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

Heart rate variability as a predictor of intraoperative autonomic nervous system homeostasis

The aim of the proof-of-concept study is to investigate the level of concordance between the heart rate variability (HRV), the EEG-based Narcotrend Index as a surrogate marker for the depth of hypnosis, and the minimal alveolar concentration (MAC) of the inhalation anesthetic sevoflurane across the entire course of a surgical procedure. This non-blinded cross-sectional study recorded intraoperative HRV, Narcotrend Index, and MAC in 31 male patients during radical prostatectomy using the Da-Vinci robotic-assisted surgical system at Mannheim University Medical Center. The degree of concordance was calculated using repeated measures correlation with the R package (rmcorr) and presented using the rmcorr coefficient (rrm). The Narcotrend Index correlates significantly across all measures with the time-dependent parameter of HRV, the standard deviation of the means of RR intervals (SDNN) (rrm = 0.2; p < 0.001), the frequency-dependent parameters low frequency (LF) (rrm = 0.09; p = 0.04) and the low frequency/high frequency ratio (LF/HF ratio) (rrm = 0.11; p = 0.002). MAC correlated significantly negatively with the time-dependent parameter of heart rate variability, SDNN (rrm = -0.28; p < 0.001), the frequency-dependent parameter LF (rrm = -0.06; p < 0.001) and the LF/HF ratio (rrm = -0.18; p < 0.001) and the Narcotrend Index (rrm = -0.49; p < 0.001) across all measures. HRV mirrors the trend of the Narcotrend Index used to monitor depth of hypnosis and the inhibitory influence of the anesthetic sevoflurane on the autonomic nervous system. Therefore, HRV can provide essential information about the homeostasis of the autonomic nervous system during general anesthesia. DRKS00024696, March 9th, 2021.

Evaluation of the Analgesia Nociception Index and videopupillometry to predict post-tonsillectomy morphine requirements in children: a single-centre, prospective interventional study

Background

Tonsil surgery causes significant and challenging postoperative pain. The Analgesia Nociception Index (ANI) and videopupillometry are two techniques of interest to monitor nociception in adults and may predict postoperative morphine requirements. We hypothesised that these techniques could predict the need for morphine after tonsillectomy in children. The main objective was to assess the prognostic significance of ANI and videopupillometry, measured at the end of surgery, on morphine consumption determined by a Face, Legs, Activity, Cry, Consolability (FLACC) scale score >3 in the Post Anesthesia Care Unit (PACU).

Methods

A single-centre, prospective, interventional study evaluating children between 2 and 7 yr old undergoing tonsil surgery was performed. ANI and videopupillometry with tetanic stimulation were measured under general anaesthesia 4 min after the end of the surgical procedure. Each child was evaluated every 10 min by a nurse using the FLACC scale in the PACU and blinded to the measurements performed in the operating theatre.

Results

Eighty-nine children were analysed and 39 (44%) received morphine in the PACU. Neither ANI values nor videopupillometry values were predictive of postoperative morphine consumption (areas under the receiver operating characteristic curve 0.54, 95% confidence interval [CI; 0.42-0.65], and P=0.57; and 0.52, 95% CI [0.41-0.63], and P=0.69, respectively). Neither ANI values nor videopupillometry values were correlated to the maximum FLACC scale score in the PACU with ρ=0.04 (P=0.71) and ρ=0.06 (P=0.57), respectively.

Conclusions

Neither ANI nor videopupillometry performed at the end of surgery can predict morphine consumption in the PACU in children undergoing tonsillectomy.

Transient activation of spinal trigeminal neurons in a rat model of hypoxia-induced headache

ABSTRACT

The mechanisms underlying headaches attributed to hypoxia are poorly known. The activation of spinal trigeminal neurons with meningeal afferent input is believed to be responsible for the generation of headaches. In the caudal spinal trigeminal nucleus of anaesthetized and ventilated rats, the spontaneous firing of neurons with input from the exposed parietal dura mater and the activity evoked by mechanical stimuli to the dura and the adjacent periosteum were recorded, whereas the O2 fraction of the ventilation gas was stepwise reduced by omitting O2 and adding nitrogen. The expiratory CO2 level, the arterial pressure, the pulse rate, and the peripheral O2 saturation (SpO2) were registered. The meningeal blood flow was recorded using laser Doppler flowmetry; video imaging was used to measure the diameter of dural and medullary arteries. Lowering O2 in the ventilation gas from hyperoxic to normoxic and finally hypoxic conditions was followed by an increase in spontaneous activity up to 300% of the initial activity in most neurons, whereas the activity in a minor fraction of neurons ceased. The mechanical threshold was reduced under hypoxia. Arterial pressure, pulse rate, and SpO2 fell during stepwise lowering of the O2 concentration, whereas the arteries of the dura mater and the medulla dilated. Increased neuronal activity in the spinal trigeminal nucleus following lowering of the inhaled O2 goes along with variations in cardiovascular parameters. The experiments may partly model the conditions of high altitudes and other hypoxic states as risk factors for headache generation.

