ABSTRACT
OBJECTIVE: Heart rate variability (HRV) reflects integrity of the autonomic nervous system. However, no study has investigated the impact of therapeutic hypothermia (TH) on HRV measures in infants with hypoxic-ischemic encephalopathy (HIE). In this study, we evaluate the influence of temperature on measures of HRV for a group of infants with favorable outcomes, as compared with a control group of infants with unfavorable outcomes. STUDY DESIGN: Term-born infants with moderate-severe HIE underwent standard TH treatment and prospective electroencephalography (EEG) and electrocardiogram (ECG) recording. Infants with favorable outcome (no seizures, normal/mild EEG scores at 96 h, no magnetic resonance imaging brain injury and normal neurodevelopmental scores at 18 to 24 months) were matched on gestational age, sex and worst encephalopathy score to a group of infants with unfavorable outcomes. Time- and frequency-domain HRV measures were calculated from 60 min of ECG data obtained at three time points: 24 h (hypothermia), 48 h (hypothermia) and 96 h (normothermia). The effect of time and temperature were evaluated using repeated-measures analysis of variance. RESULTS: Sixteen infants were included (8 favorable, 8 unfavorable). For both groups of infants, an increase in the HR, RR and HF power was associated with an increase in temperature, but was not associated with any other HRV measure. In contrast, measures of HRV increased over time, as encephalopathy decreased, for infants with favorable outcomes (reflecting increased cortical-autonomic integration), but not for those with unfavorable outcomes. CONCLUSIONS: In general, the effect of hypothermia on measures of HRV is limited to changes in heart rate (bradycardia) and respiratory rate, as opposed to changes in true variability. This supports the hypothesis that persistent changes in HRV are driven by the underlying brain injury and not by the process of TH.
Subject(s)
Bradycardia/etiology , Heart Rate , Hypothermia, Induced/methods , Hypoxia-Ischemia, Brain/diagnostic imaging , Hypoxia-Ischemia, Brain/therapy , Electrocardiography , Electroencephalography , Female , Gestational Age , Humans , Infant, Newborn , Magnetic Resonance Imaging , Male , Missouri , Prospective Studies , Respiratory Rate , Severity of Illness Index , Time FactorsABSTRACT
OBJECTIVE: Fractional tissue oxygen extraction (FTOE) is a measure derived from cerebral near-infrared spectroscopy (NIRS) and simultaneous pulse oximetry (SpO2), capturing the proportion of oxygen delivered in arterial blood that is used by the target tissue. FTOE may provide a better proxy measurement of retinal hyperoxia than pulse oximetry alone and could provide insight into the risk for retinopathy of prematurity (ROP). In this study, we directly compared hyperoxia burden calculated from FTOE with hyperoxia burden calculated from SpO2 alone in order to assess the strength of association between hyperoxia and severe ROP. STUDY DESIGN: Infants born before <30 weeks and weighing <1500 g underwent synchronized SpO2 and FTOE recording over the first 4 days following birth. After error correction of the raw recording, hyperoxia burden was calculated as the percentage of the total SpO2 or FTOE recording with measurements exceeding defined thresholds (90/93/95% and 20/15/10%, respectively) and was compared with the outcome of severe ROP, defined as ROP requiring laser therapy, after controlling for important covariates. RESULT: A total of 63 infants were included with a mean±s.d. gestational age of 25.8±1.5 weeks and birth weight of 898.5±206.9 g; 13/63 (20%) had severe ROP. SpO2 hyperoxia burden was not associated with severe ROP at any threshold. FTOE hyperoxia burden was associated with severe ROP at the 15% (P=0.04) and 10% (P=0.03) thresholds. Infants with severe ROP spent 20% and 50% more time exceeding the 15% and 10% thresholds, respectively, as compared with those without severe ROP. CONCLUSION: In the first 96 h of life, FTOE but not SpO2 hyperoxia burden is associated with severe ROP. These preliminary results suggest that NIRS may be a viable alternative technology for targeted oxygen saturation guidelines.
