Showing papers in "Acta Anaesthesiologica Scandinavica in 1988"

Primary evaluation of the local anaesthetic properties of the amino amide agent ropivacaine (LEA 103).

Abstract: The local anaesthestic properties of 1-propyl-2',6'-pipecoloxylidide, a congener of mepivacaine and bupivacaine, and its enantiomers were compared in animals. The (S)-enantiomer (ropivacaine, LEA 103) produced a longer duration of sciatic nerve block and infiltration anaesthesia than the racemate and the (R)-form. Ropivacaine and bupivacaine were equally potent in terms of block of evoked action potential in vitro and minimum effective concentration in vivo. Ropivacaine 0.25-1.0% was distinctly longer acting than bupivacaine on infiltration, equally effective in sciatic and brachial plexus block and somewhat shorter lasting in epidural and spinal blockade. There were tendencies towards a greater benefit from the addition of adrenaline with ropivacaine in epidural anaesthesia and a shorter latency to block in some of the tests. Ropivacaine seems less vasodilative than bupivacaine and capable of producing some vasoconstriction over a wider range of low concentrations, which may explain its longer duration of intradermal anaesthesia. The somewhat shorter duration of central blockade of ropivacaine is probably a result of lesser lipid solubility. Ropivacaine was less toxic (i.v. and s.c. LD50-values) than bupivacaine but more toxic than lidocaine, and produced only weak local irritation. Due to a combination of interesting local anaesthetic properties and relative safety including cardiotoxic potential, we consider ropivacaine a candidate for further studies.

Cardiac arrest during anaesthesia. A computer-aided study in 250,543 anaesthetics.

Abstract: With the aid of a computer-based anaesthetic record-keeping system, all cardiac arrests during anaesthesia at the Karolinska Hospital between July 1967 and December 1984 were retrieved. There were a total of 170 cardiac arrests and 250,543 anaesthetics in the data file, which gives an incidence of 6.8 cardiac arrests per 10,000 anaesthetics. Sixty patients died, constituting a mortality of 2.4 per 10,000 anaesthetics: 42 were considered as inevitable deaths (rupture of aortic or cerebral aneurysm, multitrauma, etc.); 13 cases of cardiac arrest were considered as non-anaesthetic, i.e. complications due to surgery and other procedures. Nine of these patients died. 115 cases of cardiac arrest were considered as caused by the anaesthetic and nine of these patients died. Thus mortality caused by anaesthesia was 0.3 per 10,000 anaesthetics. The most common cause of cardiac arrest due to anaesthesia was hypoxia because of ventilatory problems (27 patients), postsuccinylcholine asystole (23 patients) and post-induction hypotension (14 patients). The highest mortality was seen when spinal or epidural anaesthetics were given to patients with impaired physical status including hypovolaemia. The incidence of cardiac arrest has declined considerably during the period studied, and this coincides with an increasing number of qualified anaesthetists employed in the department during the same period.

Epidural versus combined spinal epidural block for cesarean section.

Abstract: In a controlled study a single segment combined spinal epidural (CSE) block was compared with epidural block for cesarean section. Thirty healthy parturients were randomly divided into two groups. In both groups a T4 block was aimed at. Bupivacaine was used to provide analgesia in both groups. All patients receiving CSE block had good to excellent analgesia, while 11 patients (74%) receiving epidural block had similar pain relief. This was reflected in the requirement for additional analgesics, sedatives or N2O anesthesia. The muscular relaxation was also better following CSE block. The total dose of bupivacaine for a T4 block was three times larger in patients receiving only epidural block. The maternal and fetal blood bupivacaine levels were correspondingly about three times higher in the epidural group. Additionally, the incidence of maternal hypotension was higher in patients receiving epidural block. Apgar scores, blood gases and neurobehavioural evaluation did not show any differences between the two groups of neonates. No postspinal headache was noted. CSE block appears to combine the reliability of spinal block and the flexibility of epidural block while minimizing their drawbacks.

