Transfusion practice in patients receiving VV ECMO (PROTECMO): a prospective, multicentre, observational study

BACKGROUND

In patients receiving venovenous (VV) extracorporeal membrane oxygenation (ECMO) packed red blood cell (PRBC) transfusion thresholds are usually higher than in other patients who are critically ill. Available guidelines suggest a restrictive approach, but do not provide specific recommendations on the topic. The main aim of this study was, in a short timeframe, to describe the actual values of haemoglobin and the rate and the thresholds for transfusion of PRBC during VV ECMO.

METHODS

PROTECMO was a multicentre, prospective, cohort study done in 41 ECMO centres in Europe, North America, Asia, and Australia. Consecutive adult patients with acute respiratory distress syndrome (ARDS) who were receiving VV ECMO were eligible for inclusion. Patients younger than 18 years, those who were not able to provide informed consent when required, and patients with an ECMO stay of less than 24 h were excluded. Our main aim was to monitor the daily haemoglobin concentration and the value at the point of PRBC transfusion, as well as the rate of transfusions. The practice in different centres was stratified by continent location and case volume per year. Adjusted estimates were calculated using marginal structural models with inverse probability weighting, accounting for baseline and time varying confounding.

FINDINGS

Between Dec 1, 2018, and Feb 22, 2021, 604 patients were enrolled (431 [71%] men, 173 [29%] women; mean age 50 years [SD 13·6]; and mean haemoglobin concentration at cannulation 10·9 g/dL [2·4]). Over 7944 ECMO days, mean haemoglobin concentration was 9·1 g/dL (1·2), with lower concentrations in North America and high-volume centres. PRBC were transfused on 2432 (31%) of days on ECMO, and 504 (83%) patients received at least one PRBC unit. Overall, mean pretransfusion haemoglobin concentration was 8·1 g/dL (1·1), but varied according to the clinical rationale for transfusion. In a time-dependent Cox model, haemoglobin concentration of less than 7 g/dL was consistently associated with higher risk of death in the intensive care unit compared with other higher haemoglobin concentrations (hazard ratio [HR] 2·99 [95% CI 1·95-4·60]); PRBC transfusion was associated with lower risk of death only when transfused when haemoglobin concentration was less than 7 g/dL (HR 0·15 [0·03-0·74]), although no significant effect in reducing mortality was reported for transfusions for other haemoglobin classes (7·0-7·9 g/dL, 8·0-9·9 g/dL, or higher than 10 g/dL).

INTERPRETATION

During VV ECMO, there was no universally accepted threshold for transfusion, but PRBC transfusion was invariably associated with lower mortality only when done with haemoglobin concentration of less than 7 g/dL.

FUNDING

Extracorporeal Life Support Organization.

783. Lung Transplantation for COVID-19-Associated Lung Injury (CALI): An International Registry

Background

SARS-CoV-2 can result in a range of infections from asymptomatic disease to progressive COVID-19 and death. In some pts with CALI, lung transplantation (LTx) may be lifesaving. Up to 10% of LTx in the US is currently for pts with CALI. Understanding the characteristics and outcomes of these pts is critical.

Methods

A open-access electronic registry was established to collect de-identified data from pts who have undergone LTx for CALI from centers globally. The study was IRB approved at Northwestern with a wavier for consent (no PHI is collected sites could submit data about pre-Tx, peri-Tx and post-Tx course). Follow-up for 1-yr post-LTx was collected.

Results

To date, 89 pts with complete day 30 post-LTx data have been entered into the registry. Pt demographics and pre-Tx status are shown in Table 1. 3 pts required oxygen prior to COVID-19. Most sites required neg PCR tests prior to listing (11 (12.4%) required no - PCRs, 11 (12.4%) required 1 and 61 (68.5%) required 2). LTx occurred 137 days post-infection and none developed COVID-19 in the first 30 d; 4 were given monoclonal antibodies post-tx. Post-tx ICU LOS averaged 24.5 d with total post-tx hospitalization of 37.6 d (See Table 2). Most experienced infectious and non-infectious morbidity. Most (47.8%) required an additional 30 days of rehab. 2 pts died within 30 days due to sepsis and anoxia. 5 died between day 30 and 90 and an additional 12 died between day 90 and 365.

