Acute kidney injury and mild therapeutic hypothermia in patients after cardiopulmonary resuscitation - a post hoc analysis of a prospective observational trial

Extracerebral multiple organ dysfunction and interactions with brain injury after cardiac arrest

Cardiac arrest and successful resuscitation cause whole-body ischemia and reperfusion, leading to brain injury and extracerebral multiple organ dysfunction. Brain injury is the leading cause of death and long-term disability in resuscitated survivors, and was conceptualized and treated as an isolated injury, which has neglected the brain-visceral organ crosstalk. Extracerebral organ dysfunction is common and is significantly associated with mortality and poor neurological prognosis after resuscitation. However, detailed description of the characteristics of post-resuscitation multiple organ dysfunction is lacking, and the bidirectional interactions between brain and visceral organs need to be elucidated to explore new treatment for neuroprotection. This review aims to describe current concepts of post-cardiac arrest brain injury and specific characteristics of post-resuscitation dysfunction in cardiovascular, respiratory, renal, hepatic, adrenal, gastrointestinal, and neurohumoral systems. Additionally, we discuss the crosstalk between brain and extracerebral organs, especially focusing on how visceral organ dysfunction and other factors affect brain injury progression. We think that clarifying these interactions is of profound significance on how we treat patients for neural/systemic protection to improve outcome.

2024 RECOVER Guidelines: Monitoring. Evidence and knowledge gap analysis with treatment recommendations for small animal CPR

OBJECTIVE

To systematically review evidence on and devise treatment recommendations for patient monitoring before, during, and following CPR in dogs and cats, and to identify critical knowledge gaps.

DESIGN

Standardized, systematic evaluation of literature pertinent to peri-CPR monitoring following Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology. Prioritized questions were each reviewed by Evidence Evaluators, and findings were reconciled by Monitoring Domain Chairs and Reassessment Campaign on Veterinary Resuscitation (RECOVER) Co-Chairs to arrive at treatment recommendations commensurate to quality of evidence, risk:benefit relationship, and clinical feasibility. This process was implemented using an Evidence Profile Worksheet for each question that included an introduction, consensus on science, treatment recommendations, justification for these recommendations, and important knowledge gaps. A draft of these worksheets was distributed to veterinary professionals for comment for 4 weeks prior to finalization.

SETTING

Transdisciplinary, international collaboration in university, specialty, and emergency practice.

RESULTS

Thirteen questions pertaining to hemodynamic, respiratory, and metabolic monitoring practices for identification of cardiopulmonary arrest, quality of CPR, and postcardiac arrest care were examined, and 24 treatment recommendations were formulated. Of these, 5 recommendations pertained to aspects of end-tidal CO2 (ETco2) measurement. The recommendations were founded predominantly on very low quality of evidence, with some based on expert opinion.

CONCLUSIONS

The Monitoring Domain authors continue to support initiation of chest compressions without pulse palpation. We recommend multimodal monitoring of patients at risk of cardiopulmonary arrest, at risk of re-arrest, or under general anesthesia. This report highlights the utility of ETco2 monitoring to verify correct intubation, identify return of spontaneous circulation, evaluate quality of CPR, and guide basic life support measures. Treatment recommendations further suggest intra-arrest evaluation of electrolytes (ie, potassium and calcium), as these may inform outcome-relevant interventions.

The future of artificial hibernation medicine: protection of nerves and organs after spinal cord injury

Spinal cord injury is a serious disease of the central nervous system involving irreversible nerve injury and various organ system injuries. At present, no effective clinical treatment exists. As one of the artificial hibernation techniques, mild hypothermia has preliminarily confirmed its clinical effect on spinal cord injury. However, its technical defects and barriers, along with serious clinical side effects, restrict its clinical application for spinal cord injury. Artificial hibernation is a future-oriented disruptive technology for human life support. It involves endogenous hibernation inducers and hibernation-related central neuromodulation that activate particular neurons, reduce the central constant temperature setting point, disrupt the normal constant body temperature, make the body "adapt" to the external cold environment, and reduce the physiological resistance to cold stimulation. Thus, studying the artificial hibernation mechanism may help develop new treatment strategies more suitable for clinical use than the cooling method of mild hypothermia technology. This review introduces artificial hibernation technologies, including mild hypothermia technology, hibernation inducers, and hibernation-related central neuromodulation technology. It summarizes the relevant research on hypothermia and hibernation for organ and nerve protection. These studies show that artificial hibernation technologies have therapeutic significance on nerve injury after spinal cord injury through inflammatory inhibition, immunosuppression, oxidative defense, and possible central protection. It also promotes the repair and protection of respiratory and digestive, cardiovascular, locomotor, urinary, and endocrine systems. This review provides new insights for the clinical treatment of nerve and multiple organ protection after spinal cord injury thanks to artificial hibernation. At present, artificial hibernation technology is not mature, and research faces various challenges. Nevertheless, the effort is worthwhile for the future development of medicine.

