Bootleg Biology: a Semester-Long CURE Using Wild Yeast to Brew Beer

Laboratory exercises for undergraduates that involve authentic discovery and research have been shown to increase student learning and engagement. To bring these advantages into the microbiology curriculum, we developed a semester-long course-based undergraduate research experience for a laboratory based on brewing beer with wild yeast. This set of lab exercises uses many of the same protocols found in traditional microbiology lab curricula-isolating and maintaining pure cultures, staining and microscopy, use of aseptic technique, PCR, gel electrophoresis, and media preparation-and integrates them into a novel and exciting project that enables students to be active participants in the scientific method. Students are assessed on their ability to brew beer successfully and to stain and visualize microorganisms; they are also assessed for knowledge gains in the traditional portion of the course, their ability to use their brewing knowledge in other settings, and their attitudes about science. After completing the course, students showed gains in general microbiology knowledge and their engagement with science.

Poor Antigen Processing of Poxvirus Particles Limits CD4+ T Cell Recognition and Impacts Immunogenicity of the Inactivated Vaccine

CD4⁺ T cells play critical roles in defending against poxviruses, both by potentiating cellular and humoral responses and by directly killing infected cells. Despite this central role, the basis for pox-specific CD4⁺ T cell activation, specifically the origin of the poxvirus-derived peptides (epitopes) that activate CD4⁺ T cells, remains poorly understood. In addition, because the current licensed poxvirus vaccines can cause serious adverse events and even death, elucidating the requirements for MHC class II (MHC-II) processing and presentation of poxviral Ags could be of great use. To address these questions, we explored the CD4⁺ T cell immunogenicity of ectromelia, the causative agent of mousepox. Having identified a large panel of novel epitopes via a screen of algorithm-selected synthetic peptides, we observed that immunization of mice with inactivated poxvirus primes a virtually undetectable CD4⁺ T cell response, even when adjuvanted, and is unable to provide protection against disease after a secondary challenge. We postulated that an important contributor to this outcome is the poor processability of whole virions for MHC-II-restricted presentation. In line with this hypothesis, we observed that whole poxvirions are very inefficiently converted into MHC-II-binding peptides by the APC as compared with subviral material. Thus, stability of the virion structure is a critical consideration in the rational design of a safe alternative to the existing live smallpox vaccine.

Reengineering respiratory support following extubation: avoidance of critical care unit costs

STUDY OBJECTIVE

We prospectively investigated alternative clinical practice strategies for critically ill trauma patients following extubation to evaluate the cost-effectiveness of these maneuvers. The primary change was elimination of the routine use of postextubation supplemental oxygen, with concurrent utilization of noninvasive positive pressure ventilatory support (NPPV) to manage occurrences of postextubation hypoxemia.

DESIGN

Prospective, consecutive accrual of patients undergoing extubation.

SETTING

Trauma ICU in a university hospital.

INTERVENTIONS AND MEASUREMENTS

All patients received mechanical ventilation using pressure support ventilation (PSV) with continuous positive airway pressure (CPAP) as the primary mode. The patients were extubated to room air following a 20-min preextubation trial of 5 cm H(2)O CPAP at FIO(2) of 0.21, and demonstrating a spontaneous respiratory rate </= 38 breaths/min, pH >/= 7.30, PaCO(2) </= 50 mm Hg, and PaO(2) >/= 50 mm Hg. The subgroup of patients who became hypoxemic (pulse oximetric saturation < 88%) within 24 h of extubation were treated with NPPV for up to 48 h duration. Patients who failed NPPV were reintubated. Four hundred fifty-one (84%) patients were successfully extubated to room air. Seventy-two patients (13%) became hypoxemic within 24 h, and NPPV was administered. Fifty-two patients (72% of those who were hypoxemic) responded to NPPV, while 20 patients failed to respond to therapy, were reintubated, and received mechanical ventilation for a mean of 4 days. Thirteen additional patients (2%) were reintubated for reasons other than hypoxemia. The overall reintubation rate for the group (n = 536) was 6.2%; for the postextubation hypoxemic group who failed NPPV, the reintubation rate was 3.7%. The elimination of routine supplemental oxygen via nasal cannula following extubation resulted in a potential direct cost avoidance of $50,006.88 for 451 patient days. Moreover, the 52 patients who were spared reintubation and mechanical ventilation provided an additional potential cost avoidance of $19,740.24 in unused ventilator days per patient.

CONCLUSION

Eliminating the routine use of supplemental oxygen and employing NPPV as a method to prevent reintubation can facilitate a more aggressive, cost-effective strategy for the management of the trauma ICU patient who has been extubated.