Fluid Resuscitation for Refractory Hypotension

Hypotension is a common occurrence, especially in anesthetized patients and in critical patients suffering from hypovolemia due to shock and sepsis. Hypotension can also occur in normovolemic animals, anesthetized or conscious, under conditions of vasodilation or decreased cardiac function. The main consequence of hypotension is decreased organ perfusion and tissue injury/dysfunction. In the human literature there is no consensus on what is the threshold value for hypotension, and ranges from < 80 to < 100 mmHg for systolic blood pressure and from < 50 to < 70 mmHg for mean arterial blood pressure have been referenced for intraoperative hypotension. In veterinary medicine, similar values are referenced, despite marked differences in normal arterial blood pressure between species and with respect to humans. Therapeutic intervention involves fluid therapy to normalize volemia and use of sympathomimetics to enhance cardiac function and regulate peripheral vascular resistance. Despite these therapeutic measures, there is a subset of patients that are seemingly refractory and exhibit persistent hypotension. This review covers the physiological aspects that govern arterial blood pressure control and blood flow to tissues/organs, the pathophysiological mechanisms involved in hypotension and refractory hypotension, and therapeutic considerations and expectations that include proper interpretation of cardiovascular parameters, fluid recommendations and therapy rates, use of sympathomimetics and vasopressors, and newer approaches derived from the human literature.

Changes in left ventricular electromechanical relations during targeted hypothermia

Background

Targeted hypothermia, as used after cardiac arrest, increases electrical and mechanical systolic duration. Differences in duration of electrical and mechanical systole are correlated to ventricular arrhythmias. The electromechanical window (EMW) becomes negative when the electrical systole outlasts the mechanical systole. Prolonged electrical systole corresponds to prolonged QT interval, and is associated with increased dispersion of repolarization and mechanical dispersion. These three factors predispose for arrhythmias. The electromechanical relations during targeted hypothermia are unknown.

We wanted to explore the electromechanical relations during hypothermia at 33 °C. We hypothesized that targeted hypothermia would increase electrical and mechanical systolic duration without more profound EMW negativity, nor an increase in dispersion of repolarization and mechanical dispersion.

Methods

In a porcine model (n = 14), we registered electrocardiogram (ECG) and echocardiographic recordings during 38 °C and 33 °C, at spontaneous and atrial paced heart rate 100 beats/min. EMW was calculated by subtracting electrical systole; QT interval, from the corresponding mechanical systole; QRS onset to aortic valve closure. Dispersion of repolarization was measured as time from peak to end of the ECG T wave. Mechanical dispersion was calculated by strain echocardiography as standard deviation of time to peak strain.

Results

Electrical systole increased during hypothermia at spontaneous heart rate (p < 0.001) and heart rate 100 beats/min (p = 0.005). Mechanical systolic duration was prolonged and outlasted electrical systole independently of heart rate (p < 0.001). EMW changed from negative to positive value (− 20 ± 19 to 27 ± 34 ms, p = 0.001). The positivity was even more pronounced at heart rate 100 beats/min (− 25 ± 26 to 41 ± 18 ms, p < 0.001). Dispersion of repolarization decreased (p = 0.027 and p = 0.003), while mechanical dispersion did not differ (p = 0.078 and p = 0.297).

Conclusion

Targeted hypothermia increased electrical and mechanical systolic duration, the electromechanical window became positive, dispersion of repolarization was slightly reduced and mechanical dispersion was unchanged. These alterations may have clinical importance. Further clinical studies are required to clarify whether corresponding electromechanical alterations are accommodating in humans.

Can postoperative pain be predicted? New parameter: analgesia nociception index

Background/aim

The Analgesia Nociception Index (ANI) is a new method of identifying nociception-analgesia balance. In this study, we investigate the correlation between the ANI and numeric rating scale (NRS) values immediately before and after extubation. The NRS values were recorded in the postanesthesia care unit, in a group of patients who underwent laparoscopic cholecystectomy, with the aim of evaluating the potential use of ANI values in the prediction of postoperative pain levels.

