1. Introduction

Inhalation methods of anesthesia, which stood at the origins of anesthesiology, today occupy a worthy place in the concept of modern multicomponent anesthesia. The advantages of inhalation anesthesia (IA) include the rarity of anaphylactoid reactions, the predictability of pharmacokinetics and pharmacodynamics, and a low risk of intraoperative awakening of the patient [1,3].

The traditional method of IA involves supplying a large gas flow into the anesthesia circuit with a calculated and fixed ratio of gas mixture components. As a result, a large amount of unused anesthetic and medical gases is lost; moreover, unfavorable conditions are created for humidification and warming of the respiratory mixture, and excessive pollution of the environment occurs. All this makes anesthesiologists think about measures to possibly reduce the flow of fresh gas. Repeated attempts in the past to use low flows of inhalation anesthetics, however, did not lead to the widespread adoption of the low-flow anesthesia method [2,4,6]. The main reasons for this were an insufficient level of patient safety and the complexity of anesthesia management techniques.

The recent development of modern medical equipment — the introduction into practice of “new generation” anesthesia and respiratory apparatuses and the expansion of multifunctional monitoring systems — makes it possible to implement effective and safe use of low-flow anesthesia (LFA), including in pediatric anesthesiology. The appearance on the commercial market of new inhalation anesthetics (sevoflurane, isoflurane, desflurane), which are characterized by low solubility in blood, low consumption, and relative costliness (therefore, their use in a circuit with high gas flow is impractical), stimulates the development of low-flow anesthesia methods [5,7,9]. The possibility of maintaining optimal temperature and humidity in the breathing circuit, significant reduction in anesthetic consumption, and hygienic and environmental safety — all these factors determine the considerable interest of anesthesiologists in LFA [8,10]. However, the experience of using this anesthesia method in pediatric anesthesiology is extremely limited and requires further study. Unlike traditional anesthesia performed in a non-rebreathing circuit with a gas flow exceeding the minute ventilation of the lungs, in low-flow anesthesia the fresh gas flow is reduced to 1 L/min or less. A variant of low-flow anesthesia is minimal flow anesthesia, with a fresh gas flow equal to 1 L/min [11,12]. In this regard, the purpose of our study is to evaluate the effectiveness and safety of the low-flow inhalation anesthesia method using sevoflurane or isoflurane in children, based on the study of oxygen transport parameters during abdominal surgeries in children.

Purpose of the study: To improve the quality of anesthetic protection by using low-flow inhalation anesthesia with sevoflurane in combination with fentanyl during abdominal surgeries in children.

2. Materials and Methods

To provide anesthetic protection in 42 pediatric patients undergoing abdominal surgery for Hirschsprung’s disease, the following combinations were used: fentanyl with sevoflurane — Group 1 (22 patients, 52%), and fentanyl with propofol — Group 2 (20 patients, 48%).

Children aged 1–2 years accounted for 56.4%, 3–6 years — 25.2%, and 6–9 years — 18.4% of the total number of patients. Anesthesia was performed during abdominal surgeries. The duration of anesthesia in 62.8% of patients was up to 1 hour 50 minutes, and in 37.2% — up to 2 hours 25 minutes. In Group 1, after premedication, inhalation with sevoflurane up to 3.0 vol% was carried out, followed by intravenous administration of fentanyl solution at a dose of 5 μg/kg.

In Group 2, induction began with intravenous administration of propofol at a dose of 4 mg/kg, along with intravenous fentanyl at a dose of 5 μg/kg.

In both groups, tracheal intubation was performed under the administration of arduan at a dose of 0.006 mg/kg. Mechanical ventilation was performed using a Dräger “Fabius Plus” (Germany) apparatus in a semi-closed circuit. Muscle relaxation was maintained by administering one-third of the initial dose of arduan. Maintenance of anesthesia was achieved by repeated administration of fentanyl at doses corresponding to 50% or 25% of the initial dose. In the first group, anesthesia was maintained with inhalation of sevoflurane at a concentration of 1.0–1.5 vol% and repeated fractional administration of fentanyl (50% or 25% of the initial dose). In the second group, anesthesia was maintained by intravenous infusion of propofol at a dose of 4 mg/kg and repeated fractional administration of fentanyl (50% or 25% of the initial dose). Infusion therapy was carried out at a rate of 10–15 ml/kg/hour. After completion of the operation, the patient was transferred to the intensive care unit. Hemodynamic parameters were measured using a “SonoScape” echocardiograph (China) with a 3.5 MHz sensor according to the standard protocol. To assess the functional state of the cardiovascular system during anesthesia, the following parameters were studied: stroke index (SI), cardiac index (CI), and total peripheral vascular resistance (TPVR).

