In recent years, the incidence of obesity has increased significantly, about 15%-20% in developed countries. The incidence of obesity in children is also on the rise, about 25% in the United States and about 7% in China. Obesity leads to an increased incidence of hypertension, type II diabetes, and coronary artery disease in adolescence and childhood. Pediatric anesthesiologists need to deal with perioperative problems previously seen only in adult patients. 1. Definition Body mass index (BMI) is commonly used to describe the degree of overweight and obesity in adults and is expressed as the patient’s weight divided by the square of the height (kg/m2). BMI for adults ≥25 is overweight, ≥30 is obese, >40 is morbidly obese. bmi does not take into account individual differences in fat and muscle distribution, nor does it take into account factors such as bone density, body size and racial differences. bmi for pediatric use needs to be changed with the age and gender of the pediatric population. The CDC’s sex-specific and age-related BMI growth charts are also used to make judgments. A child is considered overweight if he or she is at or above the 95th percentile of measurements. Therefore, the percentile corresponding to the sex and age of the child is more important than the value of BMI. 2, and obesity-related pathophysiology (1) respiratory problems obese children’s chest wall compliance decreased, chest wall muscles often can not complete the satisfactory forward movement, lung function is manifested as restrictive ventilation dysfunction, functional residual air volume, expiratory reserve, lung volume and inspiratory volume have been reduced. In addition, there is a decrease in the first second forceful expiratory volume (FEV1), interstitial forceful expiratory flow between 25% and 75% of spirometry (FEF25-75), and intrapulmonary carbon monoxide diffusion volume (DLCO). There is a clear positive correlation between increased BMI and the incidence and severity of asthma, with obese children also exhibiting obstructive pulmonary disease and an increased probability of developing asthma and exercise-induced asthma. Obese girls are more likely to develop asthma. Obese children often suffer from sleep apnea or apnea, which can lead to nocturnal hypoxia, respiratory acidosis, pulmonary hypertension, erythrocytosis and, in severe cases, heart failure (the so-called Pickwickian syndrome). Obese children are twice as likely to develop pulmonary atelectasis as other children. It may be related to the increased closed volume resulting in gas retention and ineffective ventilation of the blood flow through this region. The intrapulmonary shunt exacerbates the hypoxemia. (2) Cardiovascular problems Obesity is often associated with hypertension, dyslipidemia, insulin resistance, type II diabetes, left ventricular hypertrophy, and pulmonary hypertension. sorof and Daniels found a positive correlation between the incidence of hypertension and BMI. Obese patients have hypertension due to increased sympathetic nervous system activity, insulin resistance, and abnormal vascular structure and function. Obese patients have increased systolic blood pressure due to insulin resistance and increased visceral adiposity. Obese pediatric patients have lower arterial compliance and decreased dilatability of the arterial system. Increased cardiac output and blood volume in obese pediatric patients may be associated with vascularization of adipose tissue. It has been estimated that cardiac output increases by 0.1 L/min per 1 kg increase in adipose tissue, and that the heart rate decreases to the low limit of normal at rest and the output per beat increases in obese children, resulting in an increase in cardiac output. As the patient’s body weight increases, oxygen consumption and carbon dioxide production also increase accordingly. The increased oxygen demand is accompanied by an increased cardiac burden. Most obese patients are at risk for severe hypertension. In overweight adolescents, the left ventricle becomes hypertrophic and some patients have increased right ventricular pressure. Because of these changes, which increase their demand for oxygen, severely obese adolescents (BMI ≥ 40) may develop obesity cardiomyopathy, a risk factor for progressive heart failure and sudden cardiac death. (3) Endocrine problems The percentage of obese adolescents with type II diabetes mellitus is increasing, and some of them are insulin dependent. Insulin resistance is common in obese pediatric patients and is associated with insulin resistance metabolic syndrome, hyperlipidemia and hypertension. Serum insulin level is closely related to the systolic blood pressure level of obese children, and is also related to hyperleptinemia and increased visceral fat. 3, and obesity-related pharmacology There is a lack of pharmacokinetic and pharmacodynamic information of commonly used drugs in obese pediatric patients, and a lot of knowledge comes from the literature of adults. In addition, the existing