PRESENCE OF COPD DOES NOT AFFECT THE DIAGNOSIS OF PE

Differentiating pulmonary embolism from an exacerbation of chronic obstructive pulmonary disease (COPD) can be difficult because the conditions share similar clinical signs and symptoms. In a patient with COPD, therefore, how well can PE be diagnosed with commonly used methods–a clinical probability estimate, spiral computed tomographic (CT) angiography, D–dimer analysis, or ventilation–perfusion (V/Q) scintigraphy? Very well, according to a prospective, multicenter study.

Hartmann et al evaluated the effect of the presence of COPD on the accuracy of diagnostic procedures for PE in 627 consecutive patients; 91 (15%) patients had confirmed COPD, and 536 did not. The prevalence of PE in the two groups was 29% and 31%, respectively.

The presence of COPD did not affect the diagnostic accuracy of the clinical probability estimate made by the treating physician before objective testing was performed. Nor did it alter the accuracy of spiral CT angiography, D–dimer analysis, or V/Q scintigraphy. The sensitivity and specificity of these three techniques in patients with and without COPD are shown in Table 1. Neither age nor the presence of congestive heart failure influenced the performance of spiral CT angiography or the D–dimer test, but both factors increased the number of nondiagnostic V/Q scan results. The authors note that nondiagnostic V/Q scan results are more likely to occur in the presence of COPD, thus decreasing the procedure’s cost–effectiveness. Nevertheless, V/Q scintigraphy is still a valuable, noninvasive test for PE when screening patients with COPD.

Hartmann IJC, Hagen PJ, Melissant CF, et al. Diagnosing acute pulmonary embolism: effect of chronic obstructive pulmonary disease on the performance of D-dimer testing, ventilation/perfusion scintigraphy, spiral computed tomographic angiography, and conventional angiography. Am J Respir Crit Care Med. 2000;162:2232-2237.

WEIGHT LOSS MAY EASE SLEEP–DISORDERED BREATHING

Even moderate weight loss can reduce the severity and progression of sleep-disordered breathing (SDB), a population–based, prospective cohort study indicates. The alternative—nasal continuous positive airway pressure therapy—is burdensome and probably impractical for patients with mild or asymptomatic SDB, the study authors suggest.

Peppard et al studied 690 randomly selected subjects enrolled in the Wisconsin Sleep Cohort Study to determine the association between weight gain and increased SDB severity, as well as between weight loss and decreased SDB severity.

The primary outcome measures were the influence of a change in weight on the percentage change in the apnea–hypopnea index (AHI, the number of apnea and hypopnea events per hour of sleep) and on the possibility of developing moderate–to–severe SDB (defined as an AHI of 15 or more). The subjects were evaluated at baseline and at four–year follow–up.

After adjustments for sex, age at baseline, body mass index, and smoking behavior, weight change correlated positively with change in the AHI. Compared with no change in weight, a 10% increase was associated with a 32% increase in the AHI, and a 10% decrease was associated with a 26% decrease in the AHI. The authors’ analysis also showed that subjects who had a 10% weight gain had an odds ratio of 6.0 for the development of moderate–to–severe SDB.

Peppard et al caution that their findings may not apply to patients who experience weight changes in excess of 20%.

Peppard PE, Young T, Palta M, et al. Longitudinal study of moderate weight change and sleep-disordered breathing. JAMA. 2000;284:3015-3021.

LIMITING INSPIRATORY FLOW PROTECTS AGAINST LUNG INJURY

Positive–pressure mechanical ventilation delivered at high airway pressures leads to severe lung injury regardless of respiratory rate (RR) or inspiratory time (I t), report University of Michigan researchers. However, reducing the inspiratory flow rate protects against the development of ventilator–induced lung injury even when peak inspiratory pressure (PIP) remains high.

Rich et al studied the effects of RR and inspiratory flow in 40 mechanically ventilated sheep; all survived at least four hours. Eight sheep each were treated with one of five modes of ventilation:

• Pressure-controlled ventilation (PCV); RR, 15 breaths/min; PIP, 25 cm H2O.

• PCV; RR, 15 breaths/min; PIP, 50 cm H2O.

• PCV; RR, 5 breaths/min; PIP, 50 cm H2O; I t, 6 seconds.

• PCV; RR, 5 breaths/min; PIP, 50 cm H2O; I t, 2 seconds.