Conclusion

The contribution of cases to this international registry is ongoing. While outcomes of LTx for CALI are generally good, patients experience prolonged post-transplant hospitalization, rehabilitation and significant morbidity and infections are common.

Disclosures

Michael G. Ison, MD MS, GlaxoSmithKline: Advisor/Consultant|GlaxoSmithKline: Grant/Research Support Saima Aslam, MD, Armata: Grant/Research Support|BioMx: Advisor/Consultant|Contrafect: Grant/Research Support|Gilead: Honoraria|Merck: Honoraria|Phico: Advisor/Consultant.

OUP accepted manuscript

Background

Recent literature has demonstrated that partial oral antibiotic treatment of infectious endocarditis is non-inferior to IV therapy in select patients. Despite the rising incidence of injection drug use-related endocarditis, partial oral therapy has not been well studied in persons who inject drugs.

Objectives

To evaluate the rate of relapsed infection and 90 day mortality in patients with infectious endocarditis treated with partial oral antibiotic therapy.

Methods

Consecutive patients with infectious endocarditis treated with partial oral antibiotic therapy were identified by study investigators and reviewed by independent clinicians. The decision to use partial oral antibiotic therapy was made by the institution’s multidisciplinary endocarditis team.

Results

In 11 cases of infective endocarditis treated with partial oral antibiotic therapy, 9 of which were complicated by injection drug use, there were no relapsed infections with the primary organism. Five patients underwent surgical valve replacement, and the median duration of oral antibiotic therapy was 23 days. All patients survived to in-hospital discharge and 90 days post-discharge. Ten patients followed up with an infectious diseases provider after discharge.

Conclusions

These data add to existing literature demonstrating non-inferior outcomes with partial oral antibiotic treatment when compared with IV antibiotic treatment alone in patients with endocarditis, including persons who inject drugs.

308. Secondary Infections in Patients Requiring Extracorporeal Membrane Oxygenation (ECMO) for Severe Acute Respiratory Distress Syndrome (ARDS) due to COVID-19 Pneumonia (PNA)

Background

Rescue ECMO has been used worldwide in patients (pts) with ARDS caused by COVID-19. Bacterial super-infections affect 3.5-14.3% of hospitalized pts with COVID-19. Pts requiring ECMO may be at an increased risk of infection due to their severity of illness, gut translocation and ECMO impact on host immunity.

Methods

This was a retrospective review of pts requiring ECMO for COVID-19 from April 2020-2021 at a single center. Strict definitions of infections (including ventilator-associated PNA, VAP) were in accordance with CDC criteria.

Results

43 ECMO pts with 1065 ECMO days were evaluated. Median age was 53 yrs (range: 21-62) and median BMI was 36.2 (range: 19.4-75.8). 70% were men and 65% were white. 37 patients (86%) experienced a total of 40 infectious episodes with a median onset from ECMO cannulation to first infection of 10.5d (range: 4-50). Median SOFA and SAPSII scores at time of infection were 12 (6-20) and 63 (30-90), respectively. PNA was the most common infection (78%, with 19% of cases complicated by bacteremia and 3% by empyema) (Fig. 1). The most common organisms isolated were Enterobacterales (37%), S. aureus (25%) and P. aeruginosa (16%) (Fig. 2). Only 2% of all organisms were multi-drug resistant. 3 pts had fungal infections (1 candidemia, 2 aspergillus PNA). Duration of ECMO was significantly longer for infected pts (26d, range: 5-92d) vs (11d, range: 3-24d), p=.01. 95% of infected pts had received steroids vs. 67% of uninfected pts, p=0.09. Treatment success at 1 week was 50%, and 24% and 40% of pts had recurrent infections and persistent/recurrent organisms in clinical cultures, respectively. S. aureus (54%) and Enterobacterales (26%) were associated with persistent or recurrent clinical cultures, requiring prolonged antimicrobial therapy. Mortality rate at 30 days was 65% and was significantly higher for pts with infection than those without (67% vs 33%, p=.02).