Clinical experience of long-term treatment with epidural and intrathecal opioids--a nationwide survey.

Abstract: Long-term use of spinal opioids to treat chronic severe pain is widely established. However, the indications, shortcomings and complications of the method have not been completely described. Experience with spinal opioids was analysed for the period 1979-1984 in a nationwide Swedish survey. Out of 93 anaesthesia departments, 69 used the method. Approximately 750 patients were treated with epidural morphine for an average duration of 124 days (3-450). Eighteen patients were treated with intrathecal morphine for an average period for 47 days (3-90). The intrathecal approach was used in all clinics because of failure of the epidural route. In only one department was the intrathecal approach used as the primary route of therapy, depending on the mechanism of pain. The highest daily morphine dose was 480 mg and 50 mg for epidural and intrathecal routes, respectively. The patients given the highest dosages were not necessarily those subjected to the longest treatment. The need for increased dosage seems to be related not only to changes in receptor sensitivity but also to changes in pain mechanisms. No case of threatening ventilatory depression was reported. Thirty-two departments had treated a few patients with chronic non-cancer pain conditions. Initial results were considered "excellent" in 11 departments, but at follow-up results were excellent in only one department. In addition to dislocation, occlusion of the catheters or leakage, injection pain was an obstacle to successful treatment. Pruritus urinary retention, and local infections were not reported as significant problems, but one case of meningitis was reported.

Measurement of acceleration: a new method of monitoring neuromuscular function.

Abstract: A new method for monitoring neuromuscular function based on measurement of acceleration is presented. The rationale behind the method is Newton's second law, stating that the acceleration is directly proportional to the force. For measurement of acceleration, a piezo-electric ceramic wafer was used. When this piezo electrode was fixed to the thumb, an electrical signal proportional to the acceleration was produced whenever the thumb moved in response to nerve stimulation. The electrical signal was registered and analysed in a Myograph 2000 neuromuscular transmission monitor. In 35 patients anaesthetized with halothane, train-of-four ratios measured with the accelerometer (ACT-TOF) were compared with simultaneous mechanical train-of-four ratios (FDT-TOF). Control ACT-TOF ratios were significantly higher than control FDT-TOF ratios: 116 +/- 12 and 98 +/- 4 (mean +/- s.d.), respectively. In five patients not given any relaxant during the anaesthetic procedure (20-60 min), both responses were remarkably constant. In 30 patients given vecuronium, a close linear relationship was found during recovery between ACT-TOF and FDT-TOF ratios. It is concluded that the method fulfils the basic requirements for a simple and reliable clinical monitoring tool.

Half-life of plasma cholinesterase.

Abstract: The half-life of plasma cholinesterase (acylcholine acylhydrolase EC 3.1.1.8) was determined in three patients homozygous for the atypical gene for plasma cholinesterase by measuring the rate of disappearance of enzyme activity following intravenous injection of concentrated human cholinesterase. Half-life values of 10.9, 11.1, and 11.3 days were estimated. The distribution volume was estimated to be 18.0, 18.2, and 13.8% of body weight, respectively.

Vasopressor therapy for hypotension due to epidural anesthesia for cesarean section

Abstract: Maternal hemodynamic changes and neonatal acid-base status were assessed in 127 healthy patients undergoing elective cesarean section under epidural anesthesia. An impedance cardiograph was used to measure stroke volume (SV), ejection fraction (EF) and end-diastolic volume (EDV). In addition, neonatal umbilical venous and arterial Po2, Pco2, pH, base excess, lactate, pyruvate, excess lactate, and L/P ratio were measured at birth. Patients were divided into three groups. Group 1 (n = 53) required no vasopressor (normotensive controls). In Group 2 (n = 37), mean blood pressure (BP) decreased from 90 mmHg to 67 mmHg (12.0 to 8.9 kPa), and ephedrine was given in 5-mg increments to maintain systolic BP>100 mmHg (13.3 kPa). In Group 3 (n = 37), BP decreased from 83 mmHg to 62 mmHg (11.1 to 8.2 kPa), and phenylephrine was administered in 100 μg increments to maintain systolic BP>100 mmHg (13.3 kPa). In Groups 2 and 3 the SV and EDV decreased 43% and 33% respectively when hypotension developed. Both vasopressors restored BP, SV and EDV to near baseline values. Neonatal Apgar scores and acid-base profiles were not signficantly different among the three groups of neonates, nor were they different between the two hypotensive groups. It is concluded that: 1) transient maternal hypotension does not affect neonatal acid-base status; 2) both ephedrine and phenylephrine increase cardiac preload; and 3) an α agent like phenylephrine does not cause fetal acidosis when used for treating maternal hypotension.

