Cerebral blood flow and cerebral blood flow velocity during angiotensin-induced arterial hypertension in dogs

Pressure-passive perfusion beyond the upper limit of cerebral blood flow (CBF) autoregulation may be deleterious in patients with intracranial pathology. Therefore, monitoring of changes in CBF would be of clinical relevance in situations where clinical evaluation of adequate cerebral perfusion is impossible. Noninvasive monitoring of cerebral blood flow velocity using transcranial Doppler sonography (TCD) may reflect relative changes in CBF. This study correlates the effects of angiotensininduced arterial hypertension on CBF and cerebral blood flow velocity in dogs. Heart rate (HR) was recorded using standard ECG. Catheters were placed in both femoral arteries and veins for measurements of mean arterial blood pressure (MAP), blood sampling and drug administration. A left ventricular catheter was placed for injection of microspheres. Cerebral blood flow velocity was measured in the basilar artery through a cranial window using a pulsed 8 MHz transcranial Doppler ultrasound system. CBF was measured using colour-labelled microspheres. Intracranial pressure (ICP) was measured using an epidural probe. Arterial blood gases, arterial pH and body temperature were maintained constant over time. Two baseline measures of HR, MAP, CBF, cerebral blood flow velocity and ICP were made in all dogs (n = 10) using etomidate infusion (1.5 mg · kg^?1 · hr^?1) and 70% N₂O in O₂ as background anaesthesia. Following baseline measurements, a bolus of 1.25 mg angiotensin was injected iv and all variables were recorded five minutes after the injection. Mean arterial blood pressure was increased by 76%. Heart rate and ICP did not change. Changes in MAP were associated with increases in cortical CBF (78%), brainstem CBF (87%) and cerebellum CBF(64%). Systolic flow velocity increased by 27% and Vmean increased by 31% during hypertension (P < 0.05). Relative changes in CBF and blood flow velocity were correlated (CBF cortex — Vsyst: r = 0.94, CBF cortex — Vmean: r = 0.77; P < 0.001; CBF brainstem — Vsyst: r = 0.82, CBF brainstem — Vmean: r = 0.69; P < 0.05). Our results show that increases in arterial blood pressure beyond the upper limit of cerebral autoregulation increase CBF in dogs during etomidate and N₂O anaesthesia. The changes in CBF are correlated with increases in basilar artery blood flow velocity. These data suggest that TCD indicates the upper limit of the cerebral autoregulatory response during arterial hypertension. However, the amount of CBF change may be underestimated with the TCD technique.     

The intubating laryngeal mask airway after induction of general anesthesia versus awake fiberoptic intubation in patients with difficult airways

We performed the current study to compare tracheal intubation (TI) using awake fiberoptic intubation (AFOI) and TI using the intubating laryngeal mask airway (ILMA) in patients with difficult airway. Our hypothesis was that patients with difficult airways could be safely intubated after induction of anesthesia using the ILMA. After ethics approval and informed consent, 38 patients who were identified to have difficult airways were randomly assigned to AFOI or TI using the ILMA. Patients in the AFOI group had the usual sedation and airway topicalization. Patients in the ILMA group were induced with propofol for ILMA insertion and succinylcholine for TI. The first TI attempt was done blindly via the ILMA and all subsequent attempts were performed with fiberoptic guidance. All patients in the ILMA group were successfully ventilated. Successful TI was achieved in all patients in both groups. However, in 10% of the patients in the ILMA group, TI was achieved by a second anesthesiologist who was more experienced with the use of the ILMA. In a postoperative questionnaire, patients in the ILMA group were more satisfied with their method of TI (P < 0.01). The ILMA is a useful device in the management of patients with difficult airways and may be a valuable alternative to AFOI when AFOI is contraindicated or in the patient with the unanticipated difficult airway. IMPLICATIONS: The intubating laryngeal mask airway is a useful device in the management of patients with difficult airways and may be a valuable alternative to awake fiberoptic intubation (AFOI) when AFOI is contraindicated or in the patient with the unanticipated difficult airway.     

