Computer-calculated pulmonary carbon dioxide and oxygen exchange in human subjects during general anesthesia with mechanical ventilation

Computer calculation of minute-by-minute and breath-by-breath values for carbon dioxide excretion (VCO2) and oxygen consumption (VO2) in human subjects during general anesthesia and mechanical ventilation were obtained with position changes and after drug administration to demonstrate a method for monitoring pulmonary gas exchange. A modified response to the intravenous injection of doxapram hydrochloride was observed in 12 patients with pancuronium bromide neuromuscular relaxation when they were compared with 12 patients who had been tubocurarine. The data included representative values for VCO2 and VO2 measured simultaneously in normal women after 1-2 h of balanced nitrous oxide-oxygen-fentanyl anesthesia with muscular relaxation and mechanical ventilation.

The usefulness of electroencephalography in curarized newborns

Curare and other muscle relaxants are being used with increasing frequency in the management of infants who are mechanically ventilated for severe respiratory distress. Neurological evaluation of these paralyzed newborns is difficult and neonatal convulsions may go unrecognized. The present study includes 5 curarized infants in whom neurological impairment was suspected because of complicated pregnancies and perinatal asphyxia. All showed very abnormal EEGs with ongoing paroxysmal activity in the absence of clinical seizures or a severely depressed record. In two of these infants an improvement in the values of the blood-gases coincided with the administration of diazepam. In curarized infants the electroencephalogram is of importance in the evaluation of the background activity, the detection of convulsive brain activity, and in the management of anticonvulsive therapy.

The K+ liquid ion exchange electrode system: responses to drugs and neurotransmitters

K+-sensitive liquid ion exchange electrode systems respond with a slow potential change to acetylcholine, choline, anticholinergic drugs, biogenic amines, and glutamic acid. The response threshold has been defined, and in most cases it is at extremely low concentrations (10(-7)-10(-5)M). The direction of the potential change varies, but in most instances it is additive to that produced by external K+. The K+ electrode system is further sensitive to decreasing pH, within a narrow and possibly physiological range of pH. These findings suggest that small measured changes in extracellular K+ are biased by the chemosensitivity of the liquid ion exchange electrode system to some compounds of physiological importance.

Influence of nitrous oxide on local cerebral blood flow in awake, minimally restrained rats

In order to evaluate the effect of 70-80% N2O on local cerebral blood flow (1-CBF) in the rat brain, we developed a procedure for measuring CBF by an autoradiographic [14C]iodoantipyrine technique in awake, minimally restrained animals. Results on 1-CBF, as measured in 22 different structures, showed little variability between animals. In the majority of structures analyzed, 70-80% N2O failed to alter 1-CBF. These included all cerebral cortical and most subcortical structures. However, nitrous oxide reduced CBF in the inferior colliculus and the superior olive, in two of the limbic structures analyzed, and in the hypothalamus. In no structure, except the striatum (p less than 0.05), was a significant increase in 1-CBF obtained in N2O-breathing animals. However, the results suggest that CBF may have been increased in the auditory cortex. Immobilization was found to reduce 1-CBF in the cerebellum, inferior colliculus, superior olive, hippocampus, and septal nuclei. The results also suggest that the procedure somewhat increased CBF in frontal and parietal cortex. When the results obtained in awake, air-breathing animals were compared with those obtained in immobilized animals ventilated on N2O, there was no significant increase in any of the structures analyzed, although there were suggested increases in all cortical areas except the visual cortex. However, the data showed that ventilation with 70-80% N2O significantly decreased CBF in several structures (inferior colliculus, superior olive, hippocampus, amygdala, septal nuclei, and hypothalamus). In some of these, the effects of 70-80% N2O and of immobilization were obviously additive.

General anesthesia in "inducible" porphyrias

To evaluate the risk of inducing acute symptoms after general anesthesia in patients with "inducible " porphyrias, the authors analyzed retrospectively the effects of 78 exposure to anesthesia in 47 patients, 33 with acute intermittent porphyria and 14 with variegate porphyria. On 62 occasions, 29 involving the use of a barbiturate, anesthesia was induced in 37 patients who had no porphyric symptoms at the time. None of these patients had an acute attack postoperatively. Anesthesia was induced 16 times in 14 patients during acute episodes; 12 of these patients also received precipitating drugs other than anesthetics. Porphyric symptoms worsened in seven in the ten patients who received thiopental and in two of the four who did not. In the latent stages of acute intermittent and variegate porphyria in this patient population, the risk of incurring symptoms after exposure to thiopental and/or other anesthetics was small. During an acute episode thiopental may aggravate porphyric symptoms.