Epidural clonidine for treatment of postoperative pain after thoracotomy. A double-blind placebo-controlled study

Abstract: Clonidine has been reported to produce analgesia in humans in different painful conditions. The aim of the present study was to investigate if epidural clonidine produced a clinically important analgesia to severe postoperative pain. Using a controlled, randomized double-blind design, one group of patients received a single dose of epidural clonidine 3 micrograms/kg (n = 10) and a control group epidural 0.9% saline (n = 10), when reporting postoperative pain after thoracotomy performed under standardized anaesthesia. To quantify the effects of the given epidural drugs, the need for supplementary, intravenous pethidine analgesia was recorded. The patients had access to the supplementary analgesic by means of a patient-controlled analgesic-delivery device. The two groups were similar regarding anthropometric and clinical data. Epidural clonidine 3 micrograms/kg did not affect the need for supplementary intravenous pethidine analgesia, as compared to the control group at any time during the first 12 h postoperatively. The side-effects of epidural clonidine were tolerable, and no treatment for arterial hypotension was required. No early or delayed respiratory depression occurred. In conclusion, clonidine 3 micrograms/kg epidurally seems to lack clinically important analgesic effects on severe postoperative pain, at least following thoracotomy.

Postoperative cerebrovascular accidents in general surgery

Abstract: In a prospective study of postoperative complications, strokes occurred in 6 out of 2463 patients (0.2%) who underwent non-cardiac, non-carotid artery surgery. The patients who experienced cerebrovascular accidents, including three cases of transient ischemic attack, were significantly older than the rest of the group (mean age 79 years versus 65 years) and had manifestations of atherosclerosis in at least one organ preoperatively. Significant predictors of risk for postoperative cerebrovascular accidents were previous cerebrovascular disease, heart disease, peripheral vascular disease, and hypertension. Cerebrovascular accidents occurred late in the postoperative period, 5-26 days after surgery, and were not directly related to surgery and anesthesia. They were more frequent after acute than after elective operations. Precipitating factors for some of the stroke incidents were rapid atrial fibrillation and postoperative dehydration.

Regional anaesthesia and blood loss

Abstract: Epidural and spinal anaesthesia for various types of surgery offer advantages over general anaesthesia by decreasing blood loss and transfusion requirements. This paper focuses on the importance of the choice of anaesthesia on surgical blood loss in total hip arthroplasty. Haemodynamic differences, with lower arterial blood pressure, lower central venous blood pressure, and most importantly lower peripheral venous blood pressure in the surgical wound seem to explain the lower blood loss intra- and post-operatively in patients given regional anaesthesia. These differences in haemodynamics give rise to less arterial, and notably less venous oozing of blood from the surgical area. The latter observation is strengthened by the significant correlations between the intraoperative peripheral venous blood pressure and the intraoperative blood loss. The reduction in blood loss and consequently the reduced transfusion requirements in regional anaesthesia are beneficial in decreasing the hazards and costs of homologous blood transfusion. Although impossible to quantify, reduced bleeding also greatly facilitates the surgeon's work.

The reduction of pain on injection of propofol: the effect of addition of lignocaine

Abstract: The effects of addition of 1 ml of lignocaine (10 mg) or isotonic saline to 19 ml of the emulsified preparation of propofol (Diprivan) were studied in a randomised, double-blind trial in 80 patients. The incidence and severity of pain on injection of propofol were significantly reduced by the addition of lignocaine (P less than 0.01).

