Volatile anaesthetic actions on norepinephrine-induced contraction of small splanchnic resistance arteries

Decreases in Oral Tissue Blood Flow Induced by Remifentanil Are Not Accompanied by Deterioration of Oral Tissue Oxygen Tension in Rabbits

PURPOSE

The purpose of this study was to investigate the effects of remifentanil infusion on tissue blood flow and tissue oxygen tension in the mandibular bone marrow and masseter muscle in rabbits. In addition, changes in tissue oxygen consumption in those tissues during remifentanil infusion were investigated.

MATERIALS AND METHODS

Sixteen male tracheotomized Japanese White rabbits were anesthetized with sevoflurane under mechanical ventilation. Under oxygen and air inhalation, fraction of inspiratory oxygen was set at 0.4 and remifentanil was infused at a rate of 0.4 μg ∙ kg^-1 ∙ min^-1. Measurements were performed before remifentanil infusion, 20 minutes after the start of remifentanil infusion, and 20 and 60 minutes after the completion of remifentanil infusion (n = 8). The observed variables included heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), mandibular bone marrow tissue oxygen tension (PbO₂), and masseter muscle tissue oxygen tension (PmO₂). Another 8 rabbits were observed for arterial pH, lactate, base excess (BE), and tissue oxygen consumption in the region from which the retromandibular vein received venous blood. Measurements were performed before remifentanil infusion and 20 minutes after the start of remifentanil infusion.

RESULTS

HR, SBP, DBP, MAP, BBF, and MBF decreased during remifentanil infusion. PbO₂ increased 20 minutes after remifentanil infusion and returned to almost the baseline value 60 minutes after remifentanil infusion. PmO₂ did not change throughout the experiment. The difference between the arterial oxygen content of the femoral artery and the venous oxygen content of the retromandibular vein decreased during remifentanil infusion. Arterial pH, lactate, and BE did not change during remifentanil infusion.

CONCLUSIONS

Remifentanil decreased BBF and MBF but did not decrease PbO₂ and PmO₂. It is suggested that tissue oxygen consumption decreased during remifentanil infusion.

Rocuronium and vecuronium do not affect mandibular bone marrow and masseter muscular blood flow in rabbits

PURPOSE

The goal of this study was to investigate the effect of rocuronium and vecuronium continuous infusion on oral tissue blood flow in rabbits.

MATERIALS AND METHODS

We used 8 male Japan White rabbits. The infusion rates of rocuronium were 7, 14, and 28 microg kg(-1) min(-1) for 20 minutes, in this order. After rocuronium was discontinued and body movement confirmed, continuous infusion of vecuronium was started. The infusion rates of vecuronium were 1.6, 3.2, and 6.4 microg kg(-1) min(-1) for 20 minutes, in this order. Observed variables were systolic blood pressure, diastolic blood pressure, mean arterial pressure, heart rate, common carotid artery blood flow, tongue mucosal blood flow, oxygen partial pressure of the mandibular bone marrow, and oxygen partial pressure of the masseter muscle.

RESULTS

Heart rate in both groups tended to decrease depending on the infusion rate. Common carotid artery blood flow in the rocuronium group was increased depending on the infusion rate. Tongue mucosal blood flow in the vecuronium group was decreased depending on the infusion rate. There were no differences in diastolic blood pressure, mean arterial pressure, oxygen partial pressure of the mandibular bone marrow, and oxygen partial pressure of the masseter muscle between the 2 groups. Systolic blood pressure in both groups showed no major change.

CONCLUSION

Rocuronium and vecuronium did not change mandibular bone marrow and masseter muscular blood flows. Vecuronium decreased tongue mucosal blood flow depending on the infusion rate.

Plethysmographic pulse wave amplitude is an effective indicator for intravascular injection of epinephrine-containing epidural test dose in sevoflurane-anesthetized pediatric patients

BACKGROUND

Plethysmographic pulse wave amplitude (PPWA) was effective in detecting intravascular injection of epidural test dose with 100% sensitivity and specificity in adults. We evaluated the efficacy of PPWA in detecting intravascular injection of a simulated epidural test dose during sevoflurane anesthesia in pediatric patients.

METHODS

Eighty infants and children were randomized to receive either 0.5 minimal alveolar concentration (MAC) or 1 MAC sevoflurane and nitrous oxide in oxygen. Patients in each anesthesia group were further randomized to receive either 0.1 mL/kg of 1% lidocaine with 1:200,000 epinephrine (0.5 mug/kg of epinephrine) IV to simulate the intravascular injection of epidural test dose or saline. Heart rate (HR), systolic blood pressure (SBP), and PPWA were monitored for 5 min after injection. A positive test response was defined as HR increase > or =10 bpm, SBP increase > or =15 mm Hg, and PPWA decrease > or =10%.