Conclusion

Super-infection (most commonly PNA) occurred in almost all COVID-19 pts requiring ECMO for >4 days, and was a significant risk factor for death. Recurrent infections among survivors were common, especially when caused by Enterbacterales or S. aureus. Super-infection and mortality rates of ARDS pts on ECMO for COVID-19 were worse than for ARDS pts on ECMO for influenza at our center.

Disclosures

Ryan K. Shields, PharmD, MS, Shionogi (Consultant, Research Grant or Support) Fernanda P. Silveira, MD, MS, FIDSA, Ansun (Individual(s) Involved: Self): Grant/Research Support; Novartis (Individual(s) Involved: Self): Grant/Research Support; Qiagen (Individual(s) Involved: Self): Grant/Research Support; Shire (Individual(s) Involved: Self): Advisor or Review Panel member, Grant/Research Support; SlieaGen (Individual(s) Involved: Self): Grant/Research Support; Whiscon (Individual(s) Involved: Self): Grant/Research Support Cornelius J. Clancy, MD, Merck (Grant/Research Support)

292. Antibiotic Use Is Increased in Patients with Acute Respiratory Distress Syndrome (ARDS) Requiring Extracorporeal Membrane Oxygenation (ECMO) due to COVID-19 Compared with Influenza

Background

During the COVID-19 pandemic, >50% of hospitalized patients (pts) received an antimicrobial. ECMO is increasingly used in COVID-19 pts with severe ARDS. ECMO has been used for ARDS due to influenza at our center in prior years. Pts on ECMO are at high risk for infections. We compared the rates of antibiotic (Ab) and antifungal (AF) use in pts on ECMO for COVID-19 vs influenza ARDS.

Methods

This was a retrospective review of pts on ECMO for COVID-19 (2020-2021) or influenza (2013-2019). Antimicrobials (Abs and AFs) were categorized as anti-MRSA, anti-pseudomonal β-lactams (AP-BL), carbapenems, and new broader spectrum β-lactams. We calculated total Ab and AF utilization, adjusted for ECMO duration.

Results

Seventy-one pts (36 COVID-19 and 35 influenza) were included. COVID-19 pts had longer ECMO duration (median: 25 vs 11 days, p=.03). 100% and 97% of pts with COVID-19 and influenza received ≥1 Ab, respectively, and 42% and 33% an AF, respectively. COVID-19 pts received longer duration of Abs (26 vs 10 days, p< 0.001) and but not AF. COVID-19 group (gp) were more likely to receive anti-MRSA Ab (69% vs 33%, p=.004); otherwise, there were no differences between gps in types of Abs used. When adjusted for ECMO days, COVID-19 gp received higher median number of Abs (1.23 vs 1, p=.06). Specifically, COVID-19 gp received higher median number of anti-MRSA Ab (0.2 vs 0, p=.007) and AP-BL (0.44 vs 0.28, p=.08). There was no difference in Ab-free days between gps, though the proportion of Ab-free days was lower (0.2 vs 0.36) in COVID-19 pts (p=.08). More COVID-19 pts had pathogens recovered from clinical cultures, especially S. aureus and Enterobacterales (Figure).

Pathogens recovered from clinical cultures

Patients recovered from clinical cultures of patients with COVID-19 and Influenza ARDS requiring ECMO

Conclusion

Among pts on ECMO, those with COVID-19 received significantly longer courses of Abs than those with influenza, even after adjusting for longer durations of ECMO. Differences were driven by receipt of anti-MRSA and AP-BLs. Recovery of pathogenic bacteria was greater in COVID-19 pts than influenza pts. Given difficulties in distinguishing pneumonia from airway colonization among ARDS pts on ECMO, development of diagnostic criteria for pt care, rational antimicrobial stewardship and further research are needed.

