Circulatory responses to baroreflexes, Valsalva maneuver, coughing, swallowing, and nasal stimulation during acute cardiac sympathectomy by epidural blockade in awake humans

Antiarrhythmic Mechanisms of Epidural Blockade After Myocardial Infarction

BACKGROUND

Thoracic epidural anesthesia (TEA) has been shown to reduce the burden of ventricular tachycardia in small case series of patients with refractory ventricular tachyarrhythmias and cardiomyopathy. However, its electrophysiological and autonomic effects in diseased hearts remain unclear, and its use after myocardial infarction is limited by concerns for potential right ventricular dysfunction.

METHODS

Myocardial infarction was created in Yorkshire pigs (N=22) by left anterior descending coronary artery occlusion. Approximately, six weeks after myocardial infarction, an epidural catheter was placed at the C7-T1 vertebral level for injection of 2% lidocaine. Right and left ventricular hemodynamics were recorded using Millar pressure-conductance catheters, and ventricular activation recovery intervals (ARIs), a surrogate of action potential durations, by a 56-electrode sock and 64-electrode basket catheter. Hemodynamics and ARIs, baroreflex sensitivity and intrinsic cardiac neural activity, and ventricular effective refractory periods and slope of restitution (Smax) were assessed before and after TEA. Ventricular tachyarrhythmia inducibility was assessed by programmed electrical stimulation.

RESULTS

TEA reduced inducibility of ventricular tachyarrhythmias by 70%. TEA did not affect right ventricular-systolic pressure or contractility, although left ventricular-systolic pressure and contractility decreased modestly. Global and regional ventricular ARIs increased, including in scar and border zone regions post-TEA. TEA reduced ARI dispersion specifically in border zone regions. Ventricular effective refractory periods prolonged significantly at critical sites of arrhythmogenesis, and Smax was reduced. Interestingly, TEA significantly improved cardiac vagal function, as measured by both baroreflex sensitivity and intrinsic cardiac neural activity.

CONCLUSIONS

TEA does not compromise right ventricular function in infarcted hearts. Its antiarrhythmic mechanisms are mediated by increases in ventricular effective refractory period and ARIs, decreases in Smax, and reductions in border zone electrophysiological heterogeneities. TEA improves parasympathetic function, which may independently underlie some of its observed antiarrhythmic mechanisms. This study provides novel insights into the antiarrhythmic mechanisms of TEA while highlighting its applicability to the clinical setting.

Effects of Thoracic Epidural Anesthesia on Neuronal Cardiac Regulation and Cardiac Function

Cardiac sympathetic blockade with high-thoracic epidural anesthesia is considered beneficial in patients undergoing major surgery because it offers protection in ischemic heart disease. Major outcome studies have failed to confirm such a benefit, however. In fact, there is growing concern about potential harm associated with the use of thoracic epidural anesthesia in high-risk patients, although underlying mechanisms have not been identified. Since the latest review on this subject, a number of clinical and experimental studies have provided new information on the complex interaction between thoracic epidural anesthesia–induced sympatholysis and cardiovascular control mechanisms. Perhaps these new insights may help identify conditions in which benefits of thoracic epidural anesthesia may not outweigh potential risks. For example, cardiac sympathectomy with high-thoracic epidural anesthesia decreases right ventricular function and attenuates its capacity to cope with increased right ventricular afterload. Although the clinical significance of this pathophysiologic interaction is unknown at present, it identifies a subgroup of patients with established or pending pulmonary hypertension for whom outcome studies are needed. Other new areas of interest include the impact of thoracic epidural anesthesia–induced sympatholysis on cardiovascular control in conditions associated with increased sympathetic tone, surgical stress, and hemodynamic disruption. It was considered appropriate to collect and analyze all recent scientific information on this subject to provide a comprehensive update on the cardiovascular effects of high-thoracic epidural anesthesia and cardiac sympathectomy in healthy and diseased patients.

Cervical epidural analgesia in current anaesthesia practice: systematic review of its clinical utility and rationale, and technical considerations

Cervical epidural analgesia (CEA) is an analgesic technique, potentially useful for surgeries involving the upper body. Despite the inherent technical risks and systemic changes, it has been used for various surgeries. There have been no previously published systematic reviews aimed at assessing its clinical utility. This systematic review was performed to explore the perioperative benefits of CEA. The review was also aimed at identifying the rationale of its use, reported surgical indications and the method of use. We performed a literature search involving PubMed and Embase databases, to identify studies using CEA for surgical indications. Out of 467 potentially relevant articles, 73 articles were selected. Two independent investigators extracted data involving 5 randomized controlled trials, 17 observational comparative trials, and 51 case reports (series). The outcomes studied in most comparative studies were on effects of local anaesthetics and other agents, systemic effects, and feasibility of CEA. In one randomized controlled study, CEA was observed to decrease the resting pain scores after pharyngo-laryngeal surgeries. In a retrospective study, CEA was shown to decrease the cancer recurrence after pharyngeal-hypopharyngeal surgeries. The limited evidence, small studies, and the chosen outcomes do not allow for any specific recommendations based on the relative benefit or harm of CEA. Considering the potential for significant harm, in the face of better alternatives, its use must have a strong rationale mostly supported by unique patient and surgical demands. Future studies must aim to assess analgesic comparator effectiveness for clinically relevant outcomes.

Extraction of response waveforms of heartbeat and blood pressure to swallowing. Using mixed signal processing of time domain and respiratory phase domain

BACKGROUND

Evaluating the accurate responses of the cardiovascular system to external stimuli is important for a deeper understanding of cardiovascular homeostasis. However, the responses should be distorted by the conventional time domain analysis when a frequency of the effect of external stimuli matches that of intrinsic fluctuations.

OBJECTIVES

The purpose of this study is to propose a mixed signal processing of time domain and respiratory phase domain to extract the response waveforms of heartbeat and blood pressure (BP) to external stimuli and to clarify the physiological mechanisms of swallowing effects on the cardiovascular system.

METHODS

Measurements were conducted on 12 healthy humans in the sitting and standing positions, with each subject requested to swallow every 30 s between expiration and inspiration. Waveforms of respiratory sinus arrhythmia (RSA) and respiratory-related BP variations were extracted as functions of the respiratory phase. Then, respiratory effects were subtracted from response waveforms with reference to the respiratory phase in the time domain.

RESULTS

As a result, swallowing induced tachycardia, which peaked within 3 s and recovered within 8 s. Tachycardia was greater in the sitting position than during standing. Furthermore, systolic BP and pulse pressure immediately decreased and diastolic BP increased coincident with the occurrence of tachycardia. Subsequently, systolic BP and pulse pressure recovered faster than the R-R interval.

CONCLUSIONS

We conclude that swallowing-induced tachycardia arises largely from the decrease of vagal activity and the baroreflex would yield fast oscillatory responses in recovery.

Supraventricular arrhythmias after thoracotomy: is there a role for autonomic imbalance?

