Adaptive pharmacokinetic and pharmacodynamic modelling to predict propofol effect using BIS-guided anesthesia.

BACKGROUND AND OBJECTIVE: Propofol is widely used for hypnosis induction and maintenance of general anesthesia. Its effect can be assessed using the bispectral index (BIS). Many automatic infusion systems are based in pharmacokinetics (PK) and pharmacodynamics (PD) models to predict the response of the patient to the drug. However, all these models do not take into account intra and inter-patient variability. An adjusted intraoperative drug administration allows faster recovery and provides post-operative side-effect mitigation METHODS: BIS evolution and surgery-recorded propofol infusion data of a group of 60 adult patients (30 males/30 females) with ASA I/II physical status were used to test a real time PK/PD compartmental model. This new algorithm tunes three model parameters (ce50, γ and ke0), minimizing a performance function online. RESULTS: The error in the BIS signal predicted by the real time PK/PD model was smaller than the error measured with fixed parameter equations. This model shows that ce50, γ and ke0 change with time and patients, given a mean (95% confidence interval) of 3.89 (3.52-4.26)mg/l, 4.63 (4.13-5.13) and 0.36 (0.31-0.4)min(-1), respectively. CONCLUSIONS: The real time PK/PD model proposed provides a closer description of the patient real state at each sample time. This allows for greater control of the drug infusion, and thus the quantity of drug administered can be titrated to achieve the desired effect for the desired duration, and reduce unnecessary waste or post-operative effects.

[General anesthesia with remifentanil in two cases of emergency cesarean section]. / Anestesia general con remifentanilo en dos casos de cesárea urgente.

Remifentanil is a synthetic opiate with evident advantages for various anesthetic techniques, enhancing quality of anesthesia. Indications are increasingly well-defined. Remifentanil may be used in obstetric analgesia-anesthesia thanks to advantages demonstrated in patients with heart disease (cardiac and non-cardiac anesthesia) and in those requiring neuroanesthesia. Remifentanil is known to cross the placenta rapidly and to be rapidly metabolized and redistributed to both mother and fetus. Based on this, and on pharmacokinetic and pharmacodynamic studies in children, we judged remifentanil to be indicated for use in two patients undergoing emergency cesarean section, for whom hemodynamic stability and immediate postoperative assessment were basic requirements. The first case involved a woman 40 weeks pregnant with a history of mitral valve prolapse and an episode of acute pulmonary edema in the 28th week, who presented with ruptured membrane and the fetus in sacroposterior breech presentation without subsequent progression of labor. The second involved a woman 40-weeks pregnant with a diagnosis of Hunt-Hess grade II subarachnoid hemorrhage who had gone into labor. Outcome was satisfactory in both cases, with no complications potentially affecting the status of either mother or child. No infant respiratory insufficiency occurred and Apgar scores were favorable. We consider remifentanil to be safe and effective for general anesthesia for emergency cesarean delivery in patients with cardiac and/or neurological risk factors.

Anestesia general con remifentanilo en dos casos de cesárea urgente / General anesthesia with remifentanil in two cases of emergency cesarean section

El remifentanilo es un opiáceo sintético que aporta ventajas evidentes como componente de distintas técnicas anestésicas y permite, así, una mayor calidad anestésica, quedando cada vez más definidas sus indicaciones. En el campo de la analgesia-anestesia obstétrica puede tener sus aplicaciones, merced a sus ventajas ya demostradas en el tratamiento de pacientes cardiópatas (anestesia cardíaca y no cardíaca) y en la neuroanestesia. Desde el conocimiento de la rápida transferencia placentaria, la rápida metabolización y la redistribución del fármaco, tanto por la madre como por el feto, así como de su farmacocinética y farmacodinámica en niños, nos pareció indicada su utilización en 2 casos de cesárea urgente donde la estabilidad hemodinámica y la valoración postoperatoria inmediata eran fundamentales. El primer caso era una gestante de 40 semanas con antecedente de prolapso de la válvula mitral y episodio de edema agudo de pulmón en la semana 28, en que se evidenció bolsa rota, presentación podálica y posterior parto no evolutivo. El segundo caso era una gestante de 40 semanas con diagnóstico de hemorragia subaracnoidea de grado II de Hunt-Hess, que inició trabajo de parto. En los 2 casos conseguimos los objetivos propuestos sin complicaciones que pudieran afectar al estado de la madre y del recién nacido. No hubo depresión respiratoria en los recién nacidos, con puntuaciones del Apgar favorables. Consideramos el remifentanilo como un fármaco seguro y eficaz para las pacientes obstétricas con compromiso cardiológico y/o neurológico que se someten a anestesia general para la cesárea urgente (AU)

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[Ketamine]. / Ketamina.

Ketamine is an intravenous drug with special properties that make it the only agent that presently serves as anesthetic, sedative, amnesiac and analgesic. Although it is sometimes forgotten, ketamine is still considered a viable drug. Water soluble, stable and non-irritant when administered intravenously, ketamine has rapid onset after intravenous injection and provides acceptable anesthesia when administered in continuous infusion. There properties make ketamine useful for total intravenous anesthesia. Both propofol and midazolam are effective in reducing ketamine's adverse side effects. Administered in children by oral, nasal, rectal and intramuscular routes, ketamine allows for gentle anesthetic induction. It can also serve as an adjuvant in regional anesthesia to supplement analgesia. In adults ketamine is most often used for major surgery, particularly in the elderly or in high risk patients who are in shock, severely dehydrated or hemodynamically unstable, or in obstetric patients with hypovolemia or hemorrhage. It is probably the anesthetic of choice for patients with hyperreactive airways. Ketamine's strong analgesic effect at subanesthetic doses allows it to be used as an analgesic during postoperative intensive care or as an analgesic-plus-sedative for patients receiving mechanical ventilation. Interest in using ketamine at low doses for cancer and non-cancer patients with chronic pain has grown recently.

[Patient with tricuspid atresia undergoing orthopedic surgery: anesthetic considerations]. / Paciente con atresia tricúspide para cirugía ortopédica: cuidados anestésicos.

We describe a 52-year-old patient with rheumatoid arthritis, interventricular communication and pulmonary stenosis. After an accidental fall she was scheduled for total hip replacement. The main objective of anesthetic management was to preserve pulmonary blood circulation at arterial pressures that would assure adequate tissue perfusion. Other objectives were to maintain hydration to prevent decreases in hematocrit levels, avoid systemic embolization and allow for antibiotic prophylaxis.