Protocol-Driven Ventilator Weaning

Many patients admitted to the ICU require intubation and mechanical ventilation for respiratory failure. As their underlying condition improves, attention is quickly focused on ventilator weaning and extubation to decrease the risks associated with mechanical ventilation such as ventilator-associated pneumonia (VAP), airway trauma, and increased costs.^[32] These risks must be balanced against the risk of premature extubation, which may lead to difficulty reestablishing endotracheal intubation, hemodynamic instability, and increased mortality. ^[33] It is estimated that as much as 42% of the time a patient is mechanically ventilated is spent on ventilator weaning.^[34]

No single approach to ventilator weaning has been established as superior, resulting in the use of different techniques in various institutions. ^[35] Weaning techniques include intermittent trials of spontaneous breathing or gradually decreasing levels of intermittent mandatory ventilation and pressure support ventilation. These techniques allow the clinician to assess the patient's ability to take on an increasing proportion of the work of breathing.^{[36] [37]} Clinical trials to determine the best mode of ventilator weaning have been inconclusive. Esteban and colleagues^[38] compared techniques of weaning patients from mechanical ventilation. They found that daily spontaneous breathing trials (SBTs) led to extubation three times more quickly than weaning with intermittent mandatory ventilation and about twice as quickly as weaning with pressure support ventilation. In contrast,

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Figure 74-2a Protocol for low tidal volume mechanical ventilation of patients with acute lung injury or acute respiratory distress syndrome in use at the University of California, San Francisco. The protocol is based on that used in the ARDSnet trial.

Figure 74-2b

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Regardless of the mode employed for weaning, it is likely that physicians do not discontinue mechanical ventilation expeditiously. Clinical judgment does not accurately predict whether mechanical ventilation can be discontinued successfully, because the positive and negative predictive values of most of these assessments are low.^[40] Several trials provide strong evidence that mechanical ventilator weaning protocols driven by nonphysician health care providers can enhance clinical outcomes and reduce costs for critically ill patients.^{[41] [42] [43] [44]}

Ely and associates^[42] studied 300 patients randomized to a daily screening procedure, followed by an SBT driven by health care providers. If the patients passed the SBT, the ICU physician was notified of the patient's readiness for extubation. The control group received usual care, for which decisions about weaning were made only by physicians. Although the intervention patients had a higher severity of illness score than the control group, they were extubated 1.5 days earlier and had fewer ventilator-associated complications, and ICU costs were lower by about $5000 per patient.^[42]

Kollef and colleagues^[43] studied 357 patients randomized to receive protocol-directed weaning implemented by nurses and respiratory therapists or physician-directed weaning. Time to extubation, mortality, and length of stay were reduced in the protocol group but failed to reach statistical significance. The inability to detect a statistically significant difference may have been caused by the short period that most of their patients spent mechanically ventilated.^[43] Marelich and coworkers^[44] studied 335 patients with a study design similar to that of Kollef. Patients were randomized to a health care provider-driven weaning protocol or usual care, which was physician driven. The duration of mechanical ventilation for the intervention group was shortened from 124 hours to 68 hours (P = .001). For surgical patients, there also was a trend toward a lower incidence of VAP in the intervention group compared with the control group (5 versus 12 patients, respectively; P = .061).^[44]

The repeated demonstration of benefit using health care provider-driven weaning protocols from different ICUs and hospitals suggests that it is the use of a standardized approach to management as opposed to a particular ventilatory mode that is beneficial.^[12] The studies' data do not support any one particular ventilatory weaning mode. The preferred method of weaning is best determined by individual ICUs based on their needs and staffing.^{[45] [46]} However, daily SBTs appear at least as efficacious as more complex regimens. Surprisingly, in an international review, only 20% of patients were weaned using some form of SBT, and in the United States, less than 10% of all patients studied were weaned with SBTs.^[47] The ventilator weaning protocol employed at UCSF is shown in Figure 74-3 .

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Figure 74-3 Weaning protocol for mechanical ventilation. All patients with resolution of their underlying condition causing respiratory failure should be evaluated for extubation with a daily spontaneous breathing trial. Respiratory therapists perform the breathing trial.

In summary, weaning protocols should be used daily to identify patients who are ready for extubation, and unless contraindications exist, patients who pass the protocol should proceed to extubation. Patients who fail these protocols should be treated for any reversible causes and reassessed the next day for another weaning attempt.