Vaccine-modified NF-kB and GR signaling in cervicovaginal epithelium correlates with protection.

Cervicovaginal epithelium plays a critical role in determining the outcome of virus transmission in the female reproductive tract (FRT) by initiating or suppressing transmission-facilitating mucosal immune responses in naïve and SIVmac239Δnef-vaccinated animals, respectively. In this study, we examined the very early responses of cervical epithelium within 24 h after vaginal exposure to SIV in naive and SIVmac239Δnef-vaccinated rhesus macaques. Using both ex vivo and in vivo experimental systems, we found that vaginal exposure to SIV rapidly induces a broad spectrum of pro-inflammatory responses in the epithelium associated with a reciprocal regulation of NF-kB and glucocorticoid receptor (GR) signaling pathways. Conversely, maintenance of high-level GR expression and suppression of NF-kB expression in the epithelium were associated with an immunologically quiescent state in the FRT mucosa and protection against vaginal challenge in SIVmac239Δnef-vaccinated animals. We show that the immunologically quiescent state is induced by FCGR2B-immune complexes interactions that modify the reciprocal regulation of NF-kB and GR signaling pathways. Our results suggest that targeting the balance of NF-kB and GR signaling in early cervicovaginal epithelium responses could moderate mucosal inflammation and target cell availability after vaginal infection, thereby providing a complementary approach to current prevention strategies.

Role of L-type calcium channels in altered microvascular responses to propofol in hypertension.

BACKGROUND: Propofol acts as an L-type calcium channel (LTCC) antagonist to decrease peripheral resistance and initiate hypotension. This study investigated LTCC sensitivity/expression in hypertension and the role of LTCCs in exaggerated hypotension to propofol in this situation. METHODS: Age-matched 12- to 15-week-old normotensive rats [male Wistar Kyoto (WKY)] and spontaneously hypertensive rats (SHR) were used. Propofol (10 mg kg(-1), 10-50 mg kg(-1) h(-1) i.v.) was administered and the mesenteric microcirculation (<70 µm) observed with fluorescent in vivo microscopy using fluorescein isothiocyanate-conjugated bovine serum albumin (100 mg kg(-1) i.v.). Western blotting was used to measure tissue expression of the α(1C) LTCC subtype. Pressure myography was used to assess isolated mesenteric arterioles (<350 µm) in response to BAYK8644 (0.1 nM-1 µM), a specific LTCC channel agonist. RESULTS: Propofol dilated isolated arterioles {336.6 µM [mean (sd) change 16.2 (5.8)%]}. However, constriction to BAYK8644 was reduced at this concentration of propofol [EC(50)=8.3 (0.1) log mol(-1)] compared with controls [7.4 (0.1) log mol(-1), P<0.05], suggesting that propofol inhibited LTCCs. The sensitivity of LTCCs increased during hypertension, as in vivo there was a greater increase in mean arterial pressure (MAP) to BAYK8644 [10 µg kg(-1), WKY: 59.5 (9.3)%; SHR: 97.7 (6.3)%, P<0.05] with exaggerated constriction of arterioles [10 µg kg(-1), WKY: 9.1 (2.5)%; SHR: 19.1 (2.6)%, P<0.05]. Propofol also decreased MAP in SHR over time (P<0.05), but remained unchanged in WKY. Using western blotting, expression of α(1C) was greater in SHR compared with WKY (P<0.05). CONCLUSIONS: Propofol acts via LTCC channels, with increased channel expression and sensitivity in genetically hypertensive rats. We suggest that increased sensitivity and expression of LTCCs may be a mechanism for exaggerated hypertension during propofol anaesthesia.

What is the value of routinely testing full blood count, electrolytes and urea, and pulmonary function tests before elective surgery in patients with no apparent clinical indication and in subgroups of patients with common comorbidities: a systematic review of the clinical and cost-effective literature.

