Biomedical subjects
Publications and source records attributed to P Lotz.
On the basis of two case histories of medical device innovation, two aspects of demand are identified: (a) the prospect of new markets and (b) information about user needs. Conditions for direct interaction between the user and producer in the innovation process are identified. The article concludes with some normative implications for the publicly designed generation of new medical technology.
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The tumor-toxic effect of the photosensitizer HpD/Halle activated by laser radiation was demonstrated. Solid Ehrlich carcinoma was used as model. Investigations into the tumor growth, the HpD-distribution after different kinds of drug administration by means of fluorescence measurements, the phototoxicity and the reduction of tumor masses after HpD application and laser irradiation were carried out.
Dazoxiben, a thromboxane synthetase inhibitor, was infused i.v. in a first group of guinea pigs. Saline was given to a second group of animals as controls. Subsequently, the lateral cochlear walls of each animal were prepared and analyzed for thromboxane (TXA) and prostacyclin (PGI) using radioimmunoassay. These studies showed that dazoxiben crosses the blood-labyrinth barrier and shifts the TXA2/PGI2 balance in favor of the latter. The effects demonstrated are discussed with respect to the relevance of prostanoids in cochlear physiology.
Thirty-four otherwise healthy patients having to undergo elective upper abdominal surgery were randomly assigned to two equal groups. In the treatment group, constant positive airway pressure (CPAP) with an expiratory pressure of 12 cm H2O was applied at one hour following extubation, and at daily intervals for the first five days following surgery for a continuous period of three hours. The control group received no CPAP treatment. All patients were given postoperative physiotherapy. In patients who received postoperative CPAP with an end-expiratory pressure of 12 cm H2O, marked normalization of pulmonary function was noted.
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50 patients were investigated during induction of anaesthesia and infrarenal aortic bypass surgery. 26 were operated on under neuroleptanaesthesia (NA group) and 24 under continuous epidural combined with a light general anaesthesia (epidural group). Blood losses were replaced with 5 per cent human albumin, red cell concentrates, and fresh frozen plasma. Ringer lactate solution was used to replace the functional extracellular fluid volume. During induction and maintenance of anaesthesia body temperature fell (NA group from 36.7 to 35.3 degrees C; epidural group from 36.7 to 34.9 degrees C) but no statistically significant difference could be found between the groups, in spite of better surface perfusion of the lower part of the body in the epidural group. The increase of plasma glucose concentration was lower in the epidural group as compared to the NA group. Stress mediated hypokalaemia was of the same degree in both groups, the median values of the plasma potassium concentrations being in the lower reference range (3.5-3.7 mmol X 1(-1], although large amounts of red cell concentrates were given. During clamping of the aorta a moderate compensated acidosis developed in both groups. Declamping caused a more marked increase of paCO2 and a greater fall of pH in the NA group as compared to the epidural group. Induction of anaesthesia was followed by a fall in oxygen uptake (NA group from 221 to 163 ml X min-1; epidural group from 230 to 189 ml X min-1) which appears to be delayed in the epidural group, with a short lasting statistically significant difference between the groups after eventration of the gut (NA group: 162 ml X min-1 less than epidural group 184 ml X min-1). Later on, oxygen uptake was equal in both groups, with no further changes due to clamping or declamping of the aorta. At the end of the operation, when nitrous oxide had been turned of, the oxygen uptake increased considerably in several patients, despite continuing artificial ventilation and intravenous hypnotics and analgesics having been given. Eventration and exterioration of the gut caused the most marked changes in haemodynamics and oxygen transport with significant differences between the groups. Immediately after eventration there was a sudden fall in paO2 in both groups (NA group from 99 to 83 mm Hg; epidural group from 96 to 84 mm Hg) and an increase of the calculated intrapulmonary right-to-left-shunt (NA group from 7 to 21%; epidural group from 10 to 19%).(ABSTRACT TRUNCATED AT 400 WORDS)
One minute following electrically induced ventricular fibrillation, 12 anaesthetized pigs (hybrids between German and Belgian pedigree swine of 29 kg average body weight) were resuscitated for 30 min with a mechanical thorax compressor and ventilator. Six animals were given 1 mval sodium bicarbonate per kilogram body weight via a central venous line during the first ten minutes of resuscitation, and then 0.5 mval/kg body weight during both of the remaining ten minute intervals. The remaining 6 animals served as control group. In the control group constant volume ventilation led to a fall in the arterial partial pressure of CO2 because perfusion was diminished in relation to ventilation and despite the slowly developing metabolic acidosis this initially led to an increase in pH. At the end of the period of observation an arterial base deficit of 10 mmol/l was measured. Infusion of sodium bicarbonate led to a metabolic alkalosis and to an arterial base excess which at 10 min reached a maximum value of 13.8 mmol/l. In the bicarbonate group serum osmolality rose as a result of the sodium application from 293-334 mosm/l. In contrast, the osmolality of the control group only rose to 309 mosm/l.
