Isoflurane exposure for three hours triggers apoptotic cell death in neonatal macaque brain

Background

Retrospective clinical studies suggest there is a risk for neurodevelopmental impairment following early childhood exposure to anaesthesia. In the developing animal brain, including those of non-human primates (NHPs), anaesthetics induce apoptotic cell death. We previously reported that a 5 h isoflurane (ISO) exposure in infant NHPs increases apoptosis 13-fold compared with control animals. However, the majority of paediatric surgeries requiring anaesthesia are of shorter durations. We examined whether 3 h ISO exposure similarly increases neuroapoptosis in the NHP developing brain.

Methods

Six-day-old NHP infants ( Macaca mulatta ) were exposed to 3 h of a surgical plane of ISO ( n =6) or to room air ( n =5). Following exposure, NHP brains were screened for neuronal and oligodendrocyte apoptosis using activated caspase-3 immunolabelling and unbiased stereology.

Results

ISO treatment increased apoptosis (neurones + oligodendrocyte) to greater than four times that in the control group [mean density of apoptotic profiles: 57 (SD 22) mm -3 vs 14 (SD 5.2) mm -3 , respectively]. Oligodendrocyte apoptosis was evenly distributed throughout the white matter whereas neuroapoptosis occurred primarily in the cortex (all regions), caudate, putamen and thalamus.

Conclusions

A 3 h exposure to ISO is sufficient to induce widespread neurotoxicity in the developing primate brain. These results are relevant for clinical medicine, as many surgical and diagnostic procedures in children require anaesthesia durations similar to those modelled here. Further research is necessary to identify long-term neurobehavioural consequences of 3 h ISO exposure.

Predictors of difficult videolaryngoscopy with GlideScope® or C-MAC® with D-blade: secondary analysis from a large comparative videolaryngoscopy trial

BACKGROUND

Tracheal intubation using acute-angle videolaryngoscopy achieves high success rates, but is not without difficulty. We aimed to determine predictors of 'difficult videolaryngoscopy'.

METHODS

We performed a secondary analysis of a data set (n=1100) gathered from a multicentre prospective randomized controlled trial of patients for whom difficult direct laryngoscopy was anticipated and who were intubated with one of two videolaryngoscopy devices (GlideScope(®) or C-MAC(®) with D-blade). 'Difficult videolaryngoscopy' was defined as 'first intubation time >60 s' or 'first attempt intubation failure'. A multivariate logistic regression model along with stepwise model selection techniques was performed to determine independent predictors of difficult videolaryngoscopy.

RESULTS

Of 1100 patients, 301 were identified as difficult videolaryngoscopies. By univariate analysis, head and neck position, provider, type of surgery, and mouth opening were associated with difficult videolaryngoscopy (P<0.05). According to the multivariate logistic regression model, characteristics associated with greater risk for difficult videolaryngoscopy were as follows: (i) head and neck position of 'supine sniffing' vs 'supine neutral' {odds ratio (OR) 1.63, 95% confidence interval (CI) [1.14, 2.31]}; (ii) undergoing otolaryngologic or cardiac surgery vs general surgery (OR 1.89, 95% CI [1.19, 3.01] and OR 6.13, 95% CI [1.85, 20.37], respectively); (iii) intubation performed by an attending anaesthestist vs a supervised resident (OR 1.83, 95% CI [1.14, 2.92]); and (iv) small mouth opening (OR 1.18, 95% CI [1.02, 1.36]).

CONCLUSION

This secondary analysis of an existing data set indicates four covariates associated with difficult acute-angle videolaryngoscopy, of which patient position and provider level are modifiable.

[Ischemic complications in neurosurgery: use of calcium antagonists]

Dysregulation of the intracellular calcium concentration is thought to play a key role in the so-called ischemic cascade, as well as for the development of cerebral vasospasm after subarachnoid haemorrhaging (SAH). Therefore, the prophylactic/therapeutic administration of cerebral calcium channel blockers for neurosurgical patients appears to be a compelling idea to prevent ischemic complications. There are abundant data on the efficacy of cerebral calcium antagonists in various animal models of central nervous system pathologies, however, very little clinical evidence exists to justify their use in humans in respective situations. So far there is only evidence for a long-term treatment effect of oral nimodipine in patients suffering from SAH, and this is based essentially on one large controlled clinical trial. Experimental results suggest that blockers of other calcium channel subtypes may be promising for future clinical roles in primary or secondary ischemic brain injury. However, it is also possible that calcium-independent mechanisms play a more important role during the development of the ischemic damage than previously assumed. Currently, there is no clinical evidence to support the prophylactic use of calcium antagonists to prevent ischemic complications in neurosurgical patients without SAH.

Efficacy of vertical infraclavicular plexus block vs. modified axillary plexus block: a prospective, randomized, observer-blinded study

BACKGROUND

Despite containing severe risks, infraclavicular approaches to the brachial plexus gained increasing popularity. Likewise, the vertical infraclavicular plexus block improved anesthesia compared to the standard axillary approach but contains the risk of pneumothorax. Therefore we modified the standard axillary technique by inserting a proximal directed catheter, referred to as a high axillary plexus block. We prospectively compared quality and onset of neural blockade after vertical infraclavicular plexus block (VIP) and high axillary plexus block (HAP) in two randomized groups (30 patients in each).

METHODS

In group VIP the insulated needle was inserted midway between the ventral process of the acromion and the jugular notch. In group HAP, first an axillary needle was placed. Through this a stimulating catheter was inserted in a proximal direction (10-15 cm); correct placement was confirmed by nerve stimulation. All patients received 40 ml ropivacaine 0.75% (300 mg). Discriminating between analgesia and anesthesia, a blinded observer assessed progression of neural blockade every 5 min for 60 min by pin prick. Incomplete blocks were supplemented 60 min after initial injection.