Supraventricular arrhythmias are common rhythm disturbances following pulmonary surgery. The overall incidence varies between 3.2% and 30% in the literature, while atrial fibrillation is the most common form. These arrhythmias usually have an uneventful clinical course and revert to normal sinus rhythm, usually before patent's discharge from hospital. Their importance lies in the immediate hemodynamic consequences, the potential for systemic embolization and the consequent long-term need for prophylactic drug administration, and the increased cost of hospitalization. Their incidence is probably related to the magnitude of the performed operative procedure, occurring more frequently after pneumonectomy than after lobectomy. Investigators believe that surgical factors (irritation of the atria per se or on the ground of chronic inflammation of aged atria), direct injury to the anatomic structure of the autonomic nervous system in the thoracic cavity, and postthoracotomy pain may contribute independently or in association with each other to the development of these arrhythmias. This review discusses currently available information about the potential mechanisms and risk factors for these rhythm disturbances. The discussion is in particular focused on the role of postoperative pain and its relation to the autonomic imbalance, in an attempt to avoid or minimize discomfort with proper analgesia utilization.

Sympathetic skin responses in adult humans during sequential swallowing

STUDY AIMS

Autonomic changes, especially those of sympathetic skin responses (SSR), during sequential water swallowing (SWS) have not been systematically investigated. This study aims to electrophysiologically examine these autonomic changes (SSR and heart rate) that occur during 50 ml sequential water swallowing from a cup.

MATERIALS AND METHODS

Fifty-eight normal healthy adults were included in the study. Their submental muscle activity, respiratory activity, heart rate changes, and sympathetic skin responses were recorded during 50 ml water swallowing. In addition, we requested subjects to imagine drinking water as they did just before. The same recordings were performed during this imagination period.

RESULTS

SSR appeared at the beginning and at the end of SWS in 52% of subjects. A first sympathetic skin response was evoked at the onset of SWS, and a second one appeared 8.6±1.7 seconds after the first one and at the end of swallowing. Similar double SSRs were also obtained during imagination in most investigated subjects (33 out of 35 of selected subjects in a total group of 58 subjects). Swallowing tachycardia was observed during the SWS-associated apnea period, but not during the imagination period. Heart rate significantly increased during the SWS-associated apnea period.

CONCLUSION

The first SSR that appeared at the onset of swallowing is likely related to arousal. The appearance of a second response is a novel finding, which is probably related to the activity of subtil corticosubcortical networks. While discrete/single swallows can be used to evoke SSRs, SWS is unlikely to be clinically useful in its current form. In contrast, swallowing tachycardia could be a useful tool to examine dysphagic patients.

Cardiovasular changes after placement of a classic endotracheal tube, double-lumen tube, and Laryngeal Mask Airway

STUDY OBJECTIVE

To compare hemodynamic responses, P wave dispersion (Pd), and QT dispersion (QTd) after placement of a classic endotracheal tube (ETT), double-lumen tube (DLT), or Laryngeal Mask Airway (LMA).

DESIGN

Prospective study.

SETTING

Outpatient surgery center.

PATIENTS

75 adult, ASA physical status 1 and 2 patients undergoing cystoscopy and thoracoscopic surgery.

INTERVENTIONS

Patients were randomized to undergo placement of an ETT (Group T; n = 25), DLT (Group D; n = 25), or LMA (Group L; n = 25). Anesthesia was induced by etomidate 0.3 mg/kg and fentanyl 1.0 μg/kg, and maintained with nitrous oxide, oxygen, 2% to 3% sevoflurane, and rocuronium 0.5 mg/kg.

MEASUREMENTS

Mean arterial pressure (MAP) and heart rate (HR) were recorded immediately before intubation and after intubation at one, 3, 5, 10,15, 20, 25, and 30 minutes after intubation/airway insertion.

RESULTS

QT dispersion after tube placement was significantly higher than before tube placement in Group D (P = 0.0001) and Group L (P = 0.03). Mean arterial pressure and HR in Group T were significantly higher than in Group L at the first minute after tube placement (P = 0.02). Heart rate and MAP at baseline were significantly higher than the other measurement times in Groups T and D (P < 0.01).

CONCLUSIONS

The LMA caused no change in Pd, HR, or MAP values during or after airway placement, but caused QTd after airway insertion. The ETT caused a sudden increase at the first minute after tube placement, without any Pd or QTd. In addition, DLT caused QTd without any serious change in hemodynamics.

Systemic hemodynamic effects of sequential pneumatic compression of the lower limbs: a prospective study in healthy volunteers

STUDY OBJECTIVE

To evaluate the effects on systemic hemodynamics of sequential pneumatic compression of the lower limbs in healthy volunteers.

DESIGN

Prospective, self-controlled, volunteer study.

SETTING

University teaching hospital.

PATIENTS

11 healthy volunteers, aged 25 +/- 1.3 years.

INTERVENTIONS AND MEASUREMENTS

After volunteers underwent a 6-hour period of fasting and 15 minutes of rest in the supine position, baseline systemic hemodynamics were assessed using transthoracic electrical bioimpedance. Peripheral venous pressure was measured using a 16-gauge intravenous cannula inserted in the forearm and connected to a pressure monitor. Then sequential pneumatic compression of the lower limbs was activated for a 30-minute period, and systemic hemodynamic measurements were repeated. In each volunteer, measurements were repeated twice in two consecutive days, and average values were calculated for each volunteer.

MAIN RESULTS

After activation of sequential pneumatic compression of the lower limbs, mean arterial blood pressure increased from 90 mmHg (79-107 mmHg) to 95 mmHg (79-129 mmHg) (P = 0.02), whereas heart rate decreased from 79 bpm (51-94 bpm) to 75 bpm (53-90 bpm) (P = 0.02). This was associated with a significant increase in peripheral vascular resistance index (from 545 [440-1066] to 613 [369-1280] dynes s cm(-5) m(-2) [P = 0.013]) and reduction in cardiac index (from 3.4 [2.7- 4.5] to 3.2 [2.5-4.0] L/min per m2 [P = 0.034]).

CONCLUSIONS

The application of sequential pneumatic compression to the lower limbs is associated with minor increases in mean arterial blood pressure, with moderate reduction of cardiac output and heart rate.

The Effects of Cervical and Lumbar Epidural Anesthesia on Heart Rate Variability and Spontaneous Sequence Baroreflex Sensitivity

A high level of neuroaxial block may produce profound bradycardia and hypotension, possibly as a result of an imbalance between sympathetic and parasympathetic control of heart rate. We designed this study to test the hypothesis that cervical epidural anesthesia would increase the high-frequency (HF) component of heart rate variability (HRV) as a result of cardiac sympathectomy, whereas lumbar epidural anesthesia would cause sympathetic predominance. HRV and spontaneous baroreflex (SBR) sensitivity were assessed before and after cervical and lumbar epidural anesthesia by using plain 1.5% lidocaine (median upper/lower sensory block: C3/T8 for cervical and T11/L5 for lumbar) in healthy patients (n = 10 each). Electrocardiogram and noninvasive beat-to-beat arterial blood pressure were monitored. HRV was analyzed by using fast Fourier transformation. Least-square regression analysis relating R-R interval and systolic blood pressure during spontaneous fluctuation was performed to obtain SBR sensitivities. Cervical epidural group patients were significantly older (P < 0.01) and taller (P < 0.01). Cervical epidural anesthesia attenuated HF (0.15-0.4 Hz) and low-frequency (0.04-0.15 Hz) power of HRV with concomitant reductions in up- and down-sequence SBR sensitivities, suggesting decreased vagal modulation of heart rate. Lumbar epidural anesthesia resulted in a significant increase in the low-frequency/HF ratio of HRV and unchanged SBR indices, suggesting sympathetic predominance. HF power correlated well with SBR sensitivities under most of our study conditions. Respiratory rates and Paco(2) were unchanged by either epidural technique. Our results indicate that cervical, but not lumbar, epidural anesthesia depresses phasic and tonic dynamic modulation of the cardiac cycle by the vagal nerve in conscious humans.