BACKGROUND: The evidence base which supported the National Institute for Health and Clinical Excellence (NICE) published Clinical Guideline 3 was limited and 50% was graded as amber. However, the use of tests as part of pre-operative work-up remains a low-cost but high-volume activity within the NHS, with substantial resource implications. The objective of this study was to identify, evaluate and synthesise the published evidence on the clinical effectiveness and cost-effectiveness of the routine use of three tests, full blood counts (FBCs), urea and electrolytes tests (U&Es) and pulmonary function tests, in the pre-operative work-up of otherwise healthy patients undergoing minor or intermediate surgery in the NHS. OBJECTIVE: The aims of this study were to estimate the clinical effectiveness and cost-effectiveness of routine pre-operative testing of FBC, electrolytes and renal function and pulmonary function in adult patients classified as American Society of Anaesthesiologists (ASA) grades 1 and 2 undergoing elective minor (grade 1) or intermediate (grade 2) surgical procedures; to compare NICE recommendations with current practice; to evaluate the cost-effectiveness of mandating or withdrawing each of these tests in this patient group; and to identify the expected value of information and whether or not it has value to the NHS in commissioning further primary research into the use of these tests in this group of patients. DATA SOURCES: The following electronic bibliographic databases were searched: (1) BIOSIS; (2) Cumulative Index to Nursing and Allied Health Literature; (3) Cochrane Database of Systematic Reviews; (4) Cochrane Central Register of Controlled Trials; (5) EMBASE; (6) MEDLINE; (7) MEDLINE In-Process & Other Non-Indexed Citations; (8) NHS Database of Abstracts of Reviews of Effects; (9) NBS Health Technology Assessment Database; and (10) Science Citation Index. To identify grey and unpublished literature, the Cochrane Register of Controlled Trials, National Research Register Archive, National Institute for Health Research Clinical Research Network Portfolio database and the Copernic Meta-search Engine were searched. A large routine data set which recorded the results of tests was obtained from Leeds Teaching Hospitals Trust. REVIEW METHODS: A systematic review of the literature was carried out. The searches were undertaken in March to April 2008 and June 2009. Searches were designed to retrieve studies that evaluated the clinical effectiveness and cost-effectiveness of routine pre-operative testing of FBC, electrolytes and renal function and pulmonary function in the above group of patients. A postal survey of current practice in testing patients in this group pre-operatively was undertaken in 2008. An exemplar cost-effectiveness model was constructed to demonstrate what form this would have taken had there been sufficient data. A large routine data set that recorded the results of tests was obtained from Leeds Teaching Hospitals Trust. This was linked to individual patient data with surgical outcomes, and regression models were estimated. RESULTS: A comprehensive and systematic search of both the clinical effectiveness and cost-effectiveness literature identified a large number of potentially relevant studies. However, when these studies were subjected to detailed review and quality assessment, it became clear that the literature provides no evidence on the clinical effectiveness and cost-effectiveness of these specific tests in the specific patient groups. The postal survey had a 17% response rate. Results reported that in ASA grade 1, patients aged < 40 years with no comorbidities undergoing minor surgery did not have routine tests for FBC, electrolytes and renal function and pulmonary function. The results from the regression model showed that the frequency of test use was not consistent with the hypothesis of their routine use. FBC tests were performed in only 58% of patients in the data set and U&E testing was carried out in only 57%. LIMITATIONS: Systematic searches of the clinical effectiveness and cost-effectiveness literature found that there is no evidence on the clinical effectiveness or cost-effectiveness of these tests in this specific clinical context for the NHS. A survey of NHS hospitals found that respondent trusts were implementing current NICE guidance in relation to pre-operative testing generally, and a de novo analysis of routine data on test utilisation and post-operative outcome found that the tests were not be used in routine practice; rather, use was related to an expectation of a more complex clinical case. The paucity of published evidence is a limitation of this study. The studies included relied on non-UK health-care systems data, which may not be transferable. The inclusion of non-randomised studies is associated with an increased risk of bias and confounding. Scoping work to establish the likely mechanism of action by which tests would impact upon outcomes and resource utilisation established that the cause of an abnormal test result is likely to be a pivotal determinant of the cost-effectiveness of a pre-operative test and therefore evaluations would need to consider tests in the context of the underlying risk of specific clinical problems (i.e. risk guided rather than routine use). CONCLUSIONS: The time of universal utilisation of pre-operative tests for all surgical patients is likely to have passed. The evidence we have identified, though weak, indicates that tests are increasingly utilised in patients in whom there is a reason to consider an underlying raised risk of a clinical abnormality that should be taken into account in their clinical management. It is likely that this strategy has led to substantial resource savings for the NHS, although there is not a published evidence base to establish that this is the case. The total expenditure on pre-operative tests across the NHS remains significant. Evidence on current practice indicates that clinical practice has changed to such a degree that the original research question is no longer relevant to UK practice. Future research on the value of these tests in pre-operative work-up should be couched in terms of the clinical effectiveness and cost-effectiveness in the identification of specific clinical abnormalities in patients with a known underlying risk. We suggest that undertaking a multicentre study making use of linked, routinely collected data sets would identify the extent and nature of pre-operative testing in this group of patients. FUNDING: The National Institute for Health Research Health Technology Assessment programme.