Materials and methods

The ANI and NRS values, heartbeat rate (HR), systolic and diastolic arterial pressure (SAP/DAP), and oxygen saturation (SpO2) values of the patients were recorded into three groups based on the initial NRS values recorded in the postanesthesia care unit (group I: NRS ≤ 3, group II: NRS 4–6, group III: NRS ≥ 7). Patients whose ANI values were lower than 47, considered as the pain threshold, and the groups to which these patients belonged were also recorded.

Results

Statistically significant increases were noted in HR, SAP, and DAP after extubation, while there was no significant change in ANI values. A weak correlation was identified between the ANI and NRS values of all patient groups.

Conclusion

We failed to identify a correlation between ANI and NRS values before and after extubation. Previous studies suggested that the ANI provides more valuable information in anesthetized patients, whereas our findings show that it is ineffective in the prediction of potential postoperative pain.

Sevoflurane based anaesthesia does not affect already impaired cerebral autoregulation in patients with type 2 diabetes mellitus

BACKGROUND

The baroreflex regulates arterial blood pressure (BP). During periods when blood pressure changes, cerebral blood flow (CBF) is kept constant by cerebral autoregulation (CA). In patients with diabetes mellitus (DM), low baroreflex sensitivity (BRS) is associated with impaired CA. As sevoflurane-based anaesthesia obliterates BRS, we hypothesised that this could aggravate the already impaired CA in patients with DM resulting in a 'double-hit' on cerebral perfusion leading to increased fluctuations in blood pressure and cerebral perfusion.

METHODS

On the day before surgery, we measured CBF velocity (CBFV), heart rate, and BP to determine BRS and CA efficacy (CBFV_mean-to-BP_mean-phase lead) in 25 patients with DM and in 14 controls. During the operation, BRS and CA efficacy were determined during sevoflurane-based anaesthesia. Patients with DM were divided into a group with high BRS (DM_BRS↑) and a group with low BRS (DM_BRS↓). Values presented are median (inter-quartile range).

RESULTS

Preoperative vs intraoperative BRS was 6.2 (4.5-8.5) vs 1.9 (1.1-2.5, P<0.001) ms mm Hg^-1 for controls, 5.8 (4.9-7.6) vs 2.7 (1.5-3.9, P<0.001) ms mm Hg^-1 for patients with DM_BRS↑, and 1.9 (1.5-2.8) vs 1.1 (0.6-2.5, P=0.31) ms mm Hg^-1 for patients with DM_BRS↓. Preoperative vs intraoperative CA efficacy was 43° (38-46) vs 43° (38-51, P=0.30), 44° (36-49) vs 41° (32-49, P=0.52), and 34° (28-40) vs 30° (27-38, P=0.64) for controls, DM_BRS↑, and DM_BRS↓ patients, respectively.

CONCLUSIONS

In diabetic patients with low preoperative BRS, preoperative CA efficacy was also impaired. In controls and diabetic patients, CA was unaffected by sevoflurane-based anaesthesia. We therefore conclude that sevoflurane-based anaesthesia does not contribute to a 'double-hit' phenomenon on cerebral perfusion.

CLINICAL TRIAL REGISTRATION

NCT 03071432.

Acute Device-Based Blood Pressure Reduction: Electrical Activation of the Carotid Baroreflex in Patients Undergoing Elective Carotid Surgery

Carotid sinus baroreceptors are involved in controlling blood pressure (BP) by providing input to the cardiovascular regulatory centers of the medulla. The acute effect of temporarily placing an electrode on the carotid sinus wall to electrically activate the baroreflex was investigated. We studied 11 patients undergoing elective carotid surgery. Baseline BP was 146+30/66±17 mm Hg and heart rate (HR) 72±7 bpm (mean ± standard deviation). An electrode was placed upon the carotid sinus and after obtaining a steady state baseline of BP and HR, an electric current was applied and increased in 1-volt increments. A voltage dependent and highly significant reduction in BP was observed which averaged 18±26* and 8.0±12 mm Hg for systolic BP and diastolic BP, respectively. Maximal reductions occurred at 4.4±1.2 V: 23±24 mm Hg*, 16±10 mm Hg* and 7±12 bpm* for systolic BP, diastolic BP and HR, respectively (= p <.05). Thus, electrical stimulation of the carotid sinus activates the carotid baroreflex resulting in a reduction in BP and HR. This presents a proof of concept for device based baroreflex modulation in acute BP regulation and adds to the available data which provide a rationale for evaluating this system in the context of chronic BP reduction in hypertensive patients.

