Intravenous anesthesia and analgesia: What is the role of target-controlled infusion?☆

Extracorporeal circulation (ECC) may change drug pharmacokinetics as well as brain function. The objectives of this study are to compare emergence time and postoperative sedation intensity assessed by the bispectral index (BIS) and the Ramsay sedation scale in patients undergoing myocardial revascularization (MR) with or without ECC.

Ten patients undergoing MR with ECC (ECC group) and 10 with no ECC (no-ECC group) were administered with sufentanyl, propofol 2.0 μg.mL⁻¹ and pancuronium target controlled infusion. After surgery, propofol infusion was reduced to 1 μg.mL⁻¹ and suspended when extubation was indicated. Patients BIS, Ramsay scale and time to wake up were assessed.

The ECC group showed lower BIS values beginning at 60 minutes after surgery (no-ECC = 66 ± 13 and ECC = 53 ± 14, p = 0.01) until 120 minutes after infusion (no-ECC = 85 ± 8 and ECC = 73 ± 12, p = 0.02). Sedation level measured by the Ramsay scale was higher in the ECC group at 30 minutes after the end of the surgery (no-ECC = 5 ± 1 and ECC = 6 ± 0, p = 0.021), at the end of infusion (no-ECC = 5 ± 1 and ECC = 6 ± 1, p = 0.012) and 5 minutes after the end of infusion (no-ECC = 4 ± 1 and ECC = 5 ± 0.42, p = 0.039). Emergence from anesthesia time was higher in the ECC group (no-ECC = 217 ± 81 and ECC = 319 ± 118, p = 0.038).

There was a higher intensity of sedation after the end of surgery and a longer wake up time in ECC group, suggesting changes in the pharmacokinetics of propofol or effects of ECC on central nervous system.

A circulação extracorpórea (CEC) pode alterar a farmacocinética dos fármacos, assim como a função cerebral. Os objetivos deste estudo foram comparar o tempo de despertar e a intensidade da sedação pós-operatória avaliada pelo índice bispectral (BIS) e pela escala de sedação de Ramsay, em pacientes submetidos à revascularização miocárdica (RM) com ou sem CEC.

Dez pacientes submetidos à RM com CEC (Grupo CEC) e 10 sem CEC (Grupo sem CEC) foram anestesiados com sufentanil, infusão alvo-controlada de propofol 2,0 μg.mL⁻¹ e pancuronio. Após a cirurgia diminuiu-se a infusão de propofol para 1 μg.mL⁻¹ que foi suspensa quando da indicação da extubação. Foram avaliados o BIS, a escala de Ramsay e o tempo de despertar dos pacientes.

O grupo CEC apresentou valores menores de BIS desde 60 minutos após a cirurgia (sem CEC = 66 ± 13 e CEC = 53 ± 14, p = 0,01) até 120 minutos após a infusão (sem CEC = 85 ± 8 e CEC = 73 ± 12, p = 0,02). O nível de sedação pela escala de Ramsay foi maior no grupo CEC nos momentos 30 minutos após o final da cirurgia (sem CEC = 5 ± 1 e CEC = 6 ± 0, p = 0,021), no final da infusão (sem CEC = 5 ± 1 e CEC = 6 ± 1, p = 0,012) e 5 minutos após o final da infusão (sem CEC = 4 ± 1 e CEC = 5 ± 0,42, p = 0,039). O tempo de despertar foi maior no grupo CEC (sem CEC = 217 ± 81 e CEC = 319 ± 118, p = 0,038).

Houve maior intensidade da sedação após o final da cirurgia e o maior tempo de despertar no grupo com CEC, sugerindo alteração na farmacocinética do propofol ou efeitos da CEC sobre o sistema nervoso central.

La circulación extracorpórea (CEC), puede alterar la farmacocinética de los fármacos, como también la función cerebral. Los objetivos de este estudio, fueron comparar el tiempo de despertar y la intensidad de la sedación postoperatoria evaluada por el índice bispectral (BIS) y por la escala de sedación de Ramsay, en pacientes sometidos a la revascularización miocárdica (RM) con o sin CEC.

Diez pacientes sometidos a la RM con CEC (Grupo CEC) y 10 sin CEC (Grupo sin CEC), fueron anestesiados con sufentanil, infusión objeto-controlada de propofol 2,0 μg.mL y pancuronio. Después de la operación se redujo la infusión de propofol para 1 μg.mL que se suspendió cuando se indicó la desentubación. Se evaluaron el BIS, la escala de Ramsay y el tiempo de despertar de los pacientes.

El grupo CEC presentó valores menores de BIS desde 60 minutos después de la cirugía (sin CEC = 66 ± 13 y CEC = 53 ± 14, p = 0,01) hasta 120 minutos después de la infusión (sin CEC = 85 ± 8 y CEC = 73 ± 12, p = 0,02). El nivel de sedación por la escala de Ramsay fue mayor en el grupo CEC en los momentos 30 minutos después del final de la cirugía (sin CEC = 5 ± 1 y CEC = 6 ± 0, p = 0,021), al final de la infusión (sin CEC = 5 ± 1 y CEC = 6 ± 1, p = 0,012) y 5 minutos después del final de la infusión (sin CEC = 4 ± 1 y CEC = 5 ± 0,42, p = 0,039). El tiempo de despertar fue mayor en el grupo CEC (sin CEC = 217 ± 81 y CEC = 319 ± 118, p = 0,038).

Houve maior intensidade da sedação após o final da cirurgia e o maior tempo de despertar no grupo com CEC, sugerindo alteração na farmacocinética do propofol ou efeitos da CEC sobre o sistema nervoso central.

A thorough and efficient pre-procedure evaluation of the patient's readiness to undergo sedation for endoscopy is essential. This evaluation will allow the formulation of an appropriate sedation plan for the patient, resulting in a safe and effective examination. The post procedure assessment of the patient confirms readiness for discharge and allows for appropriate patient education and follow-up planning.

Total intravenous anaesthesia (TIVA) has several potential advantages: (i) each component of anaesthesia can be regulated independently and adapted to changes in the stimulus during surgery, (ii) lack of pollution, (iii) ease of use in ‘remote locations’, (iv) quality of recovery. The main drawback of TIVA is that it is difficult to use. Target-controlled infusion (TCI) is a new technique for the administration of intravenous agents based on real-time pharmacokinetic and pharmacodynamics simulations. Its aim is to control and maintain a steady therapeutic level of drugs with a narrow margin of safety. TCI is intended to be similar to the vaporizer of volatile anaesthetics. TCI has been used for more than 15 years for research purposes but the recent availability of a marketed system dedicated to propofol (Diprifusor) is a landmark in the dissemination of the technique. TCI can be used with other hypnotic drugs (midazolam, ketamine, etomidate) and also with opioids. Sedation and post-operative analgesia are also indications for TCI administration. TCI makes it possible to apply more easily certain tedious pharmacokinetic and pharmacodynamic concepts at the bedside at a low cost with potential clinical benefits for the patient. Clinical studies have demonstrated that TCI is as safe as manual infusion techniques but is preferred by anaesthesiologists because it reduces the workload. The main limit of this method at the present time is the large interindividual pharmacokinetic and pharmacodynamic variability and the lack of marketed systems for opioids. Population pharmacokinetics, effect compartment control and even closed-loop systems or Bayesian forecasting are possible directions for future improvements.