Andrew J. Swinburne

Bacterial Complications of Respiratory Tract Viral Illness: A Comprehensive Evaluation

Abstract Background. Respiratory tract infection is one of the most common reasons for hospitalization among adults, and recent evidence suggests that many of these illnesses are associated with viruses. Although bacterial infection is known to complicate viral infections, the frequency and impact of mixed viral-bacterial infections has not been well studied. Methods. Adults hospitalized with respiratory illness during 3 winters underwent comprehensive viral and bacterial testing. This assessment was augmented by measuring the serum level of procalcitonin (PCT) as a marker of bacterial infection. Mixed viral-bacterial infection was defined as a positive viral test result plus a positive bacterial assay result or a serum PCT level of ≥ 0.25 ng/mL on admission or day 2 of hospitalization. Results. Of 842 hospitalizations (771 patients) evaluated, 348 (41%) had evidence of viral infection. A total of 212 hospitalizations (61%) involved patients with viral infection alone. Of the remaining 136 hospitalizations (39%) involving viral infection, results of bacterial tests were positive in 64 (18%), and PCT analysis identified bacterial infection in an additional 72 (21%). Subjects hospitalized with mixed viral-bacterial infections were older and more commonly received a diagnosis of pneumonia. Over 90% of hospitalizations in both groups involved subjects who received antibiotics. Notably, 4 of 10 deaths among subjects hospitalized with viral infection alone were secondary to complications of Clostridium difficile colitis. Conclusions. Bacterial coinfection is associated with approximately 40% of viral respiratory tract infections requiring hospitalization. Patients with positive results of viral tests should be carefully evaluated for concomitant bacterial infection. Early empirical antibiotic therapy for patients with an unstable condition is appropriate but is not without risk.

Relationship of patient age to cost and survival in a medical ICU

We examined the relationship between the reason for admission to the Medical Intensive Care Unit (MICU), cost of care, and outcome of illness to patient age for 182 consecutive patients admitted to the MICU of a community hospital. The reasons for admission to the MICU for patients 70 yr and older did not differ greatly from those for patients 50–69 yr. Only 1 of 21 patients admitted with cardiopulmonary arrest occurring outside the MICU survived. If these patients admitted after cardiopulmonary arrest are excluded from analysis, 80, 87, 86, 67, and 79% of patients in the 5th through 9th decades, respectively, survived (p > 0.05). Of the 51 discharged patients older than 70 yr, 38 were alive after a mean follow-up of 19 months, 8 had died, and 5 were lost to follow-up. Total hospital costs, total hospitalization duration, duration of MICU care, laboratory, radiology, and respiratory therapy costs did not vary with patient age. Because the outcome of MICU treatment is similar for all age groups, and because cost of this care for younger and older patients is the same, age should not be a factor in determining whether or not a patient receives aggressive care in the MICU.

Comparison of noninvasive measurements of carbon dioxide tension during withdrawal from mechanical ventilation

End tidal CO2 tension (Petco2) and transcutaneous CO2 tension (Ptcco2) were compared with arterial CO2 (Paco2) before and after withdrawal of mechanical ventilation in 20 patients predisposed to hypercarbia. With stable Paco2 during mechanical ventilation, the correlation coefficient (r) between Pac

Apache Ii score and mortality in respiratory failure due to cardiogenic pulmonary edema

We reviewed retrospectively 88 patients to assess whether the APACHE II severity of disease classification system can predict mortality in patients with respiratory failure due to cardiac pulmonary edema. Mean score for survivors was higher than for nonsurvivors (24.5 +/- 6.7 vs. 20.7 +/- 5.7, p less than .01), and increasing APACHE II scores were not associated with increasing mortality. Mortality was 54% for APACHE II scores less than or equal to 18, 43% for scores greater than 18 and less than or equal to 24, 22% for scores greater than 24 and less than or equal to 31, and 25% for scores between 32 and 40. The relationship of APACHE II scores to mortality did not improve when the 25 patients with ICU stays less than 48 h were analyzed; the mean score of survivors in this group was 24.3 +/- 5.2 vs. 18.8 +/- 4.6 for nonsurvivors, p less than .001. The presence of myocardial infarction (MI) was associated with a high mortality. Mortality in the 51 MI patients was 52.9% vs. 13.5% in the 37 patients without MI (p less than .001), but APACHE II scores were similar (22.6 +/- 6.6 and 23.7 +/- 6.4, respectively). The relationship between APACHE II scores and mortality did not improve if patients with and without MI are analyzed separately. For patients with MI, mortality was 78.6% for scores between 12 and 17, 56.2% for scores between 18 and 23, 33.3% for scores between 24 and 29, and 33.3% for scores greater than 29.(ABSTRACT TRUNCATED AT 250 WORDS)

Utility of serum procalcitonin values in patients with acute exacerbations of chronic obstructive pulmonary disease: A cautionary note