• Limited inspiratory flow volume–controlled ventilation; RR, 5 breaths/min; pressure–limit, 50 cm H2O; inspiratory flow, 15 L/min.

High–pressure ventilation with a conventional pressure–controlled strategy at physiologic respiratory rates was associated with severe lung injury, which was manifested by the development of hypoxia, decreased static compliance, high histologic injury scores, increased physiologic shunt, and the accumulation of lung water and of alveolar neutrophil aggregates.

Lowering the respiratory rate did not reduce the extent of the lung damage; however, limiting the inspiratory flow rate while maintaining a similar PIP significantly protected against the development of ventilator–induced lung injury.

Rich PB, Reickert CA, Sawada S, et al. Effect of rate and inspiratory flow on ventilator-induced lung injury. J Trauma. 2000;49:903-911.

VITAMIN K LOWERS INR SAFELY IN PATIENTS TAKING WARFARIN

Patients being treated with warfarin often have an elevated international normalized ratio (INR) and are at increased risk for hemorrhage. Often, low doses of vitamin K are given in this situation, but the efficacy of such treatment in asymptomatic patients has never been firmly proved. A multicenter, randomized Canadian study now confirms that low doses of vitamin K can safely and effectively lower INR elevations in patients taking warfarin.

Crowther et al studied 89 asymptomatic patients who were being treated with warfarin and had INRs of 4.5 to 10.0. Of these patients, 45 were randomized to 1 mg of oral vitamin K and 44 to placebo. Warfarin administration was stopped in all patients. The main outcome measurement was the INR the day after treatment. Additional follow–up was obtained through telephone interviews or clinic visits at one and three months.

On the day after vitamin K administration, 25 (56%) of the vitamin K–treated patients and nine (20%) of the controls had INRs between 1.8 and 3.2. At three months, two vitamin K patients (4%) and eight controls (17%) reported having had bleeding episodes that required transfusion or hospital admission. Thrombotic episodes occurred in one vitamin K–treated patient (myocardial infarction) and one placebo control (deep venous thrombosis).

Of the 14 persons who died during follow–up, eight had been treated with vitamin K. Eleven of the 14 died of cancer, one of multisystem organ failure, one of aortic stenosis, and one of unknown causes.

Crowther MA, Julian J, McCarty D, et al. Treatment of warfarin–associated coagulopathy with oral vitamin K: a randomised controlled trial. Lancet. 2000;356:1551– 1553.

MEASURE TIDAL VOLUME AT THE AIRWAY IN VENTILATED INFANTS

Ventilator circuit compliance is particularly important in determining the actual volume of air delivered to the lungs of infants and children. Measuring airway pressure and expired tidal volume (VT) at the expiratory valve does not account for the compliance of the ventilator circuit or for uncontrolled variations in the circuit setup. In mechanically ventilated infants, therefore, delivered VT should be measured by a pneumotachometer placed at the airway.

Cannon and associates reached this conclusion after studying 98 conventionally ventilated infants and children. In all cases, VT was measured by the ventilator as well as by a pneumotachometer (coupled to a respiratory mechanics monitor) that was placed between the ventilator circuit and the endotracheal tube. In addition, the authors estimated effective VT by using mathematical formulas designed to correct for compliance in the ventilator circuit.

In 70 infants (mean age, 2.8 months), the mean VT measured by the pneumotachometer was 39.4 mL, significantly lower than the ventilator’s VT reading of 70.4 mL or the calculated effective VT of 59.2 mL. Among 28 children (mean age, 7.3 years), the mean VT measured by the pneumotachometer, 135.3 mL, was also significantly lower than the ventilator VT reading of 185.4 mL but similar to the calculated effective VT of 167.8 mL.

Analysis of data for specific infants showed that the correlations between the various types of VT measurements were usually poor. Among the children, the correlations between these measurements were much better.

The authors caution that neonates may experience significant adverse consequences, including lung injury, hypoxia, and hypercapnea, from the delivery of imprecise tidal volumes. Conversely, accurate delivery of a suitable volume may minimize barotrauma and volutrauma and decrease intrathoracic pressures, thereby avoiding adverse cardiovascular and neurologic effects.

Cannon ML, Cornell J, Tripp-Hamel DS, et al. Tidal volumes for ventilated infants should be determined with a pneumotachometer placed at the endotracheal tube. Am J Respir Crit Care Med. 2000;162:2109-2112.