Influence of thoracic epidural analgesia on cardiovascular autonomic control after thoracic surgery

BACKGROUND

Thoracic epidural analgesia (TEA) is effective in alleviating pain after major thoracoabdominal surgery and may also reduce postoperative mortality and morbidity. This study investigated cardiovascular autonomic control in patients undergoing elective thoracic surgery and its modulation by continuous TEA.

METHODS

Thirty-eight patients were randomly assigned to receive patient-controlled analgesia (PCA group) or thoracic epidural analgesia (TEA group) with doses of bupivacaine (0.25% during operation, 0.125% after operation) and fentanyl (2 microg ml(-1)). Heart rate variability (HRV), baroreflex function and pressure response to nitroglycerine and phenylephrine were assessed before operation, 4 h after the end of surgery (POD 0) and on the first and second postoperative days (POD 1 and POD 2).

RESULTS

Early after surgery, all HRV variables and baroreflex sensitivities were markedly decreased in both groups. In the TEA group, total HRV and its high-frequency components (HF) increased towards preoperative values at POD 1 and POD 2, whereas the ratio of low to high frequencies (LF/HF) was significantly reduced (mean (SD), -44 (15)% at POD 0, -38 (17)% at POD 1, -37 (18%) at POD 2) and associated with blunting of the postoperative increase in heart rate and blood pressure. In the PCA group, the ratio of LF/HF remained unchanged and the decrements in HRV variables persisted until POD 2. In the two groups, baroreflex sensitivities and pressure responses recovered preoperative values at POD 2.

CONCLUSIONS

In contrast with PCA management, TEA using low concentrations of bupivacaine and fentanyl blunted cardiac sympathetic neural drive, resulting in vagal predominance, while HRV variables were better restored after surgery.

Epidural clonidine suppresses the baroreceptor-sympathetic response depending on isoflurane concentrations in cats

Epidural administration of clonidine induces hypotension and bradycardia secondary to decreased sympathetic nerve activity. In this study, we sought to elucidate the change in baroreflex response caused by epidural clonidine. Thirty-six cats were allocated to six groups (n = 6 each) and were given either thoracic epidural clonidine 4 micro g/kg or lidocaine 2 mg/kg during 0.5, 1.0, or 1.5 minimum alveolar anesthetic concentration (MAC) isoflurane anesthesia. Heart rate (HR), mean arterial blood pressure (MAP), and cardiac sympathetic nerve activity (CSNA) were measured. Depressor and pressor responses were induced by IV nitroprusside 10 micro g/kg and phenylephrine 10 micro g/kg, respectively. Baroreflex was evaluated by the change in both CSNA and HR relative to the peak change in MAP (deltaCSNA/deltaMAP and deltaHR/deltaMAP, respectively). These measurements were performed before and 30 min after epidural drug administration. Epidural clonidine and lidocaine decreased HR, MAP, and CSNA by similar extents. deltaCSNA/deltaMAP and deltaHR/deltaMAP for depressor response were suppressed with epidural lidocaine and clonidine in all groups but the clonidine 0.5 MAC isoflurane group (0.197 +/- 0.053 to 0.063 +/- 0.014 and 0.717 +/- 0.156 to 0.177 +/- 0.038, respectively, by epidural lidocaine [P < 0.05] but 0.221 +/- 0.028 to 0.164 +/- 0.041 and 0.721 +/- 0.177 to 0.945 +/- 0.239, respectively, by epidural clonidine during 0.5 MAC isoflurane). Those for pressor response were suppressed in all groups. We conclude that thoracic epidural clonidine suppresses baroreflex gain during isoflurane anesthesia >1.0 MAC but may offer certain advantages compared with epidural lidocaine during 0.5 MAC isoflurane by virtue of preserving baroreflex sensitivity when inadvertent hypotension occurs.

Changes in blood pressure and muscle sympathetic nerve activity during water drinking in humans

To investigate the possible involvement of the sympathetic nervous system in pressor response during water drinking, muscle sympathetic nerve activity (MSNA), blood pressure (BP), and heart rate (HR) were continuously measured in healthy young volunteers throughout the experiments of a 5-min control, 2 min of drinking 500 ml water, and a 28-min recovery. To avoid the effects of water passing through the oropharyngeal and esophageal regions and/or effects of swallowing, an equal amount of water was directly infused to the stomach through a stomach tube for 2 min. Water drinking caused a transient increase in mean arterial pressure (MAP) and HR immediately after drinking (DeltaMAP, 12.6 +/- 2.1 mmHg; DeltaHR, +19.9 +/- 1.7 beats/min at the peak). An abrupt decrease of MSNA was observed directly during water drinking (Deltaburst rate, -6.9 +/- 1.3 bursts/min; Deltatotal activity, -2,606 +/- 491 U/min), and it increased to the baseline level thereafter. Gastric infusion had little or no effect on MAP, HR, and MSNA. The present study demonstrated that a pressor response during water drinking was associated with the attenuation of MSNA and not generated by gastric infusion of water at the same rate as in this drinking manner. In conclusion, the rapid rise in BP might be caused through stimulations from the oropharyngeal region, swallowing-induced factors, and/or a feedforward mechanism by a central descending signal from the higher brain centers.

The recovery profile of baroreflex control of heart rate after isoflurane or sevoflurane anesthesia in humans

Volatile anesthetics attenuate baroreflex function in a concentration-dependent manner. This study was designed to determine how long full recovery of baroreflex control of heart rate takes after isoflurane or sevoflurane anesthesia in healthy volunteers. We assessed baroreflex sensitivity in 20 subjects randomized to receive either isoflurane or sevoflurane (n = 10 each). After an 8- to 10-h fast and no premedication, mea- surements of R-R intervals obtained from the electrocardiogram (lead II) and systolic blood pressure (SBP) measured through a radial artery catheter were made at conscious baseline and 20, 60, and 120 min after the induction during end-tidal isoflurane 1.3% or sevoflurane 2.0% in air and oxygen, and 20, 60, 120, and 180 min after the emergence from general anesthesia. Baroreflex responses were triggered by bolus IV injection of phenylephrine and nitroprusside to increase and decrease SBP by 15-30 mm Hg, respectively. The linear portions of the baroreflex curves relating R-R intervals and SBP were determined to obtain baroreflex sensitivity. During anesthesia, baroreflex sensitivities of both the pressor and depressor tests were decreased by 50%-60% compared with conscious baseline values in both groups (P <0.05). Pressor test sensitivities returned to the baseline values at 120 min, whereas depressor test sensitivities returned to the baseline values at 60 min, after general anesthesia in both groups. There were no significant differences in baroreflex sensitivities between groups at any interval. Our results indicate that the recovery characteristics of baroreflex sensitivity are similar after isoflurane and sevoflurane anesthesia and that the depressor test sensitivity is restored more rapidly than the pressor test sensitivity after both anesthetic techniques.

