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Review of the use of somatosensory evoked potentials in the prediction of outcome after severe brain injury

ObjectiveReview the predictive powers of somatosensory evoked potentials (SEPs) in severe brain injury. Data SourcesPublications in the scientific literature, manual review of article bibliographies, and questioning workers in the field. Study SelectionStudies addressing the prediction of outcome after severe brain injury using SEPs. Data ExtractionTo determine the outcome of patients with either normal or bilaterally absent SEPs as categorized using the Glasgow Outcome Scale into favorable outcomes (good or moderate disability) or unfavorable outcomes (severe disability, vegetative, or dead). Studies were included if they were in English and allowed the determination of outcomes for all patients with normal or bilaterally absent SEPs. Papers were not considered if subjects were neonates, consisted of abstracts where all necessary details were unavailable, were case reports or duplications of other published studies, or dealt only with brain dead subjects. Data SynthesisFor all studies (n = 44), positive likelihood ratio, positive predictive value, and sensitivity were 4.04, 71.2%, and 59.0%, respectively, for normal SEPs (predicting favorable outcome) and 11.41, 98.5%, and 46.2%, respectively, for bilaterally absent SEPs (predicting unfavorable outcome). Summary receiver operating characteristic curve analysis detected a cut-off criterion effect for only blinded studies of bilaterally absent SEPs. Twelve patients (12/777) were identified with bilaterally absent SEPs who had favorable outcomes. These false positives are typically pediatric patients or have suffered traumatic brain injuries. We suggest criteria for the use of bilaterally absent SEPs in the prediction of poor outcome, which include absence of focal lesions, subdural or extradural fluid collections, and no decompressive craniotomy in previous 48 hrs. Using these criteria the data suggest that the false-positive rate is <0.5% for bilaterally absent SEPs. ConclusionsSEPs are powerful predictors of outcome, particularly poor outcome, if patients with focal lesions, subdural effusions, and those who have had recent decompressive craniotomies are excluded.

Are somatosensory evoked potentials the best predictor of outcome after severe brain injury? A systematic review

ObjectiveMany tests have been used to predict outcome following severe brain injury. We compared predictive powers of clinical examination (pupillary responses, motor responses and Glasgow Coma Scale, GCS), electroencephalography (EEG) and computed tomography (CT) to that of somatosensory evoked potentials (SEPs) in a systematic review.Materials and methodsMedline (1976–2002) and Embase (1980–2002) were searched, manual review of article reference lists was conducted, and authors were contacted. We selected 25 studies addressing the prediction of outcome after severe brain injury using SEPs and either GCS, EEG, CT, pupillary or motor responses. Outcomes were determined for patients with normal or bilaterally absent SEPs and graded measures of GCS, EEG, CT, pupillary responses or motor responses. For favourable outcome prediction SEPs were superior in sensitivity, specificity and positive and negative predictive values, except for pupillary responses which had superior sensitivity and GCS which had higher specificity. SEPs had superior summary receiver operating characteristic curves, with the exception of motor responses, and superior ratio of odds ratios. For unfavourable outcome prediction SEPs were superior to the other tests in sensitivity, specificity and positive and negative predictive values, except for motor and pupillary responses, GCS and CTs which had superior sensitivity. All SEP summary receiver operating characteristic curves and pooled ratio of odds ratios were superior.ConclusionsAlthough imperfect, SEPs appear to be the best single overall predictor of outcome. There is sufficient evidence for clinicians to use SEPs in the prediction of outcome after brain injury.

Severe brain injury in children: long-term outcome and its prediction using somatosensory evoked potentials (SEPs).