Background Serum procalcitonin levels have been used as a biomarker of invasive bacterial infection and recently have been advocated to guide antibiotic therapy in patients with chronic obstructive pulmonary disease (COPD). However, rigorous studies correlating procalcitonin levels with microbiologic data are lacking. Acute exacerbations of COPD (AECOPD) have been linked to viral and bacterial infection as well as noninfectious causes. Therefore, we evaluated procalcitonin as a predictor of viral versus bacterial infection in patients hospitalized with AECOPD with and without evidence of pneumonia. Methods Adults hospitalized during the winter with symptoms consistent with AECOPD underwent extensive testing for viral, bacterial, and atypical pathogens. Serum procalcitonin levels were measured on day 1 (admission), day 2, and at one month. Clinical and laboratory features of subjects with viral and bacterial diagnoses were compared. Results In total, 224 subjects with COPD were admitted for 240 respiratory illnesses. Of these, 56 had pneumonia and 184 had AECOPD alone. A microbiologic diagnosis was made in 76 (56%) of 134 illnesses with reliable bacteriology (26 viral infection, 29 bacterial infection, and 21 mixed viral bacterial infection). Mean procalcitonin levels were significantly higher in patients with pneumonia compared with AECOPD. However, discrimination between viral and bacterial infection using a 0.25 ng/mL threshold for bacterial infection in patients with AECOPD was poor. Conclusion Procalcitonin is useful in COPD patients for alerting clinicians to invasive bacterial infections such as pneumonia but it does not distinguish bacterial from viral and noninfectious causes of AECOPD.

Mechanical Ventilation: Analysis of Increasing Use and Patient Survival

To quantitate and assess an increase in the use of me chanical ventilation, we retrospectively analyzed the records of 1,589 patients treated with mechanical ven tilation. Between 1974 and 1983, there was a 156% increase in the number of patients treated each year. There were significant increases in the number of pa tients with cardiac pulmonary edema (p < 0.001), adult respiratory distress syndrome (p < 0.01), chronic ob structive lung disease (p < 0.005), neuromuscular dis ease (p < 0.025), and cardiopulmonary arrest (p < 0.005). Regression analysis versus time shows that older patients (p < 0.025) and more chronically ill patients (p < 0.05) are now being treated with mechanical ven tilation. Overall survival was 41.4%, and yearly survival rates remained constant during the ten-year period. Sur vival was 55.3% for patients with cardiogenic pulmo nary edema, 34.1 % for the adult respiratory distress syn drome, 65.7% for chronic obstructive lung disease, 90.5% for asthma, 38.7% for neuromuscular disease, 92.1% for drug overdose, 33.7% for pneumonia, and 19.1 % for cardiopulmonary arrest. Studies are needed that will determine predictors of survival from acute respiratory failure for patients with chronic heart and lung disease. Such predictors will help physicians coun sel their patients when making the decision to be treated with mechanical ventilation in the event of re spiratory failure.

Hypoxemia from Right to Left Shunting Through Patent Foramen Ovale

We report a patient with severe hypoxemia from a large (41%) right to left shunt through a patent foramen ovale after right ventricular myocardial infarction, and review 18 previous descriptions of patients with right to left shunting through patent foramen ovale. These shunts occur when right atrial pressure is elevated above left atrial pressure, or when the anatomic relationship of the interatrial septum to the inferior vena cava is altered. Since 15-35% of the population have a potentially patent foramen ovale, interatrial right to left shunting may occur more frequently than had previously been recognized, and should be considered in a differential diagnosis of hypoxemia.

Comparison of Noninvasive Measurements of Carbon Dioxide Tension During Withdrawal from Mechanical Ventilation

End tidal CO2 tension (Petco2) and transcutaneous CO2 tension (Ptcco2) were compared with arterial CO2 (Paco2) before and after withdrawal of mechanical ventilation in 20 patients predisposed to hypercarbia. With stable Paco2 during mechanical ventilation, the correlation coefficient (r) between Paco2 and Petco2 was .9, and between Paco2 and Ptcco2, .87. Ptcco2 considerably overestimated Paco2 in three patients who were receiving dopamine. After withdrawal of mechanical ventilation, changes in Paco2 were closely paralleled by changes in Petco2 and Ptcco2 (r = .82 and .86, respectively). Nine of 20 patients had an increased Paco2 of 10 torr or greater. In eight of these, Petco2 and Ptcco2 rose by at least 5 torr, and in seven, the rise in Petco2 and Ptcco2 was within 5 torr of the rise in Paco2.During mechanical ventilation, Petco2 and Ptcco2 estimated stable Paco2 with sufficient accuracy for clinical use, except in patients with cutaneous vasoconstriction. After withdrawal of mechanical ventilation, changes in Petco2 and Ptcco2 were predictive of important Paco2 increases, warranting continued exploration and evaluation as to their use in monitoring patients predisposed to hypercarbia.