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

Hypothermia and heart rate variability in a healthy newborn piglet model

Decreased heart rate variability (HRV) may be a biomarker of brain injury severity in neonatal hypoxic-ischemic encephalopathy for which therapeutic hypothermia is standard treatment. While therapeutic hypothermia may influence the degree of brain injury; hypothermia may also affect HRV per se and obscure a potential association between HRV and hypoxic-ischemic encephalopathy. Previous results are conflicting. This study aimed to investigate the effect of hypothermia on HRV in healthy, anaesthetised, newborn piglets. Six healthy newborn piglets were anaesthetised. Three piglets were first kept normothermic (38.5-39.0 °C) for 3 h, then exposed to hypothermia (33.5-34.5 °C) for 3 h. Three piglets were first exposed to hypothermia for 3 h, then rewarmed to normothermia for 3 h. Temperature and ECG were recorded continuously. HRV was calculated from the ECG in 5 min epochs and included time domain and frequency domain variables. The HRV variables were compared between hypothermia and normothermia. All assessed HRV variables were higher during hypothermia compared to normothermia. Heart rate was lower during hypothermia compared to normothermia and all HRV variables correlated with heart rate. Hypothermia was associated with an increase in HRV; this could be mediated by bradycardia during hypothermia.

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.

Efeito de frações inspiradas de oxigênio e modalidades ventilatórias diferentes sobre a idade de cães

RESUMO Objetivou-se avaliar diferentes modalidades ventilatórias em cães de diferentes idades submetidos à fração inspirada de oxigênio (FiO2) de 40% e 100%. Foram utilizados 36 cães de três grupos etários (GJ: 0-5; GA: 5-10 e GG: 10-15 anos), sem padronização de peso, sexo, raça e procedimento cirúrgico. Foram pré-medicados com acepromazina e morfina (0,02 e 0,5mg/kg), induzidos à anestesia geral com propofol dose-efeito, manutenção do plano anestésico com isoflurano em 1,3 V% e fornecimento de oxigênio conforme a FiO2 estabelecida para o grupo. Os animais foram submetidos a quatro diferentes modalidades ventilatórias: ventilação espontânea (VE), ventilação ciclada a volume (VCV), ventilação ciclada a pressão (VCP) e ventilação ciclada a pressão com PEEP (VCPP), e permaneceram 30 minutos em cada modalidade. Os parâmetros cardiovasculares mantiveram-se estáveis para todas as FiO2, modalidades ventilatórias e idades. Com relação aos parâmetros ventilatórios, na FiO2 100%, foram observados PaCO2 de 45mmHge e 29% de shunt, enquanto a FiO2 40% apresentou PaCO2 de 43 mmHg e 13% de shunt. Em relação às diferentes idades, os animais adultos e geriátricos apresentaram maiores valores de shunt (26% e 22%) e PaCO2 (44mm/Hg e 46mm/Hg). Conclui-se que a fração inspirada de 40% e a modalidade ventilatória ciclada a volume mostraram-se mais eficientes.

Comparison between intravenous lidocaine and fentanyl on cough reflex and sympathetic response during endotracheal intubation in dogs

OBJECTIVE

To compare the effects of intravenous (IV) lidocaine and fentanyl on the cough reflex and autonomic response during endotracheal intubation in dogs.

STUDY DESIGN

Randomized, blinded, superiority clinical trial.

ANIMALS

A total of 46 client-owned dogs undergoing magnetic resonance imaging.

METHODS

After intramuscular methadone (0.2 mg kg^-1), dogs were randomized to be administered either IV lidocaine (2 mg kg^-1; group L) or fentanyl (7 μg kg^-1; group F). After 5 minutes, alfaxalone was administered until endotracheal intubation was possible (1 mg kg^-1 IV over 40 seconds followed by 0.4 mg kg^-1 increments to effect). Total dose of alfaxalone was recorded and cough reflex at endotracheal intubation was scored. Heart rate (HR) was continuously recorded, Doppler systolic arterial blood pressure (SAP) was measured every 20 seconds. Vasovagal tonus index (VVTI) and changes (Δ) in HR, SAP and VVTI between pre-intubation and intubation were calculated. Groups were compared using univariate and multivariate analysis. Statistical significance was set as p < 0.05.

