Amyloid-like amelogenin nanoribbons template mineralization via a low-energy interface of ion binding sites

Protein scaffolds direct the organization of amorphous precursors that transform into mineralized tissues, but the templating mechanism remains elusive. Motivated by models for the biomineralization of tooth enamel, wherein amyloid-like amelogenin nanoribbons guide the mineralization of apatite filaments, we investigated the impact of nanoribbon structure, sequence, and chemistry on amorphous calcium phosphate (ACP) nucleation. Using full-length human amelogenin and peptide analogs with an amyloid-like domain, films of β-sheet nanoribbons were self-assembled on graphite and characterized by in situ atomic force microscopy and molecular dynamics simulations. All sequences substantially reduce nucleation barriers for ACP by creating low-energy interfaces, while phosphoserines along the length of the nanoribbons dramatically enhance kinetic factors associated with ion binding. Furthermore, the distribution of negatively charged residues along the nanoribbons presents a potential match to the Ca–Ca distances of the multi-ion complexes that constitute ACP. These findings show that amyloid-like amelogenin nanoribbons provide potent scaffolds for ACP mineralization by presenting energetically and stereochemically favorable templates of calcium phosphate ion binding and suggest enhanced surface wetting toward calcium phosphates in general.

Uniaxial Hydroxyapatite Growth on a Self-Assembled Protein Scaffold

Biomineralization is a crucial process whereby organisms produce mineralized tissues such as teeth for mastication, bones for support, and shells for protection. Mineralized tissues are composed of hierarchically organized hydroxyapatite crystals, with a limited capacity to regenerate when demineralized or damaged past a critical size. Thus, the development of protein-based materials that act as artificial scaffolds to guide hydroxyapatite growth is an attractive goal both for the design of ordered nanomaterials and for tissue regeneration. In particular, amelogenin, which is the main protein that scaffolds the hierarchical organization of hydroxyapatite crystals in enamel, amelogenin recombinamers, and amelogenin-derived peptide scaffolds have all been investigated for in vitro mineral growth. Here, we describe uniaxial hydroxyapatite growth on a nanoengineered amelogenin scaffold in combination with amelotin, a mineral promoting protein present during enamel formation. This bio-inspired approach for hydroxyapatite growth may inform the molecular mechanism of hydroxyapatite formation in vitro as well as possible mechanisms at play during mineralized tissue formation.

A Brief History of the Discovery of Amelogenin Nanoribbons In Vitro and In Vivo

Without evidence for an organic framework, biological and biochemical processes observed during amelogenesis provided limited information on how extracellular matrix proteins control the development of the complex fibrous architecture of human enamel. Over a decade ago, amelogenin nanoribbons were first observed from recombinant proteins during in vitro mineralization experiments in our laboratory. In enamel from mice lacking the enzyme kallikrein 4 (KLK4), we later uncovered ribbon-like protein structures that matched the morphology, width, and thickness of the nanoribbons assembled by recombinant proteins. Interestingly, similar structures had already been described since the 1960s, when enamel sections from various mammals were demineralized and stained for transmission electron microscopy analysis. However, at that time, researchers were not aware of the ability of amelogenin to form nanoribbons and instead associated the filamentous nanostructures with possible imprints of mineral ribbons in the gel-like matrix of developing enamel. Further evidence for the significance of amelogenin nanoribbons for enamel development was stipulated when recent mineralization experiments succeeded in templating and orienting the growth of apatite ribbons along the protein nanoribbon framework. This article provides a brief historical review of the discovery of amelogenin nanoribbons in our laboratory in the context of reports by others on similar structures in the developing enamel matrix.

Progression of Self-Assembly of Amelogenin Protein Supramolecular Structures in Simulated Enamel Fluid

Mechanisms of protein-guided mineralization in enamel, leading to organized fibrillar apatite nanocrystals, remain elusive. In vitro studies reveal recombinant human amelogenin (rH174), a matrix protein templating this process, self-assembles into a variety of structures. This study endeavors to clarify the self-assembly of rH174 in physiologically relevant conditions. Self-assembly in simulated enamel fluid was monitored up to 2 months. At alkali (7.3-8.7) and acidic (5.5-6.1) pH ranges, a distinct progression in formation was observed from nanospheres (17-23 nm) to intermediate-length nanorods, concluding with the formation of long 17-18 nm wide nanoribbons decorated with nanospheres. Assembly in acidic condition progressed quicker to nanoribbons with fewer persistent nanospheres. X-ray diffraction exhibited reflections characteristic of antiparallel β-sheets (4.7 and 9.65 Å), supporting the model of amyloid-like nanoribbon formation. This is the first observation of rH174 nanoribbons at alkaline pH as well as concurrent nanosphere formation, indicating both supramolecular structures are stable together under physiological conditions.