The influence of alfentanil on the intubating conditions after priming with vecuronium

Abstract: The ability of alfentanil 15 micrograms kg-1 or 30 micrograms kg-1 to improve intubating conditions was studied in four groups of 25 ASA class 1 patients. Induction of anaesthesia was with thiopentone 5 mg kg-1. Neuromuscular blockade was induced with vecuronium using the priming principle. The priming dose, priming interval and intubating dose were 0.01 mg kg-1, 4 min, and 0.1 mg kg-1, respectively. Intubation was attempted 1 min after the intubating dose. Intubating conditions were judged unacceptable in about 30% of the patients belonging to the control groups. Alfentanil 15 micrograms kg-1, when administered 65 s before intubation, reduced the incidence of coughing and diaphragmatic movement (P less than 0.05) but did not reduce the incidence of overall unacceptable intubating conditions. Alfentanil 30 micrograms kg-1, however, reduced the incidence of vocal cord movement (P less than 0.005) as well as coughing and diaphragmatic movement (P less than 0.002). Alfentanil 30 micrograms kg-1 reduced the incidence of unacceptable intubating conditions from about 30% to 4% (P less than 0.02).

Opioid treatment for radiating cancer pain: oral administration vs. epidural techniques

Abstract: In order to determine the optimal pain treatment for patients with cancer involvement of the brachial or lumbar nerve plexuses, a prospective comparative study was carried out using peroral opioid therapy (SO), epidural opioid by a conventional tunnelled epidural catheter (CE) or an epidural catheter connected to an implanted injection port (Port). Pain relief, measured by a visual analog scale (VAS), was similar and adequate in every group already after the first 24 h. CNS side-effects were less frequent and the Karnofsky performance grades slightly superior in the epidural groups. Occlusion and catheter disconnection complicated the pain therapy of five epidural port patients. Epidural dislocation occurred three times in the conventional epidural group. One local infection in the CE group and two in the Port group were recorded. However, no signs of epidural infection were seen at autopsy. The results suggest that due to a lower incidence of side-effects, epidural catheter techniques are superior to peroral opioid in treating pain in these patients. However, complete pain relief was not achieved in all patients, suggesting neurogenic, non-nociceptive pain components. Both epidural techniques seem suitable for long-term pain therapy. Technical improvements are needed in the epidural catheter and the port. The long-term epidural catheter does not seem to cause any major changes in the histology of the dura mater or the connective tissue of the epidural space.

Hemodilution ‐ possibilities and safety aspects

Abstract: Normovolemic hemodilution is an essential part of the overall strategy to avoid exposure of patients to the hazards of homologous blood transfusions. It includes beneficial effects on the flow properties and flow conditions of blood. A hematocrit of 30% can be regarded as an optimal compromise between the fluidity and the oxygen content of the blood. Compensatory responses such as increased cardiac output and stroke volume occur following hemodilution. In patients with compromised coronary reserve the degree of hemodilution that is tolerated has to be carefully considered. Therefore specific selection criteria for patients to be preoperatively hemodiluted are needed. For reasons of safety, efficiency and practicability colloid solutions rather than crystalloid solutions should be used for intentional hemodilution.

The Accelograph®: a new neuromuscular transmission monitor

Abstract: A new neuromuscular transmission monitor based on measurement of acceleration is presented. The monitor consists of an acceleration transducer, i.e. a piezo-electric ceramic wafer with an electrode on each side, and a stimulation and computing unit. The transducer can be fastened to the thumb, and when the finger is moved in response to nerve stimulation a voltage difference develops between the two electrodes. The voltage is then measured and registered in the computing unit. The acceleration transducer does not require preload, but merely that the muscle on which the measurement is being made can move freely. The accelograph is therefore easy to set up and operate. In daily clinical practice it has proved possible, using this new apparatus, to achieve reliable evaluation of the degree of non-depolarizing neuromuscular blockade in less than 2 min.

