To the Editor:—
I read with interest the study by Jaber et al. 1and the accompanying editorial by Tantawy and Ehrenwerth2regarding pressure-support ventilation (PSV). The Jaber study is noteworthy for documenting that the performance of PSV using modern anesthesia ventilators approaches the performance of an intensive care unit ventilator. The editorial correctly indicates that the testing was not performed under conditions of varying lung compliance and airway resistance that influence the ventilation result obtained when using PSV. Nevertheless, PSV is most likely to find application in the operating room for patients who can be allowed to breathe spontaneously rather than for patients who present a significant ventilation challenge. The question of whether we need PSV in the operating room is germane to clinical practice and needs to be addressed from the perspective of the clinical indications and potential advantages for the anesthetized patient.
Pressure-support ventilation was developed in the intensive care unit to allow patients to breathe spontaneously while intubated for long periods of time and for patients who are in the process of weaning from ventilator support. The clinical indications for PSV in the intensive care unit are not relevant to the operating room. Indeed, for many years, spontaneous ventilation was not used commonly in the operating room because of the work of breathing imposed by the airway and circuit, and the potential for respiratory compromise. The introduction of the laryngeal mask airway reintroduced spontaneous ventilation to anesthesia practice, and we have used this technique despite having learned in the intensive care unit that the work of breathing imposed by an artificial airway and breathing circuit limits the advantage of spontaneous ventilation. Fortunately, studies indicate that PSV can improve oxygenation and ventilation, and even reduce the work of breathing for anesthetized adult and pediatric patients when using a laryngeal mask airway.3,4Using PSV in conjunction with a laryngeal mask airway may well extend the use of laryngeal mask airways to longer procedures as effective ventilation can be achieved.
The potential clinical impact of PSV in the operating room extends well beyond supporting patients with a laryngeal mask airway. During emergence from anesthesia, establishing consistent spontaneous ventilation is useful to help ensure that a patient will continue to breathe effectively after extubation. Concern for hypoventilation and slow elimination of anesthetic agents has been an impediment to using spontaneous ventilation during emergence. PSV will facilitate the use of spontaneous ventilation during emergence by reducing the work of breathing and improving minute ventilation and may lead to more rapid elimination of anesthetic vapors. Certainly, establishing a consistent pattern of regular spontaneous ventilation before extubation is desirable before removing an artificial airway and ventilatory support.
Spontaneous ventilation has other advantages over controlled ventilation that may be realized now that PSV is available in the operating room. The ability to assess anesthetic depth is enhanced when the rate, rhythm, and depth of breathing can be observed. Titration of anesthetic agents, most notably opioids, is also facilitated. The abnormal ventilation/perfusion ratios that can occur during controlled ventilation may be less likely to occur when supported spontaneous ventilation is used rather than controlled mechanical ventilation. There is even evidence to suggest that PSV set to provide continuous positive airway pressure or bilevel positive airway pressure can be used in awake patients to prevent atelectasis during the preoxygenation process.5Finally, spontaneous ventilation offers the safety advantage of knowing that the patient will likely continue to breathe even if an artificial airway should become dislodged.
Pressure-support ventilation has the potential to significantly influence anesthetic practice in many ways. The Jaber study provides data to allow clinicians to use PSV with the confidence of knowing that it will perform similarly to PSV used in the intensive care unit. We should begin to learn about this new modality, selecting patients who are easy to ventilate, where the risk of using PSV is not significant. As we gain experience, the clinical indications and advantages in the operating room will become more obvious. I welcome this new tool and believe it will become widely used in anesthetic practice to facilitate emergence, titrate anesthetic drug administration, improve intraoperative gas exchange, and potentially enhance patient safety by making patients less reliant on an artificial airway and mechanical ventilator. The question of whether we need PSV in the operating room will only be answered definitively by using it. The Jaber study provides the information needed to use PSV in the operating room with confidence.
University of Pennsylvania School of Medicine, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania. feldmanj@email.chop.edu
