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Biomedical subjects

A Petrou

Publications and source records attributed to A Petrou.

At least 19 recordsLinked to original sources
PubMed2006

Successful cardiac and cerebral resuscitation with extracorporeal circulation and mild hypothermia.

Extracorporeal circulation could be effective for cardiac resuscitation in patients who do not respond to ''Advanced cardiac life support'' (ACLS), but cannot guarantee brain survival. A case of successful cardiac and cerebral resuscitation with extracorporeal circulation and mild hypothermia, in a 48 year-old man with cardiac arrest due to cardiac tamponade, is reported. The good long term neurologic outcome of the patient is also described.

Cardiopulmonary Resuscitation↗
PubMed2002

Reduction of spin injection efficiency by interface defect spin scattering in ZnMnSe/AlGaAs-GaAs spin-polarized light-emitting diodes.

We report the first experimental demonstration that interface microstructure limits diffusive electrical spin-injection efficiency across heteroepitaxial interfaces. An inverse correlation be-tween spin-polarized electron injection efficiency and interface defect density is demonstrated for ZnMnSe/AlGaAs-GaAs spin-polarized light-emitting diodes that exhibit quantum well spin polarizations up to 85%. A theoretical treatment shows that the suppression of spin injection due to interface defects results from the contribution of the defect potential to the spin-orbit interaction, which increases the spin-flip scattering.

Journal Article↗
PubMed2002

Internal transitions of negatively charged magnetoexcitons and many body effects in a two-dimensional electron gas.

Internal transitions of quasi-two-dimensional, negatively charged magnetoexcitons ( X-) and their evolution with excess electron density have been studied in GaAs/AlGaAs quantum wells. In the dilute electron limit, due to magnetic translational invariance, the optically detected resonance spectra are dominated by bound-to-continuum bands in contrast to the negatively charged donor system D-, which exhibits strictly bound-to-bound transitions. With increasing excess electron density Landau-level filling factors nu<2 the X--like transitions are blueshifted; they are absent for nu>2. The blueshifted transitions are explained in terms of a new type of collective excitation---magnetoplasmons bound to a mobile valence band hole.

Journal Article↗
PubMed2000

Continuous spinal anaesthesia/analgesia for the perioperative management of high-risk patients.

The intraoperative effects of continuous spinal anaesthesia, and the efficacy of postoperative continuous spinal analgesia in 48 elderly high risk patients undergoing major abdominal, vascular or orthopaedic surgery is reported. Intraoperative anaesthetic technique proved to be safe and provided satisfactory results in the immediate postoperative period. Furthermore, the postoperative analgesic regimen which involved intrathecal fentanyl and bupivacaine, and intravenous tenoxicam, provided effective analgesia for all patients. The intrathecal analgesic regimen was administered continuously through a PCA pump which had the facility to provide bolus doses when requested in predetermined lockout intervals. The mean doses of fentanyl and bupivacaine infused intrathecally for the first 24 h postoperatively were 14.5 +/- 1.5 microg h(-1) (mean +/- SD) and 0.72 +/- 0.08 mg h(-1) (mean +/- SD), respectively, while the requirements for analgesia decreased progressively overtime but lasted for 118 h. The technique provided effective analgesia with low pain scores that was reflected by the ease in performing physical exercises and the pleasant co-operation with the physiotherapist. Only minor complications related to anaesthesia/analgesia were encountered.

Aged↗
PubMed2000

Continuous spinal anesthesia/analgesia for perioperative management of morbidly obese patients undergoing laparotomy for gastroplastic surgery.

BACKGROUND: The authors determined prospectively the safety of continuous spinal anesthesia combined with general anesthesia and the efficacy of postoperative pain relief with continuous spinal analgesia for morbidly obese patients undergoing vertical banded gastroplasty. METHODS: 27 patients (13 men, 14 women) with a mean body mass index (BMI) of 50.4 +/- 7.8 and several co-morbidities were studied. All patients were anesthetized with the same anesthetic regimen, which included midazolam, fentanyl, propofol, muscle relaxants, nitrous oxide, isoflurane and intrathecal bupivacaine. Postoperative pain relief was provided for 5 days and all patients received the same regimen, which included intrathecal bupivacaine, fentanyl and intravenous tenoxicam. The intrathecal analgesic regimen was administered continuously through a pump which had the facility of providing bolus doses when requested in predetermined lockout intervals. Intra-operative monitoring included hemodynamic and respiratory parameters. Additional postoperative monitoring included respiratory rate, degree of sedation, sensory level of anesthesia, motor response and intensity of pain. RESULTS: Intraoperative anesthetic technique was safe and provided satisfactory results in the immediate postoperative period. Furthermore, the postoperative analgesia regimen provided effective analgesia in all patients. The mean doses of fentanyl and bupivacaine infused intrathecally for the first 24 postoperative hours were 14.1 +/- 2.0 microg.h(1) and 0.7 +/- 0.1 mg.h(1) respectively, while the requirements of analgesia decreased progressively with time. The technique provided effective analgesia with low pain scores, which was reflected by ease in mobilizing and performing physical exercises with the physiotherapist. Only minor complications related to anesthesia and analgesia were encountered. CONCLUSION: To our knowledge, this technique of anesthesia and postoperative analgesia has not been described before in morbidly obese patients. This regimen merits further controlled trials to establish its place in the perioperative management of morbidly obese patients.

