Delays in the detection of hypoxemia due to site of pulse oximetry probe placement.

STUDY OBJECTIVES: To determine if there were any differences in the time to detect hypoxemia related to the site of peripheral pulse oximetry (ear, hand, and foot) during the rapid induction of hypoxemia in healthy volunteers. DESIGN: Repeated-measures, longitudinal, observational study. SETTING: Anesthesia clinical research area of the Department of Anesthesiology. PATIENTS: 13 healthy volunteers, aged 18 to 44 years. INTERVENTIONS: Nellcor N-200 (Nellcor, Inc., Pleasanton, CA) oximeter probes were placed at the ear, hand, and foot. All units were turned on simultaneously with averaging times set for 5 seconds and signals sampled at 2 Hz. A computer-controlled anesthesia circuit was employed to induce mild hypercapnia and hyperoxia (end-tidal gas partial pressures: PETCO2 = 42 +/- 2 mmHg and PETO2 = 130 mmHg) for 5 minutes. PETO2 was then decreased to 45 +/- 2 mmHg over 60 seconds and held at that value for 5 minutes. MEASUREMENTS AND MAIN RESULTS: The mean differences in time (sec) for pulse oximeters to detect hypoxemia (read less than 90%) between probe sites were determined and compared. The following mean differences in time (sec) for pulse oximeters to detect hypoxemia (read less than 90%) between probe sites were found: ear-hand = 6; hand-foot = 57; ear-foot = 63. Paired t-tests revealed statistically significant mean time delay differences of 51 seconds (p < 0.005) and 57 seconds (p < 0.005) for ear-hand versus hand-foot and for ear-hand versus ear-foot, respectively. CONCLUSIONS: In healthy volunteers, significant delays in the detection of acute hypoxemia by pulse oximetry occur when pulse oximeters are placed at the toe as compared with probes at either the ear or hand.

Evaluation in volunteers of the VIA V-ABG automated bedside blood gas, chemistry, and hematocrit monitor.

OBJECTIVE: To evaluate the VIA V-ABG (VIA Medical Corp.) point-of-care blood gas and chemistry monitor in healthy human volunteers, with particular emphasis on the measurement of blood gases. METHODS: Experimental conditions were varied by intermittently subjecting volunteers to either isocapnic hypercapnia (end-tidal (ET), PETCO2 = 50+/-2 mmHg, ETPO2 = 130+/-5 mmHg) or isocapnic hypoxia (PETCO2 = 42+/-2, PETO2 + 45+/-2 mmHg) in addition to room air breathing. Measurements by the VIA V-ABG device were compared with paired samples and measurements performed by two ABL Radiometers (505 and 500). Analysis of results includes bias and precision plots and comparison of results with minimal performance criteria as established by CLIA. RESULTS: Nineteen volunteers yielded 222 matched samples. The range of values were 7.32-7.61 for pH, 20.9-51.6 mmHg for PCO2, 27.9-184.5 mmHg for PO2, 134-141 mmol/l for Na, 3.1-4.1 mmol/l for K, and 30.0-50.4% for hematocrit. Bias and precision (+/-2 sd) for pH was 0.01 and 0.04, for PCO2 was 0.4 and 4.8, for PO2 was 1.0 and 17.0, for Na was -0.3 and 5.2, for K was 0.1 and 0.2, and for Hct was 2.0 and 5.4. CONCLUSIONS: Over the range of blood gas values assessed, blood gas measurements by the VIA V-ABG device were clinically acceptable and met minimal performance criteria utilizing current Medicare CLIA proficiency standards. Performance criteria were also met by the VIA V-ABG device for Na, K, and Hct measurements but the range of values was too narrow to allow characterization of clinical acceptability. The VIA V-ABG device appears to perform well compared with the results which have been published for other point-of-care devices. Comparison between different studies investigating point-of-care devices is difficult due to several factors (range of values measured, comparison device, population studied, etc.). Some of these instruments, including the VIA V-ABG device, may serve quite well as point-of-care devices to perform certain tests at the bedside. Whether or not any of these devices can substitute for traditional laboratory blood gas and chemistry measurements remains an issue that is not adequately studied.

A hospital/school science fair mentoring program for middle school students.

The Massachusetts General Hospital (MGH) and the James P. Timilty Middle School established a partnership to enhance science education, promote faculty development, and improve the health status and academic performance of all Timilty students. This article describes one of the Partnership's Science Connection programs, the Science Fair Mentoring Program, designed to enhance middle school science education, inform urban early adolescents about professions in the health field, inspire them to pursue postsecondary study in the health sciences, and prepare them for rigorous academic work in high school. In this program, hospital-based clinical and research staff mentor young adolescent students. The authors describe the planning, implementation, and evaluation of the Science Fair Mentoring Program as an innovative learning experience.