RESULTS

All patients in both groups demonstrated sufficient surgical anesthesia. No patient needed systemic supplementation or general anesthesia. However, vertical infraclavicular plexus block indicated superior anesthesia compared to high axillary plexus block, regarding musculocutaneous, axillary and radial nerve, which were completely blocked with a higher success rate and in a shorter time interval (P < 0.05).

CONCLUSIONS

While both techniques provide sufficient surgical anesthesia, vertical infraclavicular plexus block demonstrated a partially higher success rate and a faster onset than high axillary plexus block.

Spinal anesthesia in an extremely low birth weight infant

A case of spinal anesthesia in an extremely low birth weight male infant (body weight of 930 g at time of surgery) is presented. He was born prematurely at a gestational age of 27 weeks because of a placenta tumor and had to undergo inguinal herniotomy at 34 weeks postconceptional age. He had bronchopulmonary dysplasia and oxygen supply was still required because of frequent deterioration of oxygen saturation. Spinal anesthesia was performed successfully without any complications. Relevant aspects concerning the technique and management of spinal anesthesia in preterm infants are discussed.

Pharmacological preconditioning in global cerebral ischemia

Single dose 3-nitropropionic acid (3-NPA) 24 hr before global ischemia improves neuronal survival in both, neocortex and hippocampus ('chemical preconditioning'). Neuronal survival after transient global ischemia requires new protein synthesis during recovery, especially of those with anti-apoptotic function. Bcl-2-protein is expressed in neurons that survive cerebral ischemia and may parallel the time course of tolerance after ischemic preconditioning. With this study we examined whether differences in bcl-2-protein expression compared to baseline may be involved in the induction of ischemic tolerance using 3-NPA. Male Wistar rats received either a single intraperitoneal (i.p.) dose of 3-NPA (20 mg/kg), and were observed for 3 (n = 4), 12 (n = 5) or 24 hours (n = 5) or the same amount of vehicle and were observed for 24 h (n = 8, controls). Immunohistochemistry allowed to compare the intensity of bcl-2 immunoreactivity at three subsequent time points in hippocampus, dentate gyrus and parietal neocortex with that of control animals. A single dose of 3-NPA caused a significant increase of bcl-2 protein immunoreactivity in hippocampal neurons, i.e. CA 1 (5 out of 5 animals, p = 0.003), CA 3 (5/5, p = 0.003), CA 4 (4/5, p = 0.025), and neocortex (5/5, p = 0.004), in a time dependent manner over a period of 24 hr after injection. Neuronal bcl-2 protein expression in CA 2 and dentate gyrus remained unchanged. The data suggest a possible role of bcl-2-protein in chemical induction of ischemic tolerance using a single subtoxic dose of 3-NPA. Bcl-2-protein expression may be initiated by increased levels of reactive oxygen species (ROS) after 3-NPA administration, as shown by others. Additional bcl-2 protein may then be available to (1) control postischemic ROS burst, (2) protect the mitochondrial membranes, and (3) inhibit pro-apoptotic mechanisms.

[Management of pediatric airway--anatomy, physiology and new developments in clinical practice]

Due to the special features of paediatric anatomy and physiology, the expected and unexpected difficult paediatric airway is one of the major challenges to every anaesthesiologist, paediatrician and emergency physician. During the last years, some new devices have been made available to improve airway management in children and infants, and several studies have advanced our understanding of the risks and benefits of our clinical practice. Certain risk factors for airway related problems during anaesthesia in children having a "cold" have been identified, and there are new aspects of the controversy concerning the use of cuffed endotracheal tube (ETT) in children. New video assisted systems have been introduced for the management of the difficult airway in paediatric patients, and new applications for well-known devices have been suggested, e.g. the laryngeal mask airway (LMA) serving as guidance for fibreoptic intubation. Recent studies have also demonstrated specific problems with the LMA in infants, as well as possible advantages of a new prototype LMA for children, similar to the ProSeal. Furthermore, the following review presents data about the use of the Cuffed Oropharyngeal Airway (COPA) and the Laryngeal Tube (LT) in paediatric patients.

[Paracetamol in childhood. Current state of knowledge and indications for a rational approach to postoperative analgesia]

The administration of paracetamol (in the US known as acetaminophen) to children and infants for postoperative pain after minor surgery is a well established and safe treatment option, if appropriately used. However, if paracetamol is dosed according to traditional recommendations (about 20 mg/kg body weight) frequently a sufficient analgetic effect cannot be achieved immediately after painful interventions. Recently, a higher initial dose (40 mg/kg body weight) was suggested for effective postoperative pain control, which seems especially important for children after ambulatory anesthesia, but may also be associated with certain risks to the patient. Current recommendations also involve appropriate timing and route of administration of paracetamol to be most effective under different clinical circumstances. In contrast, the risk for liver toxicity appears to be very low, if the daily paracetamol dose does not exceed 90 mg/kg body weight in otherwise healthy children, and if specific risk factors of the individual patient are always considered. This review discusses the recent publications on pharmacokinetics and -dynamics, the clinical use and dosing, as well as the risks and benefits of paracetamol for the treatment of postoperative pain in children and infants. Based on this information, specific dosing regimes for the postoperative period are suggested for neonates and infants, as well as for children in different age groups.

