Coasting: worth the effort?

A new anesthesia machine incorporates a "coasting mode", but the extent to which a coasting technique can maintain anesthesia at the end of a procedure under optimal conditions (closed circuit anesthesia) remains unknown. Sixty-nine patients undergoing peripheral or abdominal surgery were assigned to 1 of 9 groups, depending on when desflurane coasting (in O2/air) was started (after 4, 9, 16, 25, 36, 49, 64, 81, or 100 min). The end-expired desflurane concentration was maintained at 4.5% in O2/air prior to coasting with a conventional anesthesia machine. After initiating coasting (using a closed-circuit technique), we examined when the end-expired desflurane concentration reached 70, 60, 50, and 40% of its value during maintenance (= 30, 40, 50 and 60% decrement times, respectively). Decrement times increased with increasing duration of anesthesia, and varied widely. After 64 min of maintenance anesthesia, the end-expired desflurane concentration remained at or above 70, 60, 50, and 40% of its maintenance value during 10.3 +/- 2.3, 16.0 +/- 3.5, 25.0 +/- 5.9, and 45.4 +/- 19.3 min, respectively (average +/- standard deviation). Coasting can briefly maintain anesthesia towards the end of a procedure. While savings with an automated coasting mode are likely to be modest per patient, they may become substantial when multiplied by the number of procedures per day per operating room with no increase in the clinical workload of the anesthesia provider.

Effect of the mode of administration of inhaled anaesthetics on the interpretation of the F(A)/F(I) curve--a GasMan simulation.

The effects of blood solubility, cardiac output and ventilation on the rise of the alveolar towards the inspired concentration, the F(A)/F(I) curve, of an inhaled anaesthetic are often thought to reflect how these factors affect wash-in of the central nervous system compartment and, therefore, speed of induction because F(A) is the partial pressure ultimately attained in the central nervous system (F(VRG)). These classical F(A)/F(I) curves assumed a constant F(I). We used GasMan to examine whether changes in solubility, cardiac output and ventilation affect the relationship between the F(A)/F(I) curve and F(VRG) differently while either F(I) or F(A) are kept constant. Using GasMan, we studied the effects of solubility (desflurane vs isoflurane), cardiac output (5 vs. 10 l x min(-1)) and minute ventilation (4 vs. 8 l x min(-1)) on F(A), F(I), F(A)/F(I) and F(VRG) with either F(I) kept constant or F(A) kept constant (at 1 minimum alveolar concentration). High fresh gas flows were used to avoid rebreathing, so that the delivered concentration matched F(I). Despite similar effects on the F(A)/F(I) curve, the effects on F(VRG) differed. With constant F(I), lower solubility or higher ventilation results in a higher F(VRG) and a higher cardiac output results in a lower F(VRG). With constant F(A), solubility has only a minimal effect on F(VRG); an increase in cardiac output hastens the rise of F(VRG) to the same plateau value; and a change in ventilation has minimal effect on F(VRG). Despite similar effects on the F(A)/F(I) curve, the effects of solubility, cardiac output and ventilation on the F(VRG) are different when either F(I) or F(A) are kept constant. With the F(I) kept constant, induction of anaesthesia is slower with a higher cardiac output, but with F(A) kept constant, induction of anaesthesia is faster with a higher cardiac output. The introduction of an end-expired closed-loop feedback administration of inhaled anaesthetics makes this distinction clinically relevant.

Derivation and prospective testing of a two-step sevoflurane-O2-N2O low fresh gas flow sequence.