Total intravenous anaesthesia for neurosurgery and neuroradiology

A method of total intravenous anaesthesia for neurosurgery and neuroradiology is described using a continuous infusion of alphaxalone/alphadolone (Althesin) with analgesics and muscle relaxants. It has been used successfully on 272 occasions in 243 patients. The reasons for using such a technique and the advantages and disadvantages inherent in it are discussed.

[Althesin in surgery of the eyeball]

Evaluation of Althesin in open eyeball surgery is reported. The anaesthetic gave surgically very useful and stable hypotonia, comparable with that offered by pentothal. Its is felt that steroid anaesthesia is excellent for surgical purposes and that Althesin is ideal on account of its overall features: lack of toxicity, high therapeutic index, tranquil induction, rapid return to consciousness, excellent quality, absence of carryover effects, and easy regulation. It is, moreover, rarely responsible for coughing and vomiting. It is preferable in eye surgery to "heavy" anaesthetics, such as barbiturates and volatile halogenates, particularly in the aged.

[Relationship between level of vigilance and changes in the receptive fields of the cat visual cortex]

The activity of 118 neurones of the primary visual cortex (17th field) was studied in unanesthetized cats, immobilized with d-tubocurarine, in a state of calm wakefulness and in strained attention, alarm. The strained attention was elicited by an air-puff directed to the corner of the closed eye, not used for the photic stimulation. Considerable rearrangments of the receptive field of neurones (94%) were observed in the state of strained attention. In the majority of the studied cortical cells (75%) during 10-30 minutes the excitatory centres of their receptive fields became narrower while their inhibitory periphery widened; in the cells with the inhibitory centres of the receptive fields they were larger in 80% of the cases. It is shown that with dark, mesopic and scotopic adaptation the major characteristics of the changes in the receptive fields remain unaltered. It is assumed that these effects have a behavioural value for the organism, because the created rise in the level of alertness is accompanied by a sharpening of the receptive fields, i.e. by a greater ability to a fine analysis and recognition of visual images.

Binding of d-tubocurarine by gangliosides

The binding of d-tubocurarine by ganglioside mixtures from chicken and bovine brain as well as by the single gangliosides GGtet1-NeuAc, GGtet2aNeuAc and GGtet3aNeuAc was demonstrated by means of equilibrium gel filtration. The sialyl-oligosaccharide derivatives of GGtet1NeuAc and GGtet2aNeuAc, however, did not bind any d-tubocurarine. A lack of binding was also found for the gangliotetraosyl-ceramide GgOse4Cer, free NeuAc, mucin and sphingomyelin. Under saturation conditions, GGtet1NeuAc bound 0.58, GGtet2aNeuAc 0.92 and GGtet3a-NeuAc 1.23 mol d-tubocurarine per mol ganglioside. Half-maximal binding was achieved between 1 and 1.5 x 10(-5)M d-tubocurarine. Ca2 was found to inhibit the binding of d-tubocurarine to gangliosides (50% at 4 x 10(-4)M Ca2). Mg2 was about 4 times less effective. Acetylcholine caused a 40% inhibition at 4 x 10(-3)M, whereas K and Na had only slight effects even at 5 x 10(-2)M.

Use of labetalol during halothane anaesthesia

1 The drugs that are available to attain controlled hypotension during anaesthesia are not entirely satisfactory.

2 Problems in controlling hypotension are encountered in the young, the anxious, patients with a tachycardia, and in those for whom halothane is contra-indicated.

3 Labetalol has been investigated as an adjunct to controlled hypotension in 150 major surgical procedures. Anaesthetic technique, labetalol dosage and results are discussed.

4 Labetalol in patients under halothane anaesthesia resulted in a rapid attainment of hypotension which was easily controlled, and quickly and permanently reversed by the intravenous administration of atropine sulphate. It was especially useful in patients in whom problems with other techniques can be anticipated.

5 Controlled hypotension with labetalol was also used in patients with ischaemic heart disease with good cardiovascular control and without any untoward effects.

