Biomedical subjects
Publications and source records attributed to W F Dick.
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Inhalation of hyperpolarized (3)He allows magnetic resonance imaging (MRI) of ventilated airspaces. (3)He hyperpolarization decays more rapidly when interacting with paramagnetic O(2). We describe a method for in vivo determination of intrapulmonary O(2) concentrations ([O(2)]) based on MRI analysis of the fate of measured amounts of inhaled hyperpolarized (3)He in imaged regions of the lung. Anesthetized pigs underwent controlled normoventilation in a 1.5-T MRI unit. The inspired O(2) fraction was varied to achieve different end-tidal [O(2)] fractions (FET(O(2))). With the use of a specifically designed applicator, (3)He (100 ml, 35-45% polarized) was administered at a predefined time within single tidal volumes. During subsequent inspiratory apnea, serial two-dimensional images of airways and lungs were acquired. At least once in each animal studied, the radio-frequency excitation used for imaging was doubled at constant FET(O(2)). Signal intensity measurements in regions of interest of the animals' lungs (volume range, 54-294 cm(3)), taken at two different radio-frequency excitations, permitted calculation of [O(2)] in these regions of interest. The [O(2)] fractions in the regions of interest correlated closely with FET(O(2)) (R = 0.879; P < 0.0001). O(2)-sensitive (3)He-MRI may allow noninvasive study of regional distribution of ventilation and alveolar PO(2) in the lung.
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Evidence Based (Emergency) Medicine (EB(E)M is a term referring to the application into daily clinical practice of only those methods, procedures, medications etc. which are based on scientific evidence. Where diagnostic and therapeutic principles have not been validated on a prospective, controlled randomised basis, this should be tried out at a later time, if at all possible. This concept may allow to bridge the gap between research and clinical practice, and represents the major goal of EB(E)M. Protagonists of EBEM are at times confronted with criticism that EBEM does not constitute the only but one out of several possible approaches to quality controlled medical care. The fact that more than 50% of all emergency procedures are not evidence based give rise to the question as to whether the performance of randomised controlled studies is ethically justifiable, if control groups are included whose treatment leaves out generally recommended and recognised (though not evidence based) therapeutic and/or diagnostic principles. The following examples may enumerate some of the procedures, methods or medications, respectively, without proven scientific evidence: Medication for resuscitation of cardiac arrest victims. Medication for acute asthmatic attacks Initial treatment of uncontrolled haemorrhagic shock. Endotracheal intubation in VF/VT. The principle need for initial ventilation and the volumes of ventilation in cardiac arrest patients. Effectiveness of ACD- and VEST-CPR. A few typical examples are presented to illustrate the requirements of current study designs which have to be met before results of an evaluation are accepted by the EBEM scientists to obtain approval for application of a procedure, method or medication in clinical practice (large patient numbers, power calculations, ethical issues) as well as their benefits and drawbacks.
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UNLABELLED: 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.
In a paediatric population, we compared i.m. v oral atropine premedication to a control group without atropine and determined atropine plasma concentrations (APC). Forty-five children were randomly assigned to one of three groups. Group I received atropine, 20 micrograms.kg-1 i.m., 15 min prior to induction. Group II received atropine, 30 micrograms.kg-1 orally, group III received no atropine. APC (expressed as percent of muscarine-2 receptor subtype occupancy), heart rate, rectal temperature, and salivation were determined before atropine, and 15, 25, 45, 60, 90, 120 (no APC), and 150 min following atropine. Only 10-20% of the M2-cholinoceptors were occupied after oral atropine with a peak at 90 min compared to 60-70% occupancy with a peak 25 min after i.m. atropine. The peak in M2-cholinoceptor occupation in group I was paralleled by a peak percentage change in heart rate of 15% from baseline. The peak in receptor occupation in group II did not correspond to the peak increase in heart rate. The percentage change of heart rate over time was not significantly different from baseline values in any of the groups. Bradycardia or temperature changes did not occur in any of the groups. Antisialogogue effects were observed only in group I. We conclude that atropine; 30 micrograms.kg-1 orally is not an equipotent dosage to atropine, 20 micrograms.kg-1 i.m.