IMPLICATIONS

Arterial baroreflex function is an important neural control system for maintaining cardiovascular stability. The authors found that 2 h was required for full recovery of baroreflex function and that recovery characteristics were similar after isoflurane and sevoflurane anesthesia in healthy volunteers not undergoing surgery.

Cardiovascular and pulmonary effects of epidural anaesthesia

Epidural anaesthesia has been used since the early 1900s. Consequently the general characteristics of these procedures have been well defined. More studies have provided a better understanding of the cardiopulmonary changes produced by epidural anaesthesia. The cardiovascular effects observed with epidural anaesthesia are complex and variable, depending on a multitude of factors. The extent of sympathetic denervation, balance of sympathetic and parasympathetic activity, the pharmacological effect of systemically absorbed local anaesthetic agents, inclusion of adrenaline in the anaesthetic solution, the distribution of blood in relation to cardiac filling and cardiovascular function of the patient must be taken into account when considering the circulatory effects of epidural anaesthesia. Individual cardiovascular response to different levels of sympathetic blockade varies widely, depending on the degree of sympathetic tone before the block. Epidural anaesthesia that is restricted to the level of the low thoracic and lumbar region (T5-L4) results in a "peripheral" sympathetic blockade with vascular dilatation in the pelvis and lower limbs. High thoracic epidural anaesthesia, from the first to fifth thoracic, blocks the cardiac afferent and efferent sympathetic fibres with loss of chronotropic and inotropic drive to the myocardium. Thoracic epidural anaesthesia appears to at least partly reverse the diaphragmatic dysfunction that is a major determinant of the decrease in lung volumes observed after upper abdominal surgery. This article summarizes cardiovascular and pulmonary responses to epidural anaesthesia. Details of clinical management are not included in the review.

Complete recovery of consciousness in a patient with decorticate rigidity following cardiac arrest after thoracic epidural injection

A 46-yr-old man with dysaesthesia (burning sensation) following herpes zoster in the left upper chest region was treated with a single thoracic (T2/T3) epidural injection (1.0% lidocaine 3 ml + 0.125% bupivacaine 3 ml) as an outpatient. Twenty minutes after the injection, a nurse noticed the patient to be unconscious with dilated pupils, apnoea and cardiac arrest. Following immediate cardiopulmonary resuscitation, the patient was treated with an i.v. infusion of thiamylal sodium 2-4 mg kg-1 h-1 and his lungs were mechanically ventilated. When the patient developed a characteristic decorticate posture, mild hypothermia (oesophageal temperature, 33-34 degrees C) was induced. On the 17th day of this treatment, after rewarming (35.5 degrees C) and discontinuation of the barbiturate, the patient responded to command. Weaning from the ventilator was successful on the 18th day. About 4 months after the incident, the patient was discharged with no apparent mental or motor disturbances. We suggest that mild hypothermia with barbiturate therapy may have contributed to the successful outcome in this case.

Localized airway anesthesia with lidocaine partially suppresses cardiovascular responses To lung inflation

Lung inflation causes cardiovascular suppression via an increase in intrathoracic pressure and neural mechanisms. To examine the mechanisms involved, we mea-sured the heart rate (HR) and arterial blood pressure (AP) responses to lung inflation before and after spraying the bronchi with lidocaine to suppress airway reflex. Thirty women participated in the study. One group (n = 20, Group BT) had their tracheas intubated by using double-lumen tubes. The other group (n = 10, Group TT) received an ordinary endotracheal tube. They were all studied under general anesthesia by using nitrous oxide, isoflurane, and muscle relaxation after a thiopental induction. In each patient, airway pressure was increased for 3 s, and changes in HR and AP were measured. Lung inflation was repeated after 5 mL of 4% lidocaine had been sprayed into the main bronchi unilaterally in Group BT or bilaterally in Group TT. There were no significant differences in cardiovascular responses between left and right lung inflation with the pressure at 20 and 30 cm H(2)O. Both lungs inflated at 20 cm H(2)O caused an increase in HR with a significantly greater decrease in AP than with unilateral inflation. Anesthesia of the bronchi abolished the HR increase, but not the AP decrease. Lung inflation at 30 cm H(2)O caused significant decreases in HR and AP which were not affected with topical anesthesia. These results indicate that the cardiovascular responses elicited by lung inflation in anesthetized humans are predominantly the direct effect of the increase in intrathoracic pressure, although sympathetic afferent activity induced via stimulation of mechanoreceptors in the airways contributes.

IMPLICATIONS

Localized airway anesthesia with lidocaine is unlikely to suppress the cardiovascular responses to lung inflation. This suggests that a limited number of neurogenic mechanisms are involved in the cardiovascular responses to lung inflation in anesthetized humans.

Effects of epidural anesthesia on the cardiovascular response to a rapid increase in isoflurane concentration

STUDY OBJECTIVE

To compare circulatory variables to an abrupt increase in isoflurance concentration via mask in patients who received either upper thoracic or lumbar epidural anesthesia, or neither.

DESIGN

Prospective study.

SETTING

Operating room at a university hospital.

PATIENTS

45 ASA physical status I female patients scheduled for elective surgeries with general anesthesia.

INTERVENTIONS

Patients received thoracic (TEA group) or lumbar (LEA group) epidural anesthesia, or neither (control group) (n = 15 per group). An epidural catheter was inserted through the T1-T2 intervertebral space in the TEA group or L2-L3 in the LEA group, and 10 mL of 2% lidocaine without epinephrine was injected. Two minutes after induction of anesthesia with thiamylal, the inspired isoflurane concentration was rapidly increased from 0.5% to 5% and maintained for 5 minutes.

MEASUREMENTS AND MAIN RESULTS

Heart rate and mean arterial pressure (MAP) were measured every minute. Mean analgesic levels obtained by epidural block were C4-T6 and T10-S1 in the TEA and LEA groups, respectively. Heart rate increased after the increase in isoflurane concentration in all groups, but increased significantly less in the TEA group than in the control or LEA groups (p < 0.05). Isoflurane also increased MAP in the control group throughout the 5-minute period, but only at the first minute of inhalation in the TEA and LEA groups. The increases in MAP in the TEA and LEA groups were significantly less than that in the control group (p < 0.05).

CONCLUSION

Epidural anesthesia can blunt circulatory responses to a sudden increase in isoflurane concentration.

Orthostatic hypotension during postoperative continuous thoracic epidural bupivacaine-morphine in patients undergoing abdominal surgery

Fifty patients undergoing colonic surgery received combined thoracic epidural and general anesthesia followed by continuous epidural bupivacaine 0.25% and morphine 0.05 mg/mL, 4 mL/h, for 96 h postoperatively plus oral tenoxicam 20 mg daily. Heart rate (HR) and arterial blood pressure (BP) were measured at supine rest, during orthostatic stress, and after walking prior to and 24, 48, and 72 h and 48 h postoperatively compared to preoperatively (P < or = 0.008); 16 vs 6 patients presented resting systolic BP values < 100 mm Hg (lower range, 70 mm Hg) post- versus preoperatively (P = 0.048). During orthostatic stress the decrease in systolic BP and concomitant increase in HR was similar post- versus preoperatively (BP, P > 0.3; HR, P > 0.34) and 12 vs 8 patient; (P = 0.45) experienced a systolic BP decrease > 20 mm Hg post- versus preoperatively. After walking, systolic BP was significantly lower postoperatively compared with preoperatively (P < or = 0.01). Epidural infusion was discontinued in three patients due to either persisting resting or orthostatic hypotension. There was no correlation between ASA classification, intraoperative bleeding, or postoperative dizziness and incidence of orthostatic hypotension. The results suggest that patients undergoing abdominal surgery and treated with continuous small-dose thoracic epidural bupivacaine-morphine are subjected to a decrease of BP at rest and during mobilization, but not to an extent that seriously impairs ambulation in most patients.

