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Prevalence and predictors of hypoxemia in acute respiratory infections presenting to pediatric emergency department Singhi S, Deep A, Kaur H
Indian Journal of Critical Care Medicine
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PEDIATRIC SECTION
Year : 2003  |  Volume : 7  |  Issue : 2  |  Page : 118-123

Prevalence and predictors of hypoxemia in acute respiratory infections presenting to pediatric emergency department


Department of Pediatrics, Postgraduate Institute of Medical Education and Research, Chandigarh 160012

Correspondence Address:
Department of Pediatrics, PGIMER, Chandigarh 160012
drsinghi@glidenet.in


  »  Abstract

Rational & Objective: Early detection of hypoxemia and oxygen therapy improves the outcome of children with acute respiratory illnesses (ARI). However, facility to measure oxygen saturation (SpO2) is not available in many health facilities of resource poor countries. We have studied prevalence of hypoxemia in children with ARI and examined value of various clinical signs to predict hypoxemia. Subjects & Methods: Consecutive children, aged 2 months – 59 months, with respiratory symptom(s) attending the pediatric emergency service between Oct 2001 to December 2002 were studied. Presence or absence of cough, nasal flaring, ability to feed/drink, cyanosis, chestwall indrawing, wheeze, tachypnoea (respiratory rate >50/min in children up to 11 months and >40/min up to 59 months), crepitations on auscultation and oxygen saturation (SpO2, by Nellcore™pulse oximeter) and clinical diagnosis were recorded. Results: Of 2216 children studied 266 (11.9%) had hypoxemia (SpO2 £90%). It was seen in 73.8% of 126 patients with WHO defined very severe pneumonia, 25.8% of 331 patients with severe pneumonia, 11% of 146 patients with bronochiolitis and 6.5% of 338 patients with acute asthma. Most sensitive indicators of hypoxemia were chestwall indrawing (sensitivity-90%, negative predictive value –98%) and crepitations (sensitivity-75%, negative predictive value 95.7%) while the best positive predictive value was seen with cyanosis (71.4%) and inability to feed (47.6%). Nasal flaring had the good balance of sensitivity (64%), specificity (82%) and positive predictive value (33%) among the signs studied. Conclusion: None of the clinical signs of respiratory distress had all the attributes of a good predictors of hypoxemia. Chest wall indrawing was the most sensitive and “inability to feed/ drink” was the most specific indicator.

How to cite this article:
Singhi S, Deep A, Kaur H. Prevalence and predictors of hypoxemia in acute respiratory infections presenting to pediatric emergency department. Indian J Crit Care Med 2003;7:118-23


How to cite this URL:
Singhi S, Deep A, Kaur H. Prevalence and predictors of hypoxemia in acute respiratory infections presenting to pediatric emergency department. Indian J Crit Care Med [serial online] 2003 [cited 2014 Mar 7];7:118-23. Available from: http://www.ijccm.org/text.asp?2003/7/2/118/5739


Acute Respiratory tract infections are among the major causes of preventable morbidity and mortality worldwide, with most of the deaths occurring in under five children in developing countries.[1] Hypoxemia is the most serious manifestation of severe respiratory illness in children and a strong risk factor for mortality.[2] The case fatality rate is inversely related to oxygen saturation of arterial blood.[3] The hemoglobin oxygen saturation (SPO2) measured using a pulse oximeter has been shown to predict outcome in ARI[2] and delivery of oxygen to hypoxemic children may improve the outcome.[4],[5] The first concern of a health care provider in the acutely ill children is to detect possible hypoxemia and start oxygen therapy whether in a primary care or a tertiary care health facility. However, facilities to measure SPO2 are not available at all centers especially in the resource poor developing countries. In such a situation the indication for oxygen therapy has to be based on easily recognizable clinical surrogate markers of hypoxemia. It is therefore important to identify a minimum set of clinical signs that can reliably predict presence of hypoxemia in children with ARI that can be used by health care provider to institute oxygen therapy.

Several clinical signs and symptoms have been studied for their ability to predict hypoxemia in children with ARI.[4] Most of these studies were done at high altitude[2],[3],[5],[6],[7] data from plains is limited.[8] There is a need for more data on prevalence of hypoxemia amongst children with acute respiratory illnesses at sea level and profile of children who are hypoxemic and who might benefit from oxygen treatment. The objective of this study was to determine (1) the prevalence of hypoxemia in children presenting with signs and symptoms of ARI and with respect to specific diagnostic categories and (2) clinical signs and symptoms that could predict hypoxemia in children with ARI seen in a pediatric emergency department.


