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Clinical Considerations Concerning Detection of Venous Air Embolism. By Maurice S. Albin, Robert G. Carroll, Joseph C. Maroon. Neurosurgery 1978; 3:380-84. Abstract used with permission from the Congress of Neurological Surgeons, copyright 1978. Venous air embolism during neurosurgical procedures (detected by Doppler ultrasound and aspiration via a right atrial catheter) was noted in 100 of 400 patients in the sitting position, 5 of 60 patients in the lateral position, 7 of 48 patients in the supine position, and 1 of 10 patients in the monitored prone position. We confirmed venous air embolism in many of these patients by using serial technetium-microaggregated albumin lung scans. Gravitational gradients from the venous portal of entrance to the right side of the heart were as small as 5.0 cm, with aspiration of 200 ml of air occurring. Doppler ultrasonic air bubble detection and aspiration through a previously inserted right atrial catheter are critical factors in the diagnosis and treatment of this condition.

To determine the induction and maintenance characteristics of desflurane in pediatric patients, the authors anesthetized 206 infants and children aged 1 month to 12 yr with nitrous oxide plus desflurane and/or halothane in oxygen. Patients were assigned to one of four groups: anesthesia was 1) induced and maintained with desflurane after premedication with an oral combination of meperidine, diazepam, and atropine; 2) induced and maintained with desflurane; 3) induced with halothane and maintained with desflurane; or 4) induced and maintained with halothane. An unblinded observer recorded time to loss of consciousness (lid reflex), time to intubation, and clinical characteristics of the induction and maintenance of anesthesia. Moderate-to-severe laryngospasm (49%) and moderate-to-severe coughing (58%) occurred frequently during induction of anesthesia with desflurane; the incidence of these was not altered by premedication. In contrast, laryngospasm and coughing were rare during induction of anesthesia with halothane. In unpremedicated patients, time to loss of lid reflex (mean +/- SD) was similar for desflurane (2.4 +/- 1.2 min) and halothane (2.1 +/- 0.8 min). During induction of anesthesia, before laryngoscopy and intubation, mean arterial pressure less than 80% of baseline was more common with halothane; heart rate and mean arterial pressure greater than 120% of baseline were more common with desflurane. Intraoperatively, heart rate greater than 120% of baseline was more common with desflurane; blood pressures were similar for the two anesthetics. The authors conclude that the high incidence of airway complications during induction of anesthesia with desflurane limits its utility for inhalation induction in pediatric patients. Anesthesia can be safely maintained with desflurane if induced with a different anesthetic.

To determine whether anesthesiologists can manually detect significant changes in pulmonary compliance in neonates using an "educated hand," the authors tested whether clinicians could detect clamping of an endotracheal tube connecting a neonatal lung model to one of three anesthesia breathing circuits. The test lungs corresponded to the lung of a full-term neonate (large lung) or a premature neonate (small lung), and the circuits were a disposable Mapleson D and a disposable pediatric circle system with and without a humidifier. Clinicians having four levels of expertise (inexperienced anesthesia residents, experienced anesthesia residents, faculty not specializing in pediatric anesthesia, and specialized pediatric anesthesia faculty) were permitted to choose fresh gas flows, ventilatory pattern, and rate. After an acclimation period, the endotracheal tube connecting the test lung to the circuit was occluded once for 30 s. Clinicians were credited with a successful detection if they reported the occlusion within 15 s and had fewer than one false positive per minute. With the large lung model, only 4 of 24 clinicians detected occlusion with the Mapleson D circuit; similar results were obtained with the other circuits. With the small lung model, the only successful detection occurred with the Mapleson D circuit. Success at detecting occlusion was similarly low for clinicians with different levels of expertise. The authors conclude that the commonly held belief that the "educated hand" permits clinicians to detect subtle changes in pulmonary compliance in neonates during anesthesia (necessitating manual rather than mechanical ventilation) is not true.

Desflurane (formerly I-653) is a new inhalaticnal anesthetic with a promising pharmacokinetic profile that includes low solubility in blood and tissue, including fat. Since its lipid solubility is less than that of other volatile agents, it may have lower potency. Low solubility would be expected to increase the rate at which alveolar concentration approaches inspired concentration during induction as well as to increase the rate of elimination of desflurane from blood at emergence. We determined the minimum alveolar concentration (MAC) of desflurane in 44 unpremedicated ASA physical status 1 or 2 patients undergoing elective surgery. We prospectively studied four patient groups distinguished by age and anesthetic regimen: 18-30 versus 31-65 yr and desflurane in 60% N2O/40% O2 versus desflurane in O2. Anesthesia was induced with desflurane or desflurane in 60% N2O/40% O2. MAC was determined by a modification of Dixon's up-and-down method with increments of 0.5% desflurane. The MAC of desflurane in O2 was 7.25 +/- 0.0 (mean +/- SD) in the 18-30-yr age group, and 6.0 +/- 0.29 in the 31-65-yr group; the addition of 60% N2O reduced the MAC to 4.0 +/- 0.29 and 2.83 +/- 0.58, respectively. The median time from discontinuation of desflurane to an appropriate response to commands was 5.25 min. Desflurane appears to be a mild airway irritant but was well tolerated by all patients.

