Induced mild hypothermia reduces mortality during acute inflammation in rats

BACKGROUND

Hypothermia has been proposed as a therapeutic possibility in brain trauma, cardiac arrest and hemorrhagic shock. Experimental studies have shown that hypothermia may act by modulating the inflammatory response during endotoxemia. This study was carried out to test whether hypothermia could protect rats from endotoxemic insult.

METHODS

After general anesthesia and oro-tracheal intubation, Sprague-Dawley rats were randomly assigned to either a hypothermic group or normothermic group. In each group, rats received intraperitoneal lipopolysaccharide (LPS) (10 or 20 mg/kg). Blood samples were taken prior to and 2 h after LPS injection to measure blood gases, liver enzymes, muscular enzymes, tumor necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10) plasma levels. After 2 h of hypothermia, the rats were extubated and brought back to their cages. The mortality rate was observed for 7 days following endotoxemia. In a second set of experiments, hypothermia was induced 1 h after endotoxemia (10 mg/kg of intraperitoneal LPS) and the mortality rate was observed for the following 7 days.

RESULTS

The survival rate was significantly increased in the hypothermic group relative to the normothermic group, regardless of LPS dose. This increased survival rate was also observed when hypothermia was induced 1 h after endotoxemia. In the hypothermic group, IL-10 and the DeltaIL-10/DeltaTNF-alpha ratio were significantly increased relative to those in the normothermic group.

CONCLUSION

Induced mild hypothermia reduces mortality during endotoxemia in rats. The modulation of the inflammatory response, with an increase in anti-inflammatory cytokines, may be involved in this protective effect.

Broad-spectrum beta-lactams for treating experimental peritonitis in mice due to Escherichia coli producing plasmid-encoded cephalosporinases

OBJECTIVES

To investigate the correlation between in vitro activity and in vivo efficacy of broad-spectrum beta-lactams for treating experimental infections due to Escherichia coli expressing two types of plasmid-mediated AmpC-type beta-lactamases, LAT-1 and FOX-1.

METHODS

Susceptibility testing and time-kill curves were determined for piperacillin/tazobactam, ceftazidime, cefepime and imipenem. A mouse model of peritonitis was developed to determine 50% effective doses (ED(50)s) of beta-lactams against E. coli clinical strains producing recombinant plasmids pLAT-1 and pFOX-1.

RESULTS

MIC and MBC values correlated with the ED(50)s for ceftazidime, cefepime and imipenem. Among the beta-lactams tested, both cefepime and imipenem were effective for treating peritonitis caused by E. coli strains harbouring pLAT-1 or pFOX-1, whereas ceftazidime was effective only against E. coli (pLAT-1). Piperacillin/tazobactam was not effective for treating infections with either of these two strains.

CONCLUSIONS

Piperacillin/tazobactam was not efficacious for treating infections due to E. coli producing plasmid-mediated AmpC-type beta-lactamases, whereas cefepime and imipenem were efficacious.

Effective dose of nefopam in 80% of patients (ED80): a study using the continual reassessment method

AIMS

The effective dose in 50% of patients (ED(50)) is far from being relevant for clinical purposes. We used the continual reassessment method (CRM) to determine the effective dose of nefopam in 80% of the patients suffering from moderate pain in the postoperative period (ED(80)).

METHODS

Patients with a pain intensity >3 on a 1-10 numerical pain score (NPS) received increasing or decreasing doses of nefopam (20, 30, 40, 60, 80 mg) postoperatively. The criterion of success was a NPS <or=3, 30 min after the beginning of infusion. The initial dose was 20 mg and the subsequent doses were determined by the continuous reassessment method (CRM). The data were also fitted a posteriori with the maximum likelihood technique.

RESULTS

Twenty-four patients were enrolled. Nefopam 60 mg gave a probability of success of 0.818 (95% credibility interval 0.606-0.941). Using the maximum likelihood technique, we determined an ED(50) of 27.3 mg and a dose leading to a probability of 0.8 (ED(80)) of 74.4 mg. We did not observe a high incidence of side-effects.

CONCLUSIONS

The ED(80) of nefopam, close to 60 mg is higher than the usual dose of 20 mg. The CRM allowed us to determine the ED(80) of nefopam with reasonable accuracy in a small number of patients as compared with the classical dose-probability curve fitting. We did not observe an increased incidence of side-effects when compared with the literature or to our previous studies.

Renal arterial resistance in septic shock: effects of increasing mean arterial pressure with norepinephrine on the renal resistive index assessed with Doppler ultrasonography

OBJECTIVE

To determine the effects of increasing mean arterial pressure (MAP) on renal resistances assessed by Doppler ultrasonography in septic shock.

DESIGN AND SETTING

Prospective, single-center, nonrandomized, open-label trial in the surgical intensive care unit in a university teaching hospital.

PATIENTS AND PARTICIPANTS

11 patients with septic shock who required fluid resuscitation and norepinephrine to increase and maintain MAP at or above 65 mmHg.