IMAGING CHARACTERISTICS OF BRONCHOGENIC CYSTS

Bronchogenic cysts are congenital lesions that generally manifest within the first few decades of life; initial presentation after age 50 is unusual. Most bronchogenic cysts can be easily diagnosed with nonenhanced computed tomography (CT); however, in about one third of cases, the true nature of the lesion can be difficult to identify. The use of contrast material during CT or the addition of magnetic resonance imaging (MRI) helps differentiate cysts with soft–tissue attenuation from mediastinal neoplasia.

McAdams et al retrospectively studied 68 patients, from newborn to age 72, with histopathologic evidence of bronchogenic cyst. Sixty–two patients underwent CT, 23 had T1–weighted MRI, and 18 had T2–weighted MRI.

All but four of the 62 cysts visualized with CT were in the mediastinum. Of the 58 mediastinal cysts, 38 could be accurately diagnosed as bronchogenic cysts. In the remaining 20 cases, confident identification could not be made because of internal heterogeneity, streak artifact, or other causes.

Nine of the 20 cysts that could not be diagnosed with CT were, however, visualized with MRI. In each case, evidence of markedly increased signal intensity on T2–weighted images confirmed the cystic nature of the lesion.

Only 38 of 66 patients (58%) whose clinical histories were available were symptomatic at presentation. The authors recommend that symptomatic cysts be resected regardless of the patient’s age and that asymptomatic cysts be removed in young patients, who are at low surgical risk. Watchful waiting is the preferred course in asymptomatic adults and high–risk patients.

McAdams HP, Kirejczyk WM, Rosado-de-Christenson ML, et al. Bronchogenic cyst: imaging features with clinical and histopathologic correlation. Radiology. 2000;217:441-446.

WHO IS AT RISK FOR ACUTE RESPIRATORY FAILURE?

Acute respiratory failure is age related. Incidence increases almost exponentially with each decade of life.

Behrendt used the 1994 Nationwide Inpatient Sample (a database of all patients discharged from 904 representative nonfederal hospitals in the United States) to identify 61,223 patients (ages 5 years and older) with acute respiratory failure who had been mechanically ventilated and hospitalized for at least 24 hours. Further analysis revealed a striking age–related increase in the incidence of acute respiratory failure (Figure 1), with an 88–fold difference in risk between the youngest age group (5 to 17 years) and the oldest (85 years and older).

Overall, 35.9% of the patients with acute respiratory failure died in the hospital; most deaths (87.5%) occurred within 31 days after hospital admission. Risk factors for death within the first 31 days included age, multiple organ failure, cancer, human immunodeficiency virus infection, and chronic liver disease.

The 31–day mortality risk was significantly reduced among patients admitted for coronary bypass, drug overdose, or trauma other than a head injury or burns.

Consistent with the results of other studies, no association was seen between mortality from acute respiratory failure and gender, pneumonia, chronic obstructive pulmonary disease, congestive heart failure, or diabetes.

Figure 1

Adapted from Behrendt CE Chest. 2000.

Behrendt CE. Acute respiratory failure in the United States: incidence and 31-day survival. Chest. 2000;118:1100-1105.

ELDERLY PATIENTS CAN BENEFIT FROM PROLONGED ICU CARE

Elderly patients who are free of severe disease can survive a stay in an intensive care unit (ICU) and have a reasonable postdischarge quality of life, say the authors of a prospective French study.

Montuclard and colleagues evaluated the effects of an ICU stay of at least 30 days on 75 consecutive patients older than age 70 who required mechanical ventilation. Survivors of the ICU stay were followed up after hospital discharge through questionnaire-based telephone interviews, which were designed to assess functional status and quality of life.

During the study, 25 patients died in the ICU after more than 30 days, 12 died in an acute care facility after leaving the ICU, and three died after being admitted to a long-term care facility. An additional five patients died in the first year following discharge from the ICU.

However, in the remaining 30 patients, survival over the next four years was similar to that of age–matched controls.

The first interview took place an average of 557 days after ICU discharge. Of the 30 survivors, 23 remained independent and expressed feelings of self–respect and contentment with life. Only one patient had to be institutionalized, and three were admitted to nursing homes. Five patients reported that, if the need arose, they would not want to be readmitted to an ICU.

Montuclard L, Garrouste–Orgeas M, Timsit J–F, et al. Outcome, functional autonomy, and quality of life of elderly patients with a long–term intensive care unit stay. Crit Care Med. 2000;28:3389-3395.