literature for the same drug often exists contradictory results, which may be related to the patient’s age and obesity degree. No information is available on the nature of protein binding in obese populations. There is also some literature suggesting altered hepatic metabolism in obese individuals, and these views have not been unified. The major factors influencing drug uptake and distribution are in vivo composition, plasma protein binding, local blood flow, and the relative maturity of organ modification and excretion of the drug. The body composition of the pediatric population changes significantly with age and differs from that of the normal pediatric population in overweight children. Common terms for body composition in obese patients include total body weight (TBW), ideal body weight (IBW), and lean body mass (LBM).IBW differs from LBM in that adipose tissue increases with LBM in obese patients. In fact, 20% to 40% of the increase in TBW in obese patients is attributed to an increase in LBM. Obese patients have a significantly higher volume of distribution than normal with the application of highly lipophilic drugs, which include barbiturates and certain benzodiazepines. However, despite being highly lipophilic, the volume of distribution of ponerol is reduced, suggesting that other factors are involved. The volume of distribution of less lipophilic or water-soluble drugs was less variable. Thiopental sodium and midazolam have increased volume of distribution in obese patients. Therefore, dosing decisions are recommended based on the TBW of the patient. Isoproterenol is also a lipophilic drug but does not have an increased volume of distribution in obese patients. Drug clearance and steady-state volume of distribution correlate with TBW. It is recommended that isoproterenol be administered at an initial dose determined by IBW, followed by a continuous infusion dose determined by TBW. Isoproterenol is lipophilic, but accumulation of isoproterenol occurs less frequently because of relatively poor perfusion of adipose tissue and because a significant portion is metabolized extrahepatically. Polar and hydrophilic neuromuscular blocking drugs such as vecuronium bromide and rocuronium bromide have been widely used for anesthesia in obese patients, and both are distributed in lean tissue. Dosing based on TBW will prolong recovery time, so dosing based on IBW is recommended. Elimination of both cis-atracurium and atracurium is not dependent on any organ and the duration of action is not significantly prolonged in obese patients. However, the duration of action of cis-atracurium may be prolonged if administered according to TBW. Succinylcholine has a similar strength of action in obese adolescents as in those of normal weight and should be administered according to TBW rather than LBM or IBW. Fentanyl and sufentanil are distributed in both adipose and lean tissues with a large volume of distribution and can be administered according to TBW. Rifentanil is rapidly eliminated and has a smaller volume of distribution in obese patients. Isoflurane, sevoflurane and desflurane can be used in obese patients. Sevoflurane has a longer elimination time than desflurane. Sevoflurane has increased fluoride concentrations in obese patients compared to non-obese patients. Desflurane has the characteristics of fast uptake and rapid recovery, and does not have the possible side effects of sevoflurane. 4, anesthesia treatment (1) preoperative preparation The traditional view is that excessive preoperative drug use in obese patients may occur respiratory depression, and is therefore listed as a contraindication. Intramuscular injection of drugs can not effectively reach the corresponding muscle site, so it is also not appropriate to use. There has been concern about preoperative gastroesophageal reflux in obese pediatric patients. Early studies have shown that obese children have an increased volume of gastric juice and a lower pH of gastric juice. Therefore, it was thought that obese patients had an increased likelihood of vomiting and aspiration during induction of anesthesia and an increased risk of postoperative aspiration pneumonia. However, recent studies have challenged this view. A retrospective study of a large sample found no cases of gastric acid aspiration in obese children. Maltby et al. also found that obese patients had normal gastric emptying after a 300 mL clear drink orally. All of these results were obtained from patients who did not originally have reflux disease. Recent literature suggests that obese children without reflux disease can follow the same fasting principles as non-obese children. (2) Positioning The position of the obese patient under anesthesia has a greater impact on the respiratory and circulatory dynamics. Obese patients are relatively poorly tolerated in the supine and head-down positions, while the head-up, prone or side-lying positions are more easily tolerated by obese patients. The supine position increases venous return, pulmonary