Robert L. Vender

A clinical pilot study: High frequency chest wall oscillation airway clearance in patients with amyotrophic lateral sclerosis

Respiratory complications are common in patients with amyotrophic lateral sclerosis (ALS) with respiratory failure representing the most common cause of death. Ineffective airway clearance resultant from deficient cough frequently contributes to these abnormalities. We sought to evaluate the effectiveness of high frequency chest wall oscillation (HFCWO) administered through the Vest™ Airway Clearance System when added to standard care in preventing pulmonary complications and prolonging the time to death in patients with ALS. This is a single center study performed at the Penn State Milton S. Hershey Medical Center (HMC). Nine patients with a diagnosis of ALS and concurrently receiving non‐invasive ventilatory support with bi‐level positive airway pressure (BiPAP) were recruited from the outpatient clinic at HMC. Four patients were randomized to receive standard care and five patients to receive standard care plus the addition of HFCWO administered twice‐daily for 15 min duration. Longitudinal assessments of oxyhemoglobin saturation, forced vital capacity (FVC), and adverse events were obtained until time of death. Pulmonary complications of atelectasis, pneumonia, hospitalization for a respiratory‐related abnormality, and tracheostomy with mechanical ventilation were monitored throughout the study duration. No differences were observed between treatment groups in relation to the rate of decline in FVC. The addition of HFCWO airway clearance failed to improve time to death compared to standard treatment alone (340 days +/− 247 vs. 470 days +/− 241; p = 0.26). The random allocation of HFCWO airway clearance to patients with ALS concomitantly receiving BiPAP failed to attain any significant clinical benefits in relation to either loss of lung function or mortality. This study does not exclude the potential benefit of HFCWO in select patients with ALS who have coexistent pulmonary diseases, pre‐existent mucus‐related pulmonary complications, or less severe levels of respiratory muscle weakness.

Respiratory systems abnormalities and clinical milestones for patients with amyotrophic lateral sclerosis with emphasis upon survival

Respiratory system complications and abnormalities are common in patients with amyotrophic lateral sclerosis (ALS) and respiratory failure remains the most common cause of death. Extensive epidemiological longitudinal data have documented the extent, magnitude, and clinical course of these abnormalities, but few studies have provided objective information that can have prognostic significance for individual patients. In this study, the reported data represent results from a retrospective review of the medical records of 153 patients with ALS cared for at a single institution (The Penn State Milton S. Hershey Medical Center) over a 50‐month period. Medical information in relation to respiratory system abnormalities and complications including pulmonary function measurements was extracted for data analyses. The intent of this review of longitudinal data from a relatively large cohort of patients with ALS was to identify clinically relevant easily‐identifiable objective information and clinical milestones that could have potential prognostic significance when applied to individual patients. Demographic data including gender, survival outcome, respiratory symptoms, age of disease onset, and age at death were similar to previously published epidemiological studies: mean age at ALS disease onset was 58.9+/−12.7 years, and mean age at death was 66.7+/−10.8 years. For 151 patients with available data, the incidence of study defined respiratory complications included infectious pneumonia 13 (9%), venothromboembolism 9 (6%), and tracheostomy and mechanical ventilation 6 (4%). For 139 patients with serial measurements of forced vital capacity (FVC), median values for calculated rate of decline in FVC was 97 ml/30 days (2.4% predicted/30 days); 25% of patients had FVC rates of decline less than 52 ml/30 days (1.4% predicted/30 days) and 25% had rates of decline greater than 170 ml/30 days (4.4% predicted/30 days). Stratifying patients into two distinct clinical subgroups based upon rates of decline in FVC less than or greater than the median value of 97 ml/30 days identified an apparent two‐fold increase in survival duration for ALS patients with slower rates of pulmonary physiology deterioration when referenced to either date of dyspnea onset or time from bi‐level positive airway pressure (BiPAP) initiation (2.0+/−1.4 vs. 1.0+/−0.8 years; 1.9+/−1.5 vs. 1.0+/−0.9 years, respectively). We concluded that the correlation between clinically defined milestones, most importantly onset of dyspnea, and the calculated rate of decline in FVC represent obtainable and objective measurements that predict the natural course of respiratory muscle dysfunction in patients with ALS and provide important prognostic information in relation to individual patient survival duration.

Predicting dead space ventilation in critically ill patients using clinically available data.

Objective:To develop and validate an equation to predict dead space to tidal volume ratio (Vd/Vt) from clinically available data in critically ill mechanically ventilated patients. Design:Prospective, observational study using a convenience sample of patients whose arterial blood gas and respiratory gas exchange had been measured with indirect calorimetry. Setting:Medical and surgical critical care units of a university medical center. Patients:Adult, mechanically ventilated patients at rest with Fio2 ≤0.60 and no air leaks who had recent arterial blood gas recordings and end-tidal carbon dioxide concentration monitoring. Interventions:Observational only. Measurements and Main Results:Indirect calorimetry was used to determine carbon dioxide production and expired minute ventilation in 135 patients. Tidal volume and respiratory rate were recorded from the ventilator. End tidal carbon dioxide concentration, body temperature, arterial carbon dioxide partial pressure (Paco2), and other clinical data were recorded. Vd/Vt was calculated using the Enghoff modification of the Bohr equation (Paco2 − PECO2/Paco2). Regression analysis was then used to construct a predictive equation for Vd/Vt using the clinical data: Vd/Vt = 0.32 + 0.0106 (Paco2 − ETCO2) + 0.003 (RR) + 0.0015 (age) (R2 = 0.67). A second group of 50 patients was measured using the same protocol and their data were used to validate the equations developed from the original 135 patients. The equation was found to be unbiased and precise. Conclusions:Vd/Vt is predictable from clinically available data. Whether this predicted quantity is valuable clinically must still be determined.

