Search

Background: A case of fatal hyperammonemia complicating orthotopic lung transplantation was previously reported.Objective: To describe the incidence, clinical features, and treatment of hyperammonemia associated with orthotopic lung transplantation.Design: Retrospective cohort analysis.Setting: Academic medical center and lung transplantation center in Philadelphia, Pennsylvania.Patients: 145 sequential adult patients who underwent orthotopic lung transplantation.Measurements: Plasma ammonium levels.Results: Six of the 145 patients who had had orthotopic lung transplantation developed hyperammonemia, all within the first 26 days after transplantation. The 30-day post-transplantation mortality rate was 67% for patients with hyperammonemia compared with 17% for those without hyperammonemia (P = 0.01). Development of major gastrointestinal complications (P = 0.03), use of total parenteral nutrition (P < 0.001), and lung transplantation for primary pulmonary hypertension (P = 0.045) were associated with hyperammonemia.Conclusions: Hyperammonemia is a potentially fatal event occurring after orthotopic lung transplantation. It is associated with high nitrogen load, concurrent medical stressors, primary pulmonary hypertension, and hepatic glutamine synthetase deficiency. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to try and determine the best predictors of hospital length of stay and discharge destination in patients admitted to a neuroscience service., Methods: Valid data was collected for 170 patients. Variables included age, gender, location prior to admission, principle diagnosis, various physiological measurements upon admission, comorbidity, independence in various activities of daily living prior to admission, length of stay, and disposition upon discharge. Study design was a correlational descriptive study performed through the analysis of data and the development and validation of statistically significant factors in determining the length of stay., Results: All factors with a strong ( P < 0.05) relationship with the length of stay were entered into a forward stepwise linear regression with length of stay as the dependent variable. The three most significant variables in predicting length of stay in this study were admission from an outpatient setting, modified Rankin score on admission, and systolic blood pressure on admission., Conclusions: Functional status at admission, specifically, a higher modified Rankin score and a lower systolic blood pressure along with the acquisition of deep vein thrombosis, catheter associated urinary tract infections, intubation, and admission to an intensive care unit all have a statistically significant effect on the hospital length of stay., Competing Interests: There are no conflicts of interest.

Hyperglycemia accentuates the injury produced by anoxia both in the central and peripheral nervous system. To understand whether this is a consequence of changes in metabolic pathways produced by anoxia, the effect of the metabolic substrate used by the rat peripheral nerve on the nerve action potential (NAP) was studied in the presence and absence of anoxia. In the continuously oxygenated state, the NAP was well preserved with glucose, lactate, as well as with high concentrations of sorbitol and fructose but not β-hydroxybutyrate, acetate or galactose. With intermittent anoxia, the pattern of substrate effects on the NAP changed markedly so that low concentrations of fructose became able to support neurophysiologic activity but not high concentrations of glucose. These alterations occurred gradually with repeated episodes of anoxia as reflected by the progressive increase in the time needed for the NAP to disappear during anoxia when using glucose as substrate. This "preconditioning" effect was not seen with other substrates and an opposite effect was seen with lactate. In fact, the rate at which the NAP disappeared during anoxia was not simply related to degree of recovery after anoxia. These are distinct phenomena. For example, the NAP persisted longest during anoxia in the setting of hyperglycemia but this was the state in which the anoxic damage was most severe. Correlating the results with existing literature on the metabolic functions of Schwann cells and axons generates testable hypotheses for the mechanism of hyperglycemic damage during anoxia and lead to discussions of the role for a metabolic shuttle between Schwann cells and axons as well as a potential important role of glycogen., (Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.)

