A New Phased-Array Magnetic Resonance Imaging Receive-Only Coil for HBO2 Studies.

The paper describes a new magnetic resonance imaging (MRI) phased-array receive-only (Rx) coil for studying decompression sickness and disorders of hyperbaricity, including nitrogen narcosis. Functional magnetic resonance imaging (fMRI) is noninvasive, is considered safe, and may allow studying the brain under hyperbaric conditions. All of the risks associated with simultaneous MRI and HBO2 therapy are described in detail, along with all of the mitigation strategies and regulatory testing. One of the most significant risks for this type of study is a fire in the hyperbaric chamber caused by the sparking of the MRI coils as a result of high-voltage RF arcs. RF pulses at 128 MHz elicit signals from human tissues, and RF sparking occurs commonly and is considered safe in normobaric conditions. We describe how we built a coil for HBO2-MRI studies by modifying an eight-channel phased-array MRI coil with all of the mitigation strategies discussed. The coil was fabricated and tested with a unique testing platform that simulated the worst-case RF field of a three-Tesla MRI in a Hyperlite hyperbaric chamber at 3 atm pressure. The coil was also tested in normobaric conditions for image quality in a 3 T scanner in volunteers and SNR measurement in phantoms. Further studies are necessary to characterize the coil safety in HBO2/MRI.

Case Studies Using the Electroencephalogram to Monitor Anesthesia-Induced Brain States in Children.

For this child, at this particular moment, how much anesthesia should I give? Determining the drug requirements of a specific patient is a fundamental problem in medicine. Our current approach uses population-based pharmacological models to establish dosing. However, individual patients, and children in particular, may respond to drugs differently. In anesthesiology, we have the advantage that we can monitor our patients in real time and titrate drugs to the desired effect. Examples include blood pressure management or muscle relaxation. Although the brain is the primary site of action for sedative-hypnotic drugs, the brain is not routinely monitored during general anesthesia or sedation, a fact that would surprise many patients. One reason for this is that, until recently, physiologically principled approaches for anesthetic brain monitoring have not been articulated. In the past few years, our knowledge of anesthetic brain mechanisms has developed rapidly. We now know that anesthetic drug effects are clearly visible in the electroencephalogram (EEG) of adults and reflect underlying anesthetic pharmacology and brain mechanisms. Most recently, similar effects have been characterized in children. In this article, we describe how EEG monitoring could be used to guide anesthetic management in pediatric patients. We review previous evidence and present multiple case studies showing how drug-specific and dose-dependent EEG signatures seen in adults are visible in children and infants, including those with neurological disorders. We propose that the EEG can be used in the anesthetic care of children to enable anesthesiologists to better assess the drug requirements of individual patients in real time and improve patient safety and experience.

Impact of a fast free-breathing 3-T abdominal MRI protocol on improving scan time and image quality for pediatric patients with tuberous sclerosis complex.

BACKGROUND: Magnetic resonance imaging (MRI) of the abdomen can be especially challenging in pediatric patients because of image quality degradation from respiratory motion. Abdominal MR protocols tailored for free-breathing children can potentially improve diagnostic image quality and reduce scan time. OBJECTIVE: To evaluate the performance of a free-breathing 3-T MRI protocol for renal evaluation in pediatric patients with tuberous sclerosis complex (TSC). MATERIALS AND METHODS: A single institution, Institutional Review Board-approved, retrospective database query identified pediatric TSC patients who underwent a free-breathing 3-T MR abdominal protocol including radial and respiratory-triggered pulse sequences and who also had a prior abdominal MRI on the same scanner using a traditional MR protocol utilizing signal averaging and Cartesian k-space sampling. Scan times and use of sedation were recorded. MR image quality was compared between the two protocols using a semiquantitative score for overall image quality and sharpness. RESULTS: Forty abdominal MRI studies in 20 patients were evaluated. The mean scan time of the fast free-breathing protocol was significantly lower (mean: 42.5±9.8 min) compared with the traditional protocol (58.7±11.7 min; P=<0.001). Image sharpness was significantly improved for radial T2-weighted and T1-weighted triggered Dixon and radial T1-weighted fat-suppressed post-contrast images in the free-breathing protocol, while image quality was significantly higher on radial and Dixon T1-weighted sequences. CONCLUSION: A free-breathing abdominal MR protocol in pediatric TSC patients decreases scan time and improves image quality and should be considered more widely for abdominal MRI in children.

