant difference in ventilator hours, but numerical results were widely discordant:
- 44 patients with sepsis “auto-weaned” in a median 101 hours (5 days) vs. 144 hours (7 days) for the human-weaning group. (p=0.296)
- 41 patients with COPD took longer to escape the ventilator on auto-weaning than with standard human-driven protocols (55 hours vs. 28 hours, p=0.095).
There were abundant protocol violations: 25% of the time the automatic weaning software was supposed to be “on,” it was not. This would seem to make it harder to show a benefit (i.e., reduce the observed effect of auto-weaning).
Patients in the auto-wean group were placed on their first spontaneous breathing trial (SBT) by the machine within one hour in a majority of cases; those managed by humans took a median of 9 hours to start an SBT. There was a “trend” toward fewer tracheostomies in the automatic-weaning group (17 vs. 28, p=0.08).
What It Means
Ventilators that automatically adjust the delivered support according to a patient’s work of breathing are probably going to become standard — if for no other reason than the competition among manufacturers to offer the most whiz-bang products that seem to be advancing in capability. The product tested here (software, really) is one solution; adaptive support ventilation (ASV) and proportional assist ventilation are others popular in the U.S. (The Drager software tested here is unique in that it can also automatically initiate a spontaneous breathing trial.)
But do these new ventilator modes — advertised as more comfortable and patient-friendly, with the implication of better outcomes — offer a true advantage? There’s some suggestion of better patient-vent interaction with ASV than with pressure-controlled intermittent mandatory ventilation, and PAV reduces work of breathing. Here’s a nice review of these alternative self-adjusting ventilator modes and their potential benefits … for which there’s very little good evidence.
This trial is the first to my knowledge to suggest any real benefit to auto-weaning in actually liberating patients from the ventilator faster. Previous studies claiming a benefit with ASV were unimpressive in that they included post-surgical patients who were easy to wean — showing ASV reduced vent time by a whopping 50 minutes, for example.
The theoretical benefits of dynamic self-managing ventilator modes have so far been even less demonstrable in the more complex and hard-to-wean MICU population with COPD, sepsis, neuromuscular weakness, etc. For this reason, pulmonologist-intensivists should still have some job security for the foreseeable future … right?
Schadler D et al. Automatic Control of Pressure Support for Ventilator Weaning in Surgical Intensive Care Patients. AJRCCM 2012;185:637-644.