Beneficial microvascular and anti-inflammatory effects of pravastatin during sepsis involve nitric oxide synthase III.

BACKGROUND: Sepsis induces microvascular inflammation and production of the vasodilator nitric oxide (NO) via endothelial and inducible nitric oxide synthase (eNOS or NOS III and iNOS or NOS II). Statins are cholesterol-lowering drugs; however, they also attenuate inflammation. This study aimed to determine whether pravastatin protected against sepsis-induced hypotension, loss of vascular tone, and microvascular inflammation via NOS pathways. METHODS: Male Wistar rats (n=18) were anaesthetized and the mesentery prepared for fluorescent intravital microscopy. Animals received either lipopolysaccharide (LPS; n=6); LPS+pravastatin (18 and 3 h before LPS; n=6), or saline as a control, for 4 h. RESULTS: Mean arterial pressure decreased in LPS-treated animals (P<0.05), but not in those also receiving pravastatin. Acetylcholine-induced relaxation of venules was abolished by LPS but improved by pravastatin. Pravastatin also reduced the increase in nitrite concentration and macromolecular leak from venules induced by LPS (P<0.05). The increased leucocyte adhesion seen in LPS-treated rats was also reduced in those also treated with pravastatin. Immunohistochemical analysis showed that pravastatin increased endothelial cell expression of NOS III during sepsis, but had no effect on LPS-induced up-regulation of NOS II. CONCLUSIONS: Pravastatin improved NOS III-mediated vessel relaxation and exerted anti-inflammatory effects within the microcirculation after LPS administration in rats. Pravastatin therefore appears to have beneficial effects during sepsis, as a result of increased microvascular expression and function of NOS III.

Statins for all: the new premed?

The use of statins is widespread and many patients presenting for surgery are regularly taking them. There is evidence that statins have beneficial effects beyond those of lipid lowering, including reducing the perioperative risk of cardiac complications and sepsis. This review addresses the cellular mechanisms by which statins may produce these effects. Statins appear to have actions on vascular nitric oxide through the balance of inducible and endothelial nitric oxide synthase. The clinical evidence for these benefits is also briefly reviewed with the objective of clarifying the current status of statin use in the perioperative period. There is reasonably strong evidence that patients already taking statins should continue on them perioperatively. However, the evidence for the prophylactic use of statins perioperatively is weak and lacks prospective controlled studies.

Differential effects of propofol, ketamine, and thiopental anaesthesia on the skeletal muscle microcirculation of normotensive and hypertensive rats in vivo.

