Respiratory Care

BACKGROUND: Postextubation stridor as a result of laryngeal edema has been reported in up to 5% of patients who have received mechanical ventilation for longer than 24 hours. The cuff-leak test has been proposed as a method of determining whether patients can be extubated without developing upper airway obstruction. This test, however, has not been prospectively studied. METHODS: 100 consecutive patients who had been intubated for longer than 24 hours were studied prior to extubation. The cuff-leak test was performed by two different methods. The endotracheal cuff was totally deflated, the lumen of the endotracheal tube was then occluded, and the presence (small or large) or absence of a peritubular leak during spontaneous ventilation was determined. The test was then repeated with positive pressure ventilation using the patients’ pre-weaning tidal volume. The results were not available to the intensivist, and the patients were extubated regardless of the results of the leak tests. RESULTS: The mean (SD) length of intubation was 3.8 (3.2) days. Six patients had no leak with both tests, 22 patients had a small leak with both tests, and 60 patients had a large air leak with both tests. Twelve patients had a small leak with one test and a large leak with the other. Two patients developed postextubation stridor. Both were successfully treated with aerosolized racemic epinephrine. These two patients had no leak with either test, making the likelihood of developing stridor significantly higher in the group of patients that had no peritubular leak prior to extubation (p = 0.003). The cuff-leak tests had a negative predictive value of 100% but a positive predictive value of only 33%. CONCLUSION: The presence of a cuff leak indicates that postextubation stridor is unlikely. Although the absence of a cuff leak does not guarantee extubation difficulty, such patients should be observed closely during the immediate postextubation period [Respir Care 1996;41(6):509-511].

BACKGROUND: Levels of work of breathing imposed (WOB;) by variations in ventilator design have been addressed by a number of investigators. We conducted this study to assess the effects of tracheal pressure-triggering (TPT) on the WOB; and to compare it with conventional pressure-triggering (CPT). MATERIALS & METHODS: Sine wave breaths of = 500 mL, with mean flows of 30 and 60 L/min, were inspired through a test ventilator (Servo 900 C) set in the continuous positive airway pressure (CPAP) mode (CPAP, 5 cm H2O). WOB; was measured during CPT and TPT. In addition, we simulated 500-mL breaths through the test ventilator with its trigger sensitivity set at -10 cm H2O for both CPT and TPT. Pressure was measured at the Y-piece and within the tracheal lumen. Flow was measured at the Y-piece and volume obtained from the digital integration of flow. WOB; was calculated from the area enclosed by the pressure-volume plot (in that part of the pressure-volume loop where the pressure was below the level of PEEP). RESULTS: WOB; (including that contributed by the tracheal tube) was less during TPT, mean (SD) 258 (42) mJ/L than with CPT, 477 (24) mJ/L at 60 L/min, p < 0.05. However, for breaths simulated at flows of 60 L/min, mean inspiratory pressures within the tracheal lumen and at the Y-piece were greater during TPТ than during CPT, p < 0.05 for both. Under the test conditions used to measure trigger delay and trigger work, trigger delay was similar during TPT and CPT, 280 (20) ms and trigger work was similar for the two triggering modes 1.34 (0.3) cm H2O s vs 1.31 (0.25) cm H2O s. CONCLUSIONS: Decrease in WOB; during TPT is not due to an alteration in triggering function per se but to an inadvertent pressure assist and is no more advantageous than application of pressure support to compensate for apparatus work. [Respir Care 1996;41(6):512-518]

BACKGROUND: The use of theophylline in the treatment of patients with asthma is controversial. MATERIALS & METHOD: We assigned 120 patients with moderate-to-severe asthma into 3 groups of equal numbers in order of their presentation. All study patients received inhaled beclomethasone (500 µg daily) and a short-acting inhaled ẞ-2 agonist (salbutamol by metered dose inhaler) as necessary up to 3-4 times a day. In addition, patients in Group 2 (control group) were prescribed a placebo tablet, and patients in Group 3 received theophylline (Theo-Dur) 250 mg orally, every-other-day at bed time (10 PM). Groups 2 and 3 were blinded to their oral medication. The duration of the study was 6 months. The physician administering the pulmonary func- tion tests was blinded to the study assignment of the patients. RESULTS: The means and standard deviations for the 3 groups for FEV1, FVC, and PEFR on admission to the study did not vary significantly by ANOVA (FEV1, p = 0.718; FVC, p = 0.402; PEFR, p = 0.453); whereas, at the close of the study the improvement in all 3 values for Group 3 was significant at p = 0.0001. The number of hospital admissions from Group 3 was also significantly lower than those of the other groups (ANOVA, p = 0.0017). CONCLUSION: Although the serum theophylline concentrations were probably below the therapeu- tic range because of the low, alternate-day dose (they were not measured), this study suggests that treatment of patients with moderate-to-severe asthma with theophylline may be beneficial. [Respir Care 1996;41(6):520-523]