The stroke index (ml/m²) = stroke volume / body surface area.

The cardiac index (L/min/m²) = cardiac output / body surface area.

Total peripheral vascular resistance = systolic arterial pressure / cardiac index.

The ejection fraction (EF) of the left ventricle (LV) is an integral measure of myocardial contractility, characterizing the proportion of blood ejected by the LV relative to its diastolic volume. The results of clinical and functional studies were processed using variation statistics and Student’s t-test.

3. Results and Discussion

The results of the hemodynamic parameter analysis in children of Group I (fentanyl + sevoflurane) are presented in Figure 1.

Figure 1. Hemodynamic parameters during combined anesthesia using fentanyl and sevoflurane

Compared with the baseline data, an increase in heart rate (HR) by 16.8% and a decrease in total peripheral resistance (TPR) by 20.8% were observed during premedication. It should be noted that patients in the first group showed a more pronounced response to induction and anesthesia. Even before induction, they exhibited tachycardia and a moderate rise in blood pressure, which was associated with psycho-emotional tension. Other parameters changed insignificantly. After the administration of fentanyl, hemodynamic parameters such as stroke index (SI), cardiac index (CI), ejection fraction (EF), and HR decreased compared to those during the premedication period — by 14.2% (p<0.05), 2.6%, 8.7%, 4.2%, and 2.8%, respectively, except for TPR. The revealed significant differences in the systemic hemodynamic response are associated with the pharmacological properties of both fentanyl and sevoflurane. Ten minutes after intubation, a significant increase in SI by 18.6% and CI by 21.8% was observed, while TPR decreased by 15.08% (p<0.05). There was also a tendency toward a decrease in the ejection fraction (EF). Under the influence of premedication drugs, patients in the second group showed the following hemodynamic changes: an increase in HR by 6.7% (p<0.05), SI by 2.8%, CI by 2.3%, TPR by 3.12%, and EF by 1.14% (p>0.05), which were associated with emotional discomfort before surgery and the effect of premedication drugs.

During the induction stage of anesthesia, minor changes in hemodynamic parameters were observed — for example, stroke index (SI), heart rate (HR), and cardiac index (CI) increased by 1.39%, 2.13%, and 1.37%, respectively. At the same time, total peripheral resistance (TPR) and ejection fraction (EF) showed slight increases of 0.1% and 0.11%, which were statistically insignificant (p>0.05). A significant decrease compared with the premedication stage was noted for HR, which decreased by 11.06% (p<0.05). Considering the hypotensive effects of fentanyl, sevoflurane, and propofol, infusion therapy was initiated and carried out at a rate of 10–15 ml/kg/hour. This approach helped to prevent, and in some cases completely eliminate, critical drops in blood pressure at all stages of anesthesia management. At the end of the operation, hemodynamic parameters remained stable. The changes observed in most parameters during the operation were statistically insignificant, except for CI, which increased by 23.1% (p<0.05) compared to baseline values. In the discussion, it should be noted that central hemodynamic indicators in patients of Group 1 indicated moderate circulatory hypodynamia. Sevoflurane mainly affected the tone of the peripheral vascular bed, causing vasoplegia. At the same time, fentanyl reduced cardiac output, enhancing vascular vasoplegia. This condition was corrected through infusion therapy. In children of Group 2, the decrease in CI was due to rigidity of the microcirculatory bed, limited contractile capacity of the myocardium, and relative hypovolemia. When using fentanyl and sevoflurane, patients fell asleep smoothly and quickly without signs of excitation, maintaining stable hemodynamic parameters throughout all periods of anesthesia and in the early post-anesthetic stage. The postoperative period was uneventful — awakening occurred without signs of agitation or hemodynamic disturbances. This ensured a smooth emergence from anesthesia and enabled early tracheal extubation. With the combination of sevoflurane and fentanyl, vomiting, muscle tremors, and other complications were not observed.

4. Conclusions

Low-flow inhalation anesthesia with sevoflurane in combination with fentanyl provides optimal conditions for surgical correction, minimizes the negative effects of its individual components, and effectively fulfills the specific objectives of anesthetic management during abdominal surgical operations in children.