Hypothermia is an important means of neuroprotection. Understanding the effects of temperature on a physiologic measurement such as the nerve action potential (NAP) is important in monitoring its effects. The effects of hypothermia on the NAP amplitude, conduction velocity, and response to paired pulse stimulation were quantified in a rat sciatic nerve preparation from 37 to 10 degrees C. The time course of temperature related changes and the effect of repeated cycles of cooling and rewarming are explored using the following measures of the NAP: peak-to-peak amplitude, conduction velocity, duration, area under the curve and response to paired pulse stimuli. The NAP amplitude initially increases as temperature is reduced to 27 degrees C and then drops to roughly 50% of its baseline value by 16 degrees C while the area under the curve increases gradually until it begins to decline at 16 degrees C. Permanent loss of the NAP appears only after cooling below 10 degrees C for extended periods. Although the dependence of amplitude on temperature is approximately sigmoidal, the conduction velocity declines linearly at a rate of 2.8m/s/ degrees C. The response to paired pulse stimulation is strongly dependent on both temperature and the interstimulus interval with the responses at shorter interstimulus intervals being more temperature sensitive. With repetitive cycles of cooling and rewarming, the NAP amplitude declines by roughly 4% with every cycle without changes in the temperature at which the NAP amplitude reaches 50% of baseline. Only minor differences in conduction velocity are seen during cooling and rewarming.

Changes in temperature have profound and clinically important effects on the peripheral nerve. In a previous paper, the effects of temperature on many properties of the peripheral nerve action potential (NAP) were explored including the NAP amplitude, conduction velocity and response to paired pulse stimulation. In this paper, the effects of pharmacologic manipulations on these parameters were explored in order to further understand the mechanisms of these effects. The reduction in conduction velocity with temperature was shown to be independent of the ionic composition of the perfusate and was unaffected by potassium or sodium channel blockade. This implies that the phenomenon of reduced conduction velocities at low temperature may be related to changes in the passive properties of the axon with temperature. Blockade of sodium channels and chronic membrane depolarization produced by high perfusate potassium concentrations or high dose 4-aminopyridine impair the resistance of the nerve to hypothermia and enhance the injury to the nerve produced by cycles of cooling and rewarming. This suggests the possibility that changes in the sodium inactivation channel may be responsible for the changes in the NAP amplitude with temperature and that prolonged sodium inactivation may lead more permanent changes in excitability.

The neurologic evaluation of patients in the immediate postoperative period and postanesthetic state is unique and challenging. Neurologic assessment is complicated by the lingering residual effects of anesthetics as well as by the effects of narcotic analgesics, anxiolytics, and muscle relaxants, especially in ventilated patients. In this review we examine the suspected causes, clinical manifestations, diagnostic options, and intervention schemes for the common neurologic syndromes seen after cardiac operations., (Copyright 2000 by W.B. Saunders Company)

Retrograde cerebral perfusion with hypothermic circulatory arrest confers additional cerebral protection during repair of type A aortic dissection. We present a 42-year-old man with acute type A aortic dissection and a persistent, left superior vena cava. Cannulation of the right and left superior vena cava is used for retrograde perfusion of both hemispheres with bilateral monitoring of electroencephalogram and somatosensory-evoked potentials during and after the hypothermic circulatory arrest interval.

Background: Study physiologic changes occurring during "knockouts" produced by application of pressure point techniques during martial arts demonstrations., Experimental Design: prospective analysis of physiologic variables during and immediately following an acute event., Setting: martial arts demonstration carried out at a medical center hospital., Subjects: 12 normal volunteers participating in a martial arts demonstration., Interventions: application of various pressure point techniques that have been observed to produce states of unresponsiveness in volunteers., Measures: continuous ECG and video/EEG monitoring with measurements of blood pressure and oxygen saturation. Qualitative analysis of EEG and ECG recordings and quantitative comparison of heart rate, blood pressure, and oxygen saturation measurements before during and after the period of induced unconsciousness., Results: No significant changes in blood pressure, oxygen saturation, cardiac rate or rhythm, or electroencephalogram are noted during the knockouts produced by application of pressure point techniques. There was only variable inability for subjects to remember words spoken to them during the episode of apparent unresponsiveness., Conclusions: The mechanism for the state of unresponsiveness produced by application of pressure point techniques is not related to a significant cardiac or pulmonary process. There is no evidence of reduced cerebral blood flow during this time or of other dangerous physiologic changes. The exact mechanism for this phenomenon remains uncertain.

