American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Nov 2000
Contribution of expiratory muscle pressure to dynamic intrinsic positive end-expiratory pressure: validation using the Campbell diagram.
In spontaneously breathing (SB) patients expiratory muscle contraction leads to an overestimation of dynamic intrinsic PEEP (PEEP(i),dyn). To quantify this overestimation, PEEP(i),dyn measured with the esophageal balloon technique was corrected for the increase in Pga over the course of expiration (Pga,exp rise), for the whole decay of Pga during inspiration (Pga,total decay) or for the part of Pga decay restricted between the onset of inspiratory effort and the point of zero flow (Pga,zf decay). Corrections were compared with the reference PEEP(i),dyn (PEEP(i),dyn ref ), calculated by using the Campbell diagram. ⋯ In contrast, mean difference of PEEP(i),dyn - Pga,zf decay and PEEP(i),dyn ref was 3. 14 cm H(2)O with limits of agreement -0.46 to 6.74 cm H(2)O, indicating lack of agreement. The error in measurement due to the subtraction of Pga,zf decay from PEEP(i),dyn (i.e., [PEEP(i),dyn - Pga,zf decay] - PEEP(i),dyn ref ) was proportional to the intensity of expiratory muscle contraction, as expressed by the Pga,exp rise (r = 0.903, p < 0.001). We conclude that in actively expiring patients an adequate correction of PEEP(i),dyn for the overestimation caused by expiratory muscle contraction can be made by subtracting either Pga,total decay or Pga,exp rise from PEEP(i), dyn, the former achieving the best performance.
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Am. J. Respir. Crit. Care Med. · Nov 2000
Geographic distribution of human immunodeficiency virus-associated Pneumocystis carinii pneumonia in San Francisco.
The epidemiology of Pneumocystis carinii pneumonia (PCP) and its geographic distribution are incompletely understood. We examined the influence of geographic location as a risk factor for PCP through a retrospective case-control study of HIV-infected persons evaluated for PCP at San Francisco General Hospital. Subjects had microscopically confirmed PCP diagnosed between January 1996 and June 1999. ⋯ Interestingly, subjects living in the 94103 zip code had a significantly lower risk of PCP than subjects in other areas (odds ratio = 0.2, 95% confidence interval 0.1-0.6, p < 0.01). This effect was present despite controlling for risk factors for PCP such as use of prophylaxis or antiretroviral therapy, CD4 cell count, and HIV RNA level. We conclude that residence in the 94103 zip code of San Francisco is associated with a substantially lower risk of PCP than residence in other areas of the city.
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Am. J. Respir. Crit. Care Med. · Nov 2000
Geographic clustering of Pneumocystis carinii pneumonia in patients with HIV infection.
To detect whether there was geographic clustering of Pneumocystis carinii pneumonia cases among patients with human immunodeficiency virus (HIV) infection, we performed a retrospective analysis of a clinical database. The rates of pneumocystosis were analyzed by zip code zones for evidence of geographical clustering. ⋯ By contrast, no clustering was observed for 52 HIV-infected control subjects with respiratory disease or for 960 HIV-infected patients treated at our center during the same time period. These data raise intriguing questions about exposure to exogenous sources of P. carinii and suggest the need for prospective studies.
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Am. J. Respir. Crit. Care Med. · Nov 2000
Value of gram stain examination of lower respiratory tract secretions for early diagnosis of nosocomial pneumonia.
Except for bronchoalveolar lavage, the value of the Gram stain examination of respiratory tract samples for the diagnosis of hospital-acquired pneumonia (HAP) and their potential impact on empiric antibiotic treatment have rarely been assessed. During a 14-mo period, both plugged telescoping catheter (PTC) and endotracheal aspirate (EA) were performed when an HAP was suspected in mechanically ventilated patients. The results of Gram stain examinations and cultures and previous and subsequent antibiotic treatment were prospectively recorded. ⋯ The negative predictive value of Gram stain examination of EA and the positive predictive value of Gram stain examination of PTC were high. Our results suggest that the combination of Gram stain examination of paired PTC and EA may contribute to the early diagnosis of HAP in about two-thirds of mechanically ventilated patients, and guide the empiric therapy when needed. In the remaining one-third of patients, the Gram stain examination is not helpful in predicting HAP.
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Am. J. Respir. Crit. Care Med. · Nov 2000
The perception of respiratory work and effort can be independent of the perception of air hunger.
Dyspnea in patients could arise from both an urge to breathe and increased effort of breathing. Two qualitatively different sensations, "air hunger" and "respiratory work and effort," arising from different afferent sources are hypothesized. In the laboratory, breathing below the spontaneous level may produce an uncomfortable sensation of air hunger, and breathing above it a sensation of work or effort. ⋯ In five normal subjects we obtained simultaneous ratings of air hunger and of work and effort while independently varying PCO(2) or the level of targeted voluntary breathing. We found a difference in response to the two stimulus dimensions: air hunger ratings changed more steeply when PCO(2) was altered and ventilation was constant; work or effort ratings changed more steeply when ventilation was altered and PCO(2) was constant. We conclude that "air hunger" is qualitatively different from "work and effort" and arises from different afferent sources.