VALHUDES: A protocol for validation of human papillomavirus assays and collection devices for HPV testing on self-samples and urine samples

BACK GROUND

Systematic reviews have concluded that hrHPV DNA testing using target-amplification tests is as accurate on vaginal self-samples as on clinician-taken specimens for the detection of cervical precancer. However, insufficient evidence is available for specific HPV assay/self-sample device combinations.

OBJECTIVES

The VALHUDES protocol is designed as a diagnostic test accuracy study that aims to compare the clinical sensitivity and specificity of particular hrHPV assay(s) on vaginal self-samples and first-void-urine, collected in agreement with standardized protocols, with hrHPV testing on matched clinician-taken samples.

STUDY DESIGN

Five hundred enrolled women referred to a colposcopy clinic are invited to collect a first-void urine sample and one or more vaginal self-samples with particular devices before collection of a cervical sample by a clinician. Sample sets are subsequently analysed in a laboratory accredited for HPV testing. Disease verification for all enrolled patients is provided by colposcopy combined with histological assessment of biopsies.

RESULTS

A first VALHUDES study has started in Belgium in December 2017 with enrolment from four colposcopy centres. The following assays are foreseen to be evaluated: RealTime High Risk HPV assay (Abbott), cobas-4800 and -6800 (Roche), Onclarity (BD), Xpert HPV (Cepheid) and Anyplex II HPV HR (Seegene).

CONCLUSION

Given empirical evidence that the relative accuracy of HPV-testing on self- vs clinician-samples is robust across clinical settings, the VALHUDES protocol offers a framework for validation of HPV assay/self-sample device combinations that can be translated to a primary screening setting.

Referral population studies underestimate differences between human papillomavirus assays in primary cervical screening

OBJECTIVE

We studied how representative cytologically abnormal women ("referral populations") are with respect to uncovering differences between human papillomavirus (HPV) assays in the primary screening where most women are cytologically normal.

METHODS

A total of 4997 women were tested with SurePath® cytology, and Hybrid Capture 2 (HC2), cobas, CLART and APTIMA HPV assays. Women with positive test results were offered a follow-up. For all detected HPV infections and HPV-positive high-grade cervical intraepithelial neoplasia (≥CIN2), we studied the distributions of assay-specific signal strengths in the baseline samples as documented by the assays' automatically generated reports. We calculated the likelihood of test result discordance as the proportion of HPV-positive samples that were not confirmed by all four assays.

RESULTS

Median signal strengths for HPV infections were weaker in normal than abnormal cytology (P<.001, adjusted for women's age, multiple infections and the reason for taking the sample). For HC2, they were RLU/CO 11.0 (interquartile range, IQR: 3.3-52.8) vs 124.2 (IQR: 22.8-506.9), respectively; for cobas, Ct 33.5 (IQR: 29.6-37.5) vs 26.9 (IQR: 23.7-31.3), respectively; for APTIMA, S/CO 10.2 (IQR: 5.8-11.3) vs 11.1 (IQR: 9.4-15.5), respectively. Similar patterns were observed for HPV-positive ≥CIN2. The four HPV assays more frequently returned discordant test results in normal than in abnormal cytology. Relative frequency of discordance in detecting HPV infections was 0.39 (95% confidence interval: 0.33-0.48) for abnormal vs normal cytology.

CONCLUSIONS

These data suggest that referral population studies, by not including sufficient numbers of cytology normal women, underestimate the differences between HPV assays that would become apparent in primary screening.

High-grade cervical intraepithelial neoplasia in human papillomavirus self-sampling of screening non-attenders

BACKGROUND

Self-sampling for human papillomavirus (HPV) offered to women who do not participate in cervical cancer screening is an increasingly popular method to increase screening coverage. The rationale behind self-sampling is that unscreened women harbour a high proportion of undetected precancer lesions. Here, we compare the cervical intraepithelial neoplasia grade 2 or worse (⩾CIN2) detection rate between non-attenders who participated in self-sampling and women attending routine screening.

METHODS

A total of 23 632 women who were qualified as non-attenders in the Copenhagen Region were invited for HPV-based self-sampling. Of these, 4824 women returned a self-sample, and HPV-positive women were referred for cytology and HPV co-testing as follow-up. The entire cohort and a reference cohort (3347 routinely screened women) were followed for histopathology confirmed ⩾CIN2. Odds ratio (OR) and the relative positive predictive value of ⩾CIN2 detection between the two populations were estimated.

