Biomedical subjects
N Lomholt
Publications and source records attributed to N Lomholt.
Comparison of the renal effects of six sedating agents in rats.
This study was designed to compare the renal effects of sedation with alphaxalone-alphadolone, etomidate, propofol, midazolam, fentanyl-fluanisone, and thiopental in rats. The sedative dose was defined as the highest dose that abolished the escape response without affecting the righting reflex. Female Wistar rats were chronically catheterized with a jugular vein catheter, and urine flow rate and renal clearances of inulin (glomerular filtration rate = GFR), sodium, and lithium (used as an index of proximal tubular function) were measured in the conscious, unrestrained state (n = 107 experiments). In a separate series (n = 70 experiments), the effect of sedative doses of each drug on the nociceptive threshold was tested with the tail-flick test. Responses in sedated animals were compared to responses in animals infused with the vehicle. Fentanyl-fluanisone and thiopental had hypoalgesic actions in sedating doses. Propofol, fentanyl-fluanisone, and thiopental reduced GFR by 20-30%. Urine flow rate was significantly decreased by propofol (-24%) and thiopental (-48%). Propofol and fentanyl-fluanisone reduced fractional lithium excretion by 9-13%. Only alphaxalone-alphadolone, etomidate, and midazolam produced sedation without affecting renal function in rats. Because midazolam produced the most consistent degree of sedation, we conclude that midazolam is the least confounding sedative agent for renal function studies in conscious rats.
Tracheal models which simulate the compliance of the adult male trachea.
Earlier models of the human trachea have not taken the characteristic compliance of the trachea into account. Two tracheal models are presented, which simulate the compliance of the adult male human trachea, intended for more valid laboratory testing of the function of the cuffs of tracheal tubes. The two models simulate the conditions with and without controlled ventilation.
A device for measuring the lateral wall cuff pressure of endotracheal tubes.
A new method for measuring the lateral wall pressure on the trachea from cuffs of endotracheal tubes is presented. The method is based on measuring the force necessary to force a small, constant flow of air through a Teflon or silicone rubber envelope, placed between the cuff and the tracheal wall. The pressures recorded are 0.1 to 0.3 kPa higher than the theoretically correct values. The response time is 0.28 s for 90% of full deflection. Dynamic recordings of the lateral wall pressure of high and low residual volume cuffs can be obtained for analysis of the interaction between the cuff and the tracheal compliance. No method for accurate, dynamic recording of the lateral wall cuff pressure has previously been published.
Amiloride-sensitive lithium reabsorption during doxazosin-induced blood pressure reduction in rats.
1. The effects of acute systemic alpha 1-adrenoceptor blockade by doxazosin on glomerular filtration rate, urine flow, sodium clearance and lithium clearance were investigated in acutely prepared conscious rats. 2. Clearance experiments were performed during water diuresis (20 mmol/l NaCl and 110 mmol/l glucose, 3 ml/h). After a control period, animals were randomized to one of the following treatments: time-control (n = 9), doxazosin (50 micrograms primer, 30 micrograms h-1 kg-1) (n = 10), amiloride (1 mg primer; 2.4 mg h-1 kg-1) (n = 10) and doxazosin plus amiloride (n = 9). 3. Doxazosin reduced the mean arterial blood pressure from 125 to 108 mmHg; this was associated with transient reductions in glomerular filtration rate, urine flow and lithium clearance. After the transient antidiuresis, the sodium excretion rate remained reduced in doxazosin-infused animals. Amiloride increased the sodium excretion rate without having effects on other variables. When doxazosin was given together with amiloride, the reduction in lithium clearance observed during the transient reduction in glomerular filtration rate and urine flow, was partly abolished. Thus the fractional lithium excretion was transiently increased in rats given doxazosin plus amiloride (from 29 to 40%), whereas in rats given doxazosin alone a non-significant reduction was observed (from 28 to 25%). The dissociation between lithium clearance and fractional lithium excretion in the two doxazosin-infused groups was only significant during the transient reduction in glomerular filtration rate and urine flow. 4. The results provide evidence for an amiloride-sensitive lithium reabsorption during acute systemic alpha 1-adrenoceptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
[CO2-stunning of swine for slaughter from the anesthesiological viewpoint].
