Hemodynamic effects in dogs of nitrous oxide-meperidine and meperidine, respectively, in comparison with nitrous oxide.

The aim of this investigation on dogs, was to examine the hemodynamic effects of nitrous oxide (N2O) plus meperidine and of meperidine with room air ventilation, respectively, compared with those of N2O on its own. When meperidine (bolus dose 3 mg.kg-1 and continued infusion 4 mg.kg-1.h-1) was added to 80% N2O, mean arterial blood pressure fell from about 20 to 10 kPa (150 to 75 mmHg), as a result of a decrease in peripheral vascular resistance, but no compensatory changes in cardiac output were seen. When N2O was withdrawn, during continued meperidine infusion, cardiac output and stroke volume increased, while peripheral resistance remained low. Coronary vasodilation was noted when meperidine was added to N2O, and persisted when N2O was withdrawn. In the pulmonary circulation a different response was found. Here, no effects were observed when meperidine was added to N2O, while pressure and resistance decreased when N2O was withdrawn and meperidine continued.

Fatal iron intoxication in late pregnancy.

A case of intoxication with 5 g of elemental iron (25 g of ferrous sulfate) in a 30-year old woman at 36 weeks gestation is reported. Deferoxamine treatment was given with a delay of 26 hours after ingestion. A healthy infant was delivered by cesarean section 31 hours following ingestion. Subsequently, the patient developed hepatic necrosis, coma and hemostatic dysfunction and expired in cardiac failure after two weeks. The fatal outcome supports the view that the potential lethal dose of iron is lower for adults than for children. This case also demonstrates that major hepatic dysfunction can be a prominent feature of adult cases of iron intoxication. It is not unequivocal that early institution of deferoxamine treatment would have had a significant influence on the outcome. However, taking into account the well-documented efficacy of the drug in children and that no major adverse fetal effects have been associated with deferoxamine treatment in pregnancy, we suggest such antidote therapy to be considered for prompt institution in similar cases.

Maternal haemodynamic changes during caesarean section: a comparison of epidural and general anaesthesia.

Haemodynamic measurements were performed on 20 healthy women before and during elective caesarean section under epidural (10 women) or general anaesthesia (10 women). The influence of the two anaesthetic techniques on the haemodynamic changes associated with operative delivery was compared. The following haemodynamic variables were studied: cardiac output (CO), stroke volume (SV) determined non-invasively with impedance cardiography, heart rate (HR), systolic (SBP) and diastolic blood pressure (DBP), pulse pressure, mean arterial pressure (MAP) and total peripheral vascular resistance (TPR). During epidural anaesthesia, SV was largely unchanged before delivery but increased (P less than 0.05) following delivery. However, CO increased (P less than 0.05) prior to delivery due to an increase (P less than 0.01) in HR. A further increase (P less than 0.05) in CO was recorded following delivery. SBP, DBP, MAP and TPR decreased (P less than 0.01) during epidural anaesthesia. In the patients undergoing general anaesthesia, SV decreased (P less than 0.05) prior to delivery. However, CO remained largely unchanged due to an increase (P less than 0.01) in HR. Following delivery, CO (P less than 0.05) and SV (P less than 0.01) increased whereas HR decreased (P less than 0.01). SBP, DBP and MAP increased (P less than 0.01) prior to delivery, returning to the same level as prior to induction of anaesthesia following delivery. TPR was largely unchanged prior to delivery but decreased (P less than 0.01) following delivery.

Measurement of cardiac stroke volume during cesarean section: a comparison between impedance cardiography and the dye dilution technique.

Simultaneous determination of cardiac stroke volume by impedance cardiography and the dye dilution technique was compared in ten women undergoing elective cesarean section performed under general or epidural anesthesia. The influence of delivery and the anesthetic procedures used on stroke volume determination by the two methods was evaluated and compared. The correlation coefficients for measurements performed before and during anesthesia showed little variation and were largely unchanged after delivery of the child (r = 0.90-0.97). Mean stroke volume determined by impedance cardiography was significantly (P less than 0.001) lower than mean stroke volume calculated from the dye dilution technique. However, there was no significant difference between the mean change in stroke volume determined by the two techniques during serial measurements. Impedance cardiography was found to be a safe, reliable, non-invasive technique for the measurement of changes in stroke volume during cesarean section. The ability of the impedance method to determine changes in stroke volume was unaffected by the anesthetic procedures employed or by delivery of the child.

Measurement of cardiac stroke volume by impedance cardiography in the last trimester of pregnancy.

Simultaneous determination of cardiac stroke volume by impedance cardiography and the dye dilution technique was compared in 10 women during the last trimester of pregnancy. Measurements were performed in different body positions to investigate the influence of body position on stroke volume. The correlation coefficient for all measurements was 0.87. Mean stroke volume determined by impedance cardiography was significantly (p less than 001) lower than mean stroke volume calculated by the dye dilution technique. There was no significant difference between the mean change in stroke volume determined by the two techniques during serial measurements. The reproducibility of individual impedance-determined stroke volumes (6.1 ml) did not differ significantly from individual values obtained by dye dilution (9.3 ml). Maximum mean impedance-determined stroke volume was recorded in the left lateral position (83.8 +/- 4.0 ml). Mean stroke volume was significantly (p less than 0.01) reduced in the supine position (17.9%). A smaller (14.4%) reduction was registered in the right lateral position. These changes in stroke volume according to body position were equally evident by both methods. Impedance cardiography is a safe, reliable, non-invasive technique for the measurement of changes in stroke volume during late pregnancy. The ability of impedance cardiography to determine changes in stroke volume was unaffected by changes in body position.