Unlabelled: Retrograde cerebral perfusion (RCP) potentially delivers metabolic substrate to the brain during surgery using hypothermic circulatory arrest (HCA). Serial measurements of O2 extraction ratio (OER), PCO2, and pH from the RCP inflow and outflow were used to determine the time course for O2 delivery in 28 adults undergoing aortic reconstruction using HCA with RCP. HCA was instituted after systemic cooling on cardiopulmonary bypass for 3 min after the electroencephalogram became isoelectric. RCP with oxygenated blood at 10 degrees C was administered at an internal jugular venous pressure of 20-25 mm Hg. Serial analyses of blood oxygen, carbon dioxide, pH, and hemoglobin concentration were made in samples from the RCP inflow (superior vena cava) and outflow (innominate and left carotid arteries) at different times after institution of RCP. Nineteen patients had no strokes, five patients had preoperative strokes, and four patients had intraoperative strokes. In the group of patients without strokes, HCA with RCP was initiated at a mean nasopharyngeal temperature of 14.3 degrees C with mean RCP flow rate of 220 mL/min, which lasted 19-70 min. OER increased over time to a maximal detected value of 0.66 and increased to 0.5 of its maximal detected value 15 min after initiation of HCA. The RCP inflow-outflow gradient for PCO2 (slope 0.73 mm Hg/min; P < 0.001) and pH (slope 0.007 U/min; P < 0.001) changed linearly over time after initiation of HCA. In the group of patients with preoperative or intraoperative strokes, the OER and the RCP inflow-outflow gradient for PCO2 changed significantly more slowly over time after HCA compared with the group of patients without strokes. During RCP, continued CO2 production and increased O2 extraction over time across the cerebral vascular bed suggest the presence of viable, but possibly ischemic tissue. Reduced cerebral metabolism in infarcted brain regions may explain the decreased rate of O2 extraction during RCP in patients with strokes., Implications: Examining the time course of oxygen extraction, carbon dioxide production, and pH changes from the retrograde cerebral perfusate provided a means to assess metabolic activity during hypothermic circulatory arrest.

Objective: To report a patient who developed the paradoxical effect of increasing electrical seizure activity and confusion with initiation of valproic acid therapy., Case Summary: A 25-year-old African-American woman with a hypothalamic hamartoma had an electroencephalogram (EEG) that demonstrated frequent bursts of generalized spike and wave activity. The prevalence of spike and wave activity increased dramatically and the patient became increasingly somnolent as valproic acid was added to carbamazepine and phenobarbital therapy. Her EEG and mental status changes resolved when the valproic acid was discontinued. There was a strong positive correlation between the prevalence of spike and wave activity and the valproic acid concentration, but not between spike and wave activity and the concentrations of carbamazepine or phenobarbital., Discussion: Although this is a complex case, it is clear that the addition of valproic acid produced an increase in spike and wave activity. Possible mechanisms and pathophysiologic significance of this paradoxical effect are discussed in light of the differences between this epileptic syndrome and the primary generalized epilepsies.

Objective: The results of neurophysiologic monitoring using somatosensory evoked potentials (SSEPs) and electroencephalography (EEG) were analyzed to determine if retrograde cerebral perfusion (RCP) supported central nervous system electrical function during surgery that required temporary interruption of antegrade cerebral perfusion (IACP)., Design: A prospective, observational study., Setting: A university hospital., Participants: Fifteen adult patients who underwent aortic reconstruction using RCP and three patients who underwent thoracic aortic operations using hypothermic circulatory arrest without RCP., Interventions: SSEPs and EEG were monitored continuously throughout the operation. Regression analysis was performed to determine the factors that affected the rate of decrease in SSEP amplitudes during IACP and the time required for SSEP and EEG activity to recover after antegrade cerebral perfusion (ACP) was restored., Measurements and Main Results: The amplitude of SSEPs that were elicited decreased over time after IACP. The mean +/- standard deviation (SD) time required for the brachial plexus (Erb's point), cervicomedullary junction (N13), and brainstem (N18) SSEPs to decrease to 0.5 of their original amplitude after IACP were 30 +/- 2, 19 +/- 2, and 16 +/- 2 minutes, respectively. The rate of decrease in the N18 SSEP amplitude after IACP correlated positively to the fraction of no-flow time (p = 0.01)., Conclusion: RCP attenuated the rate of decay in SSEP amplitudes during IACP. This suggested that RCP had a measurable physiologic effect on central nervous system function and may increase the time that ACP can be safely interrupted.