Objective: To evaluate the outcome of children 1 and 5 years after severe brain injury (Glasgow Coma Score < 8) using a functional measure [Glasgow Outcome Scale (GOS)] and a health status measure (the Torrance Health State (HUI:1)) and to determine the ability of somatosensory evoked potentials (SEPs) to predict these long-term outcomes. Design: Prospective study. Setting: A 16-bed paediatric intensive care unit in a tertiary childrens hospital. Patients and participants: 105 children with severe brain injury. Interventions: SEPs were recorded once in the first week after admission. Outcome was assessed 1 and 5 years after injury using the GOS and at 5 years after injury using HUI:1. Measurements and results: At 5 years, using the GOS, 46 (43.8 %) children had a good outcome, 10 (9.5 %) were moderately disabled, 2 (1.9 %) severely disabled, 3 (2.9 %) vegetative and 44 (41.9 %) had died. At 5 years, 17 of 40 (42.5 %) survivors from 1 year had changed outcomes: 12 had improved, 3 had worsened and 2 had died. For a normal SEP, positive predictive power was 85.4 %, sensitivity 62.5 %, specificity 87.8 %, negative predictive power 67.2 % and the positive likelihood ratio was 5.1. For bilaterally absent responses, positive predictive power was 90.9 %, sensitivity 61.2 %, specificity 94.6 %, negative predictive power 73.6 % and the positive likelihood ratio was 11.4. Outcomes using HUI:1 were: 30 (28.6 %) had a good quality of life, 21 (20.0 %) had a moderate quality of life, 7 (6.7 %) a poor quality, 44 died (41.9 %) and 3 (2.9 %) survived in a state deemed worse than death. For a normal SEP, positive predictive power was 85.4 %, sensitivity 68.6 %, specificity 88.9 %, negative predictive power 75.0 % and the positive likelihood ratio was 6.2. For bilaterally absent responses, positive predictive power was 93.9 %, sensitivity 57.4 %, specificity 96.1 %, negative predictive power 68.1 % and the positive likelihood ratio was 14.6. Conclusion: The outcome for children with severe brain injury should be assessed 5 years after injury because important changes occur between 1 year and 5 years. Differences exist between outcomes assessed using the GOS and HUI:1 as they measure slightly different aspects of function. Consideration should therefore be given to using both measures. SEPs are excellent predictors of long-term outcome measured by either the GOS or the HUI:1.

Accuracy of two pulse oximeters at low arterial hemoglobin-oxygen saturation.

OBJECTIVE To evaluate the performance of two pulse oximeters in the measurement of arterial hemoglobin saturation in hypoxemic children. DESIGN Prospective, repeated-measures observational study. SETTING A 16-bed pediatric intensive care unit in a childrens tertiary hospital. PATIENTS Sixty-six patients with arterial saturation of <90%. INTERVENTIONS Three arterial blood samples were taken from each subject during a 48-hr period. Pulse oximeter measurements of arterial saturation were compared with arterial saturation determined by cooximetry. MEASUREMENTS AND MAIN RESULTS Arterial saturation was measured using one or both pulse oximeters (SpO2) and compared with the arterial hemoglobin saturation determined by cooximetry (SaO2). Sixty-two subjects were studied, using the Ohmeda pulse oximeter giving 185 data points (78 with saturations <75% [defined by the average of pulse oximeter and cooximeter]); 53 subjects were studied, using the Hewlett-Packard pulse oximeter yielding 155 data points (60 with saturations <75%). SpO2 ranged from 24% to 94%. Bias and precision of the Ohmeda pulse oximeter were -2.8% and 4.8% >75% and -0.8% and 8.0% <75%. Bias and precision of the Hewlett-Packard pulse oximeter were -0.5% and 5.1% >75% and 0.4% and 4.6% <75%. Intrapatient regression coefficient (r) for the differences between pulse oximeter and cooximeter was 0.58 for the Ohmeda and 0.59 for the Hewlett-Packard. Regression coefficients for predicting change in cooximeter value given a change in the Ohmeda pulse oximeter were 0.59 and 0.71 <75% and >75%, respectively. Similar coefficients for the Hewlett-Packard pulse oximeter were 0.50 and 0.70, respectively. CONCLUSION The performance of the Ohmeda pulse oximeter deteriorated below an SpO2 of 75%. The Hewlett-Packard pulse oximeter performed consistently above and below an SpO2 of 75%. The ability of both pulse oximeters to reliably predict change in SaO2 based on change in pulse oximetry was limited. We recommend measurement of PaO2 or SaO2 for important clinical decisions.

