Lydia Cassorla

Structural Estimation of the Newsvendor Model: An Application to Reserving Operating Room Time

The newsvendor model captures the trade-off faced by a decision maker that needs to place a firm bet prior to the occurrence of a random event. Previous research in operations management has mostly focused on deriving the decision that minimizes the expected mismatch costs. In contrast, we present two methods that estimate the unobservable cost parameters characterizing the mismatch cost function. We present a structural estimation framework that accounts for heterogeneity in the uncertainty faced by the newsvendor as well as in the cost parameters. We develop statistical methods that give consistent estimates of the model primitives, and derive their asymptotic distribution, which is useful to do hypothesis testing. We apply our econometric model to a hospital that balances the costs of reserving too much versus too little operating room capacity to cardiac surgery cases. Our results reveal that the hospital places more emphasis on the tangible costs of having idle capacity than on the costs of schedule overrun and long working hours for the staff. We also extend our structural models to incorporate external information on forecasting biases and mismatch costs reported by the medical literature. Our analysis suggests that overconfidence and incentive conflicts are important drivers of the frequency of schedule overruns observed in our sample.

The Safety and Efficacy of Sevoflurane Anesthesia in Infants and Children with Congenital Heart Disease

We tested the hypothesis that sevoflurane is a safer and more effective anesthetic than halothane during the induction and maintenance of anesthesia for infants and children with congenital heart disease undergoing cardiac surgery. With a background of fentanyl (5 &mgr;g/kg bolus, then 5 &mgr;g · kg−1 · h−1), the two inhaled anesthetics were directly compared in a randomized, double-blinded, open-label study involving 180 infants and children. Primary outcome variables included severe hypotension, bradycardia, and oxygen desaturation, defined as a 30% decrease in the resting mean arterial blood pressure or heart rate, or a 20% decrease in the resting arterial oxygen saturation, for at least 30 s. There were no differences in the incidence of these variables; however, patients receiving halothane experienced twice as many episodes of severe hypotension as those who received sevoflurane (P = 0.03). These recurrences of hypotension occurred despite an increased incidence of vasopressor use in the halothane-treated patients than in the sevoflurane-treated patients. Multivariate stepwise logistic regression demonstrated that patients less than 1 yr old were at increased risk for hypotension compared with older children (P = 0.0004), and patients with preoperative cyanosis were at increased risk for developing severe desaturation (P = 0.049). Sevoflurane may have hemodynamic advantages over halothane in infants and children with congenital heart disease.

Designing and Testing a Computer-Based Screening System for Transfusion-Related Acute Lung Injury

Computer-based systems can detect underreported adverse events. We hypothesized that a system could be designed to detect potential or unreported cases of transfusion-related acute lung injury (TRALI). We developed and tested a computer screening system using retrospective computer blood gas data after transfusions during a 45-day period at a tertiary care academic hospital. The program identified cases of posttransfusion hypoxemia. Medical records of identified cases were reviewed to diagnose TRALI. During the 45-day period, 820 patients received 6,888 blood products. Seven cases of TRALI were diagnosed, whereas only 2 had been reported. The system had 99% accuracy and 26% positive predictive value for detecting potential TRALI. Computer screening finds more cases of TRALI than are reported voluntarily, and a prospective study using this system is feasible and needed to validate this method of detecting this important adverse transfusion reaction.

Reliability of Intraoperative Contrast Transesophageal Echocardography for Detecting Interatrial Communications in Patients With Other Congenital Cardiovascular Malformations

The reliability of contrast transesophageal echocardiography (TEE) for diagnosing atrial communication has not been studied previously in patients with congenital heart disease. We prospectively evaluated the validity of intraoperative contrast TEE for determining atrial septal patency in a group of patients with congenital heart disease who underwent surgery using direct inspection for defi nitive diagnosis. Our study was prompted by the potential for surgical complications from paradoxic systemic air embolism 1 and observed cases of interatrial communications that were undetected despite a thorough preoperative assessment and intraoperative TEE including contrast studies. One child had severe neurologic damage due to systemic air embolization during open right-sided cardiac surgery with a beating heart.