The effects on near drowning of young pigs of positive end expiratory pressure and zero end expiratory pressure were studied. The arterial PO2 and blood gases were examined during recovery from near drowning and after haemorrhagic shock. The cardiovascular parameters were measured after shock. The findings were considered in relation to the use of positive and expiratory pressure in patients. It was recommended that it be only administered by experienced staff in hospitals, and should not exceed 10 mbars, while 5 mbar was adequate and avoided complications in most cases.
Three different resuscitation techniques were assessed by monitoring haemodynamic, respiratory, and cerebral parameters in 12 pigs of average body wt. (29 kg) following electrically induced cardiac arrest. All three techniques were carried out in randomised sequence, each for ten minutes, on each of the 12 animals. I = interposed ventilation and thoracic compression; S = simultaneous ventilation and thoracic compression; SA = simultaneous ventilation and thoracic compression plus abdominal binding 100 mm Hg. A compression rate of 60/min and ventilation rate of 12 min were used for each of the three techniques. 6 animals were ventilated with ZEEP for the whole of the 30 min observation period, the remainder with a PEEP of 5 cm H2O. In both ZEEP and PEEP groups the highest blood pressure and carotid artery flow rates were observed with the "SA" technique. PEEP ventilation and abdominal binding was found to be the most effective combination. Despite a rise in intracranial pressure, cerebral perfusion pressure rose when abdominal binding was applied. The CO2-production and arterio-venous oxygen difference of both ventilation groups were not significantly influenced by the different techniques. Even the technique "SA" did not markedly influence gas exchange or acid-base parameters. Despite an increase in the arterial base deficit and lactate levels during the course of resuscitation, the arterial pH did not fall below initial values because of the low paCO2. The positive effect of abdominal binding is a result of increased intrathoracic pressure, an increase in the effective circulating blood volume, and redistribution of blood flow.
The following methods for monitoring the ventilation in general anaesthesia can theoretically be applied for neonates and small infants: The use of a precordial stethoscope, measurements and observation of the ventilation pressure, analysis of the inspiratory oxygen concentration, measurement of the expiratory volume, analysis of end-tidal CO2, transcutaneous O2 and CO2 measurement and blood gas analysis. These methods are evaluated and their limitations discussed. Special attention is paid to the application of these methods used in the different paediatric anaesthetic systems. A three graded plan which classifies the risks for the patients and/or the operations is presented in order to rationalize the use of these methods, some of which require expensive equipment. The basic ventilation monitoring includes, even for short operations in healthy patients (Grade I), the precordial stethoscope, the measurement of the inspiratory oxygen concentration, the measurement of the ventilation pressure and, for school age children also measurement of the expiratory volume. For operations lasting longer than one hour (Grade II) end-tidal CO2 analysis should be used when the ventilation-perfusion ratio is undisturbed. Transcutaneous O2 is desirable, but at the present time not accurate for conditions of general anaesthesia. For all high risk patients and/or operations (Grade III), particularly in the neonates, arterial blood gases are indispensable as well as the other methods for monitoring ventilation.
The problem of how to improve postoperative pulmonary function after upper abdominal surgery was investigated in a randomized study involving 64 patients who were subjected to various treatment regimens designed to increase airway pressure. Intraoperative ventilation was carried out with either zero or positive end exspiratory pressure, and postoperatively either CPAP or a nasal oxygen catheter were applied. The following groups were formed: 1. ZEEP /O2-catheter; 2. PEEP/O2-catheter; 3. ZEEP /CPAP; 4. PEEP/CPAP. The typical reduction in vital capacity occurred postoperatively, the lowest value being recorded on the 2nd postoperative day, an alteration in respiratory pattern with reduced tidal volume and increased respiratory rate together with an initially low, later normal alveolar ventilation, and an initial hypoxaemia which was at first associated with a moderate hypercapnia, on the second postoperative day with a normocapnia, were observed. At no point in time could a difference be found between the 4 groups, no measurable improvement in respiratory function being found as a result of the treatment given. Intra- and post-operative increase in airway pressure was however found to be associated with a reduction in the incidence of post-operative pulmonary complications.
