T. A. Crozier

IMPROVED DETERMINATION OF STATIC COMPLIANCE BY AUTOMATED SINGLE VOLUME STEPS IN VENTILATED PATIENTS

A new method for determination the static compliance of the respiratory system is described (“static compliance by automated single steps”-SCASS). In 12 ventilated patients pressure/volume (P/V) curves were determined by automated repetitive occlusion (6 s) at single volume steps and compared to the conventional syringe method (SM). All measurements were corrected for effects of temperature, humidity and pressure (THP). SM was found to be significantly influenced by intrapulmonary gas exchange causing an effective mean volume deficit of 217.4±65.7 ml (BTPS) at the end of the deflation. In contrast to that, the short duration of occlusion in SCASS minimize the gas exchange effects. The methodical differences between both methods result in overestimation of the inflation compliance in the uncorrected SM (SMuncorr: 83.4±12.6; SCASS: 76.0±11.9 ml/cmH2O.p<0.01) and underestimation of the deflation compliance resp. (SMuncorr: 58.3±7.5; SCASS: 79.1±15.0 ml/cmH2O.p<0.005). In contrast to the P/V curves by SM no significant hysteresis was found by SCASS. Gas exchange seems to be the main reason for the hysteresis. Even after correcting gas exchange and THP effects a significant hyseresis remained. The SCASS method avoids these problems and allows furthermore an accurate checking of leaks.

High-dose intravenous magnesium sulfate in the management of life-threatening status asthmaticus

In severe status asthmaticus basic medical treatment often fails to improve the patients condition. Mechanical ventilation in this situation is associated with a high incidence of serious complications. After the bronchodilating effect of moderate-dose magnesium sulfate in asthmatic patients had been demonstrated in previous studies we treated five mechanically ventilated patients with refractory status asthmaticus successfully with high dosages of MgSO4 IV (10–20 g within 1 h depending on the bronchodilating effect). MgSO4 resulted in a significant decrease of peak airway pressure (43.0±6.8 to 32.0±8.0 cmH2O) and inspiratory flow resistance (22.7±7.0 to 11.9±6.0 cmH2O·l−1·s−1) within 1 h. The resulting serum magnesium levels after one hour were up to threefold of the normal serum levels. Although a main-tainance dose of 0.4 g/h had been administered continuously during the following 24 h serum magnesium decreased towards normal values within this time. The only relevant side-effect was a mild to moderate arterial hypotension in two of the five patients during the high dose administration period of MgSO4 which responded readily to dopamine treatment.

Effect of low-level PEEP on inspiratory work of breathing in intubated patients, both with healthy lungs and with COPD

ObjectiveEvaluation of low-level PEEP (5 cm H2O) and the two different CPAP trigger modes in the Bennett 7200a ventilator (demand-valve and flow-by trigger modes) on inspiratory work of breathing (Wi) during the weaning phase.DesignProspective controlled study.SettingThe intensive care unit of a university hospital.PatientsSix intubated patients with normal lung function (NL), ventilated because of non-pulmonary trauma or post-operative stay in the ICU, and six patients recovering from acute respiratory failure due to exacerbation of chronic obstructive pulmonary disease (COPD), breathing either FB-CPAP or DV-CPAP with the Bennett 7200a ventilator.InterventionsThe patients studied were breathing with zero end-expiratory pressure (ZEEP), as well as CPAP of 5 cm H2O (PEEP), with the following respiratory modes: the demand-valve trigger mode, pressure support of 5 cm H2O, and the flow-by trigger mode (base flow of 20 l/min and flow trigger of 2 l/min). Furthermore, Wi during T-piece breathing was evaluated.Measurements and resultsWi was determined using a modified Campbells diagram. Total inspiratory work (Wi), work against flow-resistive resistance (Wires), work against elastic resistance (Wiel), work imposed by the ventilator system (Wimp), dynamic intrinsic positive end-expiratory pressure (PEEPidyn), airway pressure decrease during beginning inspiration (Paw) and spirometric parameters were measured. In the NL group, only minor, clinically irrelevant changes in the measured variables were detected. In the COPD group, in contrast, PEEP reduced Wi and its components Wires and Wiel significantly compared to the corresponding ZEEP settings. This was due mainly to a significant decrease in PEEPidyn when external PEEP was applied. Flow-by imposed less Wi on the COPD patients during PEEP than did demand-valve CPAP. Differences in Wimp between the flow-by and demand-valve trigger models were significant for both groups. However, in relation to Wi these differences were small.ConclusionWe conclude that the application of low-level external PEEP benefits COPD patients because it reduces inspiratory work, mainly by lowering the inspiratory threshold represented by PEEPidyn. Differences between the trigger modes of the ventilator used in this study were small and can be compensated for by the application of a small amount of pressure support.