  »   Material & Methods   Top

Setting
Study was conducted at Pediatric emergency department (ED) of Advanced Pediatric Centre, Postgraduate Institute of Medical Education and Research, Chandigarh. The Centre is a 180 -bedded tertiary level teaching hospital for training residents in Pediatrics and its sub-specialties and is a part of 1300- bedded multi-specialty hospital and post-graduate teaching and research institute. Chandigarh is a medium sized town spread over an area of 114sq.km.with a population of approx. 900,000 (population density: 7900 persons per sq. km, male:female ratio 773:1000)). The yearly population growth over last decade (1991-2001) has been 3.3%

Children up to twelve years of age are managed in Pediatric Emergency Department (ED) that has both observational and admission facilities. It is manned around the clock by a team of four residents (trainees in pediatrics), a senior resident physician (a trained pediatrician with postgraduate qualification) and trained nursing and paramedical staff. A consultant pediatrician is available to supervise the patients' care round the clock and a senior consultant (SS) supervises the overall functioning of the ED. Our ED is utilized as a first line service by residents of Chandigarh and surrounding villages, which contributes to about 75% of total attendance. Referrals from neighboring five states make for about 25% of total attendance.

Out of 9,000 patients seen every year in Emergency Department about 16% are neonates, 31% one to twelve months, 24% between 1 to 5 years and 29 are older than five years[9]. Respiratory illnesses were the most common reason for emergency visits in the year 1995 through 2002. Upper respiratory infection was the most common diagnosis among respiratory illnesses, followed by pneumonia (26.2%). Acute asthma (22.4%) and bronchiolitis (7.7%) were the other frequent diagnosis.

Study design and Population
This was a prospective observational study and was done as part a larger study on treatment of childhood pneumonia. It included data of all children aged 2-59 months who were brought to the Pediatric Emergency services of the Centre between October 2001 to December 2002 with signs and symptoms suggestive of an acute respiratory illness.

ARI was defined as acute onset of respiratory symptom(s) including cough, rhinorrhea, fast/difficult breathing, chest wall indrawing and wheeze of less than 14 days duration. Patients with history of chronic respiratory symptoms, previously diagnosed bronchial asthma, congenital heart disease, congenital malformations and those referred after active cardiopulmonary resuscitation were excluded from the study. The study was approved by the Ethics committee of the institute.

Methods
Within half an hour of arrival to pediatric emergency a standardized history, demographic data - age and sex, a physical examination including weight and presence or absence of various clinical symptoms and signs namely tachypnea, auscultatory signs of wheeze, ronchi, and crepitations, central cyanosis, nasal flaring and inability to feed was recorded. All clinical observations were made and recorded by a medical doctor (research fellow) and a research nurse who were trained to identify clinical signs of ALRI. Informed verbal consent was obtained from the parents.

Respiratory rate was counted by observation and auscultation method. Briefly, each upward movement of abdominal and chest wall on visual observation (observation method) and each inspiratory breath sound heard with chest piece of a Littman® stethoscope placed in upper half of right axilla were counted as one breath.

Chest wall indrawing was identified as inward movement of lower chest wall on breathing in when the child was lying flat in mother's lap or on examination table. Mother was asked to lift the child's cloths gently so that lower part of chest is visible. If the child was not quiet mother was asked to hold the child over her shoulder to calm him/her. Central cyanosis was recorded if there was bluish discoloration of tongue and buccal mucosa.

Impaired consciousness was recorded if the child was abnormally sleepy or difficult to wake, not responsive to verbal or painful stimulus

Oxygen saturation (SpO2) was measured at finger or toe with a pulse oximeter (Nellcore™ N-200, USA) using an appropriate sized pediatric sensor by a research nurse, who was not involved in clinical examination. The oximetry measurement was recorded after stabilization of the reading for one minute. Hypoxemia was defined as SpO2 £ 90 %. Chest X-ray was obtained in patients wherever applicable.

Results are presented as sensitivity, specificity, positive (PPV) or negative predictive value (NPP). Each clinical finding was analyzed for association with hypoxemia using 2 x 2 table (Chi-square test). Analysis were performed using SPSS for window (version 10.0) and Epi- info software packages.


  »   Results   Top

2216 children with ARI aged 2 to 59 months met the inclusion and exclusion criteria; all were evaluated. The mean age of study population was 3.6 years. Their SpO2 ranged from 72% to 100%. Two hundred and sixty four (11.9%) children had hypoxemia (SpO2 £ 90%). The distribution of these children with respect to diagnostic category of ARI and prevalence of hypoxemia in various categories of ARI is shown in [Table - 1]. The prevalence was highest in patients with very severe pneumonia (73.8%) followed by severe pneumonia (26%), bronochiolitis (11%) and acute asthma (6.5%). Only 0.25% of the patients with upper respiratory illness (URI) had hypoxia but 3.6% of patients with non severe pneumonia had SpO2 £ 90%.

