Oxygen free radicals in abdominal aortic surgery. An experimental study.

BACKGROUND: In aortic reconstruction, intestinal and muscular ischaemia in the lower limbs occurs during cross-clamping of the aorta. After restoration of blood flow, reactive oxygen intermediates may lead to systemic injury to local or remote organs. In this study we investigated the usefulness of a shunt and vitamin E administration against the oxidant load generated in ischaemia-reperfusion phases. METHODS: In three groups of pigs (n=16) aortic reconstruction was simulated. In Group A (n=5) clamping of the infrarenal aorta was performed for 2 hours. In Group B (n=6), during aortic cross-clamping, a shunt was used to give flow to the inferior mesenteric and internal iliac arteries. In Group C (n=5) vitamin E was administered before aortic cross-clamping. In all groups we evaluated sigmoid histology after reperfusion, while the oxidant load was estimated by measuring superoxide dismutase (SOD) activity in blood samples from portal and jugular vein. RESULTS: Histology of the sigmoid revealed increased postischaemic injuries in Group A, while the protective effect of shunt and vitamin E was apparent in Group B and C, respectively. SOD activity was minimized in Group C. CONCLUSIONS: Vitamin E protected the sigmoid from postischaemic injury and is responsible for the decreased levels of SOD activity.     

Recurrent seizure activity after epidural morphine in a post-partum woman

PURPOSE: We report on a primiparous woman who suffered recurrent seizure activity after repeated small doses of epidural morphine to highlight the neuroexcitation potential of neuraxial opioids in the epileptic patient. CLINICAL FEATURES: Seizure activities as a complication of opioid administration have been reported in laboratory animals and humans. We report the case of a 30-yr-old primiparous woman with a history of epilepsy under carbamazepine treatment, who had epidural anesthesia for elective Cesarean section at 38 weeks gestation. Postoperatively, 1.5 mg of morphine were administered epidurally for pain control. Three hours later the patient suffered from clonic movements of the right arm without loss of consciousness. One day later, she again received 1 mg of epidural morphine twice at a 12-hr interval and similar seizure episodes recurred eight hours after each dose. A relation between the administration of morphine and seizure activity was suspected and the use of opioids for pain control was stopped. The patient was discharged on the fifth postoperative day and, more than one year after the last episode, she remains free of any seizure activity. CONCLUSION: Our report indicates that even a remote history of epilepsy carries a pro-convulsant potential in the peripartum period, even following the administration of small doses of epidural morphine.     

Automated Responsiveness Test (ART) Predicts Loss of Consciousness and Adverse Physiologic Responses during Propofol Conscious Sedation

Background: The authors evaluated a device designed to provide conscious sedation with propofol (propofol-air), or propofol combined with 50% nitrous oxide (N2O; propofol-N2O). An element of this device is the automated responsiveness test (ART), a method for confirming that patients remain conscious. The authors tested the hypotheses that the ART predicts loss of consciousness and that failure to respond to the ART precedes sedation-induced respiratory or hemodynamic toxicity.

Methods: The protocol consisted of sequential 15-min cycles in 20 volunteers. After a 15-min control period, propofol was infused to an initial target effect-site concentration of 0.0 [mu]g/ml with N2O or 1.5 [mu]g/ml with air. Subsequently, the propofol target effect-site concentration was increased by a designated increment (0.25 and 0.5 [mu]g/ml) and the process repeated. This sequence was continued until loss of consciousness, as defined by an Observer's Assessment of Alertness/Sedation (OAA/S) score of 10/20 or less, or until an adverse physiologic event was detected.

Results: The OAA/S score at which only 50% of the volunteers were able to respond to the ART (P50) during propofol-N2O was 11.1 of 20 (95% confidence interval [CI]: 10.6-11.8); the analogous P50 was 11.8 of 20 (95% CI: 11.4-12.3) with propofol-air. Failure to respond to the ART occurred at a plasma propofol concentration of 0.7 +/- 0.6 [mu]g/ml with propofol-N2O and 1.6 +/- 0.6 [mu]g/ml with propofol-air, whereas loss of consciousness occurred at 1.2 +/- 0.8 [mu]g/ml and 1.9 +/- 0.7[mu]g/ml, respectively. There were no false-normal ART responses.     

The predominant form of non-toxic goiter in Greece is now autoimmune thyroiditis.

