Analysis of heart rate variability to assess hemodynamic alterations following induction of anesthesia

Opioid-free anesthesia versus opioid-based anesthesia in patients undergoing cardiovascular and thoracic surgery: a meta-analysis and systematic review

BACKGROUND

Despite their extensive clinical use, opioids are characterized by several side effects. These complications, coupled with the ongoing opioid epidemic, have favored the rise of opioid-free-anesthesia (OFA). Herein, we perform the first pairwise meta-analysis of clinical outcomes for OFA vs opioid-based anesthesia (OBA) in patients undergoing cardiovascular and thoracic surgery.

METHODS

We comprehensively searched medical databases to identify studies comparing OFA and OBA in patients undergoing cardiovascular or thoracic surgery. Pairwise meta-analysis was performed using the Mantel-Haenszel method. Outcomes were pooled as risk ratios (RR) or standard mean differences (SMD) and their 95% confidence intervals (95% CI).

RESULTS

Our pooled analysis included 919 patients (8 studies), of whom 488 underwent surgery with OBA and 431 with OFA. Among cardiovascular surgery patients, compared to OBA, OFA was associated with significantly reduced post-operative nausea and vomiting (RR, 0.57; P = .042), inotrope need (RR .84, P = .045), and non-invasive ventilation (RR, .54; P = .028). However, no differences were observed for 24hr pain score (SMD, -.35; P = .510) or 48hr morphine equivalent consumption (SMD, -1.09; P = .139). Among thoracic surgery patients, there was no difference between OFA and OBA for any of the explored outcomes, including post-operative nausea and vomiting (RR, 0.41; P = .025).

CONCLUSION

Through the first pooled analysis of OBA vs OFA in a cardiothoracic-exclusive cohort, we found no significant difference in any of the pooled outcomes for thoracic surgery patients. Although limited to 2 cardiovascular surgery studies, OFA was associated with significantly reduced postoperative nausea and vomiting, inotrope need, and non-invasive ventilation in these patients. With growing use of OFA in invasive operations, further studies are needed to assess their efficacy and safety in cardiothoracic patients.

Thermodynamic Interpretation of a Machine-Learning-Based Response Surface Model and Its Application to Pharmacodynamic Synergy between Propofol and Opioids

Propofol and fentanyl are commonly used agents for the induction of anesthesia, and are often associated with hemodynamic disturbances. Understanding pharmacodynamic impacts is vital for parasympathetic and sympathetic tones during the anesthesia induction period. Inspired by the thermodynamic interaction between drug concentrations and effects, we established a machine-learning-based response surface model (MLRSM) to address this predicament. Then, we investigated and modeled the biomedical phenomena in the autonomic nervous system. Our study prospectively enrolled 60 patients, and the participants were assigned to two groups randomly and equally. Group 1 received propofol first, followed by fentanyl, and the drug sequence followed an inverse procedure in Group 2. Then, we extracted and analyzed the spectrograms of electrocardiography (ECG) and pulse photoplethysmography (PPG) signals after induction of propofol and fentanyl. Eventually, we utilized the proposed MLRSM to evaluate the relationship between anesthetics and the integrity/balance of sympathetic and parasympathetic activity by employing the power of high-frequency (HF) and low-frequency (LF) bands and PPG amplitude (PPGA). It is worth emphasizing that the proposed MLRSM exhibits a similar mathematical form to the conventional Greco model, but with better computational performance. Furthermore, the MLRSM has a theoretical foundation and flexibility for arbitrary numbers of drug combinations. The modeling results are consistent with the previous literature. We employed the bootstrap algorithm to inspect the results’ consistency and measure the various statistical fluctuations. Then, the comparison between the modeling and the bootstrapping results was used to validate the statistical stability and the feasibility of the proposed MLRSM.

