Effects of sevoflurane on intracranial pressure, cerebral blood flow and cerebral metabolism: A dose-response study in patients subjected to craniotomy for cerebral tumours

Background: Studies concerning the cerebrovascular effects of sevoflurane in patients with space-occupying lesions are few. This study was carried out as a dose-response study comparing the effects of increasing sevoflurane concentration (1.5% (0.7 MAC) to 2.5% (1.3 MAC)) on cerebral blood flow (CBF), intracranial pressure (ICP), cerebrovascular resistance (CVR), metabolic rate of oxygen (CMRO₂) and CO₂-reactivity in patients subjected to craniotomy for supratentorial brain tumours.
Methods: Anaesthesia was induced with propofol/fentanyl/atracurium and maintained with 1.5% sevoflurane in air/oxygen at normocapnia. Blood pressure was maintained constant by ephedrine. In group 1 (n=10), the patients received continuously 1.5% sevoflurane. Subdural ICP, CBF and CMRO₂ were measured twice at 30-min intervals. In group 2 (n=10), sevoflurane concentration was increased from 1.5% to 2.5% after CBF₁. CBF₂ was measured after 20 min during 2.5% sevoflurane. Finally, CO₂-reactivity was studied in both groups.
Results: In group 1, no time-dependent alterations in CBF, CVR, ICP and CMRO₂ were found. In group 2, an increase in sevoflurane from 1.5% to 2.5% resulted in an increase in CBF from 29 ± 10 to 34±12 ml 100g⁻¹ min⁻¹ and a decrease in CVR from 2.7±0.9 to 2.3±1.2 mmHg ml⁻¹ min 100g ( P <0.05), while ICP and CMRO₂ were unchanged. CO₂-reactivity was maintained at 1.5% and 2.5% sevoflurane.
Conclusion: Sevoflurane is a cerebral vasodilator in patients with cerebral tumours. Sevoflurane increases CBF and decreases CVR in a dose-dependent manner. CO₂-reactivity is preserved during 1.5% and 2.5% sevoflurane.     

Propofol sedation and gastric emptying in volunteers

Background : The purpose of this study was to evaluate the effects of light propofol sedation on gastric emptying and orocecal transit time (OCT).
Methods : Ten healthy male volunteers were studied on 2 occasions separated by at least 1 week and were randomly allocated to receive either propofol sedation or i.v. saline as a control. During propofol sedation the volunteers were sedated to grade 2–3 on a 5-grade scale. This was achieved by a propofol infusion of 5 mg kg^-1 h^-1 initially, which was then titrated down to a dose of 2.4±0.7 mg kg^-1 h^-1 Paracetamol absorption was used as an indirect measure of the rate of gastric emptying and OCT was determined by use of the hydrogen breath test after ingestion of raffinose. Student's t -test for paired samples was used and the results are presented as means± SD.
Results: During propofol sedation the maximum concentration of paracetamol (C_max) was 115±26.8μl/L, time to peak concentration (T_max) 50±38.8 min, and the area under the curve during the first 60 min (AUC₆₀4793±1538 μmolXmin/L, versus C_max 99±20.8, T_max 69±41.9 and AUC₆₀ 3897±1310 during saline infusion. These differences were not statistically significant. OCT was significantly shorter during the control study, 180±32.4 min, than during propofol sedation, 217±64.9 min (P<0.05).
Conclusion : This study in volunteers has shown that gastric emptying of liquids seems uninfluenced by light propofol sedation. OCT was slightly prolonged during light propofol sedation.     

The Venturi Anaesthesia Circuit II Carbon Dioxide Production and Gas Flow Requirements

Carbon dioxide production was measured in 20 adult patients undergoing alloplastic operation of the hip. Body weight ranged from 40 to 81 kg. Anaesthesia consisted of lumbar plexus block, i. v. diazepam, pethidine, pavulon and N₂O/O₂ under controlled ventilation. CO₂ production was 2.13 ml kg^-1 min^-1 (interquartile range 2.09-2.23). A fresh gas flow rate of about 30 ml kg^-1 min^-1 was required for the elimination of CO₂ produced when using the Venturi system for inhalation anaesthesia.     