Disclosures

Cornelius J. Clancy, MD, Merck (Grant/Research Support)

Outcomes of systemic anticoagulation with bivalirudin for Impella 5.0

Temporary mechanical circulatory support (tMCS) devices are used for the management of cardiogenic shock. The Impella 5.0 (Abiomed; Danvers, MA) (IMP5) is a commonly used, surgically implanted, tMCS device that requires systemic anticoagulation and purge solution to avoid pump failure. To avoid heparin-induced thrombocytopenia (HIT) from unfractionated heparin (UFH) use, our program has explored the utility of bivalirudin (BIV) for systemic anticoagulation in IMP5. This single center, retrospective study included patients supported on IMP5 with BIV based AC. The efficacy and safety end points were recovery, bridge to left ventricular assist device (LVAD), cardiac transplant (HTX), or death as well as clinically significant bleeding, incidence of Tissue Plasminogen Activator (tPA) use for suspected pump thrombosis, stroke, and device failure. There were 31 patients included, and 26 (84%) received BIV purge solutions. The median duration of IMP5 was 6 (IQR 4-10) days. Most patients were bridged to LVAD (39%, 12); 16% (5) were bridged to HTX, 16% (5) recovered, and 29% (9) died. One patient (3%) suffered from ischemic stroke and 12% (4) patients developed clinically significant bleeding. tPA was administered to 8 (26%) patients. Logistic regression analysis demonstrated that duration of IMP5 was a significant predictor of tPA use (OR 1.28; 95% Confidence Interval 1.04-1.56). There were no cases of pump failure. Our experience highlights the feasibility of utilizing BIV for routine AC use in IMP5.

89. Efficacy and Tolerability of Voriconazole (VOR) vs. Isavuconazole (ISA) Prophylaxis (px) in Preventing Invasive Fungal Infections (IFI) in Lung Transplant Recipients (LTR)

Background

IFI is a significant complication following lung transplant (LT). VOR was universal antifungal px in our LT program from 2004 to October 2015, at which time px was changed to ISA. We compared the efficacy and tolerability of VOR vs. ISA px in LTR.

Methods

We reviewed all LTR from September 2013 to February 2018 who received VOR or ISA Px. The standard duration of px was 3 or 4 months following basiliximab and alemtuzumab induction, respectively. All patients were followed for ≥1 years post-Tx. IFI was defined by revised EORTC/MSG criteria.

Results

In total, 310 LTR were included, 149 and 161 of whom received ISA and VOR px, respectively. There was no difference in demographics, underlying diseases, single vs. double LT, or induction therapy (alemtuzumab vs. basiliximab) between the 2 groups. At 1-year after LT, 9% (14) and 8% (13) of patients in ISA and VOR groups developed IFI, respectively (P = 0.5). 5% (7) and 3% (5) of patients developed breakthrough (BT) IFI during ISA and VOR px, respectively (P = 0.6; Figure 1, P = 0.4, Kaplan-–Meier). ISA BT included pneumonia (PNA, 2), endobronchial IFI (2), mediastinitis (1), chest wall IFI (1), and candidemia (1). ISA BT patients were infected with Aspergillus fumigatus (3; 2 with ISA MIC = 0.5 µg/mL, 1 MIC = 1 µg/mL), black mould (1), and yeasts (3; 2 C. glabrata, 1 C. albicans). VOR BT IFI included PNA (2), endobronchial IFI (1), empyema (1), and chest wall IFI (1). VOR BT IFIs were due to A. ustus, A. niger, A. lentulus, black mould, and Rhizopus spp (1 each). All Aspergillus VOR BT isolates exhibited VOR MIC ≥2 µg/mL. Patients with IFI were more likely to have positive pre-LT respiratory fungal culture (P = 0.01) and grade ≥3 ischemic reperfusion injury (IRI) post-LT (P = 0.01). VOR and ISA were prematurely discontinued in 53% (85) and 14% (21) of patients due to adverse events, respectively (P < 0.0001). Hepatotoxicity was more common with VOR (22%, 35) than ISA (5%, 7) (P < 0.0001). IFI was an independent risk factor for death at 1 year (Figure 2, P < 0.0001, Kaplan–Meier).