RESULTS

Women participating in self-sampling had a higher ⩾CIN2 detection than women undergoing routine cytology-based screening (OR=1.83, 95% CI: 1.21-2.77) and a similar detection as routinely screened women tested with cytology and HPV testing (OR=1.03, 95% CI: 0.75-1.40). The positive predictive value for ⩾CIN2 was higher in screening non-attenders than in routinely HPV- and cytology-screened screened women (36.5% vs 25.6%, respectively).

CONCLUSIONS

Self-sampling offered to non-attenders showed higher detection rates for ⩾CIN2 than routine cytology-based screening, and similar detection rates as HPV and cytology co-testing. This reinforces the importance of self-sampling for screening non-attenders in organised cervical cancer screening.

Concordant testing results between various human papillomavirus assays in primary cervical cancer screening: systematic review

OBJECTIVES

Human papillomavirus (HPV) assays are increasingly used for primary cervical screening and HPV-vaccination-effect monitoring. We undertook a systematic literature review to determine the concordance in positive test results (i.e. detection of HPV infections) between Hybrid Capture 2 (HC2) and other assays.

METHODS

We searched PubMed, Embase and Scopus for studies of primary screening with HC2 and one or more assays, with cross-tabulated testing results for the assays. Two authors applied inclusion criteria and three authors extracted data from included studies. For each inter-assay comparison, we calculated the concordance by comparing the number of concordant samples with the number of samples that tested positive on at least one assay.

RESULTS

Sixteen studies fulfilled inclusion criteria, comparing nine assays to HC2, and including 392 to 9451 patients each. The calculated concordance varied between 48% and 69% for HC2 and APTIMA, Cobas, Abbott RealTime, Cervista, GP5+/6+, CLART, BD HPV test, Amplicor and Linear Array, i.e. 31%-52% of all positive tests on any pair of compared assays were discordant. Although modest variation in the degree of concordance with HC2 was suggested for particular assays, the numbers of studies per assay were generally low. No pronounced systematic patterns were observed by study (e.g. liquid medium) or population characteristics.

CONCLUSIONS

The ten commercially available assays do not detect the same HPV infections. Even in the most favourable case, the two assays provided discordant test results in 31% of all detected infections.

A resistively heated CeB6 emissive probe

The plasma potential, V(p), is a key quantity in experimental plasma physics. Its spatial gradients directly yield the electrostatic field present. Emissive probes operating under space-charge limited emission conditions float close to V(p) even under time-varying conditions. Throughout their long history in plasma physics, they have mostly been constructed with resistively heated tungsten wire filaments. In high density plasmas (>10(12) cm(-3)), hexaboride emitters are required because tungsten filaments cannot be heated to sufficient emission without component failure. A resistively heated emissive probe with a cerium hexaboride, CeB6, emitter has been developed to work in plasma densities up to 10(13) cm(-3). To show functionality, three spatial profiles of V(p) are compared using the emissive probe, a cold floating probe, and a swept probe inside a plasma containing regions with and without current. The swept probe and emissive probe agree well across the profile while the floating cold probe fails in the current carrying region.

Magnetic flux array for spontaneous magnetic reconnection experiments

Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, A(phi). From the measured A(phi), the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of A(phi) at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.

Pharmacokinetics of remifentanil and its major metabolite, remifentanil acid, in ICU patients with renal impairment †

BACKGROUND

The pharmacokinetics of remifentanil, an opioid analgesic metabolized by non-specific esterases, and its principal metabolite, remifentanil acid (RA), which is excreted via the kidneys, were assessed as part of an open-label safety study in intensive care unit (ICU) patients with varying degrees of renal impairment.

METHODS

Forty adult ICU patients with normal/mildly impaired renal function (creatinine clearance [CL(cr)] 62.9 (sd) 14.5 ml min(-1); n=10) or moderate/severe renal impairment (CL(cr) 14.7 (15.7) ml min(-1); n=30) were included. Remifentanil was infused for up to 72 h, at a starting rate of 6-9 microg kg(-1) h(-1) titrated to achieve a target sedation level, with additional propofol (0.5 mg kg(-1) h(-1)) if required. Intensive arterial sampling was performed for up to 72 h after infusion. Pharmacokinetic parameters obtained by simultaneous modelling of remifentanil and RA data were statistically compared between the two groups.