BACKGROUND: This study utilized the dorsal microcirculatory chamber (DMC) model to determine differential effects of i.v. propofol, ketamine, and thiopental anaesthesia on the skeletal muscle microcirculation (10-180 micro m) of normotensive (Male Wistar Kyoto, WKY) and hypertensive (spontaneously hypertensive Harlan, SHR) rats, importantly, comparing responses to a conscious baseline. METHODS: Three weeks following implantation of the DMC in WKY (n=8) and SHR (n=6) (130 g) 0.25 ml 100 g(-1) FITC-BSA (i.v.) was administered and the microcirculation viewed using fluorescent in vivo microscopy for a 30 min baseline (t=0-30 min). This was followed by either propofol, thiopental, ketamine, or saline (i.v. bolus induction over 5 min (t=30-35 min)), then maintenance step-up infusion for 60 min (t=45-105 min), so that animals received all four agents 1 week apart (56 experiments). RESULTS: Dilation of A3 arterioles (15-30 micro m) and V3 venules (20-40 microm) with propofol was greater in SHR (t=95 min, A3 36.7 (12)%, V3 15.5 (2.3)%) than WKY (t=95 min, A3 19.4 (7.4)%, V3 8.0 (2.3)%) (P<0.05). Constriction of A3 with ketamine was greater in SHR (t=95 min, A3 -29.1 (6.4)%) than WKY (A3 -17.5 (8.8)%) (P<0.05). This was accompanied by hypotension with propofol in SHR (-32% decrease in systolic arterial pressure), but not WKY (-6%) and hypertension with ketamine in WKY (-15%) and SHR (-24%) (P<0.05). During thiopental anaesthesia there was dilation of A1 (80-180 microm), A3, and V3 in WKY (P<0.05). Conversely, in SHR dilation of venules (29.2 (8.7)%) was accompanied by constriction of A1 and A3 (t=95 min, A1 -25.1 (5.9)%, A3-45.2 (3.1)%) (P<0.05). CONCLUSION: Within the skeletal muscle microcirculation of hypertensive rats there is enhanced dilation with propofol and constriction with ketamine, associated with exaggerated changes in arterial pressure. Thus, dysfunctional control mechanisms at the level of the microcirculation alter responses to anaesthesia during hypertension.

Differential effects of intravenous anaesthetic agents on the response of rat mesenteric microcirculation in vivo after haemorrhage.

BACKGROUND: The differential effects of i.v. anaesthesia on the response of the mesenteric microcirculation after haemorrhage in vivo are previously unexplored. METHODS: Male Wistar rats (n=56) were anaesthetized intravenously either with propofol and fentanyl (propofol/fentanyl), ketamine or thiopental. A tracheostomy and carotid cannulation were performed and the mesentery surgically prepared for observation of the microcirculation using fluorescent in vivo microscopy. Animals were allocated to one of three groups: control, haemorrhage or haemorrhage re-infusion. RESULTS: After haemorrhage, the response of the microcirculation differed during propofol/fentanyl, ketamine and thiopental anaesthesia. During propofol/fentanyl anaesthesia there was constriction of arterioles (-16.7 (3.9)%), venules (-5.9 (1.7)) and capillaries (-16.3 (2.8)) (n=12). During ketamine and thiopental anaesthesia both constriction and dilation was observed. After haemorrhage and re-infusion, macromolecular leak occurred from venules during propofol/fentanyl and thiopental anaesthesia (P<0.05), but not during ketamine anaesthesia. CONCLUSION: In summary, i.v. anaesthetic agents differentially alter the response of the mesenteric microcirculation to haemorrhage.

Effectiveness of continuous positive airway pressure to enhance pre-oxygenation in morbidly obese women.