INTERVENTIONS

Norepinephrine was titrated in 11 patients in septic shock during three consecutive not randomized periods of 2 h to achieve a MAP at successively 65, 75, and 85 mmHg.

MEASUREMENTS AND RESULTS

At the end of each period hemodynamic parameters and renal function variables (urinary output, creatinine, clearance) were measured, and Doppler ultrasonography was performed on interlobar arteries to assess the renal resistive index. When increasing MAP from 65 to 75 mmHg, urinary output increased significantly from 76 +/- 64 to 93 +/- 68 ml/h and the resistive index significantly decreased from 0.75 +/- 0.07 to 0.71 +/- 0.06. No difference was found between 75 and 85 mmHg.

CONCLUSIONS

Doppler ultrasonography and resistive index measurements may help determine in each patient the optimal MAP for renal blood flow and may be a relevant end-point to titrate the hemodynamic treatment in septic shock.

The relationship between bispectral index and endtidal concentration of sevoflurane during anesthesia and recovery in spontaneously ventilating children

BACKGROUND

Global inverse correlation between BIS (bispectral index) and depth of anesthesia using sevoflurane has been documented in children in several studies under experimental conditions and in steady-state conditions during mechanically controlled ventilation. Because sevoflurane mask anesthesia combined with a peripheral nerve block is widely used in children, we studied the relationship between BIS and endtidal concentration of sevoflurane (PE(sevo)) under these conditions during surgery and emergence.

METHODS

In this prospective blinded study of 32 children, the relationship between BIS and PE(sevo) was studied during sevoflurane anesthesia via facemask combined with peripheral nerve block. The intraoperative phase was studied during steady-state conditions (fixed PE(sevo)) and the emergence phase was studied during fast alveolar washout (FAW). BIS and PE(sevo) data fitted using the E(max) model. Coefficients of variation of BIS and PE(sevo) during the two periods were compared.

RESULTS

Fit was adequate with the simple E(max) model. Intraoperative variation in BIS was large (28.4%), and larger than at awakening (28.4% vs 8%). At awakening, BIS varied less than PE(sevo) (8% vs 28.5%). No difference was found between children younger and those older than 5 years.

CONCLUSIONS

Caution is required for intraoperative titration based on BIS when spontaneous ventilation is maintained because of the wide variability compared with PE(sevo). During emergence using FAW, BIS varied significantly less than PE(sevo), but the clinical relevance of this point could be discussed during anesthesia without tracheal intubation.

Pharmacokinetic/pharmacodynamic modeling of anesthetics in children: therapeutic implications

Modeling the pharmacokinetics and pharmacodynamics of anesthetics in children is performed as a response to the clinical need for safe and efficacious administration of drugs with a low therapeutic index. Rates and concentrations of these drugs, which are the primary parameters used by anesthesiologists, depend on physiologic parameters that are markedly affected by development. Volatile anesthetics have been used for >50 years in pediatric patients. The pharmacokinetics of inhalation agents are context sensitive, but little difference between age groups has been described. These agents are not only eliminated unchanged by the lung but they are also metabolized by the liver. Halothane has Michaelis-Menten kinetics, with up to 40% of the administered dose metabolized by the liver. For volatile anesthetics, the effect measured is the minimum alveolar concentration (MAC) that leads to movement of the limb in response to skin incision in 50% of the patients studied. The MAC is higher in infants than in children and adults. Infants aged 6 months have a MAC 1.5-1.8 times the MAC observed in adults aged 40 years. Children have a greater clearance and volume of distribution of propofol than adults. In order to achieve similar plasma concentrations, children require three times the initial dose used in adults. In adults, an increased sensitivity to propofol has been demonstrated with aging, but nothing is known about the effects in children. However, it is clear that equipotent doses of propofol induce marked deleterious hemodynamic effects in infants compared with children. Regional anesthesia is used in pediatrics, both in combination with general anesthesia during surgery or alone for postoperative analgesia. A marked decrease in protein binding has been described in infants. In the postoperative period, a rapid increase in binding because of inflammation decreases the free fraction, but the free drug concentration remains constant because of the resulting decrease in total clearance. A low clearance because of liver function immaturity has been observed during the first year(s) of life for bupivacaine and ropivacaine. Pharmacodynamic interactions between general anesthesia and regional anesthesia need to be modeled. This is one of the future tasks for pharmacokineticists. Methods such as the Dixon up-and-down allocation and the isobolographic technique are promising in this field.

Protective effect of prior administration of magnesium on delayed hyperalgesia induced by fentanyl in rats

PURPOSE

Magnesium exerts a physiological block of the ion channel on the N-methyl-D-aspartate receptor, and may therefore prevent the induction of central sensitization. The purpose of this study was to assess whether systemic magnesium can prevent long-lasting hyperalgesia induced by sc fentanyl administration in uninjured rats.

