Remifentanil and nitrous oxide reduce changes in cerebral blood flow velocity in the middle cerebral artery caused by pain

Hypothesizing in the Face of the Opioid Crisis Coupling Genetic Addiction Risk Severity (GARS) Testing with Electrotherapeutic Nonopioid Modalities Such as H-Wave Could Attenuate Both Pain and Hedonic Addictive Behaviors

In the United States, amid the opioid overdose epidemic, nonaddicting/nonpharmacological proven strategies are available to treat pain and manage chronic pain effectively without opioids. Evidence supporting the long-term use of opioids for pain is lacking, as is the will to alter the drug-embracing culture in American chronic pain management. Some pain clinicians seem to prefer classical analgesic agents that promote unwanted tolerance to analgesics and subsequent biological induction of the "addictive brain". Reward genes play a vital part in modulation of nociception and adaptations in the dopaminergic circuitry. They may affect various sensory and affective components of the chronic pain syndromes. The Genetic Addiction Risk Severity (GARS) test coupled with the H-Wave at entry in pain clinics could attenuate pain and help prevent addiction. The GARS test results identify high-risk for both drug and alcohol, and H-Wave can be initiated to treat pain instead of opioids. The utilization of H-Wave to aid in pain reduction and mitigation of hedonic addictive behaviors is recommended, notwithstanding required randomized control studies. This frontline approach would reduce the possibility of long-term neurobiological deficits and fatalities associated with potent opioid analgesics.

Human experimental pain models for assessing the therapeutic efficacy of analgesic drugs

Pain models in animals have shown low predictivity for analgesic efficacy in humans, and clinical studies are often very confounded, blurring the evaluation. Human experimental pain models may therefore help to evaluate mechanisms and effect of analgesics and bridge findings from basic studies to the clinic. The present review outlines the concept and limitations of human experimental pain models and addresses analgesic efficacy in healthy volunteers and patients. Experimental models to evoke pain and hyperalgesia are available for most tissues. In healthy volunteers, the effect of acetaminophen is difficult to detect unless neurophysiological methods are used, whereas the effect of nonsteroidal anti-inflammatory drugs could be detected in most models. Anticonvulsants and antidepressants are sensitive in several models, particularly in models inducing hyperalgesia. For opioids, tonic pain with high intensity is attenuated more than short-lasting pain and nonpainful sensations. Fewer studies were performed in patients. In general, the sensitivity to analgesics is better in patients than in healthy volunteers, but the lower number of studies may bias the results. Experimental models have variable reliability, and validity shall be interpreted with caution. Models including deep, tonic pain and hyperalgesia are better to predict the effects of analgesics. Assessment with neurophysiologic methods and imaging is valuable as a supplement to psychophysical methods and can increase sensitivity. The models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. Knowledge obtained from this review can help design experimental pain studies for new compounds entering phase I and II clinical trials.

[Transcranial Doppler ultrasound, bispectral index, and electroencephalographic monitoring of entropy during pediatric total intravenous anesthesia]

BACKGROUND AND OBJECTIVE

Transcranial Doppler ultrasound is a noninvasive technique for monitoring the velocity of blood flow in the main intracranial arteries, particularly those in the circle of Willis. Our aim was to assess whether changes in cerebral arterial blood flow in anesthetized pediatric patients detected by pulsed Doppler ultrasound correlate with changes in the bispectral (BIS) index and electroencephalographic state and response entropy (ES and ER, respectively).

MATERIAL AND METHODS

Prospective, blinded observational study of 36 pediatric patients (age range, 5 to 11 years) under total intravenous anesthesia for minor surgical procedures. Propofol and fentanyl were used for induction; propofol and remifentanil in continuous perfusion and a single dose of cisatracurium were used for maintenance. In all patients we monitored hemodynamic and respiratory patterns, gases, temperature, and hypnosis (BIS, ES and ER) as well as cerebral blood flow estimated by pulsed Doppler ultrasound in the middle cerebral artery. Raw data were subjected to statistical smoothing. The resistance index, pulsatility index, mean velocity, and estimated baseline cerebral blood flow were calculated from the Doppler sonogram. We then studied the correlations between the Doppler-derived values and BIS, ES, ER, fraction of end-tidal carbon dioxide, and temperature. The variables were entered into logistic regression.