Conclusion

ISA was as effective as VOR in preventing IFI in LTR, and significantly better tolerated. Pre-LT fungal culture positivity and grade ≥3 IRI post-LT were risk factors for the development of IFI. IFI within 1-year post-LT had a significant impact on mortality

Disclosures

Fernanda P. Silveira, MD, MS, FIDSA, Ansun: Grant/Research Support; Qiagen: Grant/Research Support; Shire: Grant/Research Support; Whiscon: Grant/Research Support.

226. Nine-year Survey of Bloodstream Infections (BSIs) across Six Types of Solid-organ Transplant (SOT) at a Large University Medical Center

Background

BSIs are common in SOT patients. We surveyed BSIs across 6 types of SOT over 9 years at our center.

Methods

We conducted a retrospective study of BSI among patients transplanted from January 2010 to January 2019. Single blood cultures positive for coagulase-negative staphylococci, Corynebacterium, Bacillus, or Propionibacterium were excluded.

Results

3,358 patients underwent SOT, including kidney (K, 43%, 1432), lung (Lu, 23%, 778), liver (Li, 21%, 700), heart (H, 8%, 256), pancreas (P, 4%, 149), and small bowel/multivisceral (SB/MV 1%, 43). 16% (529) of patients had ≥1 episode of BSI. There were 770 BSIs; 14% (105/770) were recurrent. Median number of BSI was 1/patient (range: 1 to 7). BSI rates were highest among SB/MV patients (53%), followed by Lu (22%), Li (20%), P (15%), H (14%) and K patients (14%) (Figure 1). 20% (156), 24% (187) and 7% (52) of BSI occurred at ≤30 d, 31–180 d, and 181–365 d after SOT, respectively. BSI rates at ≤ and >180 d post-SOT were 3.6 and 0.65/1000 pt-d, respectively (P < 0.0001). Most common bacteria were Enterobacteriaceae (35%) and Enterococcus spp. (22%). Candida spp. accounted for 6% (49/770) of BSIs. Enterobactericeae were most common among intra-abdominal SOT patients, whereas Enterococcus and non-fermenting Gram-negatives were most common in Lu patients (Figure 2). 8% (65) of BSI was polymicrobial. From 2016 to 2018, 15% (14/96) of Enterobacteriaceae BSIs were multi-drug-resistant (MDR); 8% (8/96) were extensively drug resistant (XDR). 23% (3/13) of P. aeruginosa were MDR (all XDR). 70% (14/20) and 5% (1/20) of E. faecium and E. faecalis were vancomycin-resistant, respectively. Thirty-day mortality following BSI diagnosis was highest for H (31%), followed by Lu (15%), Li (10%), P (9%) and SB/MV (4%) patients. Patients with bacteremia had higher mortality than patients with no bacteremia (Figure 3).

Conclusion

BSIs are common after SOT, and associated with significant short- and long-term mortality. Almost half of BSIs occur within the first 6 months of SOT, when BSI rates are significantly higher than at later time points. Predominant BSI pathogens differ between SOT types; as such, empiric antimicrobial therapy decisions should be organ-specific. At our center, MDR and XDR Gram-negative bacteria and VRE are common; centers should use overall SOT and organ-specific antibiograms to drive empiric antimicrobial strategies.

Disclosures

All authors: No reported disclosures.