Failure to sustain recovery of Na,K-ATPase function is a possible mechanism for striatal neurodegeneration in hypoxic-ischemic newborn piglets

Hypoxia-ischemia (HI) in the newborn can lead to a variety of sensorimotor abnormalities, including movement and posture disorders. Striatal neurons undergo necrosis after HI in piglets, but mechanisms for this neuronal death are not understood. We tested the hypothesis that Na,K-ATPase is defective in striatum early after HI. Piglets (1 week old) were subjected to 30 min hypoxia (arterial oxygen saturation 30%) and then 7 min of airway occlusion (oxygen saturation 5%), producing asphyxic cardiac arrest. Animals were resuscitated and recovered for 3, 6, 12, and 24 h, respectively. Neuronal necrosis in the striatum is progressive [14]. Na,K-ATPase activity (percent of control) was 60, 98, 51, and 54% at 3, 6, 12, and 24 h after HI, respectively. Intrastriatal differences in enzyme activity were detected histochemically, with the putamen showing greater loss of Na,K-ATPase activity than caudate after 12 h recovery. Immunoblotting showed that the levels of the alpha(3) isoform (localized exclusively to neurons) were 85, 115, 101, and 79% of sham control at 3, 6, 12, and 24 h, respectively. Levels of beta(1), the predominant beta isoform, were similar to alpha(3), while levels of the alpha(1) subunit, the catalytic isoform found in neurons and glia, were 182, 179, 226, and 153% at the same recovery times. We conclude that early inactivation of Na,K-ATPase function participates in the pathogenesis of striatal neuron necrosis, but that loss of enzyme function early after HI is not caused by depletion of composite alpha/beta subunits.

The topics of international publications on paediatric anaesthesia from 1993 to 1998

A comprehensive compilation of the current international literature on paediatric anaesthesia is still lacking. It was the aim of this study to identify all publications with a focus on paediatric anaesthesia, and to determine the spectrum of topics, as well as the publication type and language for the period between 1993 and 1998. All articles published in 12 major anaesthesia journals were evaluated and, additionally, a computerized, Internet-based Medline-search was performed using selected keywords. The analysis was limited to original articles, case reports, reviews and editorials. For the period between 1993 and 1998, a total of 2259 (377 per year) publications on paediatric anaesthesia were identified in 295 different journals, the majority of which were on the topic of 'providing anaesthesia' in children (n=1424, 63.0%). In contrast, publications on, for example, 'postanaesthesia care' (6. 3%), and 'organizational aspects of paediatric anaesthesia' (2.2%) were rare. Most articles were written in English (85.1%), and more than 50% reported original data (57.1%). Our results suggest that several topics may be of interest for future research and communication in the field of paediatric anaesthesia and new results should be published in English to reach a large international readership.

Tolerance-Inducing dose of 3-nitropropionic acid modulates bcl-2 and bax balance in the rat brain: a potential mechanism of chemical preconditioning

Many studies have reported ischemia protection using various preconditioning techniques, including single dose 3-nitropropionic acid (3-NPA), a mitochondrial toxin. However, the cellular signal transduction cascades resulting in ischemic tolerance and the mechanisms involved in neuronal survival in the tolerant state still remain unclear. The current study investigated the mRNA and protein expression of the antiapoptotic bcl-2 and the proapoptotic bax. two antagonistic members of the bcl-2 gene family, in response to a single dose of 3-NPA, to global cerebral ischemia-reperfusion. and to the combination of both 3-NPA-pretreatment and subsequent global cerebral ischemia-reperfusion. Brain homogenates of adult Wistar rats (n = 25) were analyzed for bcl-2 and bax mRNA expression using a new highly sensitive and quantitative polymerase chain reaction (PCR) technique that allows real-time fluorescence measurements of the PCR product (LightCycler; Roche Diagnostics, Mannheim, Germany). Animals for mRNA analysis received 3-NPA (20 mg/kg, intraperitoneal; "chemical preconditioning") or vehicle (normal saline), and were either observed for 24 plus 3 hours or were subjected to 15 minutes of global cerebral ischemia 24 hours after the pretreatment and observed for 3 hours of reperfusion. Immunohistochemistry was applied to serial brain sections of additional rats (n = 68) to determine amount and localization of the respective Bcl-2 and Bax protein expression in various brain areas. One set of animals was injected with 3-NPA and observed for 3, 12, 24, and 96 hours; a second set was exposed to 15 minutes global cerebral ischemia, 3, 12, and 24 hours reperfusion; and a third set was pretreated with 3-NPA or saline 24 hours before the ischemic brain insult and observed for 96 hours of reperfusion. The authors found single dose 3-NPA treatment to be associated with an elevated bcl-2:bax ratio (increased bcl-2 expression, decreased bax expression), both on the transcriptional (mRNA) and the translational (protein) level. The differential influence of 3-NPA was maintained during early recovery from global cerebral ischemia (3 hours), when 3-NPA pretreated animals showed higher bcl-2 and lower bax mRNA levels compared with rats with saline treatment. Respective changes in protein expression were localized predominately in neurons vulnerable to ischemic damage. Compared with baseline, Bcl-2 protein was significantly higher in surviving neurons at 96 hours after the insult, whereas Bax protein remained unchanged. However, at this late time of postischemic recovery (96 hours), the protein expression pattern of surviving neurons was not different between animals with and without 3-NPA pretreatment. To the authors' knowledge, the current study is the first report on the differential expression of pro- and antiapoptotic genes after a single, nonlethal dose of 3-NPA. The current results suggest alterations in the balance between pro- and antiapoptotic proteins as a potential explanation for the reported protection provided by chemical preconditioning using 3-NPA in rats.

Publications on paediatric anaesthesia: a quantitative analysis of publication activity and international recognition

A comprehensive compilation of the current international literature on paediatric anaesthesia is lacking. The aim of this study was to identify all articles on clinical practice in paediatric anaesthesia, to name the respective journals, and to assess the publication activity and international recognition of selected countries for a 6-yr period (1993-1998). The search comprised an article-to-article evaluation ('hand search') of 12 peer-reviewed anaesthesia journals, as well as an Internet-based ('SilverPlatter') Medline-search (3,900 medical journals, US National Library of Medicine), both limited to original articles, case reports, reviews and editorials. Selected physical characteristics, for example the number of infants and children aged 0-14 yr old, the number of anaesthetists (specialists) and current impact factors (Science Citation Index) served to assess publication activity and international recognition. During the time period studied, 2259 articles (377/yr) were published on paediatric anaesthesia in 295 medical journals. The articles were primarily written in English (85.1%) and the majority originated from the USA (35.4%) and the UK (12.6%). The largest number of publications (77.7%) appeared in 29 anaesthesia journals, all referenced in Medline, with 46% being published by only five journals. Most authors published in journals of their home country/region. Authors from the UK ranked highest in publication activity, followed by those from Canada, Switzerland, Sweden and Denmark. The highest impact factor was achieved by US and UK authors. We conclude that publications on paediatric anaesthesia are clustered in a small number of journals and are written predominantly by authors from English-speaking countries, who achieved the highest international recognition.