Cerebral blood flow velocity during repeatedly induced ventricular fibrillation.

STUDY OBJECTIVE: To investigate the effect of induced ventricular fibrillation and defibrillation on cerebral blood flow (CBF) was investigated using a transcranial Doppler. DESIGN: Prospective clinical study. SETTING: University hospital. PATIENTS: 12 ASA physical status III and IV patients who underwent implantable cardioverter defibrillator placement during general anesthesia. INTERVENTIONS: Cerebral blood flow velocity was measured repeatedly during induced ventricular fibrillation and subsequent defibrillation. MEASUREMENTS AND MAIN RESULTS: The mean flow velocity in the middle cerebral artery was measured using a transcranial Doppler. The mean flow velocities decreased significantly immediately after ventricular fibrillation was induced, but they returned to preventricular fibrillation levels immediately after successful defibrillation. Repeatedly induced ventricular fibrillations have no cumulative detrimental effect on the CBF velocity. CONCLUSIONS: Repetitively induced ventricular fibrillation and defibrillation during the insertion of implantable cardioverter defibrillator did not show any detrimental changes in CBF. Transcranial Doppler may be a more sensitive device than other currently available cerebral monitors to detect changes in cerebral circulation during a brief episode of ventricular fibrillation and defibrillation.     

“微创”插管技术在甲状旁腺切除术全身麻醉诱导阶段的应用

目的 观察“微创”插管技术在甲状旁腺切除术气管插管全身麻醉诱导阶段的应用效果. 方法 选取拟在全身麻醉下行甲状旁腺切除术的患者100例,ASA分级Ⅲ、Ⅳ级,按随机数字表法分为微创组(L组)和对照组(C组),每组50例.麻醉诱导均采用咪达唑仑、依托咪酯、舒芬太尼、顺式阿曲库铵.L组于诱导后2.5 min用可视喉镜暴露声门,借助一次性喉麻管向喉头周围及声门内喷射2％利多卡因3 ml,继续面罩加压给氧2 min后插入7.0号超滑镇痛气管导管;C组在诱导后4.5 min应用普通喉镜插入7.5号普通气管导管.麻醉维持均采用持续泵入瑞芬太尼、丙泊酚,间断静脉注射顺式阿曲库铵.记录麻醉诱导前(T0)、插管前(T1)、插管时(T2)、插管后1 min(T3)、插管后3 min(T4)时的SBP、DBP、HR、SpO2,并分别于T1和插管后10 min(T5)抽取静脉血检测促肾上腺皮质激素(adrenocortical hormone,ACTH)和皮质醇(corticosteroid,CORT)含量(因CORT有日分泌节律,参与试验手术均安排上午). 结果 围插管期C组SBP、DBP、HR较L组明显升高,差异有统计学意义(P＜0.05),C组血中ACTH和CORT含量均较L组明显增加,差异有统计学意义(P＜0.05). 结论 “微创”插管技术可有效减少甲状旁腺切除术气管插管时心血管反应的发生,减少血液中应激激素释放,增加麻醉安全性.     

Cerebral and spinal cord blood flow in awake and fentanyl-N2O anesthetized rats: evidence for preservation of blood flow autoregulation during anesthesia

Blood flow responses to alterations in mean arterial blood pressure (MABP) were measured in the cerebral cortex, subcortex, midbrain, and spinal cord of awake rats. Data were compared with those of rats anesthetized with an i.v. fentanyl infusion and inspired nitrous oxide (N2O). Regional cerebral blood flow was measured using radioactive microspheres in the following blood pressure ranges: (a) <40 mm Hg; (b) 40-60; (c) 60-80; (d) 80-100; (e) 100-120; (f) 120-140; (g) 140-160; and (h) >160. Blood pressure was increased with phenylephrine or decreased with trimethaphan combined with blood withdrawal. Cerebral blood flow was not measured when MABP was less than 60 mm Hg in awake rats. Autoregulation was seen in all brain areas between 60 and 140 mm Hg in both treatment groups. Although regional cerebral blood flow was not different between the two treatment groups, PaCO2 was 2-4 mm Hg lower in awake rats. This suggests that PaCO2-corrected cerebral blood flow may be 10-20% lower with fentanyl-N2O anesthesia.     