Der Einfluß einer totalen intravenösen Anästhesie mit S-(+)-Ketamin/Propofol auf hämodynamische, endokrine und metabolische Streßreaktionen im Vergleich zu Alfentanil/Propofol bei Laparotomien

ZusammenfassungDie totale intravenöse Anästhesie mit Ketamin und einem Hypnotikum unterscheidet sich in zahlreichen Punkten von einer TIVA mit einem Opiat. Von besonderem Interesse sind dabei Streßreaktionen, bei denen ein direkter Opiateffekt bekannt ist oder vermutet wird. An 14 Patientinnen, mit elektiver abdomineller Hysterektomie, wurde der Einfluß einer TIVA mit S-(+)-Ketamin und Propofol auf die perioperativen Verläufe der Katecholamin-, Kortisol- und Metabolitkonzentrationen im Plasma sowie Blutdruck und Herzfrequenz untersucht und mit denen unter einer TIVA mit Propofol-Alfentanil verglichen. Die Intubation erfolgte nach Relaxation mit Vecuronium. Blutproben wurden zu festgelegten Zeiten bis 6 h postoperativ entnommen. Der Ketaminbolus und die Intubation verursachten in der Ketamingruppe vorübergehende Blutdruckanstiege trotz einer Nettoabnahme der Katecholaminkonzentrationen. Intraoperativ blieben Blutdruck und Herzfrequenz in beiden Gruppen weitgehend auf dem Ausgangsniveau stabil, während die Katecholaminkonzentrationen wieder anstiegen. Die höchsten Katecholaminkonzentrationen wurden früh postoperativ gemessen. Kortisol stieg intra- und postoperativ unter Ketamin deutlich an. Die TIVA mit S-(+)-Ketamin-Propofol dämpft intraoperative Kreislaufreaktionen in ähnlicher Weise wie die TIVA mit Alfentanil-Propofol. Intraoperative Katecholaminanstiege werden durch Ketamin geringfügig weniger beeinflußt, wohingegen der Kortisolanstieg signifikant höher ist.AbstractTotal intravenous anaesthesia with ketamine-propofol offers distinct advantages over a TIVA with an opiate, including less cardiovascular and respiratory depression and an altered neuroendocrine and immunological stress response pattern. The effects of the more active stereoisomer S-(+)-ketamine in combination with propofol on the circulatory, endocrine and metabolic responses to abdominal surgery were compared with those of alfentanil-propofol. Twenty-four patients scheduled for elective hysterectomy participated in this study, which had the approval of our institutions ethics committee. Anaesthesia was induced with 2 mg/kg S-(+)-ketamine or 0.05 mg/kg alfentanil, followed by 1 mg/kg propofol. Tracheal intubation was facilitated with 0.06 mg/kg vecuronium. Anaesthesia was maintained with 1 mg/kg per h S-(+)-ketamine or 0.125 mg/kg per h alfentanil and propofol at an initial rate of 15 mg/kg per h which was reduced to 5 mg/kg per h after 30 min. Blood samples for catecholamines, cortisol and metabolites were drawn at predetermined times from before induction to 6 h postoperatively. Adrenaline and noradrenaline concentrations decreased preoperatively in the ketamine group (K) from 55 to 29 pg/ml and 166 to 39 pg/ml, respectively, and then increased to postoperative maxima of 193 or 315 pg/ml. A similar pre- and postoperative course was seen in the alfentanil group (A) with slightly lower (P<0.05) intraoperative concentrations in A. Cortisol concentrations increased in K from 12 μg/dl to 34 μg/dl intraoperatively and further to a maximum of 42 μg/dl postoperatively. The intraoperative increase was attenuated in A and the difference between the groups was significant (P<0.0001). The initial ketamine bolus and tracheal intubation caused a marked, transient increase of mean arterial blood pressure from the baseline value of 105 mmHg to 120 mmHg with a subsequent decrease to 88 mmHg prior to skin incision and a gradual return to baseline during surgery. TIVA with ketamine-propofol had little effect on the perioperative courses of the endocrine parameters, which behaved as they do under anesthesia with isoflurane-nitrous oxide. Plasma catecholamine concentrations were not elevated in the period between induction of anaesthesia and skin incision.