Adult↗
PubMed1999

Peritoneal expansion by artificially produced ascites during perfusion chemotherapy.

HYPOTHESIS: In cases of peritoneal carcinomatosis, continuous hyperthermic peritoneal perfusion chemotherapy (CHPPC) accomplishes homogeneous distribution of the drug and heat to the entire peritoneal cavity and exposure of the visceral and parietal surfaces to the perfusate. A new closed technique for expansion that produces artificial ascites is safer for medical personnel because of less heat and drug loss and more efficacious in its hemodynamic effect on the patient. DESIGN: Prospective study. SETTING: University hospital. PATIENTS: Twenty-one patients with peritoneal carcinomatosis. INTERVENTIONS: We performed 23 continuous hyperthermic peritoneal perfusion chemotherapy (CHPPC) procedures with peritoneal cavity expansion to an intra-abdominal pressure up to 26 mm Hg, using artificially produced ascites with 4 to 9 L normal saline solution. MAIN OUTCOME MEASURES: Intraoperative and postoperative complications and hemodynamic changes during CHPPC. RESULTS: No intraoperative complications were recorded. The artificially produced ascites did not cause significant hemodynamic changes. During the immediate postoperative period, 1 patient died of intra-abdominal hemorrhage and leakage of a colorectal anastomosis, resulting in a mortality rate of 4% in our series. Minor complications were seen in 14 patients. The complications were not attributable to the expansion technique. CONCLUSIONS: Our proposed modification of closed-circuit CHPPC appears to be well tolerated and safe in patients with a high tumor load, as well as for the theater personnel. It remains to be investigated whether the theoretical advantages of the proposed technique will also lead to better long-term results.

Ascites↗
PubMed1999

Continuous spinal anaesthesia/analgesia for abdominal aortic aneurysm repair and post-operative pain management.

The intra-operative management of two patients with chronic obstructive pulmonary disease and cardiovascular pathology, who underwent peripheral reconstructive vascular surgery under continuous spinal anaesthesia, is described. Furthermore, continuous intrathecal analgesia was also continued in the post-operative period and provided effective pain relief that was reflected by the favourable surgical outcome.

Aged↗
PubMed1999

Combined protocols for myocardial perfusion imaging in patients with hypertension.

OBJECTIVE: Patients diagnosed previously with hypertension submitted to exercise testing for myocardial scintigraphy often respond with excessive elevation of the blood pressure, even when baseline blood pressure is normal, resulting in interruption of the test or false positive results for coronary artery disease. The aim of this study was to evaluate the haemodynamic changes and the safety of the combined examination protocols of dipyridamole plus handgrip exercise and of dipyridamole plus symptom-limited exercise testing on a treadmill in patients with hypertension. METHODS AND RESULTS: We performed scintigraphic myocardial single photon emission computed tomography in 240 patients with hypertension as follows: in 27 patients who were administered dipyridamole alone, in 126 patients who were administered dipyridamole and were also submitted to isometric handgrip exercise and in 87 patients who were administered dipyridamole and were also submitted to treadmill, symptom-limited exercise (modified Bruce protocol). Mean systolic blood pressure, mean diastolic blood pressure and heart rate did not rise excessively in patients submitted to exercise testing (192 +/- 18 mm Hg, 106 +/- 14 mm Hg and 111 +/- 21 bpm for the dipyridamole plus handgrip group and 180 +/- 28 mm Hg, 104 +/- 10 mm Hg and 149 +/- 19 bpm for the dipyridamole plus treadmill group, respectively), with two patients from each exercise group presenting a maximum systolic blood pressure higher than 220 mm Hg and no subsequent major cardiac complications (such as death, myocardial infarction, unstable angina or life-threatening arrhythmia). Moreover, patients in these exercise groups experienced fewer non-cardiac side effects than with dipyridamole alone, while attaining a good level of exercise stress. CONCLUSIONS: Both combined dipyridamole and exercise protocols for scintigraphic myocardial single photon emission computed tomography in patients with hypertension are safe and increase heart rate without an excessive elevation in blood pressure. Consequently, they can be recommended for clinical use. Dipyridamole combined with treadmill, symptom-limited exercise would be the first choice, with dipyridamole and isometric handgrip exercise reserved for patients with physical handicaps.