Age-Dependent Changes in the Propofol-Induced Electroencephalogram in Children With Autism Spectrum Disorder.

Patients with autism spectrum disorder (ASD) often require sedation or general anesthesia. ASD is thought to arise from deficits in GABAergic signaling leading to abnormal neurodevelopment. We sought to investigate differences in how ASD patients respond to the GABAergic drug propofol by comparing the propofol-induced electroencephalogram (EEG) of ASD and neurotypical (NT) patients. This investigation was a prospective observational study. Continuous 4-channel frontal EEG was recorded during routine anesthetic care of patients undergoing endoscopic procedures between July 1, 2014 and May 1, 2016. Study patients were defined as those with previously diagnosed ASD by DSM-V criteria, aged 2-30 years old. NT patients were defined as those lacking neurological or psychiatric abnormalities, aged 2-30 years old. The primary outcome was changes in propofol-induced alpha (8-13 Hz) and slow (0.1-1 Hz) oscillation power by age. A post hoc analysis was performed to characterize incidence of burst suppression during propofol anesthesia. The primary risk factor of interest was a prior diagnosis of ASD. Outcomes were compared between ASD and NT patients using Bayesian methods. Compared to NT patients, slow oscillation power was initially higher in ASD patients (17.05 vs. 14.20 dB at 2.33 years), but progressively declined with age (11.56 vs. 13.95 dB at 22.5 years). Frontal alpha power was initially lower in ASD patients (17.65 vs. 18.86 dB at 5.42 years) and continued to decline with age (6.37 vs. 11.89 dB at 22.5 years). The incidence of burst suppression was significantly higher in ASD vs. NT patients (23.0% vs. 12.2%, p < 0.01) despite reduced total propofol dosing in ASD patients. Ultimately, we found that ASD patients respond differently to propofol compared to NT patients. A similar pattern of decreased alpha power and increased sensitivity to burst suppression develops in older NT adults; one interpretation of our data could be that ASD patients undergo a form of accelerated neuronal aging in adolescence. Our results suggest that investigations of the propofol-induced EEG in ASD patients may enable insights into the underlying differences in neural circuitry of ASD and yield safer practices for managing patients with ASD.

A Prospective Study of Age-dependent Changes in Propofol-induced Electroencephalogram Oscillations in Children.

BACKGROUND: In adults, frontal electroencephalogram patterns observed during propofol-induced unconsciousness consist of slow oscillations (0.1 to 1 Hz) and coherent alpha oscillations (8 to 13 Hz). Given that the nervous system undergoes significant changes during development, anesthesia-induced electroencephalogram oscillations in children may differ from those observed in adults. Therefore, we investigated age-related changes in frontal electroencephalogram power spectra and coherence during propofol-induced unconsciousness. METHODS: We analyzed electroencephalogram data recorded during propofol-induced unconsciousness in patients between 0 and 21 yr of age (n = 97), using multitaper spectral and coherence methods. We characterized power and coherence as a function of age using multiple linear regression analysis and within four age groups: 4 months to 1 yr old (n = 4), greater than 1 to 7 yr old (n = 16), greater than 7 to 14 yr old (n = 30), and greater than 14 to 21 yr old (n = 47). RESULTS: Total electroencephalogram power (0.1 to 40 Hz) peaked at approximately 8 yr old and subsequently declined with increasing age. For patients greater than 1 yr old, the propofol-induced electroencephalogram structure was qualitatively similar regardless of age, featuring slow and coherent alpha oscillations. For patients under 1 yr of age, frontal alpha oscillations were not coherent. CONCLUSIONS: Neurodevelopmental processes that occur throughout childhood, including thalamocortical development, may underlie age-dependent changes in electroencephalogram power and coherence during anesthesia. These age-dependent anesthesia-induced electroencephalogram oscillations suggest a more principled approach to monitoring brain states in pediatric patients.