blood flow, cardiac output, and arterial blood pressure in obese pediatric patients due to redistribution of blood flow. In addition the abdominal contents can impede the movement of the diaphragm and alter lung volume. Anesthetics and muscle relaxants make these effects more pronounced. The physiological function will be further deteriorated in the supine position compounded by the Trendelenburg position. When supine position is used in obese children, the head can be elevated by 30° to 45° to improve the respiratory dynamics and cardiac storage function of the child. (3) Intraoperative monitoring The impedance of the pathologically obese patient is too high, and the ECG may show low voltage. Increased soft tissue thickness can interfere with pulse oximetry monitoring, and placing the probe on the nose, lips, or pinky finger can improve the accuracy of monitoring. Obese patients often do not have a properly sized cuff, causing errors in noninvasive blood pressure monitoring. In addition, the shape of the upper arm can affect blood pressure readings. Obese individuals have a conical upper arm, whereas non-obese individuals have a cylindrical upper arm, so a normal cuff may not always be appropriate for obese patients. Recently, several other noninvasive blood pressure measurement devices have been tested that are based on the principle of continuous compression of the radial artery. These devices have shown a good correlation with invasive recorders. Certainly, there is support for the use of invasive monitoring means for all but particularly short procedures. Changes in dead space volume in tidal volume due to FRC, ventilation-to-flow ratio imbalance, and obesity in morbidly obese patients have the potential to affect end-expiratory CO2 monitoring. The absolute difference between TC-CO2 and PaCO2 is 0.2 kPa, while the difference between ET-CO2 and PaCO2 is 0.7 kPa (p ≤. 0001). However, TC-CO2 has problems such as the need for preheating before monitoring, the possibility of equipment errors, and the need for calibration. (4) Site anesthesia Regional blocks and analgesic techniques can also be used in obese patients, and lumbar or epidural anesthesia combined with superficial general anesthesia has been widely used in obese patients. Peripheral nerve blocks can be used for certain procedures in obese patients. However, obesity results in altered anatomy and poor recognition of common bony landmarks, making the operation of regional anesthesia more difficult. In obese patients, the epidural volume is reduced, the local anesthetic is easily diffused, the blocking plane is easily elevated, and respiratory and cardiovascular depression can occur once the motor and sympathetic block exceeds the T5 level. (5) Postoperative complications Dindo et al. conducted a prospective study of 6336 adult patients (including 808 obese patients and 239 morbidly obese patients) and showed no difference in the number of days in hospital, morbidity and mortality between obese and non-obese patients.Klasen et al. studied 1962 patients with BMI greater than 30 and controls. The results found no significant correlation between higher BMI and the consequences of undergoing non-cardiac surgery. Therefore, it was concluded that obesity is not an independent risk factor for perioperative morbidity and mortality. Pulmonary function was reported to be measured preoperatively, 1h and 3h after extubation in 161 obese patients. The results found that spirometry proceeded to decrease with increasing BMI. Patients with morbid obesity and abdominal incisions had the worst results. Another study compared morbidly obese and non-obese patients, looking at chest CT scans before surgery, immediately after extubation, and 24h after extubation. It was found that preoperative pulmonary atelectasis was more pronounced in morbidly obese patients and continued to worsen after anesthesia and even 24 h after surgery. In contrast, pulmonary atelectasis in non-obese patients tended to disappear after 24h. In addition, in a case file of 1246 children under 12 years of age who underwent dental surgery, 183 children had a BMI greater than the 95th percentile of BMI. The study compared the incidence of accidents such as laryngospasm, difficulty in opening veins, intraoperative and postoperative vomiting, intraoperative and postoperative hypoxia, and ICU stays in obese and non-obese children, and there were no differences between the two. 5. Summary Obesity and overweight are epidemic health problems worldwide. Child and adolescent obese patients may develop cardiovascular and endocrine problems at an early age. Although the traditional view is that obese patients are at high risk in the perioperative period, recent findings from adults and children challenge this view. A growing number of issues related to obesity are now being recognized, but the results are not promising. Focusing on the potential problems associated with obesity in the perioperative period may improve the prognosis of the child.