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Biomedical subjects

Y Y Poon

Publications and source records attributed to Y Y Poon.

12 recordsLinked to original sources
PubMed2006

Differential contribution of N-methyl-D-aspartate and non-N-methyl-D-aspartate receptors in the intermediolateral cell column of the thoracic spinal cord to sympathetic vasomotor tone during experimental endotoxemia in the rat.

Although the rostral ventrolateral medulla maintains neurogenic vasomotor tone via glutamatergic excitation to sympathetic preganglionic neurons located at the intermediolateral cell column (IML) of thoracic spinal cord, the relative contribution of N-methyl-d-aspartate (NMDA) and non-NMDA receptors on IML neurons at rest or during endotoxemia remain unknown. The present study addressed this issue using a combination of physiological, pharmacological, and double-immunofluorescence approaches. Adult male Sprague-Dawley rats maintained under propofol anesthesia were used. Intrathecal administration of equimolar concentrations (75, 150, or 300 nmol) of an NMDA antagonist, dizocilpine (MK801), or a non-NMDA antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, into T10 to T12 spinal cord elicited a reduction in resting vasomotor tone that was comparable in time course and in magnitude. Although both glutamate receptor antagonists exacerbated mortality and potentiated the elicited hypotension, bradycardia, or reduction in vasomotor tone during experimental endotoxemia induced by intravenous administration of Escherichia coli lipopolysaccharide (30 mg kg-1; results comparable to 6-cyano-7-nitroquinoxaline-2,3-dione at 150 nmol) were obtained only when MK801 was given at 300 nmol. Confocal microscopy further showed that augmented immunoreactivity of NR1 subunit on IML neurons coincided with the phase of endotoxemia when vasomotor tone was augmented; GluR1 immunoreactivity remained stable throughout experimental endotoxemia. These findings suggest that NMDA and non-NMDA receptors on IML neurons contribute to the generation of resting sympathetic vasomotor tone. However, up-regulation of NMDA receptors on IML neurons plays a crucial role in the maintenance of vasomotor tone during endotoxemia.

Animals↗
PubMed2005

An improved procedure for catheterization of the thoracic spinal subarachnoid space in the rat.

Catheterization of the subarachnoid space provides a convenient means to deliver drugs to, or collect cerebrospinal fluid from, the spinal cord in animal experiments, and has been instrumental to our understanding of spinal mechanisms that underlie anesthesia, analgesia, or cardiovascular regulation. Experience gained over the years has revealed several shortcomings of this technique. We report a procedure that encompasses the benefits of direct subarachnoid catheterization of the rat thoracic spinal cord but circumvents the known shortcomings. An intrathecal catheter was fabricated with a small silicon bead at one end of a PE-10 catheter, which was cannulated with a 4/0 suture that served as a guide. Using the L-shape hook of the suture guide as an anchorage, the catheter was advanced into the subarachnoid space until the silicon bead was lodged on a drilled hole (2 x 2 mm) over the lamina proper on the T13 vertebrae. With less surgical trauma, greater precision of placement and firmer anchorage of the catheter, less leakage of cerebrospinal fluid, and minimal mortality or morbidity, our modified procedure for catheterization of the thoracic spinal subarachnoid space in the rat compared favorably to previously reported methods.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2004

Pallidal deep brain stimulation in cervical dystonia: clinical outcome in four cases.

OBJECTIVE: Report on the clinical results following bilateral globus pallidus interna deep brain stimulation in four patients (one female and three males) with severe cervical dystonia, mean age 48 years (range 37-67). METHODS: All four patients had failed extensive medical and botulinum toxin treatment. The mean duration of the disease was nine years (range 4-15 years). Patients were assessed pre and postoperatively using the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS). Pre-operatively, the mean TWSTRS total score was 43.2 (range 28-60.5). Posteroventral pallidal deep brain stimulators were inserted using MRI and microelectrode recording guidance. Last follow-up was 15 months for the four patients. RESULTS: Mean reduction in the TWSTRS total scores at last follow- up was 73% (range 61- 85%). Improvement in pain occurred soon after deep brain stimulation surgery. Motor improvement was delayed and prolonged over several months. Frequent adjustment in the stimulation parameters was necessary in the first three months. CONCLUSION: Bilateral pallidal stimulation is effective in management of selected cases of intractable cervical dystonia.

Adult↗
PubMed2000

Aspiration in chest compression alone without mechanical ventilation in the head down position in dogs.