Respiratory function was studied in 35 patients after upper abdominal surgery, who had been randomized into two groups. 15 patients (median age: 59 years) were operated on using neuroleptanalgesia and received intramuscular piritramide as postoperative analgesic. A continuous thoracic epidural was placed prior to surgery in 20 patients (median age 52 years). A light general anaesthesia was additionally given when these patients were operated on. Postoperatively, epidural analgesia was continued by infusion of 0.25-0.3 ml/kg X h 0.125% bupivacaine via epidural catheter over a period of 4 days. If pain prevention during coughing and getting up was not complete, top-ups of 6-10 ml 0.25% bupivacaine were given additionally. Respiratory function (FVC, peak expiratory flow, VT, VD/VT, RR, MV, VA, AaDO2(0.21), PaO2 and PaCO2) was investigated before surgery, and on the 1st, 3rd and 5th postoperative day, the patients breathing room air. Results (the median of each groups is plotted, the values of the epidural group being in brackets. 0: preop., 1: first, 3: third, 5: fifth postop. day): FVC 0: 3.05 (3.16) 1: 1.42 (1.40) 3: 1.64 (1.42) 5: 1.39 (2.27) 1. Peak expiratory flow 0: 310 (287) 1: 118 (113) 3: 130 (127) 5: 153 (194) 1/min. Respiratory rate 0: 16 (14.5) 1: 20 (18.5) 3: 16 (18.5) 5: 17 (17) min-1.(ABSTRACT TRUNCATED AT 250 WORDS)
The action of ketamine on intracranial pressure in the presence of haemorrhagic shock, at both the dosage levels used for emergency cases and for in-patient treatment, was investigated using an animal model. Haemodynamically stable animals with a normal or raised intracranial pressure served as a control group. All animals were normoventilated. No rise in intracranial pressure was observed with either 0.5 or 2.0 mg/kg body weight of ketamine in those animals with normal, or in those with a raised pressure. This applied to both the haemodynamically stable animals, and to those in haemorrhagic shock. This finding is probably due to the fact that PCO2 levels did not rise under the controlled ventilation.
There are two main reasons for assessing energy turnover individually and as accurately as possible; firstly, the marked variation in available data on the degree to which energy turnover increases after severe trauma, and secondly accumulating evidence of the potential dangers of an inappropriately high so-called "hypercaloric" substrate dosage, which exceeds energy requirements. The energy turnover of 50 polytraumatized intensive care patients was therefore measured by indirect calorimetry and compared with norm values. Comparison of the median values revealed an approximately 50% higher energy turnover in the polytraumatized cases than calculated basal levels. The median values of our patients all lay within a similar range, but for each individual case we found marked differences between the energy turnover as measured by indirect calorimetry, and that estimated from norm tables. The oxygen consumption and CO2 production rates of 10 polytraumatized ventilated patients, measured at short time intervals, showed only minimal variations during the course of 24 h. The separate measurements carried out at hourly intervals varied by less than 10% when compared to an 1-h period of observation between 11 and 12 a.m. The oxygen consumption of a group of 40 polytraumatized, ventilated intensive care patients receiving various different i.v. infusions and parenteral nutrition regimens was, with an average of 382 +/- 47 ml/min, much higher than physiologically normal values. The energy turnover rate of these patients was correspondingly much higher than that of a fit person at rest, despite the fact that the rates measured were relatively low when compared to values found in the older literature.(ABSTRACT TRUNCATED AT 250 WORDS)
Investigations on the delayed use of positive end-expiratory pressure (PEEP) following a standardized form of near drowning with 12.5 ml/kg body weight of either fresh or salt water were carried out on 14 anaesthetized and ventilated young pigs. After a 3-min period of apnoea the animals were ventilated with 100% oxygen and with either the same or an increased tidal volume, and a PEEP of 5 cmH2O delayed to 20 min, over a period of 2 h. In both fresh and salt water, initial values of PaO2 and AaDo2 were regained by the end of the period of observation when a delayed PEEP was applied. The intrapulmonary right to left shunt, which increased to 40% of the cardiac output, fell by a half within 10 min of beginning PEEP ventilation, initial values being regained after 120 min. During the period of apnoea the arterial partial pressure of carbon dioxide almost doubled, and, when the tidal volume remained unaltered, was still some 20-30% above initial values at the end of 2 h, despite the use of PEEP. Normal PaCO2 levels were achieved on increasing the tidal volume by a factor of 1.4. The larger tidal volume had no influence on either the degree of shunt or the PaO2. The effective compliance, which was considerably reduced after near drowning, increased again with the use of delayed PEEP ventilation. On beginning respiratory resuscitation there was an initial tachycardia and, despite a fall in stroke volume, an increase in mean arterial pressure and cardiac output because of the previous hypoxia. Only minimal cardiocirculatory changes, and no change in oxygen availability, occurred secondary to the use of PEEP.
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