LEICESTER, UK--Assisted spontaneous breathing (ASB) may be the most comfortable choice for many patients in the intensive care unit (ICU) who require assisted ventilation, a recent study found.[1] ASB allows patients to initiate a breath based on their own respiratory rate and pattern; thus, it is more balanced and adjustable to individual breathing habits than are other modes of ventilation.

Mechanical ventilation can cause discomfort, pain, and anxiety, and in some cases it may lead to long-term psychological problems. During the acute phases of critical illness, these may be necessary evils, because ventilatory mode is usually chosen on the basis of physiologic needs. During recovery, however, patients are more likely to be conscious, and thus comfort becomes a more important variable.

William C. Russell, MD, and J. Ruari Greer, MD, the authors of the British study, suggest that "the subjective feeling of comfort is important for the well-being of the patient and should be considered when choosing an appropriate mode of ventilatory support."

These researchers, both on staff at the Leicester Royal Infirmary, conducted a randomized, double-blind, crossover study to assess the comfort level of various modes of assisted ventilation used in the intensive care setting.

Twenty-four healthy, nonsmoking volunteers with no history of chest disease or direct experience with ventilation were subjected to, and then asked to rate, three ventilatory modes: ASB, synchronized intermittent mandatory ventilation (SIMV), and biphasic positive airway pressure (BIPAP). Healthy volunteers were chosen so that the study results would not be influenced by confounding factors, such as disturbed sleep, invasive monitoring, or other distractions typical of the ICU.

SIMV delivered a tidal volume of 5 mL/kg, respiratory rate of 8 breaths/min, positive end-expiratory pressure of 5 cm H2O, and flow rate of 60 L/min.

The BIPAP system used pressures of 5 and 10 cm H2O, inspiration/expiration ratio of 1:2, and respiratory rate of 8 breaths/min. Inspiratory pressure with the ASB system was set to 10 cm H2O. The degree of support selected for each mode was based on estimates of the volunteers' normal respiratory effort.

The volunteers used a visual analog scale to rank the ventilatory modes in terms of comfort and ease of use, and they were given the opportunity to comment on all methods. ASB was rated as by far the most comfortable and the easiest mode of ventilation, followed by BIPAP. SIMV was rated the least comfortable method. However, there was considerable intersubject variability.

Comments on SIMV revealed that most of the volunteers found both inspiration and expiration to be difficult with this mode. Words such as "blocking" and "sticking" were frequently used in describing SIMV.

As Drs. Russell and Greer admit, there is an important limitation to their study. Lung mechanics may be quite different in healthy volunteers than in patients in the ICU. But as critically ill patients begin to recover, and as their respiratory drive and load start returning to normal, ASB may be the best method of ventilation, these researchers suggest. By increasing patients' comfort, it may be possible to decrease their risk of psychological and physical trauma.

--Martha L. Heckel

Reference
1. Russell WC, Greer JR. The comfort of breathing: a study with volunteers assessing the influence of various modes of assisted ventilation. Crit Care Med. 2000;28:3645-3648.

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