Differences in patient sensitivity to anaesthetic drugs may create problems for anaesthesiologists, particularly when using computerized devices for propofol and opioid target controlled infusions (TCI). Pharmacokinetic and pharmacodynamic differences may be present, accounting for a variable response to anaesthetic drugs. Genetic polymorphism, for instance, may be responsible for drug inefficacy or toxicity . These problems are of great interest when dealing with patients from different ethnic groups or populations.
In a previous study, we demonstrated that the recovery time from anaesthesia with propofol and remifentanil is slower in Senegalese African blacks when compared with European Caucasians. Senegalese blacks also showed a much higher mean arterial pressure (MAP) stability than Caucasians during induction and maintenance of anaesthesia .
We have repeated the investigation in Kenya and Brazil, using propofol and fentanyl. In Kenya, we had occasion to study the same ethnic group as in Senegal under the influence of different ambient conditions, religion, diet and life habits, and to evaluate the possible role of these variables on patients' responses to anaesthesia. In Brazil, during the last five centuries, African blacks from both the West and East coast of Africa mixed with Caucasians from Portugal, Holland and with native Indians. We set out to determine whether this greater sensitivity to propofol and opioids, observed in most Africans from Senegal, was conserved or modified in Brazilians.
Indices of depth of anaesthesia in subjects from two populations, i.e. Kenyan African blacks from Nairobi and Brazilians from the area of Salvador de Bahia, have been compared with Caucasians from Italy with the aim of evaluating any different response to TCI with propofol and fentanyl. Fixed amounts of anaesthetic drugs were given to all groups and the drug response was evaluated using the bispectral index (BIS)  values and the recovery parameters. A sample size of 45 patients per group was chosen because it provides a power >95%.
The present study was carried out in three hospitals: Policlinico Careggi in Florence (Italy), Kenyatta National Hospital in Nairobi (Kenya) and Hospital Sao Rafael in Salvador de Bahia (Brazil) by the same group of anaesthesiologists. After obtaining the Institutional Ethics Committees' approval in Florence, Nairobi and Salvador, and the patients' written informed consent, Caucasian, African black and Brazilian patients (non-smokers with no hypertensive history) were enrolled. Both male and female patients, aged between 20 and 55 yr, height measuring between 1.65 and 1.75 m, weighing between 60 and 75 kg, body mass index between 20 and 25 kg m−2 and ASA I were admitted to the study. They had no associated pathology. These subjects underwent general abdominal surgery lasting 60-110 min. Patient heart rate (HR), non-invasive blood pressure and arterial oxygen saturation (SPO2) were recorded during anaesthesia. The enrolment of patients in the three groups was continued until there were 45 in each group.
Any patients with a history of liver or renal disease, drug or alcohol misuse, excess of fat body mass, presence of sickle cell trait or sickle cell anaemia were excluded.
Patients received Ringer's lactate 10 mL kg−1 intravenously (i.v.), atropine sulphate 0.5 mg and fentanyl 0.7 μg kg−1 intramuscularly (i.m.) 30 min before induction of anaesthesia. Anaesthesia was induced using a total i.v. technique including the administration of the following drugs:
- fentanyl 1.5 μg kg−1 (initial bolus)+1 μg kg−1h−1
- propofol 1.5 mg kg−1 (initial bolus)+10 mg kg−1h−1
- pancuronium 0.08 mg kg−1.
Patients underwent tracheal intubation and artificial ventilation (FiO2 = 0.4) with fixed parameters: 10 breaths min−1 and expiratory ventilation volume 120 mL kg−1min−1.
Propofol and fentanyl were delivered by Alaris® IVAC-TIVA 6000 L pumps (Alaris Medical Systems, Basingstoke, UK) with a total intravenous anaesthesia technique (TIVA).
All patients received 0.9% NaCl solution 800 mL h−1 i.v. during surgery. Propofol and fentanyl administration was both stopped 10 min before the patient's intended recovery of consciousness. Neostigmine 2 mg and atropine sulphate 1 mg i.v. were given at the same time to antagonize the muscle relaxant.
If any patient's response to anaesthesia required any increase or reduction in the amount of anaesthetic drugs compared with the protocol, the patient was excluded from the trial. Patients with a decrease of arterial pressure more than 30% of the basal were also excluded.
