摘要:

ObjectiveIt currently is recommended that electrical shocks be delivered immediately on recognition of ventricular fibrillation. However, decreased effectiveness of this approach has been reported after prolonged intervals of untreated ventricular fibrillation. We investigated the optimal strategy for successful defibrillation after prolonged untreated ventricular fibrillation by using a rat model of ventricular fibrillation and closed-chest resuscitation.DesignControlled, randomized, laboratory study.SettingResearch laboratory at a VA hospital.SubjectsSeventy pentobarbital anesthetized Sprague-Dawley rats.InterventionsAfter 10 mins of untreated ventricular fibrillation, four groups of rats were randomized to receive electrical shocks (which we designated as “experimental shocks”) immediately before or at 2, 4, or 6 mins of chest compression. Unsuccessfully defibrillated rats received additional shocks (which we designated as “rescue shocks”) after 8 mins of chest compression.Measurements and Main ResultsThe number of rats that restored spontaneous circulation after the experimental shocks increased with increasing duration of the predefibrillatory interval of chest compression (0 of 8, 0 of 8, 2 of 8, and 7 of 8, respectively,p< .005). Two additional groups then were randomized to receive repetitive experimental shocks at 2, 4, and 6 mins or a single attempt at 6 mins of chest compression. Although a comparable number of rats restored spontaneous circulation in each group, rats subjected to repetitive defibrillation attempts had more intense postresuscitation ectopic activity and worse survival. Two final groups were used to investigate whether inhibition of the sarcolemmal sodium-hydrogen exchanger isoform-1 (NHE-1) could facilitate return of spontaneous circulation during repetitive defibrillation attempts. Although spontaneous circulation was restored earlier in more rats subjected to NHE-1 inhibition, the differences were statistically insignificant. NHE-1 inhibition, however, replicated previously reported resuscitation and postresuscitation benefits. The optimal predefibrillation interval of chest compression was ≈6 mins, and this coincided with partial return of the amplitude and frequency characteristics of the ventricular fibrillation waveform to those present immediately after induction of ventricular fibrillation.ConclusionsImproved outcome after prolonged untreated ventricular fibrillation may result from strategies that provide chest compression before attempting defibrillation and avoid early and repetitive defibrillation attempts. The amplitude and frequency characteristics of the ventricular fibrillation waveform could help identify the optimal timing for attempting electrical defibrillation.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveTo assess the effect of diisopropyl phenol (propofol), with and without Intralipid, on the cardiopulmonary system and on thromboxane production in endotoxic pigs.DesignProspective, randomized animal study.SettingAnimal research laboratory at a major teaching hospital.SubjectsTwenty-four pigs, divided into three groups (n = 8).InterventionsPulmonary arterial catheters and arterial cannulas were inserted into all pigs. Each pig received a 30 ng/kg bolus of endotoxin at 1 hr, followed by a continuous infusion of endotoxin at 24 ng·kg−1·hr−1. Diisopropyl phenol at 25, 75, and 200 &mgr;g·kg−1·min−1was administered to all pigs, beginning at 1, 2, and 3 hrs, respectively. The pigs were divided into three groups to receive 0.25 g·kg−1·hr−1, 0.08 g·kg−1·hr−1, or no Intralipid, starting at time t = 0. Heart rate and mean arterial, central venous, and pulmonary arterial pressures were recorded continuously. Core temperature, arterial blood gases, mixed venous oxygen saturation, pulmonary arterial occlusion pressure, and cardiac output were measured intermittently. Thromboxane B2concentrations were measured at baseline and at 60, 75, 120, 135, 180, 195, and 240 mins. Data are expressed as mean ± sd. Groups were compared by using repeated analysis of variance, withp< .05 used for statistical significance.Measurements and Main ResultsAll pigs completed the 4-hr study. Marked variabilities were noted for individual pigs. Following the infusion of endotoxin, compared with baseline, there was a significant increase in pulmonary vascular resistance and a decrease in Pao2(p< .001 andp< .008, respectively). This response was not affected by the increasing dose of diisopropyl phenol, nor were there differences between the Intralipid and control groups. Pao2remained significantly lower in all groups, compared with the baseline measurements (p< .001) over the 4 hrs of the experiment. Thromboxane B2concentrations remained elevated compared with baseline and were significantly higher (p< .05) in the high-dose Intralipid group, compared with the low-dose and the control groups, during the last hour of the experiment.ConclusionsSmall doses of endotoxin, when given to pigs, induce major perturbations of cardiopulmonary function. Neither Intralipid, high vs. low dose, nor diisopropyl phenol, at sedating vs. anesthetizing doses, worsened the physiologic derangement associated with the stress of low-dose endotoxemia.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectivesTo investigate the settings necessary to achieve maximum gas exchange and pulmonary function while minimizing effects on cardiovascular hemodynamics during total liquid ventilation with a pressure-limited, time-cycled ventilator in a rat model.DesignProspective, randomized controlled animal study.SettingA university research laboratory.SubjectsMale Sprague-Dawley rats (n = 48).InterventionsAll animals had a tracheostomy tube designed for total liquid ventilation placed under anesthesia. The carotid artery was cannulated for blood pressure monitoring and for assessing blood gas data.Measurements and Main ResultsForty 492 ± 33 g rats were assigned to one of four inspiratory/expiratory ratio groups (inspiratory/expiratory ratio of 1:2, 1:2.5, 1:3, and 1:4). Total liquid ventilation was performed with a pressure-limited, time-cycled total liquid ventilator. Outcome measures were evaluated as a function of respiratory rate and included tidal volume, maximal alveolar ventilation, inspiratory and expiratory mean arterial pressures, the difference of mean arterial pressure between the inspiratory and expiratory phase, static end-inspiratory/expiratory pressures, Paco2, Pao2, tidal volume + approximate expiratory reserve volume, and lung volume-induced suppression of mean arterial pressure. Maximal alveolar ventilation increased and decreased in parabolic fashion as a function of respiratory rate and was maximal at rates of 4.3–6.8 breaths/min and high inspiratory/expiratory ratios that corroborated with optimal levels of Pao2and Paco2. Lung overdistention occurred at high respiratory rates and high inspiratory/expiratory ratios. Deleterious effects were observed on the difference of mean arterial pressure between the inspiratory and expiratory phase during total liquid ventilation at low respiratory rates, apparently due to increased tidal volume, and on suppression of mean arterial pressure at high inspiratory/expiratory ratios and high respiratory rate apparently due to “auto-positive end-expiratory pressure.” These effects were minimized in this model at respiratory rates ≥5.7 and ≤6.8 breaths/min and inspiratory/expiratory ratios ≤1:2.5. These settings were successfully tested in eight additional animals.ConclusionThese data demonstrate the feasibility of performing total liquid ventilation in rodents. A balance must be identified where gas exchange is optimal yet hemodynamics are least affected. In the specific system studied, an inspiratory/expiratory ratio of 1:2.5 and respiratory rate of 6.8 breaths/min appeared to provide optimal gas exchange while minimizing the effects on hemodynamics.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