RESULTS

Remifentanil pharmacokinetics were not significantly affected by renal status. RA clearance in the moderate/severe group was reduced to about 25% that of the normal/mild group (41 (29) vs 176 (49) ml kg(-1) h(-1), P<0.0001). Metabolic ratio, a predictor of the ratio of RA to remifentanil concentrations at steady state, was approximately eight-fold higher in the moderate/severe group relative to the normal/mild group (116 (110) vs 15 (4), P<0.0001). Maximum RA levels approached 700 ng ml(-1) in the moderate/severe group.

CONCLUSIONS

Although RA accumulates in patients with moderate/severe renal impairment, pharmacokinetic modelling predicts that RA concentrations during a 9 microg kg(-1) h(-1) remifentanil infusion for up to 15 days would not exceed those reported in the present study, for which no associated prolongation of mu-opioid effects was observed.

Lactic acidosis in the rectal lumen of patients with septic shock measured by luminal equilibrium dialysis

BACKGROUND

Gut ischaemia may contribute to morbidity in sepsis, but little is known about the metabolic state of the gut mucosa in such patients.

METHODS

Nine patients with abdominal septic shock treated with norepinephrine, and ten healthy subjects, were subjected to equilibrium dialysis with a rectal balloon. pH, PCO(2) and concentrations of L-lactate were measured by auto-analyser.

RESULTS

In rectal dialysis fluid from patients with septic shock, acidosis was present (pH 7.23, 95% CI 7.11-7.36) and concentrations of L-lactate were approximately five times greater than controls (2.5-5.8 vs 0.5-1.2 mmol litre(-1)). The lactate concentration was related to the dose of norepinephrine (P<0.001). In contrast, values of dialysate PCO(2) did not differ significantly between patients and controls (6.4-11.0 vs 8.9-13.8 kPa).

CONCLUSIONS

The results suggest that, either lactic acidosis in rectal mucosa is related to shock severity, or that norepinephrine causes mucosal ischaemia. In any case, metabolic dysfunction is present in the rectal mucosa in patients with abdominal septic shock treated with norepinephrine.

Assessment of the respiratory exchange ratio in mechanically ventilated patients by a standard anaesthetic gas analyser

BACKGROUND

The respiratory exchange ratio (R) is the CO2 production divided with O2 consumption. R is an essential factor included in several formulas during routine blood gas analysis. Instant and individual measurement of R may be of particular interest to improve the evaluation of each single patient. A standard anaesthetic gas analyser has been recommended for measurement of R among spontaneously breathing healthy subjects, but there is no experience using this method among mechanically ventilated critically ill patients. This study validates the assessment of R by a Brüel & Kjaer gas analyser (B & K) during positive pressure ventilation of intensive care patients.

METHODS

The B & K sampled gas from 11 mechanically ventilated patients over a period of 5 min. The recordings of end-tidal values of O2 and CO2 based on fractions (RF) allowed for calculation of RF by the alveolar equation solved for R. The continuous recordings of corresponding values were depicted into an O2-CO2 diagram. A developed computer program calculated estimates of R as the slope of the regression lines related to the full cycle (Rfull) and the expiratory phase only (Rexp). Corrected values of the full respiratory cycle (Rfull*) were also calculated assuming changes of CO2 and O2 volumes during gas exchange. The different estimates of R were compared with simultaneous measurement of a Deltatrac indirect calorimeter (Rdelta).

RESULTS

Ten values of RF were within the expected interval of 0.72 < R < 1.00. For the full respiratory cycles, the mean R-value was 0.94 +/- 0.07 and for the expiratory phase the mean R-value was 0.82 +/- 0.08. The O2-CO2 diagram appeared as a convexo-convex loop during each cycle. The agreement of Rexp and Rdelta (Rexp-Rdelta: 0.01 +/- 0.13) were good.

CONCLUSION

This study demonstrates that gas measurements by a standard anaesthetic gas monitor can be used for determination of R, and thereby we present an alternative to R calculation made by the Deltatrac monitor.

Classification for coding procedures in the intensive care unit

BACKGROUND

There is no commonly accepted coding system for non-operative procedures in general, including intensive care unit (ICU) procedures. In order to create a classification of codes for ICU procedures, a system developed at the University Hospital of Bergen was evaluated in four Nordic countries.

METHODS

Classification codes were constructed using seven main groups of related procedures that were given a letter from A to G. Within each group major procedures were given a number from 00 to 99, with the possibility of up to 10 subclassifications within each procedure. A simple questionnaire regarding the use of coding general ICU procedures and some specific procedures was sent to 171 ICUs in Sweden, Finland, Denmark, and Norway. They were also asked to give their comments on the new classification coding system, which was attached.

