Effect of mild hypothermia on nicorandil-induced vasodilation of pial arterioles in cats

OBJECTIVE

Nicorandil is characterized as hybrid between nitrates and potassium channel activators. Recent evidence suggested that mild hypothermia may alter cerebral vasodilation induced by a nitrate agent and potassium channel opener. However, the effect of mild hypothermia on nicorandil-induced vasodilation is not known. The present study was conducted to investigate whether mild hypothermia could alter nicorandil-induced cerebral vasodilation. In addition, the effects of mild hypothermia on cerebral vasodilation induced by nitroglycerin, a nitrate agent, and cromakalim, a selective adenosine 5'-triphosphate-sensitive potassium channel opener, were assessed in the same model.

DESIGN

Prospective, randomized, experimental study with repeated measures.

SETTING

Investigational animal laboratory.

SUBJECTS

Twenty-four cats.

INTERVENTIONS

Animals were anesthetized with pentobarbital. The cranial window technique, combined with microscopic video recording, was used to measure small (50-100 microm) and large (100-200 microm) pial arteriolar diameter in an experiment. Animals were assigned randomly to either a normothermic (37 degrees C) or a hypothermic (33 degrees C) group. Nicorandil, nitroglycerin, or cromakalim at concentrations of 10(-8), 10(-6), or 10(-4) mol/L was applied topically in the cranial window, and the diameter of pial arterioles was measured.

MEASUREMENTS AND MAIN RESULTS

Topical administration of nicorandil, nitroglycerin, and cromakalim significantly dilated both small and large pial arterioles in a dose-dependent manner during normothermia. Nicorandil-induced vasodilation of either large or small pial arterioles was not affected by hypothermia. However, hypothermia significantly attenuated nitroglycerine-induced vasodilation in both large and small pial arterioles and enhanced cromakalim-induced vasodilation in both large and small pial arterioles.

CONCLUSIONS

Nicorandil-induced vasodilation of cerebral pial arterioles was not affected by mild hypothermia. By contrast, mild hypothermia significantly attenuated nitroglycerin-induced vasodilation and enhanced cromakalim-induced vasodilation.

[A case of awareness during propofol anesthesia using bispectral index as an indicator of hypnotic effect]

A 77-year old, woman weighing 44 kg with mild liver dysfunction underwent lower abdominal surgery. Anesthesia was induced with propofol 60 mg and fentanyl 0.1 mg. Tracheal intubation was facilitated with vecuronium 8 mg, and the lungs were ventilated with 33% oxygen in air. The bispectral index (BIS) was continuously monitored. Anesthesia was maintained with propofol infusion and analgesia was provided by thoracic epidural infusion of lidocaine 1.5%. The infusion rate of propofol was altered to maintain the BIS value between 40 and 50. The patient was hemodynamically stable with propofol 1.5 mg.kg-1.hr-1 and the BIS value was maintained about 40 during the operation. Near the end of the operation the patient moved suddenly. Suspecting inadequate anesthesia, a total of 40 mg of propofol i.v. and 5 ml of the epidural infusion were given. Immediately before the movement the BIS value was about 40. The operation was completed 30 min later. On discharge from the operating room the patient declared that she had been awake. She had heard voices and felt the surgeon working, but had suffered no pain. The BIS is a useful indicator for hypnotic effect, but this case demonstrates that awareness might occur even when BIS value indicates adequate hypnotic state.

