Respiratory Care

Multicenter long-term oxygen therapy trials have established that low-flow oxygen is beneficial to hypoxemic patients with chronic obstructive pulmonary disease (COPD). A large percentage of these patients receive oxygen via steady-flow nasal cannula (SNC). Because of the rising cost of medical care and particularly the cost of oxygen therapy, we designed an oxygen-conserving nasal cannula (CNC). In a previous study, we demonstrated by ear oximetry that the CNC required substantially less oxygen to achieve adequate oxygen saturation than did the SNC. In this paper we describe the principles of operation of the CNC and present data comparing the CNC and SNC. Methods: We studied 4 subjects with COPD, simultaneously measuring SaO2 by ear oximetry and SaO2 and PaO2 by standard blood analysis, with the subjects breathing first room air and then supplemental oxygen at 0.5, 1.0, and 2.0 L/min with both the SNC and CNC. Ten minutes was allowed between tests for equilibration. Results: The CNC achieved significantly higher (P < 0.001) saturations than did the SNC at equivalent oxygen supply flows. Absolute improvements in PaO2 were 10.9 torr at 0.5 L/min, 18.2 torr at 1.0 L/min, and 27 torr at 2 L/min. There was a high correlation between ear oximetry and blood analysis readings. Conclusion: We conclude that the widespread use of the CNC could result in a significant financial savings while increasing the range and portability of oxygen therapy devices. (Respir Care 1985;30:19-25.)

We undertook this study to test the hypothesis that apneic oxygenation with high flows of intratracheal oxygen may increase carbon dioxide elimination over that with low intratracheal flows. Methods: We anesthetized five conditioned dogs and cannulated the femoral artery for arterial blood sampling. Heart rate was recorded by electrocar-diograph, and tracheal airway pressure was measured by transtracheal catheter. After inserting a 16-gauge plastic catheter through the cricothyroid membrane into the trachea and connecting the catheter to a high-pressure oxygen source, we started apneic oxygenation. Continuous flows of 100% oxygen were delivered under constant driving pressures of 30, 40, and 50 psi, each pressure for a period of 10 minutes. The gas flows leaving the trachea at the three pressures were measured at 19, 27, and 33 L/min, respectively, through an endotracheal tube placed above the transtracheal catheter. During apneic oxygenation, arterial blood gases were analyzed—PaCO₂ at the start and thereafter at 2-minute intervals, PaO₂ at the start and at the end of each 10-minute period. Before the institution of a different driving pressure, PaCO₂ was brought back to baseline by intermittent oxygen insufflation by jet. Results: We found that PaCO₂ increased at oxygen-line pressures of 30, 40, and 50 psi and that the amount of the increase did not differ significantly among the three pressures. The PaO₂ level after 10 minutes at 30 psi pressure was significantly lower (P < 0.01) than the baseline level, but no such differences were found at pressures of 40 and 50 psi. Airway pressures were 7, 13, and 18 torr, respectively, at 30, 40, and 50 psi driving pressures. No complications occurred in any of the animals, and their recovery was uneventful. Conclusion: We conclude that the clinical value of apneic oxygenation, even with high flows of intratracheal oxygen, is limited by carbon dioxide accumulation. (Respir Care 1985;30:26-29.)

A 60-year-old man presented with signs and symptoms of acute pulmonary edema following cardiopulmonary bypass. Hemodynamic values were normal and analysis of the edema fluid revealed a protein content of 5.2 g/dL, suggesting noncardiogenic pulmonary edema. The patient was successfully treated with corticosteroids, anti-histamines, and PEEP. (Respir Care 1985;30:30-33.)

The purpose of this review article is to identify exercise prescription components (EPCs) used and results obtained during previous respiratory muscle training studies. The need for further scientific inquiry pertaining to this topic is discussed. Respiratory skeletal muscles have proven responsive to basic training principles for improving strength and/or endurance in persons having normal health, cystic fibrosis, chronic obstructive pulmonary disease, and quadriplegia, and in persons being weaned from ventilators. The ingredients for successful training are unclear because of interstudy variations in the EPCs of frequency, intensity, and duration of a training session; level of subject supervision; training mode; length of training period; and in the initial level of fitness, the age, the gender, and the disease states of the persons to be trained. A self-selected breathing rate was a common factor in all studies cited. By the selective manipulation of each EPC in a series of future, controlled investigations, the guidelines for safe, reproducible, affordable, tolerable, and effective respiratory muscle training prescriptions could be generated. (Respir Care 1985;30:34-42.)

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