Cerebral blood flow during cardiopulmonary bypass in man: effect of arterial filtration.

Cerebral blood flow was recorded in 39 patients undergoing cardiac surgery by intraarterial injection of xenon 133. There were three subgroups of patients: 10 patients had a 20 micron arterial filter (Johnson) and 11 a 40 micron filter (Pall), and 18 had no arterial filtration. All patients had a 40 micron (Pall) filter in the coronary suction line. Significant changes in cerebral blood flow occurred during extracorporeal circulation (p less than 0.0001). For all patients cerebral blood flow increased from a resting prebypass level of 30 to 46 and 57 ml/100 g a minute during initial and stable hypothermic extracorporeal circulation respectively. Both measurements were obtained at 26 degrees C and the recordings were made on average 12 and 55 minutes after the extracorporeal circulation was started. During rewarming cerebral blood flow increased to 64, 53, 41, and 36 ml/g a minute at 31 degrees, 33 degrees, 35 degrees, and 37 degrees C respectively, and when measured four and 16 minutes on average after bypass it was 44 and 41 ml/100 g a minute. This general brain hyperperfusion was noticed in all patients with a high enough mean blood pressure to produce hyperaemia. Interposing 20 and 40 micron arterial filters reduced cerebral blood flow but did not prevent this hyperaemia. The cerebral autoregulation, which maintains a constant cerebral blood flow within wide limits of perfusion pressures, was not affected by arterial filtration. The lower limit of blood pressure at which a further reduction in blood pressure was followed by a reduction in cerebral blood flow was around 60 mm Hg in all three groups.     

Cerebral blood volume and blood flow at varying arterial carbon dioxide tension levels in rabbits during propofol anesthesia

There are little data on the effects of propofol on cerebral blood volume (CBV). We studied the effects of changes in PaCO(2) on CBV and cerebral blood flow (CBF) during propofol anesthesia in eight New Zealand white rabbits. We also investigated the effects of propofol over time on CBV and CBF during normocapnia (control group). At normocapnia, the mean (+/- SD) CBV and CBF values were 2.41 +/- 0.68 mL/100 g and 56 +/- 28 mL/100 g/min, respectively,. When PaCO(2) was reduced from 41 to 27 mm Hg, no significant change in either CBV or CBF was observed (P > 0.10). However, increasing PaCO(2) from 41 to 58 mm Hg resulted in a 30% increase in CBV (3.08 +/- 0.86 mL/100 g, P < 0.05) and a 91% increase in CBF (97 +/- 39 mL/100 g/min, P < 0.01). In the control group, there were no significant changes in CBV and CBF (P > 0.10) during 2 h of propofol anesthesia. These results indicate that, during propofol anesthesia, cerebrovascular reactivity of blood flow and blood volume is maintained during hypercapnia but is markedly diminished during hypocapnia. Implications: During propofol anesthesia in rabbits with normal brains, a reduction in the arterial carbon dioxide level may not always be accompanied by a reduction in brain blood flow and blood volume.     

Middle cerebral artery blood flow velocity during beach chair position for shoulder surgery under general anesthesia

