Effect of head posture on tracheal tube position in children.

Changes in the tracheal tube tip to carina distance were measured by radiographic screening following various head postures in 45 children undergoing cardiac catheterisation under general anaesthesia who were intubated via nasal and oral routes. Extension of the head moved the tracheal tube away from the carina and flexion moved it towards the carina in both routes. Endobronchial intubation was noted during neck flexion in a significant proportion of children intubated orally but none occurred during nasal intubation. Extension produced greater upward movement of the tracheal tube tip in the oral route than the nasal route. In contrast, flexion produced greater downward movement in the nasal route in some patients. The direction of movement with lateral rotation and use of a shoulder roll was inconsistent.

Use of implantable cardioverter defibrillator and anti-arrhythmic agents in a parturient.

We describe a case of a 36-yr-old patient who presented at 14 weeks gestation with multifocal dysrrhythmic episodes. Despite treatment with anti-arrythmic agents and an implantable cardioverter defibrillator (ICD) in situ, she continued to experience persistent dysrrhythmic episodes. She was delivered by Caesarean section at 34 weeks under general anaesthesia. We discuss some of the anaesthetic challenges of parturients with ICD devices.

Haemodynamic depression by halothane is age-related in paediatric patients.

The hypothesis that young infants are more sensitive to the haemodynamic depressant effects of halothane compared with older children was tested. One hundred and sixty unpremedicated, ASA physical status I or II paediatric patients without cardiac or pulmonary disease were divided into five age groups: term neonates, 1-6 months, 6-24 months, 2-6 years and 6-12 years. Anaesthetic induction was achieved with halothane in oxygen and air via mask. Vecuronium 0.1 mg.kg-1 was administered intravenously. During normocapnic manual ventilation by mask, endtidal halothane concentration was maintained at either 2xage-specific MAC (Method I) or 1.7% (Method II) in 20 patients in each age group for 10 min. In both Method I and Method II, systolic and mean blood pressure of term neonates and infants aged 1-6 months decreased significantly (P < 0.01) compared with other age groups. The results of this study demonstrate that neonates and young infants are more susceptible to haemodynamic depression during halothane anaesthesia than are older children, confirming clinical experience.

Flow dependence of valve area in aortic stenosis: relation to valve morphology.

OBJECTIVES: We sought to develop an index of flow dependence of valve area in aortic valve (AoV) stenosis and to determine whether this index is related to structural characteristics of the diseased valve. BACKGROUND: Many studies of AoV stenosis using Gorlin or continuity equation methods have demonstrated flow dependence (an increase in valve area with increased flow). Variation in flow dependence between patients despite similar flow rates remains unexplained. METHODS: Dobutamine Doppler echocardiography was used to calculate flow rate and valve area by the continuity equation in 27 patients with aortic stenosis. For each patient the slope of the regression line of valve area to flow rate was determined (slope of flow dependence). Transesophageal echocardiography was used to evaluate features of valve morphology potentially related to the etiology of AoV stenosis and the mechanism of flow dependence. RESULTS: Mean slope of flow dependence was 0.28 cm2/100 ml per s (range -0.06 to 0.53); flow dependence was significantly >0 in 21 patients and was lower for bicuspid valves (slope 0.21 cm2/100 ml per s) than for tricuspid valves with <10% commissural fusion (slope 0.35, p < 0.01). Off-center/ovoid orifices demonstrated the least flow dependence (slope 0.19), whereas star-shaped orifices showed the most (slope 0.36, p < 0.01). Greater flow dependence was related to a lower percentage of commissural fusion (r = -0.46, p = 0.02) as well as diffuse sclerosis, primarily involving the cusp bodies, rather than localized sclerosis, with involvement of cusp margins. CONCLUSIONS: The slope of flow dependence of valve area in AoV stenosis differs markedly between patients. More flow dependence was associated with tricuspid valves and the morphologic features characteristic of calcific AoV stenosis, whereas less flow dependence was associated with bicuspid valves and the features of rheumatic disease.