Neuronal death in newborn striatum after hypoxia-ischemia is necrosis and evolves with oxidative stress

The mechanisms for neurodegeneration after hypoxia-ischemia (HI) in newborns are not understood. We tested the hypothesis that striatal neuron death is necrosis and evolves with oxidative stress and selective organelle damage. Piglets ( approximately 1 week old) were used in a model of hypoxia-asphyxia and survived for 3, 6, 12, or 24 h. Neuronal death was progressive over 3-24 h recovery, with approximately 80% of putaminal neurons dead at 24 h. Striatal DNA was digested randomly at 6-12 h. Ultrastructurally, dying neurons were necrotic. Damage to the Golgi apparatus and rough endoplasmic reticulum occurred at 3-12 h, while most mitochondria appeared intact until 12 h. Mitochondria showed early suppression of activity, then a transient burst of activity at 6 h, followed by mitochondrial failure (determined by cytochrome c oxidase assay). Cytochrome c was depleted at 6 h after HI and thereafter. Damage to lysosomes occurred within 3-6 h. By 3 h recovery, glutathione levels were reduced, and peroxynitrite-mediated oxidative damage to membrane proteins, determined by immunoblots for nitrotyrosine, occurred at 3-12 h. The Golgi apparatus and cytoskeleton were early targets for extensive tyrosine nitration. Striatal neurons also sustained hydroxyl radical damage to DNA and RNA within 6 h after HI. We conclude that early glutathione depletion and oxidative stress between 3 and 6 h reperfusion promote damage to membrane and cytoskeletal proteins, DNA and RNA, as well as damage to most organelles, thereby causing neuronal necrosis in the striatum of newborns after HI.

Control of brain temperature during experimental global ischemia in rats

Temperature control during experimental ischemia continues to be of major interest. However, if exposure of brain tissue is necessary during the experiment, regional heat loss may occur even when the core temperature is maintained. Furthermore, valid non-invasive brain temperature monitoring is difficult in small rodents. This paper describes a method for both monitoring and maintenance of brain temperature during small animal preparations in a stereotaxic frame. The device used includes an ear-bar thermocouple probe and a small near-infrared radiator. The new equipment permitted to maintain peri-ischemic brain temperature at a desired level while carrying out non-invasive continuous recordings of cerebral blood flow (laser Doppler-flowmetry) and of electrical brain function (EEG). In contrast, without extracranial heat application, superficial and basal brain temperatures decreased during global cerebral ischemia by 4.1 +/- 0.1 and 4.6 +/- 0.4 degrees C (mean +/- SEM), respectively, returning to baseline values at 15-30 min of reperfusion while rectal (core) temperature remained stable at baseline values. The ear-bar thermocouple probe (tympanic membrane) reliably reflected basal brain temperature, and temperature in superficial brain areas correlated well with that in the temporal muscle. Our data show that the new system allows to exclude unwanted hypothermic neuroprotection, and does not interfere with optical and electrical measurement techniques.

Successful treatment of a patient with ARDS after pneumonectomy using high-frequency oscillatory ventilation

High frequency oscillatory ventilation (HFOV) was used in a patient who developed the acute respiratory distress syndrome 5 days following a right pneumonectomy for bronchogenic carcinoma. When conventional pressure-controlled ventilation failed to maintain adequate oxygenation, HFOV dramatically improved oxygenation within the first few hours of therapy. Pulmonary function and gas exchange recovered during a 10-day period of HFOV. No negative side effects were observed. Early use of HFOV may be a beneficial ventilation strategy for adults with acute pulmonary failure, even in the postoperative period after lung resection.

Quantitative EEG during early recovery from hypoxic-ischemic injury in immature piglets: burst occurrence and duration

This study examined the course of EEG recovery in an animal model of hypoxic-ischemic injury. The model used periods of hypoxia, room air and asphyxia to induce cardiac arrest. One-week-old piglets (n = 16) were exposed to a period of hypoxia, room air and complete asphyxia for 7 minutes. After cardiac arrest and resuscitation, two EEG features were evaluated as prognostic indicators of behavioral outcome as assessed by a neuroscore at 24 hours after insult. A prominent EEG feature was the number and duration of bursts evident during recovery. Episodes of bursting were detected through the thresholds on sustained periods of elevated power. After the animal was resuscitated, the EEG was monitored continuously for 4 hours. To assess outcome in the recovering animal, a behavioral testing scale was used to test the animal's neurological capabilities. Trends of EEG burst counts were measured through thresholds on sustained power changes. Bursts are energy transients in the EEG record. High degrees of bursting were characteristic of animals having good neurological condition whereas piglets having low burst counts had poor 24 hr neuroscores. At 100 min the average burst rate of the good neuroscore outcome group was more than 8 per min and was significantly different from the poor outcome group's level of 2.7 (p < or = 0.05). When these counts were weighted by their total duration, differences between groups increased (p < or = 0.02). This study showed that the QEEG measure of burst counts and duration together provided a strong prognostic indication of the 24 hour outcome after asphyxic injury in a neonatal animal model. The critical determinant of the bursting character was the time when bursting occurred. Bursting occurring early in recovery was a good gauge of outcome. We conclude that quantitative EEG analysis and interpretation can be an important tool for the outcome determination during recovery from cerebral injury states.