RESULTS

The pattern at induction indicated high resistance (low mean velocities and high pulsatility indexes) until the lowest BIS and ES values of 31 and 29, respectively, were reached. During maintenance, the Doppler sonogram pattern was slower (normalization of the pulsatility index, the resistance index, and mean velocity). Changes in flow and absolute entropy and BIS values were statistically correlated (Pearson's r values > or = 0.91); there was 95.6% agreement between Doppler values and BIS and agreement between BIS and ES values of 35-45. On awakening, flow velocities approached baseline values when BIS and ES rose to between 90 and 98. The estimated cerebral blood flow underwent fluctuations coinciding with an approximately concomitant increase or decrease in BIS (r > 0.95); the response of BIS was slightly delayed by no more than a minute but there was no corresponding response of entropy measurements.

CONCLUSIONS

We report Doppler ultrasound patterns during anesthesia with propofol. Systems for monitoring hypnosis could be considered indirect measurements of cerebral blood flow; BIS measurements are more sensitive to flow change. Transcranial Doppler ultrasound facilitates the observation of changes in blood flow that occur at different levels of hypnosis during anesthesia.

[Transcranial Doppler ultrasound, bispectral index, and electroencephalographic monitoring of entropy during sevoflurane anesthesia in children]

BACKGROUND AND OBJECTIVE

Transcranial Doppler ultrasound is a noninvasive technique for monitoring the velocity of blood flow in the main intracranial arteries, particularly those in the circle of Willis. Our aim was to assess whether changes in cerebral arterial blood flow in pediatric patients under sevoflurane anesthesia demonstrated by pulsed Doppler ultrasound correlate with changes in the bispectral (BIS) index and electroencephalographic state and response entropy (ES and ER, respectively).

MATERIAL AND METHODS

Prospective, blinded observational study of 36 pediatric patients (age range, 5 to 11 years; ASA physical status classification, 1-2) under sevoflurane anesthesia for minor surgical procedures. Anesthesia was induced with sevoflurane and maintained with 2.5% sevoflurane in an inspired oxygen fraction of 50% in air. A continuous perfusion of remifentanil was provided for analgesia. In all patients we monitored hemodynamic and respiratory patterns, gases, temperature, and hypnosis (BIS, ES and ER) as well as cerebral blood flow estimated by pulsed Doppler ultrasound in the middle cerebral artery. The resistance index, pulsatility index, mean velocity, and estimated baseline cerebral blood flow were calculated from the Doppler sonogram. Correlations (Pearson's r) were calculated between BIS, ES, ER, the pulsatility index, resistance index, mean flow velocity, estimated cerebral blood flow, fraction of end-tidal carbon dioxide, and temperature. A regression model was constructed.

RESULTS

Induction caused a pattern of high velocity (elevated mean velocity and normal or reduced pulsatility index) until the lowest BIS and ES values of 31 and 29, respectively, were reached. During maintenance, the Doppler sonogram pattern was slower (normalization of the pulsatility index, the resistance index, and mean velocity). Changes in flow and absolute entropy and BIS values were statistically correlated (Pearson's r values > or = 0.91); there was 95.6% agreement between Doppler values and BIS and agreement between BIS and ES values of 35 to 45. On awakening, flow velocities approached baseline values when BIS and ES rose to between 90 and 98. The estimated cerebral blood flow underwent fluctuations coinciding with an approximately concomitant increase or decrease in BIS (r > 0.95); the BIS response occurred with a slight delay of no more than a minute. The entropy measurements did not reflect the fluctuations.

CONCLUSIONS

We show Doppler ultrasound patterns during anesthetic induction with sevoflurane. Systems for monitoring hypnosis could be considered indirect measurements of cerebral blood flow; BIS measurements are more sensitive to change. Transcranial Doppler ultrasound facilitates the observation of changes in blood flow that occur at different levels of hypnosis during anesthesia.