Desflurane, an inhaled anesthetic, may be useful for outpatient procedures in pediatric patients because its blood solubility (similar to that of nitrous oxide and less than that of commercially available potent inhaled anesthetics) may facilitate emergence and recovery from anesthesia. Although the MAC of desflurane without nitrous oxide has been determined in pediatric patients, it is likely that clinicians will administer desflurane with nitrous oxide. To determine the potency of desflurane administered with 60% nitrous oxide in pediatric patients, the authors determined the minimum alveolar concentration that prevents movement in 50% of subjects (MAC) in 12 infants aged 17 weeks-12 months and 12 children aged 1-5 yr. Anesthesia was induced with desflurane in oxygen; nitrous oxide was not administered during induction of anesthesia to minimize the likelihood of hypoxia if laryngospasm occurred. Following tracheal intubation, nitrous oxide and desflurane were administered and maintained at target concentrations for a minimum of 10 min before surgical incision. No additional anesthetic, sedative/hypnotic, or analgesic drugs were administered prior to incision. Following surgical incision, anesthesia was maintained with nitrous oxide, desflurane, and fentanyl, 4 +/- 1 micrograms/kg (mean +/- SD). MAC, determined using a modification of Dixon's "up-and-down" technique, was 7.5 +/- 0.1% (mean +/- SE) for infants and 6.4 +/- 0.2% for children; similar values were obtained using logistic regression (7.5 +/- 0.01% and 6.3 +/- 0.03%, respectively). Time from discontinuation of anesthesia to eye-opening and tracheal extubation was 5.4 +/- 3.6 min (mean +/- SD).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of acutely elevated serum magnesium on the CNS and cardiac toxicity of bupivacaine was studied. Anesthesia was induced in mongrel dogs with thiopental, 25 mg/kg, and ventilation was controlled. Sedation was maintained with fentanyl (25 micrograms/kg bolus and 5 micrograms.kg-1h-1) and pancuronium (0.15 mg/kg bolus and 0.05 mg.kg-1h-1) provided paralysis. Two hours after the thiopental bolus, all animals received an intravenous (iv) infusion of bupivacaine (1 mg.kg-1 min-1). The control group (5 animals) received bupivacaine only. The Mg++ group (5 animals) received MgSO4 140 mg/kg iv and 80 mg.kg-1 h-1 15 min prior to beginning the bupivacaine infusion. Lead II ECG, cardiac hemodynamics, and two-channel EEG were continuously monitored. Serum magnesium concentrations in the Mg++ group rose from 0.67 mM (1.3 mEq/L) to 2.42 mM (4.8 mEq/L). The bupivacaine infusion caused PR and QRS interval prolongation in both groups, but QRS widening was greater in the control group. QT interval corrected for heart rate (QTIc) lengthened only in the control group. A depression of left ventricular stroke work index (LVSWI) occurred to an equal extent in both groups. The seizure dose of bupivacaine was not different between the two groups: 12.9 +/- 2.3 (SEM) mg/kg in the control group and 13.9 +/- 2.5 mg/kg in the Mg++ group.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of high-frequency ventilation (HFV) on cerebral blood flow (CBF) at normal and elevated intracranial pressure (ICP) was compared with flows measured under the same conditions during intermittent positive pressure ventilation (IPPV). Renal, lung (bronchial artery supply), and cardiac blood flows also were measured during HFV and compared with flows observed during IPPV. Measurements were made in canines with stable hemodynamic variables and arterial CO2 and O2 tensions in the normal range, CBF during HFV was comparable to the CBF during IPPV. Following an increase in ICP to a mean of 44 +/- 18 mmHg (SD), mean CBF decreased to 22.5 +/- 11 ml . 100 g-1 . min-1 (SD) during IPPV and 21.7 +/- 13.2 ml . 100 g-1 . min-1 (SD) during HFV. No statistical differences could be noted in regional or global flow as a function of ventilatory mode. Renal, lung (bronchial artery supply), and cardiac blood flows also showed no statistical variation between HFV and IPPV. Ventilator-synchronous fluctuations in ICP observed during IPPV were reduced during HFV at normal ICP and eliminated by HFV at elevated ICP.

A flexible Silastic casting of the human right atrium was developed to correspond to some in vivo human right atrium hemodynamic characteristics including chamber pressures, pulsatility, fluid output, and flow velocity. Using an infusion pump, air was introduced (10 ml in 30 s) into the superior vena cava of the model and aspirated via a catheter from different positions within the model atrial chamber. The tests were carried out at atrial inclinations of 60 degrees, 80 degrees, and 90 degrees from the horizontal and compared the aspiration efficiency of a single-orificed 16-gauge catheter to a 16-gauge multiorified (5 aperatures) catheter. Optimal air aspiration occurred with the multiorificed catheter tip positioned within the area 2.0 cm below the junction of the superior vena cava (SVC) and the atrial chamber at an inclination of 80 degrees. As much as 80 per cent of the incoming air could be aspirated under these conditions. At its optimal position the single-orificed catheter gave a maximal yield of 45 to 50 per cent aspiration when the tip was positioned 3.0 cm above the SVC and atrial chamber junction. Aspiration of air from mid right atrium (4.5 cm below the SVC-atrial junction) was poor regardless of the type of catheter used or atrial inclination. These data suggest a need for reappraisal of catheter design and placement.

To evaluate the effect of lowered Paco2 on the size of subsequent cerebral infarction in the dog, the middle cerebral artery was occluded at its origin and the internal carotid artery occluded between the posterior communicating artery and the anterior cerebral artery. Following occlusion, Paco2 was