Effects of the AMPA receptor antagonist NBQX on outcome of newborn pigs after asphyxic cardiac arrest

In neonates, asphyxia is a common cause of neuronal injury and often results in seizures. The authors evaluated whether blockade of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors during asphyxia and early recovery with 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo-(F)-quinoxaline (NBQX) ameliorates neurologic deficit and histopathology in 1-week-old piglets. Anesthetized piglets were exposed to a sequence of 30 minutes of hypoxia, 5 minutes of room air ventilation, 7 minutes of airway occlusion, and cardiopulmonary resuscitation. Vehicle or NBQX was administered intravenously before asphyxia (30 mg/kg) and during the first 4 hours of recovery (15 mg/kg/h). Neuropathologic findings were evaluated at 96 hours of recovery by light microscopic and cytochrome oxidase histochemical study. Cardiac arrest occurred at 5 to 6 minutes of airway occlusion, and cardiopulmonary resuscitation restored spontaneous circulation independent of treatment modalities in about 2 to 3 minutes. Neurologic deficit over the 96-hour recovery period was not ameliorated by NBQX. Seizure activity began after 24 to 48 hours in 7 of 10 animals with vehicle and in 9 of 10 of animals with NBQX. In each group, four animals died in status epilepticus. Neuropathologic outcomes were not improved by NBQX. The density of remaining viable neurons was decreased in parietal cortex and putamen by NBQX treatment. Metabolic defects in cytochrome oxidase activity were worsened by NBQX treatment. Seizure activity during recovery was associated with reduced neuronal viability in neocortex and striatum in piglets from both groups that survived for 96 hours. This neonatal model of asphyxic cardiac arrest and resuscitation generates neurologic deficits, clinical seizure activity, and selective damage in regions of basal ganglia and sensorimotor cortex. In contrast to other studies in mature brain, AMPA receptor blockade with NBQX failed to protect against neurologic damage in the immature piglet and worsened postasphyxic histopathologic outcome in neocortex and putamen.

Effect of arrest time and cerebral perfusion pressure during cardiopulmonary resuscitation on cerebral blood flow, metabolism, adenosine triphosphate recovery, and pH in dogs

OBJECTIVES

To test the hypothesis that greater cerebral perfusion pressure (CPP) is required to restore cerebral blood flow (CBF), oxygen metabolism, adenosine triphosphate (ATP), and intracellular pH (pHi) levels after variable periods of no-flow than to maintain them when cardiopulmonary resuscitation (CPR) is started immediately.

DESIGN

Prospective, randomized, comparison of three arrest times and two perfusion pressures during CPR in 24 anesthetized dogs.

SETTING

University cerebral resuscitation laboratory.

INTERVENTIONS

We used radiolabeled microspheres to determine CBF and magnetic resonance spectroscopy to derive ATP and pHi levels before and during CPR. Ventricular fibrillation was induced, epinephrine administered, and thoracic vest CPR adjusted to provide a CPP of 25 or 35 mm Hg after arrest times of O, 6, or 12 mins.

MEASUREMENTS AND MAIN RESULTS

When CPR was started immediately after arrest with a CPP of 25 mm Hg, CBF and ATP were 57 +/- 10% and 64 +/- 14% of prearrest (at 10 mins of CPR). In contrast, CBF and ATP were minimally restored with a CPP at 25 mm Hg after a 6-min arrest time (23 +/- 5%, 16 +/- 5%, respectively). With a CPP of 35 mm Hg, extending the no-flow arrest time from 6 to 12 mins reduced reflow from 71 +/- 11% to 37 +/- 7% of pre-arrest and reduced ATP recovery from 60 +/- 11% to 2 +/- 1% of pre-arrest. After 6- or 12-min arrest times, brainstem blood flow was restored more than supratentorial blood flow, but cerebral pHi was never restored.

CONCLUSIONS

A CPP of 25 mm Hg maintains supratentorial blood flow and ATP at 60% to 70% when CPR starts immediately on arrest, but not after a 6-min delay. A higher CPP of 35 mm Hg is required to restore CBF and ATP when CPR is delayed for 6 mins. After a 12-min delay, even the CPP of 35 mm Hg is unable to restore CBF and ATP. Therefore, increasing the arrest time at these perfusion pressures increases the resistance to reflow sufficient to impair restoration of cerebral ATP.

["Topless" cardiopulmonary resuscitation? Should heart-lung resuscitation be preformed without artificial resuscitation?]