Assessing analgesic actions of opioids by experimental pain models in healthy volunteers - an updated review

AIM

Experimental pain models may help to evaluate the mechanisms of action of analgesics and target the clinical indications for their use. This review addresses how the efficacy of opioids can be assessed in human volunteers using experimental pain models. The drawback with the different study designs is also discussed.

METHOD

A literature search was completed for randomized controlled studies which included human experimental pain models, healthy volunteers and opioids.

RESULTS

Opioids with a strong affinity for the micro-opioid receptor decreased the sensation in a variety of experimental pain modalities, but strong tonic pain was attenuated more than short lasting pain and non-painful sensations. The effects of opioids with weaker affinity for the micro-opioid receptor were detected by a more narrow range of pain models, and the assessment methods needed to be more sensitive.

CONCLUSION

The way the pain is induced, assessed and summarized is very important for the sensitivity of the pain models. This review gives an overview of how different opioids perform in experimental pain models. Generally experimental pain models need to be designed with careful consideration of pharmacological mechanisms and pharmacokinetics of analgesics. This knowledge can aid the decisions needed to be taken when designing experimental pain studies for compounds entering phase 1 clinical trials.

Nitrous oxide analgesia for intubating preterm neonates: a pilot study

AIM

To evaluate the administration of an equimolar mixture of N2O and O2 for intratracheal intubation in preterm neonates with respiratory distress syndrome (RDS).

DESIGN

Prospective evaluation of N2O/O2 in premature neonates with RDS.

SETTING

Tertiary neonatal unit from March to August 2003.

PATIENTS

Twenty-six of 79 neonates admitted for RDS within 48 h of birth.

INTERVENTION

N2O/O2 was administered until muscle tone was suppressed. Surfactant was given intratracheally. Patients were extubated as soon as possible.

MAIN OUTCOME MEASURES

The time needed for N2O/O2 to suppress muscle tone, an evaluation of sedation/analgesia through movements of the limbs, and indicators of stress-related haemodynamic change, all recorded by an independent observer.

RESULTS

In the 26 patients, gestational age was 30.5 (25th, 75th percentile: 30, 32) wk and median body weight was 1540 (1220, 1900) g. Postnatal age at intubation was 2 (2, 3) h. N2O/O2 administration time was 8 (6, 10) min (range 4-15 min). Sedation/analgesia was complete in 77% of patients. No significant differences between pre-procedure and post-procedure values were found for heart rate (p=0.29) or mean arterial blood pressure (p=0.13) (paired Wilcoxon test). Time needed for intubation was 30 (20, 37) s (range 10-60 s). Side effects included transient agitation (3/26) and retching (2/26). Extubation occurred 5 (5, 10) min (range 2-15 min) after surfactant instillation. Apnoeas occurred in 3/26 patients within 2 h after extubation. Two patients required reintubation to repeat surfactant administration within 24 h after extubation.

CONCLUSION

N2O/O2 may be helpful for intubation in preterm neonates. Larger randomized, double-blind studies are needed for a thorough evaluation of effectiveness and safety.

Remifentanil

Remifentanil (Ultiva), a fentanyl derivative, is an ultra-short acting, nonspecific esterase-metabolised, selective mu-opioid receptor agonist, with a pharmacodynamic profile typical of opioid analgesic agents. Notably, the esterase linkage in remifentanil results in a unique and favourable pharmacokinetic profile for this class of agent. Adjunctive intravenous remifentanil during general anaesthesia is an effective and generally well tolerated opioid analgesic in a broad spectrum of patients, including adults and paediatric patients, undergoing several types of surgical procedures in both the inpatient and outpatient setting. Remifentanil is efficacious in combination with intravenous or volatile hypnotic agents, with these regimens generally being at least as effective as fentanyl- or alfentanil-containing regimens in terms of attenuation of haemodynamic, autonomic and somatic intraoperative responses, and postoperative recovery parameters. The rapid offset of action and short context-sensitive half-time of remifentanil, irrespective of the duration of the infusion, makes the drug a valuable opioid analgesic option for use during balanced general inhalational or total intravenous anaesthesia (TIVA) where rapid, titratable, intense analgesia of variable duration, and a fast and predictable recovery are required.

