Noninvasive respiratory support in the perioperative period.

PURPOSE OF REVIEW: Pulmonary complications ranging from atelectasis to acute respiratory failure are common causes of poor perioperative outcomes. As the surgical population becomes increasingly at risk for pulmonary dysfunction due to increasing age and weight, development of an approach toward respiratory compromise in these patients is becoming ever more important. Given the utility of noninvasive respiratory support (NRS) in acute respiratory failure, it is likewise likely to also be important in the perioperative period. RECENT FINDINGS: NRS is evaluated from preoperative risk assessment to its use in prevention and treatment of acute respiratory failure. Data supporting intraoperative use of NRS including preinduction continuous positive airway pressure and postextubation NRS for high-risk individuals and surgeries are examined. Timing and duration of NRS is also addressed. Finally, NRS is proposed for treatment for postoperative acute respiratory failure as an alternative to invasive rescue maneuvers. SUMMARY: Noninvasive respiratory support should be considered an important adjunct in perioperative pulmonary care. Usage should be individually tailored in regard to timing and application modality specific to patient and surgical circumstances. More studies are needed, however, to determine the relationship demonstrated between short-term improvements in lung function and long-term outcomes.

Critical care organ support: a focus on extracorporeal systems.

PURPOSE OF REVIEW: An extensive search of the literature published in the past 2 years related to critical care organ support was undertaken. This review is limited to those that focus on extracorporeal life support modalities for adults. RECENT FINDINGS: Traditional indications for extracorporeal life support such as oxygenation, carbon dioxide exchange and support of perfusion have expanded to include solute and toxin clearance for kidney, liver and potentially neurological failure. Enhanced understanding of cell-mediated mechanisms of injury may explain multiple-organ dysfunction following single-organ damage. Extracorporeal life support systems can be used safely in patients with traumatic brain, chest, and abdominal injury. 'Emergency perfusion and resuscitation' following traumatic exsanguination is entering clinical trials. SUMMARY: Multiple-organ dysfunction followed by traumatic injury can be treated with multiple-organ support. A total extracorporeal organ support system may be used in the future as a portable, bedside organ support device.

Rapid preparation of high-quality frozen sections using a membrane and vacuum system embedding machine.

BACKGROUND: A wide variety of embedding techniques have been employed to process frozen sections for Mohs micrographic surgery. Prospective data comparing different techniques are lacking. OBJECTIVE: The purpose of this study was to compare tissue processing times and slide quality using the three embedding techniques. METHODS: Seventy-five consecutive Mohs surgery tissue specimens, measuring 1 cm in diameter, were prospectively randomized to processing with the CryoHist, the Cryocup, or the Miami Special. Tissue preparation times were recorded, and slide quality was evaluated. Tissue specimen preparation was standardized to exclude the use of relaxing incisions or other tissue manipulations. In a separate evaluation, slide quality was retrospectively evaluated for 50 large specimens (>2.5 cm) processed with the CryoHist machine. RESULTS: The mean tissue processing time was 11.4 minutes using the CryoHist, 12.9 minutes using the Cryocup, and 12.6 minutes using the Miami Special. Slide quality, using epidermal edge as a primary end point, was superior with the CryoHist compared to the other methods. For large (>2.5 cm) en bloc Mohs specimens processed using the CryoHist, the slide quality was excellent with 92.3% of epidermal edge obtained. CONCLUSIONS: The fully automated CryoHist embedding machine enables high-quality frozen sections to be processed in less time than the Cryocup or the Miami Special. Slide quality is excellent, even for larger specimens.

Pitfalls of insulin pump clocks: technical glitches that may potentially affect medical care in patients with diabetes.