Assessment of the efficiency of pulmonary oxygenation. The choice of oxygenation index.

Abstract: Oxygen-derived indices are often used as alternatives to determination of venous admixture (Qva/Qt) when a pulmonary arterial catheter is not in use, but the question of which more accurately indicates the efficiency of oxygenation is controversial. The theoretical relationships between six measures of oxygenation (PaO2, SaO2, P(A-a)O2, PaO2/FIO2, P(A-a)O2/PaO2, PaO2/PAO2) and venous admixture were analyzed with special reference to the influence of the concentration of inspired oxygen (FIO2). In addition, the predictability of Qva/Qt was evaluated on the basis of 100 authentic sets of arterial and mixed venous blood gas data. Of the above six indices, PaO2/FIO2 was most accurate (r = 0.88), but was far from independent of the FIO2 used. However, a direct Estimate of Venous Admixture (EVA) - based on arterial blood analysis and with C(a-v)O2 assigned a value of 50 ml.l-1 - predicted Qva/Qt still better (r = 0.95). It is concluded that when mixed venous blood gas data are lacking, EVA is the preferable measure of oxygenation.

Superoxide dismutase and catalase failed to improve neurologic outcome after complete cerebral ischemia in the dog.

Abstract: Superoxide dismutase (SOD) and catalase, natural scavengers of free oxygen radicals, or saline were administered as a continuous systemic infusion to 12 dogs, in a blind randomized fashion, starting 10 min prior to a 10-min episode of complete cerebral ischemia, and continued thereafter for 60 min. Reversible complete cerebral ischemia was achieved by simultaneously occluding the ascending aorta and venae cavae. There were no significant differences in physiological variables (arterial blood gases, hemoglobin, mean arterial blood pressure, heart rate, and temperature) between the two groups, either pre-ischemia or post-ischemia. There was no significant difference in neurologic outcome when evaluated at 48 h post-ischemia. It has previously been reported that the same dose of SOD and catalase as used in the current study could reduce infarct size by 50% when given systemically before reperfusion following coronary ischemia in dogs. The lack of a measurable effect on neurologic outcome in our cerebral ischemic model might be because of the failure of the free oxygen radical scavengers to reach the ischemic cells in sufficient amounts, or because free oxygen radicals do not contribute to brain injury following complete cerebral ischemia.

Pharmacokinetic implications for the clinical use of atropine, scopolamine and glycopyrrolate

Abstract: Several specific and sensitive new methods for determining atropine and its metabolites in biological fluids have increased the possibility to characterise the pharmacokinetic properties of this antimuscarinic agent. Following i.v. injection, atropine disappears very quickly from the circulation, resembling its fast onset of action. Age, but not sex, appears to have a clear effect on its kinetics, explaining at least partly the higher sensitivity of very young and very old patients to this anticholinergic agent. Following i.m. or oral atropine administration, typical anticholinergic effects coincide quite well with the absorption rate of the drug, indicating that the premedication should be given about 1 and 2 h before induction of anaesthesia. A sufficient absorption after rectal administration offers an alternative treatment, especially in children. Differing from its placental transfer, atropine has a delayed and incomplete lumbar cerebrospinal fluid penetration, indicating a fundamental difference between these two biological membranes. Oropharyngeally administered atropine has a very variable absorption, but inhaled or intratracheally given drug has produced interesting new results, e.g. pulmonary atropine administration appears to have clinical significance in special situations, such as cardiac arrest and organophosphate poisoning (military personnel). Depending on the method used, different data on the metabolism and excretion for atropine have been reported and therefore further studies are needed in this respect. The pharmacokinetics of scopolamine and glycopyrrolate and their relation to clinical response are poorly understood.

Residual curarisation: a comparative study of atracurium and pancuronium.

