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Description / Table of Contents: Abstract. Automated measurements of respiratory gas exchange recently became available for the determination of oxygen uptake (V˙O2) in critically ill patients. Whereas these metabolic gas monitoring systems (MBM) are assumed to measure total body V˙O2, the reversed Fick method in principle excludes intrapulmonary V˙O2. Previous clinical reports comparing V˙O2 measured by the reversed Fick principle (V˙O2  Fick) with V˙O2 measured by MBM (V˙O2  MBM) found that V˙O2  MBM was significantly greater than V˙O2  Fick. It was suggested that these differences between methods represent V˙O2 of pulmonary and bronchial tissue, as intrapulmonary V˙O2 had been estimated to account for 15% of total body V˙O2 in dogs with experimental pneumonia. The objective of this study was to compare V˙O2  Fick with V˙O2  MBM in patients with and without pneumonia and to assess the reproducibility of both methods in critically ill patients. Method. With institutional approval nine critically ill patients with acute pneumonia were studied under controlled mechanical ventilation. The diagnosis of pneumonia was based on respective changes of chest X-rays, body temperature 〉38 °C, and WBC counts 〉12,000/mm3. Inspiratory oxygen fractions (FIO2) ranged from 0.3 to 0.6; all patients routinely received opioids and hypnotics. Complete muscle relaxation was achieved during the periods of measurement to avoid sudden changes in V˙O2 due to shivering or involuntary movements. Arterial and pulmonary-arterial blood samples were drawn simultaneously after aspiration of the sevenfold catheter dead space. Measurements of haemoglobin concentration (Hb), fractional oxygen saturation (SO2), and O2 partial pressure (PO2) were performed by use of a calibrated haemoximeter and blood gas analyser, respectively; 2×5 thermodilution measurements of cardiac output (CO) were spread randomly over the respiratory cycle for each determination of V˙O2  Fick. To minimise systematic errors of CO measurements, the CO computer was calibrated in an extracorporeal model using an electromagnetic flowmeter. Calculations of V˙O2  Fick were based on an oxygen binding capacity of 1.39 ml/g Hb. Simultaneous measurements of V˙O2  MBM were obtained by use of a Datex Deltatrac MBM that had been validated in vitro with a gas dilution model of respiratory gas exchange. Calibration of the MBM was performed prior to each measurement. Gas supply of the respirator was provided by an external high-precision mixing device to reduce errors in V˙O2 measurements that may arise from short-term oscillations in FIO2. All patients with pneumonia were studied on three consecutive days; thus, measurements from 27 days could be analysed. On each day two sets of measurements were performed at an interval of 60 min to assess the reproducibility of differences between methods. During each set of measurements duplicate blood samples were drawn twice, before and after thermodilution measurements of CO, to evaluate the short-term repeatability of V˙O2  Fick. The beginning and the end of each set of measurements were marked in the computer record of the MBM to assess the respective repeatability of V˙O2  MBM. Fifty control measurements were performed in ten patients undergoing major neurosurgical procedures. None of these patients exhibited signs of pulmonary infection. Except for the number of repeated measures, all V˙O2 measurements were obtained in the same way as in the study group. Descriptive statistical analysis was performed according to Bland and Altman; comparisons between methods were done by multivariate analysis of variance for repeated measures. Results. Neither in the study group nor in the control group could a significant difference between methods be demonstrated. In patients with pneumonia the mean difference between methods (V˙O2  Fick−V˙O2  MBM) was 15.2 ml/min (4.2%); the double standard deviation of differences (2 SD) was 59.2 ml/min (19.2%). Control patients exhibited a mean difference of 7.2 ml/min (3.1%); 2 SD was 41.1 ml/min (20.4%). Duplicate determinations of V˙O2  Fick and V˙O2  MBM within one set of measurements showed a repeatability coefficient (2 SD of differences between repeated measures) of 43.8 ml/min (13.2%) and 15.3 ml/min (5.1%), respectively. The large variation of duplicate measurements of V˙O2  Fick was caused rather by the variability of arteriovenous O2 content determinations than by the variability of CO measurements. Discussion. These results are in contrast to previous method comparison studies, which suggested that in infected lungs V˙O2 of pulmonary and bronchial tissue represents up to 15% of total body V˙O2. Since the mean differences between V˙O2  Fick and V˙O2  MBM did not differ between the two groups of patients, pulmonary infection did not seem to cause a considerable increase in intrapulmonary V˙O2. A minor effect of intrapulmonary V˙O2 on differences between methods cannot be excluded because of the variability of data. The poor repeatability of V˙O2  Fick measurements, however, seems to limit the use of method comparison studies for estimation of intrapulmonary V˙O2.

