Will competency assessment improve the training and skills of the trainee anaesthetist?
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Anesthesiology↗
Biomedical subjects
B S Patel
Publications and source records attributed to B S Patel.
The photic sneeze reflex as a risk factor to combat pilots.
The tendency to sneeze upon exposure to bright light is autosomal dominant and affects 18-35% of the population. This uncontrolled sneezing may represent a danger to pilots during flight. Testing was conducted using Ditric narrow band (+/- 10 nm) interference filters. Wavelengths at 430, 532, and 560 nm were tested with a GE 500-W photoflood BCA #1 bulb at constant intensity. Subsequent testing of military and civilian aviation goggles and sunglasses was conducted using a Digikrom 240 monochromator. Repeated testing with interference filters in a clinical setting showed no effect on sneezing in a susceptible subject. The photic sneeze reflex does not appear to be mediated by specific wavelengths of light, but rather by the change in light intensity. This could trigger an unexpected sneezing episode during critical periods of flight. This is an unrecognized and previously unreported danger to fixed-wing and rotary aircraft pilots.
Aerospace Medicine↗
An accurate, nontraumatic ultrasonic method to monitor myocardial wall thickening in patients undergoing cardiac surgery.
Measurement of systolic wall thickening by sonomicrometry provides an accurate index of regional left ventricular function, but the trauma of crystal insertion limits its widespread clinical use. The first clinical application of a 10 MHz ultrasonic Doppler probe that can be either sutured or applied by suction to the epicardium and can measure wall thickening at any depth of the left ventricular wall is described. In 18 dogs, measurements obtained with the suction probe correlated well (r = 0.97) with those of a previously validated sutured probe. To assess clinical feasibility, the probe was applied to the epicardium of patients undergoing coronary bypass surgery. Good quality wall thickening signals were obtained with no complications. Transmural left ventricular thickening fraction before bypass surgery was 34 +/- 3% (mean value +/- SE) at the mid-ventricular lateral wall, 33 +/- 4% at the anterior basal wall and 26 +/- 4% at the mid-ventricular posterior wall. Right ventricular thickening fraction averaged 25 +/- 3%. Endocardial thickening fraction tended to exceed epicardial thickening fraction, although the difference attained statistical significance (p less than 0.05) only at the anterior basal wall. On average, thickening fraction during the immediate postoperative period remained unchanged compared with the preoperative values, but a marked individual variability was observed, with 7 of 15 patients exhibiting a decrease and 8 an increase. Exteriorization of the wires attached to the sutured probe allowed continuous in situ monitoring of wall thickening in the postoperative period and subsequent removal of the probe. In six patients the crystal was left in place for 48 to 72 h after surgery and then removed without complications; good wall thickening signals were obtained for the entire period during which the probe was implanted. Thus, the Doppler probe is an accurate, atraumatic method for measuring right and left ventricular regional function. Transmural, endocardial and epicardial function can be mapped at various sites during surgery, and post-operatively one can monitor serial changes of regional function and assess the effects of cardioplegia and other therapeutic interventions. This technique should be useful for both investigative and clinical purposes.
Adult↗
Effect of human recombinant superoxide dismutase on canine myocardial infarction.
To determine whether human recombinant superoxide dismutase (h-SOD) produces sustained reduction of infarct size, anesthetized dogs underwent a 2-h coronary occlusion followed by either 48 or 4 h of reperfusion. In the 48-h study, dogs were randomized to three intravenous treatments: 1) "low-dose" h-SOD (2 mg/kg bolus 2 min before reperfusion followed by 4 mg/kg over 45 min), 2) "high-dose" h-SOD (8 mg/kg bolus 2 min before reperfusion followed by 8 mg/kg over 45 min), or 3) equivalent volumes of saline. In the 4-h study, dogs were randomized to high-dose h-SOD or saline. Occluded bed size was measured by postmortem perfusion and infarct size by triphenyl tetrazolium chloride staining and planimetry. Investigators performing the study and measuring infarct size were blinded to the treatment given. High plasma concentrations of h-SOD were present in the arterial blood of treated dogs in the early phase of reperfusion (greater than 60 and greater than 180 micrograms/ml in low- and high-dose groups, respectively). In both studies, control and treated groups were similar with respect to occluded bed size, collateral blood flow, and rate-pressure product during ischemia. In the 48-h study, infarct size, expressed as percent of occluded bed size, was 41.3 +/- 7.6% (mean +/- SE) in the control group, 37.1 +/- 7.2% in the low-dose h-SOD group, and 48.0 +/- 7.1% in the high-dose h-SOD group. In the 4-h study, infarct size was 30.6 +/- 4.9% in the control group and 31.5 +/- 9.6% in the high-dose h-SOD group. Analysis of the flow-infarct relationships confirmed that h-SOD did not reduce infarct size at any level of collateral flow in either the 48- or 4-h study. Recovery of regional myocardial function after reperfusion was also unaffected by h-SOD in both studies. Thus in this randomized blinded study, large doses of h-SOD given at the time of reperfusion failed to limit infarct size or enhance recovery of function, both early (4 h) and late (48 h) after reperfusion following a 2-h coronary occlusion.