A prospective, randomized comparison of an in-line heat moisture exchange filter and heated wire humidifiers: rates of ventilator-associated early-onset (community-acquired) or late-onset (hospital-acquired) pneumonia and incidence of endotracheal tube occlusion

PURPOSE

To compare the performance of an in-line heat moisture exchanging filter (HMEF) (Pall BB-100; Pall Corporation; East Hills, NY) to a conventional heated wire humidifier (H-wH) (Marquest Medical Products Inc., Englewood, Colo) in the mechanical ventilator circuit on the incidence of ventilator-associated pneumonia (VAP) and the rate of endotracheal tube occlusion.

METHODS

This report describes a prospective, randomized trial of 280 consecutive trauma patients in a 20-bed trauma ICU (TICU). All intubated patients not ventilated elsewhere in the medical center prior to their TICU admission were randomized to either an in-line HMEF or a H-wH in the breathing circuit. Ventilator circuits were changed routinely every 7 days, and closed system suction catheters were changed every 3 days. HMEFs were changed every 24 h, or more frequently if necessary. A specific endotracheal tube suction and lavage protocol was not employed. Patients were dropped from the HMEF group if the filter was changed more than three times a day or the patient was placed on a regimen of ultra high-frequency ventilation. The Centers for Disease Control and Prevention (CDC) criteria for diagnosis of pneumonia were used; early-onset, community-acquired pneumonia was defined if CDC criteria were met in < or =3 days, and late-onset, hospital-acquired pneumonia was defined if criteria were met in >3 days. Laboratory and chest radiograph interpretation were blinded.

RESULTS

The patient ages ranged from 15 to 95 years in the HMEF group and 16 to 87 years in the H-wH group (p=not significant), with a mean age of 46 years and 48 years, respectively. The male to female ratio ranged between 78 to 82%/22 to 18%, respectively, and 55% of all admissions were related to blunt trauma, 40% secondary to penetrating trauma, and 5% to major burns. There was no difference in Injury Severity Score (ISS) between the two groups. Moreover, there was no significant difference in mean ISS among those who did not develop pneumonia and those patients who developed either early-onset, community-acquired or late-onset, hospital-acquired pneumonia. The HMEF nosocomial VAP rate was 6% compared to 16% for the H-wH group (p<0.05), and total ventilator circuit costs (per group) were reduced. There were no differences in duration of ventilation (mean+/-SD) if the patient did not develop pneumonia or if the patient developed an early-onset, community-acquired or a late-onset, hospital-acquired pneumonia. Moreover, total TICU days were reduced in the HMEF group. In addition, the incidence of partial endotracheal tube occlusion was not significantly different between the H-wH and the HMEF groups.

CONCLUSIONS

The HMEF used in this study reduced the incidence of late-onset, hospital-acquired VAP, but not early-onset, community-acquired VAP, compared to the conventional H-wH circuit. This was associated with a significant reduction in total ICU stay. Disposable ventilator circuit costs in the HMEF group were reduced compared to the H-wH group in whom circuit changes occurred at 7-day intervals.

CLINICAL IMPLICATIONS

The use of the HMEF is a cost-effective clinical practice associated with fewer late-onset, hospital-acquired VAPs, and should result in improved resource allocation and utilization.

A model to decrease hepatic blood flow and cardiac output with pressure breathing

This randomized, controlled, crossover study evaluated the effect of continuous positive airway pressure (CPAP) breathing on hepatic blood flow (HBF) and cardiac output in 10 healthy male subjects. A CPAP mask was placed on the face and the subject breathed at either CPAP 12.5 cm H2O or ambient airway pressure. The estimated HBF was calculated as the ratio of indocyanine green plasma clearance to one minus the hematocrit. Cardiac output was measured with Doppler ultrasound. CPAP caused HBF to decrease in 8 of 10 subjects (14.1% +/- 15.3%, mean +/- SD, p = 0.033) and cardiac index (CI) to decrease in all subjects (14.1% +/- 5.7%, p = 0.0001). Stroke volume and respiratory rate were significantly decreased; heart rate was unchanged. These results indicate that CPAP at 12.5 cm H2O causes a small, but significant decrease in both HBF and CI.