Severe Hypercapnia in Critically Ill Adult Cystic Fibrosis Patients

Background Cystic fibrosis (CF) is a monogenetic autosomal recessive multi-organ disease affecting approximately 50,000 patients worldwide. Overall median survival is continually increasing but pulmonary disease remains the most common cause of death. Guidelines have been published in relation to the outpatient maintenance of lung health for CF patients and treatment of acute lung exacerbations but little information exists about the management of the critically ill CF patient. Invasive mechanical ventilation in CF patients with acute respiratory failure is associated with poor outcome and high mortality. Methods Retrospective analysis of adult patients with CF who required endotracheal intubation and invasive mechanical ventilation in the Medical Intensive Care Unit (MICU). Results Between the years 2003 - 2009, 14 adult patients with CF required endotracheal intubation and invasive mechanical ventilation in the Medical Intensive Care Unit (MICU) of the Penn State Milton S. Hershey Medical Center, Hershey, Pennsylvania, USA. Eleven patients died in the MICU because of progressive respiratory failure and inability to liberate from mechanical ventilation. Seven individuals consistently manifested arterial partial pressures of carbon dioxide (PaCO2) greater than 20.00 kPa despite high levels of conventional modes of mechanical ventilation. Conclusion Intubated CF patients with respiratory failure have a high mortality rate. Based on our experience, multiple factors contribute to severe hypercapnia and the effectiveness of conventional modes of mechanical ventilation in many of these patients is limited. Keywords Cystic fibrosis; Mechanical ventilation; Critical care; Hypercapnia; Respiratory failure

Prediction equation to estimate dead space to tidal volume fraction correlates with mortality in critically ill patients

OBJECTIVE The measurement of dead space to tidal volume fraction (Vd/Vt) using various methodologies has been shown to be a reliable predictor of mortality in critically ill patients. In this study, we evaluated the correlation of a validated equation using clinically available information to predict calculation of Vd/Vt with clinically relevant outcome parameters in patients requiring mechanical ventilation. METHODS Calculations of Vd/Vt were obtained based upon a previously published prediction equation for dead space ventilation fraction: Vd/Vt = 0.320 + 0.0106 (Paco2--end-tidal carbon dioxide measurement) + 0.003 (respiratory rate per minute) + 0.0015 (age in years) on study days 1, 3 to 4, 6 to 9, and 14 after initiation of mechanical ventilation in adult patients who satisfied 1 of the 3 study defined diseases: (1) acute bacterial pneumonia, (2) acute respiratory distress syndrome, or (3) cystic fibrosis. RESULTS Using the final/last available time point calculation of Vd/Vt, a significant difference was observed between survivors and nonsurvivors both in relation to mean and median values (56.5% vs 71.2% and 56.0% vs 65.0%, respectively). In addition, sequential analyses of Vd/Vt calculations over time also demonstrated a statistically significant difference between survivors and nonsurvivors for days 6 to 9. CONCLUSION In this study-specific population of critically ill patients, the prediction equation of Vd/Vt using clinically available parameters correlates with mortality. In addition, we provide a simple method to estimate Vd/Vt that can be potentially applicable to all critically ill intensive care unit patients.

Characteristics of Resting Metabolic Rate in Critically Ill, Mechanically Ventilated Adults With Cystic Fibrosis

Background: Critically ill patients with cystic fibrosis may be especially sensitive to the negative consequences of overfeeding and underfeeding, yet there is almost no information available about the energy needs of these patients. The purpose of this study was to characterize the metabolic rate of critically ill adult patients with cystic fibrosis requiring mechanical ventilation. Methods: This was an observational study in which the resting metabolic rate, oxygen consumption, and carbon dioxide production of adult patients with cystic fibrosis requiring critical care, sedation, and mechanical ventilation were measured with indirect calorimetry. This group was compared with a cohort of adult critical care patients without cystic fibrosis. Results: Twelve patients with cystic fibrosis were identified and measured. These were compared with a control group of 25 critically ill patients. Both groups were underweight (body mass index, 17.4 ± 4.0 kg/m2 in cystic fibrosis and 18.4 ± 2.3 kg/m2 in control). Adjusting for differences in age, sex, height, and weight, there was no difference in resting metabolic rate between the cystic fibrosis and control groups (1702 ± 193 vs 1642 ± 194 kcal/d, P = .388). Measured resting metabolic rate matched predicted values 58% of the time in cystic fibrosis and 60% of the time in control. Conclusions: The resting metabolic rate of sedated adult patients with cystic fibrosis being assisted with mechanical ventilation is not different from that of adult critical care patients without cystic fibrosis. In both these underweight groups, accurate prediction of resting metabolic rate is difficult to obtain.

Clinical Impact of Blood Culture Results in Acutely Ill Hospitalized Adult Patients With Cystic Fibrosis.

Background Blood cultures are obtained clinically to confirm site and source of acute infection as well as to guide effective antibiotic therapies. Patients with cystic fibrosis (CF) are at risk for blood stream infection (BSI) as identified from positive blood culture results. Methods A retrospective chart review was performed of 190 adult CF patients from January 1, 2001 through December 1, 2015. All positive blood culture results were identified as to clinical relevance and source of BSI. Results There were a total of 3,053 blood cultures. One hundred fifty-one positive blood cultures were considered pathogenic and clinically significant. Venous access device-related BSI was identified in 31 evaluable patients and 106 blood cultures. Nineteen patients and 45 positive blood cultures were attributable to organ-specific sources. Conclusion Two patterns of BSI were identified: 1) venous access device infections without causal mortality and 2) organ-specific site infections with associated 26% mortality.