Septicaemia in patients with central vein catheters. An evaluation of a method including weekly exchange of catheter.

A method for the care of central vein catheters (CVC) including exchange of catheter is described. The method has been used during 6 years in an intensive care unit for patients with severe infections. Nine out of 140 patients (6%) developed catheter related septicemia which was considered as a satisfactory result for patients with plre-existing systemic infection. A bacteriological study showed that the puncture site was colonized by bacteria belonging to the skin flora one day after introduction of a CVC. Cultures from the catheter tip mainly seemed to reflect the flora at the puncture site.

The haemodynamic effects of adrenergic receptor blockade or stimulation druing nitrous oxide anaesthesia in dogs.

The effects of ventilation with normoxic and hyperoxic nitrous oxide on systemic, pulmonary and coronary haemodynamics before and after adrenergic receptor blockade or stimulation were investigated in 15 dogs. To evaluate a blocking or stimulating effect of nitrous oxide on the alpha-adrenergic receptors, the animals were given phenoxybenzamine or noradrenaline, respectively. The effects of beta-adrenergic receptor blockade or stimulation were studied after injection of propranolol or isoproterenol, respectively. The experiments showed that in spite of the lack of alpha-receptor blocking properties and despite the tendency to produce beta-receptor blockade, nitrous oxide induced vasodilation. The findings of the present study, together with the increase in cardiac output and peripheral vasodilation, suggest that the cardiovascular effects of nitrous oxide are extra-adrenergic.

The haemodynamic effects of nitrous oxide anaesthesia on myocardial blood flow in dogs.

The effects of ventilation with nitrous oxide in oxygen on myocardial blood flow any oxygen metabolism were investigated in 31 mongrel dogs. The results of this study showed that, compared with controls, hyperoxic nitrous oxide mixtures did not cause any great changes in myocardial haemodynamics, despite a decrease in cardiac output and an increase in systemic vascular resistance. Normoxic nitrous oxide mixtures produced an increase of the coronary blood flow due to decreased coronary vascular resistance. To what extent this coronary vasodilatation resulted from a increased myocardial metabolism or from a direct effect of nitrous oxide on the coronary vascular bed cannot be quantified from the present results.

The haemodynamic effects of nitrous oxide anaesthesia on systemic and pulmonary circulation in dogs.

The haemodynamic effects of nitrous oxide in normoxia (20% oxygen) and in hyperoxia (50% oxygen) were investigated in 13 dogs. Nitrous oxide in hyperoxia caused a significant rise in total peripheral resistance and a significant decrease in cardiac output, heart rate, myocardial contractility (dP/dt max) and cardiac work. On the other hand, nitrous oxide in normoxia seemed to reverse these findings and did not exert negative inotropic effects on the myocardium. The results indicate that the earlier reported sympathetic activation of the circulation may be related to hyperoxia and not to nitrous oxide as such.

The haemodynamic effects of unsupplemented nitrous oxide-oxygen-relaxant anaesthesia in cardiac patients.

The effect on the systemic and pulmonary circulation of unsupplemented nitrous oxide in about 30% oxygen, with and without IPPV, was investigated in five cardiac patients and compared with control periods at rest with air breathing. The results of this investigation show that nitrous oxide in conventional oxygen concentration does not cause any great haemodynamic changes. During tracheal intubation, however, significant increases in both systemic and pulmonary blood pressures were registered. However, these pressures reverted to the control values immediately after the tracheal intubation. The results of this study support many earlier clinicaly good experiences obtained when using this conventional nitrous oxide-oxygen mixture in cardiac patients.

An improved method of epidural analgesia with reduced instrumental delivery rate.

A detailed study on a modified technique of epidural analgesia (EDA) for pain relief in obstetrics has been performed. The aim of the modifications was to reduce the number of instrumental deliveries and at the same time to make the delivery as smooth as possible for the baby. This was achieved by the use of an anaesthetic with a favourable ratio between neonatal and maternal plasma levels (Bupivacaine) in low concentration (0.25%). A special technique of injection enabled us to limit the extent of the blockade. An epidural catheter was inserted between L2 and L3 and moved upwards 20 cm into the epidural space. 8-10 ml of the solution was then injected after a test dose. The blockade was continued by the repeated injection of smaller doses. As judged by the skin anaesthetic zones and by obstetric examinations, the patient was gradually positioned, during labour, from supine to half-sitting. The catheter was withdrawn at the end of the first stage of labour so that the lower sacral segments could be blocked. A group of 100 patients treated with the technique described was followed. The number of instrumental deliveries in the present series (15%) was significantly lower in similar series reported in the literature. The group of 100 patients treated with modified EDA was also compared with 100 control patients who received only conventional treatment without EDA. There was no differences in the number of abnormal presentations, while the number of caesarean sections and cases of atonic post-partum bleeding was insignificantly lower in the EDA group. The difference in the number of instrumental deliveries-although somewhat higher in the EDA group-was not statistically significant. The total length of labour was prolonged in the EDA group but EDA was not necessarily responsible for this undesired effect. The clinical status of the babies was found to be better after EDA than in control group, as judged from Apgar score. Furthermore, fetal bradycardia was significantly reduced with EDA. It is concluded that EDA, as used in this study, not only is a preferable way of achieving pain relif in the mother but also offers a means of facilitating the birth process for the infant, reducing the incidence of pre- and post-natal asphyxia.