Atropine premedication attenuates heart rate variability during high thoracic epidural anesthesia

BACKGROUND

Atropine premedication is used as it possesses an anticholinergic effect on the cardiac autonomic nervous system (CANS). The aim of this study was to investigate the effect of atropine premedication on the CANS during thoracic epidural anesthesia (TEA) by assessing power spectral analysis of heart rate (HR) variability.

METHOD

Female patients (n = 28) undergoing elective mammary biopsy were randomly allocated into two groups; one received intramuscular premedication of 0.01 mg/kg of atropine 30 min before the procedure (group A: n = 14), and the other did not (group N: n = 14). Each electrocardiogram was digitally recorded before and during TEA, and played back off-line to detect R-R intervals. As a power spectrum required R-R intervals of 256 s, this was analysed before TEA and repeated thereafter for 25 min. The spectra were quantified by determining the peak areas of the spectral density by integrating low frequency (Lo: 0.04-0.15 Hz) and high frequency (Hi: 0.15-0.40 Hz) bands as they showed sympathetic and parasympathetic nervous activity in the CANS. The neural balance was assessed by calculating Hi:Lo ratio.

RESULTS

Decreases in Lo and increases in Hi:Lo ratio were observed, suggesting sympathectomy and vagotonia with TEA in both groups. For 10 min after commencement, TEA maintained Hi:Lo ratios lower in group A than in group N, suggesting a vagolytic effect of premedication with atropine. With TEA, cardiac slowing was observed, which was dependent on the level of dermal analgesia.

CONCLUSION

Power spectral analysis revealed that TEA had the effect of making CANS relatively vagotonic, and that atropine premedication would attenuate the effect of TEA.

Changes in cardiocirculatory autonomic function after thoracoscopic upper dorsal sympathicolysis for essential hyperhidrosis

Essential hyperhidrosis (EH) is caused by an unexplained overactivity of the sympathetic fibers which pass through the upper dorsal sympathetic ganglia D2 and D3. Since the D2 and D3 ganglia are also involved in the sympathetic cardiac innervation, cardiocirculatory autonomic function may also be abnormal in EH. In order to study the function of the sympathetic nervous system in EH, and to assess the effects of thoracoscopic sympathiocolysis, cardiocirculatory autonomic function tests were performed in 13 consecutive patients with EH, before (baseline) and 6 weeks after the thoracoscopic intervention. Baseline data were also compared with data obtained from 13 matched healthy volunteers: EH patients showed an increased heart rate at rest, but only in the standing position (94 +/- 18.5 vs 78 +/- 10.9 bpm, P < 0.01), as well as an increased ratio of low to high frequency power of the heart rate variability in the standing position (5.92 +/- 4.4 vs 2.8 +/- 2.5, P < 0.05). Exercise tests were normal in every EH patient. After sympathiocolysis, heart rate at rest (sitting on the cycloergometer) had decreased (75.4 +/- 13 vs 90.4 +/- 16.5 bpm, P < 0.05), as well as heart rate at maximal exercise (165.2 +/- 14.8 vs 180 +/- 10 bpm, P < 0.05). Exercise capacity and the cardiorespiratory responses to exercise were, however, unchanged after sympathicolysis. Resting heart rate in the lying (66 +/- 10 vs 76 +/- 15 bpm, P < 0.05) and standing positions (82 +/- 13.8 vs 94 +/- 18.5 bpm, P < 0.05), and the diastolic blood pressure reaction to a handgrip test (73.6 +/- 8.6 vs 84.7 +/- 11.6 mmHg, P < 0.05) were also lowered after sympathicolysis. In conclusion, patients with EH show an overfunctioning of the sympathetic system which is characterised by an increased reaction to stress (standing, exercise), whereas resting sympathetic tone is unaffected. Thoracoscopic D2-D3 sympathicolysis corrects this hyperfunction and has a partial beta-blocker-like activity, which results in a decrease in heart rate at rest and during maximal exercise, and in the diastolic blood pressure response to the handgrip test. Further studies are needed to assess the long-term consequences of this procedure.

The peripheral pulse wave: information overlooked

although the waveform derived from a peripheral pulse monitor or pulse oximeter may resemble an arterial pressure waveform, it is in fact a visualization of blood volume change in transilluminated tissue caused by passage of blood: an indication of perfusion or blood flow. Most currently available pulse oximeters indicate this flow, but few display it in usable form. Since adequate tissue blood flow is a prerequisite for normal metabolic activity, it is a parameter that should merit a place in standard anesthesia or intensive care monitors. That the peripheral tissue blood flow is not routinely displayed may be in part due to the difficulty in quantifying data obtained: flow is not accurately measured as simply as pressure, even by invasive means. It is in the pattern of the waveform that beat-to-beat changes in stroke volume can be better seen than measured, or in the interaction of ventilation and circulation that tests general circulatory performance. The origin and interpretation of these changes are discussed and illustrated with examples. We indicate how new physiological tests of autonomic function and cardiac preload can be developed using pulse plethysmography. The importance and application of the Valsalva effect on the waveform is emphasized. This effect is particularly applicable for monitoring adequate fluid loading and the action of vasodilator drugs, which are both important in anesthesia. Differences between the arterial pulse pressure wave and tissue flow wave are discussed, as well as the cause of certain artifacts, including the wandering dicrotic notch.

Cardiopulmonary exercise testing following bilateral thoracoscopic sympathicolysis in patients with essential hyperhidrosis

BACKGROUND

Essential hyperhidrosis is characterised by an overactivity of the sympathetic fibres passing through the upper dorsal sympathetic ganglia D2-D3. Anatomical interruption at the D2-D3 level is a highly effective treatment for essential hyperhidrosis but also causes (partial) cardiac denervation and, after surgical sympathicolysis, important impairment of cardiopulmonary exercise function has been observed. The purpose of this study was to compare the results of cardiopulmonary exercise testing between patients with essential hyperhidrosis and a normal control population, and to examine the effects of thoracoscopic D2-D3 sympathicolysis on cardiopulmonary exercise capacity in patients with essential hyperhidrosis.

METHODS

maximal, symptom limited incremental exercise tests were performed in 26 patients with severe essential hyperhidrosis one week before and one month after D2-D3 thoracoscopic sympathicolysis, and in 14 age and sex matched healthy volunteers. D2-D3 thoracoscopic sympathicolysis was performed using a simplified one stage bilateral procedure.

RESULTS

Palmar hyperhidrosis was relieved in every patient, confirming the D2-D3 denervation. A higher peak heart rate (7%) was seen in the patient group than in the normal subjects, but ll other cardiovascular, metabolic, and respiratory parameters were similar. After D2-D3 thoracoscopic sympathicolysis, heart rate at rest (13%) and at peak exercise (7%) were reduced, together with an increase in oxygen pulse. All other parameters remained unchanged.