2271. Bacteremia Due to Multi-Drug-Resistant Organisms Is an Independent Risk Factor for Death Among Patients Supported by Extracorporeal Membrane Oxygenation (ECMO)

Background

Methods

Results

Conclusion

Disclosures

1709. Epidemiology of Invasive Fungal Infection (IFI) after Severe Influenza Requiring Intensive Care Unit (ICU) Admission: 10-Year Experience at a Tertiary Care Center in the United States

Background

Despite increasing recognition of aspergillosis complicating severe influenza and its associated high fatality in Europe, incidence and features of the disease in the United States are unknown.

Methods

We reviewed all influenza cases requiring ICU admission from 2009 to 2019 at our center.

Results

262 patients with influenza required ICU admission. 4% (10) developed IFI at median 2d after influenza diagnosis. 80% (8/10) of patients with IFI were infected with influenza A vs. 88% (221/252) without IFI. 20% were on steroids at the time of IFI diagnosis. 70% of IFI required mechanical ventilation. Types of IFI were pneumonia (70%, 6 Aspergillus and 1 Wangiella), endobronchial IFI (20%, 1 each with Aspergillus and Lictheimia), and Coccidioides fungemia (10%). 4% (10) of patients were fungal colonized, but did not have IFI (5 A. fumigatus, 1 A. terreus, 4 Penicillium). CT findings of IFI included nodules (4), cavitation (3), and ground-glass opacities (2). Serum galactomannan (GM) was positive in 3 (43%). Median time to antifungal therapy (AF) was 2 days. Triazoles were prescribed to all 7 patients with aspergillosis. Posaconazole and amphotericin B were AF for patients with Wangiellaand Lichteimia, respectively. Patients with C. immitis fungemia died before AF. Median duration of AF was 60 days among survivors. Patients with IFI required acute hemodialysis more frequently than colonized patients (60% vs. 0%, P = 0.01). 30-day mortality was 60% (6/10) and 20% 92/10) in patients with IFI and colonization, respectively (P = 0.2). Patients with IFI had significantly higher in-hospital and 60-day mortality than those without IFI (Fig 1, P = 0.009).

Conclusion

Our rate of post-influenza IFI (4%) was lower than reported in Europe (~15%), which might stem from a lack of systematic BAL GM testing at our center, over-reliance on GM to make diagnoses in Europe, and/or differences in pt populations and clinical practices in treating severe influenza. IFI and fungal colonization rates were similar at our center, highlighting the importance of using well-defined criteria to define disease. Given the high mortality of post-influenza IFI, priority should be given to defining risk factors that might identify patients for targeted AF prophylaxis. In using AF, it is important to recognize that Aspergillus is not the only cause of IFI.

Disclosures

All authors: No reported disclosures.

2033. Incorporating T2Candida Testing into Rational Antifungal (AF) Management: A Successful Pilot Study of Diagnostic Stewardship (DS) Directed Toward Specific Intensive Care Unit (ICU) Patients At-Risk for Sepsis due to Invasive Candidiasis (IC)

Background

Blood cultures (BC) are ~50% sensitive for diagnosing IC. T2Candida (T2) detects five leading Candida spp. directly in blood and was ≥90%/90% sensitive/specific (S/Sp) for candidemia in clinical trials. Optimal use of T2 in clinical practice is unclear. We targeted T2 to specific ICU patients at-risk for IC, and implemented AF management algorithms developed with ICU teams.

Methods

A DS team ordered concurrent T2 and BC, and used results to guide AF in patients fulfilling pre-specified criteria for septic shock (medical ICU (MICU)), sepsis after abdominal surgery (trauma ICU), or sepsis with mechanical circulatory support (cardiothoracic ICU). We focused on groups with anticipated pre-test IC probabilities of ~3–15%. Proven IC was defined if BC+ and possible IC if BC- but a compatible clinical picture was observed.

