Hypernatremia after cleft lip repair in a patient with holoprosencephaly.
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Cleft Palate↗
Biomedical subjects
Avery Tung
Publications and source records attributed to Avery Tung.
Brain magnetic resonance imaging increases core body temperature in sedated children.
An increasing number of children now undergo magnetic resonance imaging (MRI) under sedation. MRI requires a cool environment. Because children have a larger surface area to body weight ratio than adults and because active warming devices are not MRI compatible, hypothermia as a result of passive heat loss is a risk. Absorption of radiofrequency radiation generated by the scanning process, however, may partially offset this heat loss. To determine the effect of absorbed radiofrequency radiation on body temperature during MRI, we measured pre-MRI and post-MRI tympanic temperatures in 30 children who underwent brain MRI while sedated with chloral hydrate and covered with a hospital gown and blanket. The mean (+/- sd) age was 14.9 +/- 8.6 mo, and weight was 9.8 +/- 2.8 kg. During an average scan duration of 42 +/- 13 min, mean tympanic temperatures increased 0.5 degrees C from 36.9 degrees C +/- 0.4 degrees C to 37.4 degrees C +/- 0.3 degrees C; (95% CI difference, 0.3 degrees C to 0.7 degrees C; P < 0.001). Our findings suggest that children sedated with chloral hydrate for brain MRI did not become hypothermic but rather had increased body temperature despite minimal barriers to heat loss and no active warming. These results imply that aggressive measures to prevent passive heat loss during MRI studies may not be needed in all patients.
Body Temperature↗
Fulminant liver failure after radical prostatectomy in the hyperlordotic position.
In the hyperlordotic position, the patient's hips are above the feet and head. This position has previously been associated with partial vena caval occlusion, increased venous pressures, and spinal cord infarction. We describe a case of fulminant hepatic failure after radical retropubic prostatectomy performed in the hyperlordotic position.
Fatal Outcome↗
The biology and genetics of obesity and obstructive sleep apnea.
This article reviews current knowledge about a genetic approach to the causes and risk factors for sleep apnea. Recent evidence suggests that genetic variability may play a significant causal role in the pathogenesis of obstructive sleep apnea. The data supporting a genetic influence on sleep apnea, and the perioperative management of patients with sleep apnea are examined.
Humans↗
Effect of inspiratory time on tidal volume delivery in anesthesia and intensive care unit ventilators operating in pressure control mode.
STUDY OBJECTIVE: To compare the effect of inspiratory time and lung compliance on tidal volume (Vt) delivery in anesthesia and intensive care unit (ICU) ventilators operating in pressure control mode. SETTING: Respiratory research laboratory of a tertiary care medical center. DESIGN: Two anesthesia ventilators with pressure control capability (Narkomed 6000, Drager Medical, Inc, Telford, Pa, and the Datex-Ohmeda Aestiva 5, Datex-Ohmeda, Inc, Madison, Wis) and one critical care ventilator (Puritan Bennett 7200, Puritan-Bennett, Pleasanton, Calif) were studied under varying inspiratory time and lung compliance conditions using a mechanical lung model. INTERVENTION: Each ventilator was set to pressure control mode at a fixed inspiratory/expiratory (I/E) ratio. The respiratory rate (RR) was varied between 6 and 28 breaths per minute. Lung compliance and inspiratory time settings were set to simulate clinical conditions known to affect anesthesia ventilator performance. MEASUREMENTS: Inspiratory flow, Vts, and peak airway pressures were measured using the on-board monitor for each ventilator, and confirmed with the Bicore CP-100 pulmonary mechanics monitor (Bicore Monitoring Systems, Inc, Irvine, Calif). To assess differences in inspiratory flow between ventilators, airway pressures were continuously monitored during inspiration. MAIN RESULTS: Increasing RRs caused delivered Vts to decrease for all ventilators. However, decreases in Vts were significantly larger for anesthesia than for ICU ventilators. At a lung compliance of 0.02 L/cm H(2)O and set Vt of 700 mL, Vt delivery for the Puritan Bennett 7200 ventilator remained at 88% of baseline, but decreased to 76% for the Aestiva 5 when RRs were increased from 6 to 28 breaths per minute (P < .0025). Airway pressure tracings demonstrated a slower increase in inspiratory airway pressure for the Aestiva 5 than for the other ventilators. CONCLUSION: Differences in inspiratory flow delivery between ICU and anesthesia ventilators can cause differences in Vt delivery when the pressure control mode is used at high RRs. These differences can significantly impact the perioperative care of critically ill patients requiring ventilatory support.