RESULTS

Injecting the test dose resulted in an average maximum PPWA decrease by 69% +/- 18% and 58% +/- 14% at 79 +/- 22 and 80 +/- 19 s in the 0.5 MAC and 1 MAC sevoflurane groups, respectively. The sensitivity, specificity, positive predictive, and negative predictive values for PPWA were 100% in both sevoflurane groups, whereas by using HR and SBP criteria, the sensitivity was 90% and 95% respectively during 0.5 MAC sevoflurane anesthesia and 85% for both during 1 MAC sevoflurane anesthesia.

CONCLUSION

PPWA is effective for detection of an intravascular injection of a simulated epidural epinephrine-containing test dose in pediatric patients.

Greater peripheral blood flow but less bleeding with propofol versus sevoflurane during spine surgery: a possible physiologic model?

STUDY DESIGN

Prospective, randomized, single blind.

OBJECTIVE

To compare the effects of sevoflurane and propofol on lumbar-paraspinal-muscles regional blood flow, as well as bleeding when controlled hypotension is used.

SUMMARY OF BACKGROUND DATA

Controlled hypotension is the technique of choice to reduce blood loss during spine surgery, but changes in blood flow occurring to lumbar paraspinal muscles during controlled hypotension with propofol and sevoflurane, as well as the entity of bleeding, are unknown.

METHODS

Blood flow was assessed by means of a laser Doppler flowmeter during the prehypotensive and hypotensive (defined as a 15% reduction of baseline mean arterial pressure) period in 28 patients (aged 28-73 years, American Society of Anesthesiologists (ASA) I-II) undergoing lumbar spine surgery. Patients were randomized to receive either sevoflurane or propofol as main anesthetic agent to achieve hypotension. At the end of the surgery, blood loss was calculated and intraoperative bleeding (Visual Analogue Scale ranging from 0 to 100) was evaluated by the surgeon. RESULTS.: Peripheral Blood flow was significantly greater in the propofol group both before and during the hypotensive period (median values of 32.7 FU vs. 7.7 and 38.5 FU vs. 10.5, respectively). Despite this fact, blood loss and intraoperative bleeding were significantly reduced when propofol had been used (P < 0.05).

CONCLUSION

Despite the greater blood flow when it is used, propofol causes less bleeding than sevoflurane during spine surgery and could be more indicated to produce hypotension during anesthesia. Moreover, it is possible to explain our findings hypothesizing a selective vasodilation of propofol (postcapillary, venous vasodilation), different from that of sevoflurane (precapillary, arteriolar vasodilation).

Cellular and molecular mechanisms regulating vascular tone. Part 1: basic mechanisms controlling cytosolic Ca2+ concentration and the Ca2+-dependent regulation of vascular tone

General anesthetics cause hemodynamic instability and alter blood flow to various organs. There is mounting evidence that most general anesthetics, at clinical concentrations, influence a wide variety of cellular and molecular mechanisms regulating the contractile state of vascular smooth muscle cells (i.e., vascular tone). In addition, in current anesthetic practice, various types of vasoactive agents are often used to control vascular reactivity and to sustain tissue blood flow in high-risk surgical patients with impaired vital organ function and/or hemodynamic instability. Understanding the physiological mechanisms involved in the regulation of vascular tone thus would be beneficial for anesthesiologists. This review, in two parts, provides an overview of current knowledge about the cellular and molecular mechanisms regulating vascular tone-i.e., targets for general anesthetics, as well as for vasoactive drugs that are used in intraoperative circulatory management. This first part of the two-part review focuses on basic mechanisms regulating cytosolic Ca2+ concentration and the Ca2+-dependent regulation of vascular tone.

The efficacy of plethysmographic pulse wave amplitude as an indicator for intravascular injection of epinephrine-containing epidural test dose in anesthetized adults

