Ventilatory management during routine general anaesthesia.

Intraoperative hypoxaemia and postoperative respiratory complications remain the challenges of modern anaesthetic practice. Anaesthesia causes both depression of respiratory centres and profound changes of respiratory mechanics. Most anaesthetized patients consequently require mechanical ventilation and supplemental oxygen. Recent data suggest that intraoperative respiratory management of a patient can affect postoperative outcome. In this review, we briefly describe the mechanisms responsible for the impairment of intraoperative gas exchange and provide guidelines to prevent or manage hypoxaemia. Moreover, we discuss several aspects of mechanical ventilation that can be employed to improve patients' outcome.

Effect of adrenergic stimulation on cutaneous microcirculation immediately after surgical adventitiectomy in a rat skin flap model.

Chronic sympathetic denervation leads to the development of supersentivity to adrenergic agents. Free flap surgery results in the disruption of the autonomic nerve fibers running along the anastomosed vessels. We therefore investigated the early effect of surgical sympathectomy on the reactivity of cutaneous microcirculation challenged to adrenergic agents. Two epigastric flaps were elevated and exposed in 15 rats. On the right flap (Side A), a circular adventitiectomy of the feeder vessels was realized to provide surgical sympathectomy. On the left flap (Side N), vessels were kept intact. The following drugs were then given intravenously successively: phenylephrine (10 and 15 microg kg(-1)), norepinephrine (10 microg kg(-1)), prazocin (1 mg kg(-1)) followed by norepinephrine (10 microg kg(-1)). Cutaneous microcirculation was assessed using Laser-Doppler Flowmeters simultaneously on the two flaps after each drug administration. Mean arterial pressure was also measured. On side N, phenylephrine and norepinephrine resulted in a transient increase in cutaneous microcirculation followed by a more prolonged reduction. On side A, only the initial increase was observed, which was greater and longer as compared with side N, and paralleled the increase in mean arterial pressure. After prazocin pre-treatment, norepinephrine produced a transient increase in cutaneous microcirculation similar on both sides, and parallel to the changes in arterial pressure. No decrease in cutaneous microcirculation was observed. Immediately after surgical adventitiectomy, the vasoconstriction produced by alpha-adrenergic agents is prevented. No denervation-induced hypersentivity is observed. Surgical sympathectomy might protect cutaneous flaps from vasoconstriction induced by endogenous catecholamines release.

Pressure-controlled ventilation does not improve gas exchange in morbidly obese patients undergoing abdominal surgery.

BACKGROUND: Morbid obesity results in marked respiratory pathophysiologic changes that may lead to impaired intraoperative gas exchange. The decelerating inspiratory flow and constant inspiratory airway pressure resulting from pressure-controlled ventilation (PCV) may be more adapted to these changes and improve gas exchanges compared with volume-controlled ventilation (VCV). METHODS: Forty morbidly obese patients scheduled for gastric bypass were included in this study. Total intravenous anesthesia was given using the target-controlled infusion technique. During the first intraoperative hour, VCV was used and the tidal volume was adjusted to keep end-tidal PCO(2) around 35 mmHg. After 1 h, patients were randomly allocated to 30-min VCV followed by 30-min PCV or the opposite sequence using a Siemens Servo 300. FiO(2) was 0.6. During PCV, airway pressure was adjusted to provide the same tidal volume as during VCV. Arterial blood was sampled for gas analysis every 15 min. Ventilatory parameters were also recorded. RESULTS: Peak inspiratory airway pressures were significantly lower during PCV than during VCV (P < 0.0001). The other ventilatory parameters were similar during the two periods of ventilation. PaO(2) and PaCO(2) were not significantly different during PCV and VCV. CONCLUSION: PCV does not improve gas exchange in morbidly obese patients undergoing gastric bypass compared to VCV.

Intravenous lidocaine infusion facilitates acute rehabilitation after laparoscopic colectomy.