Subject(s)
Hyperoxia/complications , Oximetry/methods , Oxygen/blood , Retinopathy of Prematurity/etiology , Spectroscopy, Near-Infrared/methods , Birth Weight , Female , Gestational Age , Humans , Hyperoxia/diagnostic imaging , Infant, Newborn , Infant, Premature , Infant, Very Low Birth Weight , Intensive Care Units, Neonatal , Male , Oxygen/adverse effects , Oxygen Consumption , Prospective Studies , Respiration, Artificial/adverse effects , Retinopathy of Prematurity/diagnosis , Risk Factors , Sensitivity and Specificity , Spectroscopy, Near-Infrared/trendsABSTRACT
OBJECTIVE: To identify factors associated with responsiveness to dopamine therapy for hypotension and the relationship to brain injury in a cohort of preterm infants. STUDY DESIGN: The pharmacy database at St Louis Children's Hospital was retrospectively queried to identify infants who (a) were born <28 weeks gestation between 2012 and 2014, (b) received dopamine and (c) had blood pressure measurements from an umbilical arterial catheter. A control group was constructed from contemporaneous infants who did not receive dopamine. Mean arterial blood pressure (MABP) at baseline, 1 h and 3 h after initiating dopamine were obtained for each dopamine-exposed infant. MABP measurements at matched time points were obtained in the control group. RESULT: Sixty-nine dopamine-treated and 45 control infants were included. Mean ΔMABP at 3 h was 4.5±6.3 mm of Hg for treated infants vs 1±2.9 for the control. Median dopamine starting dose was 2.5 µg kg(-1) min(-1). Dopamine-treated infants were less mature and of lower birth weight while also more likely to be intubated at 72 h, diagnosed with intraventricular hemorrhage (IVH) and to die. Failure to respond to dopamine was associated with greater likelihood of developing IVH (odds ratio (OR) 5.8, 95% confidence interval (CI) 1.1-42.3), while a strong response (ΔMABP>10 mm Hg) was associated with a reduction in risk of IVH (OR 0.1, 95% CI 0.01-0.8). CONCLUSION: Low-moderate dose dopamine administration results in modest blood pressure improvements. A lack of response to dopamine is associated with a greater risk of IVH, whereas a strong response is associated with a decreased risk. Further research into underlying mechanisms and management strategies is needed.
Subject(s)
Dopamine , Hypotension , Infant, Premature, Diseases , Blood Pressure/drug effects , Blood Pressure Determination/methods , Cardiotonic Agents/administration & dosage , Cardiotonic Agents/adverse effects , Cerebral Intraventricular Hemorrhage/complications , Cerebral Intraventricular Hemorrhage/diagnosis , Cerebral Intraventricular Hemorrhage/mortality , Dopamine/administration & dosage , Dopamine/adverse effects , Dose-Response Relationship, Drug , Female , Humans , Hypotension/complications , Hypotension/diagnosis , Hypotension/drug therapy , Hypotension/mortality , Infant, Low Birth Weight , Infant, Newborn , Infant, Premature , Infant, Premature, Diseases/diagnosis , Infant, Premature, Diseases/drug therapy , Male , Retrospective Studies , Treatment Outcome , United States/epidemiologyABSTRACT
Room-temperature laser action from Cr(2+)-doped Cd(0.85)Mn(0.15)Te has been demonstrated for what is believed to be the first time. We achieved pulsed laser operation centered at ~2.5mu m by pumping into the mid-infrared absorption band of Cr(2+) ions by use of the 1.907- mum output of a H(2) Raman-shifted Nd:YAG laser. The output of the free-running Cr(2+):Cd(0.85)Mn(0.15)Te laser had a width of ~50 nm (FWHM), and the slope efficiency was calculated to be 5.5% under nonoptimum conditions.