For investigations of CO2-stunning of feeder- and slaughter-pigs parameters of behaviour, blood-gas-analyses and electroencephalograms were chosen. The following results were obtained: 1. Blood-gas-analyses proved that the CO2-stunning does not produce unconsciousness due to a lack of oxygen. 2. The criterias of general anaesthesia: unconsciousness, muscle-relaxation and analgesia with total reversibility could be confirmed. 3. The violent convulsive symptoms were evaluated as reactions identical with the stage II of GUEDEL's scheme of anaesthesia. 4. Muscular agitation, which sometimes appeared a few seconds before the stage of excitation, was judged to belong either to the start of the excitation phase or to the end of Guedel's stage of analgesia, during which the sensitivity is decreased. Neither study of behavior nor objective measurements showed, during the first 10 to 20 seconds of exposure to the CO2, any sign of pain or suffering related to the Act for Prevention of Cruelty to Animals, and accordingly such suffering should not be ascribed to the CO2 stunning method.
Prevention of silent aspiration due to leaks around cuffs of endotracheal tubes.
Significant aspiration may occur around correctly inflated high volume, low pressure endotracheal tube cuffs. The prevention of silent aspiration due to leaks around cuffs of endotracheal tubes was investigated during general anesthesia for hip replacement in 47 patients. The patients were randomly assigned to one of three groups, in which one of three endotracheal tubes of different designs were used for intubation. The following three tubes were used: the red rubber Rüsch tube with low residual volume cuff, inflated to minimum occluding volume; the Mallinckrodt Hi-Lo tube with high residual volume cuff; the NL tube with high residual volume cuff and automatic cuff pressure regulation. The cuffs on the Mallinckrodt and the NL tubes were inflated to 29-31 cm H2O. One hour before termination of the surgical procedure, 1 ml methylene blue dye was injected into the trachea just above the cuff through a thin channel built into the tubes. At termination of the operation, the trachea below the cuff was inspected with a fiberoptic bronchoscope. Aspiration was found in 12.5% with the Rüsch tube, in 31.2% with the Mallinckrodt tube, and in 0% with the NL tube. Our results show that silent aspiration is still a problem with standard endotracheal tubes, but that it may be minimized by use of appropriate tubes, cuffs, and control of cuff inflation.
Dilatation of the trachea treated with the NL-tracheostomy tube.
The NL-tracheostomy tube has a large diameter, large residual volume cuff with automatic and instant cuff pressure regulation. It has been shown in clinical studies to prevent mucosal damage; and depending on airway pressure, it should in theory prevent or delay the onset of trachea dilatation. The authors report 2 patients who developed severe tracheal dilatation with use of standard low volume cuffs during prolonged mechanical ventilation. Placement of the NL-tracheostomy tube with a special long intratracheal leg and cuff positioned below the dilatation abolished the acute problems of air leakage. Tracheal dilatation at the new cuff site did not develop in 1 patient and was slowed in onset in the 2nd patient, who needed high inflation pressures.
Design and function of tracheal suction catheters.
Tracheal suction catheters damage the mucosa of the airway, due to both the pull from the vacuum and insertion of the catheter. The pull of the vacuum from a suctioncatheter was measured on a Mettler balance. An open side hole reduced the pull by around 90% and a distance of 1 mm gave a reduction of around 90%. The combination of one side hole and a 1 mm distance gave a 99% reduction of the pull. The difference between one or more side holes was measured. The suction efficacy was higher with a single side hole than with several side holes. On the basis of these measurements and a review of the literature, the principles were outlined for the construction of a suction catheter which provided maximum suction efficacy and caused minimum damage: (1) a moderate to strong vacuum was to be used; (2) the catheter was to have a single hole at the tip and a single side hole placed at the convex side of the angle; (3) both side hole and tip hole should be so constructed that the holes were kept at a distance from the mucosa; and (4) the tip should be angulated.