Simple vaporiser setting (F(D)) and fresh gas flow (FGF) sequences make the practice of low-flow anaesthesia not only possible but also easy to achieve. We sought to derive a sevoflurane F(D) sequence that maintains the end-expired sevoflurane concentration (F(A)sevo) at 1.3% using the fewest possible number of F(D) adjustments with a previously described O2-N2O FGF sequence that allows early FGF reduction to 0.7 l min(-1). In 18 ASA physical status I to IH patients, F(D) was determined to maintain F(A)sevo at 1.3% with 2 l min(-1) O2 and 4 l min(-1) N2O FGF for three minutes, and with 0.3 and 0.4 l min(-1) thereafter. Using the same FGF sequence, the F(D) schedule that approached the 1.3% F(A)sevo pattern with the fewest possible adjustments was prospectively tested in another 18 patients. The following F(D) sequence approximated the F(D) course well: 2% from zero to three minutes, 2.6% from three to 15 minutes and 2.0% after 15 minutes. When prospectively tested, median (25th; 75th percentile) performance error was 0.8 (-2.9; 5.9)%, absolute performance error 6.7 (3.3; 10.6)%, divergence 18.2 (-5.6; 27.4)%.h(-1) and wobble 4.4 (1.7; 8.1) %. In one patient, FGF had to be temporarily increased for four minutes. One O2/N2O rotameter FGF setting change from 6 to 0.7 l min(-1) at three minutes and two sevoflurane F(D) changes at three and 15 minutes maintained predictable anaesthetic gas concentrations during the first 45 minutes in all but one patient in our study.

Desflurane consumption with the Zeus during automated closed circuit versus low flow anesthesia.

INTRODUCTION: During automated closed-circuit anesthesia (CCA), the Zeus (Dräger, Lübeck, Germany) uses a high initial fresh gas flow (FGF) to rapidly attain the desired agent and carrier gas concentrations, resulting in a desflurane consumption well above patient uptake. Because both FGF and carrier gas composition can affect consumption, we determined the Zeus' agent consumption with automated CCA and with automated low flow anesthesia (LFA) (= maintenance FGF of 0.7 L min(-1)) with 3 different carrier gases. METHODS: After IRB approval, 65 ASA PS I or II patients undergoing general surgery received desflurane in either O2, O2/air, or O2/N2O, with the Zeus to maintain the end-expired concentration (FA) at 6, 6, and 4% and the F1O2 at 1.0, 0.6, and 0.4, respectively. In addition, patients were assigned to either automated CCA (O2 n = 11; O2/air n = 11; O2/N2O n = 11) or automated LFA (selected FGF 0.7 L min(-1)) (O2 n = 12; O2/air n = 11; O2/N2O n = 9). Demographics and desflurane consumption at 2, 4, 6, 8, 10, 20, 30, 40 and 50 min were compared. RESULTS: With the same carrier gas, desflurane consumption was lower with the CCA mode than with LFA mode after 4 min in the O2 groups, 6 min in the O2/air groups, and 30 min in the O2/N2O groups. Within each mode, desflurane consumption in the O2 and O2/air groups was identical at all times. Despite the use of a lower FA in the N2O groups, initial desflurane consumption was higher than in the O2 and O2/air groups, but it was lower later (> or = 15 min) only with LFA. DISCUSSION: After 50 min, desflurane consumption with automated CCA is lower than with automated LFA. However, initial agent consumption is complex, and N2O in particular may increase initial desflurane consumption (though ultimately resulting in lower desflurane usage because of its MAC sparing effect) because initial FGF is increased to rapidly reach the target concentrations. Differences in desflurane consumption only become apparent after FGF has stabilized to the target FGF.

Should ruptured liver haemangioma be treated by surgery or by conservative means? A case report.

Spontaneous rupture of a liver haemangioma is a rare but life-threatening acute clinical situation following haemorrhage within the liver, the subcapsular space and the peritoneal cavity in cases of capsular rupture. Rupture of a liver haemangioma has been reported to occur spontaneously in the majority of cases. In the past, prompt surgical treatment was recommended but was associated with high morbidity and mortality. Currently, conservative management and, in cases of recurrent haemorrhage, delayed surgery may be proposed. We report a case of spontaneous rupture of hepatic haemangioma treated by arterial embolisation and conservative means. The literature is also reviewed.