EFFECTS OF MESENCHYMAL STEM CELLS ON POSTRESUSCITATION RENAL AND INTESTINAL INJURIES IN A PORCINE CARDIAC ARREST MODEL

ABSTRACT

Objectives: Systemic ischemia-reperfusion triggered by cardiac arrest (CA) and resuscitation often causes postresuscitation multiple organ injuries. Mesenchymal stem cells (MSCs) have been proven to be a promising treatment for regional renal and intestinal ischemia reperfusion injuries. This study aimed to investigate the effects of MSCs on renal and intestinal injuries after cardiopulmonary resuscitation (CPR) in a porcine CA model. Methods: Twenty-two male pigs were randomly assigned to the sham (n = 6), CA/CPR (n = 8), and CA/CPR + MSC (n = 8) groups. Mesenchymal stem cells were differentiated from human embryonic stem cells and then intravenously administered at a dose of 2.5 × 10 6 /kg at 1.5 and 3 d before the CA/CPR procedure. The experimental model was established by 8 min of untreated CA, followed by 8 min of CPR. Renal and intestinal injuries were evaluated based on the serum levels of creatinine, serum urea nitrogen, intestinal fatty acid-binding protein, and diamine oxidase at 1, 2, 4, and 24 h after resuscitation. At the end of the experiment, pathological damage was determined by cell apoptosis and ferroptosis in the renal and intestinal tissues. Results: During CPR, five pigs in the CA/CPR group and seven pigs in the CA/CPR + MSC group were successfully resuscitated. After resuscitation, the serum levels of creatinine, serum urea nitrogen, intestinal fatty acid-binding protein, and diamine oxidase were significantly increased in the CA/CPR and CA/CPR + MSC groups compared with those in the sham group. However, MSC administration significantly decreased the levels of renal and intestinal injury biomarkers compared with those in the CA/CPR group. Cell apoptosis and ferroptosis, which were indicated by the levels of apoptotic cells, iron deposition, lipid peroxidation, antioxidants, and ferroptosis-related proteins, were observed in renal and intestinal tissues after resuscitation in the CA/CPR and CA/CPR + MSC groups. Nevertheless, both were significantly milder in the CA/CPR + MSC group than in the CA/CPR group. Conclusions: MSC administration was effective in alleviating postresuscitation renal and intestinal injuries possibly through inhibition of cell apoptosis and ferroptosis in a porcine CA model.

The Effects of Alda-1 Treatment on Renal and Intestinal Injuries After Cardiopulmonary Resuscitation in Pigs

Aim

After successful cardiopulmonary resuscitation (CPR), most survivors will develop acute kidney injury and intestinal barrier dysfunction, both of which contribute to the poor outcomes of cardiac arrest (CA) victims. Recently, the aldehyde dehydrogenase 2 (ALDH2) agonist, Alda-1 was shown to effectively alleviate regional ischemia/reperfusion injury of various organs. In the present study, we investigated the effects of Alda-1 treatment on renal and intestinal injuries after CA and resuscitation in pigs.

Methods

Twenty-four male domestic pigs were randomly divided into one of the three groups: sham (n = 6), CPR (n = 10), or CPR+Alda-1 (n = 8). CA was induced and untreated for 8 min, and then CPR was performed for 8 min in the CPR and CPR+Alda-1 groups. At 5 min after resuscitation, a dose of 0.88 mg/kg of Alda-1 was intravenously administered in the CPR+Alda-1 group. The biomarkers of renal and intestinal injuries after resuscitation were regularly measured for a total of 24 h. Subsequently, the animals were euthanized, and then renal and intestinal tissues were obtained for the measurements of ALDH2 activity and expression, and cell apoptosis and ferroptosis.