Physiologic consequences of training.

Systematic exercise training results in changes in skeletal muscle that increase oxidative capacity and vascular conductance, which lead to an increase in maximal A-VO2. Also, maximal cardiac output is increased, largely because of an increase in maximal stroke volume. Heart rate is decreased at rest and during submaximal exercise because of increased parasympathetic tone and the effect of increased stroke volume on reflex sympathetic tone. The increases in maximal A-VO2 and cardiac output result in increased maximal VO2, the hallmark of the dynamically trained individual. Predominant static exercise training results in fewer increases in maximal VO2 and more local muscle strength enhancements. The systematic application of cross-training can increase both cardiovascular and strength parameters, leading to enhanced athletic performance.

Cerebral oxygenation measured by near-infrared spectroscopy: comparison with jugular bulb oximetry.

BACKGROUND: Near-infrared spectroscopy is a potential tool for measuring adequacy of cerebral oxygenation during cardiac operations. The cerebral microcirculation is predominantly venous (by volume) and therefore regional cerebral oxygenation measured by near-infrared spectroscopy should reflect jugular bulb venous saturations. METHODS: We compared simultaneous regional cerebral oxygenation and jugular bulb venous saturation measurements in 40 children (median age, 4.5 years; range 2 weeks to 14.5 years) in the cardiac catheter laboratory (n = 29) and during cardiac operations (n = 11). RESULTS: For all patients combined the correlation between regional cerebral oxygenation and jugular bulb venous saturation was 0.69 (p < 0.0001) and was similar for the two groups. For individual children undergoing cardiac operations excellent correlations were obtained (r = 0.78 to 0.96; median, 0.91). However, at low values of jugular bulb venous saturation, regional cerebral oxygenation tended to run high, whereas the converse was true for high values of jugular bulb venous saturation. CONCLUSIONS: These findings suggest that near-infrared spectroscopy may be a useful tool for assessing intravascular cerebral oxygenation during pediatric cardiac operations. Prospective studies of neurologic outcome will be required to establish the value of this technique for assessing the adequacy of cerebral protection.

Metabolism and cardiovascular effects of leukotrienes in the marine toad Bufo marinus.

Leukotriene (LT) metabolism and physiology have been studied extensively in mammals; however, little is known of their roles in nonmammalian vertebrates. This study examines the cardiovascular effects of leukotrienes on blood pressure and heart rate in the conscious and cannulated marine toad, Bufo marinus. The sulfidopeptide leukotrienes, LTC4, LTD4, and LTE4 elicited hypotension with equal potency. However, with respect to heart rate changes and duration of action, the responses to LTC4 and LTD4 were greater and lasted longer than those to LTE4. The nonpeptide leukotriene, LTB4, had significantly less potent effects on heart rate and blood pressure. The leukotriene-induced increases in heart rate with 1000 and 300 ng/kg body wt LTC4 and LTD4 were blocked with 5 mg/kg body wt propranolol, a beta-antagonist, suggesting sympathetic reflex regulation of heart rate. Metabolism of [3H]LTC4 to [3H]LTD4 and [3H]LTE4 occurred rapidly in blood, with complete conversion to [3H]LTE4 within 5 min. Conversion was slower in plasma, with 18.9 +/- 0.5% of the radioactivity associated with [3H]LTC4 still remaining after 120 min. The toad is more similar to mammals than the bullfrog with respect to the metabolism of leukotrienes. In contrast to mammals, leukotrienes have hypotensive effects in both toad and bullfrog, although the order of potency differs. The effectiveness of the sulfidopeptide leukotrienes in eliciting hypotension at low doses (1 ng/kg body wt) suggests that these compounds may be important cardiovascular regulators in the toad.

Anaesthetic management of renin secreting nephroblastoma.