BACKGROUND: Previous work by the authors has shown that chest compressions alone without mechanical ventilation during cardiopulmonary resuscitation in the natural supine position was associated with pulmonary aspiration in dogs. The purpose of this investigation was to test the hypothesis that a head down position may prevent aspiration during chest compressions alone and whether oxygenation can be improved by simply insufflation of oral oxygen 10 min after cardiac arrest. METHODS: Cardiac arrest was induced in ten mongrel dogs which were anesthetized and paralysed. Eight underwent chest compressions alone in different head down positions using an automatic compressor at 9 kg compression force and 3 cm compression depth. The study was composed of two parts. Part 1 evaluated the effect of insufflation of 10 l/min O2, into the mouth of the dogs, 10 min after initiation of resuscitation, using chest compressions alone. Part 2 was designed to test our hypothesis that the head down position may protect the lungs from aspiration during chest compression alone. The mouths of the dogs were filled with mixed barium and the dogs underwent serial episodes of chest compressions, for 10 min each, in the 20 degree head down, 10 degree head down and the natural supine positions. Chest X-rays with antero-posterior and lateral views were taken to evaluate pulmonary aspiration. Two additional dogs underwent direct chest compression alone in the natural supine position and the time of chest compression was shortened to 5 min. RESULTS: All dogs in the natural position showed evidence of pulmonary aspiration of barium, five or six of the dogs showed tracheal aspiration in the 10 degree head down position, while no any barium was visualized in the tracheo-broncheal trees of the dogs in the 20 degree head down position. Supplemental oxygen in the mouth improved the mean PaO2 from 67 +/- 26 to 160 +/- 97 mmHg during chest compressions alone. CONCLUSION: Chest compression alone without mechanical ventilation in the supine position caused pulmonary aspiration in the unprotected airway in dogs. This complication could be prevented by adopting a 20 degree head down position. The 10 degree head down position seemed to reduce the severity of the pulmonary aspiration, but not enough to eliminate the danger altogether. Supplemental oxygen in the mouth can improve oxygenation in chest compressions alone.

Administration, Oral↗
PubMed2000

Aspiration in transtracheal oxygen insufflation with different insufflation flow rates during cardiopulmonary resuscitation in dogs.

We investigated whether transtracheal insufflation of oxygen with different insufflation flow rates protects against aspiration of gastric contents during cardiopulmonary resuscitation (CPR). Its ventilation and oxygenation effects were also evaluated. Cardiac arrest was induced in anesthetized and paralyzed 18 mongrel dogs. Chest compression using an automatic thumper was performed while the dogs randomly received no mechanical ventilation (Group I, n = 6) or were transtracheally insufflated with 4 L/min oxygen (Group II, n = 6) or 10 L/min oxygen (Group III, n = 6). Blood samples were drawn every 5 min for 20 min for blood gas analysis. the mouths of the dogs were then filled with 70 mL mixed barium, and 10 min after chest compression, chest radiographs were taken to evaluate the incidence of pulmonary aspiration. Results showed that pulmonary aspiration occurred in all dogs of Group I and three of the six dogs in Group II, whereas dogs in Group III were free from pulmonary aspiration. Both transtracheal oxygen insufflation groups maintained oxygen saturation significantly better than Group I, but mild hypercapnia was observed in all groups after 20 min of CPR. We conclude that transtracheal oxygen insufflation, but not chest compression alone, was able to maintain oxygenation for 20 min during CPR in dogs with cardiac arrest. Mild hypercapnia was noted in all groups. Chest compression alone caused pulmonary aspiration, whereas insufflation of 10 L O(2)/min provided better protection against pulmonary aspiration than that of 4 L O(2)/min.

Animals↗
PubMed1999

Intubation of newborn during delivery with intact umbilical cord--a case report.

A 24-year-old gravida 2, para 1 woman at 38th week gestation was scheduled for elective Cesarean section (C/S) because of a previous C/S and prenatal diagnosis of congenital diaphragmatic hernia. We decided to intubate the newborn during delivery before the umbilical cord was cut. After delivery of the fetal head and part of the shoulders, the mouth of the fetus was cleared and the trachea was intubated orally with a 2.5 mm internal diameter (I.D.) endotracheal tube under sterile conditions while the uteroplacental circulation was still intact. The patient had to be repeatedly resuscitated due to bradycardia in intensive care unit. No surgical correction of the hernia was attempted because of the poor condition of the baby, which died 3.5 hours after birth. Although our case ended up in mortality despite successful perinatal intubation, we recommend that in case where airway or ventilatory problems are anticipated, tracheal intubation is done during delivery before the umbilical cord is clamped. When the fetus is sharing the maternal circulation, it will allow physicians to have more time and safety to perform corrective measures.