RESULTS

One hundred and fifty-four questionnaires were returned (response rate 90%). Some or most of the ICU procedures were registered in the ICUs (82.2%). However 38% did not use any coding system and 24% used a specific internal system. The new classification coding system was well received, and was given a mean value of 7.5 using a VAS scale from 0 to 10 (best). Most ICUs would consider using this system if introduced at a national level.

CONCLUSION

Most Nordic ICUs do register some or most of the procedures performed. Such procedures are however, registered in very different ways, using several different systems, and are often home-made. The new classification system of ICU procedures was well rated.

Gentamicin dosing in critically ill patients

Gentamicin is used worldwide in the treatment of serious infections in critically ill patients. The therapeutic efficacy of gentamicin is correlated to the peak serum concentration and the adverse effects to the trough concentrations. Information concerning the pharmacodynamics in critically ill patients is scarce, but pharmacokinetic data are available. A once-daily dosage regimen has replaced multiple dosing of gentamicin in most intensive care units. No studies evaluating the superiority of either of these dosage recommendations in critically ill patients have ever been conducted. Based on 8 meta-analyses performed addressing this issue on a wide range of patients and theoretical considerations, we consider a once-daily dosage regimen feasible in critically ill patients. In septic patients the volume of distribution is significantly increased compared to normal patients, implying that the initial dose should be increased in this patient population. Additionally a general trend towards using higher loading doses (5-7 mg/kg) has been observed in USA, and the appropriateness of this dosing strategy is based on a large descriptive American study. We recommend that the initial dosage of gentamicin in critically ill hyperdynamic septic patients should be 7 mg/kg. Optimal and appropriate monitoring of the treatment with gentamicin in the critically ill patient is still an issue for further investigation. The treatment period with gentamicin should be short (3-5 days), bearing the pharmacological properties of aminoglycosides (small volume of distribution and poor tissue penetration) in mind. In patients with reduced renal function the initial dose of gentamicin should also be increased and maintenance dose reduced preferentially by prolonging the dosing intervals. However, the use of aminoglycosides in a high dose regimen in oliguric or anuric patients or patients who present with a rapidly decreasing renal function needs further consideration.

[The pattern of medication errors in connection with intravenous administration at an intensive care unit]

In a static study, medication errors in intravenous administration were registered in a multidisciplinary intensive care unit. The most frequent type of errors included administration of incorrect doses, but also administration of diluted drugs over an excessive time period, use of previously opened ampoules, administration of unauthorized drugs, wrong infusion rates, dissolution of drugs in incorrect media, dissolution of drugs in incorrect volumes of dissolution media and wrong dosage form errors were observed.

[Incidence, severity and mortality of acute respiratory failure in Denmark]

To determine the incidence, severity and 90-day mortality of acute respiratory failure (ARF), acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) we conducted an eight-week prospective cohort study in 48 Danish ICUs, during which all ICU admissions (n = 6647) > 14 years of age were assessed. ARF was defined as intubation and mechanical ventilation > 24 hrs. ALI and ARDS were defined in accordance with the American-European Consensus Conference criteria. Among the 813 patients included, 552 were diagnosed with ARF, 117 with ALI and 95 with ARDS. The incidences (patients per 100.000/yrs) for ARF were 84.8, for ALI 17.8 and for ARDS 14.6. The 90-day mortality was 46.3% for ARF patients without ALI/ARDS, 47.3% for ALI patients and 46.2% for patients with ARDS. Compared to previously reported figures, the ARDS mortality is in the lower range whereas the incidence is slightly higher. This probably reflects a broader selection of patients when using the consensus criteria to define the ARDS population as opposed to definitions previously used.

Bioavailability and pharmacokinetics of isradipine after oral and intravenous administration: half-life shorter than expected?

Isradipine is a calcium channel-blocking agent of the dihydropyridine type, used in the treatment of hypertension. A terminal half-life of 8-9 hr has been reported, in several pharmacokinetic studies after oral administration of isradipine. In a yet unpublished study a much shorter half-life was observed, and the present trial was therefore conducted in order to estimate the half-life after intravenous administration of isradipine. The bioavailability was estimated as well. In a randomised cross-over design ten healthy young volunteers were given either isradipine orally or an intravenous infusion. The two study periods were separated by at least 3 days. Blood samples for measurement of isradipine concentration were collected for 10-12 hr after administration and half-life and bioavailability were estimated. Mean terminal half-life after intravenous administration was calculated to be 2.8 hr, and the bioavailability to be 0.28. None of the 10 subjects suffered from side effects. In the present intravenous study the half-life of isradipine seems to be of much shorter than demonstrated in previous oral studies.

