Predictive model of length of stay and discharge destination in neuroscience admissions.

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.

Anoxia-induced changes in optimal substrate for peripheral nerve.

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 ß-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.

Peripheral nerve at extreme low temperatures 2: pharmacologic modulation of temperature effects.

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.

Peripheral nerve at extreme low temperatures 1: effects of temperature on the action potential.

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.

Spontaneous extraperitoneal hemorrhage with hemodynamic collapse in patients undergoing anticoagulation: management with selective arterial embolization.

The authors report their experience with management of unstable spontaneous extraperitoneal hemorrhage (SEH) with selective transcatheter embolization. Five consecutive patients underwent angiographic evaluation for SEH complicated by hemodynamic collapse while undergoing anticoagulation therapy. Bleeding occurred via one or two lumbar arteries in psoas hematomas. Two abdominal wall hematomas were supplied by the inferior epigastric artery, with additional supply via the deep circumflex iliac artery in one. Microcoil embolization successfully controlled extravasation in all patients, with stabilization of hemodynamic parameters. Four of the five patients survived the immediate postprocedural interval. Selective transcatheter embolization may be a viable life-saving option in SEH-associated hemodynamic collapse.

Reliability of nurses' neurological assessments in the cardiothoracic surgical intensive care unit.

BACKGROUND: Alterations in mental status are common among patients in the cardiothoracic surgical intensive care unit. Changes in mental status can be caused by metabolic factors, medications, or brain injury. In this setting, reliable, serial neurological evaluations are critical for assessing the effectiveness of treatment and the need for additional studies. OBJECTIVES: To estimate the reliability of the Rancho Los Amigos Cognitive Scale and the newly developed Neurologic Intensive Care Evaluation as measures of cognitive function in the cardiothoracic surgical intensive care unit. METHODS: Nurses used 1 of the 2 scales as part of routine neurological assessments of patients in the cardiothoracic surgical intensive care unit. For each test, scores of different observers were correlated and a reliability estimate formed. RESULTS: Interrater reliability was high for both evaluations (Rancho scale, 0.91; Neurologic Intensive Care Evaluation, 0.94). Correlations between the scores of different pairs of observers were also high (mean rho values, 0.84 for the Rancho scale and 0.77 for the Neurologic Intensive Care Evaluation). CONCLUSIONS: Both scales are reliable indicators of the neurological state of patients in the cardiothoracic surgical intensive care unit. These scales measure different, although limited, aspects of cognitive function. Each test was simple to administer and did not take more time than the standard nursing neurological examination. Most of the variability in scoring was related to the different degrees of stimulation used by examiners when assessing patients, not to differences in the interpretation of patients' responses.

Suprarenal intraarterial infusion of alloxan and streptozotocin during balloon occlusion of the juxtarenal abdominal aorta: a simple technique for inducing diabetes mellitus in canines with reduced mortality.

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate the mortality and morbidity associated with a simple technique for inducing diabetes in dogs--suprarenal intraarterial infusion of alloxan and streptozotocin during balloon occlusion of the juxtarenal abdominal aorta. MATERIALS AND METHODS: The authors attempted to induce diabetes in six purpose-bred dogs. After the dogs were fasted for 12 hours, the abdominal aorta at the level of the origin of the renal arteries was occluded with an angioplasty balloon introduced by means of a femoral approach. A 3-F microcatheter (n = 1) or infusion wire (n = 5) was introduced via the percutaneous transluminal angioplasty catheter and positioned at the level of the celiac axis, and a mixture of streptozotocin (20-25 mg/kg) and alloxan (20-25 mg/kg) was infused. Diabetes was considered to have been induced if the dogs experienced sustained hyperglycemia. RESULTS: There were no deaths during the follow-up period (range, 7 months to 2 1/2 years). A diabetes-like state was induced in five of the six dogs, and no nephrotoxicity was seen. Diabetes was not induced in one dog owing to caudal migration of an undersized balloon during the infusion; this also resulted in reversible renal damage. CONCLUSION: This simple technique is effective for inducing diabetes in dogs, and morbidity and mortality rates are lower than those reported in the literature with other described techniques.

Evaluation of a spiral nitinol temporary inferior vena caval filter.