Results

Five of the 10 animals in the CPR group and six of the eight animals in the CPR+Alda-1 group were successfully resuscitated. After resuscitation, the levels of biomarkers of renal and intestinal injuries were significantly increased in all animals experiencing CA and resuscitation compared with the sham group; however, Alda-1 treatment significantly alleviated renal and intestinal injuries compared to the CPR group. Post-resuscitation ALDH2 activity was significantly decreased and its expression was markedly reduced in the kidney and intestine in those resuscitated animals compared with the sham group; nevertheless, both of them were significantly greater in those animals receiving Alda-1 treatment compared to the CPR group. In addition, renal, intestinal apoptosis and ferroptosis after resuscitation were observed in the CPR and CPR+Alda-1 groups, in which both of them were significantly milder in the CPR+Alda1 group than in the CPR group.

Conclusions

The activation of ALDH2 by Alda-1 treatment significantly alleviated post-resuscitation renal and intestinal injuries through the inhibition of cell apoptosis and ferroptosis in a pig model of CA and resuscitation.

Postresuscitation care and prognostication after cardiac arrest-Does sex matter?

Background

There are conflicting results concerning sex-specific differences in the post-cardiac arrest period. We investigated the sex distribution of patients after successful cardiopulmonary resuscitation (CPR), differences in treatment, complications, outcome and sex-specific performance of biomarkers for prognostication of neurological outcome.

Methods

Prospective observational study including cardiac-arrest (CA) patients treated with mild therapeutic hypothermia (MTH) at 33 °C for 24 h or normothermia. We investigated common complications including pneumonia and acute kidney injury (AKI) and neuron-specific enolase, secretoneurin and tau protein as biomarkers of neurological outcome, which was assessed with the cerebral performance categories score at hospital discharge.

Results

Out of 134 patients 26% were female. Women were significantly older (73 years, interquartile range (IQR) 56–79 years vs. 62 years, IQR 53–70 years; p = 0.038), whereas men showed a significantly higher rate of pneumonia (29% vs. 6%; p = 0.004) and a trend towards higher rates of AKI (62% vs. 45%; p = 0.091). Frequency of MTH treatment was not significantly different (48% vs. 31%; p = 0.081). Female sex was not associated with neurological outcome in multivariable analysis (p = 0.524). There was no significant interaction of sex with prognostication of neurological outcome at 24, 48 and 72 h after CPR. At the respective time intervals p_interaction for neuron-specific enolase was 0.524, 0.221 and 0.519, for secretoneurin 0.893, 0.573 and 0.545 and for tau protein 0.270, 0.635, and 0.110.

Conclusion

The proportion of female patients was low. Women presented with higher age but had fewer complications during the post-CA period. Female sex was not associated with better neurological outcome. The performance of biomarkers is not affected by sex.

Supplementary Information

The online version of this article (10.1007/s00508-022-02026-x) contains supplementary material, which is available to authorized users.

Experimental models of acute kidney injury for translational research

Preclinical models of human disease provide powerful tools for therapeutic discovery but have limitations. This problem is especially apparent in the field of acute kidney injury (AKI), in which clinical trial failures have been attributed to inaccurate modelling performed largely in rodents. Multidisciplinary efforts such as the Kidney Precision Medicine Project are now starting to identify molecular subtypes of human AKI. In addition, over the past decade, there have been developments in human pluripotent stem cell-derived kidney organoids as well as zebrafish, rodent and large animal models of AKI. These organoid and AKI models are being deployed at different stages of preclinical therapeutic development. However, the traditionally siloed, preclinical investigator-driven approaches that have been used to evaluate AKI therapeutics to date rarely account for the limitations of the model systems used and have given rise to false expectations of clinical efficacy in patients with different AKI pathophysiologies. To address this problem, there is a need to develop more flexible and integrated approaches, involving teams of investigators with expertise in a range of different model systems, working closely with clinical investigators, to develop robust preclinical evidence to support more focused interventions in patients with AKI.

Acute Kidney Injury in Neonates with Perinatal Asphyxia Receiving Therapeutic Hypothermia

OBJECTIVE

To assess the incidence and severity of acute kidney injury (AKI) and evaluate risk factors that predict AKI in asphyxiated infants receiving therapeutic hypothermia.