Results

Seven percent (6/88) of BC in ICU patients with sepsis were Candida +. T2 and BC results are shown in the table. Using BC as gold standard, T2 S/Sp and PPV/NPV were 50%/87% and 33%/96%, respectively. Including possible IC, T2 S/Sp increased to 69%/96%, and 67% (4/6) of T2+/BC− results were likely true positive; two false-positive results were for C. parapsilosis. We focused on MICU outcomes initially since 75% (66/88) of tests were performed here. Empiric AFs were discontinued in 12 patients following a T2- result; AFs were avoided in all others. Median combined days of therapy (DOT)/month for caspofungin and fluconazole as empiric or definitive treatment prior to and after introducing DS were 26 (range: 10–53) and 15 (3–32), respectively (P = 0.0047). AF consumption was decreased 47% (figure).

Conclusion

Targeted DS using T2 in select ICU patients with sepsis significantly reduced AF usage. 14% of patients with sepsis were diagnosed with IC using either T2+ or BC+, compared with 7% with BC+ alone, as would be expected if BC S was 50%. T2 S and T2−/BC+ results were lower and higher, respectively, than previously reported, indicating that treatment decisions should be based on results of both tests. Most T2+/BC− results were ascribed to possible IC.

Disclosures

M. H. Nguyen, Merck: Grant Investigator, Research grant. Astellas: Grant Investigator, Research grant.

Major publications in the critical care pharmacotherapy literature in 2015

PURPOSE

Recently published practice guidelines and research reports on pharmacotherapy in critical care patient populations are summarized.

SUMMARY

The Critical Care Pharmacotherapy Literature Update (CCPLU) Group is composed of over 50 experienced critical care pharmacists who evaluate 31 peer-reviewed journals monthly to identify literature pertaining to pharmacotherapy in critical care populations. Articles are chosen for summarization in a monthly CCPLU Group publication on the basis of applicability and relevance to clinical practice and strength of study design. From January to December 2015, a total of 121 articles were summarized; of these, 3 articles presenting clinical practice guidelines and 12 articles presenting original research findings were objectively selected for inclusion in this review based on their potential to change or reinforce current evidence-based practice. The reviewed guidelines address the management of intracranial hemorrhage (ICH), adult advanced cardiac life support (ACLS) and post-cardiac arrest care, and the management of supraventricular tachycardia (SVT). The reviewed research reports address topics such as nutrition in critically ill adults, administration of β-lactams for severe sepsis, anticoagulant selection in the context of continuous renal replacement therapy, early goal-directed therapy in septic shock, magnesium use for neuroprotection in acute stroke, and progesterone use in patients with traumatic brain injury.

CONCLUSION

Important recent additions to the critical care pharmacy literature include updated joint clinical practice guidelines on the management of spontaneous ICH, ACLS, and SVT.

Implication of frequenin in the facilitation of transmitter release in Drosophila

1. We have investigated the possible role of frequenin in the modulation of synaptic facilitation at the larval Drosophila neuromuscular junctions. Excitatory junctional currents (EJCs) and presynaptic nerve terminal currents were recorded by external electrodes in normal larvae and in transgenic larvae carrying an extra insertion of the frequenin cDNA. 2. Motor nerve stimulation by twin pulses or trains of stimuli provoked EJC facilitation which was about three times higher in transgenic larvae compared to controls. Unconditioned EJCs revealed, however, similar quantal content and Ca2+ sensitivity in both Drosophila strains. 3. Differences between normal and transgenic Drosophila in the quantal content of the facilitated EJC do not depend on differences in the duration of the repolarization phase of the presynaptic action potential. 4. Perfusion of tetrodotoxin or of low-Na+ solutions abolished the enhancement of the EJC facilitation observed in the transformants. These treatments only slightly affected the facilitation of normal junctions. 5. These results suggest that (i) internal Na+ accumulation can enhance facilitation of transmitter release in Drosophila neuromuscular junctions overexpressing frequenin, and (ii) this effect possibly depends on a modulation of the activity of the Na(+)-Ca2+ exchanger by frequenin.