Description / Table of Contents: Abstract. Thermodilution measurements of cardiac output (CO) by means of Swan-Ganz catheters, in a strict sense, represent pulmonary arterial blood flow (PBF). In principle, this is also true in the presence of intracardiac left-to-right shunts due to atrial or ventricular septal defects. However, early recirculation of indicator may give rise to serious methodological problems in these cases. We sought to determine the influence of intracardiac left-to-right shunts on different devices for thermodilution measurements of CO using an extracorporeal flow model. Methods. Blood flow was regulated by means of a centrifugal pump that at the same time enabled complete mixing of the indicator after injection (Fig. 1). Pulmonary and systemic parts of the circulation were simulated using two membrane oxygenators and a systemic-venous reservoir to delay systemic recirculation of indicator. Control measurements of PBF (Qp) and systemic (Qs) blood flow were performed by calibrated electromagnetic flow-meters (EMF). Blood temperature was kept constant using a heat exchanger without altering the indicator mass balance in the pulmonary circulation. Left-to-right shunt was varied at different systemic flow levels applying a Qp:Qs ratio ranging from 1:1 to 2.5:1. Thermodilution measurements of PBF were performed using two different thermodilution catheters that were connected to commercially available CO computers. Additionally, thermodilution curves were recorded on a microcomputer and analysed with custom-made software that enabled iterative regression analyses of the initial decay to determine that part of the downslope that best fits a monoexponentially declining function. Extrapolation of the thermodilution curve was then based on the respective curve segment in order to eliminate indicator recirculation due to shunt flow. Results. At moderate left-to-right shunts (Qp:Qs〈2:1) all thermodilution measurements showed close agreement with control measurements. At higher shunt flows (Qp:Qs≥2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig. 2). This was particularly true when a slow-response thermistor catheter was used (Fig. 3). The reason for this underestimation of Qp was an overestimation of the area under curve because of inadequate mathematical elimination of indicator recirculation by standard truncation methods (Fig. 4). However, curve-alert messages of the commercially implemented software did not occur. A high level of agreement could be consistently obtained using a fast-response thermistor together with individual definition of extrapolation limits according to logarithmic regression analyses. Discussion and conclusion. Under varying levels of left-to-right shunt, both the reponse time of thermodilution catheters and the algorithms for calculation of flow considerably influenced the validity of thermodilution measurements of PBF in an extracorporeal flow model. The use of computer-based regression analyses to define the optimal segment for monoexponential extrapolation could effectively eliminate indicator recirculation from the initial portion of the declining thermodilution curve and showed the closest agreement with EMF measurements of Qp. The quality of thermodilution curves with respect to recirculation peaks in the flow model was slightly better than in clinical routine. Nevertheless, the clinical applicability of the modified extrapolation algorithm could be illustrated during pulmonary thermodilution measurements in an exemplary patient with a ventricular septal defect (Fig. 5). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig. 6). Insufficient elimination of indicator recirculation resulted in flow values that closely resembled systemic rather than PBF. This finding is in accordance with a mathematical analysis of the underlying Steward-Hamilton equation if an infinite number of recirculations would be included in the area under curve.