Abstract: Sixty patients (17-78 years old, ASA group I-II) were included in the study, which was triple-blind, randomised, stratified and controlled. Patients were selected in pairs according to sex and type of operation, and randomly allocated to one of two groups, atracurium or pancuronium. Anaesthesia was achieved with thiopentone, pethidine and nitrous oxide in oxygen, and patients were then given atracurium 0.1 mg kg-1 or pancuronium 0.6 mg kg-1. Incremental doses were administered when clinically indicated. On recovery, residual curarisation was evaluated clinically and with the train-of-four method by a doctor who was unaware of the neuromuscular blocking agents used. Residual curarisation was found to be less after neuromuscular blockade with atracurium in the doses used in this study. Atracurium has advantages in this respect when neuromuscular monitoring is not used during operation.

Thoracic epidural anaesthesia decreases the incidence of ventricular arrhythmias during acute myocardial ischaemia in the anaesthetized rat.

Abstract: The aim of the present investigation was to study the effect of high thoracic epidural anaesthesia (TEA) on the incidence of ventricular arrhythmias after ligation of the left coronary artery in chloralose-anaesthetized rats. Forty animals were randomly assigned to receive either 40-50 microliter of bupivacaine (5 mg/ml) or saline in implanted thoracic epidural catheters. TEA decreased mean arterial pressure (MAP) from 118 +/- 5 mmHg to 72 +/- 4 mmHg and heart rate (HR) from 450 +/- 9 to 387 +/- 8 beats/min, while epidural saline did not affect MAP and HR. In both groups coronary artery ligation induced a transient decrease in MAP within the first 5-10 min after ligation. In the control group HR increased, during the 30-min post-ligation period, from 453 +/- 9 to 474 +/- 10 beats/min (P less than 0.05) while no significant change was seen in the TEA group. In both groups the mortality rate was 10%. In the TEA group 30% and in the control group 0% had normal sinus rhythm during the recording period (P less than 0.001). The incidence of ventricular fibrillation and/or tachycardia was significantly lower (P less than 0.05) in the TEA group (20%) compared to the control group (53%). The incidence of ventricular extrasystoles did not differ between the two groups. We conclude that TEA-induced blockade of sympathetic afferents and efferents may offer protection against malignant ventricular arrhythmias in the early phase of acute myocardial infarction.

Acute carbon monoxide poisoning

Abstract: The course and outcome in terms of cerebral morbidity and hospital mortality in 79 severely carbon monoxide poisoned patients admitted to the intensive care unit during a period of 15 years is presented. Treatment consisted of administration of pure oxygen. Ninety-four per cent of the patients were artificially hyperventilated, and the majority of the patients were also treated with moderate hypothermia, steroid hormones and diuretics. Hospital mortality was 30%, and 14% of the patients were discharged after long-term hospital treatment with signs of brain damage. Due to the unpredictable cerebral course after the acute incident long-term follow-up is recommended.

Cerebral blood flow and oxygen consumption during isoflurane and halothane anesthesia in man.

Abstract: In 13 patients, the effects on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) of isoflurane and halothane administered in a clinically relevant situation were studied. Measurements were performed during fentanyl/nitrous oxide (65%) anesthesia together with moderate hyperventilation (PaCO2 approx 4.5 kPa), and repeated after addition of 0.65 MAC of isoflurane (n = 6) or halothane (n = 7). CBF was measured after intravenous administration of 133xenon and CMRO2 was calculated from the arterial venous differences of oxygen content (AVDO2) determined in arterial and jugular venous bulb blood. CBF and CMRO2 (means +/- s.e. mean) determined prior to administration of volatile agents were 28 +/- 5 ml x 100(-1) x min-1 and 2.0 +/- 0.3 ml x 100 g-1 x min-1, respectively, in the isoflurane group. In the halothane group, CBF was 25 +/- 0.4 ml x 100 g-1 x min-1 and CMRO2 was 2.0 +/- 0.4 ml x 100 g-1 x ml-1. There were no significant intergroup differences. Isoflurane did not change CBF, whereas halothane produced an increase of 36% (P less than 0.05) compared to values obtained during fentanyl/N2O anesthesia. In addition, isoflurane caused a further decrease in CMRO2 of 12% (P less than 0.01) as compared to a 20% increase (P less than 0.05) with halothane. The cerebral metabolic depression caused by the short-acting anesthetic induction agents would be expected to decrease with time, and could partly explain the observed increase in CMRO2 produced by halothane. The study suggests that the cerebrovascular and metabolic properties of isoflurane differ from those of halothane, also in man.