Risk assessment and anesthetic management of patients with Williams syndrome: a comprehensive review

Since the first description in 1961, several case reports have documented an increased incidence of anesthesia-related cardiac arrest in patients with Williams-Beuren syndrome, commonly known as Williams syndrome (WS). Widespread arteriopathy secondary to an elastin gene defect results in various cardiac defects, including supravalvar aortic stenosis (SVAS) and coronary artery anomalies, which can increase the risk of myocardial ischemia. Even though patients with WS are known to have increased risk of adverse events during anesthesia and sedation, they often undergo several procedures that require anesthesia during their lifetimes, and cases of perianesthetic cardiac arrest continue to be reported. To date, no prospective studies have been reported that quantify anesthetic risk in individual patients with WS. In this article, we review the clinical manifestations of WS, propose a consensus, expert-informed method to estimate anesthetic risk based on the current literature, and provide recommendations for periprocedural management of this patient population.

Univariate and bivariate symbolic analyses of cardiovascular variability differentiate general anesthesia procedures

General anesthesia attenuates autonomic function and baroreflex control. This side effect should be prevented as much as possible because it limits the subject's ability in responding to physiological challenges during surgery (e.g. arterial pressure and ventricular contractility drops). This study is designed to rank two of the most commonly exploited general anesthesia treatments, i.e. intravenous anesthesia (IA) based on a propofol-opioid combination and volatile anesthesia (VA) based on a sevoflurane-opioid combination, according to their ability to maintain autonomic nervous system activity and baroreflex control. Univariate and bivariate symbolic techniques were applied to spontaneous heart period (HP) and systolic arterial pressure (SAP) variability series recorded during IA and VA procedures in 19 and 18 patients undergoing elective intracranial neurosurgery. Traditional linear univariate and bivariate frequency domain markers of the autonomic nervous system state and baroreflex control were evaluated as well. We found that: (i) univariate symbolic analysis of HP series suggests a better preservation of vagal modulation in VA than in IA; (ii) bivariate symbolic markers assessing the degree of HP-SAP association differentiate IA from VA, while baroreflex sensitivity and squared coherence function cannot; (iii) bivariate symbolic analysis indicates a better preservation of the HP-SAP association at slow frequencies in IA than in VA, thus suggesting a more active baroreflex control in IA. We conclude that symbolic indexes can be fruitfully exploited to rank general anesthesia treatments, and their performance appears to be superior to that of more traditional linear markers.

Comparison of equi-minimum alveolar concentration of sevoflurane and isoflurane on bispectral index values during both wash in and wash out phases: A prospective randomised study

BACKGROUND AND AIMS

At equal minimum alveolar concentration (MAC), volatile agents may produce different bispectral index (BIS) values especially at low BIS levels when the effect is volatile agent specific. The present study was performed to compare the BIS values produced by sevoflurane and isoflurane at equal MAC and thereby assessing which is a better hypnotic agent.

METHODS

Sixty American Society of Anaesthesiologists I and II patients undergoing elective mastoidectomy were divided into groups receiving either isoflurane or sevoflurane, and at equi-MAC. BIS value was measured during both wash in and wash out phase, keeping other parameters same. Statistical analysis was performed using the Friedman two-way analysis and Mann-Whitney U-test. A P < 0.05 was considered significant.

RESULTS

BIS value was significantly lower with sevoflurane at all MAC values as compared to isoflurane, except in the beginning and at MAC awake. However, both the drugs proved to be cardiostable.

CONCLUSION

At equi-MAC sevoflurane produces lower BIS values during wash in as well as wash out phase as compared to isoflurane, reflecting probably an agent specific effect and a deficiency in BIS algorithm for certain agents and their interplay.

[Clinical relevance of cardiopulmonary reflexes in anesthesiology]

The baroreflex, chemoreflex, pulmonary reflexes, Bezold-Jarisch and Bainbridge reflexes and their interaction with local mechanisms, are a demonstration of the richness of cardiovascular responses that occur in human beings. As well as these, the anesthesiologist must contend with other variables that interact by attenuating or accentuating cardiopulmonary reflexes such as, anesthetic drugs, surgical manipulation, and patient positioning. In the present article we review these reflexes and their clinical relevance in anesthesiology.

Antagonistic effect of flumazenil after midazolam sedation on arterial-cardiac baroreflex

BACKGROUND

Flumazenil is generally administered to antagonise the sedative effect of midazolam. However, although flumazenil completely antagonises the sedative effect of midazolam, a few effects remain unantagonised. Hence, it is unclear whether flumazenil restores the attenuation of the arterial-cardiac baroreflex (i.e. arterial-heart rate reflex) induced by midazolam. We investigated the antagonistic effect of flumazenil administered after midazolam on cardiac baroreflex, to reveal whether complete recovery from midazolam-induced sedation by flumazenil administration is accompanied by restoration of midazolam's attenuating effects on the cardiac baroreflex.