[Nitrogen oxide inhalation in critically ill patients]

Inhaled nitric oxide (iNO) has been extensively used in the treatment of severe hypoxaemic respiratory failure and/or pulmonary hypertension. Although the majority of studies have almost consistently demonstrated a beneficial effect on oxygenation and a reduction in pulmonary artery pressures, none of the randomised trials have reported a reduced mortality using iNO on patients with severe respiratory failure. In neonates with severe respiratory failure and pulmonary hypertension, however, iNO can reduce the need of extracorporal membrane oxygenation. Prior to using iNO on adult patients we suggest other measures to be taken (i.e. optimising ventilator settings, ventilation in prone position).

Incidence and mortality after acute respiratory failure and acute respiratory distress syndrome in Sweden, Denmark, and Iceland. The ARF Study Group

To determine the incidence and 90-d mortality of acute respiratory failure (ARF), acute lung injury (ALI), and the acute respiratory distress syndrome (ARDS), we carried out an 8-wk prospective cohort study in Sweden, Denmark, and Iceland. All intensive care unit (ICU) admissions (n = 13,346) >/= 15 yr of age were assessed between October 6th and November 30th, 1997 in 132 of 150 ICUs with resources to treat patients with intubation and mechanical ventilation (I + MV) >/= 24 h. ARF was defined as I + MV >/= 24 h. ALI and ARDS were defined using criteria recommended by the American-European Consensus Conference on ARDS. Calculation to correct the incidence for unidentified subjects from nonparticipating ICUs was made. No correction for in- or out-migration from the study area was possible. The population in the three countries >/= 15 yr of age was 11.74 million. One thousand two hundred thirty-one ARF patients were included, 287 ALI and 221 ARDS patients were identified. The incidences were for ARF 77.6, for ALI 17.9, and for ARDS 13.5 patients per 100,000/yr. Ninety-day mortality was 41.0% for ARF, including ALI and ARDS patients, 42.2% for ALI not fulfilling ARDS criteria, and 41.2% for ARDS.

Implementation of percutaneous dilation tracheotomy--value of preincisional ultrasonic examination?

BACKGROUND

In this observational study we have evaluated the implementation of percutaneous dilation tracheotomy (PDT), using the forceps dilation technique (Portex) in a multidisciplinary ICU.

METHODS

We included a preincisional ultrasonic evaluation of the neck in order to visualise the isthmus glandula thyroidea and major vessels. The observational period comprised one year. PDT was performed in 28 patients.

RESULTS

Implementation of PDT was uneventful. Duration of insertion was 10 min (4-40 min). Total time of tracheostomy was 8 days (1-65 days). In nine cases, the proximal end of the isthmus was overlying the space between the 1st and 2nd tracheal ring, which was considered the optimal insertion site. This resulted in seven cases of insertion between the cricoidea and the 1st tracheal ring and in two cases in a more distal insertion. Nineteen tracheotomies were performed in the interstice between the 1st and 2nd tracheal ring. In nine patients, major vessels were overlying the trachea. In none of the patients did this information result in an altered insertion site. Two cases of minor bleeding were observed; both stopped upon compression. In two patients the primary tube size (8.0) was too big and a smaller tube had to be inserted. In one patient the tube was maladapted to the stoma and had to be interchanged with an ordinary tracheostomial tube on the 5th day of tracheostomy.

CONCLUSION

Based on the experience gathered in this study and information from the literature, we have abandoned the routine use of ultrasonic examination of the neck prior to PDT. In order to achieve and maintain routine, we suggest that the procedure is performed by a restricted number of doctors.

Evaluation of five oxygen delivery devices in spontaneously breathing subjects by oxygraphy

Oxygen supply systems may be divided into constant and variable performance systems. As the variable performance systems are widely used, it is relevant to investigate the variation in performance between devices and the influence of oxygen supply on the inspired oxygen fraction. Data were collected from 10 healthy volunteers during the use of one constant performance system and four variable performance systems at different gas flows and inspired oxygen fractions. A thin sampling catheter was placed in the nasopharynx to allow the measurement of the end-tidal oxygen fraction. When oxygen was supplied to variable performance systems, end-tidal oxygen fraction values measured in this way varied less and were more easily quantifiable than inspired oxygen fraction. End-tidal oxygen fraction was used to calculate inspired oxygen fraction. With the variable performance systems, inspired oxygen fraction varied considerably between subjects whereas a constant and equal rise was found for each subject with the fixed performance system. A large nasal catheter was capable of delivering the highest inspired oxygen fraction, whereas the Venturi mask delivered the most precise inspired oxygen fraction. We found oxygraphy useful in the interpretation of measurements made in patients receiving unknown inspired fractions of oxygen.

