Anesthesia and analgesia
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Anesthesia and analgesia · Jul 2012
Using time-frequency analysis of the photoplethysmographic waveform to detect the withdrawal of 900 mL of blood.
We designed this study to determine if 900 mL of blood withdrawal during spontaneous breathing in healthy volunteers could be detected by examining the time-varying spectral amplitude of the photoplethysmographic (PPG) waveform in the heart rate frequency band and/or in the breathing rate frequency band before significant changes occurred in heart rate or arterial blood pressure. We also identified the best PPG probe site for early detection of blood volume loss by testing ear, finger, and forehead sites. ⋯ A time-frequency spectral method detected blood loss in spontaneously breathing subjects before the onset of significant changes in heart rate or blood pressure. Spectral amplitudes at the heart rate frequency band were found to significantly decrease during blood loss in spontaneously breathing subjects, whereas those at the breathing rate frequency band did not significantly change. This technique may serve as a valuable tool in intraoperative and trauma settings to detect and monitor hemorrhage.
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Anesthesia and analgesia · Jul 2012
Comparative StudyAre ultrasound-guided ophthalmic blocks injurious to the eye? A comparative rabbit model study of two ultrasound devices evaluating intraorbital thermal and structural changes.
Since Atkinson's original description of retrobulbar block in 1936, needle-based anesthetic techniques have become integral to ophthalmic anesthesia. These techniques are unfortunately associated with rare, grave complications such as globe perforation. Ultrasound has gained widespread acceptance for peripheral nerve blockade, but its translation to ocular anesthesia has been hampered because sonic energy, in the guise of thermal or biomechanical insult, is potentially injurious to vulnerable eye tissue. The US Food and Drug Administration (FDA) has defined guidelines for safe use of ultrasound for ophthalmic examination, but most ultrasound devices used by anesthesiologists are not FDA-approved for ocular application because they generate excessive energy. Regulating agencies state that ultrasound examinations can be safely undertaken as long as tissue temperatures do not increase >1.5°C above physiological levels. ⋯ The nonorbital-rated ultrasound machine (Sonosite Micromaxx) increases the ocular tissue temperature. A larger study is needed to establish safety. Until then, ophthalmic ultrasound-guided blocks should only be performed with ocular-rated devices.
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Anesthesia and analgesia · Jul 2012
The effect of obesity on the ED(95) of propofol for loss of consciousness in children and adolescents.
Anesthesiologists face a dilemma in determining appropriate dosing of anesthetic drugs in obese children. In this study we determined the dose of propofol that caused loss of consciousness in 95% (ED(95)) of obese and nonobese children as determined by loss of eye lash reflex. ⋯ A simple approach to deciding what dose of propofol should be used for induction of anesthesia in children ages 3 to 17 years is to first establish the child's BMI on readily available gender-specific charts. Obese children (BMI >95th percentile for age and gender) require a lower weight-based dose of propofol for induction of anesthesia, than do normal-weight children.
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Anesthesia and analgesia · Jul 2012
The ability of anesthesia providers to visually estimate systolic pressure variability using the "eyeball" technique.
Systemic arterial respiratory variation has been shown to be a reliable predictor of changes in cardiac output after fluid administration. Arterial respiratory variation is often estimated from visual examination of the arterial waveform tracing. Our goal in this study was to assess the ability of anesthesia providers to visually estimate systolic pressure variation (SPV) as a percentage of systolic blood pressure (SPV). ⋯ Visual estimates of respiratory variation are within clinically reasonable limits 82% of the time and lead to erroneous management decisions in 4.4% of measurements.
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Anesthesia and analgesia · Jul 2012
Unintentional dural puncture with a Tuohy needle increases risk of chronic headache.
Neuraxial analgesia is chosen by almost half of women who give birth in the United States. Unintentional dural puncture is the most common complication of this pain management technique, occurring in 0.4% to 6% of parturients. Severe positional headaches develop acutely in 70% to 80% of these parturients. Acute postdural puncture headaches are well known, but few studies have investigated long-term sequelae. We investigated the incidence of and risk factors for chronic headache and chronic back pain in parturients who experienced unintentional dural puncture with a 17-gauge Tuohy needle compared with matched controls. ⋯ Patients who incur unintentional dural punctures with large-gauge needles are surprisingly likely to continue to suffer chronic headaches. Treatment with an epidural blood patch does not enhance the risk of chronic back pain. The pathophysiology underlying these symptoms and the best treatment for this syndrome are not known.