[Propofol Concentration during Maintenance of and Emergence from Propofol/Epidural Anesthesia: Comparison between Younger and Elderly Patient]

To investigate the influence of patient age on the sensitivity to propofol, we measured blood propofol concentrations in ten elderly (over 70 years of age) and ten younger (under 60 years of age) patients undergoing elective abdominal surgery during propofol/epidural anesthesia. Bispectral index (BIS) was continuously recorded for monitoring anesthetic effect, and the infusion rate of propofol was controlled to keep BIS at 50 after the induction of anesthesia with propofol. At steady-state before skin incision, propofol concentrations to maintain BIS at 50 in younger and elderly patients were 4.3 +/- 1.6 micrograms.ml-1 and 3.2 +/- 1.3 micrograms.ml-1, respectively, and there was no significant difference. Mean blood propofol concentrations were 4.0 +/- 1.5 micrograms.ml-1 for the younger group and 3.2 +/- 1.7 micrograms.ml-1 for the elderly group at the end of surgery immediately before discontinuation of propofol, and they were 1.9 +/- 0.7 micrograms.ml-1 (BIS = 86 +/- 7) for the younger group and 1.5 +/- 0.8 micrograms.ml-1 (BIS = 84 +/- 3) for the elderly group at the time of eye opening with no significant difference. We found appreciable individual variations in the propofol concentrations both in younger and elderly patients in this study.

[Relationship between minimum alveolar concentration and electroencephalographic bispectral index as well as spectral edge frequency 95 during isoflurane/epidural or sevoflurane/epidural anesthesia]

To investigate the relationship between minimum alveolar concentration (MAC) and electroencephalographic variables, we measured the bispectral index (BIS) and the spectral edge frequency 95 (SEF 95) in 17 patients undergoing elective surgery during isoflurane/epidural (n = 8) or sevoflurane/epidural (n = 9) anesthesia. Patients received 2.0 MAC end-tidal concentrations of isoflurane or sevoflurane, and the BIS and the SEF 95 were recorded after 15 min of an unchanged end-tidal concentration. The concentration of the inhalational agent was decreased to 1.2 MAC, and measurements were repeated again. During isoflurane anesthesia, the BIS increased significantly (3.6 +/- 3.9 at 2.0 MAC, 43.5 +/- 9.2 at 1.2 MAC [mean +/- SD]). In contrast, the BIS did not change significantly during sevoflurane anesthesia (35.3 +/- 8.4 at 2.0 MAC, 42.8 +/- 6.1 at 1.2 MAC). There were significant differences in the BIS and the SEF 95 at 2.0 MAC between isoflurane and sevoflurane groups. In contrast, the BIS and the SEF 95 showed no difference at 1.2 MAC between the groups. These findings suggest that different inhalational anesthetics may have different effects on the BIS and the SEF 95.

[Ketamine lollipop for pediatric premedication]

Lollipop containing ketamine (50 mg) was evaluated for the premedication of pediatric patients. The subject of this study were 12 children aged from 1 year 7 months to 6 years. They received the lollipop and showed relatively good emotional state and no typical side effects. These results suggest good possibility of ketamine lollipop as the premedication for pediatric patients.

Hypothermia attenuates the vasodilatory response of pial arterioles to hemorrhagic hypotension in the cat

We investigated the effect of hypothermia on the vasodilatory response of pial arterioles to hemorrhagic hypotension. The cranial window technique was combined with microscopic video recording in an experiment involving 20 cats anesthetized with pentobarbital. The animals were randomly assigned to either a normothermic or a hypothermic group (32 degrees C). Mean arterial pressure (MAP) was reduced in stepwise increments of 10 mm Hg (from 100 to 50 mm Hg) by blood withdrawal. The diameter of small (50-100 microm) and large (100-200 microm) pial arterioles was measured. In the normothermic group (n = 9), small and large arterioles dilated at a MAP of 60 and 50 mm Hg, and at a MAP of 70, 60, and 50 mm Hg, respectively, compared with baseline values obtained at a MAP of 100 mm Hg. In contrast, in the hypothermic group (n = 11), vasodilation of either small or large arterioles was absent. The percentage diameter of small and large arterioles (percentage of control) was significantly lower at a MAP of 70, 60, and 50 mm Hg in the hypothermic group than the normothermic group. Our in vivo study demonstrates that hypothermia impairs autoregulatory vasodilation of pial arterioles in response to hemorrhagic hypotension.