Endemic non-toxic goiter (NTG) in Greece has been attributed primarily to iodine deficiency. Thirty years ago about 60% of the prepubertal boys and girls examined in endemic goiter regions presented with NTG and among them thyroid autoimmunity was rarely detected. Although iodine supplementation has corrected this deficiency during the past 30 years, new cases of NTG still appear. To evaluate the prevalence and type of NTG and the effect of iodine supplementation on them in Greece at present, we performed two cross-sectional clinical studies and a retrospective pathology one: (i) thyroid gland volume and urinary iodine excretion (UIE) were assessed in a representative sample of 1213 schoolchildren from previously endemic and non-endemic regions; (ii) serum thyroxine, tri-iodothyronine, TSH, thyroid autoantibodies (AAB) (anti-thyroid peroxidase and anti-thyroglobulin antibodies) and UIE (in 60 patients) were measured in 300 consecutive patients with NTG from Athens and Heraklion; and (iii) we compared the prevalence of autoimmunity among fine needle aspiration smears of benign thyroid pathologies performed by the same pathologist between 1985 and 1986 (975 cases) and between 1994 and 1995 (2702 cases). We found that 12. 5% of the schoolchildren examined in regions with a previous history of endemic goiter had NTG, whereas this percentage was only 1.7% in areas without such a history. In Athens (61.6%) and Heraklion (58. 5%) a substantial number of NTG patients were AAB positive and biochemically hypothyroid. UIE in Athens did not differ between patients with autoimmune goiter (ATG) and simple goiter. The prevalence of autoimmune stigmata in pathology smears has increased from 5.94% (years 1985-1986) to 13.91% (years 1994-1995) (P<0.05). We conclude that: (i) the persistence of endemic goiter in regional foci despite iodine deficiency correction suggests a possible role for a naturally occurring goitrogen; (ii) ATG is the predominant form of NTG in Greece nowadays; and (iii) the five-fold decrease in the prevalence of NTG during the past 30 years followed by the increase of ATG may support the relative character of the latter.     

Buspirone and meperidine synergistically reduce the shivering threshold.

Mild hypothermia (i.e., 34 degrees C) may prove therapeutic for patients with stroke, but it usually provokes shivering. We tested the hypothesis that the combination of buspirone (a serotonin 1A partial agonist) and meperidine synergistically reduces the shivering threshold (triggering tympanic membrane temperature) to at least 34 degrees C while producing little sedation or respiratory depression. Eight volunteers each participated on four randomly-assigned days: 1) large-dose oral buspirone (60 mg); 2) large-dose IV meperidine (target plasma concentration of 0.8 microg/mL); 3) the combination of buspirone (30 mg) and meperidine (0.4 microg/mL); and 4) a control day without drugs. Core hypothermia was induced by infusion of lactated Ringer's solution at 4 degrees C. The control shivering threshold was 35.7 degrees C +/- 0.2 degrees C. The threshold was 35.0 degrees C +/- 0.8 degrees C during large-dose buspirone and 33.4 degrees C +/- 0.3 degrees C during large-dose meperidine. The threshold during the combination of the two drugs was 33.4 degrees C +/- 0.7 degrees C. There was minimal sedation on the buspirone and combination days and mild sedation on the large-dose meperidine day. End-tidal PCO2 increased approximately 10 mm Hg with meperidine alone. Buspirone alone slightly reduced the shivering threshold. The combination of small-dose buspirone and small-dose meperidine acted synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. IMPLICATIONS: Mild hypothermia may be an effective treatment for acute stroke, but it usually triggers shivering, which could be harmful. Our results indicate that the combination of small-dose buspirone and small-dose meperidine acts synergistically to reduce the shivering threshold while causing little sedation or respiratory toxicity. This combination may facilitate the induction of therapeutic hypothermia in stroke victims.     

The cerebral effects of carbon dioxide during digital subtraction angiography in the aortic arch and its branches in rabbits.

PURPOSEWe studied the neurotoxicity of carbon dioxide as a contrast agent in the central nervous system by performing CO2 digital subtraction angiography (DSA) in the aortic arch and its branches in experimental animals.METHODSTwenty-five rabbits underwent intraarterial CO2 DSA while under general anesthesia, during which 50 angiograms were obtained after administration of 3 mL/kg CO2. MR imaging was performed before and after the angiographic procedure. The animals were killed 12 hours later and their brains examined macroscopically and microscopically.RESULTSThree animals died of a cause irrelevant to CO2. No animal had clinical symptoms of hemiplegia or stroke. Neither MR imaging nor macroscopic and microscopic examination of the brain revealed any ischemic infarct hemorrhage, thrombosis, or foci of necrosis.CONCLUSIONThe absence of neurologic symptoms, the lack of pathologic findings at MR imaging, and the negative pathologic findings in the brain encourage further research on CO2 neurotoxicity of the central nervous system and support its application in the imaging of intracranial vessels.     