METHODS

Long-lasting hyperalgesia was induced in male Sprague Dawley rats with sc fentanyl (four injections, 60 microg x kg(-1) per injection at 15-min intervals). Magnesium sulphate (100 mg x kg(-1)) was injected ip 30 min prior to the first sc fentanyl injection. Sensitivity to nociceptive stimuli (paw-pressure test) was assessed for several days after injections.

RESULTS

Subcutaneous fentanyl led to delayed hyperalgesia associated with a decrease in the nociceptive threshold lasting two days (35% decrease for the maximum effect). Intraperitoneal magnesium sulphate partially but significantly (P < 0.05) prevented the delayed decrease in the nociceptive threshold following sc administration of fentanyl.

CONCLUSIONS

This study shows that magnesium may prevent the delayed and prolonged hyperalgesia following fentanyl administration in rats.

Changes in cerebral energy metabolites induced by impact-acceleration brain trauma and hypoxic-hypotensive injury in rats

The aim of this study was to describe, in rats, brain energy metabolites changes after different levels of head trauma (T) complicated by hypoxia-hypotension (HH). Male Sprague Dawley rats (n = 7 per groups) were subjected to T by impact-acceleration with 450-g weight drop from 1.50 or 1.80 m (T 1.50 or T 1.80), or to a 15-min period of HH (controlled hemorrhage to mean arterial pressure [MAP] of 40 mm Hg, and mechanical ventilation with N(2) 90%/O(2) 10%), or to their association (T followed by HH). Invasive MAP, intraparenchymental intracranial pressure (ICP), and cerebral blood flow (CBF using Laser Doppler flowmetry) were recorded during the 5 post-traumatic hours. Cerebral microdialysis was used to measure each hour interstitial brain glucose, lactate, pyruvate, and glutamate. For the entire period, the levels of cerebral glucose, pyruvate, and glutamate were not statistically different between groups. In addition, there were no differences associated with the lactate-glucose ratio. Lactate was significantly higher overtime only in T 1.80 + HH group (p < 0.001 vs. every other groups). The lactate-pyruvate ratio increased with trauma level, and was significantly different vs. sham for the entire study period in T 1.50 + HH, in T 1.80, and in T 1.80 + HH. There was no correlation between CBF variations and the lactate-pyruvate ratio (r(2) = 0.00001). The cerebral perfusion pressure was greater than 70 mm Hg in all groups. The prolonged post-traumatic impairment in brain energy metabolism may be related to traumatic brain injury (TBI) severity. It became worse when T was complicated by HH, but was not related to changes in CBF.

The influence of tidal volume on the dynamic variables of fluid responsiveness in critically ill patients

Respiratory-related variabilities in stroke volume and arterial pulse pressure (Delta%Pp) are proposed to predict fluid responsiveness. We investigated the influence of tidal volume (Vt) and adrenergic tone on these variables in mechanically ventilated patients. Cyclic changes in aortic velocity-time integrals (Delta%VTI(Ao), echocardiography) and Delta%Pp (catheter) were measured simultaneously before and after intravascular volume expansion, and Vt was randomly varied below and above its basal value. Intravascular volume expansion was performed by hydroxyethyl starch (100 mL, 60 s). Receiver operating characteristic curves were generated for Delta%VTI(Ao), Delta%Pp and left ventricle cross-sectional end-diastolic area (echocardiography), considering the change in stroke volume after intravascular volume expansion (> or =15%) as the response criterion. Covariance analysis was used to test the influence of Vt on Delta%VTI(Ao) and Delta%Pp. Twenty-one patients were prospectively included; 9 patients (43%) were responders to intravascular volume expansion. Delta%VTI(Ao) and Delta%Pp were higher in responders compared with nonresponders. Predictive values of Delta%VTI(Ao) and Delta%Pp were similar (threshold: 20.4% and 10.0%, respectively) and higher than that of left ventricle cross-sectional end-diastolic area at the appropriate level of Vt. Delta%Pp was slightly correlated with norepinephrine dosage. Delta%Pp increased with the increase in the level of Vt both before and after intravascular volume expansion, contrasting with an unexpected stability of Delta%VTI(Ao). In conclusion, Delta%VTI(Ao) and Delta%Pp are good predictors of intravascular fluid responsiveness but the divergent evolution of these two variables when Vt was increased needs further explanation.

Regression of the systemic vasculature to the lung after removal of pulmonary artery obstruction

RATIONALE

Pulmonary artery occlusion stimulates angiogenesis in the systemic circulation of the ipsilateral lung and increases systemic- to-pulmonary blood flow. Whether this systemic neovascularization decreases after lung revascularization is unknown.

OBJECTIVES

To assess the influence of lung revascularization on anatomy and flow of bronchial vessels supplying a chronically ischemic lung in piglets.

METHODS

Piglets were studied before (control) and 5 wk after left pulmonary artery ligation and 5 wk after left pulmonary artery reimplantation into the pulmonary artery trunk. The systemic blood flow to the right and left lungs was measured using colored microspheres, and the bronchial vasculature was assessed using light-microscopic morphometry. Renal and total blood flow, systemic blood pressure, and pulmonary blood pressure were measured in each experimental condition.

