Anesthesiology
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The principal site of action of intravenous regional anesthesia was studied using both prilocaine HC1 0.5% and technetium pertechnetate to define their distribution in the upper limb during this method of anesthesia. Using a single upper arm tourniquet and injecting technetium pertechnetate into a cubital fossa vein, the isotope spread to the finger tips. When a double tourniquet system was used to isolate the hand from the forearm, the following results were obtained: for up to 20 min after injection of the 40 ml of normal saline and radioisotope there was no leakage into the general circulation nor into the hand; after injection of 40 ml prilocaine HCl 0.5% into a cubital fossa vein, there was no anesthesia in the hand except for a small area on the dorsum corresponding to the area of sensory distribution of the radial nerve; while the tourniquets were inflated there was cramping pain in the hand. The results indicate that the initial analgesia obtained with the intravenous regional technique was due to blockade of small nerves or possibly nerve endings and not of the major nerve trunks at the elbow as has been suggested previously.
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Eleven patients with acute respiratory failure due to diffuse, bilateral lung disease were treated according to a new ventilation concept. The patients were intubated with a double-lumen catheter and positioned in the lateral decubital posture. With two synchronized ventilators, each lung received half of the tidal volume (VT), in accordance with its presumed perfusion (differential ventilation--DV), and the end-expiratory pressure was increased locally in the dependent lung (selective PEEP). ⋯ The major findings were that DV with a selective PEEP of 12 cmH2O to the dependent lung decreased venous admixture by 38% (P less than 0.01) in comparison with conventional ventilation with no PEEP. Furthermore, it was found that selective PEEP, in contrast to general PEEP, had no deleterious effect on cardiac output. Consequently, DV with selective PEEP increased arterial oxygen tension by 23% (P less than 0.05) compared with general PEEP and by 46% (P less than 0.001) in comparison with conventional ventilation with no PEEP.
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Using the technique of ventriculocisternal perfusion, resistance to reabsorption of cerebrospinal fluid (Ra) was calculated from determinations of the rate of reabsorption of cerebrospinal fluid (Va) at differing cerebrospinal fluid pressures in dogs. Ra was examined during prolonged anesthesia (5.0-6.0 h) with enflurane (2.2%, end expired) or isoflurane (1.4%, end expired). ⋯ In contrast, the different alterations of CSF dynamics caused by isoflurane, namely decrease of Ra with no change in Vf, may explain, in part, why minimal increase of intracranial pressure is observed during prolonged anesthesia with isoflurane. Because decreased Ra improves spatial compensation by cerebrospinal fluid volume for increased intracranial pressure, isoflurane may offer an advantage over enflurane in patients at risk because of increased intracranial pressure.
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Vecuronium and atracurium provide addition flexibility to the clinician using neuromuscular blocking drugs. The shorter duration of action, lack of significant cardiovascular effects, and the lack of dependence on the kidney for elimination provide clinical advantages over, or alternatives to, currently available nondepolarizing neuromuscular blocking drugs.
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Lung perfusion was studied in 10 patients (mean age 58 yr) in the lateral position during enflurane anesthesia. They were ventilated through a double-lumen endotracheal catheter: 1) by one ventilator with free distribution of ventilation between the lungs, with no (zero) end-respiratory pressure (ZEEP); 2) as above but with a general positive end-expiratory pressure (PEEP) of 9 cmH2O; or 3) by two ventilators with equal distribution of ventilation between the lungs and with a selective PEEP of 8 cmH2O to the dependent lung only. Total ventilation was on average 8 l/min (BTPS) throughout the study. ⋯ Peak and end-inspiratory airway pressures were 5-18 cm H2O lower during selective than during general PEEP. Arterial oxygen tension was significantly greater during the third method than during either of the other ventilator settings and the alveolar-arterial oxygen tension difference was almost halved compared with the first method. It is concluded that differential ventilation with selective PEEP improves ventilation-perfusion matching and thus oxygenation.