Evaluation of anaesthesia depth and wake-up
The MAP, HR, blood oxygenation, common clinical parameters and the BIS  were used to evaluate the depth of anaesthesia. Arterial pressure, HR and SPO2 were monitored with a Dinamap® (Critikon, Tampa, FL, USA) continuous monitor.
The BIS was monitored from two fronto-parietal electroencephalogram (EEG) signals (dx and sx) with an Aspect A-1000® EEG monitor (Aspect Medical Systems, Natick, USA), software version 3.31.
The EEG signals were picked up using four Zipprep self-sticking frontal surface electrodes. Every 5 s, the Aspect A-1000® calculated the BIS based on a running average of the last 120 artefact-free epochs of data (each epoch represents 0.5 s). All data were automatically sent through a serial RS232 interface to a computer (Toshiba, Satellite 4000 CDT) at 5 s intervals using self-designed software. The A-1000® also provides a signal quality index (SQI) with each record. The SQI is the percentage of good epochs in the last 120 epochs. Data were chosen with SQI > 50. Mean BIS values for each patient were calculated from 5 min of data before the induction of anaesthesia (B0), starting from 20 and 40 min after induction (B1 and B2) and then from 3 min data starting 3 (B3) and 7 min (B4) after propofol and fentanyl discontinuation. Mean values B1 and B2 were considered as intraoperative BIS, B3 as pre-recovery BIS and B4 as recovery BIS. B3 and B4 were used in order to evaluate wake-up behaviour.
In order to assess the recovery time, verbal stimuli were given at 30 s intervals starting from discontinuation of propofol infusion. Spontaneous eye opening time and movements under verbal command were recorded.
Data from Kenyans and Brazilians were compared with data from Caucasians. End-point BIS and recovery data values were tested for normality using the Kolmogorov-Smirnov analysis. As they were normally distributed (P > 0.10), one-way analysis of variance was used to compare BIS data at B0, B1, B2, B3 and B4, wake-up data, arterial pressure and HR in the three groups. Dunnett's post hoc test was applied to evaluate statistical significance when the P value was <0.05. Statistical analysis was performed by using the GraphPad InStat® utility, v. 3 for Windows (GraphPad Software Inc., San Diego, CA, USA) and the Analyse-it Software for Microsoft Excel®, www.analyse-it.com, v. 1.62 (Leeds, UK).
Figure 1 describes the trial profile. Patient characteristics data of the 45 patients per group that fulfiled our criteria are summarized in Table 1. Table 2 describes the patients withdrawn from the trial and the reasons for exclusion.
The three groups examined in the present study showed no statistically significant differences in BIS basal values B0 and in intraoperative values B1 and B2.
B3 values (pre-recovery values) were 22% higher in African blacks compared with Caucasians (P < 0.001). No significant differences were registered between Brazilians and Caucasians. On the contrary, B4 values (recovery BIS values) were 15% lower in African blacks (P < 0.01) and 4.7% lower (P > 0.05) in Brazilians when compared with those of Caucasians (Fig. 2). After discontinuing propofol and fentanyl, BIS values of the Caucasians returned to the baseline in about 10.8 ± 4 min, Kenyan African blacks in 18 ± 7 min, but in eight of these patients BIS values remained about 5% lower than basal values for up to 30 min after stopping propofol. The BIS values of Brazilians returned to basal values within a period ranging from 5 to 25 min (14.9 ± 9.9).
The time from stopping the propofol and fentanyl infusion to eye opening was 18.8 ± 7.1 min in African blacks (P < 0.01), 13.5 ± 8.8 min in Brazilians (P > 0.05) and 11.6 ± 4.5 min in Caucasians. The time to respond to verbal commands was 16.8 ± 8 min in African blacks (P < 0.01), 12.8 ± 8.1 min in Brazilians (P > 0.05) and 9.9 ± 4.5 min in Caucasians.