Multiple Dose Kinetics of Ketobemidone in Surgical Patients

Twelve patients scheduled for major abdominal surgery were selected for a study of the kinetics of ketobemidone during the day of surgery and in a follow-up study 3–5 days after surgery. In six patients ketobemidone was administered as ketobemidone plain and in the other six, it was given as Ketogin®, a combination formula containing a spasmolytic substance in addition to ketobemidone. Plasma samples were collected for approximately 24 h following induction of anesthesia, during which time multiple doses of ketobemidone were administered. A single-dose study was performed 3–5 days after surgery using the same drug. No significant differences were found between the two formulations of ketobemidone. Plasma clearance did not change significantly between the two periods of study, being 18.0±4.4 ml · kg^-1 · min^-1 peroperatively and 21.7±7.6 ml · kg^-1 · min^-1 postoperatively. Peroperative V_{d area} was significantly larger than post-operative V_{d area}, 5.84±2.621 · kg^-1 and 3.63±0.381 ·; kg^-1, respectively. T1/2 terminal decreased from 3.84±1.6 h peroperatively to 2.06±0.44 h postoperatively.     

The Effect of Surgical Stress on Haemodynamics During Neurolept Anaesthesia

The influence of surgical stress on haemodynamics during neurolept anaesthesia (NLA) was studied in ten patients, while they were awake, under anaesthesia prior to surgery and peroperatively. Systemic arterial, pulmonary arterial, right atrial and pulmonary capillary wedge pressures, as well as cardiac output (Q_t), arterial oxygen content and mixed venous oxygen content, were measured. Systemic and pulmonary vascular resistances, arterial-venous oxygen content difference (AVD), oxygen consumption (v_o2 and cardiac index (CI) were calculated.
On institution of anaesthesia, CI fell from 2.8 ±.11 /min. m² to 2.5±0.2 l /min.m² and systolic arterial pressure (SBP) fell from 13.4±0.5 kPa to 10.2±0.3 kPa. During surgery CI rose to 3.3±0.1 1/min.m² and SBP rose to 15.7±0.6 kPa. Prior to anaesthesia, AVD was 40.2±0.2 ml/l Under anaesthesia prior to surgery, AVD did not change, but v_O2 declined from 207±13 ml/min to 171±10 ml/min. During surgery, AVD fell to 30.5±0.3 ml/l, while V_o2 remained unchanged.
It is concluded that NLA has a direct metabolic depressant effect and, in association with surgery, is accompanied by hyperkinetic circulation.     

Comparison of subhypnotic doses of thiopentone vs propofol on the incidence of postoperative nausea and vomiting following middle ear surgery

Background : Middle ear surgery is associated with a high incidence of emetic sequelae and propofol has been reported to have antiemetic activity in subhypnotic doses.
Methods : In a double-blind, randomized study, the patients received either thiopentone 1.0 mg.kg^-1 (n=26) or 0.5 mg.kg^-1 propofol (n=26) at the end of middle ear surgery under isoflurane-N₂O-fentanyl-vecuronium anaesthesia. Trained nurses, unaware of the group assignment, assessed postoperative nausea, retching and vomiting up to 24 h after the end of anaesthesia. Droperidol 10μg.kg^-1 was used as a "rescue" antiemetic.
Results : The main result was that the patients in the propofol group did not suffer from retching and vomiting (R&V) during the first 6 h, whereas these symptoms occurred in 46% ( P <0.001) of the patients in the thiopentone group. The patients in the propofol group needed significantly less droperidol during the first 24 h (mean number of doses 0.39 ± 0.57 (SD)) than the patients in the thiopentone group (1.35 ± 1.47, P <0.005). Treatment with propofol was a predictor for lowered incidence of R&V, as well as male gender and negative history of motion sickness.
Conclusion : Propofol at a subhypnotic dose of 0.5 mg.kg^-1 provides prophylaxis against retching and vomiting for the first 6 h postoperatively after middle ear surgery. The incidence of nausea was not reduced by propofol.     