CONCLUSIONS

Sympathetic overactivity relevant to cardiovascular function in essential hyperhidrosis is evident only during sympathetic stimulation. D2-D3 thoracoscopic sympathicolysis causes a small and asymptomatic reduction in maximal and resting heart rate and is not associated with a decrease in exercise capacity, in contrast with the detrimental effects on exercise capacity of open surgical sympathectomy.

Cardiovascular reflexes during anesthesia induction and tracheal intubation in elderly patients: the influence of thoracic epidural anesthesia

STUDY OBJECTIVES

To determine whether thoracic epidural anesthesia performed prior to general anesthesia provides hemodynamic protection from the stress of laryngoscopy and tracheal intubation; to access the autonomic reflex response to epidural anesthesia, general anesthesia, and airway stimulation.

DESIGN

Randomized unblind, controlled study.

PATIENTS AND SETTING

20 elderly (over 60) patients scheduled for colonic or gastric surgery at a university medical center.

INTERVENTIONS

All patients (n = 10, in each group) underwent a standardized anesthesia induction sequence that included fentanyl 2 micrograms/kg, thiopental sodium 3 to 5 mg/kg (up to loss of eyelid reflex), and vecuronium 0.1 mg/kg followed by laryngoscopy and tracheal intubation. Before general anesthesia, thoracic epidural anesthesia was performed with plain 1% lidocaine in the epidural group. Preoperatively, baroreflex function was assessed by the Valsalva maneuver and the cough test. Spectral analysis of heart rate (HR) variability was performed before as well as during anesthesia.

MEASUREMENTS AND MAIN RESULTS

There were no differences between the two groups in basal hemodynamics autonomic reflex status. Thoracic epidural anesthesia (median upper level at T2, median lower level at L2) was associated with stable hemodynamics, preservation of baroreflex sensitivity, and increased ratio of low to high frequency (LF/HF) components of HR variability, suggesting withdrawal of vagal activity. In both groups, general anesthesia induction was associated with decreased total HR variability and tracheal intubation was followed by increased LF/HF ratio, reflecting cardiac sympathetic activation. Patients with thoracic epidural anesthesia presented significant attenuation of the maximal rise in mean arterial pressure, and the increase in HR tended to be lower although not significantly.

CONCLUSIONS

Thoracic epidural blockade combined with general anesthesia was associated with preserved baroreflex function, and it afforded hemodynamic protection during laryngoscopy and tracheal intubation.

Effects of phenylephrine and ephedrine on pulmonary arterial pressure in patients with cervical or lumbar epidural anesthesia, or enflurane anesthesia

The authors studied systemic and pulmonary hemodynamic changes with ephedrine (EP) or phenylephrine (PH) when used to normalize arterial hypotension resulting from acute sympathectomy due to cervical or lumbar epidural anesthesia, or enflurane anesthesia in 52 patients. Both EP (0.2±0.05 mg·kg^-1) and PH (0.025±0.008 mg·kg^-1) produced a significant increase in pulmonary arterial pressure (PAP) with a concomitant increase in arterial pressure (AP). In the patients anesthetized with cervical epidural block and NO₂-O₂, systolic PAP increased from 22±5 to 28±8 mmHg with EP and from 23±6 to 32±10 mmHg with PH in response to approximately 30 mmHg increase of AP, and the ratio of the increment of systolic PAP to systolic AP (ΔPAP/ΔAP) was 0.15±0.08 with EP and 0.20±0.13 with PH (P<0.05); these changes did not differ significantly from those observed in the patients having lumbar epidural or enflurane-N₂O-O₂ anesthesia. The influence on cardiac output (CO) differed significantly between EP and PH; EP increased CO in all three groups (P<0.05), while PH did not elicit any significant changes in CO. A significant relationship between PAP and AP was found in patients given EP; the regression equation was ΔPAP=0.22×ΔAP-2.9 (r=0.77). The relationship in patients given PH was less significant (r=0.38). The results indicated that EP and PH elicit pulmonary hypertensive effect similarly in the patients with a high level of epidural anesthesia and that although both drugs act differently (EP mainly due to increases in the blood flow and PH solely due to its pulmonary vasconstrictive action), the increases in PAP were predictable, to some extent, from the increase of AP in anesthetized humans without predominant cardiopulmonary disorders.

Quantitative testing of sympathetic function with laser Doppler flowmetry

OBJECTIVE

The objective of this study was to develop an indirect technique for evaluating dynamic changes in sympathetic function in humans.

METHODS

We used laser Doppler to monitor sympathetic mediated vasoconstrictive responses (VRs) produced by 3 different provocative stimuli: 4-second inspiratory gasp (IG), ice-water immersion (Ice), and a spring-loaded pin prick (Pin). Skin perfusion on the thenar eminence was continuously monitored in 10 normal subjects (aged 25 to 36 years) using laser Doppler. Ten trials of the 3 stimuli were presented to each subject at 1-minute intervals. We determined the VR, the percent decrease in perfusion produced by each stimulus, and the 2 standard deviation variation in perfusion.

RESULTS

No subject found the IG maneuver uncomfortable. In contrast, the Pin and Ice stimuli were reported to be uncomfortable by 8 and 10 subjects, respectively. Five subjects found Pin and Ice stimuli overtly painful. Vasoconstrictive response was 54.1 +/- 2.3% (mean +/- SEM) with IG, 49.2 +/- 2.0% with Ice, and 24.0 +/- 1.8% with Pin. Baseline variation was approximately 15% in all trials.

CONCLUSION

Inspiratory gasp vasoconstrictive response (IGVR) is a sensitive indirect technique for evaluating sympathetic efferent function. We observed that the magnitude of the VR elicited by the IG stimuli was similar to that induced by cold water. Unlike the VR induced by Pin or Ice, IGVR is not dependent on noxious input via somatic afferents; therefore, it can be used in patients with diseases that produce a peripheral neuropathy, such as diabetes mellitus. Present uses of this technique and speculation on future uses are presented.

[Cervical epidural anesthesia]

Cervical epidural anaesthesia (CEA) results in an effective sensory blockade of the superficial cervical (C1/C4) and brachial plexus (C5/T1-T2). It is used both intraoperatively and in the treatment of postoperative or chronic pain. The approach to the epidural space at the C7-T1 interspace is not technically difficult. Patients are placed in the sitting position, increasing the negative pressure in the epidural space, with the head flexed on the thorax, in order to open the lowest cervical interspace. A 18-gauge Tuohy needle is inserted by a midline approach into the C6-C7 or C7-T1 interspace. A catheter may be inserted and left in place for postoperative analgesia. Local anaesthetics are administered either alone, or in combination with opiates. The CEA blocks the cardiac sympathetic fibers and consequently decreases heart rate, cardiac output and contractility. The mean blood pressure is unchanged or decreased, depending on peripheral systemic vascular resistance changes. The baroreflex activity is also partly impaired. Sympathetic blockade also decreases myocardial ischaemia. The cardiovascular changes induced by CEA are also partly due to the systemic effect of the local anaesthetic. The respiratory effects are minimal and depend on the extent of the blockade and the concentration of the local anaesthetic. A moderate restrictive syndrome occurs. Since the phrenic nerves originate from C3 to C5, ventilation may be impaired by CEA. Extension of the block may also impair intercostal muscle function, with a risk of respiratory failure when a CEA is used in patients with compromised respiratory function. The potential specific complications, mainly cardiovascular and respiratory, are the exacerbation of the effects of CEA. Side effects such as bradycardia, hypotension and acute ventilatory failure in relation to respiratory muscle paralysis, may be observed. Close monitoring of haemodynamics, respiratory rate and level blockade is required. Cervical epidural anaesthesia may be used either alone, or in combination with general anaesthesia depending on the surgical procedure. This technique seems to be effective in carotid artery surgery since sensitive and reliable information on cerebral function may be obtained. It is also for shoulder and upper limb surgery as well as for pharyngolaryngeal surgery, providing efficient operative anaesthesia and postoperative analgesia. CEA is used for relief of chronic pain in the head and neck or cancer pain due to Pancoast-Tobias syndrome. It seems to be effective for treating pain in patients with unstable angina pectoris or acute myocardial infarction.