Preoperative heart rate variability as a predictor of perioperative outcomes: a systematic review without meta-analysis

Heart rate variability (HRV) is a predictor of mortality and morbidity after non-lethal cardiac ischemia, but the relation between preoperatively measured HRV and intra- and postoperative complications is sparsely studied and most recently reviewed in 2007. We, therefore, reviewed the literature regarding HRV as a predictor for intra- and postoperative complications and outcomes. We carried out a systematic review without meta-analysis. A PICO model was set up, and we searched PubMed, EMBASE, and CENTRAL. The screening was done by one author, but all authors performed detailed review of the included studies. We present data from studies on intraoperative and postoperative complications, which were too heterogeneous to warrant formal meta-analysis, and we provide a pragmatic review of HRV indices to facilitate understanding our findings. The review was registered in PROSPERO (CRD42021230641). We screened 2337 records for eligibility. 131 records went on to full-text assessment, 63 were included. In frequency analysis of HRV, low frequency to high frequency ratio could be a predictor for intraoperative hypotension in spinal anesthesia and lower total power could possibly predict intraoperative hypotension under general anesthesia. Detrended fluctuation analysis of HRV is a promising candidate for predicting postoperative atrial fibrillation. This updated review of the relation between preoperative HRV and surgical outcome suggests a clinically relevant role of HRV but calls for high quality studies due to methodological heterogeneity in the current literature. Areas for future research are suggested.

Optimization of combined measures of airway physiology and cardiovascular hemodynamics in mice

Pulmonary hypertension may arise as a complication of chronic lung disease typically associated with tissue hypoxia, as well as infectious agents or injury eliciting a type 2 immune response. The onset of pulmonary hypertension in this setting (classified as Group 3) often complicates treatment and worsens prognosis of chronic lung disease. Chronic lung diseases such as chronic obstructive lung disease (COPD), emphysema, and interstitial lung fibrosis impair airflow and alter lung elastance in addition to affecting pulmonary vascular hemodynamics that may culminate in right ventricle dysfunction. To date, functional endpoints in murine models of chronic lung disease have typically been limited to separately measuring airway and lung parenchyma physiology. These approaches may be lengthy and require a large number of animals per experiment. Here, we provide a detailed protocol for combined assessment of airway physiology with cardiovascular hemodynamics in mice. Ultimately, a comprehensive overview of pulmonary function in murine models of injury and disease will facilitate the integration of studies of the airway and vascular biology necessary to understand underlying pathophysiology of Group 3 pulmonary hypertension.

The effects of brain injury on heart rate variability and the innate immune response in critically ill patients

Brain injury and its related increased intracranial pressure (ICP) may lead to increased vagus nerve activity and the subsequent suppression of innate immunity via the cholinergic anti-inflammatory pathway. This may explain the observed increased susceptibility to infection in these patients. In the present study, we investigated the association between brain injury, vagus nerve activity, and innate immunity. We determined heart rate variability (HRV) as a measure of vagus nerve activity, plasma cytokines, and cytokine production of ex vivo lipopolysaccharide-stimulated whole blood in the first 4 days of admission to the neurological intensive care unit (ICU) in 34 patients with various forms of brain damage. HRV, immune parameters, and the correlations between these measures were analyzed in the entire group of patients and in subgroups of patients with conditions associated with high (intracranial hemorrhage [ICH]) and normal ICP (subarachnoid hemorrhage [SAH] with an extraventricular drain alleviating ICP). Healthy volunteers were used for comparison. HRV total spectral power and ex vivo-stimulated cytokine production were severely depressed in patients compared with healthy volunteers (p<0.05). Furthermore, HRV analysis showed that normalized units of high-frequency power (HFnu, corresponding with vagus nerve activity) was higher, and the low-frequency:high-frequency ratio (LF:HF, corresponding with sympathovagal balance) was lower in patients compared to healthy volunteers (p<0.05). HFnu correlated inversely with ex vivo-stimulated tumor necrosis factor-α (TNF-α) production (r=-0.22, p=0.025). The most pronounced suppression of ex vivo-stimulated cytokine production was observed in the ICH group. Furthermore, in ICH patients, HFnu correlated strongly with lower plasma TNF-α levels (r=-0.73, p=0.002). Our data suggest that brain injury, and especially conditions associated with increased ICP, is associated with vagus nerve-mediated immune suppression.

