Susan P. McGrath

Impact of pulse oximetry surveillance on rescue events and intensive care unit transfers: a before-and-after concurrence study.

Background:Some preventable deaths in hospitalized patients are due to unrecognized deterioration. There are no publications of studies that have instituted routine patient monitoring postoperatively and analyzed impact on patient outcomes. Methods:The authors implemented a patient surveillance system based on pulse oximetry with nursing notification of violation of alarm limits via wireless pager. Data were collected for 11 months before and 10 months after implementation of the system. Concurrently, matching outcome data were collected on two other postoperative units. The primary outcomes were rescue events and transfers to the intensive care unit compared before and after monitoring change. Results:Rescue events decreased from 3.4 (1.89–4.85) to 1.2 (0.53–1.88) per 1,000 patient discharges and intensive care unit transfers from 5.6 (3.7–7.4) to 2.9 (1.4–4.3) per 1,000 patient days, whereas the comparison units had no change. Conclusions:Patient surveillance monitoring results in a reduced need for rescues and intensive care unit transfers.

A Review of Current and Emerging Approaches to Address Failure-to-Rescue

Failure-to-Rescue, defined as hospital deaths after adverse events, is an established measure of patient safety and hospital quality. Until recently, approaches used to address failure-to-rescue have been focused primarily on improvement of response to a recognized patient crisis, with limited success in terms of patient outcomes. Less attention has been paid to improving the detection of the crisis. A wealth of retrospective data exist to support the observation that adverse events in general ward patients are preceded by a significant period (on the order of hours) of physiologic deterioration. Thus, the lack of early recognition of physiologic decline plays a major role in the failure-to-rescue problem.

Pulse Oximeter Plethysmographic Waveform Changes in Awake, Spontaneously Breathing, Hypovolemic Volunteers

BACKGROUND:The primary objective of this study was to determine whether alterations in the pulse oximeter waveform characteristics would track progressive reductions in central blood volume. We also assessed whether changes in the pulse oximeter waveform provide an indication of blood loss in the hemorrhaging patient before changes in standard vital signs. METHODS:Pulse oximeter data from finger, forehead, and ear pulse oximeter sensors were collected from 18 healthy subjects undergoing progressive reduction in central blood volume induced by lower body negative pressure (LBNP). Stroke volume measurements were simultaneously recorded using impedance cardiography. The study was conducted in a research laboratory setting where no interventions were performed. Pulse amplitude, width, and area under the curve (AUC) features were calculated from each pulse wave recording. Amalgamated correlation coefficients were calculated to determine the relationship between the changes in pulse oximeter waveform features and changes in stroke volume with LBNP. RESULTS:For pulse oximeter sensors on the ear and forehead, reductions in pulse amplitude, width, and area were strongly correlated with progressive reductions in stroke volume during LBNP (R2 ≥ 0.59 for all features). Changes in pulse oximeter waveform features were observed before profound decreases in arterial blood pressure. The best correlations between pulse features and stroke volume were obtained from the forehead sensor area (R2 = 0.97). Pulse oximeter waveform features returned to baseline levels when central blood volume was restored. CONCLUSIONS:These results support the use of pulse oximeter waveform analysis as a potential diagnostic tool to detect clinically significant hypovolemia before the onset of cardiovascular decompensation in spontaneously breathing patients.

The feasibility of using a forehead reflectance pulse oximeter for automated remote triage

The extreme conditions of combat and multi-casualty rescue often make field triage difficult and put the medic or first responder at risk. In an effort to improve Reid triage, we have developed an automated remote triage system called ARTEMIS for use in the battlefield or disaster zone. This preliminary research seeks to empirically demonstrate that the Nonin forehead reflectance pulse oximeter is a viable sensor for measuring essential physiological parameters used in automated field triage systems such as ARTEMIS.

Using The Morphology of Photoplethysmogram Peaks to Detect Changes in Posture

The morphology of the pulsatile component of the photoplethysmogram (PPG) has been shown to vary with physiology, but changes in the morphology caused by the baroreflex response to orthostatic stress have not been investigated.Using two FDA approved Nonin® pulse oximeters placed on the finger and ear, we monitored 11 subjects, for three trials each, as they stood from a supine position. Each cardiac cycle was automatically extracted from the PPG waveform and characterized using statistics corresponding to normalized peak width, instantaneous heart rate, and amplitude of the pulsatile component of the ear PPG. A nonparametric Wilcoxon rank sum test was then used to detect in real-time changes in these features with p < 0.01.In all 33 trials, the standing event was detected as an abrupt change in at least two of these features, with only one false alarm. In 26 trials, an abrupt change was detected in all three features, with no false alarms. An increase in the normalize peak width was detected before an increase in heart rate, and in 21 trials a peak in the feature was detected before or as standing commenced. During standing, the pulse rate always increases, and then amplitude of the ear PPG constricts by a factor of two or more.We hypothesis that the baroreflex first reduces the percentage of time blood flow is stagnant during the cardiac cycle, then increases the hear rate, and finally vasoconstricts the peripheral tissue in order to reestablishing a nominal blood pressure. These three features therefore can be used as a detector of the baroreflex response to changes in posture or other forms of blood volume sequestration.