Air Pressure↗
New anesthesia techniques.
Advances in anesthesia involve refinements in understanding, technique, and technology. These refinements have led to better control of the anesthetic state, effective anesthesia for a wider variety of situations, and the ability to bring sicker patients to the operating room. Although the molecular mechanisms underlying the general anesthetic state are unknown, evidence suggests a specific, receptor-based effect. This concept has allowed anesthesiologists to treat anesthetic end points of immobility, lack of awareness, and autonomic control separately. It is likely that anesthesia and naturally occurring sleep interact physiologically. New, processed EEG monitors may allow anesthesiologists to titrate more finely anesthetic dose, with possible benefits in terms of speed of recovery and detection of intraoperative awareness. Since the 1990s, new anesthetic drugs (propofol, desflurane/sevoflurane, cisatracurium) have enhanced greatly control of the anesthetic state. The new intravenous anesthetic agent dexmedetomidine offers sedation with preserved respiration and cognitive function. Although its role has yet to be defined fully, it currently plays a role in ICU sedation and monitored anesthesia care. New anesthesia ventilators have better monitoring and better flow delivery at high airway pressures. These improvements significantly narrow the performance gap between anesthesia and ICU ventilators. In patients with COPD, pulmonary hypertension, or severe hypoxemia, heliox may improve gas flow, and NO may reduce pulmonary vascular resistance and improve oxygenation.
Anesthesia, General↗
Effect of sleep deprivation on righting reflex in the rat is partially reversed by administration of adenosine A1 and A2 receptor antagonists.
BACKGROUND: Similarities between naturally occurring sleep and general anesthesia suggest that the two states may interact physiologically. The authors have previously demonstrated that sleep deprivation potentiates anesthetic-induced loss of righting reflex (LORR) in rats. One possible mediator for this effect is adenosine, which accumulates in the brains of sleep-deprived animals and reduces anesthetic requirements. The authors tested in rats the hypothesis that potentiating effects of sleep deprivation on LORR can be altered by adenosine A1 and A2a receptor antagonists. METHODS: Five experiments were conducted. In each, rats underwent four trials, consisting of a 24-h period of either sleep deprivation or ad libitum activity followed by administration of a fixed dose of an adenosine antagonist or vehicle. Rats were then given isoflurane, and the time to LORR and recovery were measured. Each experiment tested a specific dose of an A1 receptor antagonist (8-cyclopentyltheophylline given via microinjection into the basal forebrain), an A2a receptor antagonist (ZM241385 via intraperitoneal administration), or both. In each experiment, all rats received all combinations of activity and drug/vehicle, separated by 5-7 days. RESULTS: In rested rats, neither antagonist altered the time to LORR. In sleep-deprived rats, both ZM241385 and 8-cyclopentyltheophylline prolonged the time to LORR and shortened recovery in a dose-dependent manner. Prolongation also occurred when subtherapeutic doses of both agents were coadministered. CONCLUSION: Both antagonists partially reversed the effect of sleep deprivation on anesthetic action. This result implies that deprivation-induced changes in adenosine receptor activity can alter LORR. Neither antagonist completely reversed this effect, suggesting possible non-adenosine-mediated effects of sleep deprivation.
Adenosine A1 Receptor Antagonists↗
Preoperative clinic visits reduce operating room cancellations and delays.