A comparison of the effects of fentanyl and propofol on left ventricular contractility during myocardial stunning

Background : The intravenous anaesthetic propofol has been shown to possess free radical scavenging activity and calcium channel blocking effects in a number of in vitro models. We decided to compare the effects of propofol with those of fentanyl on myocardial contractility during and after ischaemia to determine whether propofol could protect the heart and improve recovery of ventricular contractile function in open-chested dogs.
Methods : Twenty adult beagles were acutely instrumented, under halothane anaesthesia, to measure ECG; aortic, left ventricular pressures; cardiac output; coronary flow; and segmental lengths in the regions perfused by the left anterior and left circumflex coronary arteries. After surgery and a stabilisation period halothane anaesthesia was terminated and fentanyl (100 μg. kg^-1 bolus followed by 2 μ.kg^-1·min^-1 infusion; n=10) or propofol (5 mg. kg^-1 bolus followed by 0.3 mg· kg^-1 min^-1 infusion; n=10) anaesthesia commenced. After a stabilisation period the LAD coronary artery was occluded for 10 min and then reperfused for 3 h. Measurements were taken throughout the protocol.
Results : We found no significant difference in recovery of contractile function between propofol and fentanyl as assessed by normalised preload recruitable work area (50±10 vs 47±16%), normalised systolic shortening (36±12 vs 48±14%) and peak left ventricular dP/dt (1665±276 vs 1846±151 mmHg.s^-1) at the end of reperfusion.
Conclusion : We conclude that at the concentration used in this study propofol shows no improvement in contractility during "stunning" when compared to fentanyl.     

Sumatriptan-induced cerebral vasoconstriction as treatment of experimental intracranial hypertension

Background: Increased intracranial pressure (ICP) is a major cause of mortality in severe head injuries and pharmacologically induced cerebral vasoconstriction has been suggested as a possible treatment. In the present study a porcine model of increased ICP was utilized to study the changes in cerebral haemodynamics and energy metabolism induced by a selective 5-hydroxytryptaminei agonist (sumatriptan).
Methods: ICP was raised by inflation of two balloons covering both parieto-occipital regions extradurally. The animals were randomized into four groups receiving sumatriptan: 0.01 mg·kg^-1 (A), 0.03 mg·kg^-1 (B), 0.1 mg·kg^-1 (C), and 0.5 mg·kg^-1 (D) intravenously over 10 min. Measurements of cerebral blood flow (CBF), arterio-venous oxygen content difference (CavO₂), and jugular venous pH (vpH) were performed 5, 20, 40, 60, and 75 min after start of the infusion. ICP, mean arterial pressure, and EEG were recorded continuously. Direct effects of sumatriptan were also compared in cortical arteries and veins in vitro.
Results: Significant decreases in ICP were obtained in groups A, B, and C while group D exhibited a progressive increase in ICP. Significant reductions in CBF, increase in CavO₂, and slowing of EEG were observed in groups B, C, and D. Sumatriptan caused moderate constriction of the arteries and a more pronounced dilatation of veins in vitro.
Conclusion: The results indicate that a low dose of sumatriptan has the potential to reduce a raised ICP. High doses of sumatriptan cause a further increase of ICP possibly by dilatation of intracerebral veins.     

Effect of thoracic epidural anaesthesia on ventilation= perfusion distribution and intrathoracic blood volume before and after induction of general anaesthesia

Background: Gas exchange is impaired during general anaesthesia due to development of shunt and ventilation-perfusion mismatching. Thoracic epidural anaesthesia (TEA) may affect the mechanics of the respiratory system, intrathoracic blood volume and possibly ventilation-perfusion (V_A/Q) distribution during general anaesthesia.
Methods: V_A/Q relationships were analyzed in 24 patients undergoing major abdominal surgery. Intrapulmonary shunt (Qs/ Q_T), perfusion of "low" V_A/Q areas, ventilation of "high V_A/ regions, dead space ventilation and mean distribution of ventilation and perfusion were calculated from the retention/excretion data of six inert gases. Intrathoracic blood volume (ITBV) and pulmonary blood volume (PBV) were determined with a double indicator technique. Recordings were made before and after administration of 8.5±1.5 ml bupivacaine 0.5% (n=12) or 8.3±1.8 ml placebo (n=12) into a thoracic epidural catheter and after induction of general anaesthesia.
Results: Before TEA, QS/QT was normal in the bupivacaine group (222%) and the placebo group (23%). TEA covering the dermatomal segments T 12 to T 4 had no effect on V_A/Q relationships, ITBV and PBV. After induction of general anaesthesia S/T increased to 84% (bupivacaine group, P < 0.05) and to 72% (placebo group, P < 0.05). ITBV and PBV decreased significantly to the same extent in the bupivacaine group and the placebo group.
Conclusions: TEA has no effect on V_A/Q distribution, gas exchange and intrathoracic blood volume in the awake state and does not influence development of S/T and V_A/Q inequality after induction of general anaesthesia.     