A Comparison of Oxygen Saturation Data in Inpatients with Low Oxygen Saturation Using Automated Continuous Monitoring and Intermittent Manual Data Charting

BACKGROUND:The manual collection and charting of traditional vital signs data in inpatient populations have been shown to be inaccurate when compared with true physiologic values. This issue has not been examined with respect to oxygen saturation data despite the increased use of this measurement in systems designed to assess the risk of patient deterioration. Of particular note are the lack of available data examining the accuracy of oxygen saturation charting in a particularly vulnerable group of patients who have prolonged oxygen desaturations (mean SpO2 <90% over at least 15 minutes). In addition, no data are currently available that investigate the often suspected “wake up” effect, resulting from a nurse entering a patient’s room to obtain vital signs. METHODS:In this study, we compared oxygen saturation data recorded manually with data collected by an automated continuous monitoring system in 16 inpatients considered to be at high risk for deterioration (average SpO2 values <90% collected by the automated system in a 15-minute interval before a manual charting event). Data were sampled from the automatic collection system from 2 periods: over a 15-minute period that ended 5 minutes before the time of the manual data collection and charting, and over a 5-minute range before and after the time of the manual data collection and charting. Average saturations from prolonged baseline desaturations (15-minute period) were compared with both the manual and automated data sampled at the time of the nurse’s visit to analyze for systematic change and to investigate the presence of an arousal effect. RESULTS:The manually charted data were higher than those recorded by the automated system. Manually recorded data were on average 6.5% (confidence interval, 4.0%–9.0%) higher in oxygen saturation. No significant arousal effect resulting from the nurse’s visit to the patient’s room was detected. CONCLUSIONS:In a cohort of patients with prolonged desaturations, manual recordings of SpO2 did not reflect physiologic patient state when compared with continuous automated sampling. Currently, early warning scores depend on manual vital sign recordings in many settings; the study data suggest that SpO2 ought to be added to the list of vital sign values that have been shown to be recorded inaccurately.

A medical assessment algorithm for automated remote triage

Ascertaining the medical status of soldiers deployed in the battlefield is essential for medical and strategic decision-making. The diagnostic and treatment methods used in the battlefield are currently suboptimal due to limited field resources and communication mechanisms. The system described herein is designed to remotely assess the medical status of deployed soldiers to augment resources of the medic, promoting more efficient and timely treatment of battlefield injuries. Key components of this combat casualty care system are an intelligent mobile agent information management network, a sensor capable of collecting pertinent physiological data, an assessment and alert algorithm, an ad hoc wireless routing system, and a user interface. The focus of this paper is on the development and preliminary evaluation of our medical model and assessment algorithms, which were implemented using hard-coded rules and a fuzzy logic approach. We discuss results of our initial simulations, the limitations of our medical model, and present a strategy for testing and improving different implementations of our model.

A Tele-ultrasound System for Real-time Medical Imaging in Resource-limited Settings

Ultrasound has great potential as an imaging technology in resource-limited environments. We present a novel tele-ultrasound approach designed to realize that potential by connecting a remote technician to a radiologist. Our preliminary system, based on open-source software and commercial off-the-shelf hardware, uses custom software and a satellite Internet connection to create this link. We also present the results of testing this system in both laboratory and real-world environments.

Using a forehead reflectance pulse oximeter to detect changes in sympathetic tone

The extreme conditions of combat and multi-casualty rescue often make field triage difficult and put the medic or first responder at risk. In an effort to improve field triage, we have developed an automated remote triage system called ARTEMIS (automated remote triage and emergency management information system) for use in the battlefield or disaster zone. Common to field injuries is a sudden change in arterial pressure resulting from massive blood loss or shock. In effort to stabilize the arterial pressure, the sympathetic system is strongly activated and sympathetic tone is increased. This preliminary research seeks to empirically demonstrate that a forehead reflectance pulse oximeter is a viable sensor for detecting sudden changes in sympathetic tone. We performed the classic supine-standing experiment and collected the raw waveform, the photoplethysmogram (PPG), continuously using a forehead reflectance pulse oximeter. The resulting waveform was processed in Matlab using various spectral analysis techniques (FFT and AR). Our preliminary results show that a relative ratio analysis (low frequency power/high frequency power) for both the raw PPG signal and its derived pulse statistics (height, beat-to-beat interval) is a useful technique for detecting change in sympathetic tone resulting from positional change.

Identifying Airway Obstructions Using Photoplethysmography (PPG)

Objective. Central and obstructive apneas are sources of morbidity and mortality associated with primary patient conditions as well as secondary to medical care such as sedation/analgesia in post-operative patients. This research investigates the predictive value of the respirophasic variation in the noninvasive photoplethysmography (PPG) waveform signal in detecting airway obstruction. Methods. PPG data from 20 consenting healthy adults (12 male, 8 female) undergoing anesthesia were collected directly after surgery and before transfer to the Post Anesthesia Care Unit (PACU). Features of the PPG waveform were calculated and used in a neural network to classify normal and obstructive events. Results. During the postoperative period studied, the neural network classifier yielded an average (±standard deviation) 75.4 (±3.7)% sensitivity, 91.6 (±2.3)% specificity, 84.7 (±3.5)% positive predictive value, 85.9 (±1.8)% negative predictive value, and an overall accuracy of 85.4 (±2.0)%. Conclusions. The accuracy of this method shows promise for use in real-time monitoring situations.