The new NL tracheal suction catheter.
When a tube with a vacuum is approached to the surface of a liquid, a suction cone is formed and the liquid is sucked into the tube. In the new NL tracheal suction catheter, this suction cone effect is used to transport secretion into its depressed suction holes. The catheter is angle-tipped and has a U-shaped depression around a single side hole at the angle. Four large holes near the edge of the tip hole are shown to be just as effective in reducing the pulling force from the tip hole as the depression around the side hole. The new catheter was compared with three commercially available suction catheters with regard to the maximum damaging effect and the suction efficacy. The force from each suction hole pulling a flat metal base was reduced from 3 to 33 times and the efficacy in sucking was increased in relation to the other catheters when egg-white was used as model for mucus. Angle-tipped catheters are orientation-dependent. The NL catheter was the least orientation-dependent of the three angle-tipped catheters tested. Histologic examination of the mucus sucked during a clinical test showed that the NL catheter caused less tracheobronchial damage than did the Rüsch catheter.
A new tracheostomy tube. III. Bronchofiberoptic examination of the trachea after prolonged intubation with the NL tracheostomy tube.
Recent publications show that severe damage to the trachea is still a problem with high-volume, low-pressure cuffs. The NL tracheostomy tube was used in 86 patients for 3 days to 2 months (mean 16 days). This tube has a high-volume, low-pressure cuff with automatic regulation of the cuff pressure at 3 kPa. The tube has a flexible tip. Fiberoptic examination at extubation showed minimal damage to the tracheal mucosa: 33 patients had normal mucosa and the rest had hyperaemia and/or fibrin formation. Four patients had ulcerations from suction catheters and four patients had small, superficial ulcerations produced by the tip of the tube. Of these last four patients, three had skin flaps that exerted pressure on the tube. Severe tracheal damage was prevented due to the combination of automatic regulation of cuff pressure and a flexible tip of the tube.
Thin fluid-filled catheters for more accurate determination of pressures and their time derivatives.
A catheter-transducer system consisting of a thin fluid-filled teflon catheter and a transducer with a low displacement volume is presented. The thin catheter is especially suited for registration of pressure and the time derivatives in small caliber vessels. From theoretical considerations it is concluded that the best way of obtaining a correct damping ratio in the range of 0.6-0.7 in the system is to adjust the diameter of the catheter empirically to the characteristics of the transducer. Residual gas bubbles are a problem in most catheter-transducer systems, but due to the design of the catheter and to a special flushing method, reproducible results are rapidly and easily obtained. The damping ratio of the system is 0.6 and the band width is 35 Hz. In repeated experiments an identical influence of the temperature on the damping ratio could be demonstrated.
[High volume cuffs and precautionary measures].
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Reduced myocardial blood flow in acute and chronic digitalization.
The myocardial blood flow was measured by the 133Xenon disappearance curve from the left ventricular wall following an injection of 133Xenon in the left coronary artery in 8 dogs without digoxin pretreatment and in 8 chronically digitalized dogs. The myocardial blood flow was significantly less (30%) in the digitalized dogs than in the dogs without pretreatment. In the digitalized dogs as well as in those without pretreatment an intravenous injection of digoxin resulted in a further significant decrease of the myocardial blood flow of about 20% and a significant increase of the coronary vascular resistance. The reduced myocardial blood flow both during acute and chronic digitalization is beleived to be of clinical importance.
Postoperative pulmonary complications using dry and humidified anaesthetic gases.
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A new tracheostomy tube. II. Cuff with self-adjusting minimum pressure on the tracheal mucosa during inspiration and expiration.
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[Displacement of a tracheostomy tube. An unusual fatal complication of tracheostomy].
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Humidification of inspired air.
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