Effects of oral diazepam on intravenous access in same day surgery patients.

STUDY OBJECTIVE: To determine the effects of 5 mg oral diazepam on vein quality, patient anxiety, and intravenous (i.v.) access. DESIGN: Prospective, randomized, double-blind, placebo controlled study. SETTING: Preoperative holding area of a large university hospital. PATIENTS: 202 adult ASA physical status I, II, and III patients scheduled for elective outpatient surgery. INTERVENTIONS: Patients were randomized to receive either 5 mg oral diazepam or placebo, 30 minutes prior to i.v. access. MEASUREMENTS AND MAIN RESULTS: Vein quality and patient anxiety were assessed prior to, and 30 minutes following, premedication (just prior to venipuncture) using a 5 point ordinal scale and 10 cm visual analog scale, respectively. The number of attempts at venous access and the gauge of the catheter used were also recorded. Baseline patient anxiety was similar between the two groups and both showed a significant improvement in patient anxiety at 30 minutes following drug administration. The diazepam group, however, had a significantly greater reduction in anxiety scores (p < 0.05). There were no differences in baseline vein quality between the two groups; however, the quality of the vein was subjectively improved following diazepam administration. The mean number of attempts at i.v. access between the diazepam group (1.26 +/- 0.56) and the placebo group (1.32 +/- 0.65) was not significantly different. However, the ability to place larger gauge catheters was significantly enhanced in the diazepam group. CONCLUSIONS: The administration of 5 mg oral diazepam prior to the establishment of i.v. access improved vein quality and decreased patient anxiety. This technique may be a useful method for i.v. catheter placement, particularly when large gauge catheters are required, or when difficult i.v. access is anticipated.

Evaluation of the efficacy of routine preoperative electrocardiograms.

OBJECTIVE: To evaluate the efficacy of routine preoperative electrocardiograms (ECG) in predicting perioperative cardiovascular complications in an essentially healthy population. DESIGN: Retrospective chart review. SETTING: The adult hospital of a large academic medical center. PARTICIPANTS: One thousand ASA class I and II adult patients undergoing a number of different elective surgical procedures. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The mean age of the population was 48 years (range, 18 to 88), and 53% were female. Fifty-seven percent of the population had a preoperative ECG, of which 56.5% were considered normal, 37.8% were abnormal, and 6.6% were considered borderline. Twenty-seven percent of the population presented with cardiovascular risk factors, and of these, 93.2% had an ECG performed. Seventy-three percent of patients had no cardiovascular risk factors, and of these, 44.5% had a preoperative ECG. Patients who had cardiovascular risk factors had significantly more abnormal ECGs than those without (51% v 26.1%,); however, there was no difference in the prevalence of perioperative events between the two groups. The positive predictive value of an abnormal ECG for a perioperative event was slightly greater for patients with cardiovascular risk factors than for those without (42.7% v 34.7%, respectively); however, this difference was not significant. In addition, a normal ECG was just as predictive as an abnormal one. CONCLUSIONS: Results of this study suggest that the practice of routine ECG screening for patients with no cardiovascular risk factors is a poor predictor of perioperative complications in this patient population. A review of the current criteria for ordering preoperative ECGs may reduce the number of unnecessary tests and improve cost-effectiveness.

The effects of a blood-salvaging device on blood containing a hemoglobin-based oxygen carrier, HBOC-201.

OBJECTIVES: Hemoglobin-based oxygen carriers will be used concurrently with intraoperative blood salvage. The effects of salvage and processing on blood containing one such solution (HBOC-201; Biopure Corp, Boston, MA) were studied. DESIGN: Prospective, randomized. SETTING: Laboratory. INTERVENTIONS: Sixteen blood units from healthy volunteers had either HBOC (1,500 mg/dL; n = 10) or normal saline (equivalent volume; n = 6) added. All units were salvaged and processed using a blood salvage device. Samples were analyzed for the concentration and molecular weight distribution of plasma hemoglobin and red cell morphology presalvage (pre) and following processing and washing (post 1). Five of the HBOC units underwent a second 1,000 mL wash (post 2). MEASUREMENTS AND MAIN RESULTS: Processing and washing decreased the concentration of plasma hemoglobin (mg/dL) in HBOC units (1311 +/- 265 pre to 27.8 +/- 19.6 post 1 to 6.5 +/- 2.19 post 2), but did not change the plasma hemoglobin concentration in saline units (2.05 +/- 1.27 pre v 3.18 +/- 0.79 post 1). Total plasma hemoglobin in HBOC units (6.56 +/- 2.19) was significantly greater than in saline units (3.18 +/- 0.79), even after the second wash (post 2). The concentration of unstable hemoglobin in the plasma phase was not different between groups. Red cell morphology was altered by the salvage process but was not different between groups. CONCLUSIONS: Salvage and processing of blood containing HBOC yield concentrated red cells that are indistinguishable from those obtained from blood without HBOC. Residual HBOC remains but is unchanged from the HBOC initially administered.

