Thierry Deloof

Effect of propofol on cerebral blood flow and metabolism in man.

Cerebral blood flow, cerebral oxygen consumption, lactate and glucose metabolism were measured in 13 patients during anaesthesia with nitrous oxide, oxygen and enflurane 0.5% and after 30 minutes infusion of propofol. The mean blood concentration of propofol was 4.06μg/ml. Cerebral blood flow decreased by 27.6% and cerebral vascular resistance by 51%. There were no changes in lactate and glucose metabolism. Cerebral oxygen consumption decreased by 18.25%. Changes in the electroencephalograph were related to the blood levels of propofol.

Postoperative residual paralysis in outpatients versus inpatients.

Postoperative residual paralysis is an important complication of the use of neuromuscular blocking drugs. In this prospective study, the incidence of residual paralysis detected as a train-of-four response <90% was less frequent in surgical outpatients (38%) than inpatients (47%) (P = 0.001). This might have been the result of the more frequent use of mivacurium for outpatients. Before undertaking tracheal extubation, the anesthesiologists had applied clinical criteria (outpatients, 49%; inpatients, 45%), pharmacological reversal (26%, 25%), neuromuscular transmission monitoring (12%, 11%), or a combination of these. None of these measures seemed to reduce the incidence of residual paralysis except for quantitative train-of-four monitoring. Postoperatively, eight individual clinical tests or a sum of these tests were also unable to predict residual paralysis by train-of-four. Although the incidence of residual paralysis was less frequent in surgical outpatients, predictive criteria were not evident.

Desflurane consumption during automated closed-circuit delivery is higher than when a conventional anesthesia machine is used with a simple vaporizer-O2-N2O fresh gas flow sequence

BackgroundThe Zeus® (Dräger, Lübeck, Germany), an automated closed-circuit anesthesia machine, uses high fresh gas flows (FGF) to wash-in the circuit and the lungs, and intermittently flushes the system to remove unwanted N2. We hypothesized this could increase desflurane consumption to such an extent that agent consumption might become higher than with a conventional anesthesia machine (Anesthesia Delivery Unit [ADU®], GE, Helsinki, Finland) used with a previously derived desflurane-O2-N2O administration schedule that allows early FGF reduction.MethodsThirty-four ASA PS I or II patients undergoing plastic, urologic, or gynecologic surgery received desflurane in O2/N2O. In the ADU group (n = 24), an initial 3 min high FGF of O2 and N2O (2 and 4 L.min-1, respectively) was used, followed by 0.3 L.min-1 O2 + 0.4 L.min-1 N2O. The desflurane vaporizer setting (FD) was 6.5% for the first 15 min, and 5.5% during the next 25 min. In the Zeus group (n = 10), the Zeus® was used in automated closed circuit anesthesia mode with a selected end-expired (FA) desflurane target of 4.6%, and O2/N2O as the carrier gases with a target inspired O2% of 30%. Desflurane FA and consumption during the first 40 min were compared using repeated measures one-way ANOVA.ResultsAge and weight did not differ between the groups (P > 0.05), but patients in the Zeus group were taller (P = 0.04). In the Zeus group, the desflurane FA was lower during the first 3 min (P < 0.05), identical at 4 min (P > 0.05), and slightly higher after 4 min (P < 0.05). Desflurane consumption was higher in the Zeus group at all times, a difference that persisted after correcting for the small difference in FA between the two groups.ConclusionAgent consumption with an automated closed-circuit anesthesia machine is higher than with a conventional anesthesia machine when the latter is used with a specific vaporizer-FGF sequence. Agent consumption during automated delivery might be further reduced by optimizing the algorithm(s) that manages the initial FGF or by tolerating some N2 in the circuit to minimize the need for intermittent flushing.

Composition of fresh frozen plasma

We analyzed 35 samples of fresh frozen plasma (FFP), finding mean concentrations of 535 mg/dl glucose, 172 mEq/L sodium, 73 mEq/L chloride, 3.5 mEq/L potassium, 15 mEq/L bicarbonate, and 5.5 g/dl protein with 60% albumin. Thus, FFP is a hyperosmolar hyperglycemic, hypernatremic, and hypochloremic solution which may be a less effective volume expander than other albumin-containing solutions, due to its lower albumin content.

Maintaining sevoflurane anesthesia during low-flow anesthesia using a single vaporizer setting change after overpressure induction.

