Disposition and pharmacodynamics of propofol during isovolaemic haemorrhage followed by crystalloid resuscitation in humans

Recommendation for the practice of total intravenous anesthesia

This Recommendation was developed by the Japanese Society of Intravenous Anesthesia Recommendation Making Working Group (JSIVA-WG) to promote the safe and effective practice of total intravenous anesthesia (TIVA), tailored to the current situation in Japan. It presents a policy validated by the members of JSIVA-WG and a review committee for practical anesthesia management. Anesthesiologists should acquire and maintain the necessary knowledge and skills to be able to administer TIVA properly. A secure venous access is critically important for TIVA. To visualize and understand the pharmacokinetics of intravenous anesthetics, use of real-time pharmacokinetic simulations is strongly recommended. Syringe pumps are essential for the infusion of intravenous anesthetics, which should be prepared according to the rules of each individual anesthesia department, particularly with regard to dilution. Syringes should be clearly labeled with content and drug concentration. When managing TIVA, particularly with the use of muscle relaxants, monitoring processed electroencephalogram (EEG) is advisable. However, the depth of sedation/anesthesia must be assessed comprehensively using various parameters, rather than simply relying on a single EEG index. TIVA should be swiftly changed to an alternative method that includes inhalation anesthesia if necessary. Use of antagonists at emergence may be associated with re-sedation risk. Casual administration of antagonists and sending patients back to surgical wards without careful observation are not acceptable.

The Influence of Hemorrhagic Shock on the Disposition and Effects of Intravenous Anesthetics: A Narrative Review

The need to reduce the dose of intravenous anesthetic in the setting of hemorrhagic shock is a well-established clinical dogma. Considered collectively,; the body of information concerning the behavior of intravenous anesthetics during hemorrhagic shock, drawn from animal and human data, confirms that clinical dogma and informs the rational selection and administration of intravenous anesthetics in the setting of hemorrhagic shock. The physiologic changes during hemorrhagic shock can alter pharmacokinetics and pharmacodynamics of intravenous anesthetics. Decreased size of the central compartment and central clearance caused by shock physiology lead to an altered dose-concentration relationship. For most agents and adjuncts, shock leads to substantially higher concentrations and increased effect. The notable exception is etomidate, which has relatively unchanged pharmacokinetics during shock. Increased concentrations lead to increased primary effect as well as increased side effects, notably cardiovascular effects. Pharmacokinetic changes are essentially reversed for all agents by fluid resuscitation. Propofol is unique among agents in that, in addition to the pharmacokinetic changes, it exhibits increased potency during shock. The pharmacodynamic changes of propofol persist despite fluid resuscitation. The persistence of these pharmacodynamic changes during shock is unlikely to be due to increased endogenous opiates, but is most likely due to increased fraction of unbound propofol. The stage of shock also appears to influence the pharmacologic changes. The changes are more rapid and pronounced as shock physiology progresses to the uncompensated stage. Although scant, human data corroborate the findings of animal studies. Both the animal and human data inform the rational selection and administration of intravenous anesthetics in the setting of hemorrhagic shock. The well-entrenched clinical dogma that etomidate is a preferred induction agent in patients experiencing hemorrhagic shock is firmly supported by the evidence. Propofol is a poor choice for induction or maintenance of anesthesia in severely bleeding patients, even with resuscitation; this can include emergent trauma cases or scheduled cases that routinely have mild or moderate blood loss.

Non-oncotic properties of albumin. A multidisciplinary vision about the implications for critically ill patients