The objective was to raise awareness about the importance of ensuring that insulin pumps internal clocks are set up correctly at all times. This is a very important safety issue because all commercially available insulin pumps are not GPS-enabled (though this is controversial), nor equipped with automatically adjusting internal clocks. Special attention is paid to how basal and bolus dose errors can be introduced by daylight savings time changes, travel across time zones, and am-pm clock errors. Correct setting of insulin pump internal clock is crucial for appropriate insulin delivery. A comprehensive literature review is provided, as are illustrative cases. Incorrect setting can potentially result in incorrect insulin delivery, with potential harmful consequences, if too much or too little insulin is delivered. Daylight saving time changes may not significantly affect basal insulin delivery, given the triviality of the time difference. However, bolus insulin doses can be dramatically affected. Such problems may occur when pump wearers have large variations in their insulin to carb ratio, especially if they forget to change their pump clock in the spring. More worrisome than daylight saving time change is the am-pm clock setting. If this setting is set up incorrectly, both basal rates and bolus doses will be affected. Appropriate insulin delivery through insulin pumps requires correct correlation between dose settings and internal clock time settings. Because insulin pumps are not GPS-enabled or automatically time-adjusting, extra caution should be practiced by patients to ensure correct time settings at all times. Clinicians and diabetes educators should verify the date/time of insulin pumps during patients' visits, and should remind their patients to always verify these settings.

CD4+ T cells recognizing a single self-peptide expressed by APCs induce spontaneous autoimmune arthritis.

We have examined processes leading to the spontaneous development of autoimmune inflammatory arthritis in transgenic mice containing CD4+ T cells targeted to a nominal Ag (hemagglutinin (HA)) and coexpressing HA driven by a MHC class II promoter. Despite being subjected to multiple tolerance mechanisms, autoreactive CD4+ T cells accumulate in the periphery of these mice and promote systemic proinflammatory cytokine production. The majority of mice spontaneously develop inflammatory arthritis, which is accompanied by an enhanced regional immune response in lymph nodes draining major joints. Arthritis development is accompanied by systemic B cell activation; however, neither B cells nor Ab is required for arthritis development, since disease develops in a B cell-deficient background. Moreover, arthritis also develops in a recombinase activating gene-deficient background, indicating that the disease process is driven by CD4+ T cells recognizing the neo-self HA Ag. These findings show that autoreactive CD4+ T cells recognizing a single self-Ag, expressed by systemically distributed APCs, can induce arthritis via a mechanism that is independent of their ability to provide help for autoantibody production.

B cell-mediated antigen presentation is required for the pathogenesis of acute cardiac allograft rejection.

Acute allograft rejection requires the activation of alloreactive CD4 T cells. Despite the capacity of B cells to act as potent APCs capable of activating CD4 T cells in vivo, their role in the progression of acute allograft rejection was unclear. To determine the contribution of B cell APC function in alloimmunity, we engineered mice with a targeted deficiency of MHC class II-mediated Ag presentation confined to the B cell compartment. Cardiac allograft survival was markedly prolonged in these mice as compared to control counterparts (median survival time, >70 vs 9.5 days). Mechanistically, deficient B cell-mediated Ag presentation disrupted both alloantibody production and the progression of CD4 T cell activation following heart transplantation. These findings demonstrate that indirect alloantigen presentation by recipients' B cells plays an important role in the efficient progression of acute vascularized allograft rejection.

Cutting edge: impaired transitional B cell production and selection in the nonobese diabetic mouse.

Developing B cells undergo selection at multiple checkpoints to eliminate autoreactive clones. We analyzed B cell kinetics in the NOD mouse to establish whether these checkpoints are intact. Our results show that although bone marrow production is normal in NOD mice, transitional (TR) B cell production collapses at 3 wk of age, reflecting a lack of successful immature B cell migration to the periphery. This yields delayed establishment of the follicular pool and a lack of selection at the TR checkpoint, such that virtually all immature B cells that exit the bone marrow mature without further selection. These findings suggest that compromised TR B cell generation in NOD mice yields relaxed TR selection, affording autoreactive specificities access to mature pools.

The frequency of double-positive thymocytes expressing an alphabeta TCR clonotype regulates peripheral CD4 T cell compartment homeostasis.