Dopamine natriuresis in salt-repleted, water-loaded humans: a dose-response study

AIMS

The purpose of the present study was to define the dose-response relationship between exogenous dopamine and systemic haemodynamics, renal haemodynamics, and renal excretory function at infusion rates in the range 0 to 12.5 microg kg(-1) min(-1) in normal volunteers.

METHODS

While undergoing water diuresis, eight subjects were infused with 0, 1, 2, 3, 5, 7.5, 10 or 12.5 microg of dopamine kg(-1) min(-1) over 2 h in a randomized and double-blind fashion. On each study day, renal clearance studies were performed during a 1 h baseline period and subsequently during the second 1 h infusion period. Lithium clearance (CL(Li)) was used to estimate proximal tubular outflow.

RESULTS

Cardiac output increased with the four highest doses. Mean arterial pressure followed a biphasic pattern with a decrease during the two lowest doses and a dose-dependent increase from the 7.5 microg kg(-1) min(-1) dose onwards. Effective renal plasma flow increased with all doses of dopamine, but peaked with the 3 microg kg(-1) min(-1) infusion rate [from 617 (585-649) ml min(-1) with placebo to 915 (824-1006) ml min(-1) (means with 95% CI, P<0.001)]. None of the doses changed glomerular filtration rate (GFR). Sodium clearance (CL(Na)) and CL(Li) were elevated with the four lowest doses but increased further from 7.5 microg kg(-1) min(-1) onwards. Compared with placebo, the percentage increase in CL(Na) with increasing dose was 77 (5-159), 93 (13-172), 107 (24-190), 121 (60-181), 253 (65-441), 284 (74-494), and 212 (111-312) %, respectively. There were only small, inconsistent decreases in absolute proximal reabsorption rate (APR = GFR-CL(Li)). Fractional distal reabsorption of sodium (FDR(Na) = (CL(Li)-CL(Na))/CL(Li)) decreased with all doses, reaching its nadir with 7.5 microg kg(-1) min(-1) [from 95.9 (94.6-97.2) % with placebo to 91.5 (90.0-93.0) % (P<0.01)] whereafter a flat dose-response curve was observed.

CONCLUSIONS

In conclusion, the renal vasodilating effect of dopamine was maximal with 3 microg kg(-1) min(-1). The dose-dependent attenuation seen with higher doses is consistent with an increased alpha-adrenergic stimulation opposing the effect on dopaminergic receptors. The present CL(Li) studies confirm that dopamine increases proximal tubular outflow. The results suggest that the natriuretic effect of depressor doses of dopamine was primarily caused by attenuation of the increase in distal sodium reabsorption normally seen after an increase in proximal tubular outflow. Pressor doses further increased sodium excretion, indicating the presence of pressure natriuresis at these high doses.

Chemotaxis and IL-8 receptor expression in B cells from normal and HIV-infected subjects

To date, the activities of the alpha chemokines for human peripheral B cells from normal subjects (N-B cells) or from HIV-infected subjects (HIV-B cells) are not well established. No report on the IL-8R expression on N-B cells and HIV-B cells has been seen. We report in this work that the alpha chemokines IL-8 and growth-regulatory oncogene-alpha (GRO-alpha) induce a chemotactic migration of N-B cells and HIV-B cells via stimulating the IL-8RB on these cells. The chemotaxis of N-B cells can be inhibited by IFN-gamma and IL-2, and augmented by IL-4 and IL-13, whereas TNF-alpha and IL-10 have no influence. The chemotaxis of HIV-B cells can be inhibited by IFN-gamma and IL-2, and augmented by TNF-alpha, IL-4, and IL-10, whereas IL-13 has no influence. IL-8R are expressed more abundantly on freshly isolated HIV-B cells than N-B cells (51% and 15%, respectively). The IL-8R on N-B cells can be down-regulated by IFN-gamma, IL-2, and TNF-alpha (selectively on IL-8RA), and up-regulated by IL-4 and IL-13, whereas IL-10 has no influence. The IL-8R on HIV-B cells can be down-regulated by IFN-gamma and IL-2, and up-regulated by TNF-alpha, IL-4, and IL-10, whereas IL-13 has no influence. Importantly, N-B cell and HIV-B cell chemotaxis toward IL-8 and GRO-alpha can be blocked by anti-IL-8RB polyclonal Ab, but not by anti-IL-8RA polyclonal Ab. Our results demonstrate that IL-8 and GRO-alpha are important inflammatory mediators that stimulate the directional migration and recruitment of B lymphocytes. The migratory behavior and the expression of IL-8R on HIV-B cells and some of the reactions to Th1- and Th2-like cytokines are modified significantly during HIV infection.