Heart rate variability: a diagnostic and prognostic tool in anesthesia and intensive care

The autonomic nervous system (ANS) plays an important role in the human response to various internal and external stimuli, which can modify homeostasis, and exerts a tight control on essential functions such as circulation, respiration, thermoregulation and hormonal secretion. ANS dysfunction may complicate the perioperative course in the surgical patient undergoing anesthesia, increasing morbidity and mortality, and, therefore, it should be considered as an additional risk factor during pre-operative evaluation. Furthermore, ANS dysfunction may complicate the clinical course of critically ill patients admitted to intensive care units, in the case of trauma, sepsis, neurologic disorders and cardiovascular diseases, and its occurrence adversely affects the outcome. In the care of these patients, the assessment of autonomic function may provide useful information concerning pathophysiology, risk stratification, early prognosis prediction and treatment strategies. Given the role of ANS in the maintenance of systemic homeostasis, anesthesiologists and intensivists should recognize as critical the evaluation of ANS function. Measurement of heart rate variability (HRV) is an easily accessible window into autonomic activity. It is a low-cost, non-invasive and simple to perform method reflecting the balance of the ANS regulation of the heart rate and offers the opportunity to detect the presence of autonomic neuropathy complicating several illnesses. The present review provides anesthesiologists and intensivists with a comprehensive summary of the possible clinical implications of HRV measurements, suggesting that autonomic dysfunction testing could potentially represent a diagnostic and prognostic tool in the care of patients both in the perioperative setting as well as in the critical care arena.

Asystole induced by laryngosopy and tracheal intubation after induction of general anesthesia: A case report

Vagal reflex during laryngosopy and tracheal intubation may result in cardiac arrhythmia such as bradyarrhythmia and asystole. A 66-year-old woman, scheduled for coronary artery bypass surgery, received intravenous bolus of midazolam 2 mg, sufentanil 50 microgram, and vecuronium 10 mg for induction of general anesthesia. After two minutes of manual ventilation, tracheal intubation was attempted and the patient became asystolic during laryngoscopic manipulation. The laryngoscope was immediately withdrawn, and the patient returned to normal sinus rhythm. Ten minutes later, more experienced practitioner performed the second laryngoscopic intubation, but it eventually induced asystole again. External cardiac massage was commenced and normal sinus rhythm retuned at a rate of 60 beats/min after 1-2 minute later.

Correlation between heart rate variability and haemodynamic fluctuation during induction of general anaesthesia: comparison between linear and non-linear analysis

The objective of this study was to compare linear and non-linear analysis of heart rate variability (HRV) in terms of correlation with haemodynamic fluctuation during induction of general anaesthesia. Pre-operatively, HRV was estimated by the MemCalc method in 114 patients scheduled for general anaesthesia. After anaesthesia was induced with propofol, fentanyl and vecuronium bromide, tracheal intubation was performed. Haemodynamic fluctuations during induction of anaesthesia were recorded and the correlation between pre-operative HRV and haemodynamic fluctuation was examined using logistic regression analysis. As an index of non-linear analysis of HRV, ultra short-term entropy (UsEn) correlated better with blood pressure fluctuation than did the ratio of the power of low frequency component of HRV to that of high frequency component (LF/HF). In contrast, although LF/HF significantly correlated with heart rate increase caused by tracheal intubation, the correlation between UsEn and heart rate fluctuation was not significant.

Investigation of altered heart rate variability, nonlinear properties of heart rate signals, and organ dysfunction longitudinally over time in intensive care unit patients

PURPOSE

To investigate longitudinally over time heart rate dynamics and relation with mortality and organ dysfunction alterations in patients admitted to a multidisciplinary intensive care unit.

METHODS

Data from 53 patients were used, with heart rate recorded from monitors and analyzed on a daily basis (every morning) for 600 seconds and sampling rate at 250 Hz, from admission to the intensive care unit until final discharge from the unit. Variance, which is a measure of heart rate variability; exponent alpha2; and approximate entropy (ApEn), which assess long-range correlations and periodicity within a signal, respectively; were measured and compared with every day Sequential Organ Failure Assessment Score (SOFA) and mortality.

