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Biomedical subjects

Matthew T V Chan

Publications and source records attributed to Matthew T V Chan.

17 recordsLinked to original sources
PubMed2006

Preoperative folate and homocysteine status in patients undergoing major surgery.

BACKGROUND & AIMS: Patients with folate deficiency and elevated homocysteine (Hcy) levels have increased risk of cerebrovascular and cardiovascular disease. They may also be at increased risk of complications after surgery because nitrous oxide interferes with folate metabolism. The aim of this study was to assess the incidence of folate deficiency and hyperhomocysteinemia in patients presenting for major surgery. We also tested the utility of a brief preoperative medical and dietary questionnaire to identify those with low folate or elevated Hcy levels. METHODS: We enrolled 390 patients and obtained a preoperative fasting blood sample from each of the study participants (folate [n=386], homocysteine [n=387]). RESULTS: Although only one patient had folate deficiency preoperatively (incidence +/-SD folate and Hcy concentrations were 23.7+/-5.2 nmol/l and 9.4+/-4.2 micromol/l, respectively. There was a negative correlation between folate and Hcy, r=-0.27, P<0.001. Multivariate analyses indicated that vegan status and folate supplementation prevented low folate status (P<0.05), while age of the patient, and history of heart failure and anaemia predicted elevated Hcy concentration. CONCLUSIONS: Some factors identified by a brief medical and dietary questionnaire are associated with folate and homocysteine status. Hyperhomocysteinaemia occurs in about 7.5% of surgical patients; however, both low folate status and elevated Hcy concentration are less likely in those taking folate or vitamin B supplements. This has implications for patients undergoing nitrous oxide anaesthesia because of its inhibition of folate metabolism, and should prompt clinicians to consider folate and other nutritional supplementation before elective surgery.

Anesthetics, Inhalation↗
PubMed2006

Intravenous magnesium sulfate after aneurysmal subarachnoid hemorrhage: a prospective randomized pilot study.

We performed a randomized, double-blind, pilot study on magnesium sulfate (MgSO4) infusion for aneurysmal subarachnoid hemorrhage (SAH).Sixty patients with SAH were randomly allocated to receive either MgSO4 80 mmol/day or saline infusion for 14 days. Patients also received intravenous nimodipine. Episodes of vasospasm were treated with hypertensive and hypervolemic therapy. Neurologic status was assessed 6 months after hemorrhage using the Barthel index and Glasgow Outcome Scale. Incidences of cardiac and pulmonary complications were also recorded. Patient characteristics, severity of SAH, and surgical treatment did not differ between groups. The incidence of symptomatic vasospasm decreased from 43% in the saline group to 23% in patients receiving MgSO4 infusion, but it did not reach statistical significance, P=0.06. For patients who had transcranial Doppler-detected vasospasm, defined as mean flow velocity >120 cm/s and a Lindegaard index >3, the duration was shorter in the magnesium group compared with controls (P<0.01). There was, however, no difference between groups in functional recovery or Glasgow Outcome Scale score. The incidence of adverse events such as brain swelling, hydrocephalus, and nosocomial infection was also similar in patients receiving MgSO4 or saline. In this small pilot study, MgSO4 infusion for aneurysmal SAH is feasible. On the basis of the preliminary data, a larger study recruiting approximately 800 patients is required to test for a possible neuroprotective effect of magnesium after SAH.

Acute Disease↗
PubMed2006

Magnesium therapy within 48 hours of an aneurysmal subarachnoid hemorrhage: neuro-panacea.

Whereas advances in neurosurgical treatment and intensive care management improve the results from many of the devastating complications associated with aneurysmal subarachnoid hemorrhage, cerebral vasospasm remains a major cause of neurological morbidity and mortality. Experimental studies suggested that MgSO(4) inhibits excitatory amino acid release, blocks N-methyl-D-aspartate (NMDA) receptors and prevents calcium entry into the cell. Magnesium also increases red blood cell deformability. These changes may reduce the occurrence of cerebral vasospasm and minimize neuronal injury during episodes of cerebral vasospasm. Our group is currently hosting the intravenous magnesium sulfate to improve outcome after aneurysmal subarachnoid hemorrhage (IMASH) trial, which is a randomized, placebo-controlled, double-blinded, multicentered trial to evaluate the effect of magnesium sulfate infusion on the clinical outcome of patients with aneurysmal subarachnoid hemorrhage since 2002. The pilot result showed a trend towards decreased clinical vasospasm and better patient outcome. Magnesium sulfate infusion may prove to be an effective and inexpensive way to reduce the morbidity and mortality associated with aneurysmal subarachnoid hemorrhage, which is a major breakthrough in the current management.