Morbid obesity is associated with a reduction in time to desaturate during apnoea following standard pre-oxygenation and induction of anaesthesia. We have compared the effects of using 7.5 cmH2O of continuous positive airway pressure (CPAP) for pre-oxygenation with a standard technique using a Mapleson A breathing system, in 20 morbidly obese women. In a prospective, open, randomised trial, we measured the time taken to desaturate to 90% from time of giving a succinylcholine bolus as part of a rapid induction of anaesthesia. All patients received 3 min pre-oxygenation prior to induction. Tracheal intubation was confirmed and all patients kept apnoeic until oxygen saturation decreased to 90%. No statistically significant difference in mean time to desaturate to 90% could be demonstrated in the CPAP group compared to the Mapleson A group (240 s and 203 s, respectively). A brief period of lower mean heart rate in the CPAP group was the only statistically significant difference in cardiovascular parameters. There was no significant difference in the volume of gastric gas after induction between groups.

Effect of midazolam pretreatment on induction dose requirements of propofol in combination with fentanyl in younger and older adults.

In a double-blind, randomised trial, we compared the effects of pretreatment with midazolam at two different doses (0.025 and 0.05 mg x kg(-1)), with placebo, on the induction dose requirements of propofol in two different age groups. We enrolled 120 patients: 60 younger patients (aged 18-35 years) and 60 older patients (aged over 60 years). All patients received 0.75 microg x kg(-1) of fentanyl, plus a blinded pretreatment with either saline or one of two doses of midazolam. Induction continued with a fixed rate infusion of propofol. Propofol dose requirement was recorded, as were cardiovascular parameters and the occurrence of significant apnoea (> 60 s). Midazolam pretreatment was associated with a significant reduction in propofol dose requirement in both younger and older patients. The reduction in older patients was significantly greater than the equivalent response in younger groups. There was no demonstrable benefit in terms of improved cardiovascular stability or reduction in the incidence of apnoea. Caution is advised in the use of midazolam as an agent for co-induction with propofol in the elderly.

Intravenous anaesthesia and the rat microcirculation: the dorsal microcirculatory chamber.

The use of the dorsal microcirculatory chamber in male Wistar rats (n=7) to study the effects of induction and maintenance of anaesthesia on the microcirculation is described. Different patterns of responses were observed. At induction, arteriolar dilation was found following propofol and thiopental but ketamine produced constriction. During maintenance, constriction of arterioles was seen with ketamine and thiopental but dilation persisted with propofol. The dorsal microcirculatory chamber appears to be a useful tool for the study of microcirculatory changes related to anaesthesia.

Self-learning fuzzy control with temporal knowledge for atracurium-induced neuromuscular block during surgery.

Self-learning fuzzy logic control has the important property of accommodating uncertain, nonlinear, and time-varying process characteristics. This intelligent control scheme starts with no fuzzy control rules and learns how to control each process presented to it in real time without the need for detailed process modeling. In this study we utilize temporal knowledge of generated rules to improve control performance. A suitable medical application to investigate this control strategy is atracurium-induced neuromuscular block of patients in the operating theater where the patient response exhibits high nonlinearity and individual patient dose requirements may vary fivefold during an operating procedure. We developed a computer control system utilizing Relaxograph (Datex) measurements to assess the clinical performance of a self-learning fuzzy controller in this application. Using a T1 setpoint of 10% of baseline in 10 patients undergoing general surgery, we found a mean T1 error of 0.28% (SD = 0.39%) while accommodating a 0.25 to 0.38 mg/kg/h range in the mean atracurium infusion rate. This result compares favorably with more complex and computationally intensive model-based control strategies for atracurium infusion.

Evaluation of the predictive performance of a 'Diprifusor' TCI system.