RESULTS

Group F included 22 dogs and group L 24 dogs. The mean (± standard deviation) alfaxalone dose was 1.1 (± 0.2) and 1.35 (± 0.3) mg kg^-1 in groups F and L, respectively (p = 0.0008). At intubation, cough was more likely in group L (odds ratio = 11.3; 95% confidence intervals, 2.1 - 94.2; p = 0.01) and HR increased in 87.5% and 54.5% of groups L and F, respectively (p = 0.02). The median (range) ΔHR between pre-intubation and intubation was higher (13.1%; - 4.3 to + 55.1) in group L (p = 0.0021). Between groups, SAP and VVTI were similar.

CONCLUSION AND CLINICAL RELEVANCE

At the stated doses, whilst reducing the alfaxalone dose, fentanyl is superior to lidocaine in suppressing the cough reflex and blunting the increase in HR at endotracheal intubation in dogs premedicated with methadone.

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.

Autonomic cardiac regulation after general anesthesia in children

BACKGROUND

General anesthesia dramatically decreases the activity of the autonomic nervous system. Most of the hypnotic agents used to induce anesthesia inhibit sympathetic cardiovascular regulation and baroreflex control in a dose-dependent manner, lowering cardiac adaptability during the operation. The consequence of this effect in children during and after surgery has never been studied to date.

AIM

The aim of this study was to follow the variations in autonomic cardiac indices in children younger than 8 years old after general anesthesia (6-24 hours) in programmed surgery.

METHOD

A prospective descriptive monocentric study of 44 children under 8 years old who underwent scheduled surgery at our hospital center (Saint-Étienne University Hospital, France) was performed between June 1, 2016 and November 1, 2016. Heart rate variability was monitored for 24 hours using Holter-ECG devices and the resulting data were interpreted using linear and nonlinear analyses.

RESULTS

Compared to baseline thresholds before surgery, all heart rate variability indices decreased dramatically during general anesthesia. After awakening, a slight reduction in sympathetic activity persisted 6 hours after surgery, but all measurements of sympathetic and parasympathetic activity had returned to baseline thresholds 12 hours after the operation. Twenty-four hours after surgery, some parameters had increased above the corresponding baseline levels.

CONCLUSION

Autonomic nervous function normalizes rapidly (within 12 hours) in prepubertal children. This study indicates that general anesthesia does not seem to increase the long-term risk of autonomic dysfunction in these patients.

Heart rate variability: implications for perioperative anesthesia care

PURPOSE OF REVIEW

Heart rate variability (HRV) is a measure of the balance between both the parasympathetic and sympathetic nervous system and may provide useful information for anesthesia care providers. HRV may offer predictive information about critically ill and operative patients. Further, HRV collection provides real-time information of patient autonomic nervous system status and may allow tailoring of the analgesia for patients in the ICU and operating room.

RECENT FINDINGS

Reduced and abnormal resting HRV predict sudden and nonsudden cardiac death. Recent evidence shows that decreased HRV correlates with worsened outcomes in both trauma patients and patients with sepsis, as well as the risk of developing hypotension after induction of general anesthesia and placement of intrathecal local anesthesia. In addition, HRV appears to provide an accurate assessment of the nociception-analgesia balance in deeply sedated ICU patients and those under general anesthesia.

SUMMARY

No study has assessed the prognostic value of preoperative HRV in patients presenting for surgery. Use of HRV for patient risk stratification and intraoperative analgesia management may allow tailored perioperative care and improved outcomes. If intraoperative HRV data leads to decreased perioperative opioid use, opioid-related adverse events, a serious perioperative issue, may be decreased.

CLINICAL TRIALS REGISTRATION

Not applicable.

Comparison of heart rate variability response in children undergoing elective endotracheal intubation with and without neuromuscular blockade: a randomized controlled trial

BACKGROUND

The routine use of neuromuscular blocking drugs (NMBD) for endotracheal intubation in children is the subject of much controversy. The analysis of heart rate variability (HRV) can reveal information about the functional state of the autonomic nervous system (ANS).

AIM

The purpose of this study was to determine if HRV elucidates differences in the sympathovagal balance of children undergoing elective endo-tracheal intubation with and without neuromuscular blockade (NMB).