Air-oxygen mixtures in circle systems.

STUDY OBJECTIVE: To determine the effect of different air-O(2) mixtures and fresh gas flows (FGF) on the relationship between the delivered (F(Del)O(2)) and inspired O(2) fraction (FIO(2)) in a circle system. STUDY DESIGN: Randomized clinical study. SETTING: Large teaching hospital. PATIENTS: 160 ASA physical status I, II, and III patients undergoing a variety of cardiovascular procedures with general endotracheal anesthesia. INTERVENTIONS: 160 patients were randomly assigned to one of 20 groups (n = 8 each), depending on the combination of total FGF (0.5, 1, 2, 4, or 8 L/min) and air-O(2) mixture used (ratios of 4/1, 3/2, 2/3, or 1/4), corresponding to a F(Del)O(2) of 0.37, 0.53, 0.68, and 0.84. For each combination of FGF and air-O(2) mixture, FIO(2) after equilibration was compared with F(Del)O(2). MEASUREMENTS AND MAIN RESULTS: With any air-O(2) mixture with a FGF < or = 2 L/min, FIO(2) became lower than F(Del)O(2). Because FIO(2) decreased below 0.25 after 13 and 26 minutes in the first two patients of the 4/1 0.5 L/min air-O(2) group, this study limb was terminated. CONCLUSIONS: When using air-O(2) mixtures in a circle system, FIO(2) becomes lower than the F(Del)O(2) with FGF < or = 2 L/min. The relative proportion of O(2) in the FGF has to be increased accordingly.

The ADU vaporizing unit: a new vaporizer.

UNLABELLED: We determined the performance of the vaporizer of the ADU machine (Anesthesia Delivery Unit; Datex-Ohmeda, Helsinki, Finland). The effects of carrier gas composition (oxygen, oxygen/N(2)O mixture, and air) and fresh gas flow (0.2 to 10 L/min) on vaporizer performance were examined with variable concentrations of isoflurane, sevoflurane, and desflurane across the whole range of each vaporizer's output. In addition, the effects of sudden changes in fresh gas flow and carrier gas composition, back pressure, flushing, and tipping were assessed. Vaporizer output depended on fresh gas flow, carrier gas composition, dial settings, and the drug used. Vaporizer output remained within 10% of dial setting with fresh gas flows of 0.3-10 L/min for isoflurane, within 10% of dial setting with fresh gas flows of 0.5-5 L/min for sevoflurane, and within 13% of dial setting with fresh gas flows of 0.5 to 1 L/min for desflurane. Outside these fresh gas flow ranges, output deviated more. The effect of sudden changes in fresh gas flow or carrier gas composition, back pressure, flushing, and tipping was minimal. We conclude that the ADU vaporizer performs well under most clinical conditions. Despite a different design and the use of complex algorithms to improve accuracy, the same physical factors affecting the performance of conventional vaporizers also affect the ADU vaporizer. IMPLICATIONS: The ADU vaporizer performs well under most clinical conditions. Despite a different design and the use of complex algorithms to improve accuracy, the same physical factors affecting the performance of conventional vaporizers also affect the ADU vaporizer.

The probability of a successful treatment of infertility by in-vitro fertilization.

The objective of this study was to define several estimates of the success rate of in-vitro fertilization and embryo transfer treatment in relation to treatment outcome. The data were collected in a retrospective study of 591 patients treated during 3 years in one Belgian university hospital. Several models used for evaluating the treatment of infertility were fitted to the data (logistic model, binomial model, double binomial model, exponential model, the Speirs model. The number of oocytes retrieved and the proportion of fertilized oocytes at the first attempt can be used as prognostic factors. According to these factors, the success rate after five attempts varies from 28 to 88%.

Plasminogen activator activity and fertilizing ability of human spermatozoa.