METHOD

Twelve healthy male subjects received midazolam followed by flumazenil until complete recovery from midazolam sedation. Before and during midazolam sedation, and after flumazenil administration, cardiac baroreflex function was assessed by sequence analysis and transfer function analysis between spontaneous oscillations in systolic arterial pressure and R-R interval.

RESULTS

During midazolam sedation, defined by an Observer's Assessment of Alertness/Sedation scale score of 3, BIS value decreased significantly. Simultaneously, the baroreflex indices of the two analyses decreased significantly compared with baseline, suggesting attenuated cardiac baroreflex function. With complete recovery from midazolam sedation by flumazenil, indicated by an Observer's Assessment of Alertness/Sedation scale score of 5, BIS values returned to the baseline level. Simultaneously, cardiac baroreflex indices also returned to baseline levels.

CONCLUSION

The present results suggest that complete recovery from midazolam sedation by flumazenil is accompanied by restoration of the attenuated cardiac baroreflex function induced by midazolam.

Dynamic assessment of baroreflex control of heart rate during induction of propofol anesthesia using a point process method

In this article, we present a point process method to assess dynamic baroreflex sensitivity (BRS) by estimating the baroreflex gain as focal component of a simplified closed-loop model of the cardiovascular system. Specifically, an inverse Gaussian probability distribution is used to model the heartbeat interval, whereas the instantaneous mean is identified by linear and bilinear bivariate regressions on both the previous R-R intervals (RR) and blood pressure (BP) beat-to-beat measures. The instantaneous baroreflex gain is estimated as the feedback branch of the loop with a point-process filter, while the RR-->BP feedforward transfer function representing heart contractility and vasculature effects is simultaneously estimated by a recursive least-squares filter. These two closed-loop gains provide a direct assessment of baroreflex control of heart rate (HR). In addition, the dynamic coherence, cross bispectrum, and their power ratio can also be estimated. All statistical indices provide a valuable quantitative assessment of the interaction between heartbeat dynamics and hemodynamics. To illustrate the application, we have applied the proposed point process model to experimental recordings from 11 healthy subjects in order to monitor cardiovascular regulation under propofol anesthesia. We present quantitative results during transient periods, as well as statistical analyses on steady-state epochs before and after propofol administration. Our findings validate the ability of the algorithm to provide a reliable and fast-tracking assessment of BRS, and show a clear overall reduction in baroreflex gain from the baseline period to the start of propofol anesthesia, confirming that instantaneous evaluation of arterial baroreflex control of HR may yield important implications in clinical practice, particularly during anesthesia and in postoperative care.

Sudden death in the presence of overt beta-adrenergic receptor activation in guinea pigs immediately following isoflurane anesthesia

OBSERVATIONS

A case series of sudden death is reported in five consecutive guinea pigs following anesthesia with inhalational isoflurane during beta-adrenergic receptor stimulation with isoproterenol. Sustained-release isoproterenol pellets or mini-osmotic pumps were implanted subcutaneously in male Dunkin-Hartley guinea pigs as part of a research study to assess the interplay of adrenergic receptor activation and the development of atrial arrhythmias. The continuous exposure to isoproterenol resulted in a similar presentation and eventual sudden death in all guinea pigs exposed to inhalational isoflurane between 15 to 40 minutes after discontinuation of anesthesia. Death occurred in guinea pigs in this case series despite the fact that doses of isoproterenol used were more than 10-fold lower than previously reported in guinea pigs in the absence of isoflurane anesthesia. The cause of death was suspected to be due to an interaction of isoproterenol with isoflurane anesthesia, as placebo implantation or anesthesia alone did not result in cardiac arrest. Of four subsequent guinea pigs anesthetized with the combination of xylazine and ketamine (X/K), three survived isoproterenol implantation for the full 21-day study period while one died perioperatively.

CONCLUSIONS

There was an increased rate of post-anesthetic mortality associated with isoproterenol pellet implantation in guinea pigs anesthetized with isoflurane compared to X/K. This may be due to the detrimental effects of the combination of isoflurane during overt beta-adrenergic receptor activation or cardioprotective effects of X/K anesthesia during beta-adrenergic receptor hyperactivity.