BACKGROUND: Anesthesiologist-directed preoperative medicine clinics are used to prepare patients for the administration of anesthesia and surgery. Studies have shown that such a clinic reduces preoperative testing and consults, but few studies have examined the impact of the clinic on the day of surgery. The authors tested whether a visit to an anesthesia preoperative medicine clinic (APMC) would reduce day-of-surgery case cancellations and/or case delays. METHODS: The authors conducted a retrospective chart review of all surgical cases during a 6-month period at the University of Chicago Hospitals. Case cancellations and rates of first-start case delay over the 6-month period were cross-referenced with a database of APMC attendees in both the general operating rooms and the same-day surgery suite. The impact of a clinic visit on case cancellation and delay in both sites were analyzed separately. RESULTS: A total of 6,524 eligible cases were included. In the same-day surgery suite, 98 of 1,164 (8.4%) APMC-evaluated patients were cancelled, as compared with 366 of 2,252 (16.2%) in the non-APMC group (P < 0.001). In the general operating rooms, 87 of 1,631 (5.3%) APMC-evaluated patients were cancelled, as compared with 192 of 1,477 (13.0%) patients without a clinic visit (P < 0.001). For both operating areas, APMC patients had a significantly earlier room entry time than patients not evaluated in the APMC. CONCLUSIONS: An evaluation in the APMC can significantly impact case cancellations and delays on the day of surgery.
Adult↗
Anesthesia and sleep.
Although both general anesthesia and naturally occurring sleep depress consciousness, distinct physiological differences exist between the two states. Recent lines of evidence have suggested that sleep and anesthesia may be more similar than previously realized. Localization studies of brain nuclei involved in sleep have indicated that such nuclei are important in anesthetic action. Additional observations that regional brain activity during anesthesia resembles that in the sleeping brain have raised the possibility that anesthesia may exert its effects by activating neuronal networks normally involved in sleep. In animals, behavioral interactions between sleep and anesthesia appear to support these mechanistic similarities. Rat studies demonstrate that sleep debt accrued during prolonged wakefulness dissipate during anesthesia. Moreover, anesthetic potency is subject both to circadian effects and to the degree of prior sleep deprivation. Such interactions may partly explain anesthetic variability among patients. Finally, sleep and anesthesia interact physiologically. Endogenous neuromodulators known to regulate sleep also alter anesthetic action, and anesthetics cause sleep with direct administration into brain nuclei known to regulate sleep. Together, these observations provide new research directions for understanding sleep regulation and generation, and suggest the possibility of new clinical therapies both for patients with sleep disturbances and for sleep deprived patients receiving anesthesia.
Anesthesia, General↗
Recovery from sleep deprivation occurs during propofol anesthesia.
BACKGROUND: Some neurophysiologic similarities between sleep and anesthesia suggest that an anesthetized state may reverse effects of sleep deprivation. The effect of anesthesia on sleep homeostasis, however, is unknown. To test the hypothesis that recovery from sleep deprivation occurs during anesthesia, the authors followed 24 h of sleep deprivation in the rat with a 6-h period of either ad libitum sleep or propofol anesthesia, and compared subsequent sleep characteristics. METHODS: With animal care committee approval, electroencephalographic/electromyographic electrodes and intrajugular cannulae were implanted in 32 rats. After a 7-day recovery and 24-h baseline electroencephalographic/electromyographic recording period, rats were sleep deprived for 24 h by the disk-over-water method. Rats then underwent 6 h of either propofol anesthesia (n = 16) or ad libitum sleep with intralipid administration (n = 16), followed by electroencephalographic/electromyographic monitoring for 72 h. RESULTS: In control rats, increases above baseline in non-rapid eye movement sleep, rapid eye movement sleep, and non-rapid eye movement delta power persisted for 12 h after 24 h of sleep deprivation. Recovery from sleep deprivation in anesthetized rats was similar in timing to that of controls. No delayed rebound effects were observed in either group for 72 h after deprivation. CONCLUSION: These data show that a recovery process similar to that occurring during naturally occurring sleep also takes place during anesthesia and suggest that sleep and anesthesia share common regulatory mechanisms. Such interactions between sleep and anesthesia may allow anesthesiologists to better understand a potentially important source of variability in anesthetic action and raise the possibility that anesthetics may facilitate sleep in environments where sleep deprivation is common.
Anesthesia Recovery Period↗
Baseline and post-deprivation recovery sleep in SCN-lesioned rats.
