Quantifying pulse oximeter accuracy during hypoxemia and severe anemia using an in vitro circulation system.

Anemia and hypoxemia are common clinical conditions that are difficult to study and may impact pulse oximeter performance. Utilizing an in vitro circulation system, we studied performance of three pulse oximeters during hypoxemia and severe anemia. Three oximeters including one benchtop, one handheld, and one fingertip device were selected to reflect a range of cost and device types. Human blood was diluted to generate four hematocrit levels (40%, 30%, 20%, and 10%). Oxygen and nitrogen were bubbled through the blood to generate a range of oxygen saturations (O2Hb) and the blood was cycled through the in vitro circulation system. Pulse oximeter saturations (SpO2) were paired with simultaneously-measured O2Hb readings from a reference CO-oximeter. Data for each hematocrit level and each device were least-squares fit to a 2nd-order equation with quality of each curve fit evaluated using standard error of the estimate. Bias and average root mean square error were calculated after correcting for the calibration difference between human and in vitro circulation system calibration. The benchtop oximeter maintained good accuracy at all but the most extreme level of anemia. The handheld device was not as accurate as the benchtop, and inaccuracies increased at lower hematocrit levels. The fingertip device was the least accurate of the three oximeters. Pulse oximeter performance is impacted by severe anemia in vitro. The use of in vitro calibration systems may play an important role in augmenting in vivo performance studies evaluating pulse oximeter performance in challenging conditions.

Assessing contributions of value-added medical student roles.

Value-added student roles-defined as student activities that simultaneously teach physicianship and improve the healthcare system-have rapidly gained popularity in recent years. Though many agree that value-added medical student roles can contribute both to student learning and to patient outcomes, impact evaluation of these roles can pose a challenge. In this Personal View, we describe our quality improvement project at UC San Francisco aimed at reducing unnecessary physical therapist (PT) referrals. While our primary outcome measure remained unchanged, the project helped to galvanize safe mobilization efforts in the hospital and led to the establishment of a UCSF Health Safe Mobilization Committee, leading to broader and potentially more impactful institutional systems changes. How do we interpret success, and how do we appraise the potential impact students can have in a complex health system? While we agree with the importance of process-focused metrics that assess student participation in an interprofessional, data-driven quality improvement effort, we also see a role for an expanded assessment of student contributions to capture systems improvements that may occur downstream of student activities.

Parallel age-associated changes in brain and plasma neuronal pentraxin receptor levels in a transgenic APP/PS1 rat model of Alzheimer's disease.

Neuronal pentraxin receptor (NPR) is a synaptic protein implicated in AMPA receptor trafficking at excitatory synapses. Since glutamate neurotransmission is disrupted in Alzheimer's disease (AD), NPR levels measured from plasma represent a potential biomarker for synaptic dysfunction associated with AD. We sought to determine the relationship between AD pathology and brain and plasma NPR levels by examining age-associated NPR levels in these compartments in a transgenic APP/PS1 rat model of AD. NPR levels in cortical homogenate were similar in wild-type (Wt) and APP/PS1 rats at 3 months of age (prior to Aß plaque deposition), but significantly increased in APP/PS1 rats by 9 and 18-20 months of age (after the onset of plaque deposition). These age-dependent differences were driven by proportional increases in NPR in membrane-associated cortical fractions. Genotype-related differences in NPR expression were also seen in the hippocampus, which exhibits significant Aß pathology, but not in the cerebellum, which does not. Plasma analyses revealed increased levels of a 26 kDa NPR fragment in APP/PS1 rats relative to Wt rats by 18-20 months of age, which correlated with the levels of full-length NPR in cortex. Our findings indicate that cerebral accumulation of NPR and Aß occurs with similar temporal and regional patterns in the APP/PS1 model, and suggest that a 26 kDa plasma NPR fragment may represent a peripheral biomarker of this process.