The Effects of Remifentanil on Endotracheal Suctioning-Induced Increases in Intracranial Pressure in Head-Injured Patients

In patients with severe traumatic brain injury, bronchotracheal toilet may be accompanied by deleterious variations in intracranial pressure (ICP). To avoid these effects, IV opioids have been proposed. Twenty mechanically-ventilated patients received 3 ascending IV doses of remifentanil: dose 1 (1 microg/kg bolus, 0.25 microg/kg/min infusion); dose 2 (2 microg/kg bolus, 0.5 microg/kg/min infusion); and dose 3: (4 microg/kg bolus, 1 microg/kg/min infusion). Endotracheal suction was performed 20 min after the beginning of infusion to assess coughing. Heart rate, ICP, mean arterial blood pressure (MAP), cerebral perfusion pressure (CPP), middle cerebral artery mean flow velocity (V(MCA)), and bispectral index were monitored throughout the 30-min study period. Twelve, 15, and 19 patients receiving dose 1, 2, and 3, respectively, required vasopressors to maintain CPP >60 mm Hg. Suctioning resulted in coughing in 16, 15, and 5 patients receiving dose 1, 2, and 3, respectively. An increase in ICP, without change in V(MCA), corresponded to the reduction in MAP consistent with the preservation of autoregulation. Remifentanil used as a continuous infusion in head-injured patients is not an effective drug to block responses to suctioning.

The effect of remifentanil on cerebral blood flow velocity in children anesthetized with propofol

BACKGROUND

Cerebrovascular stability and rapid anesthetic emergence are desirable features of a neuroanesthetic regimen. In this randomized crossover study the effect of a low-dose remifentanil infusion on cerebral blood flow velocity (CBFV) in children anesthetized with propofol was evaluated.

METHODS

Twenty healthy children aged 1-6 years undergoing urological surgery were enrolled. Following face mask induction with sevoflurane, anesthesia was maintained with a standardized propofol infusion. Rocuronium was used to facilitate tracheal intubation and normothermia, and normocapnia were maintained. All children received a caudal epidural block, and a transcranial Doppler probe was placed to measure middle cerebral artery blood flow velocity (Vmca). Each patient received a remifentanil regimen of 0.5 microg x kg(-1) followed by 0.2 microg x kg(-1) x min(-1) in a predetermined order of remifentanil + propofol or propofol alone. Vmca, mean arterial pressure (MAP) and heart rate (HR) were recorded simultaneously at equilibrium with and without remifentanil.

RESULTS

The combination of remifentanil and propofol caused an 8.1% decrease in MAP (P = 0.0005) and an 11.8% decrease in HR (P < 0.0001) compared with propofol alone. Vmca was not different between the two groups (P = 0.4041).

CONCLUSION

The addition of remifentanil to propofol anesthesia in children causes a reduction in MAP and HR without affecting CBFV. This may imply that cerebral blood pressure autoregulation is preserved in children under propofol and remifentanil anesthesia.

Remifentanil: an update

PURPOSE OF REVIEW

Remifentanil has now reached maturity, as reflected by the increasing number of clinical papers relating to its use. Its position among anaesthetic drugs is now better understood, and this review will attempt to place it in the context of current clinical practice.

RECENT FINDINGS AND SUMMARY

Propofol reduces the initial distribution of remifentanil, leading to higher concentrations during induction. Propofol and remifentanil administered together at sedative doses display a major synergistic interaction on the respiratory drive. Remifentanil accelerates the penetration of sevoflurane to its site of effect. The risk of intraoperative awareness seems to be low when remifentanil is associated to very low concentrations of hypnotic drugs, but this field warrants further investigation. Acute tolerance to opioids and its prevention remain controversial.

SUMMARY

Remifentanil is the opioid of choice for tracheal intubation without muscle relaxants. It provides an alternative to regional anaesthesia in labour pain control. Target-controlled infusion may further improve the administration of remifentanil.