RATIONALE AND OBJECTIVES: The authors performed this study to evaluate the (a) ability of a prototype temporary inferior vena caval (IVC) filter to trap and retain emboli in an ex vivo flow circuit, (b) feasibility of filter placement and removal via a superficial vein in sheep, and (c) intermediate-term effects of the filter on the insertion vein and at the filter site. MATERIALS AND METHODS: In an iliocaval circuit, embolus capture with the prototype filter was compared to that with a Greenfield filter. In addition, prototype filters were placed into the infrarenal IVC in six sheep. Placement via a superficial venous route was initially attempted. Inferior vena cavography was performed weekly, and filters were removed after 2, 3, or 4 weeks (n = 2 each). Two weeks after the filters were removed, vena cavograms were obtained, the animals were sacrificed, and the IVC was evaluated at pathologic examination. RESULTS: The prototype filter captured all emboli, and the Greenfield filter captured 70%-100% of emboli. Successful placement via a superficial venous route was accomplished in only two sheep owing to small vein caliber; four filters were placed via a deep vein. Adverse events included perifilter thrombus, insertion site infection, and caudal migration. Two sheep died before filter removal owing to sepsis and anesthetic complications. The filters in the remaining four sheep were easily and successfully removed. Five sheep had stenosis at the filter site, and fibrosis with acute and chronic inflammation was seen at microscopic examination. CONCLUSION: The prototype filter trapped emboli as well as the Greenfield filter. Insertion via a superficial route, however, is possible only if the access vein is of an adequate size.

Outcome of polyester cuff retention following traction removal of tunneled central venous catheters.

PURPOSE: To elucidate the factors that contribute to cuff retention during traction removal of tunneled catheters, as well as to determine the risk of complication associated with polyester cuff retention. MATERIALS AND METHODS: A total of 428 tunneled, cuffed catheters were removed with traction and local anesthesia. Polyester cuff retention was recorded when it occurred, and the effects of cuff retention were determined at a mean follow-up of 250 days. Statistical analysis was performed to determine the variables influencing cuff retention. RESULTS: Traction removal was successful in 428 (100%) patients. Of 428 catheters removed, 41 (10%) cuffs were retained. Silicone 10-F double-lumen and 9.6-F single-lumen catheters had a higher rate of cuff retention (27 [32%] of 84 and nine [39%] of 23, respectively) than did the split-tip polyurethane hemodialysis catheter (two [1%] of 196; P <.001). Cuff retention rates among other catheter types compared with that of the polyurethane catheter were not significantly different. Duration of catheter dwell did not significantly influence cuff retention. Of 41 retained cuffs, three required removal with cutdown for cuff migration to the exit site, which inhibited healing (n = 1); for suspected infection (n = 1); or for cosmetic purposes as requested by the patient (n = 1). The remaining patients had no complications associated with cuff retention. CONCLUSION: Traction removal of smaller-bore silicone catheters is more likely to result in cuff retention than removal of larger silicone and polyurethane catheters, and cuff retention is usually inconsequential.

Deep hypothermic circulatory arrest: I. Effects of cooling on electroencephalogram and evoked potentials.

BACKGROUND: Deep hypothermia is an important cerebral protectant and is critical in procedures requiring circulatory arrest. The purpose of this study was to determine the factors that influence the neurophysiologic changes during cooling before circulatory arrest, in particular the occurrence of electrocerebral silence. METHODS: In 109 patients undergoing hypothermic circulatory arrest with neurophysiologic monitoring, five electrophysiologic events were selected for detailed study. RESULTS: The mean nasopharyngeal temperature when periodic complexes appeared in the electroencephalogram after cooling was 29.6 degrees C +/- 3 degrees C, electroencephalogram burst-suppression appeared at 24.4 degrees C +/- 4 degrees C, and electrocerebral silence appeared at 17.8 degrees C +/- 4 degrees C. The N20-P22 complex of the somatosensory evoked response disappeared at 21.4 degrees C +/- 4 degrees C, and the somatosensory evoked response N13 wave disappeared at 17.3 degrees C +/- 4 degrees C. The temperatures of these various events were not significantly affected by any patient-specific or surgical variables, although the time to cool to electrocerebral silence was prolonged by high hemoglobin concentrations, low arterial partial pressure of carbon dioxide, and by slow cooling rates. Only 60% of patients demonstrated electrocerebral silence by either a nasopharyngeal temperature of 18 degrees C or a cooling time of 30 minutes. CONCLUSIONS: With the high degree of interpatient variability in these neurophysiologic measures, the only absolute predictors of electrocerebral silence were nasopharyngeal temperature below 12.5 degrees C and cooling longer than 50 minutes.

Deep hypothermic circulatory arrest: II. Changes in electroencephalogram and evoked potentials during rewarming.