MEASUREMENTS AND MAIN RESULTS

Systemic blood flow to the left lung increased from 0.4 +/- 0.1 to 11.5 +/- 3.8 ml/min/g (p < 0.05) after left pulmonary artery ligation and returned toward the control value (1.2 +/- 0.6 ml/min/g) after revascularization, whereas it remained unchanged in the right lung. The number of bronchial vessels increased twofold in the ligated lung (p = 0.01), and did not decrease after reperfusion; however, vessel diameters decreased markedly. Renal and total blood flows, as well as mean pulmonary and systemic arterial pressures, were similar in the three experimental conditions.

CONCLUSION

Revascularization after a period of left pulmonary artery occlusion normalizes the systemic blood flow to the left lung and induces partial loss of collateral vessels.

A Single Dose of Intrathecal Morphine in Rats Induces Long-Lasting Hyperalgesia: The Protective Effect of Prior Administration of Ketamine

An active pronociceptive process involving N-methyl-D-aspartate (NMDA) receptor activation is initiated by opioid administration, leading to opioid-induced pain sensitivity. Experimental observations in rats have reported reduction of baseline nociceptive threshold after prolonged spinal opioid administration. In this study we sought to determine whether a single dose of intrathecal morphine can induce hyperalgesia in uninjured rats and to assess the effects of pretreatment with the NMDA-antagonist ketamine on nociceptive thresholds. Sensitivity to nociceptive stimuli (paw pressure test) was assessed for several days after an acute intrathecal injection of morphine (5 microg and 10 microg) in male Sprague-Dawley rats. The effects of subcutaneously administered NMDA-receptor antagonist ketamine (10 mg/kg) before intrathecally administered morphine were also evaluated. A single intrathecal injection of morphine led to a biphasic effect on nociception; early analgesia associated with an increase in the nociceptive threshold lasting 3-5 h was followed by delayed hyperalgesia associated with a decrease in the nociceptive threshold lasting 1-2 days. Subcutaneous ketamine did not significantly modify the early analgesic component but almost completely prevented the delayed decrease in nociceptive threshold after intrathecal administration of morphine. A single intrathecal injection of morphine in rats produces a delayed and sustained hyperalgesia linked to the development of opioid-induced pain sensitivity.

Hydrocortisone increases the sensitivity to α1-adrenoceptor stimulation in humans following hemorrhagic shock*

OBJECTIVE

To assess the pressor response to phenylephrine infusion before and after hydrocortisone in severe trauma patients and to correlate this response with their adrenal reserve.

DESIGN

Prospective clinical study.

SETTING

Surgical intensive care unit in a university teaching hospital.

PATIENTS

Twenty-three young trauma patients (Injury Severity Score, 38 +/- 14) were studied at the end of the resuscitative period (27 +/- 15 hrs after trauma).

INTERVENTIONS

Total cortisol response to intravenous corticotropin bolus (250 microg) was obtained. Total cortisol response <9 microg/dL defined an impaired adrenal function and the patient was called a nonresponder. Twelve to 24 hrs following this stimulation, phenylephrine was infused in a stepwise manner to establish the phenylephrine-mean arterial pressure dose-response curve before and after intravenous hydrocortisone administration (50 mg). An Emax model was used to describe the curve; the influence of the group (responder/nonresponder), the sequence (before/after hydrocortisone), and three covariates (Injury Severity Score, shock, and interleukin-6) were thereafter tested.

MEASUREMENTS AND MAIN RESULTS

Forty-three percent of patients were nonresponders. Total cortisol response was not correlated with serum albumin concentration and was negatively correlated with the interleukin-6 concentration. A trend for a higher incidence of nonresponders (53% vs. 36%) and a lesser total cortisol response (7.9 +/- 5.1 vs. 12.5 +/- 5.1 microg/dL) was observed in the shock patients. A phenylephrine dose-response structure (E0, ED50, and Emax) was described without influence of the group and the sequence. However, hydrocortisone induced a 37% decrease in ED50 without change in Emax in the shock patients.

CONCLUSION

An acute administration of hydrocortisone increases the sensitivity to alpha1-adrenoceptor stimulation in fully resuscitated severe trauma patients following hemorrhagic shock. This effect is independent of the adrenal reserve of the patients and different from that previously reported in septic patients.

Median effective dose (ED50) of nefopam and ketoprofen in postoperative patients: a study of interaction using sequential analysis and isobolographic analysis

BACKGROUND

The analgesic efficacy of ketoprofen has been shown after moderate- and severe-pain surgery, and the analgesic efficacy of nefopam has been shown after moderate-pain surgery. The aim of this study was to define the median effective analgesic doses of each drug and to determine whether the interaction of nefopam and of ketoprofen is synergistic.

