A Paediatric Pot Pourri

Journal Reviewed: British Journal of Anaesthesia Issues: August, September 1999 Reviewer: Dr T Masood MB BCh (Registrar, University of the Witwatersrand) Summary From recent paediatric-orientated articles in the BJA, Dr Masood has selected two review articles he thinks are particularly pertinent. He's added a haematological bagatelle from the journal Paediatric Anaesthesia : Medical Assessment of the paediatric patient; Low flow anaesthesia; Venous thromboembolism in paediatrics. Our editor did not entirely agree with Dr Masood's assessment of the second article! Click here for editorial comment. 1. Medical assessment of a paediatric patient "Careful preoperative assessment is the cornerstone of safe anaesthetic practice" - paediatric anaesthesia is no exception. Black's article gives us a thorough but fairly pedestrian review of several conditions which we may unexpectedly encounter in paediatric anaesthetic practice. Cardiac Disease: Congenital heart disease occurs in 0.8% of live births. The possibility of a cardiac lesion should always be considered in conditions like TOF, esophageal atresia, Down's syndrome and VATER. Two groups of patients are considered - those with 'known' cardiac disease corrected or uncorrected; and those with features suggestive of cardiac disease. Pulmonary hypertension also needs mention especially with congenital heart disease, chronic airway disease, upper airway obstruction, adenotonsilar hypertrophy, cystic fibrosis, bronchopulmonary dysplasia and neuromuscular dystrophy. Consequences of unnoticed and untreated pulmonary hypertension are very serious. Respiratory disorders. In neonates and infants, postoperative apnea is a special concern. Premature babies are at high risk and day-care surgery is a real issue. Risk factors include gestational age, post-conception age, history of apnea, apnea in the recovery room and anemia. 'Light anaesthesia' and sedation with regional anaesthesia do not decrease the risk. In children URTI is a problem. Recent episode increases the incidence of complications. Risk factors include recent infection, an inexperienced anesthetist and tracheal intubation. Asthma and cystic fibrosis should be assessed and optimized preoperatively. Children with major organ transplants. Assessment of function, problems, medication and protection of the transplanted organ are reviewed. Issues common to all transplant patients are constant threat of rejection, risk of infection and effects of immunosuppression. Diabetes mellitus type 1 is the commonest endocrine disorder in children (1 in 500). Control can be a problem due to changing energy demands and food intake. Latex allergy is IgE mediated and reactions can be very severe, possibly the commonest cause of intraoperative sensitivity reactions. Children with spina bifida are at very high risk (500-1000 times). Another identified high risk group is that with a history of sensitivity reactions such as bronchospasm, urticaria or eye irritation to balloons or other latex-containing toys. Sickle cell disease. Apart from incidental surgery, these children can present for cholecystectomy for gall stones and for splenectomy. Vaso-occlusive disease, chest syndrome and end-organ damage need special mention and concern. Hypoxia and hydration are other key factors to remember as is optimization of haemoglobin. Article 1: Medical assessment of the paediatric patient Journal: British Journal of Anaesthesia 1999 83 (1) 3-15 Article type: Review Author: Black AE 2. Low-flow anaesthesia in infants and children H. Meakin suggests the definition of low flow as fresh gas flow less than patient's alveolar ventilation. Advantages of low flow and circle system are obvious. Special concerns in paediatrics can be divided into two main groups, those about circle system use, and doubts about the feasibility and effectiveness of low-flow methods. Concerns about use of circle system in paediatric anaesthesia Resistance to breathing: Resistance occurs in the breathing system and ETT and is measured in terms of pressure drop across the equipment at a given flow. Tubing and absorber share one third of the resistance equally and two thirds is shared by three valves. Data also suggested that a size 3.5 ETT in a 3 month old infant has 10 times the resistance of a circle system. Apparatus deadspace: there is adequate compensation for short term deadspace increments by increasing the minute ventilation but no doubt dead space should be minimized and controlled ventilation should be used liberally. Paediatric circle system: Resistance is inversely proportional to the diameters of the valves and tubing. Anatomical and physiological differences: Respiration is almost entirely diaphragmatic as ribs are horizontal. There are very few type 1 muscle fibers making the child susceptible to fatigue. FRC is reduced due to chest wall compliance. With the acceptance of controlled