STUDY DESIGN

Infants ≥36 weeks' gestation diagnosed with moderate-to-severe perinatal asphyxia and received therapeutic hypothermia were reviewed retrospectively (n = 166). Modified Acute Kidney Injury Network criteria were used to diagnose AKI. The results of infants with AKI were compared with the infants who did not develop AKI.

RESULTS

AKI developed in 49 (29.5%) infants, of whom 22 had stage I, 13 had stage II, and 14 had stage III AKI. The overall mortality rate was 15.7% and was significantly higher in infants with AKI when compared with infants without AKI (41 vs. 5%; p < 0.001). Asystole at birth (p = 0.044), placental abruption (p = 0.041), outborn status (p = 0.041), need for vasopressor support (p = 0.031), increased bleeding tendency (p = 0.031), initial lactate level (p = 0.015), and 12-hour lactate level (p = 0.029) were independent risk factors for the development of AKI. Receiver operating characteristic curve analysis demonstrated a good predictive value for initial lactate level (>15 mmol/L), with 69% sensitivity (95% CI: 55-82) and 82% specificity (95% CI: 74-89), and for 12-hour lactate level (>6 mmol/L), with 83.7% sensitivity (95% CI: 70-93) and 73.5% specificity (95% CI: 64.5-81), to predict AKI.

CONCLUSION

AKI is still a common complication of perinatal asphyxia despite treatment with therapeutic hypothermia. Identification of risk factors associated with the development of AKI in asphyxiated infants would be potentially beneficial to reduce morbidity and mortality. Besides perinatal risk factors, initial and 12-hour lactate concentrations can be used for the early prediction of AKI.

Fast hypothermia induced by extracorporeal circuit cooling alleviates renal and intestinal injury after cardiac arrest in swine

BACKGROUND

Continuous renal replacement therapy (CRRT) was currently demonstrated to be an effective way to induce fast hypothermia and had proective effects on cardiac dysfunction and brain damage after cardiac pulmonary resuscitation (CPR). In the present study, we aimed to investigate the influence of extracorporeal circuit cooling using CRRT on renal and intestinal damage after CPR based on a porcine model.

METHODS

32 pigs were subjected to ventricular fibrillation for 8 min, followed by CPR for 5 min before defibrillation. All were randomized to receive extracorporeal circuit cooling using CRRT (CRRT, n = 9), surface cooling (SC, n = 9), normothermia (NT, n = 9) or sham control (n = 5) at 5 min post resuscitation. Pigs in the CRRT group were cooled by 8-h CRRT cooling with the infusion line initially submerged in 4 °C of ice water and 16-h SC, while in the SC group by a 24-h SC. Temperatures were maintained at a normal range in the other two groups. Biomarkers in serum were measured at baseline and 1, 3, 6, 12, 24 and 30 h post resuscitation to assess organ functions. Additionally, tissues of kidney and intestine were harvested, from which the degree of tissue inflammation, oxidative stress, and apoptosis levels were analyzed.

RESULTS

The blood temperature decreased faster by extracorporeal circuit cooling using CRRT than SC (9.8 ± 1.6 vs. 1.5 ± 0.4 °C/h, P < 0.01). Post-resuscitation renal and intestinal injury were significantly improved in the 2 hypothermic groups compared to the NT group. And the improvement was significantly greater in animals received extracorporeal circuit cooling than those received surface cooling, from both the results of biomarkers in serum and pathological evidence.

CONCLUSION

Fast hypothermia induced by extracorporeal circuit cooling was superior to. surface cooling in mitigating renal and intestinal injury post resuscitation.

Identification of risk factors for renal failure after cardiac surgery by RFILE classification

OBJECTIVE

Acute kidney injury (AKI) is a major complication after cardiovascular surgery. The unclear etiology of this highly complex event challenges definition, diagnosis and prediction of AKI, and hence hampers adequate patient management. Identification of associated risk factors have the potential to overcome this limitation.

METHODS

This retrospective study comprised 3574 patients who underwent cardiac surgery in a hospital in Germany. The patient cohort was interrogated for risk factors for AKI.