METHODS

In this prospective study, 38 children (2-6 years) scheduled for adenotonsillectomy were randomized into two groups to receive fentanyl 2 μg·kg(-1) and propofol 4 mg·kg(-1) , with either mivacurium 0.25 mg·kg(-1) (NMB group) or saline solution (NoNMB group) for anesthesia induction. The same experienced, blinded anesthesiologist performed endotracheal intubation. Heart rate variability, RR intervals, ECG as well as an electroencephalogram were recorded with HRV and BIS XP monitors, respectively. Heart rate variability was analyzed in the frequency domain.

RESULTS

There was no significant difference in HRV changes immediately after mivacurium administration compared with an administration of saline. The groups were comparable for the bispectral index value (NMB 35 [33-41] vs NoNMB 34 [32-42]) during endotracheal intubation. Changes in both the low-frequency power and the low-/high-frequency ratio immediately after endotracheal intubation compared with the unstimulated state before laryngoscopy were significantly higher without NMB (P = 0.015 and P = 0.006, respectively), whereas there was no significant difference with respect to the high-frequency power.

CONCLUSIONS

The stress response during endotracheal intubation in pediatric patients represented by the frequency domain analysis of HRV was found to be higher without NMB. When mivacurium was added to a propofol-fentanyl induction regimen, the ANS alterations during endotracheal intubation decreased significantly.

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.

Recent advance in patient monitoring

Recent advance in technology has developed a lot of new aspects of clinical monitoring. We can monitor sedation levels during anesthesia using various electroencephalographic (EEG) indices, while it is still not useful for anesthesia depth monitoring. Some attempts are made to monitor the changes in sympathetic nerve activity as one of the indicators of stress, pain/analgesia, or anesthesia. To know the balance of sympathetic and parasympathetic activity, heart rate or blood pressure variability is investigated. For trend of cardiac output, low invasive monitors have been investigated. Improvement of ultrasound enables us to see cardiac structure and function continuously and clearer, increases success rate and decreases complication of central venous puncture and various kinds of nerve blocks. Without inserting an arterial catheter, trends of arterial oxygen tension or carbon dioxide tension can be monitored. Indirect visualization of the airway decreases difficult intubation and makes it easier to teach tracheal intubation. The changes in blood volume can be speculated non-invasively. Cerebral perfusion and metabolism are not ordinary monitored yet, but some studies show their usefulness in management of critically ill. This review introduces recent advances in various monitors used in anesthesia and critical care including some studies of the author, especially focused on EEG and cardiac output. However, the most important is that these new monitors are not almighty but should be used adequately in a limited situation where their meaning is confirmed.

Cardiac autonomic regulation during gastroscopy

BACKGROUND

Gastroscopy is sometimes associated with adverse cardiovascular events.

AIMS

We evaluated the effects of sedation and pharyngeal anaesthesia on cardiac autonomic regulation during gastroscopy.

PATIENTS

Two hundred thirteen outpatients undergoing gastroscopy.

METHODS

The patients were assigned to 4 groups: (1) sedation with intravenous midazolam and placebo throat spray (midazolam group), (2) placebo sedation and pharyngeal anaesthesia with lidocaine (lidocaine group), (3) placebo sedation and placebo throat spray (placebo group), and (4) no intravenous cannula nor throat spray (control group). Continuous electrocardiogram was recorded. Heart rate variability was assessed; the powers of low frequency (0.04-0.15 Hz) and high frequency (0.15-0.40 Hz) components as well as total power (0.0-0.4 Hz) were calculated.

RESULTS

Gastroscopy was associated with a decrease in high frequency normalized units, increases in low frequency normalized units and low frequency/high frequency ratio indicating activation of sympathetic and withdrawal of vagal modulation. Sympathetic activation resulted in a decrease in total power and all components of heart rate variability. The decrease was most prominent in the midazolam treated patients (p<0.001 vs the lidocaine group and p<0.01 vs placebo and control groups during the postendoscopy phase).

CONCLUSION

Gastroscopy induces a shift towards dominance of the sympathetic modulation of the heart. Premedication with midazolam potentiates this shift.

Effect of fentanyl on heart rate variability during spontaneous and paced breathing in healthy volunteers

BACKGROUND

Many studies have been conducted to assess the effects of fentanyl on the autonomic nervous system (ANS) by heart rate variability (HRV) analysis, but disagreement on the results is still present due to confounding influences introduced by concomitant administration of other drugs or opioid-related transitory respiratory depression. We performed a single-drug controlled-breathing study on healthy volunteers to assess the impact of fentanyl on ANS.