STUDY OBJECTIVE A sevoflurane vaporizer dial setting of 1.9% was previously found to maintain the end-expired sevoflurane concentration (Et(sevo)) at 1.3% during maintenance of anesthesia for procedures up to one hour with an O(2) FGF of 1 L/min. We examined whether applying these parameters could simplify low-flow sevoflurane anesthesia after overpressure induction using two slightly different techniques. DESIGN Prospective clinical study. SETTING Large teaching hospital. PATIENTS Sixteen patients receiving general anesthesia for a variety of peripheral procedures. INTERVENTIONS Anesthesia was induced with overpressure with sevoflurane (8%) in an 8 L. min(-1) O(2)/N(2)O mixture (30%/70%). After a laryngeal mask airway (LMA) was placed, fresh gas flow (FGF) was lowered to 1 L. min(-1) using O(2) and N(2)O (FiO(2) 30%) with patients breathing spontaneously. In group I patients (n = 8), the vaporizer dial was set at 1.9% at the same time the FGF was lowered. In group II patients (n = 8), the vaporizer was turned off until Et(sevo) had decreased to 1.3%, after which the dial was set at 1.9%. The course of Et(sevo) in the two groups was examined. MEASUREMENTS AND MAIN RESULTS In group I, Et(sevo) after 3 min was 4.88 +/- 1. 12%. Et(sevo) decreased slowly after reduction of FGF to 1.83 +/- 0. 19%, 1.59 +/- 0.18%, and 1.52 +/- 0.19% at 10, 20, and 30 min, respectively. In group II, Et(sevo) after 3 min was 4.34 +/- 0.84%, and decreased more rapidly after reduction of FGF to 1 L. min(-1) than in group I. Et(sevo) was 1.40 +/- 0.09%, 1.40 +/- 0.11%, and 1. 38 +/- 0.13% at 10, 20, and 30 min, respectively. CONCLUSIONS After high-flow overpressure induction with sevoflurane, a single change in vaporizer setting (to 1.9%) and FGF (to 1 L. min(-1)) suffices for the Et(sevo) to approach the predicted Et(sevo) (1.3%) within 10-15 min; thereafter the Et(sevo) remains nearly constant. As expected, the predicted Et(sevo) is attained slightly faster when the vaporizer is temporarily turned off. Clinically applying previously derived pharmacokinetic parameters simplifies low-flow sevoflurane anesthesia after overpressure induction.

Effect of N2O on sevoflurane vaporizer settings during minimal- and low-flow anesthesia.

Background Uptake of a second gas of a delivered gas mixture decreases the amount of carrier gas and potent inhaled anesthetic leaving the circle system through the pop-off valve. The authors hypothesized that the vaporizer settings required to maintain constant end-expired sevoflurane concentration (Etsevo) during minimal-flow anesthesia (MFA, fresh gas flow of 0.5 l/min) or low-flow anesthesia (LFA, fresh gas flow of 1 l/min) would be lower when sevoflurane is used in oxygen–nitrous oxide than in oxygen. Methods Fifty-six patients receiving general anesthesia were randomly assigned to one of four groups (n = 14 each), depending on the carrier gas and fresh gas flow used: group Ox.5 l (oxygen, MFA), group NOx.5 l (oxygen–nitrous oxide, MFA after 10 min high fresh gas flow), group Ox1 l (oxygen, LFA), and group NOx1 l (oxygen–nitrous oxide, LFA after 10 min high fresh gas flow). The vaporizer dial settings required to maintain Etsevo at 1.3% were compared between groups. Results Vaporizer settings were higher in group Ox.5 l than in groups NOx.5 l, Ox1 l, and NOx1 l; vaporizer settings were higher in group NOx.5 l than in group NOx1 l between 23 and 47 min, and vaporizer settings did not differ between groups Ox1 l and NOx1 l. Conclusions When using oxygen–nitrous oxide as the carrier gas, less gas and vapor are wasted through the pop-off valve than when 100% oxygen is used. During MFA with an oxygen–nitrous oxide mixture, when almost all of the delivered oxygen and nitrous oxide is taken up by the patient, the vaporizer dial setting required to maintain a constant Etsevo is lower than when 100% oxygen is used. With higher fresh gas flows (LFA), this effect of nitrous oxide becomes insignificant, presumably because the proportion of excess gas leaving the pop-off valve relative to the amount taken up by the patient increases. However, other unexplored factors affecting gas kinetics in a circle system may contribute to our observations.

Implications of the use of neuromuscular transmission monitoring on immediate postoperative extubation in off-pump coronary artery bypass surgery

Background and objective: When continuous infusions of neuromuscular blocking drugs are administered during lengthy interventions and no routine antagonism of their effects is applied, there is a dramatic incidence of residual curarization. We have examined whether the use of neuromuscular transmission monitoring results in differences in the incidence of postoperative residual curarization, the use of antagonist agents, and the endotracheal extubation rate and outcome after continuous infusion of rocuronium in patients undergoing off-pump coronary artery bypass surgery. Methods: Twenty patients were assigned to group 1 (n = 10, non-blinded neuromuscular transmission monitoring) or group 2 (n = 10, blinded neuromuscular transmission monitoring). In group 1, patients were given rocuronium at an infusion rate of 6 μg kg−1 min−1. The rate was manually adjusted in order to maintain T1/T0 at 10%. In group 2, a rocuronium infusion was started 30 min after induction of anaesthesia, at a rate of 6 μg kg−1 min−1; this rate was left unchanged during surgery. The rocuronium infusion was discontinued on completion of all vascular anastomoses; propofol was stopped at the beginning of closure of the subcutis and pirinitramide (piritramide) 15 mg was administered intravenously. Remifentanil was discontinued at the beginning of skin closure and neostigmine (50 μg kg−1) administered at the end of surgery when the train-of-four ratio was <0.9 in group 1, and routinely in group 2. A 20 min test period for spontaneous ventilation was allowed once surgery had been accomplished. When the train-of-four ratio was ⩾0.9 (group 1), patients were extubated if also breathing spontaneously, fully awake and able to follow commands. When they met the clinical criteria for normal neuromuscular function after induced blockade, patients in group 2 were extubated when fully awake and able to follow commands. Results: In group 1, the rate of rocuronium infusion required to keep T1/T0 at 10% was 5 ± 1.9 μg kg−1 min−1; this was not significantly different from the fixed rate in group 2 (P = 0.15). One patient in group 2 was excluded. Eight out of 10 and eight out of nine patients in groups 1 and 2, respectively, reached the extubation criteria. Three out of eight, and five out of eight, patients from groups 1 and 2, respectively, were extubated in the operating room. At that time of endotracheal extubation, all three patients from group 1, but only four of the five patients from group 2 had a train-of-four ratio ⩾0.9. In group 2, one patient was reintubated in the intensive care unit. The incidence of pharmacological reversal was high in group 1. Conclusions: Although we found no additional benefit of using neuromuscular transmission monitoring, it seems an absolute necessity for safety reasons. Pharmacological antagonism was mandatory. However, in our opinion, it is not wise routinely to perform immediate postoperative extubation in off-pump coronary artery bypass surgery.