IMPLICATIONS

Deliberate mild hypothermia has been proposed as a means of providing cerebral protection during neurosurgical procedures. Our results suggest that cerebral blood flow autoregulation in response to hemorrhagic hypotension may be impaired during hypothermic conditions, indicating the importance of maintaining perfusion pressure during hypothermic therapy to prevent cerebral ischemia.

[Relationship between changes in estimated and measured blood concentrations of propofol and serum albumin concentration during propofol anesthesia: effects of intraoperative bleeding (a case report)]

We investigated the effect of intraoperative bleeding on the changes in estimated and measured blood concentrations of propofol, and the relationship between anesthetic effect of propofol and serum albumin concentration in a patient undergoing prostatectomy during propofol/epidural anesthesia. The rate of propofol infusion was titrated to keep the BIS value about 50. The estimated blood concentration of propofol calculated by ConGrase, a program for on-line simulation of blood propofol concentration, was monitored during anesthesia. Blood samples were obtained at nine points during surgery and the blood concentrations of propofol and albumin were measured postoperatively. When the amount of bleeding reached about 2000 mg, the difference between estimated and measured blood concentrations of propofol did not increase. As the serum albumin concentration decreased, the concentration of propofol to keep bispectral index about 50 decreased. This study suggests that the change in serum albumin concentration following intraoperative bleeding is an important factor in the anesthetic effect of propofol.

[The influence of ketamine on the bispectral index, the spectral edge frequency 90 and the frequency bands power during propofol anesthesia]

To investigate the influence of ketamine on the bispectral index (BIS), the spectral edge frequency 90 (SEF 90) and relative power in four frequency bands (beta, alpha, theta, sigma), we studied 13 patients (ASA I-II) undergoing elective surgery. In the first study (n = 7), we administered ketamine (1.0 mg.kg-1, bolus, i.v.) during propofol anesthesia. Thirty minutes after the administration, BIS, SEF 90 and relative beta power increased significantly. In the second study (n = 6), bolus administration of ketamine (0.5 mg.kg-1 i.v.) followed by continuous infusion was started during propofol anesthesia. The infusion rate of ketamine was 0.5 mg.kg-1.h-1 for 30 minutes and then increased to 1.0 mg.kg-1.h-1. BIS, SEF 90 and relative beta power increased significantly after ketamine administration, but the parameters did not change in dose-related manner. We conclude that further investigation is necessary to use electroencephalographic parameters as an indicator of the anesthesia depth during propofol/ketamine anesthesia.

Mild hypothermia can attenuate nitroglycerin-induced vasodilation of pial arterioles in the cat

The purpose of the present study was to investigate the effect of mild hypothermia on nitroglycerin-induced vasodilation of cerebral vessels. The cranial window technique, combined with microscopic video recording, was used in an experiment involving 26 cats anesthetized with isoflurane. Animals were randomly assigned to either a normothermic or a mildly hypothermic group (33 degrees C). We administered three different concentrations of nitroglycerin (10[-6], 10[-5], 10[-4] M) under the window and measured the diameter of small (< 100 microm) and large (100-200 microm) pial arterioles. In the normothermic group (n = 13), nitroglycerin produced a significant dilation of both small and large arterioles in a dose-dependent manner. In the hypothermic group (n = 13), a significant dilation of arterioles was observed only after topical application of nitroglycerin at a concentration of 10(-4) M. The percent increase in diameter of small and large arterioles was less in the hypothermic group than the normothermic group. Our in vivo study demonstrates that topically applied nitroglycerin produces a dose-dependent dilation of pial arterioles in normothermic cats anesthetized with isoflurane, but the reduction of temperature to 33 degrees C significantly attenuates nitroglycerin-induced vasodilation of pial arterioles.

IMPLICATIONS

Although nitroglycerin may be used in hypothermic patients, the effect of mild hypothermia on nitroglycerin-induced vasodilation of cerebral vessels is unknown. In this study, we investigated the effects of nitroglycerin on pial arteriolar diameter in normothermic and hyperthermic cats. Hypothermia was found to attenuate nitroglycerin-induced vasodilation.