Description / Table of Contents: Abstract Heated humidifiers (HH) as well as heat and moisture exchangers (HME) are commonly used in intubated patients as air-conditioning devices to raise the moisture content of the air, thus preventing mucosal damage and heat loss resulting from ventilation with dry inspired gases. In contrary to HME, HH are able to add heat and moisture to the inspired air in surplus, which is often stressed as an advantage in warming hypothermic patients or reducing major heat losses, e.g., during long operations. The impact of air conditioning on the energy balance of man was calculated comparing HME and HH. Methods. The efficiency of a HME (Medisize Hygrovent) and a HH (Fisher & Paykel MR 730) was evaluated in a mechanically ventilated lung model simulating the physiological heat and humidity conditions of the upper airways. The gas flow from the central supply was dry; the model temperature varied between 32 and 40 °C. By using a HH in the inspiratory limb, a circle system was simulated with water-saturated inspired air at room temperature. The water content of the ventilated air was determined at the tracheal tube connection using a fast, high-resolution humidity meter and was compared with the moisture return of the HME. The energy balance was calculated according to thermodynamic laws. Results. Both HME and HH were able to create physiological heat and humidity conditions in the airways. With the normothermic patient model, the moisture return of the HME was equal to that of the HH set at 34 °C. Increasing the heating temperature resulted only in reduced water loss from the lung; heat and water input in the normothermic model was not possible. This was only effective with almost negligible amounts under hypothermic patient model conditions. Discussion. The water content in the inspired and expired air is the most important parameter for estimating pulmonary heat loss in mechanically ventilated patients. In adults (minute volume ∼7 1/min) the main fraction of pulmonary heat loss results from water evaporation from the airways (∼6 kcal/h), whereas the heat loss due to convection is negligible (∼1.2 kcal/h). In intubated patients ventilated with dry air, the heat loss increases to ∼8 kcal/h due to greater water evaporation from the airways. Both HME and HH are able to reduce the pulmonary heat loss to 1–2 kcal/h. In normothermic as well as hypothermic patients, HH do not offer significant advantages in heat balance compared to effective HME. In conclusion, air conditioning in intubated patients is neither a powerful too for maintaining body temperature during long-lasting anaesthesia nor a sufficient method of warming hypothermic patients in intensive care units.

Description / Table of Contents: Abstract Objective: The data of 60 postoperatively sedated and ventilated patients were studied for analysis of oesophageal, bladder, and rectal temperatures. The purpose of the investigation was to clarify whether changes of oesophageal temperature are adequately reflected by bladder and rectal temperatures and whether the rate of rewarming has an influence on the accuracy of the latter two sites. Methods: For temperature recording, a Hi-Lo Temp® esophageal stethoscope (Mallinckrodt Medical), a Foley FC400-18 catheter temperature sensor (Respiratory Support Products, Mallinckrodt Medical), and a rectal temperature probe N401 (YSI) were used. Each probe and matching recording unit was calibrated over a range of 30–40 °C against a reference quartz thermometer (Hewlett packard Model 2801 A) in a thermostated water bath before the investigation. Five measuring points distributed over the whole period of rewarming were evaluated. Patients were assigned to groups with slow and fast rewarming, respectively. Agreement between the methods of measurement was assessed as described by Bland and Altman. Furthermore, differences between the oesophageal and bladder or rectal temperature were checked at each measuring point for statistical significance using the t-test. Results: In regard to oesophageal temperature, the bladder and rectal temperatures had biases of –0.01 °C and –0.03 °C, respectively. Limits of agreement (±2 s) were ±0.68 °C and ±0.82 °C, respectively. The bias of the bladder temperature was independent of the rate of rewarming (Fig. 3). The bias of the rectal temperature, however, differed in regard to the rewarming rate, being +0.06 °C in the group with slow rewarming and –0.13 °C in the group with fast rewarming (Tables 1 and 2, Fig. 1 and 2). These differences were significant for the measuring points 4 and 5 (Fig. 4). Conclusions: Bladder and rectal temperatures can accurately indicate the oesophageal temperature with a very small bias in postoperatively sedated and ventilated patients. Since the rate of rewarming influences the accuracy of rectal temperature readings, monitoring of bladder temperature seems to be more favourable in the postoperative period.

