Atropine premedication attenuates heart rate variability during high thoracic epidural anesthesia

Factors influencing intraoperative bradycardia in adult patients

PURPOSE

In order to elucidate the prominent factors involved in intraoperative bradycardia in adult patients, we retrospectively investigated the association between the potential risk factors and intraoperative bradycardia, using multiple logistic regression.

METHODS

The perioperative records for 499 adult patients who had undergone any of six elective surgeries were retrospectively examined. The potential factors included patient characteristics, the use of perioperative drugs for anesthesia, and the types of operational procedures. Heart rates were extracted at five points perioperatively. The frequencies and total doses of atropine injections to treat bradycardia were examined. Simple and multiple logistic regressions were used to analyze the relative risk factors for a intraoperative bradycardia.

RESULTS

The multiple logistic regression analysis revealed that the absence of atropine premedication was the most prominent risk factor for bradycardia (odds ratio; 1.86-5.51) from arrival in the operating room until the end of the operation. Other prominent factors, whose effects were only temporary, were as follows. Males had a higher risk of bradycardia than females upon arrival in the operating room. Surgical procedures with an epidural or subarachnoid blockade tended to have a higher risk for bradycardia after the operation. Propofol induction had a greater risk for bradycardia than thiopental after the end of the operation. Endotracheal intubation had a lower risk for bradycardia than no endotracheal intubation after induction. Vecuronium tended to induce bradycardia after operation.

CONCLUSION

The most prominent factor affecting heart rate was atropine premedication. It was noteworthy that a single preoperative administration of atropine affected heart rate throughout the operation.

Variabilidade da freqüência cardíaca em cães anestesiados com infusão contínua de propofol e sufentanil

Foram avaliados os efeitos do propofol associado ao sufentanil sobre o balanço das atividades simpática e parassimpática do coração, investigando-se um possível efeito dose dependente do opióide. Analisou-se a variabilidade da freqüência cardíaca (VFC) de 12 cães adultos pré-medicados com maleato de acepromazina e anestesiados com propofol e três doses diferentes de sufentanil, que variou de 0,025 a 0,1µg/kg/min. Registrou-se o eletrocardiograma 15 minutos após a medicação pré-anestésica e 15, 30, 60, 90 e 120 minutos após a indução anestésica. A VFC foi calculada no domínio da freqüência, mediante análise de 10 intervalos RR consecutivos. Houve redução acentuada da freqüência cardíaca, mas a VFC permaneceu relativamente inalterada.

The role of premature atrial contractions as the main triggers of postoperative atrial fibrillation

To better understand the pathogenesis of postoperative atrial fibrillation (AF), the mode of onset of AF after coronary artery bypass grafting was analyzed with respect to the autonomic balance, the heart rate (HR), and the presence of arrhythmias preceding the onset of sustained AF.

METHOD

Holter recordings of 24 hours, obtained from the first postoperative morning until clinically documented sustained AF, were analyzed in 29 untreated patients and in 13 patients treated with thoracic epidural anesthesia (TEA), who all developed AF after coronary artery bypass grafting. The presence of arrhythmias, the HR, and the autonomic balance, assessed by heart rate variability in the frequency domain, were analyzed at predefined time intervals within the 3-hour period before AF onset. Supraventricular premature beats (SPBs) and ventricular premature beats triggering the onset of AF were also evaluated.

RESULT

An SPB triggering the onset of AF can be identified in 21 (72.4%) of 29 untreated patients and in 12 (100%) of 12 TEA-treated patients in whom the recordings permitted such an analysis. The heart rate variability components analyzed during 5-minute periods for 30 minutes before AF onset did not differ significantly from those at corresponding times at the first postoperative day in either patient group. The HR during the 8 beats immediately before AF onset was lower in TEA-treated than in untreated patients.

CONCLUSION

The finding of an SPB at the onset of postoperative AF in most of the patients and irrespective of changes in HR supports the hypothesis that postoperative AF is primarily triggered by latent focal atrial activity. The autonomic tone did not seem to be of major importance in the population studied.

Comparison of the effects of propofol and midazolam on the cardiovascular autonomic nervous system during combined spinal and epidural anesthesia

STUDY OBJECTIVE

To investigate the effect of propofol and midazolam on cardiac autonomic nervous system (CANS) activity during combined spinal-epidural anesthesia.

DESIGN

Prospective, clinical study.

SETTING

Operating room of a university hospital.

PATIENTS

Forty ASA physical status I and II patients scheduled for knee surgery.