BACKGROUND: Intravenous infusion of lidocaine decreases postoperative pain and speeds the return of bowel function. The authors therefore tested the hypothesis that perioperative lidocaine infusion facilitates acute rehabilitation protocol in patients undergoing laparoscopic colectomy. METHODS: Forty patients scheduled to undergo laparoscopic colectomy were randomly allocated to receive intravenous lidocaine (bolus injection of 1.5 mg/kg lidocaine at induction of anesthesia, then a continuous infusion of 2 mg.kg.h intraoperatively and 1.33 mg.kg.h for 24 h postoperatively) or an equal volume of saline. All patients received similar intensive postoperative rehabilitation. Postoperative pain scores, opioid consumption, and fatigue scores were measured. Times to first flatus, defecation, and hospital discharge were recorded. Postoperative endocrine (cortisol and catecholamines) and metabolic (leukocytes, C-reactive protein, and glucose) responses were measured for 48 h. Data (presented as median [25-75% interquartile range], lidocaine vs. saline groups) were analyzed using Mann-Whitney tests. P<0.05 was considered statistically significant. RESULTS: Patient demographics were similar in the two groups. Times to first flatus (17 [11-24] vs. 28 [25-33] h; P<0.001), defecation (28 [24-37] vs. 51 [41-70] h; P=0.001), and hospital discharge (2 [2-3] vs. 3 [3-4] days; P=0.001) were significantly shorter in patients who received lidocaine. Lidocaine significantly reduced opioid consumption (8 [5-18] vs. 22 [14-36] mg; P=0.005) and postoperative pain and fatigue scores. In contrast, endocrine and metabolic responses were similar in the two groups. CONCLUSIONS: Intravenous lidocaine improves postoperative analgesia, fatigue, and bowel function after laparoscopic colectomy. These benefits are associated with a significant reduction in hospital stay.

Epidural levobupivacaine 0.1% or ropivacaine 0.1% combined with morphine provides comparable analgesia after abdominal surgery.

UNLABELLED: Ropivacaine appears attractive for epidural analgesia because it produces less motor block than racemic bupivacaine. The potential benefits of levobupivacaine with regard to motor blockade require further investigations. In this study, we compared the efficacy, dose requirements, side effects, and motor block observed with epidural levobupivacaine and ropivacaine when given in combination with small-dose morphine for 60 h after major abdominal surgery. Postoperatively, 50 patients were randomly allocated, in a double-blinded manner, to patient-controlled epidural analgesia with the same settings and without basal infusion, using 0.1% levobupivacaine or 0.1% ropivacaine. Both were combined with an epidural infusion of 0.1 mg/h morphine. Pain scores, side effects, motor block, and local anesthetic consumption were measured for 60 h. Pain scores measured on a 100-mm visual analog scale were approximately 20 mm at rest and 40 mm during mobilization in both groups. Bromage scores were 1 for all patients after the fourth postoperative hour. Consumption of levobupivacaine and ropivacaine were similar: 344 +/- 178 mg levobupivacaine versus 347 +/- 199 mg ropivacaine 48 h postoperatively. On postoperative day 2, 19 patients in the ropivacaine group versus 12 in the levobupivacaine group were able to ambulate (P < 0.05). No difference was noted concerning incidence of side effects. We conclude that when used as patient-controlled epidural analgesia and combined with small-dose epidural morphine, 0.1% levobupivacaine and 0.1% ropivacaine produce comparable postoperative analgesia with a similar incidence of side effects. IMPLICATIONS: Small concentrations (0.1%) of epidural levobupivacaine and ropivacaine combined with morphine (0.1 mg/h) produce comparable analgesia and have similar side effects for similar dose requirements.

Spinal mechanisms contribute to analgesia produced by epidural sufentanil combined with bupivacaine for postoperative analgesia.