A home respiratory support programme for children by parents and layperson carers

Aim:  To describe a respiratory support programme for children at home by parents and layperson carers.

Outcomes of surgical treatment of infants with hypoplastic left heart syndrome: an institutional experience 1983-2004.

Aim:  To determine outcomes of surgical treatment of infants with hypoplastic left heart syndrome (HLHS).

Cerebrovascular Pressure Reactivity in Children With Traumatic Brain Injury.

Objective: Traumatic brain injury is a significant cause of morbidity and mortality in children. Cerebral autoregulation disturbance after traumatic brain injury is associated with worse outcome. Pressure reactivity is a fundamental component of cerebral autoregulation that can be estimated using the pressure-reactivity index, a correlation between slow arterial blood pressure, and intracranial pressure fluctuations. Pressure-reactivity index has shown prognostic value in adult traumatic brain injury, with one study confirming this in children. Pressure-reactivity index can identify a cerebral perfusion pressure range within which pressure reactivity is optimal. An increasing difference between optimal cerebral perfusion pressure and cerebral perfusion pressure is associated with worse outcome in adult traumatic brain injury; however, this has not been investigated in children. Our objective was to study pressure-reactivity index and optimal cerebral perfusion pressure in pediatric traumatic brain injury, including associations with outcome, age, and cerebral perfusion pressure. Design: Prospective observational study. Setting: ICU, Royal Children’s Hospital, Melbourne, Australia. Patients: Patients with traumatic brain injury who are 6 months to 16 years old, are admitted to the ICU, and require arterial blood pressure and intracranial pressure monitoring. Interventions: None. Measurements and Main Results: Arterial blood pressure, intracranial pressure, and end-tidal CO2 were recorded electronically until ICU discharge or monitoring cessation. Pressure-reactivity index and optimal cerebral perfusion pressure were computed according to previously published methods. Clinical data were collected from electronic medical records. Outcome was assessed 6 months post discharge using the modified Glasgow Outcome Score. Thirty-six patients were monitored, with 30 available for follow-up. Pressure-reactivity index correlated with modified Glasgow Outcome Score (Spearman &rgr; = 0.42; p = 0.023) and was higher in patients with unfavorable outcome (0.23 vs –0.09; p = 0.0009). A plot of pressure-reactivity index averaged within 5 mm Hg cerebral perfusion pressure bins showed a U-shape, reaffirming the concept of cerebral perfusion pressure optimization in children. Optimal cerebral perfusion pressure increased with age (&rgr; = 0.40; p = 0.02). Both the duration and magnitude of negative deviations in the difference between cerebral perfusion pressure and optimal cerebral perfusion pressure were associated with unfavorable outcome. Conclusions: In pediatric patients with traumatic brain injury, pressure-reactivity index has prognostic value and can identify cerebral perfusion pressure targets that may differ from treatment protocols. Our results suggest but do not confirm that cerebral perfusion pressure targeting using pressure-reactivity index as a guide may positively impact on outcome. This question should be addressed by a prospective clinical study.

External and internal biphasic direct current shock doses for pediatric ventricular fibrillation and pulseless ventricular tachycardia