In humans, advancing age alters sleep patterns, reducing high voltage NREM sleep, sleep bout length, and delta power during NREM sleep. Although the mechanism by which these alterations occur is unknown, age-related changes in normal circadian processes may play a role. Increased age produces histological and functional changes in the suprachiasmatic nucleus (SCN), and alters the amplitude and phase of circadian rhythms. To examine the relationship between SCN function and age-related changes in sleep, we produced radiofrequency (RF) lesions of the SCN in rats of different ages and examined sleep behavior before and after sleep deprivation. Three-, 12- and 18-month-old rats received RF or sham lesions of the SCN. After verifying loss of circadian rhythm, 24-h EEG/EMG/temperature recordings were made in dim light before and after 24 h of sleep deprivation using the disk-over-water method. Age-related changes in NREM sleep, sleep bout length, and delta EEG power persisted despite SCN lesions. SCN lesions in all age groups increased baseline NREM sleep by 4% and NREM delta power by 15%, and decreased REM sleep by 10%. Although SCN lesions initially produced more REM and NREM sleep during recovery, 24-h values did not differ. Deteriorating SCN function is unlikely to cause the characteristic changes in sleep that occur with age. Our data also imply that an intact SCN slightly inhibits NREM sleep in the rat. Changes in NREM sleep and delta EEG power during recovery in lesioned rats suggest that the SCN may influence homeostatic regulation.
Age Factors↗
Risk index for postoperative pneumonia.
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Anesthesia↗
Use of the BIS monitor to detect onset of naturally occurring sleep.
OBJECTIVES: Inadvertent sleep episodes are a recognized complication of sleep deprivation. Although such events can be life threatening, no system currently exists to detect and prevent sleep onset. Because sleep shares electroencephalographic similarities with the anesthetized state, we hypothesized that the BIS monitor, a currently available EEG-based monitor of anesthetic depth, would detect the onset of physiologic sleep. To test our hypothesis, we monitored volunteers during the transition from waking to sleep. METHODS: Non-medicated volunteers were asked to lie down in a dark room for 30-minutes and fall asleep while attached to a BIS monitor located outside the room. A laptop computer was used to generate an audio tone inside the room. Speaker volume was adjusted to the lowest level detectable by the awake subject. Testing was begun by activating a computer to play a tone at random intervals. The subject was instructed to click a mouse connected to the computer upon hearing the tone to verify wakefulness. The session was terminated upon loss of response to three consecutive tones or after 30 minutes. Subjects were questioned afterwards regarding their perceptions of sleep during testing. RESULTS: 11 out of 28 self-described good sleepers could not sleep under testing conditions. BIS values for the remaining 17 fell from 96.4 +/- 2.1 to 86.5 +/- 0.79 (p < 0.01) upon sleep onset. All subjects responded to audio stimuli at BIS values >90, and were asleep either by subjective or objective report at BIS values <80. Three subjects retained the mouse-click response despite low BIS scores and subjective descriptions of sleep. CONCLUSION: Although variability in the BIS value marking sleep onset was noted, the BIS monitor detected all episodes of sleep onset in our testing regimen. We conclude that a threshold BIS value can be defined to allow the BIS monitor to detect sleep onset.
Adult↗
Modeling the effect of progressive endotracheal tube occlusion on tidal volume in pressure-control mode.
UNLABELLED: A recognized hazard of prolonged endotracheal intubation is progressive airway occlusion resulting from deposition of secretions on the inner surface of the endotracheal tube (ETT). When volume-controlled ventilation is used, progressive ETT occlusion may be detected by monitoring the difference between peak and plateau airway pressures. In pressure-controlled modes, however, inspiratory airway pressures are preset and thus cannot act as a warning indicator. Instead, changes in delivered tidal volumes may aid the diagnosis of ETT occlusion. To determine whether tidal volume monitoring effectively detects progressive ETT occlusion, we mathematically modeled the response of a ventilator operating in pressure-controlled mode to increasing airway resistance. To corroborate our model, we then bench-tested the Siemens 300 and Puritan-Bennett 7200 ventilators by using a test lung and a series of ETTs ranging in size from 9.0 to 3.5 mm inner diameter to simulate progressive occlusion. We found that when pressure-controlled mode was used, progressive ETT occlusion did not reduce delivered tidal volumes until occlusion was nearly complete. We conclude that prolonged use of pressure-controlled mode may allow significant ETT obstruction to build up undetected, risking complete ETT occlusion and complicating the perioperative care of patients ventilated with this mode. IMPLICATIONS: Although increasing airway pressures during volume-controlled ventilation allow early recognition of endotracheal tube (ETT) obstruction, airway pressures with pressure-controlled ventilation are fixed. We found during tests of two intensive care unit ventilators that although ETT obstruction reduces delivered tidal volumes during pressure-controlled ventilation, reductions do not occur until occlusion is advanced.