RESULTS

The analysis identified risk factors for AKI development, such as type of surgery (particularly bypass surgery) (P = 0.02), previous coronary surgeries (P < 0.01), the application of intra-aortic balloon pump in surgery (P < 0.01), and blood loss during surgery (P < 0.01). In addition, old age, duration of surgery as well as ischemia, perfusion and reperfusion times contributed to AKI development (P < 0.01). Further, perioperative hypothermia also appeared as putative risk factor in the analysis (P < 0.01).

CONCLUSIONS

This study identified several risk factors for the development of AKI after cardiac surgery. Further validation of these risk factors could allow the implementation of adequate patient management, and the appropriate implementation of risk-adverse interventions in cardiovascular surgery.

Acute kidney injury after in-hospital cardiac arrest

AIM

Determine 1) frequency and risk factors for acute kidney injury (AKI) after in-hospital cardiac arrest (IHCA) in the Therapeutic Hypothermia after Pediatric Cardiac Arrest In-Hospital (THAPCA-IH) trial and associated outcomes; 2) impact of temperature management on post-IHCA AKI.

METHODS

Secondary analysis of THAPCA-IH; a randomized controlled multi-national trial at 37 children's hospitals.

ELIGIBILITY

Serum creatinine (Cr) within 24 h of randomization.

OUTCOMES

Prevalence of severe AKI defined by Stage 2 or 3 Kidney Disease Improving Global Outcomes Cr criteria. 12-month survival with favorable neurobehavioral outcome. Analyses stratified by entire cohort and cardiac subgroup. Risk factors and outcomes compared among cohorts with and without severe AKI.

RESULTS

Subject randomization: 159 to hypothermia, 154 to normothermia. Overall, 80% (249) developed AKI (any stage), and 66% (207) developed severe AKI. Cardiac patients (204, 65%) were more likely to develop severe AKI (72% vs 56%,p = 0.006). Preexisting cardiac or renal conditions, baseline lactate, vasoactive support, and systolic blood pressure were associated with severe AKI. Comparing hypothermia versus normothermia, there were no differences in severe AKI rate (63% vs 70%,p = 0.23), peak Cr, time to peak Cr, or freedom from mortality or severe AKI (p = 0.14). Severe AKI was associated with decreased hospital survival (48% vs 65%,p = 0.006) and decreased 12-month survival with favorable neurobehavioral outcome (30% vs 53%,p < 0.001).

CONCLUSION

Severe post-IHCA AKI occurred frequently especially in those with preexisting cardiac or renal conditions and peri-arrest hemodynamic instability. Severe AKI was associated with decreased survival with favorable neurobehavioral outcome. Hypothermia did not decrease incidence of severe AKI post-IHCA.

[Preclinical management of cardiac arrest-extracorporeal cardiopulmonary resuscitation]

BACKGROUND

The chances of surviving out-of-hospital cardiac arrest (OHCA) are still very low. Despite intensive efforts the outcome has remained relatively poor over many years. In specific situations, new technologies, such as extracorporeal cardiopulmonary resuscitation (eCPR) could significantly improve survival with a good neurological outcome.

OBJECTIVE

Does the immediate restoration of circulation and reoxygenation via eCPR influence the survival rate after OHCA? Is eCPR the new link in the chain of survival?

MATERIAL AND METHODS

Discussion of current study results and guideline recommendations.

RESULTS

The overall survival rates after OHCA have remained at 10-30% over many years. Despite low case numbers more recent retrospective studies showed that an improved outcome can be achieved with eCPR. In selected patient collectives survival with a favorable neurological outcome is possible in 38% of the cases.

CONCLUSION

Survival after cardiac arrest and the subsequent quality of life dependent on many different factors. The time factor, i.e. the avoidance of a no-flow phase and reduction of the low-flow phase is of fundamental importance. The immediate restoration of the circulation and oxygen supply by eCPR can significantly improve survival; however, large randomized, controlled trials are currently not available.

Renal replacement therapy is independently associated with a lower risk of death in patients with severe acute kidney injury treated with targeted temperature management after out-of-hospital cardiac arrest

BACKGROUND

The effect of renal replacement therapy (RRT) on the outcomes of severe acute kidney injury (AKI) after out-of-hospital cardiac arrest (OHCA) is uncertain. This study aimed to evaluate the association of RRT with 6-month mortality in patients with severe AKI treated with targeted temperature management (TTM) after OHCA.