Development and performance of a two-step desflurane-O2/N2O fresh gas flow sequence

STUDY OBJECTIVE To determine if the previously described single-step O(2)/N(2)O fresh gas flow (FGF) sequence could be combined with a simple desflurane vaporizer (F(D)) sequence to maintain the end-expired desflurane (F(A)des) at 4.5% with the anesthesia delivery unit machine (ADU Anesthesia Machine(R); General Electric, Helsinki, Finland). DESIGN Prospective randomized clinical study. SETTING Onze Lieve Vrouw Hospital, Aalst, Belgium, a large teaching hospital. PATIENTS 42 ASA physical status I and II patients requiring general endotracheal anesthesia and controlled mechanical ventilation. INTERVENTIONS In 18 patients undergoing general anesthesia with controlled mechanical ventilation, F(D) was determined to maintain F(A)des at 4.5% with O(2)/N(2)O FGF of two and 4 L per minute for three minutes and 0.3 and 0.4 L per minute thereafter. Using the same FGF sequence, we prospectively tested the F(D) schedule that approached this observed F(D) pattern with the fewest possible adjustments in another 24 patients. MAIN RESULTS F(D) of 6.5% for 15 minutes followed by 5.5% thereafter approximated the observed F(D) course well. When it was prospectively tested, the median (25th, 75th percentiles) performance error was -1% (-5.1%, 5.2%); absolute performance error, 7.1% (3.9%, 9.5%); divergence, -6.6% per hour (23.1%, 3.1%/h); and wobble, 2.2% (1.8%, 3.2%). Because F(A)des increased above 4.9%, F(D) was decreased in 5 patients after 23 minutes (0.5% decrement once or twice); in two patients, F(D) was temporarily increased. In one patient, FGF was temporarily increased because the bellows volume became insufficient. CONCLUSIONS One O(2)/N(2)O rotameter FGF setting change from 6 to 0.7 L per minute after three minutes and one desflurane F(D) change from 6.5% to 5.5% after 15 minutes maintained anesthetic gas concentrations within predictable and clinically acceptable limits during the first 20 minutes.

The ADU vaporizing unit: a new vaporizer.

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/N2O 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.

Perioperative blood glucose management in patients undergoing tumor hepatectomy

STUDY OBJECTIVE To determine whether our institutional insulin management (modified Atlanta) protocol is efficient and safe in controlling blood glucose levels in the perioperative period in surgical patients undergoing tumor hepatectomy. DESIGN Retrospective study. SETTING Large community hospital. PATIENTS 20 consecutive patients undergoing liver resection for hepatocellular carcinoma, liver metastasis, or other hepatobiliary tumors. INTERVENTIONS AND MEASUREMENTS All patients continuously received intravenous glucose (5% dextrose in water, one mL/kg/hr); insulin was administered according to a strict algorithm, and dose adjustments were based on measurements of whole-blood glucose intraoperatively at one-hour intervals, and in the intensive care unit (ICU). Lower and upper blood glucose limits were set at 85 mg/dL and 110 mg/dL, respectively, in the operating room (OR). In the ICU, lower and upper limits were 90 mg/dL and 140 mg/dL, respectively. MAIN RESULTS Intraoperatively, 51.3% of measurements were within the target range. In the ICU, 75.2% of measurements showed a blood glucose level of 90 - 140 mg/dL. Two of 78 (2.6%) and two of 363 (0.5%) measurements had a blood glucose level < 70 mg/dL in the OR and ICU, respectively. The lowest blood glucose levels were 65 mg/dL (OR) and 66 mg/dL (ICU). CONCLUSIONS The modified Atlanta protocol is efficient and safe in controlling blood glucose levels in the perioperative period of hepatic tumor resection. Because of decreased insulin needs in the ICU, the use of a more liberal algorithm successfully reduced the risk of hypoglycemia.