METHODS

HRV as a measure of sympathovagal balance was prospectively analyzed with an autoregressive model in 11 subjects during spontaneous and paced breathing (PB) at 20 breaths/min both before and after fentanyl 1 mcg/kg administration. HRV total power, sympathovagal balance (low-frequency/high-frequency ratio) and normalized spectral powers were considered (LFnu, HFnu).

RESULTS

Fentanyl led to a reduction of LFnu (from 55.2+/-23.3 to 43.2+/-24.1, P<0.05) without HFnu increase during PB. A decrease in R-R interval variance (from 3345.6+/-3333.4 to 1806.9+/-1328.6 ms(2), P<0.05) was shown after fentanyl administration during spontaneous but not PB. PB alone decreased the HRV total power and R-R interval variance.

CONCLUSIONS

Low-dose fentanyl administration in healthy volunteers leads to sympathetic and overall ANS modulation decrease, with a trend toward vagal activation.

Heart rate variability does not discriminate between different levels of haemodynamic responsiveness during surgical anaesthesia †

BACKGROUND

Hypnotic depth but not haemodynamic responsiveness is measured with EEG-based monitors. In this study we compared heart rate variability (HRV) in unstimulated patients and stimulation-induced HRV at different levels of anaesthesia.

METHODS

A total of 95 ASA I or II patients were randomly assigned to five groups (Group 1: BIS 45(5), remifentanil 1 ng ml(-1); Group 2: BIS 45(5), remifentanil 2 ng ml(-1); Group 3: BIS 45(5), remifentanil 4 ng ml(-1); Group 4: BIS 30(5), remifentanil 2 ng ml(-1); Group 5: BIS 60(5), remifentanil 2 ng ml(-1)). A time- and frequency-domain analysis of the RR interval (RRI) from the electrocardiogram was performed. HRV before induction, before and after a 5 s tetanic stimulus of the ulnar nerve, and before and after tracheal intubation was compared between groups, between stimuli, and between responders to intubation [systolic arterial pressure (SAP) increase >20 mm Hg, a maximal heart rate (HR) after intubation >90 min(-1) or both] and non-responders (anova).

RESULTS

Induction of anaesthesia significantly lowered HR and HRV. Mean RRI before stimulation was higher in G3 than in G1, G2, and G4 (P < 0.001), whereas the other HRV parameters were similar. Intubation induced a greater HRV response than tetanic stimulation. The mean RRI after intubation was lower in G3 compared with the other groups and the sd of the RRI after tetanic stimulation was lower in G3 compared with G5. Otherwise, unstimulated HRV and stimulation-induced HRV were similar in responders and non-responders.

CONCLUSION

HRV parameters discriminate between awake and general anaesthesia, are different after tracheal intubation and a 5 s ulnar nerve stimulation, but do not discriminate between different levels of haemodynamic responsiveness during surgical anaesthesia.

Effects of Pericardial Lidocaine on Hemodynamic Parameters and Responses in Dogs Anesthetized With Midazolam and Fentanyl

OBJECTIVE

Tachycardia during anesthesia should be avoided, especially during off-pump coronary artery bypass graft surgery. Decreasing heart rate without reducing cardiac contractility is an ideal goal. To achieve this, the authors attempted to block the cardiac nerves by pericardial administration of local anesthetic.

DESIGN

A prospective study.

SETTING

A laboratory.

PARTICIPANTS

Anesthetized, mechanically ventilated dogs (n = 69).

INTERVENTIONS

The pericardial space was infused with 2.5 or 5 mL of 1% lidocaine, 5 mL of 2% lidocaine, or normal saline solution. The hemodynamic changes and the cardiac responses to atropine or isoproterenol were measured during cardiac nerve blockade. To examine the inhibitory action of pericardial lidocaine on arrhythmias, an electrical fibrillator was installed. Furthermore, the blood level of lidocaine was measured.

MEASUREMENTS AND MAIN RESULTS

Pericardial injection of lidocaine significantly decreased heart rate without a change in stroke volume. Under pericardial lidocaine, the tachycardia response to isoproterenol was similar to that observed without pericardial lidocaine, but response to atropine was significantly reduced. Pericardial lidocaine increased the voltage thresholds for inducing arrhythmias and ventricular fibrillation. Intravenous injection of lidocaine elevated the plasma concentration of lidocaine immediately, whereas the plasma concentration peaked at 10 minutes after pericardial administration.