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The concept of uniform reporting of data in resuscitation has demonstrated its potential value in pre-hospital and in-hospital cardiac arrest in adults, infants and children, in laboratory research, in disaster research and, hopefully, also in trauma care and research.
The current increase in the cost of health care must be considered as a severe threat to the prehospital emergency services system. Two examples have been selected--the patient with polytrauma and the patient in cardiac arrest--to demonstrate the dilemma between a need for objective data and the requirements of emergency patients. Study results obtained in trauma patients indicating that total prehospital time, including scene time, is correlated to patient outcome have led to the conclusion that at the scene treatment by emergency physicians may be dispensable. It has, however also been demonstrated that the time required for medical treatment at the scene is equivalent to 20% of the total scene time, thus representing only a fraction of the total prehospital time. Correlating the total prehospital time or scene time to outcome therefore appears absurd. The treatment principle of aggressive shock treatment in polytrauma needs critical reevaluation on the basis of results obtained by recent preclinical studies in patients with penetrating torso injuries. Small volume resuscitation could not be demonstrated to improve outcome in polytrauma patients, although a slight improvement in patients with brain injury may be assumed. Endotracheal intubation and early artificial ventilation are proven therapeutic principles in polytraumatized patients. Unfortunately, for ethical reasons randomised carefully controlled comparative studies can not be performed in polytrauma patients unless the patient is fully conscious. The importance of endotracheal intubation and artificial ventilation in unconscious trauma patients becomes apparent under conditions of anaesthesia where the application of the endotracheal tube averts regurgitation, aspiration and concomitant morbidity and mortality. The common causes of cardiovascular collapse and their pathomechanisms, as well as the mechanisms of cardiopulmonary resuscitation, have been widely investigated. Nevertheless, various aspects of their application are still controversial. The most recent study results have recommended initial ventilation prior to thoracic compression. New methods of assisting mechanical cardiopulmonary resuscitation, such as ACD CPR or vest CPR, have shown promising results in animal experiments. However, the importance of results obtained by preclinical randomised controlled investigations in humans need to be confirmed by further studies as to outcome. The efficacy of defibrillation in cases of ventricular fibrillation has been clearly demonstrated, particularly with a view to the interval between ventricular fibrillation and defibrillation. It has further been demonstrated that basic cardiopulmonary resuscitation preserves ventricular fibrillation and thus improves the chance of survival. The present generation of defibrillators has been further improved, particularly by the introduction of biphasic defibrillator wave forms, which may reduce the required energy, as well as possible complications, while offering an increase in the efficacy of defibrillation and a reduction in defibrillator size. Scientific emergency medicine is responsible not only for the development and validation of new methods and concepts, but in particular for their application under quality control conditions. Politicians require an improvement in the quality of the validation of emergency measures, although the instruments available for the investigation of these measures are known to be obsolete (experimental models, experimental design). Additionally, the financial support of research in emergency medicine suffers from being accourded low priority by public research funds such as the German Research Fund. However, in view of the rapid application of experimental results to daily practice it should be emphasized that patients also support research in emergency medicine via their direct financial contributions to the health insurance companies.