Description / Table of Contents: Abstract Major abdominal surgery often leads to a marked sympathoadrenal stress response with high concentrations of plasma catecholamines, hypertension, and tachycardia. We compared the effects of sufentanil-propofol with fentanyl-propofol anaesthesia in a controlled, randomised, double-blind study of 18 ASA I–II patients aged 23–64 years undergoing major abdominal surgery. Study parameters were haemodynamics (heart rate [HR], arterial [ABP], central venous, and pulmonary arterial pressures, cardiac index [CI]), arterial catecholamine concentrations, and the median frequency of the electroencephalogram (EEG) power spectrum. Methods. After premedication with flunitrazepam 1–2 mg, promethazine 25–50 mg, and piritramide 7.5–15 mg, a five-lead electrocardiograph and a Lifescan brain activity monitor were attached and indwelling cannulae were inserted into the radial artery and two forearm veins. A thermodilution catheter was placed in the pulmonary artery via the right internal jugular vein. Anaesthesia was induced with either fentanyl 7 μg/kg followed by 5 μg/kg·h or sufentanil 1 μg/kg followed by 0.7 μg/kg·h up to the end of surgery. Additional boli of the opioids were given according to set criteria, resulting in an average consumption of 9.03 μg/kg·h fentanyl or 1.22 μg/kg·h sufentanil. Propofol 2 mg/kg was given followed by 6 μg/kg·h up to the end of surgery. Relaxation was obtained with pancuronium 0.025–0.05 mg/kg before intubation and every 60–120 min. Measurements were performed before and after induction, after tracheal intubation, before and after skin incision, after opening of the peritoneum, and at the end of surgery. Results. No significant differences were observed between the two groups with regard to the study parameters. The duration of surgery and blood loss were similar in both groups, as were patient characteristics. After induction 2 patients in each group developed thoracic rigidity, which was reversible after muscle relaxation. HR, ABP, and CI decreased significantly before skin incision; after surgical stimulation the baseline values were again reached, but not exceeded. No patient developed tachycardia (〉100/min) or hypertension (〉15% higher than baseline pressure) for longer than 10 min during the study period until the end of surgery. The plasma concentrations of epinephrine and norepinephrine decreased significantly during anaesthesia, and under maximum surgical stimulation did not increase higher than the physiological baseline concentrations. The EEG median frequencies decreased after induction, and during the entire anaesthetic period the main activity was in the delta and theta frequency bands. Conclusions. With both regimens, the sympathoadrenal stress response to major abdominal surgery was nearly completely suppressed, resulting in stable haemodynamics during the operations. Sufentanil and fentanyl were equally well suited as analgesic components of total IV anaesthesia with propofol.

Description / Table of Contents: Abstract. Hypothermia (Tcore〈36 °C) can be observed in 60% – 80% of all admissions to the post-anaesthetic recovery unit. Effective warming devices may accelerate rewarming, improve patient comfort, and suppress shivering thermogenesis. This study was designed to compare the efficiency of warming devices in extubated postoperative patients and their effect on postoperative oxygen uptake (V˙O2). Methods. Thirty-five ASA I and II patients after laparoscopic hernioplastic repair with core temperatures 〈36 °C were randomly assigned to either postoperative nursing under a radiant heater (group R, n=11, Aragona Thermal Ceilings CTC X, Aragona Medical AB, Täby, Sweden), a forced air system (group L, n=12, Bair Hugger, Augustine Medical Inc., Eden Prairie, Minnesota, USA), or a normal cotton hospital blanket (group K, n=12). Anaesthesia was conducted totally intravenously with propofol, alfentanil, and vecuronium. Mean body temperature and total body heat were calculated from urinary bladder temperature and four subcutaneous temperature measurements. The rate of thermogenesis was calculated from continuous measurement of V˙O2 (Datex Deltatrac Metabolic Monitor, Datex Instrumentarium Corp., Helsinki, Finland). Heat balance was derived from the increase in total body heat minus body heat production. Heart rate and noninvasive blood pressure were measured by the Cardiocap (Datex Instrumentarium Corp., Helsinki, Finland). All data were transferred to an IBM-compatible computer at 60-s intervals. Measurements were stopped when core temperature reached 37 °C. The rate of change was calculated for each variable for the period 15 min after the beginning of rewarming to attainment of 37 °C. Data are presented as median, minima, and maxima (min↔max); the Mann-Whitney U test was used to