CONCLUSIONS

Pericardial lidocaine (1) decreased heart rate without affecting stroke volume, (2) preserved the tachycardiac response to isoproterenol but completely blocked the response to atropine, and (3) increased the voltage thresholds for arrhythmias and ventricular fibrillation induced by an electrical fibrillator. These results suggest that pericardial lidocaine may be useful for controlling heart rate during off-pump coronary artery bypass graft surgery.

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.

Modulation of Cardiac Autonomic Nervous Activity Early after Cardioversion of Atrial Fibrillation by Biphasic Waveform

BACKGROUND

Imbalance of cardiac autonomic nervous modulation might prominently contribute to early relapses of atrial fibrillation (AF) after cardioversion (CV). The biphasic (Bi) waveform is more effective than the monophasic (Mo) waveform in CV of AF. Whether these waveforms have different effects on autonomic modulation early after CV is unknown.

METHODS

We investigated 171 consecutive patients after successful electrical CV (mean age 65.4 years, 82% male, 80% structural heart disease). Bi waveform was used in 89, Mo waveform in 82. Heart rate variability (HRV) was analyzed from 24-hour Holter recordings, started directly after CV.

RESULTS

Mean delivered total energy was significantly lower in the Bi group (Bi 223 +/- 163 W, Mo 355 +/- 211 W, P < 0.001). Mean RR interval decreased within 5 hours after CV and increased again within the remaining hours, without significant differences between Bi and Mo groups. Time courses of time domain parameters of HRV revealed Bi profiles with the lowest levels 6 hours after CV in both groups. However, the hourly values of HRV were significantly higher in the Bi subgroup.

CONCLUSION

Our study indicates that waveform and total delivered energy significantly influence autonomic modulation of the sinus node in the early phase after CV of AF. In contrast to Bi CV, Mo CV is characterized by a significant decrease of cardiac vagal modulation, which may have an arrhythmic effect by increasing the degree of early electrical stunning after CV of AF.

Opioids and opiates: analgesia with cardiovascular, haemodynamic and immune implications in critical illness

Traumatic injury, surgical interventions and sepsis are amongst some of the clinical conditions that result in marked activation of neuroendocrine and opiate responses aimed at restoring haemodynamic and metabolic homeostasis. The central activation of the neuroendocrine and opiate systems, known collectively as the stress response, is elicited by diverse physical stressor conditions, including ischaemia, glucopenia and inflammation. The role of the hypothalamic-pituitary-adrenal axis and sympathetic nervous system in counterregulation of haemodynamic and metabolic alterations has been studied extensively. However, that of the endogenous opiates/opioid system is still unclear. In addition to activation of the opiate receptor through the endogenous release of opioids, pharmacotherapy with opiate receptor agonists is frequently used for sedation and analgesia of injured, septic and critically ill patients. How this affects the haemodynamic, cardiovascular, metabolic and immune responses is poorly understood. The variety of opiate receptor types, their specificity and ubiquitous location both in the central nervous system and in the periphery adds additional complicating factors to the clear understanding of their contribution to the stress response to the various physical perturbations. This review aims at discussing scientific evidence gathered from preclinical studies on the role of endogenous opioids as well as those administered as pharmacological agents on the host cardiovascular, neuroendocrine, metabolic and immune response mechanisms critical for survival from injury in perspective with clinical observations that provide parallel assessment of relevant outcome measures. When possible, the clinical relevance and corresponding scenarios where this evidence can be integrated into our understanding of the clinical implications of opiate effects will be examined. Overall, the scientific basis to enhance clinical judgment and expectations when using opioid sedation and analgesia in the management of the injured, septic or postsurgical patient will be discussed.

Effect of remifentanil with and without atropine on heart rate variability and RR interval in children