Sitting position does not alter minimum alveolar concentration for desflurane

PURPOSE: Hypotension is a common complication of the sitting position during anesthesia, and is often counteracted by decreasing anesthetic depth, thereby exposing patients to the risk of being inadequately anesthetized. Baroreceptor unloading and the consequent sympathoexcitation, as during head up tilt, decreases pain threshold and arouses the central nervous system (CNS), whereas hypotension exerts a direct CNS depressant effect. We estimated the minimal alveolar concentration (MAC) of desflurane for immobility in patients undergoing surgery in the sitting position, in comparison to MAC desflurane for patients having a similar type of surgery in the supine position. METHODS: The Dixon up-and-down method was used to evaluate the MAC for desflurane in patients undergoing cervical spine laminoplasty (n = 24) or discectomy (n = 24) in the sitting and supine positions, respectively. Logistic regression with co-variate adjustment was employed to examine if the two positions (sitting and supine) have different or share the same concentration vs response relationship for immobility. Monte Carlo simulation was used to calculate 95% confidence intervals (CI) for the MAC in each position, and to estimate the difference in MAC (delta MAC) between the sitting and supine positions. RESULTS: Modeling both sitting [6.54% (6.50-6.66, 95% CI)] and supine [6.70 (6.55-6.81)] patients as having different MAC concentrations did not significantly improve our simplified model, which treats the two patient groups as one [6.61 (6.52-6.70), delta -2 log likelihood = 2.735, P = 0.098]. Mean delta MAC (95% CI) was -0.14 (-0.30, 0.03). CONCLUSION: The sitting position does not change desflurane anesthetic requirements for immobility.     

The timing of acupuncture stimulation does not influence anesthetic requirement

Studies suggest that acupuncture is more effective when induced before the induction of general anesthesia than afterwards. We tested the hypothesis that electro-acupuncture initiated 30 min before the induction reduces anesthetic requirement more than acupuncture initiated after the induction. Seven volunteers were each anesthetized with desflurane on 3 study days. Needles were inserted percutaneously at four acupuncture points thought to produce analgesia in the upper abdominal area and provide generalized sedative and analgesic effects: Zusanli (St36), Sanyinjiao (Sp6), Liangqiu (Sp34), and Hegu (LI4). Needles were stimulated at 2 Hz and 10 Hz, with frequencies alternating at 2-s intervals. On Preinduction day, electro-acupuncture was started 30 min before the induction of anesthesia and maintained throughout the study. On At-induction day, needles were positioned before the induction of anesthesia, but electro-acupuncture stimulation was not initiated until after the induction. On Control day, electrodes were positioned near the acupoints, but needles were not inserted. Noxious electrical stimulation was administered via 25-gauge needles on the upper abdomen (70 mA; 100 Hz; 10 s). The desflurane concentration was increased 0.5% when movement occurred and decreased 0.5% when it did not. These up-and-down sequences continued until volunteers crossed from movement to no movement four times. The P(50) of logistic regression identified desflurane requirement. Desflurane requirement was similar on the Control (mean +/- sd; 5.2% +/- 0.6%), Preinduction (5.0% +/- 0.8%), and At-induction (4.7% +/- 0.3%; P = 0.125) days. This type of acupuncture is thus unlikely to facilitate general anesthesia or decrease the requirement for anesthetic drugs.     

Physiology and clinical relevance of induced hypothermia

Experimental evidence and clinical experience suggest that mild hypothermia protects numerous tissues from damage during ischemic insult. However, the extent to which hypothermia becomes a valued therapeutic option will depend on the clinician’s ability to rapidly reduce core body temperature and safely maintain hypothermia. To date, general anesthesia is the best way to block autonomic defenses during induction of mild-to-moderate hypothermia; unfortunately, general anesthesia is not an option in most patients likely to benefit from therapeutichy pothermia. Induction of hypothermia in a wake humans is complicated by both the technical difficulties related to thermal manipulation and the remarkable efficacy of thermoregulatory defenses, especially vasoconstriction and shivering. The most effective thermal manipulation devices are generally invasive and, therefore, more prone to complications than surface methods. In an effort to inhibit thermoregulation in awake humans, several agents have been tested either alone or in combination with each other. For example, the combination of meperidine and buspirone has already been applied to faciltate induction of hypothermia in human trials. However, pharmacological induction of thermoregulatory tolerance to cold without excessive sedation, respiratory depression, or other serious toxicity remains a major focus of current therapeutic hypothermia research.