Efecto del fentanilo intratecal en hiperlagesia secundaria posoperatoria de cirugía ligamento cruzado anterior de rodilla / Effect of Intrathecal fentanyl on secondary hyperalgesia, in patients undergoing anterior cruciate ligament repair

BACKGROUND AND OBJECTIVES: Fentanyl addition is a common practice when administering spinal anesthesia. Intrathecal fentanyl has been associated to increased postoperative pain and increase morphine consumption, but considered to be related to acute opioid tolerance. This prospective, randomized, blind study evaluates the effect of intrathecal fentanyl in the development of secondary hyperalgesia, measured with Von Frey filaments, in patients undergoing anterior cruciate ligament repair. METHODS: 46 patients having anterior cruciate ligament repair, received intrathecal hyperbaric bupivacaine 13.5 mg with fentanyl 20 mcg or no fentanyl addition. Light touch pain threshold was measured with von Frey filaments before anesthesia, at 6 and 24 hours post anesthesia in the non-operated thigh and in the forearm. Visual analogue pain scores and morphine consumption were also measured at the same time. RESULTS: Baseline thresholds to mechanical stimuli were similar in both groups. In the forearm, analysis showed a decreased threshold for the non-fentanyl group at 24 h p = 0.036. In the lower extremity, control and treatment group showed lower thresholds (secondary hyperalgesia) p = 0.002 but no difference between them p = 0.795. VAS score and morphine consumption did not differ among groups. CONCLUSIONS: Spinal fentanyl added to hyperbaric bupivacaine showed no evidence of an augmented state of hyperalgesia after ACL repair, neither by pain threshold modification nor clinical outcomes. On the contrary, at 24 h, fentanyl may have a protective effect at levels above the spinal block.

ANTECEDENTES Y OBJETIVOS: El uso de fentanilo es una práctica común en la administración de anestesia espinal. Su aplicación se ha asociado a un aumento del dolor post operatorio y a un aumento en el uso de morfina; por otro lado, se ha vinculado a una tolerancia aguda a opioides. El siguiente estudio prospectivo, randomizado y ciego, evalúa los efectos del fentanilo intratecal en la aparición de hiperalgesia secundaria, medida a través de filamentos Von Frey, en pacientes operados de ligamento cruzado anterior. METODOLOGÍA: Se incluyeron a 46 pacientes operados de ligamento cruzado anterior (LCA) con una dosis intratecal de bupivacaína hiperbárica de 13,5 mg; con y sin la adición de fentanilo de 20 mcg. Se midió el umbral del dolor mecánico, a través de filamentos Von Frey, antes de la anestesia, a las 6 y 24 horas postanestesia en el muslo no operado y en el antebrazo. Al mismo tiempo, se midió la puntuación del dolor en la escala verbal numérica (EVN) y el consumo de morfina. RESULTADOS: Los umbrales basales ante la estimulación mecánica resultaron similares en ambos grupos. En el antebrazo, el análisis mostró una disminución del umbral en el grupo de pacientes sin fentanilo, a las 24 h, p = 0,036 comparado con uso de fentanilo. En el muslo, el grupo control y tratamiento mostró umbrales más bajos (hiperalgesia secundaria) p = 0,002; no obstante, no se mostraron diferencias entre ellos. No se mostraron diferencias entre las puntuaciones de la EVN y el consumo de morfina en los dos grupos. CONCLUSIÓN: No hay evidencia que la adición de fentanilo espinal, a la dosis de bupivacaína hiperbárica, haya contribuido a un aumento en la hiperalgesia tras la reparación del LCA, medido por la modificación del umbral del dolor, ni en los resultados clínicos. Al contrario a las 24 h fentanilo puede tener un efecto protector de la hiperalgesia secundaria sobre el nivel del bloqueo espinal.

Intra-operative lidocaine in the prevention of vomiting after elective tonsillectomy in children: A randomised controlled trial.

BACKGROUND: Postoperative vomiting (POV) is a frequent complication of tonsillectomy in children. In adult patients undergoing abdominal surgeries, the use of intravenous lidocaine infusion can prevent POV. OBJECTIVE: To evaluate the anti-emetic effect of an intravenous lidocaine infusion used as an adjuvant to general anaesthesia, in children undergoing elective ear, nose and throat surgery. DESIGN: Double-blind, randomised, controlled study. SETTING: Hospital-based, single-centre study in Chile. PATIENTS: ASA I-II children, aged 2 to 12 years, scheduled for elective tonsillectomy. INTERVENTION: We standardised the induction and maintenance of anaesthesia. Patients were randomly allocated to lidocaine (1.5 mg kg intravenous lidocaine over 5 min followed by 2 mg kg h) or 0.9% saline (at the same rate and volume). Infusions were continued until the end of the surgery. MAIN OUTCOME MEASURES: Presence of at least one episode of vomiting, retching or both in the first 24 h postoperatively (POV). SECONDARY OUTCOMES: Plasma concentrations of lidocaine and postoperative pain. RESULTS: Ninety-two children were enrolled. Primary outcome data were available for 91. In the Lidocaine group, 28 of 46 patients (60.8%) experienced POV, compared with 37 of 45 patients (82.2%) in the Saline group [difference in proportions 21.3% (95% confidence interval (CI) 2.8 to 38.8), P = 0.024]. The intention-to-treat analysis showed that when we assumed that the patient in the Saline group lost to follow-up did not have POV, the difference in proportions decreased to 19.6% (95% CI, 0.9 to 37.2), with an unadjusted odds ratio of 0.38 (95% CI, 0.15 to 0.97, P = 0.044). The odds of having POV were 62% less likely in those patients receiving lidocaine compared with patients in the Saline group. The mean lidocaine plasma concentration was 3.91 µg ml (range: 0.87 to 4.88). CONCLUSION: Using an intravenous lidocaine infusion as an adjuvant to general anaesthesia decreased POV in children undergoing elective tonsillectomy. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01986309.

Dexmedetomidine pharmacokinetics in the obese.

PURPOSE: This study aims to characterize the influence of body weight and composition on the pharmacokinetics of dexmedetomidine. METHODS: Twenty obese patients and 20 non-obese patients scheduled for elective laparoscopic surgery were given dexmedetomidine infusion schemes. Venous blood samples were taken during and after dexmedetomidine administration. Population pharmacokinetic modeling was undertaken to investigate fat free mass (FFM) and normal fat mass (NFM) as size descriptors of volumes and clearances using non-linear mixed effects modeling. NFM partitions total body weight into FFM and fat mass calculated from total body weight (TBW) minus FFM. The relative influence of fat mass compared to FFM is described by the fraction of fat mass that makes fat equivalent to FFM (Ffat). RESULTS: Theory-based allometric scaling using FFM best described weight and body composition differences in clearances and volumes A negative effect of fat mass of with an exponential parameter of -0.00541/kg (95 % CI -0.0118 to -0.00246) was estimated for clearance which indicates increased fat mass is associated with impairment of clearance. CONCLUSIONS: The use of theory-based allometry with predictions of fat free mass has been able to separate the influences of weight and body composition and indicates that size-normalized clearance of dexmedetomidine is impaired in patients who are obese.