Remifentanil can cause bradycardia either by parasympathetic activation or by other negative chronotropic effects. The high frequency (HF) component of heart rate variability (HRV) is a marker of parasympathetic activity. This study aimed to evaluate the effect of remifentanil on RR interval and on HRV in children. Forty children ASA I or II were studied after approval by the human studies committee and informed parental consent was obtained. After stabilisation at sevoflurane 1 MAC, they were randomly divided into two groups: one received a 20 microg.kg(-1) atropine injection (AT + REMI) and the other ringer lactate solution (REMI). Three minutes later, a 1 microg.kg(-1) bolus of remifentanil was administered over 1 min, followed by a continual infusion at 0.25 microg.kg(-1).min(-1) for 10 min increased to 0.5 microg.kg(-1).min(-1) for a further 10 min. A time varying, autoregressive analysis of RR sequences was used to estimate classical spectral parameters: low (0.04-0.15 Hz; LF) and high (0.15-0.45 Hz; HF) frequency, whereas the root mean square of successive differences of RR intervals (rmssd) was derived directly from the temporal sequence. Statistical analyses were conducted by means of the multiple correspondence analysis and with non parametrical tests. Remifentanil induced an RR interval lengthening, i.e. bradycardia, in both groups compared to pretreatment values and was associated with an increase of HF and rmssd only for the REMI group. The parasympathetic inhibition by atropine did not totally prevent remifentanil's negative chronotropic effect. A direct negative chronotropic effect of remifentanil is proposed.

Midazolam sedation increases fluctuation and synchrony of the resting brain BOLD signal

The blood oxygen level-dependent (BOLD) magnetic resonance signal of functional brain cortices is dominated by very low frequency (VLF) fluctuations in anesthetized child patients. The temporal synchrony of the BOLD signal is also higher in anesthetized children compared with awake adults. The origin of the synchronous fluctuations can be related to maturation, pathological status or the anesthesia used in the imaging. Two of the three confounding variables (maturation and pathology) were controlled in this study. The effect of midazolam (4+/-0.8 mg) sedation on the BOLD signal was assessed in 12 healthy adults (aged 24+/-1.5 years) at 1.5 T. The VLF fluctuation power and temporal synchrony of the BOLD signal increased significantly after the sedation in the auditory and visual cortices. The fast Fourier transformation power spectral baseline fit parameters of the BOLD signal were also found to change significantly after sedation. It is concluded that the VLF fluctuation and temporal synchrony of the BOLD signal become increased after sedation in functional brain regions.

Comparison of bolus remifentanil versus bolus fentanyl for induction of anesthesia and tracheal intubation in patients with cardiac disease

OBJECTIVE

Large bolus-dose remifentanil may be advantageous for use during induction of anesthesia because of its short duration of effect. Currently, there are little data on the use of large bolus-dose remifentanil because of reports of severe bradycardia and hypotension. The purpose of this study is to compare the hemodynamic effects of bolus remifentanil versus fentanyl with glycopyrrolate for induction of anesthesia in patients with heart disease.

DESIGN

A randomized, double-blinded study.

SETTING

A tertiary-care academic medical center.

PARTICIPANTS

One hundred patients for coronary artery bypass or valvular surgery.

INTERVENTION

Subjects received either (1) remifentanil, 5 microg/kg, with glycopyrrolate, 0.2 mg, or (2) fentanyl, 20 microg/kg, with 0.2 mg of glycopyrrolate, and both groups also received midazolam, 70 microg/kg, for induction of anesthesia.

MEASUREMENTS AND MAIN RESULTS

Heart rate, mean arterial pressure, systemic vascular resistance, and cardiac output were similar between the 2 groups during induction of anesthesia and tracheal intubation. The incidence of adverse events such as bradycardia (remifentanil 10%, fentanyl 10%), hypotension (remifentanil 16%, fentanyl 10%), and ischemia (remifentanil 0%, fentanyl 2%) were also similar. A greater percentage of patients in the remifentanil group lost consciousness within 1 minute of opioid administration (86% v 66%, p = 0.034).

CONCLUSION

Remifentanil with glycopyrrolate is associated with rapid and predictable clinical anesthetic effect, cardiac stability, and the ability to blunt the hemodynamic responses to tracheal intubation. Bolus remifentanil may be a feasible alternative to bolus fentanyl for induction of anesthesia in patients with heart disease because of its short duration of action and its ability to blunt the hemodynamic responses to tracheal intubation.

Linear and nonlinear analysis of heart rate variability during propofol anesthesia for short-duration procedures in children

OBJECTIVE

To determine whether heart rate variability metrics provide an accurate method of monitoring depth of anesthesia, assessing the response to painful stimuli, and assessing neuroautonomic regulation of cardiac activity in children receiving propofol anesthesia for short-duration procedures.

DESIGN

Prospective, case series.

SETTING

Sixteen-bed pediatric intensive care unit, oncology unit, and endoscopy suite in a tertiary care children's hospital and ophthalmology examination rooms in an associated eye institute.