Objective: To determine the effects of intra-aortic counterpulsation (IABP) on cerebral blood flow velocity., Design: Prospective self-controlled study., Setting: University hospital surgical intensive care unit., Participants: Nineteen cardiac surgical patients requiring perioperative IABP assistance., Interventions: Simultaneous recording of transcranial Doppler middle cerebral artery blood flow velocity and arterial pressure in response to changes in the magnitude of augmentation and trigger ratio., Measurements and Main Results: Instantaneous cerebral blood flow velocities correlated with arterial pressures during IABP (r = 0.650) at different magnitudes of augmentation and trigger ratios. The increase in arterial pressure during balloon inflation was associated with an increase in cerebral blood flow velocity, and the decrease in arterial pressure in response to balloon deflation was associated with a decrease in cerebral blood flow velocity that was dependent on the magnitude of augmentation. Different magnitudes of augmentation or trigger ratios had no effect on peak systolic cerebral blood flow velocity, mean cerebral blood flow velocity, mean arterial pressure, or the mean velocity-to-pressure ratio. Instantaneous cerebral blood flow velocity to arterial pressure ratios were lowest in response to balloon deflation at the time of pre-ejection., Conclusions: IABP modified the phasic profile of cerebral blood flow to reflect the arterial pressure waveform without affecting mean cerebral blood flow velocity. Peak systolic cerebral blood flow velocity was maintained in augmented beats despite the decreased systolic arterial pressure associated with afterload reduction. The acute decrease in cerebral blood flow velocity at pre-ejection was balanced by increased cerebral blood flow velocity during balloon inflation in diastole.

Purpose: We compared propofol with high-dose barbiturates in the treatment of refractory status epilepticus (RSE) and propose a protocol for the administration of propofol in RSE in adults, correlating propofol's effect with plasma levels., Methods: Sixteen patients with RSE were included; 8 were treated primarily with high-dose barbiturates and 8 were treated primarily with propofol., Results: Both groups of patients had multiple medical problems and a subsequent high mortality. A smaller but not statistically significant fraction of patients had their seizures controlled with propofol (63%) than with high-dose barbiturate therapy (82%). The time from initiation of high-dose barbiturate therapy to attainment of control of RSE was longer (123 min) than the time to attainment of seizure control in the group receiving propofol (2.6 min, p = 0.002). Plasma concentrations of propofol associated with control of SE were 14 microM +/- 4 (2.5 microg/ml). Recurrent seizures were common when propofol infusions were suddenly discontinued but not when the infusions were gradually tapered., Conclusions: If used appropriately, propofol infusions can effectively and quickly terminate many but not all episodes of RSE. Propofol is a promising agent for use in treating RSE, but more studies are required to determine its true value in comparison with other agents.

Case Report: Emergency physicians are well versed in the recognition and management of certain poisonings which present with characteristic toxidromes. We present a case of a young pharmacy student who presented with altered mental status, tachycardia, facial flushing, dilated pupils, and dry skin and mucous membranes presumably due to anticholinergic poisoning. She improved with a combination of benzodiazepines and the acetylcholinesterase inhibitor physostigmine. However, following resolution of her initial symptoms, she became ill again and the subsequent neurologic evaluation revealed a diencephalic lesion consistent with a viral encephalitis. The acute anticholinergic signs and symptoms resulted from this lesion in an area of large cholinergic outflow. Although recognition and management of her acute anticholinergic findings were appropriate, they were not the manifestations of an acute anticholinergic ingestion.

Objectives: The objectives of this study were to determine if monitoring of intraoperative somatosensory evoked potentials could be used to detect stroke during cardiac operations and to establish indicators of cerebral ischemia based on changes in these potentials., Methods: Twenty-five patients undergoing cardiac operations underwent preoperative and postoperative neurologic examinations as well as intraoperative recording of somatosensory evoked potentials. Detailed analysis of the waveforms of these potentials was performed., Results: Two of the 25 patients had intraoperative strokes. These patients and only these patients had changes in their somatosensory evoked potentials during the operation suggesting cerebral ischemia. The unilateral disappearance of the cortical somatosensory evoked potential waves correlated significantly with the clinical outcome of stroke (p < 0.004). Ischemic changes were detected in real time and were related to the removal of the aortic crossclamp in one patient and to the initiation of cardiopulmonary bypass in the other., Conclusions: Somatosensory evoked potentials can detect intraoperative stroke during cardiac operations. Acute, unilateral decreases in amplitude of the cortical potential are more useful than changes in latency in detecting intraoperative stroke.