A paper published in various US journals on Emergency Medicine in 1997, has raised considerable concerns. The authors question if it is justified to continue to recommend initial ventilation as part of basic CPR when performed by lay-bystanders. A few aspects need to be discussed and some questions have to be answered before any changes in the current recommendations may even be considered: e.g. 1. How convincing does the available evidence support the following hypotheses: 1.1. Lay CPR without mouth-to-mouth-ventilation provides better outcome after cardiac arrest than lay CPR with mouth-to-mouth-ventilation. 1.2. Endotracheal intubation may be detrimental in patients suffering from hemodynamic compromises, particularly from VF. 2. Is it scientifically and ethically acceptable to design and perform prospective randomized controlled trials (RCTs) to evaluate the efficacy of those components of BCLS and ACLS which have in accordance with AHA-, ERC Guidelines and ILCOR Statements in the past been applied in millions of cardiac arrest victims and have obviously enabled the patients to lead a meaningful life after survival; under conditions of the proposed study design patients of the study group would be left without the treatment option ventilation, thus diminishing their chances of survival. Ad 1: The arguments presented by the authors are hardly convincing. The authors themselves state elsewhere that reluctance to perform mouth-to-mouth-ventilation should not represent a major problem because most cardiac arrests of cardiac etiology occur at home and in the presence of a relative or friend. Moreover, unreliable recommendations for mouth-to-mouth-ventilation (AHA), lack of training, retention of skills and knowledge, and a deficit in motivation include the main causes of the disappointingly low figures of bystander CPR worldwide. This situation cannot be improved simply by eliminating a lifesaving component of CPR-ventilation. Instead, the proposal to abandon the administration of unreasonably high ventilation volumes (800-1200 ml/breath) from the present guidelines and to recommend volumes ranging from 400-500 ml/breath recently made by the ERC should be given serious consideration. Furthermore, equipment and training manikins need to be adapted to these more reasonable volumes. Independently of the mechanisms of slow decreases in SaO2 after cardiac arrest (provided no compressions are performed) independently of gasping, ventilatory effects of standard compression or ACD-HCPR in the absence of mouth-to-mouth-ventilation, it is essential to realise that the patient's airways need to be maintained open at all times (this is unlike animal experiments where the airways are primarily kept open by the respective tissue structures): The minimum requirement of First Responder CPR is the guarantee that open airways are maintained. It may possibly be discussed if the present sequence of ABC might be changed to CAB, a practice adopted in the Netherlands many years ago, however, outcome trials an CAB have not been published to date. In addition, greater demands should be made of training requirements in BLS, attendance of refresher courses should be required, and other groups of the population should be included into these programmes than only relatives or friends of patients at risk of a cardiac arrest. The programmes need to be made mandatory for greater variety of groups and individuals to increase the efficacy and efficiency of bystander resuscitation. The hypotheses made by the above-mentioned authors are neither scientifically nor ethically acceptable. Ad 2: Pepe's argument regarding the efficacy of endotracheal intubation (ETI) in VF-patients has not been scientifically proven and lacks conclusive evidence. ETI serves to protect the airways and lungs against aspiration of regurgitated material and to facilitate artificial ventilation including PEEP, both under anaesthesia and resuscitation. The efficacy of ETI in the OR has long b

Effects of propofol (intravenous propofol emulsion) on cell membranes measured by electrofusion and electroporation

The influence of propofol (CAS 2078-54-8 (intravenous propofol emulsion) on cell membrane properties was investigated in vitro with techniques of cell electrofusion and cell electroporation. Human lymphoma cells and plant protoplasts were chosen as a model system. Propofol (intravenous propofol emulsion) decreased the electrofusion yield of the cells and their membrane permeability. A 50% decrease in relative electrofusion was observed in human lymphoma cells in the presence of about 0.05 mmol/l propofol (intravenous propofol emulsion) and in plant protoplasts in the presence of about 0.1 mmol/l. The fusion of human lymphoma cells was inhibited to 100% at concentrations higher than 0.2 mmol/l propofol and 0.4 mmol/l intravenous propofol emulsion. The membrane permeability of human lymphoma cells decreased by the factor of two with increasing propofol concentrations up to about 0.1 mmol/l. The effects of electroporation were highly reversible. Propofol (intravenous propofol emulsion) was more effective than tetracaine. These sensitive techniques are suitable for the investigation of interactions between anesthetic drugs and the cell membrane.

Poor outcome after hypoxia-ischemia in newborns is associated with physiological abnormalities during early recovery. Possible relevance to secondary brain injury after head trauma in infants

"Secondary hypoxia/ischemia" (i.e. regional impairment of oxygen and substrate delivery) results in secondary deterioration after traumatic brain injury in adults as well as in children and infants. However, detailed analysis regarding critical physiological abnormalities resulting from hypoxia/ischemia in the immature brain, e.g. acid-base-status, serum glucose levels and brain temperature, and their influence on outcome, are only available from non-traumatic experimental models. In recent studies on hypoxic/asphyxic cardiac arrest in neonatal piglets, we were able to predict short-term outcome using specific physiologic abnormalities immediately after the insult. Severe acidosis, low serum glucose levels and fever after resuscitation were associated with an adverse neurologic recovery one day after the insult. The occurrence of clinically apparent seizure activity during later recovery increased mortality (epileptic state), and survivors had greater neocortical and striatal brain damage. Brain damage after transient hypoxia/ischemia and "secondary brain injury" after head trauma may have some mechanistic overlap, and these findings on physiological predictors of outcome may also apply to pathologic conditions in the post-traumatic immature brain. Evaluation of data from other models of brain injury will be important to develop candidate treatment strategies for head-injured infants and children and may help to initiate specific studies about the possible role of these physiological predictors of brain damage in the traumatically injured immature brain.

Neurodegeneration in excitotoxicity, global cerebral ischemia, and target deprivation: A perspective on the contributions of apoptosis and necrosis