Postoperative neurological deterioration following the revascularization surgery in children with moyamoya disease

We describe four children with moyamoya disease who developed neurologic deterioration following revascularization surgery. In all cases, anesthesia was smoothly induced and the intraoperative course was uneventful. Emergence from anesthesia was prompt and no new neurological deficit was observed. However, the children suffered strokes on 2, 4, 5, and 10 days, postoperatively, respectively. Dehydration and crying were thought to be closely associated with the stroke in each case. This report suggests that attention should be paid during entire the perioperative period to avoid stroke in patients with moyamoya disease.

Risk factors for neurologic deterioration after revascularization surgery in patients with moyamoya disease

To investigate the risk factors for postoperative neurological deterioration in patients with moyamoya disease, we retrospectively reviewed the perioperative course of 368 cases of revascularization surgery in 216 patients with this disease. Risk factors anecdotally associated with postoperative ischemic events were analyzed by comparing groups with or without a history of such events on the operative day. Ischemic events were noted in 14 cases (3.8%), 4 of which were defined as strokes and the others as transient ischemic attack (TIA). Postoperative neurological deterioration more often developed in patients who suffered from frequent TIAs, had precipitating factors for TIA, and underwent indirect nonanastomotic revascularization. The authors conclude that the incidence of postoperative ischemic events were related more to the severity of moyamoya disease and the type of surgical procedure than to other factors, including anesthetic management.

IMPLICATIONS

Although preventing stroke is the major concern for patients with moyamoya disease, risk factors for perioperative cerebral ischemia have not been clarified. We retrospectively analyzed the perioperative course in 368 cases with this disease and found that the severity of the disease and type of surgical procedure were major determinants of postoperative cerebral ischemia.

[Anesthetic management of a patient with 21-hydroxylase deficiency]

21-hydroxylase deficiency was described as a fatal disease in infancy manifested by severe adrenal insufficiency with lack of differentiation of the external genitalia in males. Patients are in adrenal insufficiency or receiving long term corticosteroid therapy and are unable to respond normally to surgery or other forms of stress. Therefore, supplementation with corticosteroids and various regimens are required for surgery and anesthetic management. A 3 year 10 months correction of 6] old phenotypic female [correction of male] with 21-hydroxylase deficiency and congenital adrenal hyperplasia was scheduled for critroplasty. Anesthesia was induced with sevoflurane, nitrous oxide and oxygen. After endotracheal intubation, a caudal epidural catheter was placed. At the induction of anesthesia, the patient received a bolus of hydrocortisone 30 mg i.v. followed by a continuous infusion of hydrocortisone. The patient's general condition was good during surgery without any major complications. Caudal epidural anesthesia is considered to be effective for anesthetic management of these patients.

Long-term follow-up study of "epileptic type" moyamoya disease in children

Twenty-three patients with epileptic type moyamoya disease are reviewed among 200 moyamoya disease patients. Ten boys and 13 girls aged 5 months to 12 years were followed over 6 months to 17.3 years. Six had generalized seizure and 17 had focal seizure. Operations were performed within 1 year in eight patients, within 1-3 years in five, and more than 3 years after onset in 10. Nineteen patients improved and suffered no seizure without receiving antiepileptic drugs, but four patients developed true epilepsy and three of these suffered cerebral infarction. Multivariate analyses showed that toddlers aged less than 1 year and mild or severe abnormal computed tomographic (CT) findings correlated with a bad outcome. This study showed that epileptic type moyamoya disease has the same clinical features as transient ischemic attack or infarction type. Age under 1 year and CT abnormalities indicate a poor prognosis and necessity for early reconstructive surgery.