Animals↗
Effect of superoxide dismutase and catalase, given separately, on myocardial "stunning".
Controversy persists regarding which oxygen metabolites are cytotoxic. Although the combination of superoxide dismutase (SOD) and catalase has been shown to attenuate postischemic myocardial dysfunction ("stunning"), it is unknown whether this beneficial effect is due to scavenging of O2-., H2O2, or both. Accordingly, 85 open-chest dogs underwent a 15-min occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. In phase A, dogs received an intravenous infusion of saline (group I), SOD (5 mg/kg, group II), catalase (12,000 U/kg, group III), or the combination of SOD and catalase (same doses, group IV). Recovery of regional myocardial function (assessed as systolic wall thickening) after reperfusion was significantly improved by the combination of SOD and catalase but not by SOD alone or catalase alone. To determine whether higher doses of enzymes are more effective, in phase B dogs received an intracoronary infusion of normal saline (group V), SOD in low dose (1.5 mg/kg, group VI), SOD in high dose (6.3 mg/kg plus 1.5 mg/kg iv, group VII), catalase in low dose (18,000 U/kg, group VIII), or catalase in high dose (240,000 U/kg plus 40,000 U/kg iv, group IX). Despite the fact that the local plasma levels of enzymes were considerably higher than those achieved in phase A, none of the treatments in phase B significantly enhanced recovery of contractile function. This study demonstrates that the combination of SOD and catalase is more effective than either enzyme alone in attenuating postischemic myocardial dysfunction and that increasing the doses of SOD or catalase does not provide additional protection. The results suggest that both O2-. and H2O2 contribute significantly to the pathogenesis of myocardial stunning after regional ischemia in the intact animal. Furthermore, the data imply that if SOD and catalase are to be used clinically to prevent postischemic dysfunction, protection may be achieved most effectively by combining the two enzymes.
Animals↗
Iron-mediated radical reactions upon reperfusion contribute to myocardial "stunning".
Recent evidence suggests that postischemic myocardial dysfunction ("stunning") is mediated by iron-catalyzed free radical reactions, but the exact time window during which the critical iron-mediated damage develops remains unknown. Furthermore, the evidence that iron promotes free radical reactions in vivo is indirect. Thus open-chest dogs undergoing a 15-min coronary occlusion and 4 h of reperfusion were given one of the following intracoronary infusions: desferrioxamine (DF) beginning 2 min before reperfusion (group I), DF beginning 1 min after reperfusion (group II), iron-loaded DF in dosage identical to group I (group III), or vehicle (controls, group IV). Recovery of contractile function was substantially greater in group I than in controls, whereas in groups II and III it was indistinguishable from controls. To determine whether the protection afforded by DF was due to inhibition of free radical reactions, myocardial production of free radicals was directly assessed by intracoronary infusion of the spin trap alpha-phenyl N-tert-butyl nitrone (PBN). In controls (group VI), radical adducts of PBN were released in the coronary venous blood after reperfusion. DF given as in group I (group V) markedly suppressed myocardial production of PBN adducts. These results strongly suggest that a substantial portion of the damage responsible for myocardial stunning is caused by iron-catalyzed free radical reactions that develop in the initial seconds of reperfusion and can be prevented by administration of iron chelators started just before reflow. Furthermore, the results demonstrate that attenuation of postischemic dysfunction by DF is associated with attenuation of free radical reactions in vivo, thereby providing direct evidence for a pathogenetic role of iron-catalyzed free radical reactions in myocardial stunning in the intact animal.