METHODS

Seventy-two patients scheduled to undergo moderately painful surgery were enrolled in one of three groups. The dose of nefopam and ketoprofen received by a particular patient was determined by the response of the previous patient of the same group, using an up-and-down technique. Initial doses were 18 and 40 mg, with dose adjustment intervals of 2 and 5 mg, in the nefopam and ketoprofen groups, respectively. The initial doses of nefopam and ketoprofen were 8 and 20 mg, respectively, in the nefopam-ketoprofen group, with the same dose adjustment intervals. Analgesic efficacy was defined as a decrease to less than 3 on a 0-10 numeric pain scale, 45 min after the beginning of drug infusion.

RESULTS

The median effective analgesic dose (median value and 95% confidence interval) of nefopam and ketoprofen were, respectively, 28 mg (17-39 mg) and 30 mg (14-46 mg). The median effective analgesic dose of the combination was 1.75 mg (0.9-2.3 mg) for nefopam and 4.3 mg (2.2-6.5 mg) for ketoprofen.

CONCLUSION

The isobolographic analysis demonstrated that the combination of the two drugs produces effective analgesia with an important synergistic interaction.

Paravertebral Block With Ropivacaine 0.5% Versus Systemic Analgesia for Pain Relief After Thoracotomy

PURPOSE

Paravertebral block in combination to intravenous analgesics could be an alternative to epidural analgesia for postoperative pain control after thoracotomy, but it has been scarcely evaluated so far. We thus assessed the efficacy of paravertebral block using a continuous infusion of ropivacaine in a multimodal analgesic approach.

DESCRIPTION

Forty patients were randomized to receive ketoprofen, paracetamol, and patient-controlled-analgesia (PCA) with intravenous morphine (control group) or the same treatment with a continuous 48-hour infusion of ropivacaine 0.5% (0.1 mL/kg(-1)/h(-1)) in a thoracic paravertebral catheter (thoracic paravertebral block [TPVB] group). Visual analog scale (VAS) at rest and when coughing, morphine consumption, and side effects were recorded during the first 48 hours after surgery. Venous blood was sampled at 24 and 48 hours for ropivacaine plasma concentration measurements.

EVALUATION

Mean VAS scores at rest and when coughing were significantly decreased in the TPBV group (p < 0.005). Despite a decrease in the morphine-titrated dose given in the postanesthesia care unit, cumulated morphine consumption was not significantly different between the two groups (51 +/- 29 mg and 57 +/- 24 mg in the TPVB and control groups, respectively). Side effects (nausea, vomiting, urinary retention) were less frequent in the TPBV group (30% vs 75%; p < 0.005). Plasma ropivacaine concentrations remained below the toxic threshold.

CONCLUSIONS

Continuous paravertebral ropivacaine 0.5% infusion improves pain control after thoracic surgery using a multimodal analgesic approach.

Propacetamol and ketoprofen after thyroidectomy

BACKGROUND AND OBJECTIVE

The combination of non-opioid analgesic drugs, though widely used, has been rarely evaluated. The aim of this study was to compare the efficacy of propacetamol and the non-steroidal analgesic drug ketoprofen, alone or in combination, on pain relief after thyroid surgery performed using remifentanil.

METHODS

Ninety-seven patients were randomly allocated to one of the three groups: propacetamol 2 g (32), ketoprofen 100 mg (33) and propacetamol 2 g + ketoprofen 100 mg (32). Each regimen was administered intravenously (i.v.) 30 min before the end of surgery and then every 6 h. If pain was not relieved, patients received an i.v. bolus of tramadol 100 mg. Tramadol consumption and pain intensity using a visual analogue scale was recorded at 1, 2, 8 and 14 h after the end of surgery.

RESULTS

Pain scores were significantly higher with propacetamol compared with ketoprofen 2 h after surgery (35 +/- 3.7, 21 +/- 2.6, respectively; P < 0.01). The number of patients receiving tramadol was higher with propacetamol alone compared with the two other groups, 1 h (14/32, 4/33, 2/32, respectively; P > 0.01) and 2 h (24/32, 6/33, 8/32, respectively; P < 0.01) after surgery. There was no difference between ketoprofen alone and ketoprofen plus propacetamol, and there was no difference between the three groups from the 8th hour onward.

CONCLUSIONS

In the immediate postoperative period after thyroid surgery performed using remifentanil, the concomitant use of propacetamol and ketoprofen does not improve analgesia compared with ketoprofen alone.