Mature spermatozoa contain a number of proteases that are supposed to contribute to their fertilizing ability. The present study was directed at plasminogen activator (PA), a protease that belongs to the group of serine proteases and converts the zymogen plasminogen to the active broad-spectrum protease plasmin. To investigate the possible role of PA in the fertilization process, we have measured sperm-bound PA activity in 63 patients included in an in-vitro fertilization (IVF) programme and assessed their relationship to standard semen parameters and the rate of fertilization. PA activity was correlated significantly with the sperm count, as well as with sperm motility and morphology. Using logistic regression analysis, specific PA (pmol pNA 10(-6) cells min-2) was found to significantly influence the probability of fertilization. Other significantly predictive factors were motility and the percentage of spermatozoa with normal morphology. The sperm concentration (10(6) cells ml-1) did not significantly affect the outcome of IVF. We suggest that sperm-bound PA is involved in the fertilization process and may represent a potential indicator of sperm fertilizing capacity.

Effects of hyaluronate, strontium and prolonged incubation on different sperm parameters.

The aim of this study was to evaluate the effect of hyaluronate and strontium with short and prolonged incubation periods on different sperm parameters. For sperm intended for in vitro fertilization good progressive motility, a high percentage of normal form, a suitable linear velocity and a low acrosome-reacted proportion of sperm are required. The semen washing procedure in the self-migration method with medium containing hyaluronate Ca2+ after 3 h of incubation complies better with these criteria.

Low bone mass in hypogonadal males. Effect of testosterone substitution therapy, a densitometric study.

Sixteen (16) male patients who were suffering from hypogonadism but who were free from bone symptoms were recruited from the Andrology Clinic. Their bone mineral density (BMD) was assessed by single photon absorptiometry in the non-dominant radius, at both the distal radius (DR) (27% trabecular bone) and the midshaft radius (MR) (90% cortical bone). Measurements were carried out before and during testosterone substitution therapy. BMD was found to be lower in the subjects than in the controls, to a similar extent at both the DR (0.47 +/- 0.02 g/cm2, i.e. 83.1 +/- 4.3% of the value in the controls, or Z score -1.42 +/- 0.39; P less than 0.01) and the MR (0.68 +/- 0.02 g/cm2, i.e. 87.8 +/- 2.4% of the value in the controls, or Z score -1.49 +/- 0.33; P less than 0.01). There was no correlation between testosterone levels and BMD at either the DR or the MR at the beginning of the study. Following testosterone substitution therapy, bone mineral content (BMC) increased significantly at the DR (+5.9 +/- 1.4% per year; P less than 0.01) and at the MR (+1.1 +/- 0.9% per year; P less than 0.01). If the study is limited to the subjects who had achieved full bone age maturity before the start of therapy, the bone gain remains significant only at the DR, a site with a sizeable proportion of trabecular bone.

In-vitro fertilization: how many attempts before success?

Repeated attempts increase the overall rate of success of sterility therapy by in-vitro fertilization. The present study, using data collected between 1983 and 1987 in a Belgian hospital, attempts to investigate the expected number of treatment cycles before success is achieved. The answer requires some knowledge about the degree of independence between success probability and treatment duration. Using mathematical models of implantation, it can be shown that success probability actually decreases during treatment. A method for updating individual probabilities is suggested; it could be used as a prognostic estimation for women undergoing this kind of therapy.

Hormonal changes induced by short-term administration of gonadotropin-releasing hormone agonist during ovarian hyperstimulation for in vitro fertilization and their consequences for embryo development.