Ultrasound-Guided Regional Anesthesia for Pediatric Burn Reconstructive Surgery: A Prospective Study.

Pediatric patients face multiple reconstructive surgeries to reestablish function and aesthetics postburn injury. Often, the site of the harvested graft for these reconstructions is reported to be the most painful part of the procedure and a common reason for deferring these reconstructive procedures. This study in pediatric burn patients undergoing reconstructive procedures examined the analgesia response to local anesthetic infiltration versus either a single ultrasound-guided regional nerve block of the lateral femoral cutaneous nerve (LFCN) or a fascia iliaca compartment block with catheter placement and continuous infusion. Nineteen patients were randomized to one of three groups (infiltration, single-shot nerve block, or compartment block with catheter) and received intraoperative analgesia intervention. Postoperatively, visual analog scale pain scores were recorded-for pain at the donor site-every 4 hours while awake-for 48 hours. This nonparametric data was analyzed using a two-way ANOVA, Friedman's test, and Kruskal-Wallis test, with significance determined at P < 0.05. The analysis demonstrated that the patients in the regional anesthesia groups were significantly more comfortable over the 48 hour hospital course than the patients in the control group. The patients receiving a single-shot block of the LFCN were more comfortable on postoperative day (POD) 0 while the catheter patients were more comfortable on POD 1 and POD 2. There was not a statistically significant difference in opioid requirements in any group. Regional anesthetic block of the LFCN, with or without catheter placement, provides an improved postoperative experience for the pediatric patient undergoing reconstructive surgery with lateral/anterolateral skin graft versus local anesthesia infiltration of donor site. For optimal comfort throughout the postoperative period, an ultrasound-guided block with continuous catheter may be beneficial.

Continuous noninvasive cardiac output in children: is this the next generation of operating room monitors? Initial experience in 402 pediatric patients.

BACKGROUND: Electrical Cardiometry(™) (EC) estimates cardiac parameters by measuring changes in thoracic electrical bioimpedance during the cardiac cycle. The ICON(®), using four electrocardiogram electrodes (EKG), estimates the maximum rate of change of impedance to peak aortic blood acceleration (based on the premise that red blood cells change from random orientation during diastole (high impedance) to an aligned state during systole (low impedance)). OBJECTIVE: To determine whether continuous cardiac output (CO) data provide additional information to current anesthesia monitors that is useful to practitioners. METHODS: After IRB approval and verbal consent, 402 children were enrolled. Data were uploaded to our anesthesia record at one-minute intervals. Ten-second measurements (averaged over the previous 20 heart beats) were downloaded to separate files for later comparison with routine OR monitors. RESULTS: Data from 374 were in the final cohort (loss of signal or improper lead placement); 292,012 measurements during 58,049 min of anesthesia were made in these children (1 day to 19 years and 1 to 107 kg). Four events had a ≥25% reduction in cardiac index at least 1 min before a clinically important change in other monitored parameters; 18 events in 14 children confirmed manifestations of other hemodynamic measures; eight events may have represented artifacts because the observed measurements did not seem to fit the clinical parameters of the other monitors; three other events documented decreased stroke index with extreme tachycardia. CONCLUSIONS: Electrical cardiometry provides real-time cardiovascular information regarding developing hemodynamic events and successfully tracked the rapid response to interventions in children of all sizes. Intervention decisions must be based on the combined data from all monitors and the clinical situation. Our experience suggests that this type of monitor may be an important addition to real-time hemodynamic monitoring.

Cardiovascular Effects of Continuous Dexmedetomidine Infusion Without a Loading Dose in the Pediatric Intensive Care Unit.