Potency and maintenance requirement of atracurium and vecuronium given alone or together

A synergism exists between some competitive muscle relaxants. However, maintenance requirement of a combination of muscle relaxants has been evaluated only in paediatric patients. We studied 45 elective adult surgical patients (ASA I-II) during propofol-alfentanyl-N₂O-O₂-anaesthesia. The first 30 patients were randomized to receive either atracurium or vecuronium to create individual dose-response curves for these muscle relaxants. ED₉₅-values for atracurium and vecuronium were 260±9 and 59±3 μg · kg^-1, respectively (mean±s.e.mean). Requirements of atracurium and vecuronium to maintain an 85–95% neuromuscular blockade were 301 and 83 μg kg^-1 h^-1, respectively. An additional 15 patients received a combination of atracurium and vecuronium (cAV) in an equipotent dose ratio. An ED₉₅ of a cAV was 94± 7 μg · kg^-1 of atracurium together with 21±2 μg · kg^-1 of vecuronium, or 72±6% of one ED₉₅ dose of a parent agent. Potentiation was significant ( P =0.0001). A maintenance requirement of a cAV was 120 μg kg^-1 h^-1 of atracurium together with 27 μg kg^-1 h^-1 of vecuronium. Thus, a significant potentiation was maintained also during the course of anaesthesia. A cAV had an effect like one intermediate-acting agent. If a cAV is used instead of using atracurium or vecuronium alone, the maximal reduction of drug consumption would be approximately 30%.     

Propofol influences the electroretinogram to a lesser degree than thiopentone

Background: The Electroretinogram (ERG) is used clinically to assess the function of retina. Anaesthetic agents are known to affect ERG, and as anaesthesia is often needed in children and uncooperative patients, knowledge about its effects is of clinical importance. Barbiturates selectively depress ERG components, and we compared thiopentone with propofol to assess if the latter preserved retinal function better.
Methods: Ten pigs, average weight 17 kg (SD ± 2 kg) were anaesthetized randomly with propofol 10 mg kg^-1 or thiopentone 30 mg kg^-1. Anaesthesia was maintained by 65% nitrous oxide in oxygen and continuous infusion of the induction agent, i.e. 10 mg kg^-1 h^-1 of propofol, or 10 mg kg^-1 h^-1 for the first hour, then 5 mg kg^-1 h^-1 of thiopentone, with doses being based on pilot studies. After an interval of one week the programme was repeated using the other agent. After 40 minutes dark-adaptation, responses to single flashes of graded intensities from a xenon flashlamp were recorded at five-minute intervals. The a- and b-wave amplitudes and implicit times (time to peak), and a-wave slopes were determined.
Results: The b-wave implicit time was significantly shorter during propofol anaesthesia than when using thiopentone. The effect was most pronounced at the lowest intensities (P < 0.01). No statistically significant differences were found in the amplitudes of the b-waves. The a-wave appeared at lower stimulus intensity (P < 0.05) and the a-wave slopes were significantly steeper (P < 0.01) during propofol anaesthesia.
Conclusion: Propofol accordingly appeared to preserve the photoreceptor response better than thiopentone, and may therefore be considered to be more suitable for ERG recordings than thiopentone.     

Differential effects of dobutamine, dopamine, and noradrenaline on splanchnic haemodynamics and oxygenation in the pig