The present study aimed to determine whether the frequency of double positive (DP) thymocytes expressing alphabeta T-cell receptor (TCR) clonotypes at the time of selection regulates peripheral CD4 T-cell compartment size. Scid recipients were inoculated with various ratios of TCR Calpha(0/0) and wild-type bone marrow (BM) stem cells. Increasing the frequency of TCR Calpha(0/0) thymocytes at steady-state introduced a graded decrease in the maturation probability of the total DP thymocyte pool. At 12-14 weeks following BM inoculation, the frequency of TCR Calpha(0/0) DP thymocytes was inversely correlated with that of CD4 single positive (SP) thymocytes. Notwithstanding, a decreased frequency of wild-type DP thymocytes led to a marked increase in their transit efficiency from the DP to SP compartments. The frequency-dependent increase in thymocyte transit efficiency was associated with a CD4 SP cell surface phenotype indicative of increased antigenic experience. Importantly, the frequency of DP thymocytes capable of expressing TCR clonotypes dictated the steady-state size of the peripheral CD4 T cell compartment and its potential for homeostatic proliferation. Collectively, these results indicate that the efficiency of DP to CD4 SP transit is a frequency dependent process, which determines (1) the steady-state size of the peripheral T cell compartment and (2) the threshold for homeostatic expansion of peripheral CD4 T cells.

Specificity-based negative selection of autoreactive B cells during memory formation.

Autoreactive B cells are not completely purged from the primary B cell repertoire, and whether they can be prevented from maturation into memory B cells has been uncertain. We show here that a population of B cells that dominates primary immune responses of BALB/c mice to influenza virus A/PR/8/34 hemagglutinin (HA) are negatively selected in transgenic mice expressing PR8 HA as an abundant membrane-bound Ag (HACII mice). However, a separate population of B cells that contains precursors of memory B cells is activated by PR8 virus immunization and is subsequently negatively selected during the formation of the memory response. Negative selection of PR8 HA-specific B cells altered the specificity of the memory B cell response to a mutant virus containing a single amino acid substitution in a B cell epitope. Strikingly, this skewed reactivity resulted from an increase in the formation of memory B cells directed to non-self-epitopes on the mutant virus, which increased 8-fold in HACII mice relative to nontransgenic mice and precisely compensated for the absence of autoreactive PR8 HA-specific memory B cells. Negative selection of PR8 HA-specific B cells was a dominant process, since B cells from HACII mice could induce negative selection of PR8 HA-specific B cells from BALB/c mice. Lastly, HA-specific memory responses were unaffected by self-tolerance in another lineage of HA-transgenic mice (HA104 mice), indicating that the amount and/or cell type in which self-Ags are expressed can determine their ability to prevent autoreactive memory B cell formation.

Alloreactive CD4 T cell activation in vivo: an autonomous function of the indirect pathway of alloantigen presentation.

Activation of alloreactive CD4 T cells occurs via the direct and indirect pathways of alloantigen presentation. A novel TCR/alloantigen transgenic system was designed that permitted in vivo visualization of CD4 T cell priming through these pathways. When both pathways of alloantigen presentation were intact, CD4 T cell activation in response to cardiac allografts was rapid and systemic by day 4 after transplantation, in contrast to that seen in response to skin allografts, which was delayed until 10-12 days after transplantation. Despite this systemic CD4 T cell activation in response to cardiac allografts, there was a paucity of activated graft-infiltrating CD4 T cells at 4 days posttransplantation. This finding suggests that the initial priming of alloimmune CD4 T cell responses occurs within draining lymphoid organs. Furthermore, alloantigens derived from cardiac allografts failed to promote thymic negative selection of developing thymocytes expressing the alloreactive TCR clonotype. In the absence of a functional direct pathway, the kinetics of activation, anatomic localization, and effector function of alloreactive CD4 T cells remained unchanged. Overall, the present study defines the anatomic and temporal characteristics of CD4 T cell alloimmune responses and demonstrates that CD4 T cell priming via the indirect pathway proceeds optimally in the absence of the direct pathway of alloantigen presentation.

The impact of T helper and T regulatory cells on the regulation of anti-double-stranded DNA B cells.

Autoreactive B cells that appear to be inactivated can be found in healthy individuals. In this study, we examined the potential of these anergic cells to become activated. We show that anergy of anti-double-stranded DNA (dsDNA) B cells in BALB/c mice is readily reversed, requiring only the provision of T cell help. We further show that spontaneous loss of anergy among anti-dsDNA B cells in autoimmune lpr/lpr mice occurs in two phases: an abortive initial response to T help followed by full loss of tolerance. Strikingly, the abortive response can be reproduced in nonautoimmune mice when CD4+CD25+ T regulatory cells are administered in conjunction with CD4+ T helper cells, suggesting that loss of B cell tolerance may require both the production of T cell help and the overcoming of T suppression.