INTRODUCTION

Effective resuscitation with human albumin solutions is achieved with less fluid than with crystalloid solutions. However, the role of albumin in today's critical care unit is also linked to its multiple pharmacological effects. Areas covered: The potential clinical benefits of albumin in select populations of critically ill patients like sepsis seem related to immunomodulatory and anti-inflammatory effects, antibiotic transportation and endothelial stabilization. Albumin transports many drugs used in critically ill patients. Such binding to albumin is frequently lessened in critically ill patients with hypoalbuminemia. These changes could result in sub-optimal treatment. Albumin has immunomodulatory capacity by binding several bacterial products. Albumin also influences vascular integrity, contributing to the maintenance of the normal capillary permeability. Moreover, the albumin molecule encompasses several antioxidant properties, thereby significantly reducing re-oxygenation injury, which is especially important in sepsis. In fact, most studies of albumin administration are a combination of a degree of resuscitation with a degree of maintenance or supplementation of albumin. Expert commentary: The potential clinical benefits of the use of albumin in selected critically ill patients such as sepsis seem related to its immunomodulatory and anti-inflammatory effects, antioxidant properties, antibiotic transportation and endothelial stabilization. Additional studies are warranted to further elucidate the underlying physiologic and molecular rationale.

Significant decreases in blood propofol concentrations during adrenalectomy for phaeochromocytoma

AIM

The kinetics of propofol are influenced by cardiac output. The aim of this study was to examine changes in blood propofol concentrations during phaeochromocytoma surgery using target-controlled infusion (TCI) anaesthesia with propofol.

METHODS

This is a prospective observational study. Ten patients with phaeochromocytoma who underwent unilateral adrenalectomy were included. Cardiac output was measured using an arterial pressure-based cardiac output analysis method. The target blood propofol concentrations were adjusted to maintain an approximate bispectral index (BIS) value of 40 before initiating surgery. The settings remained constant during surgery. Blood samples for propofol concentrations were collected from the radial artery at seven time points: two before tumour manipulation (T1, 2), two during tumour manipulation (T3, 4), and three after tumour vein ligation (T4-7). BIS values, the arterial pressure cardiac index (APCI) and haemodynamic parameters were measured at the same time points as the blood samples. The prop-ratio was calculated by dividing blood propofol concentrations by target concentrations of TCI.

RESULTS

APCI increased during tumour manipulation and after tumour vein ligation. The prop-ratio was reduced significantly by approximately 40% and showed a significant negative correlation with APCI. BIS values increased significantly and showed a significant negative correlation with the prop-ratio.

CONCLUSION

The increased APCI during tumour manipulation and after tumour vein ligation was associated with markedly reduced blood propofol concentrations. These results reveal that significant decreases in the anaesthetic effect may be observed in patients undergoing phaeochromocytoma surgery even if TCI anaesthesia is used with propofol.

Effect of acute hypervolemic hemodilution of 6% hydroxyethyl starch 130/0.4 on the EC50 of propofol at two clinical endpoints in patients

Preoperative acute hypervolemic hemodilution (AHHD) is a technique used in anesthesia to reduce the number of blood cells lost during intraoperative bleeding. The aim of the present study was to evaluate the effect of the hypervolemic hemodilution of 6% hydroxyethyl starch 130/0.4 on the EC₅₀ of propofol at two clinical endpoints. A total of 20 patients undergoing AHHD following epidural anesthesia were studied, and 20 patients who did not receive hemodilution were used as a control group. All patients were American Society of Anesthesiologists grade I, aged 20-40 years and undergoing hip arthroplasty surgery. In the AHHD group, 10 ml/kg lactated Ringer's solution was infused over 20 min at the same time as the epidural test dose. The infusion was followed by the infusion of 6% hydroxyethyl starch 130/0.4 over 30 min. Patients in the control group received 10 ml/kg Ringer's solution over 50 min. Propofol was then delivered by a Diprifusor target-controlled infusion. The predicted blood and effect-site propofol concentrations were recorded at loss of consciousness (LOC) and return of consciousness (ROC). Probit analysis was used to estimate the values for predicted blood and effect-site concentrations at the two clinical endpoints. The results showed that the potency of propofol was decreased during AHHD. Compared with the controls, the predicted blood and effect-site concentrations of propofol at LOC were higher in patients of the hemodilution group, resulting in higher EC₅₀ values (P=0.001 and 0.025, respectively). At ROC, the effect-site EC₅₀ was 2.9 µg/ml [95% confidence interval (CI), 2.8-3.0] in hemodilution patients and 2.5 µg/ml (95% CI, 2.2-2.6) in control patients (P=0.001). With AHHD, the LOC time was significantly longer and the propofol dose was higher, while ROC times were comparable. In conclusion, AHHD increases the requirement for propofol at LOC and prolongs LOC time. Patients with AHHD recovered consciousness at higher effect-site concentrations of propofol. Thus, the induction dose of propofol should be increased during AHHD.