INTERVENTION

Patients were randomized to receive sedation with either propofol or midazolam.

MEASUREMENTS

Heart rate (HR), HR variability (HRV), systolic arterial pressure (SAP), and SAP variability (SAPV) were used for the analysis. These values were measured at the preanesthetic period, after intrathecal injection for spinal anesthesia, after sedation with propofol or midazolam, and just before the end of surgery with sedation. Cross-spectral analyses of the HR and SAP data were assessed to quantify the frequency-related coherence spectra and phase spectra.

MAIN RESULTS

Spinal anesthesia itself had no effect on power spectral changes in both groups. After sedation, as for HRV, high-frequency (HF) power (HF, 0.15-0.40 Hz) did not change, whereas low-frequency (LF) power (LF, 0.04-0.15 Hz) and LF/HF, an indicator of CANS balance, significantly decreased with propofol. Further, coherence in cross-spectra presented depression in the LF band area after sedation with propofol. Before the end of surgery with sedation, LF and LF/HF in both HRV and SAPV were correlated with age in those with propofol; however, scarce relation was observed in those who received midazolam.

CONCLUSIONS

Propofol was more potent than midazolam in causing CANS activity to be sympatholytic during combined spinal and epidural anesthesia and which was correlated with age only with propofol.

Heart rate to arterial pressure impulse response during one lung ventilation

BACKGROUND

Although one lung ventilation (OLV) is commonly used, little is known about the modulation of the autonomic nervous system with OLV while under general anesthesia. As the frequency domain and time domain analyses are powerful analytic tools, we investigated their modulation during OLV.

METHODS

Patients undergoing thoracic surgery were classified into two groups: those who did (group A, n=8) and those who did not (group N, n=8) receive atropine. After a double lumen tube was placed endotracheally, mechanical ventilation of both lungs (BLV) was established at 18 min(-1) while under isoflurane anesthesia. Electrocardiogram, systolic arterial pressure (SAP), and inspiratory flow (Finsp) were digitally recorded as follows: awake before anesthesia; BLV after anesthesia; BLV after intravenous 10 microg kg(-1) of atropine (group A) or not (group N); left OLV; and right OLV. Power spectral analyses of heart rate (HR) and SAP were computed by determining low-(LF, 0.04-0.15 Hz) and high-frequency (HF, 0.15-0.40 Hz) components, and impulse response analysis was executed among HR, SAP, and Finsp. Impulse responses were assessed by the maximum values in the time domain.

RESULTS

In frequency domain analysis, atropine depressed LF and LF/HF but not HF in HR variability, while no difference was observed between right OLV and left OLV. The heart rate to SAP impulse response was maintained at a significantly higher level in group A than in group N (905+/-360 vs. 425+/-375 mmHg beats(-1)min(-1)) at right OLV. A significant difference was also observed between left and right OLV within group N.

CONCLUSION

Impulse response analysis demonstrated that there is a greater effect on autonomic nervous system modulation during right OLV than in left OLV, which mainly results from a parasympathetic neural linkage origin.

Thoracic epidural anesthesia does not influence the occurrence of postoperative sustained atrial fibrillation

BACKGROUND

To evaluate whether thoracic epidural anesthesia (TEA) can reduce the incidence of atrial fibrillation (AF) after coronary artery bypass grafting (CABG).

METHODS

Forty-one patients undergoing CABG were treated with TEA intraoperatively and postoperatively. Another 80 patients served as the control group. The sympathetic and parasympathetic activities were evaluated by analysis of neuropeptides, catecholamines and heart rate variability (HRV), preoperatively and postoperatively.

RESULTS

Postoperative AF occurred in 31.7% of the TEA-treated patients and in 36.3% of the untreated patients (p = 0.77). TEA significantly suppressed sympathetic activity, as indicated by a less pronounced increase of norepinephrine and epinephrine (p = 0.03, p = 0.02) and a significant decrease of neuropeptide Y (p = 0.01) postoperatively in TEA-treated patients compared to untreated patients. The HRV variable expressing sympathetic activity was significantly lower and the postoperative increase in heart rate was significantly less in the TEA group than in the control group after surgery (p = 0.01, p < 0.001). Among patients developing AF, the maximal number of supraventricular premature beats per minute increased significantly in untreated patients postoperatively but remained unchanged in TEA-treated patients (p = 0.004 versus p = 0.86).

CONCLUSIONS

TEA has no effect on the incidence of postoperative sustained AF, despite a significant reduction in sympathetic activity.

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.