Animals↗
Direct evidence that oxygen-derived free radicals contribute to postischemic myocardial dysfunction in the intact dog.
Electron paramagnetic resonance (EPR) spectroscopy was used to investigate whether (i) the free radicals produced in the "stunned" myocardium (myocardium with postischemic contractile dysfunction) are derived from O2, (ii) inhibition of radical reactions improves function, and (iii) i.v. spin traps are effective. Open-chest dogs undergoing a 15-min coronary occlusion received an i.v. infusion of the spin trap, alpha-phenyl N-tert-butylnitrone (PBN) (50 mg/kg). In group I (n = 6), EPR signals characteristic of radical adducts of PBN appeared in the coronary venous blood during ischemia and increased dramatically after reperfusion. In group II (n = 6), which received PBN and i.v. superoxide dismutase (SOD; 16,000 units/kg) plus catalase (12,000 units/kg), myocardial production of PBN adducts was undetectable during ischemia (delta = -100%, P less than 0.01 vs. group I) and markedly inhibited after reperfusion (delta = -86%, P less than 0.001). This effect was seen at all levels of ischemic zone flow but was relatively greater in the low-flow range. In group III (n = 8), the same dosages of SOD and catalase without PBN markedly enhanced contractile recovery (measured as systolic wall thickening) after reperfusion [P less than 0.01 at 3 hr vs. controls (group IV, n = 7)]. Systemic plasma activity of SOD and catalase averaged 127 +/- 24 and 123 +/- 82 units/ml, respectively, 2 min after reperfusion. PBN produced no apparent adverse effects and actually improved postischemic contractile recovery in group I (P less than 0.05 at 3 hr vs. controls). This study shows that (i) SOD and catalase are highly effective in blocking free radical reactions in vivo, (ii) the radicals generated in the "stunned" myocardium are derived from univalent reduction of O2, and (iii) inhibition of radical reactions improves functional recovery. The results provide direct, in vivo evidence to support the hypothesis that reactive oxygen metabolites play a causal role in the myocardial "stunning" seen after brief ischemia.
Animals↗
Nonuniform transmural recovery of contractile function in stunned myocardium.
With the use of an epicardial Doppler probe, systolic wall thickening was selectively measured in the inner, mid, and outer layers of the left ventricular (LV) wall in 16 conscious dogs undergoing a 15-min left anterior descending artery (LAD) occlusion followed by 7 days of reperfusion (REP). Under control conditions, percent thickening fraction (ThF) was significantly greater (P less than 0.01) in the inner layer [36.0 +/- 2.3% (mean +/- SE)] than in the mid (28.6 +/- 2.1%) or outer (21.3 +/- 2.2%) layers. During LAD occlusion, 11 dogs exhibited transmural dyskinesis (group 1), whereas 5 had transmural hypokinesis (group 2). In group 1, all layers exhibited comparable degrees of paradoxical systolic thinning during LAD occlusion. After REP, however, recovery was delayed in the inner compared with the mid and outer layers. At 2 h, ThF averaged 34.2 +/- 11.9% of base line in the endocardium vs. 61.7 +/- 16.2% in the midmyocardium and 51.0 +/- 12.3% in the epicardium (F = 4.29, P less than 0.002); similar differences were noted at 3 and 4 h. In the mid and outer layers, ThF returned to base-line values by 24 h, whereas in the inner layer it was still significantly depressed (P less than 0.05) at 24 h (77.3 +/- 5.1% of base line) and recovered by 48 h. The inner-to-outer ThF ratio was decreased (P less than 0.01) for 24 h after REP, indicating maldistribution of thickening in the "stunned" myocardium. In group 2, all layers exhibited hypokinesis during LAD occlusion. Again, recovery of function after REP was delayed in the endocardium compared with the other layers. This study demonstrates that after both severe ischemia resulting in dyskinesis and mild ischemia resulting in hypokinesis, REP is associated with slower recovery of function in the inner than in the outer layers. Thus myocardial "stunning" is a nonuniform phenomenon with maximal severity in the subendocardium.
