 |
|
Editorial Indian Pediatrics 2002; 39:909-913 |
|
Oxygen Therapy for Acute Respiratory Infections in Young Children |
|
The Problem Acute respiratory infections cause more than two million deaths in children less than five-year-old; mostly in developing countries(1). These deaths are associated with hypoxemia, which is a manifestation of severe lower respiratory tract infection. Depending upon the severity of the illness, a review reported a wide range of prevalence of hypoxemia (31%-72%), because various investigators have used different definitions(2). Studies from Kenya, Zambia and Zimbabwe have reported that the risk of death in hypoxemic children ranged from 1.4 to 4.3 times higher than non-hypoxemic children(3-5). Oxygen was isolated in 1744, but was effectively used only during the First World War. No randomized clinical trials have been ever conducted to assess the impact of oxygen therapy on mortality in pneumonia. Some adult studies in the pre-antibiotic era with retrospective controls showed the benefit of oxygen therapy on mortality from pneumonia(6). These studies had some methodological problem, but do represent the best evidence available from that era. In a small study in children in Papua New Guinea, mortality was lower in children, who received oxygen as compared to children, who did not get oxygen, because supply was intermittent(6). Recognition of Hypoxemia Traditionally in tertiary care settings, oxygen concentration in the plasma (PO2) has been used to assess hypoxemia. But, this method requires a blood sample and a laboratory. In the past 15 years or so the cutaneous measurement of oxygen through pulse oximeters has nearly completely replaced the older techniques, particularly in developed countries. Pulse oximeters, although relatively expensive are very useful in the detection of early hypoxemia and require little maintenance. A recent study reported use of pulse oximetry to assess hypoxemia in critically ill children with respiratory and non-respiratory illnesses(7). Depending upon the altitude, hypoxemia can be defined accordingly by measuring oxygen saturation (SaO2) percutaneuously. No universal definition of hypoxemia exists. Investigators have defined hypoxemia from <96.6% to <90% oxygen saturation at sea level and <85% to <88% at higher altitudes(2). For simplicity, a couple of on-going international multicentre clinical trials for pneumonia therapy are using cut-offs of <90% at sea level and <88% at higher altitude to define hypoxemia. In most developing country situations, where facilities to measure plasma concentration and oxygen saturation are not available, most clinicians rely on clinical signs to identify hypoxemia. Often standardized criteria and methods are not used for providing oxygen therapy(9-11). The World Health Organization (WHO) acute respiratory infection (ARI) control guidelines recommend that where oxygen supply is scarce, it should be provided to children with cyanosis and who are unable to drink(6,11). Infants under 2 months of age with ARI are always considered a priority. In presence of ample supply, oxygen should be provided to children with severe lower chest indrawing, with a respiratory rate of 70 breaths/minute or more or with restlessness (if improved by oxygen). WHO guidelines were recently modified to include lethargy/unconsciousness, head nodding, vomiting everything or convulsions(12). A recent review of predictors of hypoxemia also identified grunting and nasal flaring alongwith above-mentioned signs(13). Reliance on a single clinical sign may not be optimal, as some clinical signs like lower chest indrawing or fast breathing may be sensitive but not very specific for identification of hypoxemia. Whereas, other signs like cyanosis, unable to drink, grunting or lethargy, etc may be very specific, but not very sensitive. So it is better to use a combination of signs. A study from Gambia prospectively evaluated a combination of WHO recommended signs of inability to feed or drink or cyanosis or respiratory rate of 70 or more breaths per minute or severe chest indrawing and found them to be 80.9% sensitive and 62.5% specific for predicting hypoxemia(14). This combination, which is fairly sensitive though not highly specific, could be used in most developing country situations. How to Give Oxygen? Several methods are used to provide oxygen and the oxygen concentration varies according to the method used. Oxygen concentration delivered to a child of 5 kg at a 1 liter/minute flow is 45-60% with nasopharyngeal catheter, 35-40% with nasal catheter, 30-35% with nasal prongs and 29% with head box, whereas with face mask it is variable(6). WHO recommends three low flow methods. It recommends using nasal prongs when giving oxygen to young children. This method delivers adequate concentration of oxygen safely to hypoxemic children. It also does not require humidification. Where prongs are not available, nasal catheters are an alternative. WHO guidelines recommend 0.5 liter per minute oxygen flow for a child less than 2 months old (or less than 5 kg) and 1 liter per minute for above that. Where oxygen supply is limited and adequate oxygenation is not achieved with prongs or catheters, a nasopharyngeal catheter may be used as it achieves the highest concentration. This requires trained staff, as a thin flexible tube is passed through the nostril until the tip lies in the patient’s throat, just beyond the soft palate. Before inserting the catheter the distance for insertion can be measured from side of the nostril to the front of ear. This method