In the human brain and spinal cord, neurons degenerate after acute insults (e.g., stroke, cardiac arrest, trauma) and during progressive, adult-onset diseases [e.g., amyotrophic lateral sclerosis, Alzheimer's disease]. Glutamate receptor-mediated excitotoxicity has been implicated in all of these neurological conditions. Nevertheless, effective approaches to prevent or limit neuronal damage in these disorders remain elusive, primarily because of an incomplete understanding of the mechanisms of neuronal death in in vivo settings. Therefore, animal models of neurodegeneration are crucial for improving our understanding of the mechanisms of neuronal death. In this review, we evaluate experimental data on the general characteristics of cell death and, in particular, neuronal death in the central nervous system (CNS) following injury. We focus on the ongoing controversy of the contributions of apoptosis and necrosis in neurodegeneration and summarize new data from this laboratory on the classification of neuronal death using a variety of animal models of neurodegeneration in the immature or adult brain following excitotoxic injury, global cerebral ischemia, and axotomy/target deprivation. In these different models of brain injury, we determined whether the process of neuronal death has uniformly similar morphological characteristics or whether the features of neurodegeneration induced by different insults are distinct. We classified neurodegeneration in each of these models with respect to whether it resembles apoptosis, necrosis, or an intermediate form of cell death falling along an apoptosis-necrosis continuum. We found that N-methyl-D-aspartate (NMDA) receptor- and non-NMDA receptor-mediated excitotoxic injury results in neurodegeneration along an apoptosis-necrosis continuum, in which neuronal death (appearing as apoptotic, necrotic, or intermediate between the two extremes) is influenced by the degree of brain maturity and the subtype of glutamate receptor that is stimulated. Global cerebral ischemia produces neuronal death that has commonalities with excitotoxicity and target deprivation. Degeneration of selectively vulnerable populations of neurons after ischemia is morphologically nonapoptotic and is indistinguishable from NMDA receptor-mediated excitotoxic death of mature neurons. However, prominent apoptotic cell death occurs following global ischemia in neuronal groups that are interconnected with selectively vulnerable populations of neurons and also in nonneuronal cells. This apoptotic neuronal death is similar to some forms of retrograde neuronal apoptosis that occur following target deprivation. We conclude that cell death in the CNS following injury can coexist as apoptosis, necrosis, and hybrid forms along an apoptosis-necrosis continuum. These different forms of cell death have varying contributions to the neuropathology resulting from excitotoxicity, cerebral ischemia, and target deprivation/axotomy. Degeneration of different populations of cells (neurons and nonneuronal cells) may be mediated by distinct or common causal mechanisms that can temporally overlap and perhaps differ mechanistically in the rate of progression of cell death.

Effects of normobaric oxygen on ciliary beat frequency of human respiratory epithelium

Respiratory infection is a major cause of morbidity after general anaesthesia. Impairment of respiratory ciliary beat frequency (CBF) by different stress factors causes a decrease in mucus transport rate (MTR). We have tested the effect of different concentrations of oxygen on CBF of human respiratory epithelium in a prospective, randomized, in vitro study. Samples of superficial mucosa of the inferior nasal turbinates of 20 non-smoking healthy volunteers were harvested and exposed to three different oxygen environments (group I = 21% oxygen, group II = 60% oxygen and group III = 95% oxygen) for 2 h. In 50% of the samples, exposure time was prolonged. At 30, 60, 90, 120 and 240 min, light microscopic images of cilia activity were videotaped and CBF was later assessed in slow motion. Compared with baseline, group I showed no difference in CBF throughout the study. CBF was increased in group II from mean 9.7 (SD 0.4) to 11.2 (0.4) Hz (16%, P < 0.001) and in group III from 9.5 (0.6) to 12.1 (0.5) Hz (28%, P < 0.001) at 120 min. After 240 min of exposure to 95% oxygen, the CBF trend in group III was reduced to 11.8 (0.6) Hz but still remained above baseline. We conclude that oxygen appeared to have a dose- and time-dependent accelerating effect on CBF. Prolonged exposure to high oxygen concentrations reversed this trend. Direct oxygen toxicity ("oxygen stress") is a possible explanation for this effect. These changes may result in impaired MTR.

Neurogenic pulmonary oedema after generalized epileptic seizure

The diagnosis 'tonic clonic seizure' is frequently established by emergency physicians on scene. In patients with epilepsy mortality due to accidents, asphyxia, cardiac arrhythmias or postictal neurogenic pulmonary oedema (NPO) is twice as high as in the general population. We report a case of acute pulmonary oedema after a tonic clonic seizure. Following this event, the patient developed respiratory insufficiency and evidence of pulmonary oedema not associated with the classic aetiologies of congestive heart failure, aspiration or toxic exposure. The patient survived the incident after aggressive prehospital treatment, long-term intensive care and subsequent rehabilitation. A systematic case analysis and an introduction to the pathophysiology of NPO are presented. We recommend a positive approach to the management of NPO consisting primarily of interventions to stabilize vital functions, decrease intracranial pressure and normalize vegetative dysregulation. Emergency physicians need to consider the possibility of NPO in all cases of pulmonary oedema of unknown origin.

[Neurogenic pulmonary edema. Pathogenesis, clinical picture and therapy]

Neurogenic pulmonary edema (NPE) is a rare but always life-threatening complication in patients with central nervous system lesions. NPE is evident if patients shortly after cerebral lesions suddenly develop pulmonary edema and other causes of the symptoms, such as aspiration of gastric content, congestive heart failure and direct toxic exposure, are ruled out.

METHODS

The current body of literature, partially obtained by computer-guided search (Winspirs) regarding epidemiology, pathophysiology and therapy of NPE was reviewed. Additionally, the case of a patient who developed a sudden pulmonary edema after an episode of tonic-clonic seizures is analyzed. We first provide information about history, definition, incidence and mortality of NPE. Second, a case report of a postictal NPE is presented to illustrate the clinical picture of NPE, and the applied therapeutic strategies are discussed. Third, recent pathophysiologic concepts about symptoms and possible therapeutic principles are reviewed. Fourth, a rational therapeutic plan for the prehospital emergency therapy of NPE is outlined.

RESULTS

The different etiologies all have one characteristic feature: an acute emergency which causes increased intracerebral pressure (ICP). NPE is known in patients after cerebral trauma, intracranial hemorrhage, stroke, intracranial tumor or seizures. The incidence is estimated at around 1% after cerebral trauma, at 71% after cerebral hemorrhage and at 2% after seizures. Mortality is appraised to lie between 60 and 100%, independent of etiology. There is a definite pathophysiologic sequence leading to NPE: a central nervous system lesion causes a sudden increase in ICP which triggers an upregulation of sympathetic signal transduction to assure brain perfusion. Increased tonus of venous and arterial vessels and of myocardial function are the immediate consequences. However, if systemic vascular resistance (SVR) increases excessively, left ventricular failure and finally pulmonary edema (NPE) may result. Additionally, the protein-rich edema fluid points to an increased endothelial permeability within the pulmonary circuit. This is thought to be caused by the acute pressure increase and by neurohumoral mechanisms, possibly similar to those described for the systemic inflammatory response syndrome (SIRS). The most important central nervous system structures involved in NPE are the medulla oblongata and the hypothalamus.