Supranormal oxygen (O₂) transport may benefit critically ill patients. Catecholamines are clinically employed for this purpose. However, their effects on splanchnic haemodynamics and oxygenation are not well defined. The effects of dobutamine (DOBU), dopamine (DOPA), and noradrenaline (NA) on splanchnic blood flows (electromagnetic flow probes), O₂ deliveries and uptakes (catheterisation of portal and hepatic veins) were studied in nine anaesthetised (ketamine/flunitrazepam), ventilated, paralysed, and laparotomised pigs. All three catecholamines (DOPA at 15 μg·kg^-1 · min^-1, DOBU at 13 μg · kg^-1 · min^-1, NA at 0.4 μg · kg^-1 · min^-1) significantly ( P <0.05) increased cardiac output and systemic O₂ delivery. Only DOPA increased small intestinal and total hepatic blood flows, and O₂ deliveries, and decreased O₂ extractions. The same parameters did not change during DOBU. During NA, total hepatic blood flow and O₂ delivery decreased, and hepatic O₂ extraction increased. During all three catecholamines, small intestinal and total hepatic O₂ uptakes did not change significantly. Whereas hepatic arterial blood flow decreased during both DOPA and NE, portal venous flow increased during DOPA. These data suggest that in the experimental model used splanchnic O₂ supply and O₂ reserve capacity appear improved by DOPA, unaffected by DOBU, and impaired by NA.     

Influence of Dixyrazine on Intestinal and Renal Vasoconstrictor Responses During Fentanyl-Nitrous Oxide Anaesthesia

In cats (n=24) anaesthetized with fentanyl-nitrous oxide and diazepam, stimulation of the hypothalamic defence-alarm area (DA) or afferent activation of somatic pain fibres (SA), elicited a pronounced increase in intestinal (DA 297%, SA 107%) and renal (DA 214%, SA 90%) vascular resistance as well as a decrease in diuresis. These stress-related responses were markedly counteracted by dixyrazine (0.15-0.5 mg · kg^-1 b.w. i.v.), especially in the kidney where the subsequent increase in vascular resistance to DA and SA stimulations amounted to only 25% and 13%, respectively, while diuresis increased. Corresponding data for stimulation-induced increases in intestinal vascular resistance after dixyrazine were DA 156% and SA 28%. Dixyrazine is suggested to act both through interaction with peripheral α-adrenergic mechanisms in control of vascular tone and through central nervous cardiovascular reflex depression. In man (n=7), during a similar form of anaesthesia, portal vein blood flow (1137±177 ml) was measured by the continuous thermodilution method. Preportal tissue vascular resistance during surgery decreased significantly (11.3 vs 8.7 kPa · min ml^-1 · 10^-3) after i.v. dixyrazine (0.15mg · kg^-1 b.w.). A concomitant increase in oxygen uptake in preportal tissues occurred (19.9 ml min^-1 vs 24.5 ml · min^-1).     

Quantifying the interaction of vecuronium with enflurane using closed-loop feedback control of vecuronium infusion

The influence of different levels of enflurane anaesthesia on infusion requirements of vecuronium was studied in 40 adult surgical patients. Ninety percent neuromuscular block was maintained by computer controlled infusion of vecuronium. During the first 90 min study period all patients received fentanyl-nitrous oxide-oxygen (2:1) anaesthesia. For the following 90 min the patients were randomly assigned to receive enflurane at different end-tidal concentrations: group I, control, fentanyl-nitrous oxide anaesthesia; group II, enflurane 0.3%-nitrous oxide; group III, enflurane 0.6%-nitrous oxide; group IV, enflurane 0.9%-nitrous oxide. Every patient served as his/her own control and the changes of vecuronium infusion requirements were determined individually. When the administration of enflurane was started, vecuronium infusion requirements decreased progressively until 90 min. In group II the infusion rate lowered from 80±28 to 56±20 μg . kg^-1 . h ^-1, in group III from 61 ±29 to 34±17 μg . kg^-1 . h^-1 and in group IV from 65±20 to 30± 14 μg . kg^-1 . h^-1. In the control group the infusion rate decreased during the three hour study period from 69± 17 (first 90 min period) to 59± 16 μg . kg^-1 . h^-1 (second 90 min period). Enflurane reduces the dose requirements of vecuronium administered by continuous infusion in a dose- and time-dependent manner.     