Objective: To determine energy dose and number of biphasic direct current shocks for pediatric ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT). Design: Observation of preshock and postshock rhythms, energy doses, and number of shocks. Setting: Pediatric hospital. Patients: Shockable ventricular dysrhythmias. Interventions: None. Measurements and Main Results: Forty-eight patients with VF or pulseless VT received external shock at 1.7 ± 0.8 (mean ± sd) J/kg. Return of spontaneous circulation (ROSC) occurred in 23 (48%) patients with 2.0 ± 1.0J/kg, but 25 (52%) patients remained in VF after 1.5 ± 0.7J/kg (p = .05). In 24 non-responding patients, additional 1–8 shocks (final dose, 2.8 ± 1.2 J/kg) achieved ROSC in 14 (58%) with 2.6 ± 1.1 J/kg but not in 10 (42%) with 3.2 ± 1.2 J/kg (not significant). Overall, 37 (77%) patients achieved ROSC with 2.2 ± 1.1 J/kg (range, 0.5–5.0 J/kg). Eight patients without ROSC recovered with cardiopulmonary bypass and internal direct current shock. At 13 subsequent episodes of VF or VT among eight patients, five achieved ROSC and survived. In combined first and subsequent resuscitative episodes, doses in the range of 2.5 to <3 J/kg achieved most cases of ROSC. Survival for >1 yr was seen in 28 (78%) of 36 patients with VF and seven (58%) of 11 patients with VT, with 35 (73%) overall. Lack of ROSC was associated with multiple shocks (p = .003). Repeated shocks with adhesive pads had significantly less impedance (p < .001). Pads in an anteroposterior position achieved highest ROSC rate. Internal shock for another 48 patients with VF or VT achieved ROSC in 28 (58%) patients with 0.7 ± 0.4 J/kg but not in 20 patients with 0.4 ± 0.3 J/kg (p = .01). Nineteen of the nonresponders who received additional internal 1–9 shocks at 0.6 ± 0.5 J/kg and one patient given extracorporeal membrane oxygenation all recovered, yielding 100% ROSC, but 1-yr survival tallied 43 (90%) patients. Conclusions: The initial biphasic direct current external shock dose of 2 J/kg for VF or pulseless VT is inadequate. Appropriate doses for initial and subsequent shocks seem to be in the range of 3–5 J/kg. Multiple shocks do not favor ROSC. The dose for internal shock is 0.6–0.7 J/kg.

Oxygen delivery using self-inflating resuscitation bags.

Objective: Oxygen-filled self-inflating resuscitators are used by some as a source of oxygen for spontaneously breathing patients. In this application, the bag is not compressed and oxygen is assumed to flow freely from the patient outlet through a mask positioned loosely over the patient’s face. We tested 11 resuscitators to determine the delivery of oxygen from the patient outlet using different inlet flows. Design: Bench test. Setting: A pediatric intensive care unit. Interventions: Patient outlet flow was measured at inlet flows of 5, 10, and 15 L/min at two different orientations of the reservoir valve assembly (upright and inverted). Measurements and Main Results: Patient outlet flow varied between resuscitators but was always less than the inlet flow and, in some cases, was as little as approximately 20% of the inlet flow. As the inlet flow rate was increased, the percentage of outlet flow that a patient received decreased, particularly in the upright position. At inlet flows of 5, 10, and 15 L/min, patient outlet flow ranged from 1.1 to 4.6 L/min, 1.6 to 5.1 L/min, and 2.0 to 6.5 L/min, respectively. Conclusions: Self-inflating resuscitators deliver a significantly lower flow of oxygen than the provided inlet flow and should not be relied on to deliver a precise amount of flow of oxygen to spontaneously breathing patients.

The Effect of Inlet Gas Temperatures on Heated Humidifier Performance

The aim of the current study was to determine the temperature range of gas at the point at which it passes into a heated humidifier within an intensive care unit and to experimentally examine the effect of different inlet gas temperatures on the performance of a heated humidifier. Various gas and ambient temperatures were measured in an intensive care unit and within ventilator circuits. Ventilator oxygen and air inlet temperatures, ventilator gas outlet temperatures, and humidifier gas inlet temperatures were measured in conjunction with the use of a number of ventilators. Ambient temperatures within the ward ranged from 22.8 degrees C to 28.9 degrees C, while typical ward humidifier gas inlet temperatures ranged from 24.3 degrees C to 28.8 degrees C. Humidity output from a heated humidifier was then determined in an experimental setup at controlled levels of inlet gas temperature using a constant gas flow. A decrease in humidity production, from approximately 36 mg/L at a humidifier inlet gas temperature of 18 degrees C, to 26 mg/L at a humidifier inlet gas temperature of 32 degrees C, was observed with increasing gas inlet temperature. We conclude that humidity output from a heated humidifier varies with inlet gas temperature, decreasing as inlet gas temperature increases. Inlet gas temperatures above 26 degrees C may result in inadequate humidification.