METHODS

This was a retrospective analysis of a prospectively collected multicentre observational cohort study that included adult OHCA patients treated with TTM across 22 hospitals in South Korea between October 2015 and December 2018. AKI was diagnosed using the Kidney Disease: Improving Global Outcomes criteria. The primary outcome was 6-month mortality and the secondary outcome was cerebral performance category (CPC) at 6 months. Multivariate Cox regression analysis was performed to define the role of RRT in stage 3 AKI.

RESULTS

Among 10,426 patients with OHCA, 1373 were treated with TTM. After excluding those who died within 48 h of return of spontaneous circulation (ROSC) and those with pre-arrest chronic kidney disease, our study cohort comprised 1063 patients. AKI developed in 590 (55.5%) patients and 223 (21.0%) had stage 3 AKI. Among them, 115 (51.6%) were treated with RRT. The most common treatment modality among RRT patients was continuous renal replacement therapy (111 [96.5%]), followed by intermittent haemodialysis (4 [3.5%]). The distributions of CPC (1-5) at 6 months for the non-RRT vs. the RRT group were 3/108 (2.8%) vs. 12/115 (10.4%) for CPC 1, 0/108 (0.0%) vs. 1/115 (0.9%) for CPC 2, 1/108 (0.9%) vs. 3/115 (2.6%) for CPC 3, 6/108 (5.6%) vs. 6/115 (5.2%) for CPC 4, and 98/108 (90.7%) vs. 93/115 (80.9%) for CPC 5, respectively (P = 0.01). The RRT group had significantly lower 6-month mortality than the non-RRT group (93/115 [81%] vs. 98/108 [91%], P = 0.04). Multivariate Cox regression analyses showed that RRT was independently associated with a lower risk of death in patients with stage 3 AKI (hazard ratio, 0.569 [95% confidence interval, 0.377-0.857, P = 0.01]).

CONCLUSION

Dialysis interventions were independently associated with a lower risk of death in patients with stage 3 AKI treated with TTM after OHCA.

Recovery from acute kidney injury as a potent predictor of survival and good neurological outcome at discharge after out-of-hospital cardiac arrest

Background

Acute kidney injury (AKI) after out-of-hospital cardiac arrest (OHCA) is a well-known predictor for mortality. However, the natural course of AKI including recovery rate after OHCA is uncertain. This study investigated the clinical course of AKI after OHCA and determined whether recovery from AKI impacted the outcomes of OHCA.

Methods

This retrospective multicentre cohort study included adult OHCA patients treated with targeted temperature management (TTM) between January 2016 and December 2017. AKI was diagnosed using the Kidney Disease: Improving Global Outcomes criteria. The primary outcome was the recovery rate after AKI and its association with survival and good neurological outcome at discharge.

Results

A total of 3697 OHCA patients from six hospitals were screened and 275 were finally included. AKI developed in 175/275 (64%) patients and 69/175 (39%) patients recovered from AKI. In most cases, AKI developed within three days of return of spontaneous circulation [155/175 (89%), median time to AKI development 1 (1–2) day] and patients recovered within seven days of return of spontaneous circulation [59/69 (86%), median time to AKI recovery 3 (2–7) days]. Duration of AKI was significantly longer in the AKI non-recovery group than in the AKI recovery group [5 (2–9) vs. 1 (1–5) days; P < 0.001]. Most patients were diagnosed with AKI stage 1 initially [120/175 (69%)]. However, the number of stage 3 AKI patients increased from 30/175 (17%) to 77/175 (44%) after the initial diagnosis of AKI. The rate of survival discharge was significantly higher in the AKI recovery group than in the AKI non-recovery group [45/69 (65%) vs. 17/106 (16%); P < 0.001]. Recovery from AKI was a potent predictor of survival and good neurological outcome at discharge in the multivariate analysis (adjusted odds ratio, 8.308; 95% confidence interval, 3.120–22.123; P < 0.001 and adjusted odds ratio, 36.822; 95% confidence interval, 4.097–330.926; P = 0.001).

Conclusions

In our cohort of adult OHCA patients treated with TTM (n = 275), the recovery rate from AKI after OHCA was 39%, and recovery from AKI was a potent predictor of survival and good neurological outcome at discharge.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2535-1) contains supplementary material, which is available to authorized users.