Cortical blood flow response to hypercapnia during anaesthesia in Moyamoya disease

Cortical blood flow (CoBF) was measured continuously by the laser-Doppler method to evaluate the effect of hypercapnia on cortical blood flow during ten surgical procedures in ten young patients (mean +/- SD 9.3 +/- 6.4 yr) with Moyamoya disease. The CoBF was 42.8 +/- 13.4 (ml.100 g-1.min-1) during normocapnia (PaCO2 = 39.0 +/- 2.4 mmHg), and 38.7 +/- 14.4 during hypercapnia (PaCO2 = 47.1 +/- 2.5 mmHg). There was a decrease in CoBF with hypercapnia (P < 0.05) so that the normal CoBF response to hypercapnia was impaired during surgery in the patients with Moyamoya disease. He concluded that patients with Moyamoya disease have a precarious cerebral circulation and hypercapnia may be detrimental to the cortical circulation. This suggests that normocapnia is preferable to hypercapnia in patients with Moyamoya disease during anaesthesia.

[Perioperative monitoring of cerebral circulation in a patient with Takayasu disease]

Transcranial Doppler (TCD) and fiberoptic oximetry for continuous measurement of jugular venous oxygen saturation (SjO2) were used as perioperative monitoring of cerebral circulation in a patient with Takayasu disease who received bilateral aorto-carotid bypass. Following revascularization of the left carotid artery, mean velocity in the middle cerebral artery (MV) increased (lt 300%, rt 200% of control values) and SjO2 also increased. Following revascularization of right carotid artery, MV increased (lt 500%, rt 400% of control values) but SjO2 was unchanged. After bilateral revascularization, high velocity continued for about 10 days, and convulsion with headache occurred. Therefore hyperperfusion syndrome was suspected. By perioperative monitoring of MV and SjO2, it might be possible to evaluate intracranial hemodynamics, necessity of shunt operation as well as bilateral bypass, and postoperative hyperperfusion syndrome.

Effects of nicardipine on cerebral vascular responses to hypocapnia and blood flow velocity in the middle cerebral artery

We noninvasively evaluated the effects of nicardipine on cerebral vascular responses to hypocapnia and blood flow velocity in the middle cerebral artery of 10 patients aged 17-60 (mean +/- SD 46.1 +/- 11.8) years. During fentanyl/diazepam/nitrous oxide anesthesia, mean blood flow velocity in the middle cerebral artery was measured and cerebral vascular reactivity to hypocapnia induced by hyperventilation was assessed before and during the administration of nicardipine. Mean blood flow velocity was measured using transcranial Doppler ultrasonography, and the cerebral vascular reactivity was expressed as the percentage change in mean blood flow velocity per unit change in end-tidal PCO2. During the administration of 5.1 +/- 1.3 micrograms/kg/min nicardipine, which caused a 26% reduction in mean arterial blood pressure, mean blood flow velocity increased significantly from 57.2 +/- 19.2 to 64.2 +/- 21.6 cm/sec (p less than 0.01, paired t test), whereas cerebral vascular reactivity showed no significant change (4.0 +/- 1.2% and 4.9 +/- 2.5%, respectively). In conclusion, during fentanyl/diazepam/nitrous oxide anesthesia in patients, cerebral vascular reactivity to hypocapnia was maintained and nicardipine-induced hypotension resulted in increased middle cerebral artery blood flow velocity with maintenance of carbon dioxide reactivity to hypocapnia.

[Anesthetic management of revascularization for moyamoya disease]

Anesthetic management during 85 STA-MCA anastomoses with or without encephalo-myosynangiosis for 64 patients with Moyamoya disease was evaluated retrospectively. Anesthetic agents included nitrous oxide-NLA (GONLA), nitrous oxide-halothane (GOF), nitrous oxide-enflurane (GOE), and their combinations. Slight hypercarbia (40 mmHg less than PaCO2 less than 50 mmHg) was essential to avoid cerebral ischemia. Several procedures to control heart rate by beta blockade or to control hypertension by nitroglycerin were required, because tachycardia and hypertension interfered with fine surgical procedure. During microsurgery HR of GONLA anesthetized patients was significantly lower. Postoperatively the patients anesthetized by GOE showed significantly lower PaCO2 compared with the GONLA anesthetized patients. So we recommend GONLA for anastomosis in patients with Moyamoya disease.