RESULTS

Nonsurvivors had lower ApEn mean (greater periodicity in their signals) and minimum values compared to survivors (0.53 +/- 0.25 vs 0.62 +/- 0.23, P = .04; 0.24 +/- 0.23 vs 0.48 +/- 0.23, P = .01, respectively). Patients in better conditions with SOFA of less than 7 (mean value) had higher variance and ApEn (more variable, less periodic signals) than those with SOFA of 7 or higher (0.47 +/- 0.51 vs 0.10 +/- 0.65, P < .001; 0.67 +/- 0.28 vs 0.49 +/- 0.24, P < .001, respectively). The alpha2 exponent and variance were correlated with length of stay (r = 0.55, P = .02, and r = 0.53, P = .02, respectively) and minimum ApEn with mortality (r = 0.41, P = .01).

CONCLUSIONS

Loss of variability and increase in periodicity in heart rate of critically ill patients are linked with parallel deterioration of organ dysfunction and high mortality.

Blood pressure and heart rate variability changes during cardiac surgery with cardiopulmonary bypass

This study investigated patients undergoing elective cardiac surgery to evaluate the effects of cardiopulmonary bypass (CPB) on the spontaneous variability of mean arterial pressure (MAP) and heart rate (HR). Forty-one adult patients receiving different cardiovascular system drugs were included in the study. Patients were divided into three groups: no preoperative pharmacological cardiovascular treatment (n = 12), beta-blocker (BB) (n = 13), and angiotensin-converting enzyme inhibition (ACEI) (n = 16). MAP was recorded before anaesthesia until the end of surgery. MAP and HR variability was analysed in very low- (VLF), low- (LF) and high-frequency bands. The LF spectral component of MAP was observed to decrease in patients under ACEI (-92%) or BB (-87%) following induction of anaesthesia. In addition, during CPB, VLF power decreased in BB group (-67%), and LF power decreased in ACEI group (-77%). Concerning HR, VLF spectral power decreased following anaesthesia in BB group (-74%). In addition, after CPB, VLF power reached lower value in ACEI group than in BB group (P < 0.05). LF spectral power of HR showed a large decrease after CPB in ACEI group (-89%). This study showed that MAP variability did not change during CPB in patients with no preoperative pharmacological cardiovascular treatment, suggesting an unaltered vascular control of MAP. Moreover, the change in LF spectral power of MAP in ACEI and BB groups, suggests that both the renin-angiotensin and sympathetic systems participate to the genesis of LF variability of MAP.

Instant centre frequency at anaesthetic induction--a new way to analyse sympathovagal balance

The instant centre frequency (ICF) of RR interval has been proposed as a global index to analyse the sympathovagal interaction in the heart. The aim of this study was to assess the ICF during anaesthesia to test if it can reliably capture the neural control of the cardiovascular system. Twenty-four ASA II or III patients scheduled for cardiac surgery were included in the study. They were allocated in two groups: control, no treatment (group 1, n = 12), and beta-adrenergic blockade by atenolol (group 2, n = 12). Spectra of pulse interval series were computed with a time-frequency method and they were divided into: very low frequency (VLF, 0.000-0.040 Hz), low frequency (LF, 0.050-0.150 Hz) and high frequency (HF, 0.160-0.500 Hz). Normalized power was obtained by dividing the cumulative power within each frequency band (LF or HF) by the sum of LF and HF; the ratio of LF/HF was also calculated. Instant centre frequency is a time-varying parameter that the evolution along time of the gravity centrum of a local spectrum. All spectral indexes were recorded at the following time points: before induction, after induction and before intubation, during intubation, and after intubation. The atenolol group had lower normalized LF and the LF/HF ratio (P < 0.05) higher HF before induction; and lower LF/HF ratio after induction and before intubation (P < 0.05). The ICF was higher in atenolol group at all times. The ICF shifted towards HF frequency after induction and before intubation and shifted towards LF during intubation in both groups. The autonomic nervous system control on the heart through the interaction of sympathetic and parasympathetic reflex mechanisms could be studied by the ICF. The ICF may assess the autonomic cardiac modulation and may provide useful information for anaesthetic management.