[Comparative characteristics of mechanisms regulating tubocurarine and cold tremor]

Tubocurarine tremor and shivering show identical topography in different muscle groups and identical frequency patterns of the EMG. Electrical stimulation of the medial preoptic area inhibits tubocurarine tremor and shivering. Reflexes from peripheral thermoreceptors are less important in regulating the tubocurarine tremor as compared with the shivering regulation. The data obtained show that tubocurarine tremor is a centrally induced analog of shivering.

Dequaternization of curare bases with sodium thiophenoxide and ethanolamine

To prepare (+)-tubocurine and O,O-dimethyl-(+)-tubocurine, the commonly used dequaternization procedures with sodium theophenoxide and ethanolamine were investigated. The quaternary compounds were (+)-tubocurarine chloride and the chloride and iodide salts of O,O-dimethyl-(+)-chondocurarine. The results obtained with ethanolamine indicate that Hofmann elimination is a major pathway and that N-demethylation is minor. The elimination products of O,O-dimethyl-(+)-chondocurarine iodide with ethanolamine were identified as O,O-dimethyltubocurinemethine, O,O-dimethyltubocurineisomethine, and O,O-dimethyltubocurinedimethine. N-Demethylation was the primary reaction with sodium thiophenoxide. Thus, dequaternization of (+)-tubocurarine chloride with sodium thiophenoxide provided (+)-tubocurine which, on diazomethylation, yielded O,O-dimethyl-(+)-tubocurine, identical to the compound obtained by N-demethylation of O,O-dimethyl-(+)-chondocurarine chloride with the same reagent.

Contralateral influence on recruitment of curarized muscle fibres during maximal voluntary extension of the legs

The force of maximal voluntary contraction (MVC) was compared during extension of one leg alone and during simultaneous extension of both legs. In 6 subjects MVC of two legs extension was 75 +/- 3.6 (S.E.)% of the sum of the single one leg MVC. This may indicate a reduced muscle fibre involvement during two leg extension as compared with one leg extension. We investigated the possibility that either red (type I) or white (type II) muscle fibre recruitment was restricted during two leg extension. The neuromuscular transmission in the two types of fibres was partially blocked with d-tubocurarine (dtc) or decamethonium (C10) for either type I or II, respectively. In 5 subjects receiving dtc the ratio between the reduced two leg and one leg extension forces (75 +/- 2.3%) did not change. During administration of C10, however, this ratio decreased by 16 +/- 3.1%. Partial blocking with dtc caused a two component curve during tension development with a first maximum at 0.22 s, and another maximum at 1.03 s of a 3 s attempt to reach MVC. During partial blocking with C10 results in muscle contractions where a relatively large amount of type I muscle fibres are contributing to the force developed. The experiment suggests that type I fibre recruitment is restricted during severe static exercise in normal muscles. Furthermore, it demonstrates that fibre recruitment can vary in the same muscle function performed with one leg or two legs.

Myasthenia gravis: review of diagnosis and management

Although the cause of myasthenia gravis is still unknown, its pathogenesis appears clear: immunologic attack on synaptic receptors in muscle causes receptor deficiency, decreased miniature endplate potentials, and decrements in the compound action potentials evoked from muscles on repetitive stimulation of peripheral nerves. In addition to the involvement of skeletal muscle, some MG patients may manifest subtle alterations of the function of heart, lung, smooth muscle, and CNS, indicating that this is truly a systemic disorder. Modern therapy involves adjusting treatment to the needs of individual patients. Anticholinesterases, calcium, ephedrine, potassium, and germine partially correct the defect in neuromuscular transmission; prednisone, ACTH, cytotoxic drugs, antilymphocyte serums, gamma globulin, thoracic duct drainage, plasmapheresis, and thymectomy partially modify the abnormalities of the immune system.

Myasthenia gravis: a personal view of pathogenesis and mechanism, part 2

A review of our current knowledge of the etiology and pathogenesis of myasthenia gravis is presented, with particular emphasis on the immunological aspects of the disease. Part 1, published in the January/February issue of MUSCLE & NERVE, dealt with the clinical and genetic features of myasthenia gravis which led to the autoimmune theory of the etiology of the disease. Part 2, which appears in this issue, provides a review of the dysfunction of physiology, pharmacology, and structure of the neuromuscular junction in myasthenia gravis, and the part played by the autoimmune process.