Clinical evaluation of a prototype motion artifact resistant pulse oximeter in the recovery room.

The frequency and nature of spurious pulse oximetry readings were compared using both a conventional pulse oximeter (CPO) and a prototype Masimo signal extraction technology pulse oximeter (Masimo SET). At a university hospital, 50 ASA physical status I-IV adult patients who underwent general or spinal-epidural anesthesia were selected from a group of 250 patients on the basis of high-alarm generation with routine postoperative pulse oximetry. Pulse oximetry data were recorded simultaneously from both devices with a computer. Overall, the CPO alarm frequency (i.e., oxygen saturation < 90%, or complete signal loss) was once every 13 min, and 87% of these alarms were considered false. Alarms were considered false based on reference electrocardiographs (16 patients), arterial blood gases (7 patients), and clinical assessment. The prototype Masimo SET device alarm frequency was once every 30 min, and 59% of these were considered false. During arm motion with 15 patients, the CPO device produced spurious signals on 54 occasions compared with five for the prototype Masimo SET. The incidence of artifactual pulse oximetry events during patient motion appear to be substantially reduced with the prototype Masimo SET device, relative to a CPO device.

Accuracy and precision of a new, portable, handheld blood gas analyzer, the IRMA.

OBJECTIVE: The accuracy and precision of the new IRMA (Immediate Response Mobile Analysis System, Diametrics, Inc., St. Paul, MN) handheld blood gas analyzer was compared with that of two benchtop blood gas analyzers. The IRMA consists of a notebook-sized machine and disposable cartridges, each containing a pH, a CO2 and an O2 electrode, and provides bedside (point-of-care) blood gas analysis. METHODS: A total of 172 samples (arterial and mixed venous) were obtained from 25 informed, consenting patients undergoing cardiopulmonary bypass. The pH, PCO2 and PO2 of each sample was determined on four blood gas analyzers: NOVA Statlabs Profile 5 (NOVA Biomedical, Waltham, MA), the ABL-50 (Radiometer, West Lake, OH), and two IRMA machines. Linear regression and bias +/- precision were determined, comparing each of the analyzers with the NOVA. RESULTS: All three machines showed a similar, high degree of correlation with the NOVA for pH, PCO2, and PO2. The bias and precision of the IRMA machines compared with the NOVA was similar to that of the ABL compared with the NOVA for pH (NOVA:ABL -0.005 +/- 0.011; NOVA:IRMA 1 = 0.0026 +/- 0.025; NOVA:IRMA 2 = 0.0021 +/- 0.025), for PCO2 (NOVA:ABL = -1.4 +/- 1.3 mmHg; NOVA: IRMA 1 = -1.3 +/- 1.9 mmHg; NOVA: IRMA 2 = -1.2 +/- 2.1 mmHg) and PO2 (NOVA:ABL = 3.6 +/- 21.1 mmHg; NOVA:IRMA 1 = 3.4 +/- 19.9 mmHg; NOVA:IRMA 2 = 6.3 +/- 20.9 mmHg). The bias found for pH, PCO2, and PO2 was not affected by extremes of temperature (range 25.5-40 degrees C) or hematocrit (range 11-44%) for any machine. CONCLUSIONS: The new technology incorporated in the IRMA blood gas analyzer provides results with an accuracy that is similar to that of benchtop analyzers, but with all of the advantages of point-of-care analysis.

Near-infrared spectroscopy: theory and applications.

In conclusion, NIRS appears to offer both a new monitoring modality and new information about cerebral oxygenation. Technical problems in the application of this technology persist, most notably determination of pathlength and the volume of tissue interrogated. Those familiar with the history of pulse oximetry will recall that although Millikan developed an ear oximeter in 1947, it was not until Aoyagi combined recognition of the pulse signal with spectroscopy in the 1970s that oximetry was transformed into a clinically applicable monitor. In much the same way, NIRS may find the same tremendous usefulness as a noninvasive monitor of cerebral oxygen utilization, pending resolution of the remaining technical problems.

A pilot study of the effects of a perflubron emulsion, AF 0104, on mixed venous oxygen tension in anesthetized surgical patients.