Total intravenous anaesthesia with methohexitone-alfentanil or propofol-alfentanil. Clinical aspects and hemodynamic, endocrine, and metabolic effects

Zusammenfassung. Die totale intravenöse Anästhesie (TIVA) gewinnt zunehmend an Popularität als Narkoseverfahren auch für abdominalchirurgische Eingriffe. Bei weniger traumatisierenden Eingriffen, bei denen eine absichtlich verzögerte Aufwachphase nicht erforderlich ist, bieten sich Methohexital und Propofol aufgrund ihrer Pharmakokinetik als hypnotischer Bestandteil eines solchen Anästhesieverfahrens an. In der vorliegenden randomisierten und kontrollierten Studie an 27 gesunden Frauen, bei denen eine Hysterektomie durchgeführt wurde, wurden beide Hypnotika in Kombination mit Alfentanil als Analgetikum miteinander und mit einer balanzierten Anästhesie (Isofluran-Lachgas, Fentanyl) verglichen. Als Zielparameter dienten Hämodynamik (arterieller Blutdruck, Herzfrequenz), postoperative Befindlichkeit (Übelkeit-Erbrechen, Zittern, Schmerzmittelbedarf) sowie endokrine und metabolische Streßreaktionen (Katecholamine, Kortisol, Prolaktin, Glukose, freie Fettsäuren, Laktat). Es fanden sich kaum nennenswerte Unterschiede zwischen den beiden TIVA-Verfahren, wohl aber zwischen den TIVA-Verfahren und der balanzierten Anästhesie. Der hämodynamische Verlauf war in allen Gruppen im wesentlichen gleich, aber die intraoperativen Streßreaktionen wurden durch die TIVA effektiver gedämpft. Die Aufwachzeit war nach der balanzierten Anästhesie, die Inzidenz des postoperativen Zitterns nach der Propofol-Alfentanil TIVA am geringsten. Die Häufigkeit postoperativen Erbrechens war in allen Gruppen gleich. Die Ergebnisse der Studie belegen einige Vorteile der TIVA gegenüber der balanzierten Anästhesie. Sie geben jedoch keine eindeutige Entscheidungsgrundlage für oder gegen eines der untersuchten Hypnotika.Abstract. Total intravenous anaesthesia (TIVA) using a combination of a hypnotic and an analgesic agent is gaining increasing popularity as an alternative to balanced anaesthesia with volatile anaesthetics for abdominal surgery. Among the required characteristics of the drugs used in this technique are a good correlation between dose, plasma concentrations, and effect as well as rapid elimination from the circulation, allowing close control of anaesthetic depth. Two hypnotic drugs with similar pharmacokinetic and pharmacodynamic profiles are propofol and methohexitone, both of which can be employed as a component of a TIVA technique. Two TIVA combinations utilising either of these drugs with alfentanil were tested against isoflurane-nitrous oxide in a balanced regimen. Methods. Twenty-seven healthy women undergoing hysterectomy for non-malignant diseases participated in the study after having given written consent. They were randomly allocated to receive either isoflurane (Iso), methohexital-alfentanil (M-A), or propofol-alfentanil (P-A). Blood samples for determination of cortisol, prolactin, catecholamines, glucose, lactate, non-esterified