BACKGROUND: Electrophysiologic studies during rewarming after deep hypothermic circulatory arrest probe the state of the brain during this critical period and may provide insight into the neurological effects of circulatory arrest and the neurologic outcome. METHODS: Electroencephalogram (EEG) and evoked potentials were monitored during rewarming in 109 patients undergoing aortic surgery with hypothermic circulatory arrest. RESULTS: The sequence of neurophysiologic events during rewarming did not mirror the events during cooling. The evoked potentials recovered first followed by EEG burst-suppression and then continuous EEG. The time to recovery of the evoked potentials N20-P22 complex was significantly correlated with the time of circulatory arrest even in patients without postoperative neurologic deficits (r = 0.37, (p = 0.002). The nasopharyngeal temperatures at which continuous EEG activity and the N20-P22 complex returned were strongly correlated (r = 0.44, p = 0.0002; r = 0.41, p = 0.00003) with postoperative neurologic impairment. Specifically, the relative risk for postoperative neurologic impairment increased by a factor of 1.56 (95% CI 1.1 to 2.2) for every degree increase in temperature at which the EEG first became continuous. CONCLUSIONS: No trend toward shortened recovery times or improved neurologic outcome was noted with lower temperatures at circulatory arrest, indicating that the process of cooling to electrocerebral silence produced a relatively uniform degree of cerebral protection, independent of the actual nasopharyngeal temperature.

Hematocrit, volume expander, temperature, and shear rate effects on blood viscosity.

UNLABELLED: Our goal was to determine and predict the effects of temperature, shear rate, hematocrit, and different volume expanders on blood viscosity in conditions mimicking deep hypothermia for cardiac operations. Blood was obtained from six healthy adults. Dilutions were prepared to hematocrits of 35%, 30%, 22.5%, and 15% using plasma, 0.9% NaCl, 5% human albumin, and 6% hydroxyethyl starch. Viscosity was measured over a range of shear rates (4.5-450 s(-1)) and temperature (0 degrees -37 degrees C). A parametric expression for predicting blood viscosity based on the study variables was developed, and its agreement with measured values tested. Viscosity was higher at low shear rates and low temperatures, especially at temperatures less than 15 degrees C (P: < 0.016 for all conditions in comparison with 37 degrees C). Decreasing hematocrit, especially to less than 22.5%, decreased viscosity. Hemodilution with albumin or 0.9% NaCl decreased blood viscosity more than hemodilution with plasma or 6% hydroxyethyl starch (P: < 0.01 for all cases). The derived mathematical model for viscosity as a function of temperature, hematocrit, shear rate, and diluent predicted viscosity values that correlated well with the measured values in experimental samples (r(2) > 0.92, P: < 0.001). IMPLICATIONS: A theoretical model for blood viscosity predicted independent effects of temperature, shear rate, and hemodilution on viscosity over a wide range of physiologic conditions, including thermal extremes of deep hypothermia in an experimental setting. Moderate hemodilution to a hematocrit of 22% decreased blood viscosity by 30%-50% at a blood temperature of 15 degrees C, suggesting the potential to improve microcirculatory perfusion during deep hypothermia.

Acute type A aortic dissection: retrograde perfusion with left superior vena cava.

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.

Generalized averaging and noise levels in evoked responses.

A formal relationship between the mean square noise level in an evoked potential experiment, the number of averages and the autocorrelation function of the noise is derived. The generalized averaging process is recast as a filter applied to the noise signal. This filter is computed for a number of different types of evoked potential experiments in which various weighting factors and stochastic stimulation times are allowed. Although the variance in noise level estimates can be large, there is a general trend for noise reduction to occur more slowly than the expected 1/N when the total time over which averaging occurs is small in comparison to the correlation time of the noise. When the total averaging time exceeds the temporal extent of the autocorrelation function, the expected 1/N behavior is observed.

Irreversible spinal cord injury as a complication of subarachnoid ethanol neurolysis.

Subarachnoid neurolysis using ethanol to destroy selectively the posterior roots of the spinal cord is a method for providing pain relief in patients with advanced cancer. Weakness of the extremities is a complication of the procedure that has been attributed to spread of the neurolytic agent to the anterior roots. The authors provide evidence of spinal cord injury as a cause of lower extremity weakness in a patient after subarachnoid ethanol neurolysis.

Fatal hyperammonemia after orthotopic lung transplantation.

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.

Postoperative neurologic assessment and management of the cardiac surgical patient.

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.