ObjectivesThe goal of the present study was to examine changes of middle cerebral artery (V_MCA) blood flow velocity in patients scheduled for shoulder surgery in beach chair position.DesignProspective observational study.SettingOperating room, shoulder surgery.PatientsFifty-three consecutive patients scheduled for shoulder surgery in beach chair position.InterventionsTranscranial Doppler performed after induction of general anesthesia (baseline), after beach chair positioning (BC1), during surgery 20 minutes (BC2), and after back to supine position before stopping anesthesia (supine).MeasurementsMean arterial pressure (MAP), end-tidal CO₂, and volatile anesthetic concentration and V_MCA were recorded at baseline, BC1, BC2, and supine. Postoperative neurologic complications were searched.Main ResultsBeach chair position induced decrease in MAP (baseline: 73 ± 10 mm Hg vs lower MAP recorded: 61 ± 10 mm Hg; P < .0001) requiring vasopressors and fluid challenge in 44 patients (83%). There was a significant decrease in V_MCA after beach chair positioning (BC1: 33 ± 10 cm/s vs baseline: 39 ± 14 cm/s; P = .001). The V_MCA at baseline (39 ± 2 cm/s), BC2 (35 ± 14 cm/s), and supine (39 ± 14 cm/s) were not different. The minimal alveolar concentration of volatile anesthetics, end-tidal CO₂, SpO₂, and MAP were not different at baseline, BC1, BC2, and supine.ConclusionBeach chair position resulted in transient decrease in MAP requiring fluid challenge and vasopressors and a moderate decrease in V_MCA.     

Complications during rapid sequence induction of general anesthesia in children: a benchmark study

Objectives: Determine incidence of complications such as difficult or failed intubation, hypoxemia, hypotension, and bradycardia in children undergoing rapid sequence intubation (RSI) in a pediatric anesthesia department in a tertiary care children’s hospital. Aim: To establish a benchmark to be used by other institutions and nonanesthesiologists performing RSI in children. Background: RSI is being increasingly performed in the nonoperating room setting by nonanesthesiologists. No published studies exist to establish a benchmark of intubation success or failure and complications in this patient population. Methods/Materials: Retrospective cohort analysis of children aged 3–12 undergoing RSI from 2001 to 2006. Results: One thousand seventy children underwent RSI from 2001 to 2006. Twenty (1.9%) developed moderate hypoxemia (SpO₂ 80–89%), 18 (1.7%) demonstrated severe hypoxemia (SpO₂ < 80%), 5 (0.5%) developed bradycardia (heart rate <60), and 8 (0.8%) developed hypotension (systolic blood pressure <70 mmHg). One patient had emesis of gastric contents but no evidence of pulmonary aspiration or hypoxemia. Eighteen (1.7%) children were noted to be difficult to intubate and required more than one intubation attempt. All were eventually intubated without significant complications. Patients between 10 and 19 kg had a higher incidence of severe hypoxemia when compared with older children (P < 0.001). There was no association between choice of muscle relaxant and any complication. Conclusions: In our cohort of 1070 children who underwent RSI, difficult intubation was encountered in 1.7% and transient oxyhemoglobin desaturation occurred in 3.6%. Severe hypoxemia was more likely in children <20 kg. There were no children who could not be intubated, and there were no long‐term or permanent complications.     

Cerebral blood flow velocity during isovolemic hemodilution and subsequent autologous blood retransfusion

PURPOSE: To quantify the influence of hematocrit on cerebral blood flow velocity (CBFV) in healthy volunteers undergoing acute isovolemic hemodilution (HD) with hydroxyethyl starch 10% (HES) and subsequent autologous whole blood retransfusion (RT). METHODS: In 11 volunteers 20 ml x kg(-1) blood was withdrawn over 30 min and simultaneously replaced with HES 10%. Thirty min later, RT was started at a constant rate over 30 min. Recorded parameters included: CBFV pulsatility-index (PI) and resistance-index (RI) of the middle cerebral artery (MCA). Blood pressure (BP), heart rate (HR), hemoglobin (Hb), hematocrit (Hc) peripheral O2-saturation (SpO2), P(ET)CO2, arterial oxygen content (CaO2) and cerebral arterial O2-transport (C(E)-DO2= CaO2 x Vm-MCA) were monitored. RESULTS: An average of 1570 total blood was withdrawn which resulted in a decrease in Hb from 14.5 mg x dl(-1) to 10.3 mg x dl(-1); Hc (and CaO2) decreased from 41.8% (19.8 ml x dl(-1)) to 29.6% (14.2 ml x dl(-1); P < 0.01). Vm-MCA increased from 61.2 cm x sec(-1) to 77.3 cm x sec(-1) (P < 0.01). Following RT, Vm-MCA decreased again, but remained higher than baseline (P < 0.01). PI decreased by 13% following RT (P < 0.05). There were no changes in RI, HR, BP SpO2 and P(ET)CO2. Regression lines could be fitted between Hc and Vm-MCA, Vm-MCA and CaO2, and between Hc and C(E)DO2. CONCLUSIONS: Transcranial Doppler changes in blood flow velocities correlated with the simultaneously recorded systemic Hc and CaO2 values. We found a 2% increase in CBFV for each 1% decrease in Hc and CaO2.     