BackgroundClinical trials of induced hypothermia have suggested that this treatment may be beneficial in selected patients with neurologic injury.ObjectivesTo review the topic of induced hypothermia as a treatment of patients with neurologic and other disorders.DesignReview article.InterventionsNone.Main ResultsImproved outcome was demonstrated in two prospective, randomized, controlled trials in which induced hypothermia (33°C for 12–24 hrs) was used in patients with anoxic brain injury following resuscitation from prehospital cardiac arrest. In addition, prospective, randomized, controlled trials have been conducted in patients with severe head injury, with variable results. There also have been preliminary clinical studies of induced hypothermia in patients with severe stroke, newborn hypoxic-ischemic encephalopathy, neurologic infection, and hepatic encephalopathy, with promising results. Finally, animal models have suggested that hypothermia that is induced rapidly following traumatic cardiac arrest provides significant neurologic protection and improved survival.ConclusionsInduced hypothermia has a role in selected patients in the intensive care unit. Critical care physicians should be familiar with the physiologic effects, current indications, techniques, and complications of induced hyperthermia.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveTo evaluate the effects of helium on the function of four ventilators commonly used in pediatrics: the Bird VIP, Bird VIP Gold, Servo 300, and Servo 900C.DesignProspective setting.SettingResearch laboratory at a university hospital.SubjectsHelium was administered as an 80:20 mixture of helium-oxygen through the air inlet of the ventilator. Delivered fraction of inspired oxygen (Fio2) was compared with the Fio2set on the blender dial. Inspiratory displayed tidal volume was recorded as an indicator of what the ventilator “believed” it had delivered and was compared with the VTdisplayed during ventilation with 100% oxygen (control). Actual delivered VTwas measured by a Neonatal Bicore connected to the side port of a “bag-in-box” spirometer, making measurements independent of inspired gas properties, and was compared with VTdelivered during ventilation with 100% oxygen.InterventionsFive gas mixtures were evaluated: Fio2= 0.2, 0.4, 0.6, 0.8, and 1.0 (balance helium).Measurements and Main ResultsDelivered Fio2was less than set Fio2on the Servo 900C and VIP ventilators. VTdisplayed was minimally altered by helium during volume-controlled ventilation but substantially decreased during pressure-controlled ventilation, particularly with the Bird ventilators. During volume-controlled ventilation, VTdelivered was substantially increased by helium with the Bird and, to a lesser degree, the Servo 900C ventilators. In contrast, VTdelivered decreased slightly in helium with the Servo 300. The same pattern, but with a decreased magnitude, was observed for VTdelivered during pressure-controlled ventilation.ConclusionsThe addition of helium has a significant effect on Fio2delivery, displayed inspiratory VT, and actual delivered VTduring both volume- and pressure-controlled ventilation in four ventilators commonly used in pediatric critical care. These effects are both ventilator specific and ventilation mode specific, mandating vigilance during helium ventilation in clinical practice.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveTo develop a power-law model for measurement of heart rate variability (HRV) and to compare this model with established methods for measuring HRV in a group of children with organ failure (OF).DesignProspective, observational study.SettingPediatric intensive care unit of a tertiary children’s hospital.PatientsA total of 104 measurements were made on 50 patients (median age, 8 months; range, 2 days to 16 yrs) and categorized into three groups according to the number of simultaneous organs failing: 0–1 OF, 2 OF, and ≥3 OF.InterventionsHeart rate was recorded over a 5-min period when patients were hemodynamically stable. The power-law model represents a power function relating frequency distribution to magnitude of effect (in this case, squared deviation from the mean heart rate). Plotting the data on a bi-logarithmic scale produces a regression line for each measurement, described in terms ofr2, slope, and x-intercept. Comparison with other HRV measures included two time-domain measures (sd of the normal R-R intervals and the square root of the mean squared differences of successive normal R-R intervals), one frequency-domain method (power spectral analysis), and one nonlinear method (detrended fluctuation analysis).Measurements and ResultsFor the power-law model, patients exhibited a similar r2of .87 (.09) (mean [sd]) and slope of −1.80 (0.29), regardless of the degree of OF. HRV could thus be described purely in terms of x-intercept, which demonstrated a left shift with increasing OF (p< .001). This was independent of age and heart rate. Loss of HRV with increasing OF was demonstrated by all methods; however, only the power-law model was able to discriminate between each OF group. Using the model, change in HRV in individual patients over successive days often concurred qualitatively with the change in OF status.ConclusionThe power-law model is an appropriate measure of HRV in pediatric patients, being neither age nor heart rate sensitive. Loss of HRV occurs with increasing OF; this effect was better demonstrated by the model compared with other measures of HRV.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