Effects of propofol on ipecacuanha-induced nausea and vomiting

Background : The purpose of this study was to evaluate if propofol has 5-HT₃ antagonistic effects. Ipecacuanha is known to release serotonin (5-HT) in the gastrointestinal tract and therefore ipecacuanha syrup was used to induce nausea and vomiting. The 5-HT₃ antagonist ondansetron was used as a control substance.
Results : During the first 150 min after ingestion of ipecacuanha there were no retchings during the ondansetron infusion ( P = 0.01 vs placebo, P =0.02 vs propofol) and significantly fewer retchings during propofol infusion compared to placebo ( P <0.02). There was no nausea during the ondansetron infusion ( P <0.01 vs placebo and propofol) but the volunteers experienced nausea both during the placebo and propofol infusion (NS).
Conclusion : This study in volunteers has shown that propofol reduces the intensity of retching after oral intake of ipecacuanha syrup. As ipecacuanha releases 5-hydroxytryptamine, it can be concluded that propofol may have a weak 5-HT₃ antagonistic effect.
Method : Ten healthy male volunteers (20–37 years) were studied on three occasions and were randomly allocated to receive a concomitant infusion of propofol (initial bolus 0.1 mg kg^-1 then 1 mg kg^-1h^-1), ondansetron (initial bolus 0.11 mg kg^-1 then 14 μg kg^-1 h^-1) and placebo on either occasion. The infusions started 30 min before oral ingestion of 30 ml of ipecacuanha and continued until 150 min after the intake. The number of retchings was recorded and the intensity of nausea was estimated by the subjects on a visual analog scale.     

Effects of induced hypotension on arterial blood–gases under spontaneous breathing

The effects of deliberate hypotension on both Pao₂ and Paco₂ were investigated under isoflurane anaesthesia with spontaneous breathing from a laryngeal mask. Lumbar epidural block was introduced; anaesthesia was induced with thiamylal (4 mg kg^-1) and maintained with 0.5% isoflurane in nitrous oxide (4 1 min^-1) and oxygen (2 1 min^-1) under spontaneous breathing. After that nitroglycerin, trimetaphan or prostaglandin E₁ were used to induce a hypotension of 70% of control. All three drugs significantly decreased Pao₂, from 19.9 ± 3.3, 19.2 ±2.7, and 19.6 ± 3.1 kPa to 14.6 ± 1.9, 16.6 ± 2.2, and 16.2 ± 2.4kPa (mean ± s.d.), respectively; none of them increased Paco₂. In spite of the sparing of functional residual capacity under spontaneous breathing, the levels of reduction of Pao₂ were the same as levels reported in paralyzed and mechanically ventilated subjects. In conclusion, under deliberate hypotension Pao₂ decreases to a considerable degree, even under spontaneous breathing, presumably not because of alveolar hypoventilation, but because of the suppression of hypoxic pulmonary vasoconstriction by the drugs used in this study.     

Minimum Cerebral Blood Flow and Metabolism During Craniotomy. Effect of Thiopental Loading

Cerebral blood flow and metabolism were measured repeatedly during surgery for cerebral tumours by a modification of the classical Kety & Schmidt method using ¹³³Xe infusion intravenously. Our standard procedure for neuroanaesthesia (pentobarbitone-fentanyl induction, halothane-nitrous oxide maintenance) reduced blood flow from 47.1 to 24.2 ml.100 g . ml^-1 and metabolism from 3.30 to 1.83 ml O₂ . 100 g^-1 . ml^-1. PacO₂ was reduced by hyperventilation from 5.3 to 3.6 kPa. Additional thiopental loading and maintenance using 4 + 4 mg.kg^-1 (n=5) or 8 + 8 mgkg^-1 (n = 5) reduced cerebral metabolism by an additional 15% ( P <0.0) and blood flow by 16.5% ( P <0.01), while mean arterial blood pressure fell from 11.0 to 9.9 kPa ( P <0.05). Paco₂ remained unchanged. This additional reduction in cerebral metabolism and blood flow is small, but we nevertheless conclude that it may well be of clinical interest to the problem of protecting the brain in case of episodes of focal cerebral ischaemia which may arise peroperatively during intracramal surgery.     

