Anesthesia and analgesia
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Anesthesia and analgesia · Feb 1999
The effect of halothane on the amplitude and frequency characteristics of heart sounds in children.
Although continuous auscultation has been used during surgery as a monitor of cardiac function for many years, the effect of anesthetics on heart sounds has never been quantified. We determined the root mean squared amplitude and frequency characteristics (peak frequency, spectral edge, and power ratios) of the first (S1) and second (S2) heart sounds in 19 healthy children during induction of anesthesia with halothane. In all patients, halothane decreased the amplitude of S1 (R2 = 0.87 +/- 0.12) and S2 (R2 = 0.66 +/- 0.33) and the high-frequency components (>80 Hz) of these sounds. These changes were clearly audible and preceded decreases in heart rate and blood pressure. The spectral edge decreased for S1 in 18 patients (R2 = 0.73 +/- 0.24) and for S2 in 13 patients (R2 = 0.58 +/- 0.25). Peak frequency did not change. The rapidity with which myocardial depression and its associated changes in heart sound characteristics occurred confirms that continuous auscultation of heart sounds is a useful clinical tool for hemodynamic monitoring of anesthetized infants and children. ⋯ Heart sound characteristics can be used to monitor cardiac function during halothane anesthesia in children. The changes occur rapidly and precede noticeable changes in heart rate and blood pressure.
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Anesthesia and analgesia · Feb 1999
Predicting the size of a double-lumen endobronchial tube using computed tomographic scan measurements of the left main bronchus diameter.
We investigated the use of chest computer tomographic (CT) scan measurement of the left mainstem bronchial diameter to predict the correct left-sided double-lumen endobronchial tube (DLT) size in Asian patients who may require smaller DLT sizes. Fifty consecutive Asian adults aged 17-80 yr with preoperative chest CT scans undergoing elective thoracic surgery were entered into the study. The measurements of the left main bronchus diameter were made by using the electronic calipers of the spiral scanner to the nearest millimeter. The sizes of DLT selected were 32F, 35F, 37F, 39F, and 41F for left main bronchus diameters of <10 mm, 10 mm, 11 mm, 12 mm, and >12 mm, respectively. All DLT placements were confirmed and positioned by using fiberoptic bronchoscopy. The tracheas of all patients were successfully intubated with the predicted DLT sizes. Thirty-four patients (68%) were predicted to require smaller DLTs (37F or smaller). Six patients were correctly predicted to receive 32F DLTs. Twelve patients (24%) received an oversized DLT, but none received an undersized DLT. The overall positive predictive value for the male and female patients was 84.4% and 61.1%, respectively. Our study showed that CT scan measurements of the diameter of the left bronchus were especially useful in choosing smaller DLTs. ⋯ We used computer tomographic scans to measure the diameter of the left mainstem bronchus, then selected the size of the left-sided double-lumen endobronchial tube (DLT) accordingly. We found that we could predict the sizes of the DLT fairly accurately, especially the smaller DLTs.
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Anesthesia and analgesia · Feb 1999
Comparative StudyDynamic cerebral autoregulation during sevoflurane anesthesia: a comparison with isoflurane.
We investigated dynamic cerebral pressure autoregulation awake and during 1.5 minimum alveolar anesthetic concentration (MAC) sevoflurane or isoflurane anesthesia in 16 patients undergoing nonintracranial neurosurgical procedures. All patients received a standardized anesthetic, and their lungs were ventilated with 1.5 MAC volatile anesthetic in 100% oxygen to normocapnia. Routine monitors included electrocardiogram, pulse oximetry, end-tidal capnography, and continuous noninvasive blood pressure. In addition, middle cerebral artery blood velocity (Vmca) was measured continuously using transcranial Doppler ultrasonography. Dynamic cerebral autoregulation was tested by inducing a rapid transient decrease in mean arterial pressure by deflation of large thigh cuffs, which were placed around both thighs and inflated to 100 mm Hg above systolic pressure. The Vmca response to the decrease in blood pressure was fitted to a series of curves to determine the rate of dynamic cerebral autoregulation (dRoR). Awake dRoR values were similar in the isoflurane and sevoflurane groups, 32 +/- 2%/s and 29 +/- 2%/s, respectively. dRoR decreased to 5 +/- 1%/s during isoflurane anesthesia but to only 24 +/- 2%/s during sevoflurane anesthesia. We conclude that dynamic cerebral autoregulation is better preserved during sevoflurane than isoflurane anesthesia in humans. ⋯ We investigated the effect of sevoflurane and isoflurane on dynamic cerebral pressure autoregulation using transcranial Doppler ultrasonography. At 1.5 minimum alveolar anesthetic concentration, dynamic autoregulation was better preserved during sevoflurane than isoflurane anesthesia.