Assessment of neuromuscular transmission by the evoked acceleration response

Abstract: This paper presents preliminary observations on an acceleration-responsive transducer designed to monitor neuromuscular transmission. Simultaneously evoked acceleration and tension responses of the adductor pollicis muscles were studied. Registrations were obtained during recovery from atracurium-induced block in 29 individuals in neurolept II anaesthesia (Group I) and in 4 ICU patients (Group II) sedated with pentobarbital or midazolam. Regression analysis of 1567 train-of-four (TOF) registrations, in regard to TOF-ratio (T4/T1) and first twitch ratio (T1/T0), demonstrated regression coefficients (b) and correlation coefficients (r) in the range 0.91-1.06 and 0.89-0.98, respectively. During 1 Hz single twitch stimulation and post-tetanic count stimulation, b and r were in the range 0.85-1.03 and 0.77-0.90, respectively. Following administration of edrophonium (n = 6, Group I) a deviation of T1/T0 regression values was observed in four individuals, i.e. 0.48 (b) and 0.56 (r). This investigation proved a good level of accuracy of the acceleration transducer compared to the force displacement transducer during spontaneous and neostigmine-induced recovery from atracurium block. The acceleration transducer-based system does not require a rigid suspension and seems to have a good monitoring potential in clinical assessment of neuromuscular transmission.

Sedation by the use of inhalation agents in dental care

Abstract: Nitrous oxide/oxygen has long been the mixture of gases used in dental practice to produce light sedation. The main indication for use of nitrous oxide/oxygen sedation is fear-anxiety. The equipment used is a continuous flow machine with a fail safe system set at a minimum of 30 or 40 per cent oxygen. A standardized sedation technique starting with administration of 100 per cent oxygen, is recommended. The concentration of nitrous oxide is then slowly increased and individually set, mostly between 30 and 50 per cent. In most cases the analgesia produced by nitrous oxide is not sufficient to ensure pain-free dental treatment. The sedation must therefore be supplemented by local anaesthesia. Side effects, e.g. restlessness, vomiting, and nausea are infrequent. About 90 per cent patients, who have difficulty in co-operating during dental treatment, mainly because of anxiety, show excellent or fair co-operation during nitrous oxide/oxygen sedation. Occupational exposure to nitrous oxide can be minimized by the use of scavenging systems, local exhaust systems, careful sedation technique, and equipment management.

The acceleration transducer--an assessment of its precision in comparison with a force displacement transducer.

Abstract: A new and simple acceleration transducer (ACT)-based system of neuromuscular monitoring has recently been introduced. The precision of this transducer has been evaluated as compared to a conventional force displacement transducer (FDT) in the present study. Ten progressions of spontaneous recovery from atracurium-induced block with simultaneous measurements using the ACT on one hand and the FDT on the other were studied. Five individuals undergoing elective surgery in modified neurolept anaesthesia and one ICU-patient requiring prolonged neuromuscular blockade, sedated with pentobarbital, were included. Measurements were carried out on the latter patient on 5 consecutive days. Train-of-four (TOF) stimulation was used, readings were given in twitch heights (TH) (T1/control value), and when four responses were obtained in TOF-ratios (T4/T1). Linearity was achieved after logit-transformation and the values regressed on time for each progression of recovery. Analysis of variance was applied to the regressions for the TH and TOF-ratio readings of each transducer. No significant differences were found, either between variation due to differences between slopes or variation due to technical error between the two transducers. The study indicates that the ACT is equal to the FDT with regard to precision in clinical recordings on atracurium-relaxed individuals.

Severe anaphylactic reactions outside hospital: etiology, symptoms and treatment.

