Expanding Horizons of Noninvasive Ventilation
Noninvasive ventilation (NIV) for acute respiratory failure has the potential to improve dyspnoea, to reduce the need for endotracheal intubation (ETI) and the number of complications associated with mechanical ventilation and intensive care unit (ICU) st
- PDF / 2,486,517 Bytes
- 15 Pages / 439.37 x 666.142 pts Page_size
- 62 Downloads / 214 Views
J. Mancebo
Noninvasive ventilation (NlV) for acute respiratory failure has the potential to improve dyspnoea, to reduce the need for endotracheal intubation (ETI) and the number of complications associated with mechanical ventilation and intensive care unit (lCU) stay, and subsequently to reduce mortality (Brochard et al. 1990; Meduri et al. 1996). Patients with hypercapnic forms of acute respiratory failure are more likely to benefit from this technique, but recent studies also showed that these results may be extended to selected forms of hypoxaemic respiratory failure. Most of these benefits are explained by the fact that ETI can be avoided by this procedure, which, as a consequence, means a reduction in ICU complications. Knowledge of the benefits of and indications for NIV is important. It is also necessary to understand what can cause the failure of the technique in an individual ICU patient, and to estimate well the importance of the specific aspects of NlV. NlV is based on the absence of ETI and requires merely the same ventilator equipment as the standard approach, in combination with a device providing the interface between the patient and the ventilator, which in most instances is a nasal or facial mask. It has several specific features that constitute a new area of knowledge for everyone who wants to implement this technique in his/her own department.
21.1 Physiologic Effects and Mechanisms of Action of Noninvasive Ventilation in Acute Respiratory Failure 21.1.1 Breathing Pattern The spontaneous breathing pattern of patients developing acute ventilatory failure markedly differs from normal and can result in respiratory acidosis. In patients with chronic obstructive pulmonary disease (COPD), rapid shallow breathing, i.e. small tidal volumes at a high respiratory frequency, is a typical feature of the acute exacerbation, resulting in alveolar hypoventilation despite preserved minute ventilation. This pattern can be modified by the use of NIV, which allows the patient to take deeper breaths with less effort. Although continuous positive airway pressure, used to counterbalance intrinsic positive end-expiratory pressure, can signif-
J. Mancebo et al. (eds.), Mechanical Ventilation and Weaning © Springer-Verlag Berlin Heidelberg 2003
21 Expanding Horizons of Noninvasive Ventilation
299
icantly reduce the patient's effort (Petrof et al. 1990; Smith and Marini 1988), it seems that the addition of positive inspiratory pressure, as delivered with pressure-support (PSV) or assist-control ventilation, is necessary to substantially alter the breathing pattern and improve CO 2 elimination. The reduction in respiratory rate and the increase in tidal volume under NIV are the best markers of the efficacy of the technique (Appendini et al. 1994; Brochard, et al. 1990).
21.1.2 Gas Exchange In case of hypercapnic respiratory failure, improvement of arterial blood gas disturbances can be achieved with NIY. In patients with chronic CO 2 retention, PaC0 2 usually worsens under oxygen treatment; however, NIV improves o
Data Loading...