Calcium Channel Blockers↗
PubMed2006

The additive interactions between ondansetron and droperidol for preventing postoperative nausea and vomiting.

Prophylactic ondansetron or droperidol reduces the incidence of postoperative nausea and vomiting (PONV). Previous studies showed that the combination of these two drugs produced better antiemetic effect than either drug alone. We present a nonparametric method to determine the pharmacologic interaction between ondansetron and droperidol and compared the observed response of the drug combination with that predicted from additivity. This is calculated as the product of the individual drug response, normalized to that of the controls. Five minutes before induction of anesthesia, 400 patients scheduled for laparoscopic gynecologic surgery were randomly assigned to receive 1) saline IV; 2) ondansetron 4 mg IV; 3) droperidol 1.25 mg IV; or 4) a combination of droperiodol 1.25 mg and ondansetron 4 mg IV. A standardized anesthetic technique and postoperative analgesic regimen were used. Patients were reviewed regularly for 48 h. Changes in the heart rate adjusted QT (QTc) interval were measured from electrocardiograms recorded before and 5 min after study drug administration. In a subgroup of 160 patients, QTc intervals were measured again at 2-3 h after surgery. During the first 48 h after the surgery, the proportion of patients experiencing PONV was 68% (95% CI 58-77) in the control group. A single dose of ondansetron or droperidol decreased the incidence of PONV to 30% (95% CI 21-40) and 28% (95% CI 20-38), respectively. The predicted incidence of PONV after drug combination, 11.8% (7.1-11.9), was similar to that observed, 12.1% (6.4-20.2), P = 0.94. The corresponding predicted and observed treatment responses in the combination group were 88.2% and 87.9%, respectively. There was a modest and transient increase in QTc interval after administration of ondansetron, droperidol, or their combination. The changes were however similar among groups. We conclude that the interaction between ondansetron and droperiodol was additive. Both drugs acted independently of each other through their specific mechanisms of action. The incidence of QTc prolongation did not increase with the drug combination.

Adolescent↗
PubMed2006

Noninvasive positive-pressure ventilation: An experimental model to assess air and particle dispersion.

BACKGROUND: Health-care workers are concerned about the risk of acquiring contagious diseases such as severe acute respiratory syndrome and avian influenza after recent outbreaks. We studied exhaled air and particle dispersion through an oronasal mask attached to a human-patient simulator (HPS) during noninvasive positive-pressure ventilation (NPPV). METHODS: Airflow was marked with intrapulmonary smoke for visualization. Therapy with inspiratory positive airway pressure (IPAP) was started at 10 cm H2O and gradually increased to 18 cm H2O, whereas expiratory positive airway pressure was maintained at 4 cm H2O. A leakage jet plume was revealed by a laser light sheet and images captured by video. Smoke concentration in the plume was estimated from the light scattered by smoke particles. FINDINGS: A jet plume of air leaked through the mask exhaust holes to a radial distance of 0.25 m from the mask during the application of IPAP at 10 cm H2O with some leakage from the nasal bridge. The leakage plume exposure probability was highest about 60 to 80 mm lateral to the median sagittal plane of the HPS. Without nasal bridge leakage, the jet plume from the exhaust holes increased to a 0.40-m radius from the mask, whereas exposure probability was highest about 0.28 m above the patient. When IPAP was increased to 18 cm H2O, the vertical plume extended to 0.45 m above the patient with some horizontal spreading along the ward ceiling. CONCLUSION: Substantial exposure to exhaled air occurs within a 0.5-m radius of patients receiving NPPV. Medical wards should be designed with an architectural aerodynamics approach and knowledge of air/particle dispersion from common mechanical ventilatory techniques.