Algorithms↗
Cardiac arrest after labetalol and metoclopramide administration in a patient with scleroderma.
IMPLICATIONS: Although recent Food and Drug Administration warnings have noted proarrhythmic effects of droperidol, other antiemetic drugs may have similar effects. We report a case of cardiac arrest after uncomplicated regional anesthesia in a patient with scleroderma who received labetalol and metoclopramide after surgery. Metoclopramide should be used with caution when risk factors for dysrhythmia are present.
Adult↗
Sleep deprivation potentiates the onset and duration of loss of righting reflex induced by propofol and isoflurane.
BACKGROUND: Sleep and anesthesia differ physiologically but produce a similar loss of responsiveness to environmental stimuli. Recent data suggest that neuronal networks active in naturally occurring sleep also play a role in the anesthetized state. Changes in the propensity to sleep may then modify the response to anesthetic agents. The authors tested the hypothesis that sleep-deprived rats would require less anesthetic than rested rats to achieve a similar loss of responsiveness. METHODS: Rats were subjected to a 24-h period of either sleep deprivation or ad libitum activity. Sleep deprivation was produced by placing rats on a disk that rotated when sleep was detected by electroencephalographic and electromyographic (EEG, EMG) monitoring. A fixed dose of anesthetic agent was then administered, and the time required to induce loss of righting reflex was measured. Anesthetic administration was then stopped, and the time to recovery measured. All rats received both treatments separated by 7 days. RESULTS: Sleep deprivation reduced the time to loss of righting reflex by 40% for propofol (P < 0.025) and 55% for isoflurane (P < 0.025) and prolonged the time to recovery. In a separate control experiment, exposure to the deprivation environment but with disk rotation modified to allow adequate sleep did not affect the response to anesthetic administration. CONCLUSIONS: Sleep deprivation significantly potentiated the ability of inhaled and intravenous anesthetic agents to induce a loss of righting reflex. These results support the hypothesis that neuronal networks active in sleep are also involved in the anesthetized state and suggest that sleep deprivation may partly explain the variability in patient response to anesthesia.
Administration, Inhalation↗
Modification of a critical care ventilator for use during magnetic resonance imaging.
INTRODUCTION: The unique electromagnetic environment of the magnetic resonance imaging (MRI) scanner presents particular problems for critically ill patients requiring mechanical ventilation during MRI. Most currently available MRI-compatible ventilators are limited in scope and function and thus may not be suitable for patients requiring high peak inspiratory pressure or flow. METHODS: To determine whether a standard critical care ventilator could be used under MRI conditions, we modified a Siemens Servo 900C by replacing the standard oxygen blender with an MRI-compatible blender. We then calibrated the ventilator and tested it on a mechanical lung during active MRI scanning at magnetic fields up to 1.5 tesla. After verifying adequate function, we used the ventilator to support 21 critically ill patients requiring mechanical ventilation during MRI. RESULTS: In all cases we found no alterations in ventilator performance resulting from the electromagnetic interference typical of an MRI scan. We also found no abnormalities in the alarm systems for fraction of inspired oxygen, high inspiratory pressure, or minute volume. Finally, we found no degradation of MRI image quality resulting from ventilator operation during test scanning. CONCLUSIONS: We conclude that with minor modifications the Siemens 900C ventilator can safely ventilate critically ill patients during MRI.
Adolescent↗