fatty acids, and pharmacon concentrations were drawn repeatedly from before induction until 360 min after surgery. Anaesthesia was induced in group Iso with fentanyl 0.1 mg and M 1.5 mg⋅kg−1 and maintained with Iso-N2O. In the TIVA groups M or P was given in a two-step infusion to load peripheral compartments and then maintain plasma concentrations within the hypnotic range. A was given as a continuous infusion in an identical dose (0.1 mg⋅kg−1 initial, 0.125 mg⋅kg−1⋅h−1 maintenance) in both groups. If signs of insufficient depth of anaesthesia occurred (heart rate or systolic blood pressure >25% above baseline), then first A (0.5 – 1 mg), and if that was ineffective, then 50 mg hypnotic was administered. The A infusion was stopped 30 min before the end of surgery, and Iso or the hypnotic was stopped at skin closure. Recovery time was the time until the patients were able to give their birth date after stopping the Iso or hypnotic. Results. The three groups were comparable with regard to age, weight, and duration of surgery. The total doses of M and P were 1,357±125 mg (mean±SEM) and 1,315±121 mg, respectively, and the total A doses were 20.7±2.5 mg (M-A) and 23.4±3.5 (P-A). The peak plasma concentrations were P 10.6±1.5 µg⋅ml−1 and M 12.4±2.6 µg⋅ml−1. At the end of surgery the P concentrations were in the projected range while those of M were somewhat lower than expected (P3.7±0.4 µg⋅ml−1; M 3.5±0.6 µg⋅ml−1). Three patients each in the P-A and M-A groups required supplementary A injections. Five patients in the P-A group required additional bolus injections of the hypnotic as compared to 2 in the M-A group. The median recovery times were Iso 15 min, M-A 50 min, and P-A 25 min (P<0.05). The incidence of shivering was Iso 3/9, M-A 5/9, and P-A 0/9 (P<0.05); vomiting occurred with equal frequency in all groups (Iso 33%, M-A 33%, P-A 22%). The patients were somewhat more restless in group M-A. Systolic blood pressure dropped in a similar manner in all groups after induction of anaesthesia (Iso −31%, M-A −37%, P-A −36%) but recovered during surgery. The intraoperative response of cortisol (Iso +216%, M-A +92%, P-A +43%) and catecholamines (noradrenaline Iso +56%, M-A +30%, P-A −21%) was lower in the TIVA groups, whereas prolactin increased after induction in all groups. Plasma concentrations of glucose, lactate, and fatty acids were lower in the TIVA groups than in the Iso group intraoperatively, but increased to comparable postoperative levels. Conclusions. Both TIVA regimens are acceptable alternatives to balanced anaesthesia with Iso N2O. Both are similar with regard to haemodynamic, endocrine, and metabolic changes and are able to reduce the stress response more effectively than Iso N2O. Of the two, P seems to offer the advantage of a somewhat shorter recovery time, less shivering, and calmer patients in the immediate postoperative period, although M might be preferred if economic considerations are important.