In this study, I evaluated the efficacy of plethysmographic pulse wave amplitude (PPWA) in detecting intravascular injection of a simulated epidural test dose containing 15 microg of epinephrine in adults during either sevoflurane or isoflurane inhaled anesthesia and compared its reliability to the classical heart rate (HR; positive if > or =10 bpm) and systolic blood pressure (SBP; positive if > or =15 mm Hg) criteria. Eighty patients were randomized to receive either 1 mean alveolar anesthetic concentration of sevoflurane or 1 mean alveolar anesthetic concentration of isoflurane (n = 40 for each anesthesia group). Patients in each anesthesia group microg of epinephrine IV or 3 mL of saline IV (n = 20 each). HR, SBP, and PPWA were monitored for 5 min after injection. Injection of the test dose resulted in peak PPWA decrease by 61% +/- 17% and 58% +/- 15% at 61 +/- 12 s and 63 +/- 13 s in the sevoflurane and isoflurane groups, respectively. Positive PPWA criterion, as determined from peak increases during saline administration, was a decrease in PPWA > or =10%. Using this value, the sensitivity, specificity, positive predictive, and negative predictive values of PPWA were 100% in both anesthetic groups. On the contrary, sensitivities of 85% and 95% were obtained based on HR criterion in the sevoflurane and isoflurane patients, respectively, and a sensitivity of 90% was obtained in both anesthesia groups on the basis of SBP criterion. In conclusion, PPWA is a reliable alternative to conventional hemodynamic criteria for detection of an intravascular injection of epidural test dose.

Effects of sevoflurane on sympathetic neurotransmission in human omental arteries and veins

BACKGROUND

Sevoflurane reduces blood pressure, the regulation of which requires an intact sympathetic neurotransmission. This study was designed to evaluate the effect of sevoflurane on the coupling between peripheral sympathetic neurones and vascular smooth muscle in isolated human omental vessels.

METHODS

Segments of arteries and veins were exposed to sevoflurane 1%, 2% and 4% (corresponding to approximately 0.5, 1 and 2 MAC in humans, respectively). The vessels were studied in vitro to determine the effects on (i) isometric contraction during electrical field stimulation (EFS) or in the presence of exogenous norepinephrine (NE); (ii) electrical field stimulated release of [(3)H]-NE from vessel segments previously incubated with [(3)H]-NE; (iii) uptake of [(3)H]-NE.

RESULTS

In artery segments, sevoflurane 4% attenuated the contraction induced by both EFS and exogenous NE. In vein segments, sevoflurane 4% attenuated only the EFS-induced contractions. Sevoflurane 1% and 2% had no effect. The release of [(3)H]-NE was inhibited by sevoflurane 2% and 4% in arteries and by sevoflurane 1%, 2% and 4% in veins. Sevoflurane had no effect on the uptake of [(3)H]-NE in either vessel.

CONCLUSIONS

Sevoflurane depresses sympathetic neuromuscular transmission in human omental vessels by reducing neuronal NE release and NE sensitivity in arteries and by reducing NE release in veins. This could contribute to the hypotension seen during sevoflurane anaesthesia, at least at concentrations above 1 MAC.

Sevoflurane and bradykinin-induced calcium mobilization in pulmonary arterial valvular endothelial cells in situ: sevoflurane stimulates plasmalemmal calcium influx into endothelial cells

Kinins locally synthesized in the cardiovascular tissue are believed to contribute to the regulation of cardiovascular homeostasis by stimulating the endothelial cells to release nitric oxide, prostacyclin, or a hyperpolarizing factor via autocrine-paracrine mechanisms. This study was designed to investigate the action of sevoflurane on bradykinin-induced Ca2+ mobilization in endothelial cells in situ. Utilizing fura-2-loaded rat pulmonary arterial valve leaflets, the effects of sevoflurane were examined on bradykinin-induced increases in intracellular Ca2+ concentration ([Ca2+]i) in endothelial cells in situ. In the presence of extracellular Ca2+ (1.5 mM), bradykinin (3-30 microM) produced an initial phasic and a subsequent tonic increase in [Ca2+]i in a concentration-dependent manner. However, it produced only the phasic increase in [Ca2+]i in the absence of extracellular Ca2+. Sevoflurane (5%, 0.67 mM) inhibited both the phasic and tonic responses to bradykinin. In these experiments, sevoflurane (3-5%) generated sustained increases (approximately 20-40% of the bradykinin-induced maximal increase in [Ca2+]i) in the resting [Ca2+]i level. Sevoflurane still increased [Ca2+]i after depletion of the intracellular Ca stores with ionomycin (0.1 microM ). However, the sevoflurane-induced increase in [Ca2+]i was eliminated by removal of the extracellular Ca and attenuated by NiCl (1-3 mM). In conclusion, in the pulmonary arterial valvular endothelial cells, sevoflurane inhibits both bradykinin-induced Ca2+ release from the intracellular stores and bradykinin-induced plasmalemmal Ca2+ influx. In addition, sevoflurane appears to stimulate the plasmalemmal Ca2+ influx and thereby increase the endothelial [Ca2+]i level. Sevoflurane might influence the pulmonary vascular tone through its direct action on the pulmonary arterial valvular endothelial cells.