test for significance of group differences. Results. All groups were comparable for body weight, height, age, and amount of postoperative infusions. Temperatures at admission were 35.2 (33.4↔35.9), 34.7 (34.3↔35.8), and 35.4 (34.3↔35.9) °C for groups R, B, and K, respectively. No significant differences in the rate of central rewarming could be found for these groups with 0.81 (0.41↔1.32), 0.76 (0.40↔1.07), and 0.70 (0.37↔1.13) °C/h (Fig. 1). The mean V˙O2 of 3.41 (3.07↔3.73), 3.55 (2.78↔4.06), and 3.79 (2.51↔7.00) ml/kg/min also did not differ significantly (Fig. 3). Significant differences between groups R and B [4.39 (3.74↔6.19) and 4.30 (3.46↔6.67) ml/kg/min] and K [5.92 (3.79↔10.64) ml/kg/min] were found for V˙O2 maxima during the course of investigation (Fig. 4). The heat balance revealed significant differences among treatment and control groups with −88 (−266↔+30), −41 (−212↔+12), and −191 (−265↔−86) kJ/h for groups R, B, and K. We additionally calculated the heat balance as a quotient, which showed 0.70 (0.22↔1.07), 0.86 (0.44↔1.04), and 0.49 (0.31↔0.79) for groups R, B, and K (Fig. 4). The mean rate-pressure product of all groups did not differ significantly during the period of investigation. Conclusions. Neither external heat supply by radiant heat nor by a forced warm air system significantly reduced rewarming time in extubated, awake patients. As measured by heat balance, both active treatments saved about 20% more body heat production than in the control group. Continuing peripheral vasoconstriction may be the reason for the low efficiency of heat transfer. Thermal treatment did reduce the peak load (max. V˙O2) on the oxygen transport systems, though shivering was treated by pethidine if it occurred. External rewarming did not reduce the average load (mean V˙O2). Thus, concerning the goal of accelerating rewarming, it appears more rational to prevent intraoperative heat loss. For a comparison of efficiency of different warming devices, postoperative extubated patients do not appear to be an ideal model for study.

Description / Table of Contents: Abstract Heat loses during surgery occur mainly to the environment and due to infusions and irrigations. Infusions given at room temperature account for a great deal of the total heat deficit during major operations, e.g., the infusion of 53 ml/kg 20° C fluid leads to a loss of 1° C in mean body temperature. Hence, heating i.v. fluids will add to the effect of other measures aimed at reducing heat loss to the environment. We investigated the efficacy of different warming methods for i.v. fluids in an experimental model by measuring the temperature at the end of the delivery line. Methods. The following in-line warmers were studied: Hotline HL-90 and System H-250/heat exchanger D-50 (Level 1 Technologies, Marshfield, USA), Astotherm IFT 260 (Stihler Elektronic GmbH, Stuttgart, Germany), RSLB 30 H Gamida (Productions Hospitalieres Francaises, Eaubonne, France), Bair Hugger 241/Modell 500 Prototype (Augustine Medical, Eden Prairie, USA). They were compared with prewarming infusions (39° C) only using the Clinitherm S (Labor Technik Barkey GmbH, Bielefeld, Germany) and prewarming with “active insulation” of the delivery line using the Autotherm/Autoline system (Labor Technik Barkey GmbH, Bielefeld, Germany). We investigated the influence of four variables on the efficacy of warming: (1) flow rate (50–15,000 ml/h); (2) ambient temperature (20° C and 25° C); (3) infusion bag temperature (6° C, 20° C, and 39° C); and (4) length of infusion system downstream from the heat exchanger. Fluid temperatures were measured using thermistors of 1 mm diameter (Modell YSI 520, Yellow Springs Instruments Co., Yellow Springs, USA) incorporated into 3-way stopcocks. Temperatures were recorded using Hellige temperature monitors (Hellige GmbH, Freiburg im Breisgau, Germany) and the signals were collected at 10 Hz through an AD converter and averaged over 1 min. Flows were calculated by timed collection into calibrated cylinders; 10 to 12 different flow rates were taken to define one temperature/flow plot. Effective warming was defined as a temperature 〉33° C at the end of the infusion line. Results. At high flow rates (〉2,500 ml/h) using 20° C fluids at 20° C ambient temperature, the H-250/D-50 system gave the highest temperatures throughout the range and showed effective warming from 1,300 ml/h on over the entire range tested (35° C at 17,000 ml/h) compared to the RSLB 30 H Gamida system (3,000–18,000 ml/h) (Fig. 2). This difference in performance was almost abolished with fluids at 6° C (Fig. 4). Similar efficacy could be reached by using prewarmed infusions that gave effective warming at 〉2,000 ml/h and reached 39° C at 13,000 ml/h. Prewarmed infusions could be used effectively down to 〉80 ml/h applying “active