also requires humidification as the catheter tip lies in the oropharynx. Nasal prongs or nasal catheter require a higher flow of oxygen than nasopharyngeal catheter. A few complications with the use of nasopharyngeal catheter have been reported(15). When the patient develops mucus in the nose, it requires cleaning. The catheters and prongs should be cleaned once or twice every day. One study from India has reported the use of oropharyngeal catheter for oxygen delivery, but these results have not yet been replicated(16). Use of face mask and head box for delivery of oxygen is discouraged in less developed countries, because higher flows of oxygen are required (4-5 liters/minute) and danger of carbon dioxide accumulation exists if the oxygen flow is low(6). Head boxes are used widely in developed countries for babies because they are tolerated well and do not need humidification. But they require a mixing device to ensure correct oxygen concentration. Because child’s mouth and nose are close to the opening of the box, the actual concentration inspired is lower than expected. The concentration falls further when head box is opened. Furthermore, the oxygen therapy has to be discontinued during feeding. When to Stop Oxygen? In severely hypoxemic children, the oxygen saturation may not be corrected soon and the clinical signs may persist. When the child is improving, oxygen could be withdrawn for a few minutes (nasal catheter or prongs could be cleared at this time) and child should be observed for about 10 minutes. Oxygen therapy is no longer needed, if the child is comfortable without oxygen. If a pulse oximeter is available, oxygen saturation can be monitored. Oxygen Sources In most situations in developing countries, oxygen cylinders are the main source of oxygen. They are expensive, bulky and difficult to transport(17-19). A high pressure gauge is needed with individual cylinders. Full cylinders contain oxygen at a pressure of 132 atmospheres or bars (2000 p.s.i. or 13,400 kPa). When the pressure falls below 8 atmospheres or bars (120 p.s.i. or 800 kPa) the cylinder is nearly empty. A flow meter must be attached to the regulator to allow the precise flow of oxygen to the patient. One limitation of individual cylinder is assessing the remaining quantity of oxygen in order to prevent the risk of supply running out. Size and pressure of the cylinder and oxygen flow per minute can be used to calculate the remaining oxygen in the cylinder. Cylinders come in variable sizes. For example size ‘D’ contains 340 litres, size ‘E’ contains 680 liters, size ‘F’ contains 1360 liters and size ‘G’ contains 3400 litres. One can calculate how many hours the contents will last by using the formula V/F/60, where ‘V’ is numbers of litres remaining in the cylinder, ‘F’ flow of oxygen per minute (60 is minutes in an hour). Oxygen concentrators, developed in 1960s are widely used in the industrialized world to provide oxygen at home to patients with chronic lung disorders. Their success is attributed to provision of oxygen at a low cost. WHO has identified some models that fulfil the requirements for use in high temperature, humidity and altitude. The use of such oxygen concentrators in district hospitals in Papua New Guinea, Malawi, Mongolia and Egypt has been very satisfactory. It was found to be economical way of delivering oxygen(18). Although the initial cost (approximately US$1500) may seem high, it is estimated that this cost is equivalent to 6-12 months cost of oxygen supply for a typical district hospital. One oxygen concentrator can provide low flow oxygen to up to four sick children. Flow meters should also be attached to concentrator to ensure adequate flow. The cost savings provided by the oxygen concentrators could be used to provide other essential medicines and supplies in a resource constrained setting. Oxygen concentrator requires electricity to run, but use with solar power has been reported(19). Provision of oxygen optimally is a quality care issue. In resource poor settings, there is a need to look for more cost-effective ways of oxygen management. The use of oxygen concentrators and provision of oxygen by nasal prongs or catheter can reduce the cost of oxygen therapy tremendously. The use of pulse oximeter can improve the care of critically ill children and provide cost savings, especially if the oxygen source is cylinders. To improve the affordability, professional academic organizations can encourage their government and local manufacturers to explore the possibility of local production of pulse oximeters and oxygen concentrators. There is also a need to address research issues such as the impact of using pulse oximeter and/or oxygen concentrator on disease outcome and mortality, cost effectiveness studies of various oxygen sources and effectiveness of various methods of oxygen delivery especially the less studied oropharyngeal route. The results of these studies could potentially impact the outcome of children with ARI. With large number of pediatricians as its members, IAP can help in improving the management of hypoxemia and pneumonia in children, by ensuring that - i) health workers are aware that hypoxemia can potentially lead to death and that it is assessed appropriately; ii) oxygen is available to those who need it and iii) oxygen is delivered efficiently and effectively for the required duration. Shamim Qazi, Department of Child and Adolescent Health, and Development, World Health Organization, 20 Avenue Appia, CH 1211, Geneve-27, Switzerland. E-mail: [email protected]
|
|
References |
|
