PURPOSETo determine if the ultimate ability of a long-term ventilated patient to wean can be predicted at the time of his or her admission to a long-term ventilator unit.DESIGNTwo-phased prospective study.SETTINGLong-term ventilator facility, university-affiliated.SUBJECTSAdults ventilated for an average of 3 weeks, who did not have sepsis and who did not have chest tubes or progressive neurologic impairment.INTERVENTIONSOn admission to the long-term ventilator unit, historic factors, ventilator history, and the following laboratory and metabolic tests were obtained: electrolytes, serum calcium, magnesium, and phosphorus, WBC, hemoglobin, albumin, total protein, transferrin, oxygen consumption, carbon dioxide production, respiratory quotient, and dead space/tidal volume. The patients were then placed in a weaning protocol utilizing increasing duration of pressure support ventilation during the day with complete rest at night. Forty-two days after enrollment in the study, representing three times the duration of the weaning protocol, the patients who successfully weaned were compared to those who remained ventilator dependent (n = 20). Patients who died or were transferred to another institution were excluded from this phase of the study, because we were trying to develop parameters that would be predictive of successful weaning. A parameter was considered to be predictive, and retained for the scoring system, if it produced at most 15% false-positives and false-negatives. A score of 0 was then assigned to the threshold value that produced no false-positives; 2 to the threshold value that produced no false-negatives and 1 to the intermediate values. The scoring system was then applied to a new prospective group of patients (n = 72).MEASUREMENTS AND MAIN RESULTSOf all the parameters evaluated, only the following satisfied the false-positive and false-negative requirements; static compliance, airway resistance, dead space to tidal volume ratio, PaCO2, and frequency/tidal volume. Applying these, in the scoring system, to the initial group of patients, demonstrated that a score greater than 3 was associated with failure to wean; a score less than 3 was associated with successful weaning, and a score of 3 was not predictive. Using these thresholds, the data were applied to the new prospective group of patients, which again demonstrated that a score of greater than 3 was associated with failure to wean in all cases. A score less than 3 was again associated with successful weaning but there were two false-positives. The sensitivity, specificity, and positive predictive and negative predictive values for the scoring system were 1.0, 0.91, 0.83, and 1.0, respectively. None of the individual parameters included in the scoring system demonstrated equivalent statistical results. All but two of the patients who died prior to finishing the weaning period had weaning scores, which suggested that they would not be successfully weaned.CONCLUSIONSParameters that are generally available, when combined into a scoring system, can predict at the time of admission to a long-term ventilator unit, in most cases, whether a patient will eventually wean. The scoring system resulted in no false-negatives and an acceptable number of false-positives. None of the individual parameters were as reliable as the scoring system as a whole.

A quick, focused history and physical are needed to gauge the severity of an asthma attack. Measuring the peak expiratory flow rate or performing spirometry provides an objective means of assessing both episode severity and response to therapy. Beta-agonists, using aerosol delivery systems, and intravenous steroids form the basis for therapy in patients suffering an acute asthma attack. Theophylline compounds have not shown any benefit and may exacerbate side effects. Ipratropium bromide may be useful as an adjunct to beta-adrenergic drugs but should not be used in lieu of them. Adjuvant therapy includes the use of helium-oxygen mixtures and anesthetic gases. Frequent monitoring of these patients and availability of appropriate services and personnel are essential to good outcome.

Seven patients with status asthmaticus intubated for respiratory failure who had elevated airway pressures and persistent respiratory acidosis were successfully ventilated using a mixture of 60 percent helium and 40 percent oxygen. All patients experienced a rapid reduction in airway pressures, CO2 retention, and resolution of acidosis while breathing a helium-oxygen mixture. There were no untoward effects. Helium-oxygen mixtures improve ventilation by reducing the Reynolds number and reducing density dependent resistance. Helium's beneficial effects are due to its high kinematic viscosity, high binary diffusion coefficient for CO2, and high diffusivity. Helium-oxygen mixtures should be considered for use in mechanically ventilated asthmatics with respiratory acidosis who fail conventional therapy.

High-frequency ventilation techniques have been demonstrated to be useful in decreasing gas loss from bronchopleural fistulas. We performed the present study to evaluate the impact of a new jet ventilator design and ventilatory frequency on hemodynamics, gas exchange, and bronchialstump gas flow in an animal model of bronchopleural fistula. Ten pigs underwent a right-sided thoracotomy and right-sided upper pulmonary lobectomy with cannulation of the upper lobe bronchus for measurement of bronchial fistula flow rate. Animals underwent a random sequence of conventional ventilation (12 to 20 breaths per minute), conventional high-frequency jet ventilation (120 breaths per minute), and ultra-high-frequency jet ventilation (UHFJV; 450 breaths per minute). Hemodynamic measurements were similar in the three ventilatory modes, but oxygenation was best with UHFJV. Bronchial fistula flow was lowest with UHFJV and greatest with conventional ventilation. Ultra-high-frequency jet ventilation demonstrated superior oxygen loading, adequate carbon dioxide elimination, and the least flow through the fistula, suggesting that both ventilator design and frequency are important therapeutic variables in the management of major airway disruption.

Three patients with severe chronic lung disease had left ventricular failure develop with marked impairment of cardiac function. Ejection fractions by radioactive blood pool ventriculography were 0.17, 0.24, and 0.20. Right ventricular endomyocardial biopsy specimens showed interstitial hemorrhage and foci of interstitial polymorphonuclear leukocytes, strongly suggestive of catecholamine myocarditis. These patients had used beta-adrenergic agonist inhalants and methylxanthines. One of them clearly abused the inhalant and had elevated levels of urinary catecholamines. Progressive deterioration of pulmonary and cardiac function occurred in two patients, with death within three months of the initial myocardial biopsy. Concomitant use of beta-adrenergic agonists and methylxanthines may cause myocarditis with left ventricular failure in susceptible patients.

Ninety-seven acutely ill patients with bronchial asthma were enrolled in a double-blind, placebo-controlled, randomized trial of intravenous methylprednisolone (125 mg), given on presentation in the emergency room in addition to standard emergency treatments for asthma. Subjective and spirometric indexes of the severity of the asthma were similar on entry into the study in all patients, but only 9 of 48 patients (19 percent) treated with methylprednisolone required hospital admission, as compared with 23 of 49 patients (47 percent) in the control group (P less than 0.003). Our results suggest that prompt use of glucocorticoids in the emergency treatment of severe asthma can prevent significant morbidity, reduce the number of hospitalizations, and effect substantial savings in health care costs.