Adult↗
PubMed1998

The influence of premedication on heart rate variability.

Analysis of heart rate variability has been used to study the effects of midazolam, morphine and clonidine on the autonomic nervous system, when administered to patients for premedication. Ninety-five patients were studied 60 min before and 60 min after premedication. Normal saline (n = 25), midazolam 0.08 mg.kg-1 (n = 24), morphine 0.15 mg.kg-1 (n = 23), or clonidine 2 micrograms.kg-1 (n = 23) were administered intramuscularly by random allocation. A Holter device was connected to the patient during the study period. Using power spectral analysis the low-frequency and high-frequency components were calculated from the Holter recordings. These are markers for sympathetic and parasympathetic activity respectively; the low- to high-frequency ratio was also calculated, a ratio of > 1 signifying sympathetic dominance. A significant reduction was noticed in both low-frequency and high-frequency power in the three premedicated groups, whereas no changes were observed in the normal saline group. In the case of midazolam, both the low and high frequencies were decreased but the low- to high-frequency ratio did not change significantly. Morphine and clonidine depressed the low-frequency component more than the high-frequency component and the low- to high-frequency ratio was decreased, suggesting parasympathetic dominance. We conclude that heart rate variability may be a useful tool for investigating the effect of drugs on the autonomic nervous system.

Adrenergic alpha-Agonists↗
PubMed1998

Anaesthesia and the QT interval. Effects of isoflurane and halothane in unpremedicated children.

The effects of isoflurane and halothane on the QT interval were investigated during induction of anaesthesia. Fifty-one unpremedicated, ASA grade 1 children were studied. Anaesthesia was induced with either isoflurane (n = 25) or halothane (n = 26) and was maintained to the end of the study with end-tidal concentrations of between 2.5% and 3%. Recording of the electrocardiograph, heart rate and systolic arterial pressure were obtained at the following times: before induction of anaesthesia; 1 min and 3 min after stable end-tidal concentrations of anaesthetic agent had been reached; 1 min and 3 min following vecuronium administration; at the time of tracheal intubation and 1 min and 3 min later. Isoflurane significantly prolonged the QT interval (p < 0.001), in contrast to halothane which shortened it (p < 0.01). Heart rate remained largely unchanged during isoflurane anaesthesia but it decreased in the presence of halothane (p < 0.001). In both groups, systolic arterial pressure decreased significantly after induction of anaesthesia (p < 0.001) and remained so to the end of the study. In the isoflurane group, 12 children developed ECG repolarisation abnormalities and in one child an arrhythmia was noticed. In the halothane group, one child developed repolarisation changes while arrhythmias were observed in 10 children. There were no adverse sequelae. It is concluded that halothane may be a better anaesthetic agent than isoflurane for use in children with a prolonged QT interval.

Anesthetics, Inhalation↗
PubMed1996

Anaesthesia for intra-peritoneal perfusion of hyperthermic chemotherapy. Haemodynamic changes, oxygen consumption and delivery.

We investigated the intra-operative application of intraperitoneal perfusion of hyperthermic chemotherapy and its effects on cardiovascular status and oxygen consumption and delivery in 11 patients following laparotomy for surgical resection of recurrent tumours or peritoneal metastases. Closed peritoneal irrigation was carried out with perfusate at a temperature of 45-47 degrees C. External cooling was applied during the procedure to prevent systemic hyperthermia. Data were collected 5 min before the commencement of the hyperthermic peritoneal perfusion, at 5, 30, 60 and 90 min during perfusion and 5 min after perfusion was discontinued. During the hyperthermic perfusion period, the core body temperature increased significantly but remained within clinically acceptable values. Heart rate, central venous pressure and pulmonary artery pressure increased significantly during perfusion; these returned to control values immediately after discontinuation of perfusion, except for the heart rate, which remained high. Mean arterial pressure, cardiac output, oxygen delivery and oxygen consumption did not change significantly although a metabolic acidosis developed during the study period. These findings suggest that the intraperitoneal perfusion of hyperthermic chemotherapy may be safe in humans, provided that appropriate monitoring, cooling and technical support are applied.

Adult↗