Animals↗
Marked reduction of free radical generation and contractile dysfunction by antioxidant therapy begun at the time of reperfusion. Evidence that myocardial "stunning" is a manifestation of reperfusion injury.
Recent evidence suggests that postischemic myocardial dysfunction ("stunning") may be mediated by oxygen free radicals, but the exact time window during which the critical radical-mediated damage develops remains unknown. Furthermore, the evidence for the oxyradical hypothesis is indirect and, therefore, inconclusive. Thus, the potent and cell-permeable antioxidant N-(2-mercaptopropionyl)-glycine (MPG) was administered as an intra-coronary infusion (8 mg/kg/hr) to three groups of open-chest dogs undergoing a 15-minute coronary occlusion followed by 4 hours of reperfusion. In group I (n = 8), the infusion of MPG was started 15 minutes before occlusion and ended 2 hours after reperfusion; in group II (n = 9), MPG was started 1 minute before reperfusion and ended 2 hours thereafter; in group III (n = 10), MPG was started 1 minute after reperfusion and ended 2 hours and 15 minutes thereafter. Control dogs (group IV) (n = 10) received vehicle. Recovery of contractile function (assessed as systolic wall thickening) was equivalent in groups I and II, and in both groups it was substantially greater than in controls (p less than 0.005 at 4 hours). In contrast, in group III recovery of function was indistinguishable from controls. To determine whether the protection afforded by MPG was due to inhibition of free radical reactions, myocardial production of free radicals was directly assessed by intracoronary infusion of the spin trap alpha-phenyl N-tert-butyl nitrone (PBN). In control dogs (group VII, n = 6), radical adducts of PBN were released in the coronary venous blood after reperfusion, with a burst occurring in the first 5 minutes. MPG given as in group II (group V, n = 5) markedly suppressed myocardial production of PBN adducts (delta = -98% over 3 hours, p less than 0.01 vs. controls); this effect was evident immediately after reperfusion. MPG given as in group III (group VI, n = 5) also suppressed PBN adduct production (delta = -83% over 3 hours, p less than 0.025 vs. controls), but this effect was delayed. Hence, the radicals important in myocardial stunning appear to be those generated immediately after reperfusion. In vitro studies demonstrated that MPG is an exceptionally powerful scavenger of .OH (rate constant = 8.1 x 10(9) M-1 sec-1 by pulse radiolysis) but has no significant effect on .O2- (rate constant less than 10(3) M-1 sec-1), H2O2 (rate constant = 1.6 M-1 sec-1), or non-.OH-initiated lipid peroxidation, suggesting that removal of .OH is the major mechanism of the beneficial effects of MPG.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Demonstration of free radical generation in "stunned" myocardium of intact dogs with the use of the spin trap alpha-phenyl N-tert-butyl nitrone.
Recent studies suggest that oxygen free radicals may mediate postischemic myocardial dysfunction ("stunning"), but all the evidence for this hypothesis is indirect. Thus, we used electron paramagnetic resonance (EPR) spectroscopy and the spin trap, alpha-phenyl N-tert-butyl nitrone (PBN), to directly investigate whether free radicals are produced after a 15-min coronary artery occlusion and subsequent reperfusion in 30 open-chest dogs. After intracoronary infusion of PBN, EPR signals characteristic of oxygen- and carbon-centered radical adducts were detected in the venous blood draining from the ischemic/reperfused vascular bed. The myocardial release of PBN adducts began during coronary occlusion but increased dramatically in the first few minutes after reperfusion. After this initial burst, the production of radicals abated but did not cease, persisting up to 3 h after reflow. The EPR spectra (aH beta = 2.67-2.79 G, aN = 14.75-15.00 G) were consistent with the trapping by PBN of secondary oxygen- and carbon-centered radicals, such as alkoxy and alkyl radicals, which could be formed by reactions of primary oxygen radicals with membrane lipids. There was a linear, direct relationship between the magnitude of PBN adduct production and the degree of ischemic flow reduction. Recovery of contractile function (measured as systolic wall thickening) after reperfusion was greater (P less than 0.05) in dogs given PBN than in controls. This study demonstrates that reversible regional myocardial ischemia in the intact animal is associated with prolonged free radical generation, and that the intensity of such generation is related to the severity of ischemia. The results provide direct evidence to support the hypothesis that reactive oxygen metabolites contribute to the persistent contractile dysfunction (myocardial stunning) observed after brief ischemia in vivo.
