Key Point

Contrary to current practice and thought, low tidal volume ventilation for patients with acute lung injury does not increase the need for sedation, analgesia, or neuromuscular blockade.

SEATTLE—Historically, the literature has cautioned against using low tidal volumes for ventilated patients with acute lung injury. Part of this is because low tidal volumes cause the patient to take smaller breaths that can bring about dyspnea and ventilator asynchrony—both thought to increase discomfort. Thus, patients receiving low tidal volume ventilation have been perceived as needing higher levels of sedation and pain-relieving medication.

Recently, the ARDS Network reported a 22% reduction in mortality with a strategy that included low tidal volume ventilation. They also reported no significant differences between low and high tidal volume recipients in the percentage of days in which patients required sedation and neuromuscular blocking agents. Despite these findings, concerns about sedation use with low tidal volumes persist.

A group of researchers from Harborview Medical Center in Seattle conducted a secondary analysis of an ARDS Network clinical trial and found that using low tidal volumes had no effect on the decision to use sedatives or opioid analgesics.¹

Sixty-one patients were randomized to receive either high or low tidal volume ventilation (12 or 6 mL/kg, respectively). Doses of sedatives and opioid analgesics were recorded, as was the use of neuromuscular blockade. Throughout the study, patients’ levels of anxiety, pain, oxygenation, and ventilator synchrony were assessed regularly. The low tidal volume group had 33 patients and the high tidal volume group, 28 patients.

SEDATIVE USE WAS NOT INCREASED

Both patient groups were similar regarding age, ethnicity, and APACHE scores. No significant between-group differences were observed in duration of mechanical ventilation. Use of sedation, analgesia, and neuromuscular blockade was also similar in both groups (Table).

The results were consistent whether sedative use was calculated as the proportion of study days in which sedatives were required, as the proportion of patients receiving sedatives on days 1, 2, 3, and 7 of mechanical ventilation, or as the total dose that each patient received on those days. The authors pointed out that these findings are important because of recent studies suggesting better outcomes with reduced sedative doses.

Yet, a recent qualitative study found that nurses and respiratory therapists frequently cited patient discomfort and increased sedation needs as key reasons for not implementing the ARDS Network’s protocol of low tidal volume ventilation.²

Thus, any strategies to increase lung-protective ventilation will need to provide clinicians with both tools and practical advice on recognizing the symptoms of acute lung injury or ARDS and assessing patients who are receiving ventilation at low tidal volumes.

“It is possible that the rapid shallow breathing pattern created by lower tidal volumes and higher respiratory rates simply appears uncomfortable to caregivers but is not a source of discomfort for the patient,” wrote the authors of the present analysis. “Furthermore, other factors, such as the presence of an endotracheal tube, airway suctioning, ambient noise, sleep disruption, or procedures may contribute to patient discomfort to such a degree that the mode of ventilation has a minor effect.”

—Gale Jurasek

References
1. Kahn JM, Andersson L, Karir V, et al. Low tidal volume ventilation does not increase sedation use in patients with acute lung injury. Crit Care Med. 2005;33:766-771.
2. Rubenfeld GD, Cooper C, Carter G, et al. Barriers to providing lung-protective ventilation to patients with acute lung injury. Crit Care Med. 2004;32:1289-1293.

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