CONCLUSION

NPE is always a life-threatening symptom after increased ICP, where immediate therapeutic interventions are imperative. A rational therapeutic approach needs to be focused on decreasing ICP as primary goal. Additionally, attempts should be made to optimize body oxygenation, decrease pre- and afterload and increase myocardial contractility. Postictal patients suspicious for incipient ventilation problems must be admitted to hospital for further evaluation.

Hypoxia-ischemia causes abnormalities in glutamate transporters and death of astroglia and neurons in newborn striatum

The neonatal striatum degenerates after hypoxia-ischemia (H-I). We tested the hypothesis that damage to astrocytes and loss of glutamate transporters accompany striatal neurodegeneration after H-I. Newborn piglets were subjected to 30 minutes of hypoxia (arterial O2 saturation, 30%) and then 7 minutes of airway occlusion (O2 saturation, 5%), producing cardiac arrest, followed by cardiopulmonary resuscitation. Piglets recovered for 24, 48, or 96 hours. At 24 hours, 66% of putaminal neurons were injured, without differing significantly thereafter, but neuronal densities were reduced progressively (21-44%). By DNA nick-end labeling, the number of dying putaminal cells per square millimeter was increased maximally at 24 to 48 hours. Glial fibrillary acidic protein-positive cell body densities were reduced 48 to 55% at 24 to 48 hours but then recovered by 96 hours. Early postischemia, subsets of astrocytes had fragmented DNA; later postischemia, subsets of astrocytes proliferated. By immunocytochemistry, glutamate transporter 1 (GLT1) was lost after ischemia in the astroglial compartment but gained in cells appearing as neurons, whereas neuronal excitatory amino acid carrier 1 (EAAC1) dissipated. By immunoblotting, GLT1 and EAAC1 levels were 85% and 45% of control, respectively, at 24 hours of recovery. Thus, astroglial and neuronal injury occurs rapidly in H-I newborn striatum, with early gliodegeneration and glutamate transporter abnormalities possibly contributing to neurodegeneration.

[End-tidal CO2 measurement in anesthetic gases. An important global measurement in emergency medicine: theoretical background, indications and overview of available, transportable measurement systems]

Currently, even in prehospital emergency medicine (PEM), continuous end-tidal CO2 monitoring is frequently used as a sensitive and non-invasive technique in ventilated patients. Due to its central role, the continuous measurement of exhaled CO2 provides immediate information about the status of three essential functions of the organism: ventilation, circulation, and metabolism.

METHODS

Recent literature, obtained by a computer-guided search (Winspirs), and product information of all currently available capnometry devices were reviewed in detail. Firstly, the theoretical background of different CO2-measurement methods and techniques is described. Secondly, indications and specific implications for the out-of-hospital use of capnometry are discussed. Thirdly, different monitoring systems suitable for pre-hospital care are evaluated.

RESULTS

There are two basic principles to reliably determine end-tidal CO2 (EtpCO2) that can be realised in portable monitors: qualitative measurements with a paper indicator and quantitative measurements using non-dispersive infrared spectroscopy. Capnography is a feature of more advanced units to provide the emergency physician with additional information by displaying EtpCO2 values versus time. Multiple indications for capnometry in emergency situations are listed, all related to the evaluation of patient's ventilation, circulation, and metabolism. Specific implications regarding mobility, ease of use, patient hygiene and accuracy of measurements are mentioned. Five units, each representing a different type of CO2 monitor, are described and evaluated for their use in PEM.

CONCLUSIONS

Some current portable CO2 monitors allow fast and reliable measurement of EtpCO2 even in the out-of-hospital care of critically ill patients. However, the development of a new portable monitoring system comprising the three most important ventilation parameters (ventilation rate, EtpCO2 and peripheral O2 saturation) seems to be a promising step for the improvement of monitoring in out-of-hospital emergencies.

Dominant frequency analysis of EEG reveals brain's response during injury and recovery

A new method of monitoring an analyzing electroencephalogram (EEG) signals during brain injury is presented. EEG signals are modeled using the autoregressive (AR) technique to obtain the frequencies where there are peaks in the spectrum. The powers at these dominant frequencies are analyzed to reveal the state of brain injury during an experimental study involving progressive hypoxia, asphyxia, and recovery. Neonatal piglets (n = 8) were exposed to a sequence of 30 min of hypoxia (10% oxygen), 5 min of room air, and 7 min of asphyxia. They then received cardiopulmonary resuscitation and were subsequently monitored for 4 h. An optimal AR model order of six was obtained for these data, resulting in three dominant frequencies. These dominant frequencies, referred to as the low, medium, and high frequency components, fell in the bands 1.0-5.5 Hz, 9.0-14.0 Hz, and 18.0-21.0 Hz, respectively. A remarkable feature of our data is the spectral dispersion, or diverging trends in the three frequency bands. During hypoxia, the relative powers of the medium and high-frequency components of EEG increased up to 160% and 176%, from their respective baseline values. During the first minute of asphyxia the medium- and high-frequency powers (relative to baseline) increased by 280-400%. The power in three frequency components went down to nearly zero within 40-80 s of asphyxia. During recovery, the phenomenon of burst-suppression was clearly exhibited in the low-frequency component. A new index, called mean normalized separation, representing the degree of disproportionality in the recovery of powers of the three dominant components relative to their mean recovered power, is presented as a possible single indicator of electrical function recovery. In conclusion, dominant frequency analysis helps reveal the brain's graded electrical response to injury and recovery.