Could the oxygen cost of breathing be used to optimize the application of pressure support ventilation?

Pressure support ventilation (PSV) is a new ventilator modality that augments spontaneous inspiratory pressure with selected levels of positive airway pressure. There is presently considerable interest in its use in the management of critically ill, ventilator-dependent patients. The optimal method for application has not yet been established. This study investigated the effects of PSV on the oxygen cost of breathing (OCOB), a clinically applicable technique for quantitating the work of breathing. The OCOB and other bedside variables of pulmonary function were measured during PSV in ventilator-dependent patients where weaning was limited by an inability to sustain respiratory work. Nine studies were performed in 8 patients in the surgical intensive care unit. The OCOB, tidal volume (VT), respiratory rate (RR), and minute ventilation (VE) were measured at various levels of pressure support. The OCOB was calculated from the difference in oxygen consumption (VO2) during mechanical and spontaneous ventilation both at CPAP and with PSV. With increasing levels of PSV, the OCOB was observed to steadily decrease from 22% to 8% (p < 0.001). There were also statistically significant increases in VT and decreases in RR. VE appeared not to be influenced. The results of this study suggest that the bedside measurement of the OCOB may be an accurate, simple, and reproducible method of titrating the level of applied pressure support in order to optimize respiratory work.

Tolerance to reduction of oral steroid dosage in severely asthmatic patients receiving nedocromil sodium.

We examined the efficacy of nedocromil sodium as an oral steroid sparing agent in a group of 37 severe, oral steroid-dependent asthmatics. All were receiving daily or alternate-day prednisone. These patients had taken part in an earlier, 12-week double-blind trial of nedocromil sodium 16 mg daily by inhalation or matching placebo. They continued with test treatment (26 patients on nedocromil sodium and 11 on placebo) on a double-blind basis for a further 12 weeks. During this time, patients visited the clinic every 2 weeks, when asthma severity and symptoms were assessed. On the basis of these assessments, the dose of oral steroid was either decreased, or maintained at the same level, or the patient was withdrawn if the asthma had deteriorated to a clinically unacceptable level. The nedocromil sodium group was able to achieve a greater percentage reduction in oral steroid dose (P less than 0.05). The rate of withdrawal due to worsening asthma was 31% from active and 55% from placebo treatment. Trends in other variables (time before withdrawal and numbers of patients able to withstand complete removal of oral steroids) favoured nedocromil sodium but the differences between the groups were not statistically significant.

A 3-month evaluation of the efficacy of nedocromil sodium in asthma: a randomized, double-blind, placebo-controlled trial of nedocromil sodium conducted by a Canadian multicenter study group.

Nedocromil sodium is a pyranoquinoline dicarboxylic acid derivative, formulated in a metered-dose inhaler. Because nedocromil sodium has in vitro and in vivo anti-inflammatory properties, it was evaluated in a group of steroid-dependent patients with asthma to observe how well it might be tolerated and for evidence of any beneficial effects. In a double-blind, group-comparative study, 127 patients received nedocromil sodium and 61 received placebo, administered as two puffs of 2 mg, four times per day, for 12 weeks. Ten patients developed adverse reactions, seven receiving active drug and three patients receiving placebo. Two patients of each group withdrew because of worsening asthma. Despite selecting patients whose asthma was stable, when they were receiving established therapeutic regimens that included steroids and bronchodilators, it was found that diary-card symptom scores, morning and evening peak expiratory flow rate values, and inhaled beta-agonist usage all demonstrated slight but significant benefit with addition of nedocromil sodium. It is concluded that the inhaled, anti-inflammatory agent, nedocromil sodium, may be added to asthma-treatment regimens with the reasonable expectation of further modest symptomatic benefit.

Primary alveolar hypoventilation managed by negative-pressure ventilators.

A girl who had a history of repeated apnea was found to have absent chemical drive to ventilation and, on sleep monitoring, both central and obstructive types of apnea. She is currently undergoing successful mechanical ventilation at night with negative-pressure ventilators.