UNLABELLED: When used alone, lipid-soluble epidural opioids are thought to produce analgesia supraspinally via systemic absorption. However, spinal opioids and local anesthetics have been shown to act synergistically at the spinal level in animal studies. We, therefore, tested the hypothesis that sufentanil requirements will be less when given epidurally than IV in patients simultaneously given epidural bupivacaine after major abdominal surgery. Forty patients were anesthetized with isoflurane and epidural bupivacaine for major abdominal surgery. After surgery, each was given a continuous epidural infusion of bupivacaine at a rate of 5 mg/h and sufentanil patient-controlled analgesia (PCA). In a randomized, double-blinded fashion, the sufentanil was given either epidurally or IV. PCA settings were the same in each group. For 60 hrs after surgery, the following variables were measured: pain scores at rest, during mobilization, and during coughing; extension of sensory block; side effects; and sufentanil consumption. Pain scores, extension of sensory block, and the incidence of side effects did not differ between the two groups. Consumption of sufentanil in the epidural group was half that of the IV group (48 h after surgery: 107 +/- 57 microg versus 207 +/- 100 microg for the epidural and IV groups, respectively; P < 0.05). We conclude that spinal mechanisms contribute to the analgesia produced by epidural sufentanil in combination with a local anesthetic. IMPLICATIONS: When combined with epidural bupivacaine, the sufentanil requirement was 50% less when given epidurally than IV. Epidural sufentanil thus appears to have a spinal mechanism of action.

Investigation of the reaction of peroxynitrite with propofol at acid pH: predominant production of oxidized, nitrated, and halogenated derivatives.

We reported here the reaction, in acidic conditions, of peroxynitrite (ONOO(-)) with the anaesthetic agent propofol (2,6-diisopropylphenol, PPF). The most interesting finding is that peroxynitrite is able to nitrate and to oxidize propofol leading to 4-nitropropofol, quinone, and diphenylquinone as the major products. More surprisingly, we also found that peroxynitrite is capable of halogenating propofol in the presence of halide ions, suggesting the formation of nitrosyl chloride (NOCl) or nitryl chloride (NO(2)Cl) from the reaction of peroxynitrite with chloride ions. A significant enhancement of the halogenation yield is observed with a simultaneous decrease of the yields of the other products in the presence of methanol or hydrogen peroxide. Increased halogenation of PPF probably results from the formation of peroxynitrate (O(2)NOO(-)), that further oxidizes chloride ions in hypochlorous acid (HOCl) or molecular chlorine (Cl(2)). Spontaneous decay of peroxynitrate is relatively slow in acidic medium, thus explaining the decrease of the yields of the other products. By direct EPR techniques, we also observed that this reaction occurs via a radical pathway.

A comparison of 0.1% and 0.2% ropivacaine and bupivacaine combined with morphine for postoperative patient-controlled epidural analgesia after major abdominal surgery.

UNLABELLED: Ropivacaine (ROPI), which is less toxic and produces less motor block than bupivacaine (BUPI), seems attractive for epidural analgesia. Few data are available concerning dose requirements of epidural ROPI when combined with morphine. In this study, we compared the dose requirements and side effects of ROPI and BUPI combined with small-dose morphine after major abdominal surgery. Postoperatively, 60 patients were randomly allocated (double-blinded manner) to four groups: patient-controlled epidural analgesia with the same settings using 0.1% or 0.2% solution of ROPI or BUPI combined with an epidural infusion of 0.1 mg/h of morphine. Pain scores, side effects, motor block, and local anesthetic consumption were measured for 60 h. Pain scores and the incidence of side effects did not differ among the groups. Consumption of ROPI and BUPI were similar in both 0.1% groups. Doubling the concentration significantly reduced the consumption (milliliters) of BUPI (P < 0.05) but not of ROPI. Consequently, using ROPI 0.2% significantly increased the dose administered as compared with ROPI 0.1% (ROPI 0.1% = 314 +/- 151 mg and ROPI 0.2% = 573 +/- 304 mg at Hour 48; P < 0.05). Patient-controlled epidural analgesia with the 0.1% or 0.2% solution of ROPI or BUPI combined with epidural morphine resulted in comparable analgesia. As compared with ROPI 0.1%, the use of ROPI 0.2% increased consumption of local anesthetic without improving analgesia. IMPLICATIONS: Small-dose (0.1%) ropivacaine and bupivacaine have similar potency and result in comparable analgesia and incidence of side effects.