Several regimens have been developed to administer gonadotropin-releasing hormone agonists in association with human menopausal gonadotropins (hMG) during follicular growth stimulation for in vitro fertilization. The aim of this study was to characterize hormonal changes induced by short-term administration of agonist, and to evaluate a putative impact of the flare-up effect on follicular recruitment and subsequent IVF. Eighteen highly selected patients were randomely divided in two groups. Nine patients received a short-term administration of Buserelin (Hoechst, AG, Franfurt/Main, FRG) (day 1). They were compared with 9 patients who were exposed to a long-term protocol (day 21), and 13 control patients. Agonist-induced luteinizing hormone (LH) and follicle-stimulating hormone (FSH) increase, in early follicular phase, stimulated follicular growth, shortened follicular phase, and induced a transient rise in progesterone. This was followed by a phase of reduced LH secretion associated with a significant modification of LH immunoreactivity. The short-term regimen did not improve the follicular recruitment, and appeared to reduce the oocytes fertilization rate and embryo quality when compared with prolonged administration of peptide.

Short-term utilization of a gonadotropin-releasing hormone agonist (buserelin) for induction of ovulation in an in vitro fertilization program.

Benefits of the short-term utilization of a gonadotropin-releasing hormone (GnRH) agonist (Buserelin, Hoechst, AG, Frankfurt am Mein, FRG) for induction of ovulation in an in vitro fertilization program (IVF) program were assessed. Eighteen patients underwent consecutively an induction of ovulation by clomiphene citrate (CC) and human menopausal gonadotropin (hMG), then by hMG alone, and finally by Buserelin and hMG. The switchover from CC and hMG to hMG alone significantly increased the number of aspirated follicles and the oocyte recovery rate. The addition of Buserelin prevented the outcome of spontaneous luteinizing hormone (LH) surges. It reduced the preovulatory luteinization and increased the number of recovered oocytes as well as the number of embryos available for transfer. A 33% clinical pregnancy rate per ovum pick-up was achieved with the Buserelin-hMG treatment.

[The beneficial effects of short-term administration of a LHRH agonist (buserelin) in in vitro fertilization]. / Effets bénéfiques de l'administration de courte durée d'un agoniste de la LHRH (buséréline) en fécondation in vitro.

We have assessed the beneficial effects of administering a short course of an agonist of LHRH (Buserelin) in vitro fertilisation. 274 cycles were treated with CC-HMG, 159 were treated with HMG alone and 253 by Buserelin-HMG. These were compared retrospectively. The use of a short course of Buserelin lowered significantly the rate of failed treated cycles (7% instead of 19% when it was used with CC-HMG and 27% when used with HMG). This made it possible to administer hCG in all cases in the programme (100% as against 69% and 89% respectively for CC-HMG and HMG without Buserelin), and increase significantly the number of oocytes that could be recovered and the number of embryos available for transfer. The overall number of pregnancies per cycle treated is significantly raised when Buserelin is used with HMG (20.4% as against 13.5% for CC-HMG and HMG). The number of pregnancies that progressed, on the other hand, was similar when the cycle was stimulated with HMG alone (10.6%) or with Buserelin-HMG (10.6%).

Feminizing testicular Leydig cell tumor: hormonal profile before and after unilateral orchidectomy.

The effect of chronic hyperestrogenism on gonadal function was studied in three men who had estrogen-secreting Leydig cell tumors before unilateral orchidectomy and for 11-43 months after surgery. All three men had low plasma gonadotropin and testosterone levels and increased estradiol levels. Impairment of testicular steroidogenesis was also suggested by increased progesterone to 17-hydroxyprogesterone and 17-hydroxyprogesterone to androstenedione ratios in both spermatic venous plasma and the medium of Leydig tumor cells from one patient incubated in vitro. Before surgery, spermatogenesis was abnormal in two men. Testicular endocrine function and spermatogenesis did not return to normal after surgery. During the follow-up period, plasma gonadotropin levels were high in all three men, and testosterone was low normal. Estradiol levels decreased to normal immediately after surgery and then returned to the upper normal limit. The response to hCG stimulation in one man was subnormal. We conclude that chronic hyperestrogenism produced hypothalamo-pituitary inhibition as well as direct steroidogenic blockade at the testicular level. Long term impairment of both endocrine and exocrine testicular functions may be secondary to slowly reversible (or irreversible) estrogen-induced damage to tubular and Leydig cells.