Effects on skeletal muscle oxygenation and capillary blood flow by adenosine-, sodium nitroprusside- and acetylcholine-induced hypotension

Background: Adenosine (ADO)-induced hypotension during diethyl ether anesthesia has been shown to increase skeletal muscle oxygenation. Whether this beneficial effect of ADO hypotension is present also during another anesthetic technique was tested in the present study using ketamine-xylazine anesthesia, and its actions were compared with sodium nitroprusside (SNP) and acetylcholine (ACh) induced hypotension in rabbits.
Methods: Local oxygen pressure and capillary blood flow were measured with a multiwire microelectrode which was placed on the surface of the left vastus medialis muscle. The experiments were performed in three groups, in which either ADO, SNP or ACh was infused into a central vein in a dose that produced a reduction of the mean arterial pressure by 20–25%, to approximately 60 mmHg.
Results: In the ADO group (60–170 μg kg^-1 min^-1) the tissue oxygen pressures increased by 23% while capillary blood flow decreased by 38%. During SNP administration (1–3 μg kg^-1 min^-1) the oxygen pressures decreased by 21% and an increase of 31% in capillary flows was seen. When ACh was infused (1–4 μg kg^-1 min^-1) the oxygen pressures decreased by 21% and, in parallel, capillary blood flow decreased by 50%. During hypotension no low tissue oxygen pressure values (<1.5 kPa) were found in the ADO group, whereas they were present in both the SNP and ACh group.
Conclusion: Compared to sodium nitroprusside and acetylcholine, adenosine appears to have an oxygen-sparing effect in the skeletal muscle during pharmacologically induced hypotension.     

Comparison of intubating conditions after rocuronium and suxamethonium following "rapid-sequence induction" with thiopentone in elective cases

Background : Rocuronium (Org 9426) was shown to have the fastest onset of action of all currently available non-depolarizing neuromuscular blocking drugs and to provide intubating conditions similar to those of suxamethonium 60 to 90 s after administration. We compared the intubating conditions after rocuronium and suxamethonium following rapid-sequence induction of anaesthesia.
Methods : Fifty unpremedicated patients of ASA physical status I or II, scheduled for elective surgery were studied. Anaesthesia was induced with thiopentone 6 mg kg^-1 followed randomly by suxamethonium 1 mg kg^-1 or rocuronium 0.6 mg kg^-1 and, 45 s later, intubation was commenced. Muscle fasciculations, intubating conditions and intubation time, haemodynamic variables and oxygenation were assessed.
Results : Intubation time did not differ between suxamethonium (9.8±2.2 s) (mean±SD) and rocuronium (10.5±2.9 s), respectively. Intubating conditions were clinically acceptable (good or excellent) in all patients given suxamethonium and in 96% of the patients given rocuronium. However, the condition of the vocal cords was better (P<0.05) and diaphragmatic response to intubation was less pronounced with suxamethonium (P<0.05). Changes in heart rate and arterial blood pressure were similar in both groups.
Conclusion : The authors conclude that rocuronium is a suitable alternative to suxamethonium for rapid tracheal intubation even under unsupplemented thiopentone anaesthesia, at least in elective, otherwise healthy patients. Its use for rapid-sequence induction under emergency conditions, however, needs further investigation.     

The effect of succinylcholine on energy metabolism studied by 31 P-NMR spectroscopy in rat denervated skeletal muscle

Background : The goals of this study were: (1) to demonstrate the differences of metabolic changes induced by succinylcholine (SCh) administration between normal and denervated muscle by ³¹P-NMR spectroscopy: (2) to determine whether three kinds of drugs (vecuronium, midazolam and magnesium sulfate) could prevent these metabolic changes.
Methods : Following unilateral sciatic nerve section, 20 male Wistar rats were studied at three-week intervals. After SCh 1 mg·kg^-1 was administered intravenously, the changes of the inorganic phosphate/phosphocreatine (Pi/PCr) ratio, the β ATP/(PCr+Pi) ratio, and intracellular pH were measured by ³¹P-NMR both in normal and denervated hind limb muscles of 5 rats. The other 15 rats were allocated to the pretreatment groups by the following drugs: vecuronium 0.02 mg·kg^-1, midazolam 0.1 mg·kg^-1 and magnesium sulfate 60 mg·kg^-1. After pretreatment 3 min before SCh administration, we measured the same parameters by ³¹P-NMR.
Results: SCh administration did not change the Pi/PCr ratio in normal muscle, but significantly increased that in denervated muscle (P<0.05). This increase of the Pi/PCr ratio was also observed in all pretreated groups but was minimal as compared with that in non-pretreatment denervated muscle.
Conclusion : These data suggested that SCh administration decreased the level of "energy reserve" in denervated muscle, and that this metabolic change was not totally inhibited by vecuronium, midazolam, or magnesium sulfate.