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International guidelines for cardiopulmonary resuscitation (CPR) in adults advocate that cardiac arrest be recognized within 5-10 s, by the absence of a pulse in the carotid arteries. However, validation of first responders' assessment of the carotid pulse has begun only recently. We aimed (1) to develop a methodology to study diagnostic accuracy in detecting the presence or absence of the carotid pulse in unresponsive patients, and (2) to evaluate diagnostic accuracy and time required by first responders to assess the carotid pulse. In 16 patients undergoing coronary artery bypass grafting, four groups of first responders (EMT-1: 107 laypersons with basic life support (BLS) training; EMT-2: 16 emergency medical technicians (EMTs) in training; PM-1: 74 paramedics in training; PM-2: 9 certified paramedics) performed, single-blinded and randomly allocated, carotid pulse assessment either during spontaneous circulation, or during non-pulsatile cardiopulmonary bypass. Time to diagnosis of carotid pulse status, concurrent haemodynamics and diagnostic accuracy were recorded. In 10% (6/59), an absent carotid pulse was not recognized as pulselessness. In 45% (66/147), a pulse was not identified despite a carotid pulse with a systolic pressure > or = 80 mmHg. Thus, although sensitivity of all participants for central pulselessness approached 90%, specificity was only 55%. Both sensitivity and, to a lesser degree, specificity improved with increasing training; blood pressure or heart rate had no significant effect. The median diagnostic delay was 24 s (minimum 3 s). When no carotid pulse was found, delays were significantly longer (30 s: minimum 13 s), than when a carotid pulse was identified (15 s; minimum 3 s) (P < 0.0001). Of all participants, only 15% (31/206) produced correct diagnoses within 10 s. Only 1/59 (2%) identified pulselessness correctly within 10 s. Our cardiopulmonary bypass model of carotid pulse assessment proved to be feasible and realistic. We conclude that recognition of pulselessness by rescuers with basic CPR training is time-consuming and inaccurate. Both intensive retraining of professional rescuers and reconsideration of guidelines about carotid pulse assessment are warranted.
Setting standards and implementing quality improvement in trauma care needs consideration of the definitions of standards, guidelines, recommendations and the present quality of trauma care. Essential factors for consideration are the chain of survival and different intervals which may decide on patient outcome: (a) the trauma (occurrence) to trauma recognition interval which has, until now, not been taken into consideration with regard to morbidity and mortality; (b) the scene time is part of the total prehospital time which comprises rescuing the entrapped patient, preparation of the patient for treatment, and transfer to a rescue vehicle. The medical part of the scene time, however, represents only 25% of the total scene time and an even lower percentage of the total prehospital time. Correlating scene time with outcome and concluding that medical treatment at the scene may be detrimental to the patient are thus inaccurate suppositions. It has been shown that the quality of care is not always based on scientific evidence. This is the case for fluid administration, endotracheal intubation, etc. Furthermore, the qualification of the different personnel responding to trauma alert needs to be taken into consideration as well as the quality of care provided by the individual hospitals. The following conclusions may thus be drawn: that, currently there is no scientifically proven standard or care for trauma patients; the role of trauma care standards in the reduction of mortality and morbidity has not yet been identified; implementing incorrect standards may lead to entirely inappropriate conclusions; and that it is essential to perform scientific investigations of the outlined factors in order to establish future standards of trauma care.
Anaesthesia may impair the condition of the neonate either directly (largely mechanically in utero or due to the influence of drugs) or indirectly via alteration of placental perfusion. These influences may further differ during normal caesarean section from those under complicated conditions. The criteria with which neonatal conditions are estimated need to be carefully distinguished with respect to results obtained. Neurobehavioural test results may give different information to the observer. A variety of drugs, not simply one, is used during general anaesthesia (GA). Even the consequences of maternal stress-fetal and neonatal levels of catecholamines or endogenous peptides may play a role. Local anaesthetics are known to cross the placenta as general anaesthetics do; in most cases, their effects are clinically irrelevant. Fetal and neonatal deliterious effects of regional anaesthesia (RA) are mainly related to maternal hypotension and the administration of large doses of local anaesthetics. If adequate doses of local anaesthetics and/or opioids are used, alterations in neurobehavioural scores are subtle and transient. Under normal maternal and fetal conditions, GA and RA are almost identically useful with respect to neonatal well being after caesarean section; subtle and inconsistent neurobehavioral residua may be present for a short period of time following GA. Under conditions of a compromised fetus, the neonate may however benefit from epidural anaesthesia more than from GA.