STABILITY AND LONG-TERM DURABILITY OF RAMAN-SPECTROSCOPY

Objective. The purpose of this study was to assess in the clinical set ting the reliability and long-term stability of Raman spectroscopy as implemented in the RASCAL multiple gas analyzer, and to describe/analy ze failure modes that manifest in regular use. Methods. Twenty-one RAS CAL analyzers were tested for accuracy and precision. Without any prio r external calibration or alignment, all gas analyzers were systematic ally tested over a consecutive 36-hour period with standard gas mixtur es. Data were analyzed by evaluating the difference between the predic ted value and observed value (bias residual) as reported by each RASCA L. All service data (29 months) also were analyzed for information on durability and failure modes. Results. The RASCAL exhibited a signific ant tendency to overread high concentrations of agent (isoflurane/enfl urane); 4 of 16 instruments misread an agent by more than +/-0.30%. Fo ur of 16 instruments could not properly identify volatile agents in lo w concentrations (0.31 vol%). Inventory records show that water contam ination 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 instrumen ts had not been externally calibrated for over 63 days, linearity prov ed acceptable for CO2, O2, N2O, and N2. A rationale for instrument beh avior and major failure modes, based on the instrument design, was dev eloped. Conclusions. The manufacturer's suggested calibration interval s (30 days) were found to be more than adequate for reliable gas analy sis using Raman spectroscopy. Without the benefit of frequent calibrat ions and as time passes, volatile agent quantification can be expected to drift significantly upward.