The predictive performance of a 'Diprifusor' target controlled infusion system for propofol was examined in 46 patients undergoing major surgery, divided into three age groups (18-40, 41-55 and 56-80 years). Measured arterial propofol concentrations were compared with values calculated (predicted) by the target controlled infusion system. Performance indices (median performance error and median absolute performance error) were similar in the three age groups, with study medians of 16.2% and 24.1%, respectively. Mean values for 'divergence' and 'wobble' were -7.6%.h-1 and 21.9%, respectively. Measured concentrations tended to be higher than calculated concentrations, particularly following induction or an increase in target concentration. The mean (SD) propofol target concentration of 3.5 (0.7) micrograms.ml-1 during maintenance was lower in older patients, compared with higher target concentrations of 4.2 (0.6) and 4.3 (0.7) micrograms.ml-1 in the two younger age groups, respectively. The control of depth of anaesthesia was good in all patients and the predictive performance of the 'Diprifusor' target controlled infusion system was considered acceptable for clinical purposes.

Remifentanil in combination with propofol for spontaneous ventilation anaesthesia.

We have investigated the effect of four doses of remifentanil on the incidence of respiratory depression and somatic response at incision. Remifentanil was administered as a loading dose of 0.125, 0.25, 0.375 or 0.5 microgram kg-1 and at a maintenance infusion rate of 0.025, 0.05, 0.075 or 0.1 microgram kg-1 min-1, respectively, with an infusion of propofol 6 mg kg-1 h-1. Responses occurred in 88% of patients with remifentanil 0.025 microgram kg-1 min-1 compared with 30-40% in the other groups. Respiratory depression after incision increased from 6% with remifentanil 0.025 microgram kg-1 min-1 to 73% with 0.1 microgram kg-1 min-1. Increases in propofol infusion rate to 7.2-8.4 mg kg-1 h-1 produced adequate maintenance of anaesthesia. Reductions in remifentanil doses to 0.025-0.05 microgram kg-1 min-1 resulted in adequate respiration at the end of surgery in 88% of patients. Maintenance infusions of the two drugs for spontaneous ventilation are likely to be in these ranges. However, the ideal loading doses and infusion rates for induction remain to be established.

Self-learning fuzzy control of atracurium-induced neuromuscular block during surgery.

Self-learning fuzzy logic control has the important property of accommodating uncertain, non-linear and time-varying process characteristics. This intelligent control scheme starts with no fuzzy control rules and learns how to control each process presented to it in real time, without the need for detailed process modelling. A suitable medical application to investigate this control strategy is atracurium-induced neuromuscular block (NMB) of patients in the operating theatre. Here, the patient response exhibits high non-linearity, and individual patient dose requirements can vary five-fold during an operating procedure. A portable control system was developed to assess the clinical performance of a simplified self-learning fuzzy controller in this application. A Paragraph (Vital Signs) NMB device monitored T1, the height of the first twitch in a train-of-four nerve stimulation mode. Using a T1 setpoint = 10% of baseline in ten patients undergoing general surgery, a mean T1 error of 0.45% (SD = 0.44%) is found while a 0.13-0.70 mg k-1 h-1 range in the mean atracurium infusion rate is accommodated. The result compares favourably with more complex and computationally-intensive model-based control strategies for the infusion of atracurium.

Development of a portable closed-loop atracurium infusion system: systems methodology and safety issues.

Safety of closed-loop drug infusion systems is an issue often raised as a matter of concern. As a result, many closed-loop control systems are reported in the literature merely as computer simulation studies and few ever reach the stage of physical realisation and formal clinical evaluation. We address the safety issues involved with such systems by describing the development of a portable closed-loop control system for atracurium-induced muscle relaxation. This is a safety-critical system particularly when applied to brain and eye surgery where movement could have serious deleterious effects. The benefits of closed-loop muscle relaxation in providing stable surgical operating conditions over a wide range of patient sensitivities while infusing the minimum amount of drug makes this a worthwhile aim and serves to demonstrate safety issues which are generally applicable to other closed-loop drug infusion systems. It is hoped that the described methodology will facilitate and encourage the clinical application of closed-loop drug infusion systems so that clinical staff and patients may receive the benefits of closed-loop drug therapy.