A single amino acid determines the subunit-specific spider toxin block of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate receptor channels

Joro spider toxin (JSTX) is one of the most potent antagonists of glutamatergic AMPA/KA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate/kainate) receptor channels in invertebrates and vertebrates. A differential blocking effect on certain types of glutamatergic synapses--e.g., parallel and climbing fiber synaptic inputs to rat cerebellar Purkinje neurons--has been shown by using a synthetic analog of the spider toxin. By investigating the molecular basis of the JSTX action on the recombinant AMPA/KA receptors GluR1-GluR4 and GluR6 expressed in Xenopus oocytes, we found that submicromolar concentrations of JSTX exert a subunit-specific block. Thus, receptor subunits forming a receptor channel with a linear current-voltage (I-V) relationship (GluR1/2, GluR2/3, and GluR6) were not affected, while receptor subunits with rectifying I-V relationships (GluR1, GluR3, GluR4, and GluR1/3) were reversibly blocked by JSTX. By using receptor-subunit mutants obtained by site-directed mutagenesis, we have identified a single amino acid position (glutamine in the proposed second transmembrane domain) that is critical for the JSTX block. Since this site has previously been shown to control the I-V relationship of the AMPA/KA receptor channel and to participate in the regulation of the channel's permeability for calcium ions, our findings suggest that JSTX binds close to the central pore region of the channel.

Frequenin--a novel calcium-binding protein that modulates synaptic efficacy in the Drosophila nervous system

The T(X;Y)V7 rearrangement in Drosophila has originally been recognized as a Shaker-like mutant because of its behavioral and electrophysiological phenotype. The gene whose expression is altered by the V7 rearrangement has been characterized. It encodes a novel Ca(2+)-binding protein named frequenin, which is related to recoverin and visinin. In vitro, the frequenin protein functions like recoverin as a Ca(2+)-sensitive guanylyl cyclase activator. Anti-frequenin antibodies stain the central and peripheral nervous system in Drosophila embryos and in larval and adult tissue sections. Frequenin appears to be particularly enriched in synapses, such as the motor nerve endings at neuromuscular junctions. Neuromuscular junctions of transgenic flies, which overexpress frequenin upon heat shock, exhibit an extraordinarily enhanced, frequency-dependent facilitation of neurotransmitter release, with properties identical to those observed in V7 junctions. We propose that frequenin represents a new element for the Ca(2+)-dependent modulation of synaptic efficacy.

Identification of a subunit-specific antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptor channels

Excitatory synaptic transmission in the mammalian central nervous system is mediated predominantly by glutamate receptor (GluR) channels of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate (AMPA/KA) receptor type. A major improvement in our understanding of glutamatergic synaptic transmission has been achieved after the identification of quinoxalinediones (e.g., 6-cyano-7-nitroquinoxaline-2,3-dione) as specific antagonists of AMPA/KA receptors. In addition to their effects on neurons, quinoxalinediones were also shown to block glutamate-induced responses mediated by recombinant AMPA/KA receptor channels expressed in heterologous systems, irrespective of their particular subunit composition. Here we report the identification of an AMPA/KA receptor antagonist that selectively blocks a subset of AMPA/KA receptors. We found that Evans blue, a biphenyl derivative of naphthalene disulfonic acid, blocks at low concentrations (IC50 = 355 nM for the subunit combination GluR1,2) KA-mediated responses of the subunits GluR1, GluR1,2, GluR1,3, and GluR2,3 expressed in Xenopus oocytes but not responses of GluR3 or GluR6. The blocking action of Evans blue was partially reversible and did not compete with KA for the agonist binding site. These findings suggest not only that Evans blue is a potent tool for elucidating the functional role of specific AMPA/KA receptor subtypes for excitatory synaptic transmission but also that it may also represent a powerful starting point for clinically useful drugs that are able to reduce the excitatory drive in specific neuronal populations of the central nervous system.