We report the successful preoperative control and anaesthetic management of severe hypertension in a 7-month-old baby with nephroblastoma and increased renin activity. The strategy for selection of appropriate antihypertensive pharmacological agents and the anaesthetic implications and management of the condition are discussed.

Characterization of leukotriene C4 binding sites in the brain of the American bullfrog, Rana catesbeiana.

In this study, specific binding sites for [3H]-LTC4 on membrane preparations from American bullfrog (Rana catesbeiana) brain were characterized. Binding assays were done in the presence of serine (5mM) borate (10 mM) for 30 min at 23 degrees C. Under these conditions, no metabolism of LTC4 to LTD4 occurred. Specific binding of [3H]-LTC4 reached steady state within 10 min, remained constant for 60 min, and was reversible with the addition of 1,000-fold excess unlabelled LTC4. Scatchard analysis of the binding data indicated a single class of binding sites with an estimated Kd of 89.83 nM and Bmax of 43.79 pmol/mg protein. Competition binding studies demonstrated that LTD4 and LTE4 were ineffective in displacing [3H]-LTC4 from its binding site. The Ki for LTC4 was 51 nM. S-decylglutathione, glutathione and hematin had Ki values of 44, 312,602, and 25,576 nM, respectively. The mammalian cysteinyl leukotriene antagonist L-660,711 inhibited specific binding of [3H]-LTC4, with a Ki of 87,149 nM. Guanosine-5'-0-3-thiotriphosphate (GTP gamma S) did not affect specific binding of [3H]-LTC4 indicating that, like mammalian LTC4 receptors, a Gi protein is not involved in the transduction mechanism. The LTC4 binding site in bullfrog brain demonstrates both similarities and differences from its mammalian counterpart.

The effect of micropore filters on the aspiration test in epidural analgesia.

Continuous epidural analgesia may be complicated by intravascular or subarachnoid injection of local analgesic, with disastrous consequences. One of the techniques described to prevent these complications is the aspiration test. It is the current standard of practice to employ a micropore bacterial filter for epidural infusions. We present an in vitro study of nine commercially available bacterial filters to determine whether or not the aspiration test could be reliably performed through them. Eight of the nine filters (except the Perifix, Braun) were found to be unreliable if air and liquid were both present in the system (air lock). The role of the aspiration test and the use of micropore filters in epidural analgesia are discussed, as are the implications and possible solutions in practice of this cause of failure of the test.

Metabolism and cardiovascular effects of leukotrienes in warm- and cold-acclimated American bullfrogs (Rana catesbeiana).

Sulfidopeptide leukotrienes are important mediators in mammals, but much less is known of their metabolism and action in nonmammalian vertebrates. This study examines the cardiovascular effects of leukotrienes on blood pressure and heart rate and compares the metabolism of leukotrienes in vivo and in vitro in warm- and cold-acclimated bullfrogs. Leukotriene C4 (LTC4) is more potent than leukotriene D4 (LTD4) and leukotriene E4 (LTE4) in eliciting hypotension. The leukotrienes are more potent in warm-acclimated animals. Conversion of [3H]LTC4 to [3H]LTD4 occurs rapidly in warm-acclimated bullfrogs, with 15.2 +/- 1.7% of the [3H]LTC4 remaining at 1.5 min. Conversion is slower in vivo in cold-acclimated frogs, with 20.2 +/- 1.7% of the [3H]LTC4 remaining by 6 min. In blood taken from warm-acclimated frogs, conversion of [3H]LTC4 to [3H]LTD4 occurs more rapidly at 22 than at 5 degrees C. This pattern is similar in blood taken from cold-acclimated frogs, suggesting that no modification of gamma-glutamyl transpeptidase occurs at low temperature. [3H]LTE4 production is not observed in vivo or in vitro during the time course of the experiments. The rapid metabolism of LTC4 to LTD4 may represent an inactivation mechanism in amphibians. The cardiovascular effects of LTC4 in vivo may be much greater than current measurements indicate because of rapid conversion of LTC4 to the less potent LTD4.