Chemotaxis and IL-8 receptor expression in B cells from normal and HIV-infected subjects

To date, the activities of the alpha chemokines for human peripheral B cells from normal subjects (N-B cells) or from HIV-infected subjects (HIV-B cells) are not well established. No report on the IL-8R expression on N-B cells and HIV-B cells has been seen. We report in this work that the alpha chemokines IL-8 and growth-regulatory oncogene-alpha (GRO-alpha) induce a chemotactic migration of N-B cells and HIV-B cells via stimulating the IL-8RB on these cells. The chemotaxis of N-B cells can be inhibited by IFN-gamma and IL-2, and augmented by IL-4 and IL-13, whereas TNF-alpha and IL-10 have no influence. The chemotaxis of HIV-B cells can be inhibited by IFN-gamma and IL-2, and augmented by TNF-alpha, IL-4, and IL-10, whereas IL-13 has no influence. IL-8R are expressed more abundantly on freshly isolated HIV-B cells than N-B cells (51% and 15%, respectively). The IL-8R on N-B cells can be down-regulated by IFN-gamma, IL-2, and TNF-alpha (selectively on IL-8RA), and up-regulated by IL-4 and IL-13, whereas IL-10 has no influence. The IL-8R on HIV-B cells can be down-regulated by IFN-gamma and IL-2, and up-regulated by TNF-alpha, IL-4, and IL-10, whereas IL-13 has no influence. Importantly, N-B cell and HIV-B cell chemotaxis toward IL-8 and GRO-alpha can be blocked by anti-IL-8RB polyclonal Ab, but not by anti-IL-8RA polyclonal Ab. Our results demonstrate that IL-8 and GRO-alpha are important inflammatory mediators that stimulate the directional migration and recruitment of B lymphocytes. The migratory behavior and the expression of IL-8R on HIV-B cells and some of the reactions to Th1- and Th2-like cytokines are modified significantly during HIV infection.

Improved flow cytometric identification of myelopoiesis by the simultaneous labelling with CD13, CD14 and CD66 monoclonal antibodies

The aim of the present study was to increase our knowledge of myelopoiesis evaluated by flow cytometry. We therefore designed a triple-marker assay employing monoclonal antibodies against the CD13 (immature), the CD14 (monocytic), and the CD66 (mature myeloid) antigens using three-colour immunofluorescence. In normal donor bone marrow the assay enables simultaneous identification of immature (CD13+, CD14-, CD66-), intermediate (CD13+, myelopoietic differentiation stages through the exclusion of CD14+ monocytic cells. In the diagnosis and longitudinal follow-up of AML patients the assay was of value in the fast determination of remission state. In MDS, the immature myeloid component could be distinguished in patients defined according to the FAB classification with the possibility of identifying aberrant phenotypes, the assay should also be of interest in other myeloproliferative disorders. Moreover, because it is easy to perform, time-saving, and yields comparable results to single antibody reactivity controls, it can replace more tedious and less-informative flow cytometric immunophenotyping procedures.

[Invasive ventilation. Classification, technique and clinical experiences with BiPAP/APRV (Biphasic Positive Airway Pressure/Airway Pressure Release Ventilation)]

BiPAP (bilevel or biphasic positive airway pressure) and APRV (airway pressure release ventilation) are new, and from a technical viewpoint closely related techniques recently introduced to the field of invasive ventilatory support. BiPAP/APRV can be described as a pressure controlled continuous high flow positive airway pressure system with a time-cycled change between a high inspiratory pressure level and a lower expiratory pressure level. Due to highly sensitive valves placed in the inspiratory and expiratory part of the system, unrestricted spontaneous breathing is possible at any moment of the mechanically supported ventilatory cycle. During invasive ventilation BiPAP offers potential advantages by allowing unrestricted spontaneous breathing thus reducing the need for sedation and facilitating weaning. APRV has primarily been investigated in conditions of moderate to severe acute lung injury and it seems that APRV is associated with less detrimental effects on the cardiopulmonary system compared to conventional ventilatory strategies. Apart from a review of the literature the article gives a classification and a technical description of the systems and focuses on the practical approach to BiPAP/APRV, e.g. the initiation and adjustment of respiratory support and the weaning from ventilatory support when applying these techniques.