Animals↗
Visual acuity loss in patients with Stargardt's macular dystrophy.
Ninety-five patients with Stargardt's macular dystrophy were appraised for visual loss with age by both life-table analyses and cross-sectional procedures. The probability of maintaining a visual acuity of 20/40 or better in at least one eye was 52% by age 19, 32% by age 29, and 22% by age 39. In the population studied, once a patient's visual acuity dropped below 20/40, it tended to decrease rapidly and stabilize at 20/200. Fluorescein angiograms obtained on 64 of the 95 patients showed a "dark choroid" in 55 (85.9%). This finding, therefore was present in the majority of the patients, although its absence does not rule out Stargardt's macular dystrophy.
Actuarial Analysis↗
The iron chelator desferrioxamine attenuates postischemic ventricular dysfunction.
Recent evidence suggests that postischemic myocardial dysfunction ("stunning") may be mediated by oxygen free radicals, but the mechanism by which they produce myocellular damage remains unknown. Since iron catalyzes formation of hydroxyl radicals (HO.) as well as HO.-initiated lipid peroxidation, we explored the potential role of this metal in the pathogenesis of myocardial stunning. Open-chest dogs undergoing a 15-min occlusion of the left anterior descending coronary artery (LAD) followed by 4 h of reperfusion (REP) received the iron chelator desferrioxamine intravenously (10 mg/kg over 45 min beginning 30 min before occlusion, then 1.7 mg.kg-1.h-1 throughout REP, n = 19) or normal saline (n = 17). Regional myocardial function was assessed by measuring systolic wall thickening with an epicardial Doppler probe. The two groups exhibited comparable systolic thickening under base-line conditions and similar degrees of dyskinesis during ischemia. After REP, however, recovery of contractile function (expressed as percent systolic thickening) as considerably greater in desferrioxamine-treated compared with control dogs: 5 +/- 3 (mean +/- SE) vs. -3 +/- 2% (P less than 0.05) at 1 h, 6 +/- 3 vs. -2 +/- 3% (P less than 0.05) at 2 h, 5 +/- 3 vs. -6 +/- 2% (P less than 0.005) at 3 h, and 6 +/- 3 vs. -6 +/- 2% (P less than 0.002) at 4 h. These differences could not be ascribed to hemodynamic factors. The results suggest that iron-catalyzed reactions (possibly HO. generation) play a significant role in myocardial stunning after a brief episode of reversible regional ischemia.
Animals↗
Induced moderate hypotensive anesthesia for spinal fusion and Harrington-rod instrumentation.
The effect of moderate hypotensive anesthesia on blood loss, need for transfusion, and length of surgery of forty-nine patients who underwent posterior spinal fusion and Harrington-rod instrumentation was compared retrospectively. Twenty-seven patients were given enflurane as the main anesthetic agent, with fentanyl supplementation, and their blood pressure was maintained at twenty to thirty millimeters of mercury less than the preoperative systolic blood pressure. These patients were compared with twenty-two patients who had been anesthetized with nitrous oxide, oxygen, and narcotic technique and were normotensive throughout the duration of the anesthesia. The results were analyzed by the unpaired Student t test. Moderate hypotensive anesthesia was found to significantly decrease the average blood loss by nearly 40 per cent, reduce the need for transfusion by nearly 45 per cent, and shorten the average operating time by nearly 10 per cent. No complications attributable to the anesthetic technique occurred. The findings of this study suggest that moderate hypotensive anesthesia with enflurane and fentanyl supplementation may be of benefit in scoliosis surgery by reducing blood loss, the need for blood replacement, and operating time.
Adolescent↗
Fluoresceine angiography in myopic degeneration.
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Atrophy↗
Transient bacteremia associated with debridement of decubitus ulcers.
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Adult↗