Adult↗
PubMed1997

Unsuspected difficult intubation caused by a laryngeal web.

We report a case of unsuspected difficult intubation in an adult caused by laryngeal web formation in the anterior commissure of the larynx. After induction of anaesthesia, most parts of the posterior commissure of the vocal cords were seen clearly at laryngoscopy, but a 7.5-mm internal diameter (id) tracheal tube could not be advanced below the level of the vocal cords because of resistance. Intubation was re-attempted several times after oxygenation by mask with trials of smaller tubes. Finally, a 5.0-mm id cuffed tube was passed successfully through the vocal cords, and secured in place. Because of the unexpected difficulties in intubation, an otolaryngologist was consulted to examine the larynx with a microscope. A web of 0.5 cm in the anterior commissures was found which caused subglottic stenosis.

Aged↗
PubMed1997

Comparison of sevoflurane with halothane in pediatric ambulatory anesthesia: an experience in Taiwan.

BACKGROUND: Sevoflurane, with blood/gas partition coefficient of 0.69 and MAC of 1.76 is a fast acting, potent inhalation anesthetic. Its suitability and safety for pediatric ambulatory anesthesia were assessed and compared with that of halothane. METHODS: Thirty two unpremedicated pediatric patients undergoing elective herniorrhaphy on day-surgery basis were randomly allocated to 2 groups of equal number to receive either sevoflurane or halothane anesthesia. Employing mask technique, anesthesia was induced with 60% nitrous oxide and 3 MAC of either sevoflurane or halothane in oxygen. Anesthesia was maintained respectively with 1-1.5 MAC of sevoflurane or halothane. The induction time, emergence time and untoward effects during anesthesia were analyzed and compared. RESULTS: It was shown that both the induction time and emergence time were significantly shorter in patients receiving sevoflurane. None had major complications. CONCLUSIONS: The results strongly suggest that sevoflurane is preferable to halothane for pediatric ambulatory anesthesia.

Ambulatory Surgical Procedures↗
PubMed1989

The depth to the epidural space.

Two hundred and ten patients, 145 males and 65 females, aged 20 to 72 years old, ready to receive extracorporeal shock wave lithotripsy under epidural anesthesia were studied to evaluate if any correlation existed between body weight, body surface area, body mass index and body height and the depth to the epidural space. The mean value for the depth to the epidural space was 4.77 +/- 0.55 cm for males, 4.25 +/- 0.55 cm for females and the overall average was 4.61 +/- 0.60 cm. The range of the depth to the epidural space was 3.0-7.0 cm. Linear regression analysis revealed significant correlation between body weight, body surface area, body mass index, body height an the depth to the epidural space, in the order of BW greater than BSA greater than BMI greater than BH. It is concluded that body weight, body surface area, body mass index and body height affect the depth to the epidural space and play an important role in predicting the depth to the epidural space.

Adult↗
PubMed1989

Combined epidural lidocaine-fentanyl-epinephrine for cesarean section.

The combined use of fentanyl-epinephrine-lidocaine in epidural analgesia was investigated in 60 mothers who underwent elective Cesarean section. They were randomly classified into 4 groups of 15 each. Group A received 20 mL of 2% lidocaine 3 mL normal saline. Group B received 20 mL of 2% lidocaine with freshly added 1:200000 epinephrine and 5 mL normal saline. Group C received 20 mL of 2% lidocaine and 2 mL of fentanyl in 3 mL normal saline. Group D received 20 mL of 2% lidocaine and 5 mL normal saline. The duration of action was nearly doubled in the groups with epinephrine added. The quality of the analgesia was assessed by the degree of intraoperative analgesia; 93% of the patients in group A were classified as "Excellent"; while only 67% in group B were classified as "Excellent". The difference in patient's acceptance was statistically significant. 93% vs 27% in Group A and Group C; 67% vs 6.7% in Group B and Group D rated "Excellent". The results suggest that both fentanyl and epinephrine improve intraoperative analgesia. Epinephrine offers a greater analgesic effect than fentanyl.

Adult↗