The rat: a laboratory model for studies of the diving response

Underwater submersion in mammals induces apnea, parasympathetically mediated bradycardia, and sympathetically mediated peripheral vasoconstriction. These effects are collectively termed the diving response, potentially the most powerful autonomic reflex known. Although these physiological responses are directed by neurons in the brain, study of neural control of the diving response has been hampered since 1) it is difficult to study the brains of animals while they are underwater, 2) feral marine mammals are usually large and have brains of variable size, and 3) there are but few references on the brains of naturally diving species. Similar responses are elicited in anesthetized rodents after stimulation of their nasal mucosa, but this nasopharyngeal reflex has not been compared directly with natural diving behavior in the rat. In the present study, we compared hemodynamic responses elicited in awake rats during volitional underwater submersion with those of rats swimming on the water's surface, rats involuntarily submerged, and rats either anesthetized or decerebrate and stimulated nasally with ammonia vapors. We show that the hemodynamic changes to voluntary diving in the rat are similar to those of naturally diving marine mammals. We also show that the responses of voluntary diving rats are 1) significantly different from those seen during swimming, 2) generally similar to those elicited in trained rats involuntarily "dunked" underwater, and 3) generally different from those seen from dunking naive rats underwater. Nasal stimulation of anesthetized rats differed most from the hemodynamic variables of rats trained to dive voluntarily. We propose that the rat trained to dive underwater is an excellent laboratory model to study neural control of the mammalian diving response, and also suggest that some investigations may be done with nasal stimulation of decerebrate preparations to decipher such control.

The effects of surgical levels of sevoflurane and propofol anaesthesia on heart rate variability

BACKGROUND AND OBJECTIVE

The laryngeal mask has become a widely accepted alternative to endotracheal intubation and mask ventilation. The laryngeal tube is a relatively new supraglottic airway device for airway management. We compared the new version of the laryngeal tube with the laryngeal mask.

METHODS

In a randomized design, either a laryngeal tube (n = 66) or a laryngeal mask (n = 66) were inserted. Ease of insertion, oxygenation and ventilation, spirometry data and postoperative airway morbidity were determined.

RESULTS

After successful insertion, it was possible to maintain oxygenation and ventilation in all the patients. Insertion success rates after the first, second and third attempts were 84.8% (n = 56), 12.1% (n = 8) and 3% (n = 2) for the laryngeal tube compared with 56.1% (n = 37), 25.8% (n = 17) and 18.2% (n = 12) for the laryngeal mask (P = 0.001). There was no significant difference in peak airway pressure, and dynamic compliance between the groups (P > 0.05). Blood on the cuff after removal of the device was noted in one patient with the laryngeal tube and in 10 patients with the laryngeal mask. Six patients in the laryngeal mask group complained of hoarseness (P = 0.012).

CONCLUSION

With respect to clinical function, the new version of the laryngeal tube and the laryngeal mask are similar and either device can be used to establish a safe and effective airway in paralysed patients.

An implantable carotid sinus stimulator for drug-resistant hypertension: surgical technique and short-term outcome from the multicenter phase II Rheos feasibility trial

BACKGROUND

A large number of patients have hypertension that is resistant to currently available pharmacologic therapy. Electrical stimulation of the carotid sinus baroreflex system has been shown to produce significant chronic blood pressure decreases in animals. The phase II Rheos Feasibility Trial was performed to assess the response of patients with multidrug-resistant hypertension to such stimulation.

METHODS

The system consists of an implantable pulse generator with bilateral perivascular carotid sinus leads. Implantation is performed bilaterally with patients under narcotic anesthesia (to preserve the reflex for assessment of optimal lead placement). Dose-response testing at 0 to 6 V is assessed before discharge and at monthly intervals thereafter; the device is activated after 1 month's recovery time. This was a Food and Drug Administration-monitored phase II trial performed at five centers in the United States.

RESULTS

Ten patients with resistant hypertension (taking a median of six antihypertensive medications) underwent implantation. All 10 were successful, with no significant morbidity. The mean procedure time was 198 minutes. There were no adverse events attributable to the device. Predischarge dose-response testing revealed consistent (r = .88) reductions in systolic blood pressure of 41 mm Hg (mean fall is from 180-139 mm Hg), with a peak response at 4.8 V (P < .001) and without significant bradycardia or bothersome symptoms.

CONCLUSIONS

A surgically implantable device for electrical stimulation of the carotid baroreflex system can be placed safely and produces a significant acute decrease in blood pressure without significant side effects.

Different effects on circulatory control during volatile induction and maintenance of anesthesia and total intravenous anesthesia: autonomic nervous activity and arterial cardiac baroreflex function evaluated by blood pressure and heart rate variability analysis

STUDY OBJECTIVE

To evaluate the different effects on autonomic circulatory control during volatile induction/maintenance of anesthesia (VIMA) vs total intravenous anesthesia (TIVA).

DESIGN

Prospective study.

SETTING

Operating theater of a university hospital.

