The cardiorespiratory effects of Althesin and ketamine. A comparison

Ketamine-diazepam N2O combination anesthesia--a new "circulatory-system-sparing" type of anesthetic in experimental surgery

For studying the hemodynamics of the greater and lesser circulatory system in animals, the impact of general anesthesia upon cardiovascular functions should be as small, as possible. The marked circulation-depressing effect of halothane, which has so far been given preference for experiments on large animals, was confirmed by the present study of the miniature pig. There was a significant decrease in MAP, cardiac index and dp/dtmax/IP, and an increase in PAPp. Useful insights into hemodynamics, derived from experiments modeling the heart, lungs or vascular system cannot be gained for a cardiovascular system, the functions of which are greatly altered by such an anesthesia. As a new form of anesthesia with minimal cardiovascular influence, the ketamine-diazepam N2O combination, which has already been successfully applied in operations on the open human heart, is introduced into experimental surgery.

[Anesthetic induction with Althesin or diazepam in patients undergoing an aortocoronary bypass]

The haemodynamic effects of induction of anaesthesia with diazepam (group D) and Althesin (group A) were studied in 25 coronary patients under betablockers with good myocardial function. Haemodynamic variables monitored were vascular pressures, cardiac output and systolic time intervals. The effects of both drugs were observed when used alone (time I) and in combination with fentanyl, pancuronium and nitrous oxide (time II). The results seemed to show that Althesin (12.51% fall in SI and 10.79% increase in PEP/LVET) depressed myocardial function more than diazepam (no significant difference), but the introduction of fentanyl, pancuronium and nitrous oxide removed the differences between the drugs as to their effect on myocardial performance. These drugs added a depressant effect to diazepam (13.83% fall in SI and 15.77% increase in PEP/LVET) without increasing Althesin's negative inotropic effect. However, in group A at time II, the pulmonary arterial pressure, the wedge pressure and the pulmonary vascular resistance were significantly reduced, while they remained stable in the diazepam group.

Total intravenous anaesthesia with low dose ketamine and Althesin. Assessment of a technique for minor surgery in difficult situations

In 38 patients subjected to minor surgery, totally intravenous anaesthesia with low dose ketamine and Althesin produced adequate operating conditions in 92% of patients with minimal cardiorespiratory disturbance. Problems arose from muscular hypertonus, spontaneous movement and occasionally salivation. Initial recovery was quicker and the incidence of side-effects lower, than those reported when ketamine was used as the sole agent. The technique could be useful in difficult situations as an alternative to inhalation anaesthesia or other intravenous techniques.

Cardiovascular and respiratory effects of some anesthetics in the decerebrate rat

The cardiovascular and respiratory effects of pentobarbital, ketamine, chloralose and urethane were studied in decerebrate rats. All the anesthetics reduced blood pressure and heart rate. Pentobarbital, chloralose and ketamine, but not urethane, reduced respiratory rate. None of these agents had a significant effect on tidal volume. All these anesthetics significantly attenuated the carotid occlusion, tilt and sodium cyanide chemo-receptor response. These results suggest that the decerebrate rat may be a more suitable preparation, compared to the anesthetized one, for studying cardiovascular and respiratory responses in this species.

A comparison between ketamine and diazepam as induction agents for pericardiectomy

Ketamine 1 · 0 mg/kg and diazepam 0 · 3 mg/kg was used to induce anaesthesia in patients requiring pericardiectomy. A significant rise in blood pressure in patients receiving ketamine was noted. In contrast, a fall in blood pressure was seen when diazepam was administered. Changes in cardiac output, cardiac index, central venous pressure and systemic vascular resistance are discussed.

Ketamine appears to be a more satisfactory agent for induction of anaesthesia in patients for pericardiectomy, whereas diazepam should be used with caution.

Total intravenous anaesthesia. A technique based on alphaxalone/alphadolone and pentazocine

Two hundred and eight patients were anaesthetised using incremental doses of intravenous alphaxalone/alphadolone (Althesin). Analgesia was provided by supplements of pentazocine, which also helped eliminate the excessive movements associated with pure Althesin anaesthesia. This is a total intravenous technique and consequently eliminates the problem of atmospheric pollution. It provides adequate anaesthesia for most minor surgical procedures.