Blood pressure and heart rate during orthostatic stress and walking with continuous postoperative thoracic epidural bupivacaine/morphine

Thirty-one patients scheduled for elective cholecystectomy performed through a mini-laparotomy, were randomized to received either combined thoracic epidural anaesthesia/light general anaesthesia and postoperative balanced analgesia with continuous epidural bupivacaine 10 mg.h-1 and morphine 0.2 mg.h-1 for 38 h after surgery plus systemic ibuprofen 600 mg x 8 h-1 (N = 15) or general anaesthesia and postoperative analgesia with systemic morphine and ibuprofen 600 mg x 8 h-1 (N = 16). During postoperative epidural infusion sensory blockade to pinprick was Th4 to L1, and analgesia at rest and during mobilisation was superior compared to systemic morphine and NSAID. There were no significant differences between groups in haemodynamic responses (BP and heart rate) during rest, orthostatic stress and after walking assessed before, 24 and 48 h after operation except for a clinically unimportant lower heart rate (approximately 10 bpm) 48 h after surgery at rest and during orthostatic stress in the epidural group. There was no significant difference between groups in number of patients with a reduction > 20 mmHg (2.7 kPa) in systolic blood pressure during orthostatic stress (two in each group at 24 h) or in number of episodes of dizziness, nausea or vomiting during rest or mobilisation. These results do not support the common belief that low-dose thoracic epidural bupivacaine/morphine may prevent ambulation due to sympathetic blockade or to impaired cardiovascular adaptation to the upright position.

The effects of an intravenous nicardipine injection on baroreflex control of heart rate in man

The effects of nicardipine injection on baroreflex control of heart rate were investigated by both pressor and depressor tests in 17 adult patients. Baroreflex sensitivity was attenuated after nicardipine injection by the pressor test using phenylephrine, whereas it was not changed by the depressor test using nitroglycerine. No resetting of the baroreflex occurred after nicardipine injection. By the pressor test, the plasma norepinephrine level was decreased, indicating that parasympathetic activity increased, and by the depressor test, the plasma norepinephrine concentration was increased, indicating that sympathetic activity increased. These results suggest that it is safe to use nicardipine clinically even when reduction in blood pressure for hypovolemia or unclamping the main artery is expected, and it is disadvantageous to administer the drug when an increase in blood pressure due to cross-clamping of the main artery is forecasted.

Baroreflex control of heart rate during high thoracic epidural anaesthesia. A randomised clinical trial on anaesthetised humans

Baroreflex control of heart rate after cardiac sympathectomy induced by thoracic epidural anaesthesia was evaluated in 30 patients who were randomly assigned to group 1 (bupivacaine 0.25%), group 2 (bupivacaine 0.5%) or group 3 (control). Plasma volume expanders were given to equalize preload conditions, as assessed using transoesophageal echocardiography. All measurements were made under general anaesthesia. Baroreflex sensitivity was determined from the heart rate response to phenylephrine and nitroglycerin. There was no difference in cardiac slowing in response to phenylephrine between the three groups. Baroreflex sensitivity, measured as cardiac acceleration in response to nitroglycerin, was significantly lower (p < 0.01) in groups 1 and 2 (1.8 and 1.5 ms.mmHg-1 respectively) compared with group 3 (3.5 ms.mmHg-1) with no differences between the two bupivacaine concentrations. The results suggest that baroreflex-mediated response to decreases in arterial pressure is dependent on the integrity of the sympathetic nervous system.

Response to the Valsalva manoeuvre after spinal anaesthesia

The waveform from a Criticare 504 pulse oximeter was recorded during the performance of a standard Valsalva manoeuvre in 20 patients before and after spinal anaesthesia. The pulse oximeter waveform showed changes typical of the expected heart rate and pulse volume changes seen in each phase of the Valsalva manoeuvre. There were no significant changes in the typical pulse volume changes of the Valsalva manoeuvre after spinal anaesthesia, which achieved a sensory block ranging in upper extent from T3-T12. There was, however, a significant delay in recovery of the pulse volume in phase 4 of the Valsalva manoeuvre after spinal anaesthesia from a mean (SD) of 3.1 (0.9) s to 6.2 (3.1) s (p less than 0.05). There was also a significant reduction in reflex bradycardia seen in phase 4. However, this was found only at 5, 10 and 15 min after spinal anaesthesia and was not associated with a significant change in Valsalva ratio or maximum-to-minimum rate ratio. The study confirms that the normal response to a standard Valsalva manoeuvre is suppressed only mildly during spinal anaesthesia in normovolaemic fit patients.

Effects of epidural anesthesia on sympathetic nerve discharge to the skin

Direct intraneural recordings of skin sympathetic activity (SSA) were performed to determine the magnitude of blockade of sympathetic fibers to the lower extremities during epidural anesthesia. Lumbar epidural catheters were inserted in nine volunteers. Multiunit postganglionic sympathetic activity was recorded in a skin fascicle of the peroneal nerve before and after injection of 4 ml of mepivacaine 2% epidurally, followed by an additional 12-16 ml after 5 min. Arousal stimuli such as sudden loud noises and noxious electrical skin stimulation were used to elicit transient sympathetic activation. Epidural anesthesia with upper level of sensory blockade at T4-T8 (n = 7) completely blocked spontaneous SSA and no detectable skin sympathetic activity could be provoked by arousal stimuli later than 14 min after the test dose. Sympathetic blockade was accompanied by marked increases in foot skin blood flow and loss of skin resistance responses to arousal. Epidural anesthesia with sensory blockade up to T10-11 (n = 2) only produced a partial sympathetic blockade. The result shows that epidural anesthesia with sensory blockade at T8 or above is equally as effective as injections of local anesthetics directly at postganglionic nerve fibers or ganglionic blockade in producing a complete sympathetic blockade of intraneurally recorded SSA. This neural blockade was paralleled by skin vasodilatation and a loss of sudomotor responses in the foot.