Heart rate variability and the prone position under general versus spinal anesthesia

STUDY OBJECTIVE

To evaluate heart rate (HR) variability in the prone position with power spectral heart rate (PSHR) analysis during spinal and general anesthesia.

DESIGN

Prospective, clinical evaluation of HR variability in the prone position.

SETTING

Tertiary care teaching hospital.

PATIENTS

20 healthy, ASA physical status I and II patients scheduled for elective lumbar spine surgery in the prone position.

INTERVENTIONS

Anesthetic technique was either a standard general anesthetic or spinal anesthetic, based on the preference of the patient. Power spectral heart rate, HR, and blood pressure (BP) readings were determined prior to anesthetic intervention and as soon as a stable PSHR reading was available in the prone position.

MEASUREMENTS AND MAIN RESULTS

Heart rate and BP were recorded at baseline prior to anesthesia and at the time of stable PSHR data in the prone position. Power spectral heart rate data included low-frequency activity (LFa), high-frequency activity (HFa), and the ratio (LFa/HFa). Spinal anesthesia level was recorded by thoracic dermatome at complete onset. Data were collected from 20 patients; 12 patients chose spinal anesthesia and 8 chose general anesthesia. The prone position resulted in significant increase in HR in the spinal group and significant decrease in BP in the general anesthesia group. Low-frequency activity and LFa/HFa ratio were unchanged in the spinal anesthesia group and were significantly decreased in the general anesthesia group. Spinal level was T8.7.

CONCLUSIONS

The association of less change in LFa activity and preservation of BP on assumption of the prone position in patients during low spinal anesthesia suggests better preservation of autonomic nervous system compensatory mechanisms during low spinal anesthesia than with general anesthesia.

Comparison of the haemodynamic actions of desflurane/N2O and isoflurane/N2O anaesthesia in vascular surgical patients

BACKGROUND

The purpose of this study was to compare heart rate and arterial blood pressure response to desflurane/N2O vs isoflurane/N2O anaesthesia in a randomized clinical trial performed in patients before vascular surgery.

METHODS

To evaluate associated changes in the autonomic nervous system with maintenance of anaesthesia, we used power spectral analysis (PSA) of heart rate and blood pressure and measured plasma catecholamine concentrations. Twenty-five patients whose trachea had been intubated after propofol induction were given either desflurane or isoflurane at 1 and 1.5 MAC in N2O (60%) in a random manner.

RESULTS

At an anaesthetic depth of up to 1.5 MAC, arterial blood pressure, indices of sympathetic activity derived from PSA, decreased with both anaesthetics, while heart rate and plasma catecholamine concentrations did not significantly change. Plasma renin activity significantly increased at 1.5 MAC anaesthesia in both groups.

CONCLUSIONS

We conclude that sympathetic hyperactivity previously reported during desflurane anaesthesia in healthy volunteers is not frequent in clinical practice in elderly vascular surgical patients under desflurane/N2O anaesthesia, since it occurs at an anaesthetic depth which cannot be reached in these patients because of the lowering arterial blood pressure effects of desflurane, which are similar to those of isoflurane.

Tourniquet-induced hypertension correlates with autonomic nervous system changes detected by power spectral heart rate analysis

STUDY OBJECTIVE

To determine the autonomic changes associated with pneumatic tourniquet-induced hypertension as measured by power spectral heart rate analysis (PSHR).

DESIGN

Prospective study.

SETTING

Tertiary teaching hospital.

PATIENTS

21 healthy-patients scheduled for lower extremity surgery, during which pneumatic tourniquet inflation was expected to exceed 90 minutes.

INTERVENTIONS

Hemodynamic and PSHR data collected at 5 minute intervals during inflation of the pneumatic tourniquet. Tourniquet-induced hypertension (T-HTN) defined at 30% increase above baseline.