Comparison of linear and branched peptide forms (MAPs) in the induction of T helper responses to point-mutated ras immunogens.

The utility of multiple antigenic peptides (MAPs) for the induction of antibody and cellular immune responses in animal models has been demonstrated for a variety of peptide epitopes involved in human disease. However, little is known about immune responses to MAPs constructed with antigenic tumor epitopes, nor has peptide specificity in branched forms been addressed. A potentially important advantage of the MAP system over linear peptide immunogens for clinical applications is elimination of the need for a protein carrier with its associated toxicity and immunogenicity. Here, we examined cellular immune responses following in vivo administration of MAPs incorporating a 13-mer T helper epitope from point-mutated ras p21 (ras V12) and compared the potency of the responses to that of the linear peptide. The Gly --> Val mutation in position 12, which is associated with a range of human carcinomas, represents a useful system for evaluating the specificity of the immune response. In initial studies with the point-mutated linear peptide epitope, optimal in vitro proliferation responses were obtained following sc administration of the peptide in a squalane-containing adjuvant formulation. Comparative immunization studies using point-mutated MAPs bearing two, four, or eight branches were administered either in saline or in adjuvant. These studies showed that adjuvant was required for the induction of cellular immune responses using both linear and all three forms of branched peptides. Moreover, there was no apparent advantage of using any of the MAPs vs linear peptide when equivalent mass amounts were administered, i.e., the intensity of the immune response was no greater using any of the branched structures compared to the linear form. Specificity of the in vivo responses for both the linear and the MAP immunogens was demonstrated by the higher stimulation indices observed in vitro in the presence of the mutant ras V12 vs the normal ras G12 linear peptide. No apparent cellular immune response to the MAP core structure itself was observed. However, a nonspecific response to the two-branched MAP2G12 structure was observed in some assays, the nature of which is unknown at this time. This work represents the first reported investigation of a cellular immune response using MAP immunogens incorporating a tumor-specific peptide epitope and demonstrates that linear peptides are as efficient as three different MAP structures in the generation of specific T cell responses.

Peptide-specific activation of cytolytic CD4+ T lymphocytes against tumor cells bearing mutated epitopes of K-ras p21.

Alterations in the ras p21 protein have been associated with both rodent and human neoplasia. Thus, mutated ras p21 proteins may bear unique antigenic epitopes for immune recognition, such as by T cells, which have been implicated in host antitumor activity. Synthetic peptides that mimic segments of mutated ras p21 have been reported to be immunogenic in mice in vivo, although detailed functional analyses remains undefined. Here, in a murine model, we explored and characterized distinct effector properties of host-derived T lymphocytes reactive to mutated ras peptides, which was consistent with the CD4+ T helper type 1 (Th1) subset. BALB/c mice (H-2d) were immunized with a purified peptide, 13 amino acids in length, containing the substitution of Gly (G12) to Val (V12) at position 12, which is commonly found in human carcinomas. An alpha beta T cell receptor-positive, CD3+, CD4+, CD8- T cell line was established, which expressed peptide-specific proliferation. Cytokine assays revealed the production of interleukin-2, interferon-gamma, tumor necrosis factor and granulocyte-macrophage colony-stimulating factor. Moreover, antigen-specific cytotoxicity was demonstrable against: (1) Iad-bearing A20 tumor cells incubated with exogenously bound V12 peptide; and (2) A20 tumor cells transduced with the K-ras p21 oncogene encoding the corresponding point mutation. CD4(+)-mediated cytotoxicity was major histocompatibility complex (MHC) class II-restricted, as revealed by the absence of lysis against MHC class II- P815 targets, inhibition of A20 lysis with anti-Iad monoclonal antibodies, and induction of lysis against L cell targets transfected with E alpha A beta d. Independent isolation of a second CD4+ V12 line revealed a very similar cytolytic and MHC class II-restricted profile. Overall, these data demonstrated that peptide immunization produced a CD4+ Th1 response that specifically recognized tumor cells expressing endogenous activated K-ras epitopes, which may have implications for the development of peptide-based active immunotherapies.

Subcutaneous emphysema in a finger following an injection injury.

This is a case report of surgical emphysema in a finger resulting from a high velocity injection accident.

Skin grafts on fingers: a simple and effective method for use in the accident and emergency department.

A method is described of retaining small skin grafts in place on fingers by means of adhesive paper skin closures, and the results obtained in 20 consecutive cases are analysed. It is suggested that the technique may be of particular value in the Accident and Emergency Department.