Abstract: Twenty-seven patients with severe anaphylactic reactions were treated by two anesthesiologist-staffed ambulance helicopters during a 5-year period. All patients had signs of respiratory and/or circulatory failure. Cutaneous symptoms were described in 70% of the patients, gastrointestinal symptoms in 30% and central nervous symptoms in 85%. Wasp sting and drugs were the most common causes. Other etiologies were bee sting, snakebite, nuts and exercise. All patients were provided with advanced pre-hospital medical care. Epinephrine was employed in 78% of the patients. I.v. fluid therapy was started in 77%. Three patients (11%) needed endotracheal intubation. The time-span from onset of symptoms to medical attendance exceeded 45 min in two patients; both died. Of the surviving patients, 23 were hospitalized. The majority had no signs of respiratory or circulatory failure on arrival in the emergency room and needed only observation in the hospital.

Pulmonary complications after upper abdominal surgery: their prevention with intercostal blocks.

Abstract: A prospective study of postoperative pulmonary complications (PPC) appearing during the hospital stay was carried out in 417 patients undergoing surgery through a subcostal or midline incision. Postoperative pain was relieved either by intercostal block and centrally-acting analgesics on demand or by centrally-acting analgesics alone. Pulmonary complications were diagnosed from combined physical and radiological signs. After biliary surgery through a subcostal incision, PPC were less frequent (P less than 0.05) in patients receiving intercostal blocks (6%) than in those given centrally-acting analgesics (11%). After surgery through a midline incision, the complication rate was higher, 15-57%, and was related to the type of surgery, the highest incidence being found after partial gastrectomy and operations for malignancy, and no significant reduction in the rate of PPC after intercostal blocks with this incision was found in any age group. Indeed, an increased rate of PPC was found in our patients over the age of 60 who had received bilateral intercostal blocks. Irrespective of the type of incision, surgery or method of postoperative pain relief, the patients with PPC more often had respiratory or other disorders preoperatively or a surgical complication intra- or postoperatively than those with normal postoperative recovery. Predisposing physical factors and high age were more common among the patients developing PPC in spite of treatment with intercostal blocks compared to those without such treatment.

Importance of correct handling of samples for the results of blood gas analysis

Abstract: The importance of correct handling of samples for blood gas analysis was studied in 100 patients. Sixty minutes storage in iced water lowered pH by 0.02 pH–units. Storage at room temperature caused considerable changes in Pco2 and Po2 (+ 0.45 kPa and –1.05 kPa). Air bubbles in the syringes increased Po2 if not expelled within 30 s. Thirty minutes storage with air trapped inside the syringe caused an increase in Po2 of 1.8 kPa and a decrease in Pco2 of 0.16 kPa. The use of plastic syringes induced significant changes in Pco2 and Po2, of which the latter (+ 1.0 kPa) may be clinically significant. The findings indicate that sample collection and storage must be guarded by strict rules in order to avoid false results.

Continuous measurement of pulmonary gas exchange during general anaesthesia in man.

Abstract: We report a system for the continuous measurement of oxygen uptake (Vo2) and carbon dioxide output (Vco2) during open-circuit anaesthesia. Gas concentrations were measured by a mass-spectrometer, and expired flow by a pneumotachograph. The values measured by the system were compared in vitro to values produced by a nitrogen-dilution technique. Excellent correlations were found. Continuous measurements were performed in 21 patients anaesthetized for abdominal surgery. Compared to pure intravenous anaesthesia (flunitrazepam-fentanyl), anaesthesia including the administration of nitrous oxide or nitrous oxide and halothane led to more pronounced and sustained decreases in Vo2 and core temperature, with a better cardiovascular stability. Two hours postoperatively, Vo2 was not different from preoperative values. After a transient increase at the onset of anaesthesia, the respiratory exchange ratio (Vco2/Vo2) returned to preoperative values, and then remained subsequently unchanged. Based on these observations, the system described provides an accurate approach to noninvasively monitoring the pulmonary gas exchange in the operating room.