ventilation in paediatrics especially in neonates and infants, arguments against circle system have disappeared. Doubts about the feasibility and effectiveness of low flow methods Problems posed by leak around the tracheal tube. No leaks in the working pressure range of 0-20 cm of water are advantageous. Economics of low flow in children. Benefits of conservation of heat and moisture are always there but economy of fresh gas and volatile is not much in neonates and very small infants. In case of bigger children there are saving of more than 50%. Predicting volatile anaesthetic concentration: There is little information on this topic but studies indicate that low solubility agents like sevoflurane are more suitable for short term cases. Oxygen concentration during low flow anaesthesia: To avoid hypoxic mixture VO2 must be taken into account. First dial in required VO2 and then rest of FG should be split to get the required FIO2. Degradation of sevoflurane by CO2 absorbents: Production of compound A and its nephrotoxic potential is the concern. Concentration of compound A increases with decreased flow, increased volatile, increased CO2, increase in absorbent temperature and drying of absorbent. These increases are greater with the use of Baralyme. On the other hand sevoflurane is attractive for paediatric use. FDA prohibits the use of sevoflurane with less than 2L fresh gas flow but no such restriction is in force in UK. It is argued that children have a small body weight and surface area, so a small amount of CO2 is produced for a given amount of FG and volatile concentration. Article 2: Low-flow anaesthesia in infants and children Journal: British Journal of Anaesthesia 1999 83 (1) 50-57 Article type: Review Author: Meakin GH 3. Paediatric venous thromboembolism Venous thromboembolism is thought to be rare in paediatric practice, and although it is tempting to file this interesting review under "exotica", we suggest you read it if only to avoid missing a dangerous and treatable disorder through lack of awareness. Article 3: Venous thromboembolism in paediatric practice. Journal: Paediatric Anaesthesia 1999 9 (6) 475-484 Article type: Review Authors: Clark DJ Editorial pointers The article by Meakin is superb, and should be read in full and carefully by all paediatric anaesthetists, especially those that still feel the T-piece reigns supreme! The author immediately cuts to the quick. Definitions of low flow are cumbersome and difficult to remember. Meakin's definition of low flow as FGF "less than the patient's alveolar ventilation" is concise and memorable. The rationale is that this FGF is the minimum flow necessary to ensure adequate CO 2 elimination during spontaneous or controlled ventilation with the most efficient non-absorber breathing circuit i.e. an EEAR / Humphrey ADE. Contrary to popular myth, measurements of resistance to breathing are less than those found in adults. Meakin is again worth quoting: "For an infant of 9 months, whose peak flow is approximately 10 L.min -1 , the pressure decrease across the systems tested by Orkin, Siegal and Rovenstein should be less than 0.25 cm H 2 O. In contrast, the pressure decrease across a 3.5mm tracheal tube in a 3-month-old infant with a peak flow of approximately 6 L.min -1 should be approximately 2.5 cm H 2 O." In paediatric circle circuits, it is logical to use connectors with minimal dead space, to have 15mm flexible lightweight plastic tubes to reduce bulk, and make use of a smaller reservoir bag (800 to 1000ml) to aid visualisation. Concerns regarding technique . Well-addressed is the age-old debate concerning cuffed versus non-cuffed endotracheal tubes in children. More important than this sterile debate is our technique in placing the tube and the associated trauma when the tube is allowed to move within the trachea (with coughing or head manipulation). The practice of selecting the smallest tube that passes easily into the trachea and does not leak from 0 to 30 cm H 2 O is a sound one. Demonstration of a decrease in fresh gas and volatile usage within a circle system is one of the classic arguments for the system. When stratified by age the saving is negligible in infants reflecting the low FGF rates needed in an E-EAR/ADE system. However compared to a T-piece where the minimum FGF is 3 L/min, the saving is conspicuous. Predicting volatile anaesthetic concentration and inspired O 2 . Although the physics and mathematics explained are elegant and must be understood, there is no excuse not to use appropriate monitoring. Degradation of sevoflurane to Compound A is only of significance if you are a rat anaesthetist, and is irrelevant to humans. For a recent review see the following article. Kharasch ED, Jubert C Anesthesiology 1999 91(5) 1267-1278 Now, go and read Meakin's article! Ed       Up Date of First Publication : 2000-02-07 Date of Last Update : 2006/10/23 Web page author: Click here