Efficiency of warming devices in extubated postoperative patients

Zusammenfassung. Die vorliegende Untersuchung vergleicht die Effektivität radiativer und konvektiver Wärmezufuhr an wachen, extubierten Patienten. 35 Patienten, die nach laparoskopischen Operationen eine Harnblasentemperatur <36 °C erreicht hatten, wurden randomisiert entweder unter einem deckenmontierten Strahler (Gr. R, n=11), unter einem Warmluftgebläse (Gr. L, n=12) oder einer Baumwollsteppdecke (Gr. K, n=12) behandelt. Die zentralen Erwärmungsgeschwindigkeiten zeigten im Median (Min↔Max) geringe, aber nicht signifikante Unterschiede von 0,81 (0,41↔1,32) °C/h gegenueber 0,76/0,40↔1,07) und 0,70 (0,37↔1,13) °C/h in den Gruppen R, L und K. Ein signifikanter Unterschied ergab sich für die Medianwerte der maximalen, während der Untersuchungsperiode gemessenen VO2 für beide Therapiegruppen gegenüber der Kontrollgruppe. Diese ergaben 4,39 (3,74↔6,19) ml/kg/min, 4,30 (3,46↔6,67) ml/kg/min und 5,92 (3,79↔10,64) ml/kg/min für die Gr. R, L und K. Eine Effektivität der Wärmetherapien wird erst in dem Quotienten von Zunahme an Körperwärmemenge/körpereigene Wärmeproduktion deutlich, der eine über 20% größere Konservierung der körpereigenen Wärmeproduktion der Therapiegruppen im Vergleich zur Kontrollgruppe zeigt. Bei wachen postoperativen Patienten scheint mit keinem der beiden Therapieverfahren eine wesentlich schnellere Aufwärmung als mit einer Baumwollsteppdecke möglich. Zur Verkürzung der Aufwärmzeit erscheint bei geplanter Extubation unter diesen Umständen eine Optimierung intraoperativer Wärmeprotektion sinnvoller.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.

Neuromuscular effects of rapacuronium on the diaphragm and skeletal muscles in anaesthetized patients using cervical magnetic stimulation for stimulating the phrenic nerves

Background and objective: Non-depolarizing neuromuscular blocking agents have a shorter duration of action on the diaphragm than on skeletal muscles. It was to be tested if this also held true for rapacuronium, a short-acting, amidosteroid non-depolarizing neuromuscular blocker, lately withdrawn from the market, using a novel technique for stimulating the diaphragm and assessing its function. Methods: Anaesthesia was induced with propofol 2 mg kg−1 and remifentanil 1 μg kg−1, and the trachea was intubated after topical anaesthesia. Rapacuronium was given at a dose of 1.5 mg kg−1. The diaphragm was stimulated by cervical magnetic stimulation of the phrenic nerves (2 Tesla, single coil) and airway pressure responses were measured at the endotracheal tube connector. The neuromuscular effects at the adductor pollicis and orbicularis oculi muscles were measured by acceleromyography. Results: Fifteen males and five females (ASA I and II; 27 ± 8 yr; 73 ± 13 kg; mean ± SD) were recruited. Median maximal relaxation was less (P < 0.01) for the diaphragm (89%) than for the adductor pollicis or orbicularis oculi muscles (each 100%). The time to 25% recovery was shorter for the diaphragm than for adductor pollicis or orbicularis oculi (7.5 ± 3.1 versus 14.1 ± 3.7 and 15.1 ± 3.5 min, respectively, P < 0.01). Recovery from 25 to 75% was identical for the diaphragm and adductor pollicis (9.4 ± 2.9 versus 9.1 ± 3.5 min), but longer for orbicularis oculi (13.4 ± 4.2 min, P < 0.01). The median recovery time to TOF0.8 was shorter for the diaphragm (23.9 min) than for the adductor pollicis or orbicularis oculi muscles (31.5 and 28.4 min, respectively; P < 0.05). Conclusions: As with other non-depolarizing muscle relaxants, the duration of the clinical effect of rapacuronium was shorter for the diaphragm than for skeletal muscle. The recovery index was identical for the diaphragm and adductor pollicis.

