Marcel Baum

Comparison of mask and nasal continuous positive airway pressure after extubation and mechanical ventilation

ObjectiveTo examine the effects of continuous positive airway pressure applied via face masks and nose masks on the change in functional residual capacity and gas exchange. DesignDescriptive and prospective study. SettingIntensive care unit of a university hospital. PatientsTen patients with acute lung injury who had required mechanical ventilation. InterventionsContinuous positive airway pressure at a level of 10 cm H2O applied in random order via face and nose masks. Measurements and Main ResultsBoth continuous positive airway pressure methods resulted in an almost identical increase of functional residual capacity. During nasal continuous positive airway pressure, the increase in functional residual capacity was 294 ± 82 mL. During mask continuous positive airway pressure, the increase in functional residual capacity was 290 ± 85 mL. Pao2 increased and the alveolar-arterial oxygen tension/alveolar oxygen tension quotient decreased significantly during mask continuous positive airway pressure and nasal continuous positive airway pressure at a level of 10 cm H2O. Two patients showed a periodic change in their breathing patterns; they took a few breaths at an increased lung volume, followed by one deep expiration caused by mouth opening. Change in mask pressure was negligible in these two patients. Using a visual analog scale (10 = highly comfortable; 0 = severely uncomfortable), the patients rated nasal continuous positive airway pressure (8.6 ± 0.9) significantly more comfortable than mask continuous positive airway pressure (2.6 ± 0.8). ConclusionThe major advantages of continuous positive airway pressure (the improvement of functional residual capacity and oxygen transfer) can also be achieved with nasal continuous positive airway pressure in the postextubation period in patients who have been mechanically ventilated for acute lung injury. (Crit Care Med 1993; 21:357–362)

Physical characteristics of a jet in the airways

A number of High Frequency Ventilator Systems (HFV) are summarized as High Frequency Jet Ventilators (HFJV), suggesting that the particular properties of a jet are in some way responsible for the gas exchange during this type of ventilation. To examine whether this assumption is always correct one has to remember the fundamental physical characteristics of a jet. Following a possible pathway for the jet into the lungs, one must consider the points given in Table 1. They will be dealt with in detail in this article (Table 1) .

Intraoperative application of high-frequency ventilation.

High-frequency pulsation (HFP), a modified highfrequency jet ventilation (HFJV) technique, was applied intraoperatively as an alternative to conventional inter mittent positive-pressure ventilation in 16 patients undergoing major thoracic operations. Gas exchange and hemodynamic stability were maintained at a frequency of 300 cycle/min. Surgical maneuvers were easier because the lungs were almost completely immobilized.

Subglottic positive end-expiratory pressure in extubated patients recovering from acute lung injury.

Objective: To examine the glottic function in extubated patients recovering from acute lung injury by simultaneous measurement of airway opening and subglottic airway pressures while patients are breathing at ambient pressure and receiving continuous positive airway pressure by a face mask. Design: Descriptive, prospective study. Setting: Intensive care unit at a university hospital. Patients: Ten patients who required continuous positive airway pressure of at least 7 cm H2O in order to restore gas exchange after mechanical ventilation for acute lung injury. Interventions: Spontaneous breathing at ambient airway pressure and with continuous positive airway pressures of 5 and 10 cm H20 via face mask. Measurements and Main Results: Intratracheal pressure, airway opening pressure, and airflow at the airway opening were measured. Breathing at ambient pressure resulted in significantly higher end‐expiratory intratracheal pressure than end‐expiratory airway opening pressure (p < .01). No significant differences between endexpiratory intratracheal pressure and end‐expiratory airway opening pressure were observed during breathing with continuous positive airway pressures of 5 and 10 cm H2O. A significant end‐expiratory airflow at the airway opening (p < .01), observed during ambient pressure breathing, was not detectable while the patient received mask continuous positive airway pressure. The partial pressure of oxygen in the arterial blood (Pao2) increased significantly while patients breathed with 10 cm H20, but not while patients breathed 5 cm HˆO continuous positive airway pressure compared with breathing at ambient pressure (p < .05). Conclusions: Our data imply that patients recovering from acute lung injury create an intratracheal positive end‐expiratory pressure by braking the expiratory airflow, probably by glottic narrowing. Despite compensatory glottic narrowing, extubated patients with reduced lung function may benefit from higher levels of continuous positive airway pressure. (Crit Care Med 1994; 22:67‐73)

Clinical experience with several types of high frequency ventilation.

INTRODUCTION In clinical practice, only the following parameters are used routinely to evaluate the effectiveness of artificial ventilation: pressures volumes blood-gas analyses composition of breathing gases. Therefore the clinical usefulness of today’s well-established methods is not yet proven. This hypothesis can best be substantiated with the example of “intermittent mandatory ventilation” (IMV). IMV is a standard method in the field of artificial ventilation. However, up to now there has been no prospective randomized study of the benefits of IMV in comparison with controlled mechanical ventilation techniques. The questions to be answered include: ~ Are there any physiological or pathophysiological explanations for the superiority of this method? Is IMV by itself advantageous against other methods (duration of weaning, clinical outcome, etc.)? Sometimes clinical circumstances, such as ethical aspects or the well-established practical use of a technique, will hinder such a trial, as will the lack of sensitive methods of examination. Taking into account these considerations, monitoring methods developed for conventional ventilation techniques will not necessarily be applicable to methods of assessing different principles of gas transport ( 1 ) . The intention to evaluate high frequency ventilation (HFV) -methods under clinical conditions must lead to the question: what is clinically measurable when using HFV?

Time-cycled inverse ratio ventilation

negative pressure-type oedema due to respiratory depression or muscle weakness. Further, a thorough retrospective analysis of the course of the 211 patients should include data on all possible causes of respiratory failure, such as narcotics. Without this information, the conclusion that diazepam caused respiratory depression is only speculative. Another possible explanation for respiratory depression in this clinical setting is that it may result from a combination of drugs, for example, diazepam plus cyclosporine. Finally, it is not surprising that effects of operation and neuromuscular blockade differ between patients who received halothane and those who received isoflurane, t Isoflurane, compared with halothane followed by vecuronium, has been shown clinically to augment neuromuscular blockade. 2