PATIENTS

Twenty patients, with American Society of Anesthesiologists physical status of I or II, were randomly allocated into the VIMA group (n = 10) or the TIVA group (n = 10).

INTERVENTIONS

In the VIMA group, anesthesia was induced with 5% sevoflurane and 60% N2O in oxygen and maintained with 2% sevoflurane and 60% N2O in oxygen. In the TIVA group, anesthesia was induced with propofol 2.0 mg/kg intravenously by bolus injection and fentanyl 2 microg/kg, and maintained with an intravenous infusion of propofol 5 mg/kg.per hour and air-oxygen mixture.

MEASUREMENTS

Monitoring included recordings of electrocardiographic and arterial blood pressure waveforms. Autonomic nervous activity and arterial cardiac baroreflex function were evaluated by analysis of blood pressure variability, heart rate variability, and transfer function analysis between these 2 variables.

MAIN RESULTS

In the VIMA group, the low-frequency component of blood pressure variability (LF(SBP)) and low- and high-frequency components of the R-R interval variability (LF(RR) and HF(RR)) decreased significantly during anesthesia. In the TIVA group, LF(SBP) and LF(RR) decreased significantly. The degree of reduction in LF(SBP) was greater in the VIMA group than in the TIVA group. However, changes in R-R interval variability and cardiac baroreflex indices were not significantly different between the 2 groups.

CONCLUSIONS

Our results demonstrated that although reductions in autonomic nervous modulation to the heart might not be so different between the 2 groups, reduction in sympathetic nervous modulation to peripheral vasculature is greater in the VIMA group than in the TIVA group.

The concentration-dependent effects of general anesthesia on spontaneous baroreflex indices and their correlations with pharmacological gains

Beat-to-beat assessment of spontaneously occurring fluctuations in heart rate and arterial blood pressure allows noninvasive determination of cardiovagal function, but little is known regarding the effects of general anesthesia on spontaneous baroreflex (SBR) indices. We examined (a) concentration-dependent effects of sevoflurane on SBR indices, heart rate variability (HRV), and blood pressure variability and (b) correlation and agreement between pharmacological baroreflex gains and SBR indices during sevoflurane anesthesia. Continuous electrocardiogram and invasive arterial blood pressure were monitored in nine healthy volunteers before, during, and for 3 h after sevoflurane anesthesia, during which end-tidal sevoflurane was maintained at 0.7%, 1.4%, and 2.0% in random sequences. We derived three SBR indices (sequence method, alpha-index, and low-frequency transfer function) and compared them with pressor and depressor test gains by the pharmacological method. HRV and blood pressure variability were analyzed at a fixed respiratory rate (12 breaths/min) in awake and anesthetized conditions. Except for low-frequency transfer function, SBR indices were depressed by sevoflurane and remained depressed for 30 min after emergence from anesthesia, compared with the conscious baseline value. Spontaneous sequence indices and high- and low-frequency powers of HRV demonstrated concentration-dependent depression. Pharmacological gains and SBR indices during anesthesia generally correlated well, but Bland-Altman analysis revealed that SBR indices had limits of agreement as large as the baroreflex gain itself. These data suggest that spontaneous indices are inadequate estimates of, and are inconsistent with, the pharmacological baroreflex gain during sevoflurane anesthesia.

Baroreflex control of heart rate during and after propofol infusion in humans

BACKGROUND

This study was designed to determine cardiovagal baroreflex gain during propofol infusion and to characterize its recovery profile using the pharmacological and spontaneous sequence methods in 13 healthy volunteers without cardiovascular or autonomic disorders.

METHODS

After an 8- to 10-h fast and no premedication, measurements of RR intervals obtained from the electrocardiogram and non-invasive beat-to-beat systolic blood pressure (SP) were made at conscious baseline, at 60 and 120 min after induction of general anaesthesia using propofol, and at 20, 60, 120 and 180 min after emergence from anaesthesia. During propofol anaesthesia, ventilation was mechanically controlled to maintain normocapnia and calculated propofol concentration was adjusted by a TCI system at 5 microg ml(-1). Baroreflex responses were triggered by bolus i.v. injections of phenylephrine and nitroprusside to alter SP by 15-30 mm Hg. The linear portions of the baroreflex curves relating RR intervals and SP by least-square regression analysis were determined to obtain pharmacological gains. In addition, spontaneous sequence baroreflex gains were calculated from spontaneously fluctuating SP and RR intervals.