insulation” (Autotherm/Autoline) to the whole infusion system. The Hotline HL-90 (50–4,700 ml/h) appeared to be the most effective in-line warmer in the low (〈250 ml/h) and middle (250–2,500 ml/h) flow range, followed by the Astotherm IFT 260 (400–4,000 ml/h), but only if used with a length of 40 cm down-stream from the heat exchanger (Fig. 1). Increasing this distance to 145 cm markedly reduced its efficacy below the range of 2,000 ml/min (1,200–3,000 ml/h) (Fig. 5). The Bair Hugger 241 Prototype showed a narrow effective range (700–1,300 ml/h) that could be extended beyond 1,300 ml/h by the use of prewarmed infusions (Figs. 1 and 3). The performance for 6° C solutions and ambient temperatures of 25° C are given in Fig. 4 and Table 1. Conclusions. The importance of infusion warming increases with the amount of fluid given. In general, the infusion bag temperature only influenced the efficacy of in-line warmers within the high-flow range, challenging the performance of the heat exchanger. The length of uninsulated i.v. line downstream from the heat exchanger influenced the efficacy within the low- and middle-flow range, as did the room temperature. Prewarmed solutions can be infused very effectively within the high-flow range. This efficiency can be preserved down to the low-flow range by using “active insulation” of the infusion system. In-line warming is essential for emergency and rapid massive transfusions.

Description / Table of Contents: Abstract Temperature of the tympanic membrane is recommended as a “gold standard” of core-temperature recording. However, use of temperature probes in the auditory canal may lead to damage of tympanic membrane. Temperature measurement in the auditory canal with infrared thermometry does not pose this risk. Furthermore it is easy to perform and not very time-consuming. For this reason infrared thermometry of the auditory canal is becoming increasingly popular in clinical practice. We evaluated two infrared thermometers – the Diatek 9000 Thermoguide and the Diatek 9000 Instatemp – regarding factors influencing agreement with conventional tympanic temperature measurement and other core-temperature recording sites. In addition, we systematically evaluated user dependent factors that influence the agreement with the tympanic temperature. Materials and Methods. In 20 volunteers we evaluated the influence of three factors: duration of the devices in the auditory canal before taking temperature (0 or 5 s), interval between two following recordings (30, 60, 90, 120, 180 s) and positioning of the grip relative to the auditory-canal axis (0, 60, 180 and 270°). Agreement with tympanic contact probes (Mon-a-therm tympanic) in the contralateral ear was investigated in 100 postoperative patients. Comparative readings with rectal (YSI series 400) and esophageal (Mon-a-therm esophageal stethoscope with temperature sensor) probes were done in 100 patients in the ICU. The method of Bland and Altman was taken for comparison. Results. Shortening of the interval between two consecutive readings led to increasing differences between the two measurements with the second reading decreasing. A similar effect was seen when positioning the infrared thermometers in the auditory canal before taking temperatures: after 5 s the recorded temperatures were significantly lower than temperature recordings taken immediately. Rotation of the devices out of the telephone handle position led to increasing lack of agreement between infrared thermometry and contact probes. Mean differences between infrared thermometry (Instatemp and Thermoguide, CAL-Mode) and tympanic probes were −0.41±0.67 °C (2 SD) and −0.43 ±0.70 °C, respectively. Mean differences between the Thermoquide (Rectal-Mode) and rectal probe were −0.19±0.72 °C, and between the Thermoguide (Core Mode) and esophageal probe −0.13±0.74 °C. Discussion. Although easy to use, infrared thermometry requires careful handling. To obtain optimal recordings, the time between two consecutive readings should not be less than two min. Recordings should be taken immediately after positioning the devices in the auditory canal. Best results are obtained in the 60° position with the grip of the devices following the ramus mandibulae (telephone handle position). The lower readings of infrared thermometry compared with tympanic contact probes indicate that the readings obtained represent the temperature of the auditory canal rather than of the tympanic membrane itself. To compensate for underestimation of core temperature by infrared thermometry, the results obtained are corrected and transferred into core-equivalent temperatures. This data correction reduces mean differences between infrared recordings and traditional core-temperature monitoring, but leaves limits of agreement between the two methods uninfluenced.