A New Approach For Induction Anaesthesia With Propofol Target Controlled And Remifentanil. We Need Bolus Dosis Of Remifentanil?

Fernando Squeff Nora, Brazil

Introduction

A good control of haemodynamic responses after intubation is a very important characteristics of opioids during induction of anaesthesia. This task depends on onset of opioid that has been used. The time of onset depends on Ke0 of each opioid and how opioid is administered. Remifentanil and alfentanil are the faster onset of the opioids in clinical practice, but the incidence of bradicardia, hypotension and rigid chest are the main problems with them. To minimize this problems we administered this drugs slowly. Many papers have been writing about remifentanil in bolus doses through induction of anesthesia in 60 or 90 seconds. When we used the old drugs as fentanil that has a long onset of action, bolus doses is an important approach, but with drugs as remifentanil this is not necessary When we administered the drug with pump infusion with rates about 0,3mcg/kg/min, the results will be the same in regard doses administered at the same time. The objective of this study was compare two different ways for induction intravenous anaesthesia with infusion of remifentanil without bolus doses.

Methods:

Patients were randomized in two groups in an open clinic study. All patients were schedule for ambulatory surgeries. No premedication was used. Intravenous anaesthesia had used with propofol PFS in target controlled infusion system and remifentanil in manual pump infusion system. All patients received neuromuscular block agents after loss of consciousness. Rocurônio-0,6mg/kg has been taken. After PNI, ECG and Sp02 monitorization a venous had taken for liquid and anaesthesia infusion. All patients received propofol target controlled to start in 4mcg/ml. In Group I (n=16) remifentanil was started 2 min. before induction of anaesthesia with propofol. In Group II(n=14) remifentanil and propofol was administered together when we are starting induction of anaesthesia. Rocurônio was administered when patient loose consciousness. When the effect site concentration of propofol was 2,7mcg/kg we did the intubation. We had measured PAS, PAS, PAD, HR and effect site concentration of propofol and remifentanil in 4 times. Basal(T1), 2min. after start remifentnail infusion(GroupI) and 2 min a later start propofol and remifentanil infusions(GroupII)(T2), loss of verbal response(T3), and after intubation(T4). For propofol we measured effect site concentration on the pump and with remifentanil we obtain this value with simulation using Minto model described in TIVATRAINER software. The protection during induction anaesthesia was compared in both groups.  

Results

Demographic datas were similar in both groups(table1). When we compared both groups the PAS,PAD, PAM and HR after and before intubation were not different results in protection of intubation reflex and this were very good in both(table II). The median of effect site concentration of remifentanil in group I was 5,27ng/ml and in group II was 6,31ng/ml during T4(tableIII). After loss of verbal response the hemodynamic datas were not statistical differences.The median of effect site concentration of propofol and remifentanil in group I in T3 were 1,4mcg/ml and 4,35ng/ml respectively(tableIII) . The median of effect site concentration of propofol and remifentanil in group II in T3 were 1,68mcg/ml e 3,15ng/ml respectively(tableIII). Loss of verbal response in group I has occurred with median effect site concentration of propofol lower than group II(1,43 x 168). We did not have any problems as hypotension, rigid chest and bradicardia in both groups.

Discussion

During intravenous anaesthesia with propofol target controlled and remifentanil in pump infusion we automatically are doing a bolus dosis of remifentanil because we must wait the plasmatic concentration of propofol start to equilibrate with effect site concentration. Because this we have been postulating the infusion of remifentanil in the same time that we start propofol infusion and not previously. Minor median effect site concentration of propofol for loss of verbal response in group I is good approach to prevent hypotension and probably was possible because the synergistic effect with remifentanil has occurred. Bolus dosis of remifentanil can cause hypotension, rigid chest and bradicardia, because is difficult do it slow(90 or 120 seconds) without pump infusion. The protection against intubation reflex was good in both groups.                

Table I

                    MALE     FEMALE     Total

        GROUP 1     4(13%)     12(40%)      16(53%)

        GROUP 2     2 (7%)      12  ( 40%)   14(47%)

Fisher's Exact Test                      

P value is 0.6567, not significant.

Relative risk = 1.750

95% Confidence Interval: 0.3756 to 8.153

                           ASA I        ASA II      Total

        GROUP 1    9(30%)     7 (23%)       16( 53%)

        GROUP 2    8 (27%)    6 (20%)       14(47%)

Fisher's Exact Test                      

P value is not significant.

Relative risk = 0.9844

95% Confidence Interval: 0.5260 to 1.842

Table II: Median e Dp

GII                                                                GI

Table III. Median and Dp

                         GI                                                                   GII

Bibliography

1.Servin F. Remifentanil: when and how to use it. European Journal of Anaesthesiology 1997; 15(Suppl):41-4.

2. Glass PS. Gan TJ. Howell S. A review of the pharmacokinetics and pharmacodynamics of remifentanil. Anesthesia & Analgesia 1999; 89(4 Suppl):S7-14.

3. Reves JG. Educational considerations for the clinical introduction and use of remifentanil. Anesthesia & Analgesia 1999; 89(4 Suppl):S4-6.

4. Nora FS, Fortis EAF: Remifentanil: Porque precisamos de outro opióide? Revista Brasileira de Anestesiologia, 2001; 51(2): 146-159

5. Vuyk J, Mertens MJ, Olofsen E, et al. Propofol anesthesia and rational opioid selection. Anesthesiolgy 1997, 87; 1549-1562