RESULTS

Baseline pressor and depressor test gains before propofol anaesthesia were 29.1 (SD 14.9) and 12.5 (7.8) ms mm Hg(-1), respectively. They were significantly depressed by 65-73% during propofol infusions. Similarly, baseline up- and down-sequence baroreflex gains were 33.8 (28.9) and 27.3 (19.8) ms mm Hg(-1), respectively, and were significantly depressed by 71-87% during propofol anaesthesia. Pressor test and up-sequence baroreflex gains returned to the baseline values 20 min after emergence from propofol anaesthesia, but depressor test and down-sequence baroreflex gains did not recover until 60 min after emergence.

CONCLUSIONS

We conclude that heart rate responses to both lowering and elevating blood pressure were depressed by propofol anaesthesia, and 60 min was required for their full recovery after discontinuation of propofol infusion.

Left ventricular mechanical performance in elderly patients after induction of anaesthesia. A comparison of inhalational induction with sevoflurane and intravenous induction with fentanyl and propofol

We investigated changes in left ventricular mechanical performance in 40 patients aged > 70 years in whom anaesthesia had been induced with sevoflurane or with fentanyl and propofol. The ratio of ventricular contractility to arterial properties, which reflects left ventricular performance, was estimated from the ratio of ventricular end-systolic elastance to effective arterial elastance. This ratio decreased after induction in both groups, the magnitude of the decrease being significantly greater in the fentanyl/propofol group than in the sevoflurane group. Decreases in mean arterial pressure after induction of anaesthesia in the two groups were similar, whereas the magnitude of the decrease in heart rate in the sevoflurane group was greater than that in the fentanyl/propofol group. Sevoflurane may therefore be preferable to fentanyl and propofol for induction of anaesthesia in elderly patients because of its lesser effect on left ventricular performance.

Asynchronism of the Recovery of Baroreflex Sensitivity, Blood Pressure, and Consciousness from Anesthesia in Rats

Anesthesia inhibits arterial baroreflex functions such as baroreflex sensitivity (BRS). The main objective of the present study was to determine the time course of BRS recovery from anesthesia and to determine whether BRS recovery is synchronous with the recovery of consciousness and blood pressure (BP). Experiments were performed in male Sprague-Dawley rats using different commonly used anesthetics at routine doses through intraperitoneal administration: (1) diazepam/ketamine, a mixture of diazepam (5 mg/kg) and ketamine (50 mg/kg); (2) chloral hydrate (0.3 g/kg); (3) sodium pentobarbital (30 mg/kg); and (4) urethane (1.0 g/kg). The anesthetic state, evaluated by algesthesia and cornea reflex, was maintained for 1-2.5 hours. The BRS, assessed by intravenous injection of phenylephrine, was inhibited rapidly and dramatically, with maximum depressions of 51%-80%. The BRS recovery time was approximately 5 hours for diazepam/ketamine, chloral hydrate, and pentobarbital, but more than 24 hours for urethane. Compared with BRS inhibition, BP reduction was less pronounced by 8% (not significant) for diazepam/ketamine and by 12%-30% for the others. The BP recovery time was approximately 2 hours, with the exception of chloral hydrate (>6 hours). In conclusion, after anesthesia, BRS inhibition is more obvious than BP reduction, and the recovery of BRS lags behind the recovery of consciousness or BP.

Orthostatic Hypotension Occurs Frequently in the First Hour After Anesthesia

Symptoms of orthostatic intolerance are common after general anesthesia and are associated with an increased risk of postoperative morbidity. The contribution of orthostatic hypotension (OH) has not been well defined. We conducted a head-up tilt test on patients after general anesthesia for minor surgery to assess the incidence of and risk factors for OH after general anesthesia. One-hundred-four patients were enrolled and were prospectively divided into four groups: older female, older male, young female, and young male. The incidence of OH was 76.0%, 72.0%, 45.5%, and 62.5% respectively and was associated with increasing age (P < 0.05) and posttest dizziness (P < 0.05). Body mass index, preoperative blood pressure, ASA class, anesthetic duration, IV fluid administration, and use of analgesics and antiemetics in the postanesthetic care unit were not different in subjects who demonstrated OH compared with those with a normotensive response. Subjects with OH after general anesthesia did not increase their heart rate and diastolic blood pressure with a head-up tilt which may have been caused by persistent effects of anesthetics on reflex cardiovascular control and/or bedrest-induced dysregulation of reflex cardiovascular control. We conclude that OH is common after general anesthesia for minor surgery and may be the major cause of postoperative orthostatic intolerance.

IMPLICATIONS

Orthostatic hypotension, a failure to maintain blood pressure on assuming an upright posture, is common after general anesthesia for minor surgery and may be the major cause of postoperative orthostatic intolerance.

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.