Bupivacaine???s Action on the Carrageenan-Induced Inflammatory Response in Mice: Cytokine Production by Leukocytes After Ex-Vivo Stimulation

We aimed to study the effect of bupivacaine on the systemic response elicited by intraplantar injection of carrageenan. To that purpose, we studied the effects of carrageenan, bupivacaine, or both on the production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-10 by whole blood cultured in the presence of lipopolysaccharide (LPS) and of heat-killed Staphylococcus Aureus Cowan (SAC). Mice received a hindpaw injection of carrageenan with or without encapsulated IM bupivacaine given contralaterally. Whole blood was sampled 15 h later and cultured for 24 h with LPS or SAC. The amounts of TNF-alpha, IL-1beta, and IL-10 in the supernatants were measured. In the presence of LPS or SAC, proinflammatory cytokine (TNF-alpha and IL-1beta) production was increased after carrageenan. Bupivacaine prevented this inflammatory response: 992 +/- 102 versus 2146 +/- 338 versus 919 +/- 116 pg/mL for TNF-alpha (bupivacaine + carrageenan versus carrageenan versus control after LPS stimulation). This effect of bupivacaine was less after SAC stimulation. Moreover, IL-10 was not involved in the inhibition of proinflammatory cytokine production observed after treatment by bupivacaine alone. These experiments show that carrageenan-induced hindpaw inflammation modifies the blood cell reactivity to LPS and SAC and that bupivacaine regulates the systemic response elicited by carrageenan. Furthermore, IL-10 does not seem to be a factor of the antiinflammatory response induced by bupivacaine. The precise mechanism underlying this effect of bupivacaine remains to be clarified.

The median effective dose of tramadol and morphine for postoperative patients: a study of interactions

Tramadol is a centrally-acting analgesic drug. In a search of an effective balanced analgesia technique with a morphine-sparing component, we studied the median effective analgesic doses (ED(50)) of tramadol, morphine, and their combination to determine the nature of their interaction using an isobolographic analysis. In this double-blind, randomized, two-stage prospective study, 90 postoperative patients were enrolled in one of three groups. The dose of tramadol and morphine received by a particular patient was determined using an up-down allocation technique. Initial doses and increments were, respectively, 100 mg and 10 mg in the tramadol group and 5 mg and 1 mg in the morphine group. In the second part, a 40:3 tramadol:morphine dosing ratio was used. The threshold of effective analgesia was defined as 3 or less on a numerical pain score (0-10). Isobolographic analysis was subsequently applied. The ED(50) values (95% confidence interval) of tramadol and morphine were, respectively, 86 mg (57-115 mg) and 5.7 mg (4.2-7.2 mg). The ED(50) of the combination was 72 mg (62-82 mg) for tramadol and 5.4 mg (4-6.6.2 mg) for morphine. The combination of tramadol and morphine was infra-additive and thus not recommended for postoperative analgesia.

Effect of Isoproterenol on the Cardiac Troponin I Degradation and Release during Early TNFα-Induced Ventricular Dysfunction in Isolated Rabbit Heart

We studied the consequences of an early phase of TNFalpha-induced LV dysfunction and of its treatment by isoproterenol on an isolated rabbit heart preparation. Two dosages of TNFalpha (2 and 4 microg) were infused, followed by isoproterenol (ISO), infused by increasing concentrations from 10 to 10 M. Left ventricular developed pressure (DP) was recorded. Creatine kinase (CKtot) and cardiac Troponin I (cTnI) were measured in the effluent perfusate. An anatomic score was calculated by histologic examination of the hearts while a structural analysis of cTnI was done. TNFalpha induced a dose-dependent decrease in DP (-43 +/- 18% for 4 microg) without change in coronary vascular resistances, which was not followed by biochemical or structural abnormalities. TNFalpha reduced the maximum effect (Emax) of ISO on DP (mean DeltaDPmaxISO = -40% for 4 microg) without change in the concentration leading to half Emax (ED50ISO). ISO treatment of TNFalpha (4 microg)-induced LV dysfunction resulted in a selective release of cTnI, myocardial tissue contraction bands, and a significant proteolysis of cTnI. Within the limits of the model, the myocardial injury reported during severe sepsis would not be related to an early cytotoxic effect of TNFalpha but could be attributed to an enhancement of the effects of isoproterenol by TNFalpha.

Effect of Bupivacaine on the Isolated Rabbit Heart

Background

Newborns and infants seem to be at greater risk of bupivacaine cardiotoxicity than adults do. Few experiments have studied the effects of local anesthetics on myocardium associated with developmental changes, and their conclusions are conflicting. The authors compared the effects of bupivacaine on an isolated heart preparation in newborn and adult rabbits.

Methods

The authors used a constant-flow, nonrecirculating Langendorff preparation paced atrially. Adult and newborn rabbit hearts were exposed to step-increasing concentrations of bupivacaine. For each concentration, heart rate was modified with pacing from 180 to 360 beats/min by increments of 30 beats/min. QRS complex duration (index of ventricular conduction) and the first derivative of left ventricular pressure (index of contractility) were measured. The two groups were compared using an Emax model.

Results

In newborn and adult rabbits, QRS complex duration increased with increasing bupivacaine concentration. No difference was observed between neonatal and adult hearts. Contractility decreased with increasing bupivacaine concentration. Newborn rabbits were approximately three times more sensitive than adult rabbits to the effects of bupivacaine. However, the concentration leading to 50% decrease in the first derivative of left ventricular pressure was much higher than the concentration leading to half maximum increase in QRS complex duration.