PATIENTS

Thirty-three pediatric patients undergoing propofol anesthesia for short procedures.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Heart rate variability metrics studied included mean, SD, low- and high-frequency power, detrended fluctuation analysis (represented by correlation coefficient, alpha), and approximate entropy. Compared with the initial anesthetized state, we found increased heart rate SD (3.17 +/- 1.31 vs. 7.05 +/- 0.26 bpm, p <.0001), heart rate low-frequency power (3.69 +/- 0.36 vs. 4.48 +/- 0.41 bpm(2)/Hz, p <.0001), heart rate low-/high-frequency ratio (1.47 +/- 0.26 vs. 1.26 +/- 0.24, p =.001), and heart rate alpha (1.12 +/- 0.24 vs. 1.35 +/- 0.21, p <.0001) during painful procedure. Mean heart rate (105.8 +/- 13.4 vs. 101.5 +/- 12.4 bpm, p =.005) and heart rate approximate entropy decreased with painful procedure (0.75 +/- 0.19 vs. 0.53 + 0.16, p <.001), whereas there was no significant change in heart rate high-frequency power (3.04 +/- 0.63 vs. 3.16 +/- 0.71 bpm(2)/Hz, p =.26).

CONCLUSIONS

We conclude that power spectral analysis of heart rate variability may be an accurate and clinically useful measure of depth of propofol anesthesia. We speculate that high-frequency heart rate power during propofol anesthesia correlates with depth of anesthesia, whereas low-frequency power allows for assessment of the patient's sympathetic response to pain.

Could heart rate variability predict outcome in patients with severe head injury? A pilot study

Despite major improvements in the resuscitation of patients with head injury, the outcome of patients with head trauma often remains poor and difficult to establish. Heart rate variability (HRV) analysis is a noninvasive tool used to measure autonomic nervous system (ANS) activity. The aim of this prospective study was to investigate whether HRV analysis might be a useful adjunct for predicting outcome in patients with severe head injury. Twenty patients with severe head trauma (Glasgow Coma Scale [GCS] <or= 8) underwent 24-hour electrocardiogram recording 1 day after trauma and again 48 hours after withdrawal of sedative drugs. Heart rate variability was assessed, in both time domain and spectral domain. The authors initially compared (on Day 1) HRV in patients who progressed to brain death to HRV in survivors; then during the awakening period compared HRV in surviving patients with good recovery (GCS >or= 10) to HRV in patients characterized by a worsened neurologic state (GCS < 10). Statistical analysis used the Kruskal-Wallis test, P < .05. To assess whether HRV could predict evolution to brain death, receiver operating characteristic (ROC) curves were generated the day after trauma for Total Power, natural logarithm of high-frequency component of spectral analysis (LnHF), natural logarithm of low-frequency component of spectral analysis (LnLF), and root mean square for successive interval differences (rMSSD). Seven patients died between Day 1 and Day 5 after trauma. Six of those had progressed to brain death. In these six patients, at Day 1, Global HRV and parasympathetic tone were significantly higher. Referring to the area under the rMSSD ROC curve, HRV might provide useful information in predicting early evolution of patients with severe head trauma. During the awakening period, global HRV and the parasympathetic tone were significantly lower in the worsened neurologic state group. In conclusion, HRV could be helpful as a predictor of imminent brain death and a useful adjunct for predicting the outcome of patients with severe head injury.

Oculocardiac reflex in sedated patients having laser in situ keratomileusis

PURPOSE

To eliminate stress as a variable in assessing the frequency of the oculocardiac reflex during laser in situ keratomileusis (LASIK).

SETTING

Merida Ophthalmological Hospital and Oftalmedica, Mexico City, Mexico.

METHODS

A pulse oximeter registered the heart rate of 30 sedated patients having LASIK. Sedation was accomplished with a combination of midazolam and fentanyl. The heart rate was noted before and during suction. The results in 1 eye of each patient were recorded. Oculocardiac reflex was defined as a decrease of 10% or more of the basal heart rate.

RESULTS

Fourteen patients (46.7%) had a 10% or more decrease in heart rate when suction was applied. Ten of the 14 had a decrease in heart rate between 10% and 19%, 3 between 20% and 29%, and 1 of more than 30%. Two patients (6.6%) had an increase in the basal heart rate of more than 10%.

CONCLUSIONS

The findings suggest that the oculocardiac reflex occurs more frequently in sedated patients than in nonsedated patients.