The stress of coronary artery surgery overcomes the inhibition of cortisol synthesis caused by etomidate-fentanyl anaesthesia

Zusammenfassung. Etomidat ist ein Hypnotikum mit hervorragender kardiovaskulärer Stabilität und rascher Elimination, das sich als Bestandteil einer totalen intravenösen Anästhesie bei kardialen Risikopatienten anbietet. Die nachgewiesene Hemmung der Kortisolsynthese führte dazu, daß von einer repetitiven oder kontinuierlichen Etomidatgabe abgeraten wurde. Hinweise auf eine unvollständige Inhibition der Kortisolsynthese machen eine erneute Überprüfung der endokrinen Wirkungen erforderlich. 19 Patienten zur Myokardrevaskularisation nahmen an der Studie teil. Sie erhielten randomisiert eine intravenöse Anästhesie mit Etomidat-Fentanyl oder Midazolam-Fentanyl. Es wurden serielle Bestimmungen der Parameter Kortisol, Aldosteron, ACTH, β-Endorphin, Adrenalin und Noradrenalin durchgeführt sowie mehrfache Nebennierenrindenstimulationen mit exogenem ACTH. Es zeigte sich, daß die Kortisolkonzentrationen in beiden Gruppen sich nicht signifikant unterschieden, bis auf den ersten postoperativen Tag, an dem die Kortisolspiegel in der Etomidatgruppe signifikant höher lagen. Die ACTH-, β-Endorphin- und Katecholaminkonzentrationen lagen postoperativ in der Etomidatgruppe signifikant höher als in der Midazolamgruppe. Nach diesen Ergebnissen kann die Hypothese einer unmittelbaren Gefährdung aufgrund einer etomidatbedingten Kortisolsynthesehemmung im perioperativen Zeitraum nicht aufrechterhalten werden. Vielmehr sollte die totale intravenöse Anästhesie mit Etomidat in Kombination mit einem Opiat in der Kardiochirurgie einer neuerlichen, umfangreichen Überprüfung unterzogen werden.Abstract. Etomidate is a hypnotic with only minor effects on haemodynamics. Although its rapid elimination kinetics would suggest its use in total intravenous anaesthesia (TIVA) and sedation, its administration in higher doses or for a prolonged period has been discouraged due to its inhibitory effects on corticosteroid synthesis. Newer evidence that the suppression of cortisol synthesis might not be total requires a re-evaluation of this drug as a component of a TIVA technique. The effects of high-dose etomidate with fentanyl on spontaneous and stimulated corticosteroid levels as a measure of the magnitude and duration of adrenocortical suppression, as well as on plasma concentrations of adrenocorticotropic hormone (ACTH) β-endorphin, and catecholamines during cardiac surgery were investigated in a prospective, randomised study and compared to those following the administration of midazolam-fentanyl. Patients and methods. Nineteen patients undergoing myocardial revascularisation were assigned to two groups: group 1: etomidate-fentanyl (n=9) and group 2: midazolam-fentanyl (n=10). Anaesthesia was induced with fentanyl 0.5 mg and either etomidate 0.3 mg/kg or midazolam 0.2 mg/kg. Relaxation was achieved with pancuronium 0.1 mg/kg. Anaesthesia was maintained during extracorporeal circulation (ECC) with an infusion of etomidate (0.36 mg⋅kg−1⋅h−1) or midazolam (0.16 mg⋅kg−1⋅h−1) and fentanyl (10 µg⋅kg−1⋅h−1. Blood samples were drawn before induction, before ECC, and 1, 6, and 20 h after surgery. Cortisol secretion was stimulated with 0.25 mg ACTH1 – 24 IV at 6 and 20 h postoperatively. Results. The total drug doses were etomidate 87±3 mg and midazolam 46±2 mg. Plasma cortisol concentrations decreased in the etomidate group from 20 (10 – 31) to 10 (6 – 31) µg⋅dl−1 (median and range) before ECC, but had returned to baseline at 1 h and were significantly increased at 6 h [29 (15 – 47) µg⋅dl−1] and 20 h [46 (29 – 62) µg⋅dl−1]. There was no difference between the groups except at 20 h, when cortisol levels were higher in the etomidate group. The stimulated cortisol increase was markedly impaired in this group at both measuring points. ACTH and β-endorphin were markedly increased in the etomidate group and ACTH concentrations were eight times greater than the corresponding values in the midazolam group after surgery (ACTH 141 vs. 18 pmol⋅l−1). Plasma catecholamine concentrations increased significantly in both groups. Noradrenaline concentrations were greater in the etomidate group at 6 h after surgery. Two patients in the midazolam group and none in the etomidate group required circulatory support with exogenous catecholamines. Discussion. It is concluded that the stress of cardiac surgery can overcome the block in cortisol synthesis caused by the administration of high-dose etomidate by substantially increasing ACTH secretion. The administration of high-dose etomidate was not associated with cardiovascular instability. The use of etomidate as a component of TIVA can therefore not be ruled out on the grounds of insufficient cortisol secretion.