Electrical interference at mains power supply frequency can adversely affect the recording of evoked potentials and can be especially destructive in an operating room setting. We investigated 60 Hz interference in electrode cables running from subject to preamplifier and further examined methods to eliminate such interference. We conclude that braiding electrode wires is highly efficacious in such interference reduction, presumably by reducing the magnetic flux enclosed by the wires. We further indicate that the use of flexible metal hose fabricated from Permalloy 80 may effect further interference reduction.

Previous electrophysiological studies have demonstrated interactions between dichoptic visual stimuli presented to the same location in visual space. In this study, we used non-liner spectral analysis, in particular the bispectrum, to study interactions between the electrocerebral activity resulting from stimulation of the left and right visual fields. The stimulus consisted of two squares, one in each visual field, flickering at different frequencies. Bispectra, bichoherence and biphase were calculated for 8 subjects monocularly observing a visual stimulus. Both phase vs. frequency and biphase vs. frequency plots were made to determine weighted time delays from stimulus application to signal appearance in the EEG electrodes. Bispectral analysis reveals non-liner interactions between visual fields occurring with weighted delay times of 410 + / - 58 msec while non-interactive components propagated with weighted time delays of 202 + / - 39 msec. Evaluating these results in light of the predictions of various models, we were able to conclude that this interaction does not occur in the retina. These results illustrate how bispectral analysis can be a powerful tool in analyzing the connectivity of neural networks in complex systems. It allows different neuronal systems to be labeled with stimuli at specific frequencies, whose connections can be traced using frequency analysis of the scalp EEG.

A kinetic analysis of water signal intensity changes measured in human visual cortex by PRESS localized 1H spectroscopy at 500 ms resolution with light-emitting diode (LED) goggle stimulation was used to determine vascular transit times for transitions between rest and activation. Monoexponential curve fitting was used to determine both R2* values for each free induction decay and the time constants for R2* changes with activation and deactivation. Measured transit time values were in general agreement with the literature, and were significantly shorter for "Off-->On" than for "On-->Off" transitions, consistent with known alterations in blood flow with activation and deactivation. The differences in transit times between "Off-->On" and "On-->Off" also varied with stimulus frequency in accordance with known physiology. This type of analysis may provide a useful means of analyzing functional activation data and for quantitatively comparing functional activation results from differing subjects and imaging sessions.

Unlabelled: In this paper we correlate the findings on 99mTc-HMPAO brain SPECT with the results of clinical examinations and electroencephalography to determine the utility of SPECT in the evaluation of patients with suspected status epilepticus., Methods: Thirteen patients with suspected status epilepticus underwent serial neurologic examinations, serial electroencephalograms, CT/MRI scanning and 99mTc-HMPAO SPECT. Seven patients were diagnosed with status epilepticus and six patients received other neurological diagnoses., Results: All patients with status epilepticus at the time of the brain SPECT scan demonstrated focal hyperperfusion on SPECT in an area concordant with that suggested by EEG. One patient with status epilepticus demonstrated a persistent area of hyperperfusion on SPECT 24 hr after the cessation of status with no evidence of breakdown in the blood-brain barrier demonstrated by 99mTc-DTPA SPECT. No patient in this study without a diagnosis of status epilepticus had focal areas of hyperperfusion on SPECT., Conclusion: We suggest that a 99mTc-HMPAO SPECT scan demonstrating focal hyperperfusion in a patient being evaluated for partial status epilepticus is nonspecific. Even in the absence of a structural lesion causing local breakdown in the blood-brain barrier, it may indicate either ongoing status epilepticus or recently terminated status. However, a SPECT scan demonstrating no area of focal hyperperfusion argues against the diagnosis of partial status.