A pilot study of a perfluorochemical (PFC) emulsion was undertaken to determine whether administration of a perflubron emulsion could result in measurable changes in mixed venous oxygen tension. Seven adult surgical patients received a 0.9-g PFC/kg intravenous dose of perflubron emulsion after acute normovolemic hemodilution (ANH). Hemodynamic and oxygen transport data were collected before and after ANH, immediately after PFC infusion, and at approximate 15-min intervals throughout the surgical period. There were no clinically significant hemodynamic changes associated with the administration of the PFC emulsion. There was a significant increase in mixed venous oxygen tension (PVO2) after the PFC infusion, while cardiac output and oxygen consumption were unchanged. As surgery progressed, the hemoglobin concentration decreased with ongoing blood loss while PVO2 values remained at or above predosing levels. Peak perflubron blood levels were 0.8 g/dL immediately postinfusion, and approximately 0.3 g/dL at 1 h. This pilot study demonstrates that administration of perflubron emulsion results in measurable changes in mixed venous oxygen tension during intraoperative ANH.

Pulse oximetry.

Pulse oximetry is a reliable, noninvasive, easy to use means of continuously determining arterial oxygen saturation in virtually any setting. This article details the historical and technical development of this monitor; reviews the literature on application, accuracy, and response; and presents an overview of future advances.

Noninvasive oxygen monitoring techniques.

As this article demonstrates, tremendous progress has been made in the techniques of oxygen measurement and monitoring over the past 50 years. From the early developments during and after World War II, to the most recent applications of solid state and microprocessor technology today, every patient in a critical care situation will have several continuous measurements of oxygenation applied simultaneously. Information therefore is available readily to alert personnel of acute problems and to guide appropriate therapy. The majority of effort to date has been placed on measuring oxygenation of arterial or venous blood. The next generation of devices will attempt to provide information about living tissue. Unlike the devices monitoring arterial or venous oxygen content, no "gold standards" exist for tissue oxygenation, so calibration will be difficult, as will interpretation of the data provided. The application of these devices ultimately may lead to a much better understanding of how disease (and the treatment of disease) alters the utilization of oxygen by the tissues.

Effect of carboxyhemoglobin on the accuracy of mixed venous oximetry monitors in dogs.

OBJECTIVE: To assess the accuracy of mixed venous hemoglobin oxygen saturation estimated, using in vivo pulmonary artery reflectance oximetry with ranging concentrations of carboxyhemoglobin. DESIGN: Criterion standard, a comparison of an alternative test to the "gold standard." SETTING: Laboratory animal facility of a large university. SUBJECTS: Five mongrel dogs. INTERVENTIONS: Anesthetized dogs were mechanically ventilated to normocarbia and instrumented with arterial catheters and pulmonary artery oximetry catheters. The dogs were ventilated with increasing inspired concentrations of carbon monoxide, and blood samples were analyzed for fractional concentrations of oxyhemoglobin and carboxyhemoglobin. Carboxyhemoglobin levels ranged from 0% to 70%. At each level of carboxyhemoglobin, FIO2 was varied from 0.21 to 0.09. Co-oximeter readings were compared with mixed venous oxygen saturation measurements of the pulmonary artery oximetry catheter. MEASUREMENTS AND MAIN RESULTS: Mixed venous oxygen saturation measurements from the pulmonary artery oximetry catheter system progressively overestimated fractional oxyhemoglobin in the presence of carboxyhemoglobin. This catheter's mixed venous oxygen saturation reading could be corrected for the presence of carboxyhemoglobin by a derived formula. Regression analysis for corrected mixed venous oxygen saturation (calculated) vs. fractional oxyhemoglobin yields a slope and intercept of 0.98 and -1.01, respectively, with a correlation coefficient of .98. The bias and precision values for fractional oxyhemoglobin vs. mixed venous oxygen saturation (calculated) are 1.9 and 2.2 (n = 66), with bias representing the degree of systematic error or deviation from the true measurement, and precision representing the confidence limits (or standard deviation) for individual variations from the true measurement. CONCLUSIONS: Mixed venous oxygen saturation monitoring does not detect the presence of carboxyhemoglobin and progressively overestimates fractional oxyhemoglobin as carboxyhemoglobin increases. Mixed venous oxygen saturation values of the standard pulmonary artery oximetry catheter approximately equal functional hemoglobin saturation. Bench co-oximeter blood analysis is required in patients suspected of having increased carboxyhemoglobin levels.

Continuous intravascular blood gas monitoring.

The benefit of a continuous intra-arterial blood gas monitor is apparent to any physician who has ever waited for the return of blood gas values at the bedside of a critically ill patient. The potential for rapid detection and prompt treatment of blood gas changes, coupled with immediate evaluation of the effectiveness of a therapeutic intervention, appears great. Whereas these systems may offer a tremendous advance in the physician's ability to track and treat alterations in cardiopulmonary physiology, no large-scale in vivo human trials have yet been reported. The only data available on accuracy, bias, precision, drift, and complication rate are from relatively small trials. Hopefully, when large-scale trials are completed, these systems will live up to their tremendous potential.