MEASUREMENTS AND MAIN RESULTS

Blood pressure, heart rate, maximum changes in low frequency variability (LFa), high frequency variability (HFa), and their ratio (LFa/HFa) were measured. Of the 21 patients, 11 had T-HTN. A significantly greater increase in LFa and LFa/HFa ratio was seen in the T-HTN group, where patients were greater in age. LFa, HFa, and ratio were not significantly different with T-HTN until 60 minutes or greater. Best correlation with T-HTN occurred with maximum increase in LFa/HFa ratio compared with increase in LFa or decrease in HFa.

CONCLUSION

Tourniquet hypertension correlated with activation of the sympathetic nervous systems, as measured by PSHR variables.

Heart rate, heart rate variability, and blood pressure during perioperative stressor events in abdominal surgery

STUDY OBJECTIVE

To define the behavior of power spectral heart rate variability (PSHR) during potentially stressful events in the perioperative period, and relate it to changes in blood pressure (BP) and heart rate (HR).

DESIGN

Longitudinal clinical study.

SETTING

Operating room and recovery suites of a large tertiary care referral center.

PATIENTS

26 ASA physical status I, II, and III patients undergoing elective abdominal surgery.

INTERVENTIONS

Anesthesia was induced with thiopental sodium and fentanyl, and maintained with isoflurane/nitrous oxide (N2O)/relaxant or enflurane/N2O/relaxant. The trachea was intubated and intraabdominal surgery was performed.

MEASUREMENTS AND MAIN RESULTS

Observations consisted of HR, noninvasive blood pressure, and PSHR. They were made before and after induction of anesthesia, tracheal intubation, and surgical incision, and during maximal surgical stimulation and skin closure. HR and mean arterial pressure (MAP) maxima were also recorded for one hour before and after emergence from anesthesia. PSHR was obtained using a special algorithm and data acquisition system for real time spectral analysis of the instantaneous HRversus time function. The HR power spectrum parameters analyzed were low-frequency (LFA; powerband = 0.04 to 0.10 Hz), respiratory-induced frequency (RFA; powerband = respiratory frequency +/- 0.06 Hz), and the ratio of LFA to RFA. With induction of anesthesia, only RFA power decreased significantly. LFA power reduction became significant only after intubation and continued so until after incision. Immediately after induction, the decline in RFA power (vs. preinduction) was more pronounced when compared with the decline in LFA power (76% vs. 34%; p = 0.01). Hence, the ratio LFA/RFA increased significantly after induction of anesthesia. It was significantly higher than at postintubation, preincision, or skin closure. A significant elevation in LFA, LFA/RFA ratio, and BP occurred with maximal abdominal surgical stimulation. Only preinduction LFA, RFA, and LFA/ RFA ratio were predictive of MAP changes with induction of anesthesia (p = 0.006). In 8 of the 15 patients who had MAP changes of at least 10 mmHg with induction, PSHR indices correctly predicted a change of this magnitude. Late intraoperative HR maxima were positively correlated with the change in HR and incision (r2 = 0.58; p < 0.01). The change in BP with incision was positively correlated with early postoperative HR maxima (r2 = 0.60; p < 0.01).

CONCLUSIONS

On anesthetic induction, preoperative, but not intraoperative, spectral indices were predictive of BP changes. Power spectral analysis of HR may provide information about the autonomic state that is not evident from BP or HR. The HR power spectrum, in particular, indicated a striking autonomic imbalance immediately after the induction of anesthesia despite stable HR and BP. LFA and LFA/RFA ratio appeared to track sympathetic autonomic activation during abdominal surgical stimulation, but not during other perioperative stressor events.

Determinants of heart rate variability

OBJECTIVES

This study sought to examine clinical determinants of heart rate variability and to report normative reference values for eight heart rate variability measures.

BACKGROUND

Although the clinical implications of heart rate variability have been described, clinical determinants and normative values of heart rate variability measures have not been studied systematically in a large community-based population.