Effects of althesin, etomidate and fentanyl on haemodynamics and myocardial oxygen consumption in man

The acute effects of althesin, etomidate and fentanyl upon haemodynamics, myocardial contractility and oxygen comsumption of the heart were studied in healthy premedicated patients (n = 15) lightly anaesthetized with N2O-O2 (ratio 2:1), 0.3 volumes per cent of halothane and isoflurane respectively. All individuals were ventilated at a normal level. The patients (n = 9) in the halothane group received etomidate 0.3 mg/kg and 20 minutes later althesin 0.075 ml/kg intravenously. In a second group of 6 patients on isoflurane fentanyl 0.01 mg/kg was given. Etomidate did not affect the cardiovascular system significantly. While the decrease in blood pressure after althesin (24 per cent) was the result of a reduction in total peripheral resistance (32 per cent), hypotension associated with fentanyl (23 per cent) was caused by diminished output due to bradycardia (18 per cent). Load data,heart rate, and maximum dp/dt indicated moderate negative inotropic properties only of althesin. Using the complex haemodynamic parameter developed by Bretschneider the myocardial oxygen consumption was calculated. The energy demand of the heart decreased with etomidate, althesin and fentanyl by 14 per cent, 16 per cent and 32 per cent respectively. It is concluded that the risk of cardiovascular depression at induction in patients with impaired myocardial performance and coronary insufficiency can be minimized with etomidate and/or fentanyl.

Anaesthesia for Caesarean section with ketamine

Fifty healthy mothers, with normal placental function, were anaesthetised with ketamine for Caesarean section. Anaesthesia was maintained with nitrous oxide, oxygen, muscle relaxants and controlled ventilation. Surgery was conducted in the lateral tilt position. Arterial blood samples were drawn from the mothers, and from the vessels of a double clamped section of umbilical cord, for blood-gas analysis. Results obtained were compared with those of a previous series anaesthetised with thiopentone, nitrous oxide, oxygen and muscle relaxants. Eight infants were clinically depressed, judged on the basis of their modified Apgar score 2 minutes after delivery. The average time to sustained respiration (TSR) was 58.1 seconds. The mean maternal pH and base excess values in the ketamine group were significantly greather than those reported after thiopentone anaesthesia. Mean Uv and Ua pH levels were also significantly higher after ketamine; in contrast, the average fetal base excess values did not differ from those obtained previously with thiopentone. The mean (Ma-Uv) and (Ma-Ua), pH gradients were 0.019 and 0.025 pH units greater respectively in the ketamine group compared to the thiopentone (P less than 0.005). The average (Uv-Ua) PO2 gradient was 3.4 mmHg less after ketamine anaesthesia (P less than 0.005). A significant inverse correlation was observed relating the I-D interval to the Ma and Ua pH values. Maternal arterial base deficit values appeared to increase with delay in delivering the fetus. Prolongation of the uterine incision to delivery (U-D) interval was associated with a decrease in Ua pH and base excess values. (Ma-Ua) pH and base excess gradients increased with lengthening of the U-D interval. No convincing evidence of awareness during anaesthesia was found during the study. Five patients, appeared to be hallucinated in the immediate post-anaesthetic period. Unpleasant dreams were reported in 5 instances. In this study ketamine appeared to be unassociated with significant biochemical asphyxia, but may have been responsible for some element of drug induced neonatal depression. In view of our own experience and that of other workers, it is suggested that ketamine induction for Caesarean section should be re-evaluated using a lower dose of the drug.

The cardiovascular effects of ketamine in man

The arterial hypertension of ketamine is prevented by verapamil, a calcium ion antagonist. This indicates that ketamine is a direct myocardial stimulant acting by increasing the availability of calcium across the cell membranes of the myocardial and the Purkinjé systems. The positive chronotropic action of ketamine is not reversed by verapamil. Both the chronotropic and the inotropic effects of ketamine are prevented by halothane which acts partly by increased vagal tone and partly by what appears to be a verapamil-like depression of calcium availability. Ketamine blocks the reflex sympathetic response of the peripheral blood vessels to surgical stimuli. The site of the block within the sympathetic reflex arc has not been identified. It is not at the alpha adrenoceptor level. The clinical implications of the findings have been discussed.

Ketamine anaesthesia for medical procedures in children

Ketamine hydrochloride 2 mg/kg, together with atropine 0.2 mg, has been given intravenously on 100 occasions on a general paediatric ward. No serious side effects occurred. Dreams followed in 4 children but did not reduce acceptability of the drug. In our hands it has greatly reduced the pain and distress of children undergoing many routine medical procedures, particularly the dread which builds up when these have to be repeated in the same child. It has also produced close to ideal conditions for the operator, and probably increased his efficiency by reducing the emotional strain which occurs when doing painful things to a frightened patient.