Air Movements↗
PubMed2006

Airflows around oxygen masks: A potential source of infection?

Patients with respiratory infections often require the use of supplemental oxygen via oxygen masks, which, in the hospital, may become sources of aerosolized infectious pathogens. To assess this risk, a human lung model (respiration rate, 12 breaths/min) was designed to test the potential for a simple oxygen mask at a common setting (4 L/min) to disperse potentially infectious exhaled air into the surrounding area. A laser sheet was used to illuminate the exhaled air from the mask, which contained fine tracer smoke particles. An analysis of captured digital images showed that the exhaled air at the peak of simulated exhalation reached a distance of approximately 0.40 m.

Aerosols↗
PubMed2006

Placental transfer of ondansetron during early human pregnancy.

BACKGROUND AND OBJECTIVE: Nausea and vomiting are common conditions that occur during early pregnancy and can be disabling. Ondansetron had been used in pregnant women when treatment with conventional antiemetics has failed; however, the safety and tolerability of this relatively new antiemetic drug during pregnancy is still uncertain. The objective of this study was to quantify the placental transfer of ondansetron in the first trimester of human pregnancy. PATIENTS AND METHODS: This was a prospective, observational study. Forty-one patients who requested surgical termination of pregnancy at the first trimester were administered three doses of ondansetron 8 mg before surgery. Maternal venous blood, coelomic fluid, amniotic fluid and fetal tissue were collected from each patient for analysis of ondansetron by liquid chromatography-mass spectometry. RESULTS: Ondansetron was found in all samples. Drug concentration in fetal tissue was significantly higher than that in the amniotic fluid and similar to that in the coelomic fluid. The median (interquartile range) fetal/maternal ratio was 0.41 (0.31-0.52) and there were no significant correlations between ondansetron concentrations in each compartment and gestational age. CONCLUSIONS: A significant amount of ondansetron was present in all embryonic compartments. The developmental significance of this drug exposure requires further investigation, i.e. whole embryo culture.

Adult↗
PubMed2004

Interventional neurophysiologic monitoring.

PURPOSE OF REVIEW: Intraoperative neurophysiologic monitoring provides useful information on the functional status of the nervous system. This review focuses on recently published data concerning the impact of monitoring on patient outcome. RECENT FINDINGS: There is level I evidence to support the use of bispectral index monitoring to prevent awareness during anesthesia in high-risk patients. A number of randomized trials have shown that monitoring-guided anesthesia using the bispectral index or other devices will expedite recovery and improve perioperative drug utilization. There are also preliminary reports suggesting that anesthesia dictated by bispectral index monitoring may alter long-term outcome and reduce mortality. In surgical procedures, however, it is less clear whether neurophysiologic monitoring will improve patient outcome. Currently, the majority of data are derived from respective case series. Nonetheless, monitoring with somatosensory evoked potential has been shown to reduce postoperative neurologic deficits after spinal surgery. There is also evidence to suggest that electromyography and motor evoked potential are essential complements to somatosensory evoked potential for monitoring of spinal cord surgery. SUMMARY: Brain monitoring facilitates anesthetic drug administration. An increasing number of neurosurgical procedures will require some form of intraoperative neurophysiologic monitoring to achieve higher degrees of safety and accuracy. In many instances, the data derived from monitoring will guide and influence surgical decisions. In this context, neurophysiologic monitoring should be regarded as interventional.

Journal Article↗
PubMed2004

Preoperative ketamine improves postoperative analgesia after gynecologic laparoscopic surgery.