METHODS

The first 2 h of ambulatory electrocardiographic recordings obtained in Framingham Heart Study subjects attending a routine examination were reprocessed for heart rate variability. Recordings with transient or persistent nonsinus rhythm, premature beats > 10% of total beats, < 1-h recording time or processed time < 50% of recorded time were excluded; subjects receiving antiarrhythmic medications also were excluded. Among five frequency domain and three time domain measures that were obtained, low frequency power (0.04 to 0.15 Hz), high frequency power (0.15 to 0.40 Hz) and the standard deviation of total normal RR intervals based on 2-h recordings were selected for the principal analyses. Variables with potential physiologic effects or possible technical influences on heart rate variability measures were chosen for multiple linear regression analysis. Normative values, derived from a subset of healthy subjects, were adjusted for age and heart rate.

RESULTS

There were 2,722 eligible subjects with a mean age (+/-SD) of 55 +/- 14 years. Three separate multiple linear regression analyses revealed that higher heart rate, older age, beta-adrenergic blocking agent use, history of myocardial infarction or congestive heart failure, diuretic use, diastolic blood pressure > or = 90 mm Hg, diabetes mellitus, consumption of three or more cups of coffee per day and smoking were associated with lower values of one or more heart rate variability measures, whereas longer processed time, start time in the morning, frequent supraventricular and ventricular premature beats, female gender and systolic blood pressure > or = 160 mm Hg were associated with higher values. Age and heart rate were the major determinants of all three selected heart rate variability measures (partial R2 values 0.125 to 0.389). Normative reference values for all eight heart rate variability measures are presented.

CONCLUSIONS

Age and heart rate must be taken into account when assessing heart rate variability.

Heart rate variability as an assessment of cardiovascular status

In summary, HRV is a useful tool for cardiovascular risk stratification and assessment of sympathovagal balance. It has been shown to be a useful investigative tool in anesthesia to study autonomic balance and dysfunction but has limitations with regard to a depth-of-anesthesia monitor because of the confounding effects of multiple drugs and surgical stimuli. When assessing HRV, it is important to understand the limitations of the methodology. In particular, absolute power is not a surrogate of autonomic tone, but the relationship between the power in the different frequency bands may better reflect autonomic balance.

Changes in heart rate variability during induction of anesthesia with fentanyl and midazolam

OBJECTIVE

The study was designed to evaluate changes in autonomic nervous system function during induction of anesthesia with fentanyl, midazolam, and pancuronium and to answer the question of dose-dependency of these effects.

DESIGN

Prospective, randomized.

SETTING

A university hospital.

PARTICIPANTS

Forty consecutive cardiac surgical patients.

INTERVENTIONS

Anesthesia was induced with fentanyl, midazolam, and pancuronium. The patients were assigned to four groups differing in dosages of fentanyl plus midazolam and speed of injection. Fentanyl, 7.5 micrograms/kg (group A), 12.5 micrograms/kg (group B), and 20.0 micrograms/kg (group C) plus midazolam, 0.075 mg/kg (group A), 0.125 mg/kg (group B), and 0.200 mg/kg (group C) were administered over 10 minutes; in group D, fentanyl, 7.5 micrograms/kg, and midazolam, 0.075 mg/kg, were administered within 1 minute.

MEASUREMENTS AND MAIN RESULTS

Heart rate variability (HRV) was measured using parameters in the time domain and the frequency domain. The comparison of preinduction HRV with the intra-anesthetic epochs did not show significant differences with respect to heart rate, coefficient of variation, and root mean squared successive differences. Spectral analysis showed significant reductions of power in the vasomotor band (0.01 to 0.05 Hz) and the low-frequency band (0.05 to 0.15 Hz) in all groups. Power in the high-frequency band (0.15 to 0.50 Hz) decreased slightly, but this did not reach the significance level. A dose dependency of these changes was found in the low-frequency band only.

CONCLUSIONS

Parameters of HRV suggest that induction with fentanyl, midazolam, and pancuronium decreases sympathetic but not parasympathetic autonomic system activity. The anesthetic induction technique's modulation of autonomic nervous system balance is better represented by means of spectral analysis than by analysis in the time domain. This modulation was largely independent of the doses administered and independent of the speed of injection.