The efficacy of the time-scheduled decremental continuous infusion of fentanyl for postoperative patient-controlled analgesia after total intravenous anesthesia

BACKGROUND

Intravenous fentanyl has been used for acute postoperative pain management, but has not always provided reliable adequate analgesia, including patient-controlled analgesia (PCA). The purpose of this study was to investigate the efficacy of time-scheduled decremental infusion of fentanyl for postoperative analgesia.

METHODS

Ninety-nine patients, aged 20-65 years, undergoing laparoscopic-assisted hysterectomy using total intravenous anesthesia (TIVA) were randomly assigned into one of the three groups. Their background infusions of fentanyl diluent (2 ml/hr of diluent was equivalent with 0.5 µg/kg/hr of fentanyl) with PCA were maintained at the fixed-rate of 2 ml/hr until the postoperative 24 hr (FX2-2-2), or at the decremental rates of 6.0, 4.0, 2.0 ml/hr (D6-4-2) and 8.0, 4.0, 2.0 ml/hr (D8-4-2). The visual analogue score (VAS), incidence of inadequate analgesia, frequency of PCA intervention, and side effects were evaluated.

RESULTS

VAS was significantly higher in FX2-2-2 than in D6-4-2 and D8-4-2 until postoperative 3 hr (P < 0.05). After postoperative 4 hr, VAS was significantly higher in FX2-2-2 than D8-4-2 (P < 0.05). The incidence of inadequate analgesia of FX2-2-2 was significantly greater than D6-4-2 (P = 0.038) and D8-4-2 (P < 0.001) until postoperative 1 hr. None of the patients had ventilatory depression, and postoperative nausea and vomiting were not significant among the groups.

CONCLUSIONS

The time-scheduled decremental background infusion regimens of fentanyl, based on the pharmacokinetic model, could provide more effective postoperative pain management after TIVA, and the side effects and the risk for morbidity were not different from the fixed-rate infusion regimen.

Influence of acute normovolaemic haemodilution on bispectral index monitoring and propofol dose requirements

BACKGROUND

Numerous medical and physiological conditions that might alter electroencephalography (EEG), such as hypoglycaemia, hypothermia or hypovolaemia, were shown to result in the bispectral Index (BIS) indicating an incorrect hypnotic state. Recently, acute normovolaemic haemodilution (ANH) was shown to be associated with significant impairment of cognitive functions that could alter EEG and consequently BIS monitoring, an EEG derived parameter.

METHODS

In a randomised clinical study, we assessed the effect of ANH on BIS monitoring before induction and after propofol target controlled infusion (TCI) anaesthesia in 45 unmedicated patients randomly allocated to ANH with oxygen insufflation (oxygen group), ANH with air insufflation (air group), or control group.

RESULTS

With ANH, mean BIS values briefly declined in the oxygen group (82+/-4) and air group (84+/-3) before returning to baseline values. The loss of consciousness time was significantly shorter, with fewer propofol TCI dose requirements, and BIS was significantly higher in the oxygen group (1.3+/-0.5 min, 2.41+/-0.15 microg/ml, 73+/-7) and air group (1.2+/-0.6 min, 2.44+/-0.17 microg/ml, 75+/-5), compared with the control group (1.7+/-0.4 min, 2.75+/-0.17 microg/ml, 61+/-5), respectively. Whereas, there was no significant difference in BIS values between the oxygen group (38+/-7), air group (36+/-5) and control group (40+/-6) at propofol TCI 4 microg/ml anaesthesia maintenance.

CONCLUSIONS

BIS values briefly declined with ANH before returning to baseline values before anaesthesia induction. Despite transient ANH enhancement of propofol effect during induction, there was no significant difference in BIS values with or without ANH during propofol maintenance of anaesthesia.