Physiologic implications of mechanical ventilation on pharmacokinetics

Numerous factors present in the critically ill patient decrease drug clearance. The contribution of one factor, mechanical ventilation, to this decrease is largely unknown and unquantified. This article attempts to review the physiologic effects of mechanical ventilation and to propose theoretical changes in the pharmacokinetics of concomitantly administered drugs. Mechanical ventilation with or without positive end-expiratory pressure is a well-documented cause of decreases in cardiac output, hepatic and renal blood flow, glomerular filtration rate, and urine flow. The mean airway pressure delivered, the pathophysiologic state of the patient, and coexisting therapeutic interventions affect the degree of hemodynamic alteration. Theoretically, these hemodynamic changes can decrease the clearance of several drugs frequently administered to critically ill patients. Decreased hepatic blood flow decreases the clearance of nonrestrictively cleared drugs. The pharmacokinetics of drugs predominantly renally cleared, by either glomerular filtration or tubular secretion, are affected by a decrease in renal blood flow or glomerular filtration rate. Also, the clearance of agents for which tubular reabsorption is important may decrease because the reduction in urine flow resulting from mechanical ventilation allows increased time for drug reabsorption. Interventions that minimize the decrease in cardiac output and organ blood flow and, theoretically, the risk of the adverse drug reactions from decreased drug clearance include expansion of intravascular volume, administering positive inotropic agents, and decreasing mean airway pressure. Monitoring serum concentration of critical and toxic agents suspected to have altered clearance in patients receiving mechanical ventilation is recommended. We hope that our article will stimulate future research in this area to give clinicians guidelines for drug dosing in patients receiving mechanical ventilation.

Optimum versus clinically established levels of continuous positive airway pressure in respiratory therapy

To evaluate the efficacy of our routine method of cardiopulmonary monitoring of accurate management of respiratory therapy, continuous positive airway pressure (CPAP) was titrated in 11 surgical intensive care patients within +/- 7.5 cm H2O of the clinically selected level. Cardiopulmonary data were independently and retrospectively reviewed by three experienced critical care physicians from three outside hospitals. Each physician estimated the optimum level of CPAP for each patient. Variability between reviewers was not statistically significant. The optimum CPAP level based on all reviewers' opinions (8.6 +/- 5.7 cm H2O, mean +/- SD) was significantly lower than that selected clinically (13.2 +/- 4.5 cm H2O; P less than 0.05). We conclude that current methodology for monitoring respiratory therapy is inefficient for rapid adjustment of CPAP to appropriate levels. Continuous arterial and pulmonary artery oximetry may provide an improvement in the efficacy of cardiopulmonary monitoring in the future.

Real-time continuous estimation of gas exchange by dual oximetry

We designed a ventilation-perfusion index (VQI) to estimate venous admixture (Qsp/Qt) in a real-time fashion by simultaneous pulse and pulmonary artery oximetry in 17 patients with acute respiratory failure. Changes in Qsp/Qt were produced by altering the level of continuous positive airway pressure. VQI correlated well with Qsp/Qt (r = 0.78). This contrasts with the poor correlation found between Qsp/Qt and the commonly used oxygen tension based indices such as PaO2/FIO2 (r = -0.51), PaO2/PAO2 (r = 0.47), and PAO2-PaO2 (r = 0.23). The use of dual oximetry to derive a VQI appears to be a reliable and accurate method for real-time assessment of pulmonary gas exchange in patients with acute respiratory failure.

Titration of continuous positive airway pressure by real-time dual oximetry

The clinical utility of combined pulse and pulmonary artery oximetry (dual oximetry) in titrating continuous positive airway pressure (CPAP) therapy was tested in 17 patients with acute respiratory failure. The level of CPAP was altered in 2.5 cmH2O increments and decrements, while conventional measurements of cardiopulmonary function and continuous dual oximetry were performed. Then, optimum CPAP levels were selected using both techniques independently. The difference in optimum CPAP determined by the two methods was 0 cmH2O in ten of 17 patients, less than or equal to 2.5 cmH2O in 14 of 17 patients, and 5.0 to 7.5 cmH2O in the remaining three patients. When a difference existed, CPAP level determined with dual oximetry was consistently lower than the level selected by conventional means. The results indicate that the estimates of venous admixture and oxygen utilization coefficient obtained using dual oximetry provide sufficient information for rapid and accurate titration of CPAP in the majority of patients with acute respiratory failure.

Estimation of oxygen utilization by dual oximetry

Total body oxygen utilization coefficient was estimated using continuous pulse and pulmonary artery oximetry (dual oximetry) in 17 patients with respiratory failure. Change in arterial and mixed venous oxygen saturations was induced by altering airway pressure. Continuous measurement of mixed venous oxygen saturation provided an accurate and linear estimate of oxygen utilization coefficient (r = -0.92), the true values being overestimated by 0.05 +/- 0.06 (mean +/- SD). Addition of pulse oximetry improved the correlation (r = 0.93) and decreased the difference between absolute values (0.02 +/- 0.06). Oxygen utilization coefficient can be estimated reliably in an online fashion using pulmonary artery oximetry. However, the use of dual oximetry will further improve the estimate.