COSTAMASNAGA, ITALY--Although all forms of noninvasive ventilatory assistance have been shown to improve gas exchange in hypercapnic patients, the degree of improvement depends more on the type of interface used than on the mode of ventilation, a recent study found.[1] In patients with hypercapnic respiratory failure, ventilation via either a full-face mask or nasal plugs resulted in a greater fall in arterial carbon dioxide tension (PaCO2) than did use of a nasal mask.

"All interfaces, when well-positioned, may improve arterial blood gases, regardless of the mode of ventilation and underlying pathologies," said Stefano Nava, MD, in an interview with PULMONARY REVIEWS. However, "in our study, we observed that each of the masks studied produced different effects on arterial blood gases," explained Dr. Nava, Head of the Respiratory Intensive Care Unit at the Fondazione Salvatore Maugeri in Pavia, Italy.

Researchers there investigated the effects of the three types of masks on arterial blood gas levels, breathing pattern, and tolerance to ventilation in patients undergoing noninvasive mechanical ventilation (NIMV) for chronic hypercapnic respiratory failure. They also assessed the impact of underlying disease and mode of partial ventilatory support (assist control vs pressure support ventilation) on NIMV outcome. Subjects included 26 stable hypercapnic patients with COPD or restrictive thoracic disease who had not previously received NIMV.

BENEFIT VERSUS TOLERANCE

Overall, patients were significantly better able to tolerate the nasal mask than either the full-face mask or the nasal plugs.

Regardless of the device selected, NIMV significantly lowered PaCO2, increased arterial oxygen tension (PaO2) and pH, and improved the breathing pattern. However, the decline in PaCO2 was almost 10 mm Hg when either the full-face mask or the nasal plugs were used but only about 7 mm Hg when the nasal mask was used. The choice of device had no effect on the NIMV-induced improvement in either PaO2 or pH, but both tidal volume and minute ventilation were higher when ventilation was administered via a full-face mask rather than through the nasal plugs.

If patients are most likely to tolerate the device that produces the smallest improvement in PaCO2, how should physicians administer NIMV? "It is important to tailor the type of mask according to individual patient needs, because tolerance and cooperation can influence the outcome of intervention," Dr. Nava said. "When patient cooperation is lacking during severe acute respiratory failure, the facial mask is the first line of intervention. If the patient improves after a few hours, it is safe to switch to a nasal mask," he suggested.

In this study, the type of respiratory disease did not appear to influence patients' acceptance of any particular mask. Similarly, the response to NIMV did not differ significantly between COPD patients and those with restrictive thoracic disease.

--Deborah L. O'Connor

Reference
1. Navalesi P, Fanfulla F, Frigerio P, et al. Physiologic evaluation of noninvasive mechanical ventilation delivered with three types of masks in patients with chronic hypercapnic respiratory failure. Crit Care Med. 2000;28:1785-1790.

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