BACKGROUND: Use of dexmedetomidine in pediatric critical care is common, despite lack of prospective studies on its hemodynamic effects. OBJECTIVE: To describe cardiovascular effects in critically ill children treated with a constant continuous infusion of dexmedetomidine without a loading dose at highest Food and Drug Administration-approved adult dose. METHODS: Prospective, pilot study of 17 patients with dexmedetomidine infused at a rate of 0.7 µg/kg/h for 6 to 24 hours. Heart rate (HR) and blood pressure (BP) values over time were analyzed by a random effects mixed model. RESULTS: Patients with median age of 1.6 years (1 month to 17 years) and median weight of 11.8 kg (2.8-84 kg) received an infusion for a mean of 16 ± 7.2 hours. There were no cardiac conduction abnormalities. One patient required discontinuation of infusion for predetermined low HR termination criteria at hour 13 of infusion; there was no clinical compromise and it coincided with planned extubation. Decreased HR of 20% from baseline was found in 35% of patients. The mean HR reduction was largest at hour 13 of infusion with a decrease of 13 ± 17 bpm from baseline, but HR changes over time were not statistically significant. Blood pressure effects included a decrease in 12% and an increase in 29%. There was a small but statistically significant increase in systolic BP of 0.4 mm Hg/h of infusion, P < .001. CONCLUSION: A continuous infusion of 0.7 µg/kg/h of dexmedetomidine without a loading dose for up to 24 hours in critically ill children had tolerable effects on HR and BP.

Acute and perioperative care of the burn-injured patient.

Care of burn-injured patients requires knowledge of the pathophysiologic changes affecting virtually all organs from the onset of injury until wounds are healed. Massive airway and/or lung edema can occur rapidly and unpredictably after burn and/or inhalation injury. Hemodynamics in the early phase of severe burn injury is characterized by a reduction in cardiac output and increased systemic and pulmonary vascular resistance. Approximately 2 to 5 days after major burn injury, a hyperdynamic and hypermetabolic state develops. Electrical burns result in morbidity much higher than expected based on burn size alone. Formulae for fluid resuscitation should serve only as guideline; fluids should be titrated to physiologic endpoints. Burn injury is associated basal and procedural pain requiring higher than normal opioid and sedative doses. Operating room concerns for the burn-injured patient include airway abnormalities, impaired lung function, vascular access, deceptively large and rapid blood loss, hypothermia, and altered pharmacology.

Hemodynamic responses to dexmedetomidine in critically injured intubated pediatric burned patients: a preliminary study.

Because of ineffectiveness and tolerance to benzodiazepines and opioids developing with time, drugs acting via other receptor systems (eg, α-2 agonists) have been advocated in burn patients to improve sedation and analgesia. This study in severely burned pediatric subjects examined the hemodynamic consequences of dexmedetomidine (Dex) administration. Eight intubated patients with ≥20 to 79% TBSA burns were studied between 7 and 35 days after injury. After baseline measurements of mean arterial blood pressure and heart rhythm were taken, each patient received a 1.0 µg/kg bolus of Dex followed by an ascending dose infusion protocol (0.7-2.5 µg/kg/hr), with each dose administered for 15 minutes. There was significant hypotension (27±7.5%, average drop in mean arterial pressure [MAP] ± SD), and a decrease in heart rate (HR; 19% ± 7, average drop in HR ± SD). The average HR decreased from 146 beats per minute to 120. No bradycardia (HR < 60) or heart blocks were observed. In three patients, the MAP decreased to <50mm Hg with the bolus dose of Dex. Of the remaining five patients, three patients completed the study receiving the highest infusion dose of Dex (2.5 µg/kg/hr), whereas in 2 patients the infusion part of the study was begun, but the study was stopped due to persistent hypotension (MAP < 50mm Hg). These observations indicate that a bolus dose of Dex (1.0 µg/kg for 10 minutes) and high infusion rates may require fluid resuscitation or vasopressor support to maintain normotension in critically injured pediatric burn patients.

Infrared ear thermometry in water-related accidents-not a good choice.