High-dose intravenous magnesium sulfate in the management of life-threatening status asthmaticus — authors' reply

Sir: The report by Sydow et al. [1] draws attention to the possible use of intravenous magnesium sulfate in the management of status asthmaticus. In 1991, we published our own experience of magnesium in the treatment of the same condition [2]. We used magnesium chloride (MgC12), which is less concentrated than magnesium sulfate (MgSO4) prepared in the usual manner. We observed that MgC12 administered as a rapid infusion in 2 patients resulted in a decrease in peak airway pressure, auto PEEP, and flow resistance. In 1 of the 2 cases, improvement lasted only a short while, and exacerbation of bronchospasm was successfully controlled by halothane anesthesia. After 1 h serum magnesium concentrations reached 1.80-1.87 mmol/1. These concentrations are slightly lower than those published by the authors; however, the concentration infused was considerably smaller (only 4g as opposed to 10-20g) . We have consequently been led to believe that the regulation of serum magnesium concentrations gives rise to rapid urinary loss of magnesium. Furthermore, serum magnesium concentrations over 2.5 mmol/1 may result in temporary non-specific depressions of CNS activity [3], which may prove useful in the management of bronchospasm despite blocking voltage-sensitive calcium channels. As regards myocardial infarction, magnesium infusion is widely used at concentrations much lower than those in this study [4]. These concentrations are specifically chosen so as to avoid respiratory depression and cardiac toxicity. In conclusion, we think the concentration used by the authors might have been too high, and that a similarly satisfactory result could have been obtained with low-dose magnesium.

Vergleich einer sufentanil-Propofol-Anästhesie mit Fentanyl-Propofol bei grossen abdominalchirurgischen Eingriffen

ZusammenfassungDie totale intravenöse Anästhesie (TIVA) mit Sufentanil-Propofol wurde in einer kontrollierten, randomisierten Doppelblindstudie erstmals im Vergleich zu Fentanyl-Propofol bei ASA I-II-Patienten untersucht, die sich großen, elektiven, abdominalchirurgischen Eingriffen unterziehen mußten. Zielparameter waren Hämodynamik (Herzfrequenz, arterielle, zentralvenöse und pulmonalarterielle Drücke, Herzindex), arterielle Katecholaminkonzentrationen sowie der Median der Amplitudenfrequenzspektren des EEG. Zwischen den beiden TIVA-Verfahren wurden keine signifikanten Unterschiede beobachtet. Nach Narkoseeinleitung fielen Herzfrequenz, arterieller Druck und Herzindex ab; erst nach Eröffnung des Peritoneums wurden die Ausgangswerte wieder erreicht, aber nicht überschritten. Die Plasmakonzentrationen von Adrenalin und Noradrenalin fielen bis zur analytischen Nachweisgrenze ab und stiegen im Mittel nie auf Werte oberhalb des physiologischen Konzentrationsbereichs. Die Hauptaktivität im EEG zeigte sich während der gesamten Narkose im Delta- und Thetabereich. Die TIVA mit Sufentanil-Propofol oder Fentanyl-Propofol zeichnete sich durch eine nahezu vollständige Unterdrückung der sympathoadrenalen Streßantwort und der daraus folgenden Hypertensionen und Tachykardien aus.AbstractMajor 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.