Spinal cord blood flow change by intravenous midazolam during isoflurane anesthesia

We investigated the effects of IV midazolam on spinal cord blood flow in 32 cats anesthetized with isoflurane. Cats underwent laminectomy, and the lumbar spinal cord was exposed. A platinum electrode was inserted stereotaxically into the spinal cord to a depth of 1 mm-2 mm lateral to midline at L2. Arterial blood pressure, heart rate, and spinal cord blood flow (using the hydrogen clearance method) were measured before and at 5, 15, 30, 60, 90, and 120 min after an IV bolus of midazolam (0, 1, 2, or 4 mg/kg in saline 5 mL; n = 8 cats per dose). Arterial blood pressure was not affected by 0 or 1 mg/kg of midazolam but was decreased for 30 min by 2 or 4 mg/kg of midazolam. Heart rate did not change. Spinal cord blood flow was increased for 90 min by midazolam 1 mg/kg and for 15 min by midazolam 2 mg/kg but was not changed by midazolam 4 mg/kg. In conclusion, 1 mg/kg of midazolam increased feline spinal cord blood flow without changing arterial blood pressure. In contrast, a larger dose of midazolam (4 mg/kg) did not change spinal cord blood flow but substantially decreased arterial blood pressure during isoflurane anesthesia.     

Cerebral blood flow measurements during blood pressure control with intravenous labetalol following craniotomy

Cerebral blood flow measurements using a thermal diffusion technique were made in conjunction with an extensive cardiovascular evaluation, during and after administration of intravenous labetalol given for blood pressure control in craniotomy patients. Eighteen patients, ages 30-65 years, ASAII and III, scheduled for elective craniotomy, became hypertensive during emergence and recovery from a pentothal/fentanyl/vecuronium/N2O/isoflurane general anesthesia. Labetalol was administered in a stepwise manner every 10 minutes during an average period of 1 h. After this titration period, an 8-h maintenance period followed. During titration and maintenance periods, comprehensive systemic hemodynamic parameters were collected through intra-arterial and flow-directed pulmonary artery catheters. Cerebral cortical blood flow (CBF) was continuously recorded using a thermal diffusion cortical blood flow probe (Saber System). Data were analyzed using variance F tests to evaluate changes from baseline over time. Labetalol controlled postoperative hypertension in all cases with a total dose range of 0.4-6.8 mg/kg. During titration, statistically significant decreases in blood pressure were obtained, accompanied by a small decrease in systemic vascular resistance (SVR) and slight increase in cardiac index (CI). Heart rate decreased in a manner directly proportional to the dose of labetalol administered. In the maintenance period, further decreases in blood pressure and heart rate were observed, with significant decreases in central venous pressure, pulmonary capillary wedge pressure, and SVR and an increase in CI. All values remained within normal ranges and no adverse effects were observed. CBF decreased slightly during the study period, although not significantly (from 67 +/- 8 to 57 +/- 7 ml 100 g min). Blood pressure control achieved with labetalol in postoperative neurosurgical patients seems to be the result of mild alpha-adrenoceptor blocking effects (i.e., reduced SVR) and beta-adrenoceptor blocking effects (i.e., reduced heart rate) at higher doses. The 6-8 h duration of effect of labetalol was enough to control postoperative hypertension in all patients with no additional therapy. Compared with alternative drugs available for blood pressure control in similar clinical conditions, labetalol appears to be reliable, safe, and effective, by providing a lasting effect with no evidence of rebound hypertension, increased CBF, or cardiac dysfunction.     