Hypothermia in near-drowning victims is a serious problem that impacts clinical decision-making. The purpose of this trial was to determine the reliability of tympanic temperature measurements compared to oral temperature measurements after immersion in water. After ethical approval was obtained, we studied oral and tympanic temperature in 25 volunteer swimmers (aged 18-49 years). Sublingual (Fixotherm; Tradesell Europe, Eglharting, Germany) and tympanic (First Temp Genius; Sherwood Medical, Sulzbach, Germany) temperature measurements were performed before entering the water, after 45 min of immersion in water, and 15 min after leaving the water. During the immersion phase, the ears were temporarily immersed. A control group (the same 25 volunteers) had to swim for the same amount of time without ever immersing their heads in the water. The trial was performed in an indoor swimming pool at 28 degrees C water and 30 degrees C air temperature. The oral temperature did not change over time in either group. The tympanic temperature was significantly lower after immersion compared to baseline in the "immersed" group (33.7 degrees C vs. 37.5 degrees C, p < 0.001), increased significantly in the recovery period, but remained significantly lower than baseline (36.0 degrees C vs. 37.5 degrees C, p < 0.001). At baseline, the oral temperature was lower compared to the tympanic temperature. This relationship reversed after immersion and remained reversed until the end of the trial in the immersion group. The control group maintained oral temperatures lower than tympanic throughout the study; furthermore, the control group had no clinically relevant change in oral or tympanic temperature over the time (tympanic temperature: 37.4 degrees C vs. 37.2 degrees C, p = 0.06). Our data suggest that in water-related accidents such as near drowning, the values of body (core) temperature obtained via use of infrared ear thermometry are unreliable, and should not be used for clinical decision-making.

Selective ablation of GABA neurons in the ventral tegmental area increases spontaneous locomotor activity.

Gamma-aminobutyric acid (GABA) neurons in the ventral tegmental area (VTA) provide innervation to cortical and subcortical regions of the brain. To solidify the importance of these VTA GABA neurons in behavioral function, we employed the neurotoxin dermorphin-saporin (DS) to selectively lesion VTA GABA neurons prior to assessing spontaneous motor activity. Rats were bilaterally microinfused with DS (1.0 or 2.0 pmol/200 nl/side) or blank-saporin control (BS, 200 nl/side) into the VTA. Seven days later, DS-treated rats exhibited significantly elevated motility in comparison with BS-treated rats; this elevated motility normalized by Day 14 following pretreatment with 1.0 pmol of DS but was sustained on Day 14 after pretreatment with 2.0 pmol of DS. A selective loss of VTA GABA neurons on Day 14 was demonstrated through reduced expression of mRNA for glutamic acid decarboxylase-67 and micro-opioid receptor, but not tyrosine hydroxylase (a dopamine neuron marker), in the VTA. Thus, a dose- and time-related selective loss of VTA GABA neurons was accomplished using this novel neurotoxin. This loss of GABA VTA neurons was associated with hypermotility, further supporting their important regulatory role in the generation of behavior.

Anesthetic management for thoracopagus twins with complex cyanotic heart disease in the magnetic resonance imaging suite.

We report a case of thoracopagus twins undergoing magnetic resonance imaging (MRI) studies under general anesthesia. The twins had a complex shared cardiac anatomy that posed additional challenges to an already-difficult anesthesia care area. This report emphasizes the approach to anesthetic management of conjoined twins in the MRI environment.

Evaluation and management of decompression illness--an intensivist's perspective.

Decompression illness (DCI) is becoming more prevalent as more people engage in activities involving extreme pressure environments such as recreational scuba-diving. Rapid diagnosis and treatment offer these patients the best chance of survival with minimal sequelae. It is thus important that critical care physicians are able to evaluate and diagnose the signs and symptoms of DCI. The cornerstones of current treatment include the administration of hyperbaric oxygen and adjunctive therapies such as hydration and medications. However, managing patients in a hyperbaric environment does present additional challenges with respect to the particular demands of critical care medicine in an altered pressure environment. This article reviews the underlying pathophysiology, clinical presentation and therapeutic options available to treat DCI, from the intensivist's perspective.