Conclusions

In conclusion, using a whole organ preparation, the authors demonstrated that bupivacaine induces similar impairment in ventricular conduction in newborn and adult rabbits. In particular, the tonic and the phasic blocks were of similar intensity in both groups. Conversely, the effect of bupivacaine on contractility was markedly higher in newborn rabbits than in adult rabbits. Also, contractility was less impaired than ventricular conduction in both groups.

The Median Effective Dose of Nefopam and Morphine Administered Intravenously for Postoperative Pain After Minor Surgery: A Prospective Randomized Double-Blinded Isobolographic Study of Their Analgesic Action

The aim of this study was to characterize the nature of analgesic interaction between nefopam and morphine administered i.v. for postoperative pain after minor surgery. To do so, we defined the median effective analgesic dose (ED(50)) for each drug and also the median ED(50) of their combination and compared them using the isobolographic method. Determination of median effective doses was performed by the up-and-down sequential drug administration in a two-stage study. First, in a prospective, randomized, double-blinded study, we enrolled 60 patients with mild to moderate pain after minor surgery; this was followed by an open study enrolling 30 patients. The end-point was a pain score less than 3 on a Numerical Pain Scale (0-10). Initial doses were 16 mg in group N, 5 mg in group M, and 7.5 mg of N combined with 2.5 mg of M in group N+M. The testing interval was 2 mg in group N, 1 mg in group M, and 1.5 mg of N combined with 0.5 mg of M in group N+M. ED(50) (95% confidence interval) was 5 mg (4-6 mg) for morphine, 18 mg (16-18 mg) for nefopam, and 4 mg (3.5-4.5 mg) with 12 mg (10.5-13.5 mg) for the combination of morphine and nefopam administered at a 3:1 dose ratio. Isobolographic analysis demonstrated a significant infra-additive interaction. The incidence of side effects did not differ significantly among morphine, nefopam, and their combination. These findings suggest that the combination of nefopam and morphine does not offer any advantage compared to each drug administered i.v. or alone after minor surgery. This study is the first to define the ED(50) of nefopam and morphine in postoperative patients. In conclusion, the addition of nefopam has a morphine-sparing effect, but the combination is infra-additive.

IMPLICATIONS

Pharmacologic interaction between nefopam and morphine shows infra-additivity but their combination may be clinically useful as morphine consumption is decreased in postoperative patients.

Pharmacokinetics of Local Anaesthetics in Infants and Children

Amide local anaesthetics used for regional anaesthesia in paediatric patients are potent sodium channel blockers with marked stereospecificity, which consistently influences their action, especially their toxic action on the heart. At toxic concentrations, they induce severe arrhythmias with the potential for cardiac arrest. These agents are all bound to serum proteins, mainly to alpha(1)-acid glycoprotein (AAG), but also to human serum albumin. Protein binding ranges from 65% (lidocaine) to more than 95% (bupivacaine, ropivacaine). Because AAG is a major acute phase protein, its concentration rapidly increases when inflammatory processes develop, particularly during the postoperative period. Neonates and infants have a lower AAG concentration in serum as compared with adults; therefore, their free fraction of local anaesthetics is increased accordingly. This has important clinical implications since, at least at steady state, the toxic effects of local anaesthetics are directly related to the free (unbound) drug concentration. After injection into the epidural space, absorption into the bloodstream follows a biphasic process. The buffering properties of the epidural space are important and prevent a rapid rise in concentration. In infants and children, the epidural space seems to protect patients in a similar manner. Moreover, it has been observed that the peak plasma concentration (C(max)) of ropivacaine is delayed in infants and children when compared with adults. The time to C(max) decreases from 90-120 minutes in infants aged less than 6 months to 30 minutes in children aged more than 8 years. This delay in C(max) may also be related to the lower clearance observed in younger patients. Local anaesthetics are metabolised by cytochrome P450 (CYP). The main CYP isoforms involved are CYP3A4 for lidocaine and bupivacaine and CYP1A2 for ropivacaine. CYP3A4 is not mature at birth but is partly replaced by CYP3A7. The intrinsic clearance of bupivacaine is only one-third of that in adults at 1 month of age, and two-thirds at 6 months. CYP1A2 is not fully mature before the age of 3 years. Indeed, the clearance of ropivacaine does not reach its maximum before the age of 5 years. However, at birth this clearance is not as low as expected, and ropivacaine may be used even in younger patients.

Propofol and remifentanil for intubation without muscle relaxant: the effect of the order of injection

BACKGROUND

Common practice in intubation without muscle relaxant is to inject the opioid drug prior to the hypnotic drug. Because remifentanil reaches adequate cerebral concentration more rapidly than does propofol, we tested the hypothesis that injection of remifentanil after propofol might lead to better intubating conditions.