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Anesthesia and analgesia · Feb 1999
Comparative StudyPre- versus postinjury effects of intravenous GABAergic anesthetics on formalin-induced Fos immunoreactivity in the rat spinal cord.
We evaluated the suppression of spinal Fos-like immunoreactivity (FLI) by i.v. anesthetics in the rat formalin model. Preformalin injection (1.5% subcutaneously) treatment groups included i.v. saline controls and three i.v. GABAergic anesthetic groups (pentobarbital 20 mg/kg, propofol 10 mg/kg, or alphaxalone 1.5 mg/kg; n = 12 per group). After perfusion 2 h postformalin, spinal cords were dissected, sliced at 30 microm, and processed by immunoperoxidase staining with an antibody against the Fos protein. Quantification and determination of the laminar distribution of Fos-labeled nuclei were performed at the L4-5 spinal level ipsilateral to formalin injection. Drug groups demonstrating FLI suppression were comparatively studied in a 5-min postformalin treatment group. Pentobarbital pretreatment failed to suppress FLI. However, significant reductions (percent decrease) of FLI were observed with propofol (63%) and alphaxalone (30%) compared with saline controls. Pre- versus postformalin comparison studies showed that propofol, but not alphaxalone, suppressed FLI more effectively when given preformalin. Given the observed inconsistencies between this study of Fos expression and our previous behavioral study, it is questionable whether anesthetic modulation of noxious stimulus-induced FLI parallels that of behavioral responses. ⋯ In this study, we examined whether i.v. general anesthetics (propofol, alphaxalone, and pentobarbital) prevent injury-induced spinal cord changes. We measured spinal Fos protein after rats received anesthetics before versus after a formalin injection. Fos inhibition patterns were inconsistent with behavioral studies of these anesthetics, suggesting that Fos inhibition does not always correlate with behavioral analgesia.
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Anesthesia and analgesia · Feb 1999
Endobronchial intubation causes an immediate increase in peak inflation pressure in pediatric patients.
Our purpose was to determine whether endobronchial intubation always causes an immediate increase in peak inflation pressure and, if so, the magnitude of the increase. Fourteen children scheduled for central line placement for prolonged antibiotic administration comprised the study group. After routine premedication and induction of anesthesia (halothane in oxygen), an endotracheal tube was inserted, and its position was verified by auscultation and fluoroscopy. Children were mechanically ventilated using a preset volume pressure-limited ventilator with a 5-L fresh gas flow. All children received a constant tidal volume using a similar circuit, similar tubing, and a similar compression volume. The lowest peak inflation pressure to deliver a tidal volume of 15 mL/kg was used. After adjusting the respiratory rate (end-tidal CO2 30 mm Hg) and anesthetic level (halothane end-tidal 1.2%), the peak inflation pressure at this endotracheal position was recorded. The endotracheal tube was advanced into a bronchus, the position was verified as above, and peak inflation pressure was recorded. The endobronchial tube was then pulled back into the trachea, and placement of the central line proceeded. The peak inflation pressure at the endobronchial position was significantly greater than the peak inflation pressure at the endotracheal position (P < 0.0001). The increase was instantaneous at the endobronchial position. Monitoring peak inflation pressure while inserting an endotracheal tube and during anesthesia can help to diagnose endobronchial intubation. ⋯ Monitoring peak inflation pressure while inserting an endotracheal tube and during anesthesia can help to diagnose endobronchial intubation.