Cervical epidural anaesthesia for carotid artery surgery

A series of 394 patients (251 men, 143 women; mean age 70.0 +/- 8.4 yr) selected for carotid artery surgery (CAS) performed under cervical epidural anaesthesia (CEA) was analysed retrospectively. Carotid endarterectomy was performed in 326 patients and saphenous vein bypass in 68. The cervical epidural administration of 15 ml 0.5 per cent bupivacaine or 0.37-0.40 per cent bupivacaine plus fentanyl (50-100 micrograms) resulted in an effective sensory blockade from C2 to T4-T8. Patients were maintained awake during the surgical procedure in comfortable condition. Serious complications included dural puncture in two patients, epidural venipuncture in six patients and respiratory muscle paralysis in three patients. Hypotension (10.9 per cent) and bradycardia (2.8 per cent) were the most frequent side-effects of CEA. Transient neurological events were noticed in 84 patients during the surgical procedure. A definite neurological deficit occurred postoperatively in 12 patients. Three patients suffered postoperative myocardial infarction. The mortality rate was 2.3 per cent (nine patients). Carotid artery surgery may be performed under CEA but haemodynamic variables should be monitored closely and managed closely during the procedure.

Cardiopulmonary responses to the tracheobronchial suction with a fiberoptic bronchoscope during and after anesthesia

The cardiopulmonary responses to endobronchial suction with a fiberoptic bronchoscope (FOB suction) during and after anesthesia were compared in 12 patients underwent elective surgeries. FOB suction for 1 mm was performed during enflurane anesthesia (1.5% enflurane in oxygen) with muscle relaxant (anesthetized stage) and after anesthesia during spontaneously breathing of oxygen (awake stage). FOB suction lowered PaO2 to a greater extent in the awake than in the anesthetized stage. Mean PaO2 decreased from 414 to 111 torr in the awake and from 447 to 333 in the anesthetized stage. During suction, PaCO2 slightly increased in both stages. In response to FOB suction, heart rate increased significantly in the awake stage (P < 0.001), while mean blood pressure increased significantly in the anesthetized stage (P < 0.01). These findings indicate that the cardiopulmonary responses to FOB suction for 1 min during and after anesthesia differed. The procedure might be less dangerous during anesthesia.

Baroreceptor control after cervical epidural anesthesia in patients undergoing carotid artery surgery

Baroreceptor (BR) reactivity was studied in 16 patients scheduled for carotid artery surgery performed under cervical epidural anesthesia with 0.375% bupivacaine (15 mL). In the first seven patients, BR reactivity was assessed by measurement of the slopes of the linear relationship between systolic arterial pressure (SAP) and the RR interval on the electrocardiogram. Alterations of blood pressure (BP) were produced using sequential intravenous (IV) doses of nitroglycerin (NTG; 100 to 200 micrograms) or phenylephrine (PHE; 100 to 200 micrograms), before and 30 minutes after epidural anesthesia. The changes in SAP and heart rate (HR) determined during the four phases of a Valsalva maneuver were evaluated in a second set of measurements before and after cervical epidural blockade. In nine additional patients, a third set of measurements studying BR reactivity after carotid clamping and unclamping was performed in order to assess the effect of carotid handling on BP control. Cervical epidural anesthesia induced moderate decreases in BP (SAP, 150 +/- 18 mmHg before cervical block, 143 +/- 27 mmHg after cervical block, P less than 0.05) and HR (RR, 812 +/- 120 ms before cervical block, 938 +/- 130 ms after cervical block, P less than 0.05). Cervical epidural anesthesia depressed BR reactivity during deactivation as assessed by the decrease in the BR slope after PHE injection (6.6 +/- 4.4 ms/mmHg before cervical block v 2.5 +/- 1.8 ms/mmHg after cervical block, P less than 0.01) and activation as assessed by the changes in SAP and HR during phases II and IV of the Valsalva maneuver.(ABSTRACT TRUNCATED AT 250 WORDS)

[Comparison of blood pressure profiles with flunitrazepam/fentanyl/nitrous oxide vs cervical epidural anesthesia in surgery of the carotid artery]

A study was carried out to compare the evolution of arterial blood pressure during carotid endarterectomy performed under either general anaesthesia (GA) or cervical epidural anaesthesia (CEA). 20 patients were randomly assigned to two equal groups. In the CEA group, 15 ml of 0.375% bupivacaine and 150 micrograms fentanyl were injected into the epidural space at C7-D1 level. In the GA group, patients were anaesthetized with 0.2 mg.kg-1 flunitrazepam and 5 micrograms.kg-1 fentanyl; intubation was carried out using 0.08 mg.kg-1 vecuronium, and the patients were ventilated with a mixture of nitrous oxide and oxygen (50% of each). Further injections, every 30 min, of 2 micrograms.kg-1 fentanyl were given to the patients in group GA. Blood pressure was monitored continuously, up to 4 h postoperatively, with a radial arterial catheter. Per- or postoperative hypertension was defined as a rise in systolic arterial blood pressure (Pasys) over 180 mmHg for greater than 3 min; this was treated with 20 mg nifedipine intranasally (group CEA) or 100 micrograms fentanyl with 0.5 mg flunitrazepam with or without nifedipine (group GA). Per- or postoperative hypotension was defined as a fall in Pasys below 100 mmHg and or a 30% fall in mean arterial blood pressure for greater than 3 min; this was treated, in both groups, with an intravenous bolus of 3 mg ephedrine. Patients in group CEA experienced more frequent episodes of peroperative hypertension (8/2; p less than 0.02) and postoperative hypotension (5/1) than group GA.(ABSTRACT TRUNCATED AT 250 WORDS)

Heart rate response to atropine in humans anaesthetized with five different techniques

Atropine, 0.01 mg.kg-1, was given intravenously before the start of surgery to 169 patients who were anaesthetized with one of five different techniques; halothane, enflurane, cervical epidural, lumbar epidural or narcotic anaesthesia in addition to nitrous oxide and oxygen. Atropine produced a significant increase in heart rate (HR) within 1 min in all patients studied; the HR increases in patients anaesthetized with halothane (37 +/- 11 beats.min-1, n = 37) or narcotic (34 +/- 12 beats.min-1, n = 30) were significantly greater than in those anaesthetized with enflurane (25 +/- 10 beats.min-1, n = 35; P less than 0.01) or epidural anaesthesia. Because of the presence of an acute cardiac sympathectomy, the patients who received cervical epidural anaesthesia were expected to have different responses to the atropine. However, there was no significant difference in the HR increases between the patient groups with cervical (19 +/- 12 beats.min-1, n = 32) and lumbar (22 +/- 8 beats.min-1, n = 35) epidural anaesthesia. Atropine also produced a small but significant increase in arterial pressure in all five groups of patients. These results suggest that the cardiac responses to atropine may differ depending on the individual anaesthetic agent used, and are likely dependent upon the agent's effect on autonomic nervous system activity.

Computerized evaluation of Valsalva's Maneuver before and during alpha-adrenoceptor blockade with alfuzosin

Methodological differences exist in the evaluation of Valsalva's Maneuver. Linear and nonlinear mathematical models were described for beat-to-beat changes in blood pressure and R-R intervals occurring during the strain and release phases of Valsalva's Maneuver. This study indicated that the strain phase is linear, whereas the release phase is nonlinear; the release phase consists of a "lag phase," a "breakpoint," and an "overshoot phase." The alpha-adrenoceptor antagonist, alfuzosin, reduced baroreflex-mediated tachycardia during the strain phase and prolonged the "time lag" and "pressure lag" during the release phase; the latter change was due entirely to the reduced systolic pressure that occurred with alfuzosin at the end of the strain phase.