METHODS

Thirty ASA I-II patients scheduled for elective surgery and with no anticipated difficult intubation were enrolled in the study. Five minutes after midazolam 30 microg kg(-1), patients were randomized into two groups: group PR received propofol 2.5 mg kg(-1) followed by remifentanil 1 microg kg(-1), and group RP received remifentanil 1 microg kg(-1) followed by propofol 2.5 mg kg(-1). Intubating conditions were compared using a well-validated score, and continuous arterial pressure was recorded non-invasively.

RESULTS

Compared with group RP, intubating conditions were significantly better in group PR. The mean arterial pressure decrease was more pronounced in group RP.

CONCLUSIONS

We therefore conclude that in premedicated healthy patients with no anticipated risk of difficult intubation, intubating and haemodynamic conditions are better when remifentanil is injected after propofol.

Efficacy of augmentation of epidural analgesia for Caesarean section

BACKGROUND

Extension of a labour epidural for Caesarean delivery is thought to be successful in most cases and avoids the use of general anaesthesia. However, most previous studies that have estimated the failure rate of pre-existing epidural catheters were performed in small numbers of patients.

METHODS

Therefore, we undertook to retrospectively measure the failure rate of indwelling epidural catheters in a large number of patients.

RESULTS

The anaesthetic team was available at all times and was permanently led by a senior anaesthetist specialized in obstetrics. Extension was performed using lidocaine 2% with epinephrine (mean 18 (SD 6) ml), combined in most patients with sufentanil (9 (2.2) microg) and/or clonidine (75 microg). Among 194 consecutive extensions performed in a 1-yr period, general anaesthesia was required in five patients (2.6%) while sedation and/or i.v. analgesia were used in 27 patients (13.9%). In three cases where general anaesthesia was required, the interval between decision to incision was <10 min. No factor associated with failure could be identified. Addition of a lipophilic opioid or of clonidine did not modify the efficacy of the block (i.e. general anaesthesia or supplementation were required in a similar proportion).

CONCLUSIONS

The augmentation of labour epidurals for Caesarean section using lidocaine 2% plus epinephrine is a reliable and effective technique. No factor associated with failure could be identified.

Ropivacaine in infants and children

PURPOSE OF REVIEW

Ropivacaine is considered less toxic than bupivacaine. In addition, at the low concentrations used for providing postoperative analgesia, ropivacaine seems to produce less motor blockade than bupivacaine. These two properties are of particular interest in paediatric practice.

RECENT FINDINGS

In paediatric practice regional anaesthesia is usually performed under general anaesthesia, and postoperative analgesia was until recently the major concern for most practitioners. The question now is: what is the right concentration to provide adequate intraoperative anaesthesia when ropivacaine is used in combination with volatile anaesthetic agents? The low concentration of ropivacaine used for postoperative analgesia seems to provide adequate intraoperative anaesthesia when general anaesthesia with a 0.5 minimum concentration of volatile anaesthetic is used in combination. However, potential toxicity is still the subject of debate because ropivacaine clearance is low in infancy and early childhood. Ropivacaine has a longer absorption process than bupivacaine, which leads to a lower maximum peak concentration with ropivacaine than with bupivacaine either after central or peripheral blocks, thus increasing the safety of the drug. The addition of adjuvant drugs also permits lower concentrations of ropivacaine, while providing excellent analgesia. The addition of adrenaline at very low concentrations has recently been found to increase the quality of epidural analgesia.

SUMMARY

Ropivacaine is now the reference drug for regional anaesthesia in paediatric patients, mainly because it is considered less toxic than bupivacaine and provides excellent postoperative analgesia even when used at low concentrations.

Usefulness of combined quantitative assessment of myocardial perfusion and velocities by myocardial contrast and doppler tissue echocardiography during coronary blood flow reduction

OBJECTIVES

We sought to characterize regional myocardial perfusion and contraction in a closed-chest swine model during and after coronary blood flow reduction using myocardial contrast and Doppler tissue echocardiography.

METHODS AND RESULTS

Regional myocardial perfusion was assessed by myocardial contrast echocardiography using the corrected contrast peak intensity (baseline-subtracted contrast peak intensity), the peak intensity ratio (contrast peak intensity in ischemic/control wall), and a transmural video-intensity gradient. Regional peak systolic velocities and strain rate were measured using M-mode color Doppler tissue echocardiography. In 12 pigs, coronary blood flow reduction resulted in a significant decrease in peak intensity ratio and in peak systolic velocities in the subendocardium. At baseline and during ischemia, corrected contrast peak intensity and peak systolic velocities in the subendocardium, video-intensity gradient, and strain rate were closely related (r = 0.88 and 0.93, respectively). After reperfusion, in contrast to peak systolic strain rate that remained altered, the peak intensity ratio and video-intensity gradient recovered nearly baseline values.

CONCLUSION

The combination of myocardial contrast and Doppler tissue echocardiography may distinguish between ischemic and postischemic myocardial wall dysfunction during severe coronary blood flow reduction.