Figure 3 shows the distribution of the patients of each ethnic group into three ranges of eye opening times: less than 8 min, from 8 to 13 min and more than 13 min after stopping propofol and fentanyl. The distribution was very different in the three groups. The Caucasian group showed 80% patients in the recovery range of 8-13 min, 4.5% in the range of <8 min and 15.5% in the range of >13. Patients of the African group were quite equally distributed into two ranges: 42.3% in the range 8-13 min and 57.7% in the range > 13. None of the 45 Kenyan patients observed was in the recovery range <8 min.
Brazilians are more homogeneously distributed into all the three ranges of recovery time: 20% of patients had a recovery <8 min, 44.5% in the range 8-13 min and 35.5% with a recovery time >13 min. Table 3 shows the behaviour of MAP, HR and SPO2 during the observed period. There were no significant variations in SPO2 and HR during our trial while MAP differences were observed within the groups 10 min after anaesthesia induction, as the MAP fell by 20% in Caucasians but only by 10% in both African blacks and Brazilians (P < 0.01).
The different sensitivities towards drugs are possibly because of pharmacokinetic/pharmacodynamic factors that may be affected by genetic factors and/or by life style and environment (health, nutrition, enzymatic induction, physical exercise, religious practices, etc.). In a previous paper , we have shown that the recovery time from anaesthesia with propofol and remifentanil is faster in Caucasians than in Senegalese Africans. The present study with propofol and fentanyl confirms these results for another African population, the Kenyans, with very different living habits. Thus, the slower recovery from anaesthesia in comparison with Caucasians may not be closely linked to environment factors.
Pharmacogenetic studies have recently shown that genetic polymorphisms may account for the inefficacy or toxicity of a drug in different individuals or ethnic groups. One of the most studied polymorphic enzymes involved in drug metabolism is the cytochrome P450 2D6 (CYP2D6), but there are many other cytochromes sharing similar functions . Different allelic variants for P450 enzymes are present in different races, possibly accounting for a variable metabolic response to some anaesthetic drugs. Recent studies have demonstrated that in European Caucasians and in their descendants functional alleles of cytochrome P450 are predominant (71%), whereas in Africans and African Americans the frequency of functional alleles is about 50% . There are no specific studies in Kenyans and Brazilians, but about 40% of black Tanzanians (very near to Kenya) show a variant CYP2D6 which accounts for a reduced capacity for metabolizing some drugs  and a study performed on the Columbian population, which has Amerindian ascendants, showed that ultra-fast metabolizers were represented .
In the case of propofol, the main route of metabolism is the glucuronidation by UDP-glucuronosyl-transferase 1A9 , but propofol is also widely metabolized in the liver by cytochrome P450 to form 4-hydroxyprofol that has about one-third of the hypnotic activity of propofol [8-10]. Also fentanyl metabolism is linked to the cytochrome P450 and propofol and fentanyl interact in a synergistic fashion .
The population of Northeast Brazil, mainly Bahia, where the study was performed, consisted originally of Portuguese, black Africans and native Indians. Intermarrying has mixed their gene pools since the Sixteenth Century . Today, there is no unmixed group in Brazil. Even the group classified as 'white' has about 18% of genes coming from African black ascendants and 12% of genes from Indians .
Native Indians lived in the bush, eating different herbs, some toxic for other populations, and have been preparing for thousands of years the many different poisons to be used for hunting. There are 170 different species of arrow poison frogs used for deadly darts in the Amazonian area with different non-proteic synaptic blocking nerve poisonous agents. A resistance to many drugs could have been selected in the genes of Indians during thousands of years of close contact with deadly poisons.
In conclusion, the recovery of Kenyan African blacks from anaesthesia with propofol and fentanyl is much slower in comparison with Caucasians. The recovery time of Brazilians is much more variable, from 5 to 25 min, when compared to Caucasians, possibly due to genetic mixing and selecting mechanisms. These results are very suggestive of pharmacokinetic and pharmacodynamic differences among different ethnic groups, in metabolizing propofol and fentanyl.
A much greater stability of arterial pressure during anaesthesia induction and maintenance with propofol and fentanyl is present in both Africans and Brazilians compared with the Caucasians.
The work was carried out at the Dipartimento di Area Critica Medico Chirurgica, University of Florence, Italy; at the Department of Surgery, University of Nairobi, Kenya and at the Chefia de Anesthesia, Hospital Universitario Sao Rafael, Brazil. The study was supported by public funds from the University of Florence.
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