卡托普利对全麻诱导气管内插管时循环反应的作用

目的 探讨卡托普利静注预防全麻窥喉插管(LTI)循环副反应的效果及作用机制。方法 插管全麻30例患者随机分为两组,试验组(麻醉诱导前10min静注卡托普利0.30～0.35mg·kg~(-1)和对照组各15例。两组均以氟哌利多、芬太尼、硫喷妥钠及氯化琥珀胆碱诱导插管。于LTI前后不同时点测定收缩压(SP)、舒张压(DP)、心率(HR)、心率收缩压乘积(RPP)及血浆血管紧张素Ⅰ(AⅠ)、血管紧张素Ⅱ(AⅡ)、醛固酮(ALD)、去甲肾上腺素(NE)、肾上腺素(E)、心钠素(ANP)、血栓素B_2(TXB_2)的水平。结果 ①试验组LTI期间SP、DP、HR及RPP比较平稳;而对照组于插管即刻及其后1～1.5、3min上述指标明显升高(P<0.05或0.01)。②试验组插管即刻及其后1～1.5minAⅠ明显升高(P<001),AⅡ、ALD显著降低(P<0.05或0.01),NE、E、ANP插管期间及TXB_2插管后无明显变化;而对照组AⅠ、AⅡ及ALD各时点差异无显著性,NE、E插管即刻及其后1～1.5min及ANP、TXB_2插管即刻及其后1～1.5、5min明显升高(P<0.01)。且各内分泌指标组间差异亦显著(P<0.05或0.01)。结论 卡托普利0.30～0.35mg·kg~(-1)麻醉诱导前10min静注,可削弱LTI期间交感神经活动升高,能有效地预防LTI循环副反应。     

Sinus arrest during laryngoscopy for induction of general anesthesia with intravenous fentanyl and propofol

A 43-year-old woman with Plummer's disease underwent left thyroid lobectomy without premedication using ambulatory electrocardiogram monitoring under general anesthesia. Anesthesia was induced with an intravenous bolus of fentanyl 100 microg, lidocaine 40 mg, propofol 80 mg and vecuronium 7 mg. As she moved 5 min after induction of anesthesia, fentanyl 100 microg and propofol 30 mg were administered additionally. After positive pressure ventilation by mask for 8 min, heart rate decreased from 71 beats x min(-1) to 48 beats x min(-1), and laryngoscopy was performed. When the tip of the laryngoscope was pressed on the base of the tongue and on lifting the epiglottis, the electrocardiogram showed RR interval prolongation and gradually going to sinus arrest. The laryngoscope was removed immediately and mask ventilation was performed. The heart beat resumed at 5.5 sec after sinus arrest. Atropine 0.5 mg was given intravenously and heart rate increased to 50 beats x min(-1). Additionally atropine 0.25 mg increased heart rate to 70 beats x min(-1). The second laryngoscopy was performed uneventfully. We consider this phenomenon as a result of vagovagal reflex. Fentanyl and propofol, by reducing sympathetic tone to a greater extent than parasympathetic tone, decrease blood pressure and heart rate, and predispose to a parasympathetic response for noxious stimulation. This case indicates that intravenous injection of atropine must be immediately used for bradycardia during laryngoscopy for induction of general anesthesia with fentanyl and propofol.     

Catecholamine crisis during induction of general anesthesia

Catecholamine crises associated with pheochromocytoma may cause life-threatening cardiovascular conditions. We report the case of a 75-year-old male who developed a hypertensive crisis during induction of general anesthesia for elective resection of a cervical neuroma due to an undiagnosed pheochromocytoma. Hemodynamic instability occurred immediately after the injection of fentanyl, propofol and rocuronium, prior to laryngoscopy and in the absence of any manipulation of the abdomen. In this case report, we present the management of this incident and discuss the underlying pathophysiology triggering a catecholamine crisis.