UNLABELLED: In this study, we evaluated the preemptive effect of a small dose of ketamine on postoperative wound pain. In a randomized, double-blinded, controlled trial, we compared the analgesic requirement in patients receiving preincision ketamine with ketamine after skin closure or placebo after gynecologic laparoscopic surgery. One-hundred-thirty-five patients were randomly assigned to receive preincision or postoperative ketamine 0.15 mg/kg or saline IV. Anesthetic technique was standardized. Patients were interviewed regularly up to 4 wk after surgery. Pain score, morphine consumption, side effects, and quality of recovery score were recorded. Patients receiving preincision ketamine had a lower pain score in the first 6 h after operation compared with the postoperative (P = 0.001) or placebo groups (P < 0.001). The mean (95% confidence intervals) time to first request for analgesia in the preincision group, 1.8 h (1.4-2.1), was longer than the postoperative group, 1.2 h (0.9-1.5; P < 0.001), or the placebo group, 0.7 h (0.4-0.9; P < 0.001). The mean +/- SD morphine consumption in the preincision group, 1.5 +/- 2.0 mg, was less than that in the postoperative group, 2.9 +/- 3.1 mg (P = 0.04) and the placebo group, 3.4 +/- 2.7 mg (P = 0.003). There was no significant difference among groups with respect to hemodynamic variables or side effects. No patient complained of hallucinations or nightmares. We conclude that a small dose of ketamine is not only safe, but it also provides preemptive analgesia in patients undergoing gynecologic laparoscopic surgery. IMPLICATIONS: In women undergoing laparoscopic gynecologic surgery, a small preoperative dose of ketamine (0.15 mg/kg) produced preemptive analgesia. There were no significant hemodynamic and psychological side effects with this dose.

Adult↗
PubMed2002

A prospective randomized trial comparing patient-controlled sedation using propofol and alfentanil and physician-administered sedation using diazepam and pethidine during transvaginal ultrasound-guided oocyte retrieval.

BACKGROUND: This open label study compared the effectiveness of patient-controlled sedation (PCS), with physician-administered sedation (PAS) during transvaginal ultrasound-guided oocyte retrieval (TUGOR). METHODS: A total of 106 patients was randomized using a computer model to receive either PCS (n = 51) or PAS (n = 55). Intra-operative sedation and co-operation were measured on a 5-point scale while severity of pain, and doctor and patient satisfaction were assessed using a 100 mm visual analogue scale. Number of oocytes retrieved and fertilization, cleavage and clinical pregnancy rates were also recorded. RESULTS: Levels of sedation and co-operation were similar between groups. The pain score was higher in the PCS group during (mean +/- SD, 53 +/- 23 versus 35 +/- 24; P < 0.01) and 2 h after the procedure (29 +/- 27 versus 17 +/- 22; P < 0.05). Doctors were less satisfied with PCS than PAS (62 +/- 25 versus 71 +/- 26; P < 0.05) while patients were highly satisfied with both methods (76 +/- 23 versus 74 +/- 21; not significant). There were no oversedation or peri-operative complications. Fertility outcomes were similar. Patients tended to prefer PCS when given the choice of sedation method. CONCLUSION: Although PCS provides less analgesia then PAS during TUGOR, it is safe, satisfactory and accepted by patients.

Adult↗
PubMed2002

Prolonged neuromuscular block after rocuronium in postpartum patients.

UNLABELLED: Postpartum patients have not completely lost the weight gained during pregnancy. Drug dosing according to total body weight (TBW) can cause exaggerated effects and dosing by lean body mass (LBM) may provide a more consistent response despite the increased weight. We compared the duration of a rocuronium neuromuscular block in 22 women undergoing postpartum tubal ligation 31--79 h after delivery, with that in 22 women undergoing gynecological surgery. Anesthesia was induced and maintained with propofol and alfentanil. Half of the patients in each of the Postpartum and Control groups received a bolus dose of rocuronium 0.6 mg/kg TBW and the remaining half received rocuronium 0.6 mg/kg LBM. Neuromuscular block was monitored by electromyography and the ulnar nerve was stimulated transcutaneously using a train-of-four pattern. When rocuronium was given by TBW, median (range) duration of neuromuscular block until 25% recovery of the first twitch response was longer in the Postpartum group, 35.3 (29.7--48.7) min, compared with the Control group, 24.8 (21.5--28.6) min (P < 0.001). After dosing by LBM, the duration of block was similar between groups. The prolonged block with rocuronium in the Postpartum patients can be explained by relative drug overdose when dose calculation is based on their temporarily increased body weight. IMPLICATIONS: Neuromuscular block is prolonged in the postpartum period after standard doses of rocuronium. Drug administration according to lean body mass will produce a more consistent duration of block.

Adult↗