Stability and long-term durability of Raman spectroscopy.

OBJECTIVE: The purpose of this study was to assess in the clinical setting the reliability and long-term stability of Raman spectroscopy as implemented in the RASCAL multiple gas analyzer, and to describe/analyze failure modes that manifest in regular use. METHODS: Twenty-one RASCAL analyzers were tested for accuracy and precision. Without any prior external calibration or alignment, all gas analyzers were systematically tested over a consecutive 36-hour period with standard gas mixtures. Data were analyzed by evaluating the difference between the predicted value and observed value (bias residual) as reported by each RASCAL: All service data (29 months) also were analyzed for information on durability and failure modes. RESULTS: The RASCAL exhibited a significant tendency to overread high concentrations of agent (isoflurane/enflurane); 4 of 16 instruments misread an agent by more than +/- 0.30%. Four of 16 instruments could not properly identify volatile agents in low concentrations (0.31 vol%). Inventory records show that water contamination led to the replacement of gas sample sets an average of 1.5 +/- 1.2 times per case over the 29-month period. Although many instruments had not been externally calibrated for over 63 days, linearity proved acceptable for CO2, O2, N2O, and N2. A rationale for instrument behavior and major failure modes, based on the instrument design, was developed. CONCLUSIONS: The manufacturer's suggested calibration intervals (30 days) were found to be more than adequate for reliable gas analysis using Raman spectroscopy. Without the benefit of frequent calibrations and as time passes, volatile agent quantification can be expected to drift significantly upward.

Clinical evaluation of a Raman scattering multiple gas analyzer for the operating room.

A Raman spectrometer multiple gas analyzer was used to monitor inspired and expired concentrations of oxygen (O2), nitrogen (N2), carbon dioxide (CO2), nitrous oxide (N2O), halothane, and isoflurane in 10 patients. The Raman spectrometer and a dedicated mass spectrometer were connected to each patient to provide a comparison of the two instruments. Results show that readings from the Raman spectrometer are within 0.62 vol% of known gas standards for O2, N2, N2O; within 0.03 vol% for CO2; and within 0.04 vol% for halothane, enflurane and isoflurane. Clinical results show that Raman spectrometer readings are within 1.36 vol% of the mass spectrometer readings for O2, N2, N2O; within 0.01 vol% for CO2; and within 0.22 vol% for halothane and isoflurane. The clinical and laboratory results indicate the Raman spectrometer monitors airway gases and vapors as accurately as a dedicated mass spectrometer.

Dedicated monitoring of anesthetic and respiratory gases by Raman scattering.

The monitoring of respiratory and anesthetic gases in the operating room is important for patient safety. This study measured the accuracy and response time of a multiple-gas monitoring instrument that uses Raman light scattering. Measurements of oxygen, carbon dioxide, nitrogen, nitrous oxide, halothane, enflurane, and isoflurane concentrations were compared with a gas mixer standard and with measurements made with an infrared anesthetic agent analyzer. Correlation coefficients were all greater than 0.999, and probable errors were less than 0.43 vol% for the gases and less than 0.03 vol% for the volatile anesthetics. Response time was 67 ms with a sample flow rate of 150 ml/min. There was some signal overlap between nitrogen and nitrous oxide and between the volatile anesthetic agents. Such overlap can be compensated for by linear matrix analysis. The Raman instrument promises a monitoring capability equivalent to the mass spectrometer and should prove attractive for the monitoring of respiratory and anesthetic gases in the operating room.

Retrieval and analysis of a clinical total artificial heart.

Examination by light microscopy, scanning electron microscopy (SEM), and x-ray microanalysis of a clinical total artificial heart (TAH) implanted for 112 days revealed no evidence of calcification, pannus, or vegetative thrombus. A macroscopic thrombus was seen along the suture line in the right atrium but did not obstruct blood flow or valve function. Microscopic thrombi (less than 0.1 mm) and evidence of microemboli were observed on the pumping diaphragm using SEM. Characterization of selected polyetherurethane (PEU) samples from the pumping bladders and housing by Curie-point pyrolysis mass spectrometry (Py-MS) revealed unexpected differences between postmortem retrieved ventricles. Although the origin of these differences could be traced back to batch-to-batch variations in the original PEU material (Biomer), the precise nature of the observed differences in chemical structure and/or composition is still unknown. Numerical comparison between pyrolysis mass spectra from PEU samples exposed to blood or tissue and unexposed samples from the same ventricles did not detect evidence of biodegradation. Continual improvements in fabrication and quality control should minimize surface imperfections and ensure polymer reproducibility; however, existing materials and design parameters appear to be adequate for continued clinical implantation.

Blood-materials interactions: the minimum interfacial free energy and the optimum polar/apolar ratio hypotheses.

Numerous hypotheses exist to explain observed blood-materials interactions. It is the purpose of this article to test two popular hypotheses, namely, the minimum interfacial free energy hypothesis and the optimum polar/apolar ratio hypothesis. Methacrylate polymers and copolymers were characterized using the captive bubble underwater contact angle method; bulk water content was determined by gravimetric methods; streaming potential measurements were made; and surface roughness and possible particulate contamination were evaluated by reflected light microscopy. In vitro blood tests include whole blood clotting time measurements on polymer-coated tubes; centrifugal force platelet adhesion on polymer-coated coverslips; and a measure of the partial thromboplastin time, Russell's viper venom time (Stypven time), and the prothrombin time of native whole blood exposed to polymer-coated microscope slides. Results suggest that platelet adhesion correlates in the opposite direction of whole blood clotting time and partial thromboplastin time, emphasizing the need for a multiparameter approach to blood-materials testing. Based on these tests the minimum interfacial free energy hypothesis is not supported. In fact, the data suggest the opposite to be true. It is apparent that platelet adhesion can be a misleading indicator of blood compatibility. Neither hypothesis can explain the apparent conflict between the platelet adhesion data and the coagulation time data.

Progestin permeation through polymer membranes III: Polymerization solvent effect on progesterone permeation through hydrogel membranes.

Hydrogels prepared from poly(hydroxyethyl methacrylate) are biocompatible and highly permeable to low molecular weight solutes. Permeation rates can be varied by altering the cross-linker concentration or using copolymers; the latter are chosen to alter the hydrogel equilibrium hydration. These factors suggest that hydrogels are good candidates for controlled-release drug delivery devices. Hydrogels may be synthesized using various temperatures, initiators (nature and concentration), and solvents (nature and concentration). This study demonstrated that progesterone permeation through poly(hydroxyethyl methacrylate) films is independent of polymerization solvent (nature and concentration) for the solvents, water, ethanol, and tert-butyl alcohol. The importance of hydrogel equilibrium hydration in progesterone permeation is emphasized.