ObjectiveImmunoparalysis has recently emerged as a possible cause explaining the failure of clinical trials in septic shock. Because human peripheral blood CD4+CD25+ T cells have been characterized as suppressor T cells, we hypothesized they might be increased in sepsis-induced immunoparalysis.DesignProspective, observational, clinical study.SettingAdult intensive care units in a university hospital.SubjectsPatients with septic shock (n = 16) and healthy individuals (n = 36).InterventionsNone.Measurements and Main ResultsIn patients with septic shock (mortality rate at 28 days, 56%; mean admission Simplified Acute Physiology Score II, 47), we first illustrated immunoparalysis by showing a severe diminished monocytic human leukocyte antigen (HLA)-DR expression. Afterward, compared with control values, we found in these patients a marked elevation of circulating CD4+CD25+ T cells that were also CD45RO+ and CD69- and overexpressed CTLA-4. Importantly, nonsurvivors (n = 9) presented prolonged lower monocytic HLA-DR expression and higher percentage of CD4+CD25+ T-suppressor T cells.ConclusionsThese data support the concept that the persistence of a pronounced immunoparalysis after septic shock is associated with a poor outcome. Whether CD4+CD25+ T cells directly participate in sepsis-induced immunoparalysis remains to be investigated.

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0090-3493    

出版商:OVID    

年代:2003

数据来源: OVID