Hypoxemia was significantly more frequent (16.1%, 159 to 986) in infants 2-11 months as compared to children 12-59 months (8.5%, 105 of 1230, P<0.05, [Table - 2]). Across the disease category prevalence of hypoxia was similar in infants 2-11months and children 12-59 months with URI, non-severe and severe pneumonia [Table - 2], but it was more frequent in children 12-59 months with acute asthma (<0.05).

[Table - 3] shows the sensitivity, specificity and predictive value (PV) of individual clinical signs for hypoxemia. In general physical signs were specific but not sensitive for predicting hypoxemia. The most sensitive indicators of hypoxemia were chest wall indrawing (sensitivity 90% and PV 98%), crepitations (sensitivity 75% and positive PV 95.7%) while the best predictor was cyanosis (PV 71.4%) and inability to feed (PV 47.6%). Cyanosis was found to effectively predict hypoxia but if used alone would have failed to detect more than 60% of children with hypoxia. Nasal flaring had a good balance combination of sensitivity (64%) and PPV 33%.


  »   Discussion   Top

We found that hypoxemia was common in patients with ALRI; more so in infants than in children 1-5 years old. The prevalence of hypoxemia had been quite variable in different settings. In a study by Duke et al[5] 73% of patients with ALRI had hypoxemia (defined as SpO2< 88%), while it was 5.9% in Gambian children with ALRI.[8]

The principal mechanism for hypoxia of acute respiratory infection is a mismatch between ventilation and perfusion in areas of pneumonic consolidation Lung compliance decreases as consolidation develops, leading to increased work required for ventilation. Dehydration from fever, panting and inability to drink lead to hemoconcentration, peripheral under perfusion and increase metabolic acidosis leading to compensatory hyperventilation, which limits the usefulness of elevated respiratory rate in assessing the degree of hypoxia despite its usefulness in gauging the degree of systemic disturbance.

A systematic review of studies on the prevalence and predictors of hypoxemia in children by Lozano et al[7] found that the prevalence of hypoxemia was dependent upon a number of factors including the type of health facility (setting of the study).[9],[10] In their study, the prevalence ranged from 6 to 9% in outdoor setting to 31- 43% in emergency departments to a maximum of 47% in hospitalized children. Selection biases are likely between different health care facilities. Hypoxemia is more likely in a emergency department of referral hospital than a primary care setting and still more common in selected hospitalized children.[5],[7],[10],[11] At our facility, an emergency department at sea level, the prevalence of hypoxemia was much lower (11.9%) than that reported at higher altitude.

At what level of SpO2 should oxygen be supplemented to patients with ARI is of major concern. Published data shows lower prevalence of hypoxemia in our study and plains as compared to high altitude[12] Hypoxemia may be more frequent and more severe in children who live at high altitude because of reduced pressure of atmospheric oxygen. Physiological responses to high altitude hypoxemia namely shunting of pulmonary blood flow to the lung apices, increased cardiac output, increased ventilation and pulmonary arterial pressure, exaggerated vasoconstriction in the basal lung, and resultant ventilation perfusion mismatch in the supine position may further worsen the severity and prolong duration of hypoxemia seen at higher altitude. SpO2 values considered abnormal at sea level are frequently found at high altitude in healthy children, and normal values vary at different altitudes. In light of difference in normal SpO2 values at plains and high altitude [7],[13],[14],[15],[16] the SpO2 cut off to define hypoxia and to administer supplementary oxygen to sick children can not be uniform at high altitude and plains. There is a need to study outcome of children with ALRI who are given supplemental oxygen therapy using varying SpO2 cut off values, to optimize use of oxygen for a cost effective health car.

Studies on predictors of hypoxemia in patients living at sea level are scarce,[8] though similar studies have been conducted at high altitude.[2],[3],[5],[10],[13] Such studies might help in the selection of sick children for oxygen treatment in a busy emergency room in places where oximeters are not available. In addition, physiological management is related to clinical signs. The presence of certain clinical signs and symptoms in patients with ARI is predictive of hypoxemia indicating that detection of these signs and hence hypoxemia may be a crucial part in the clinical management of patients with ARI.[17] This aspect is very important especially in resource poor developing countries where facilities to measure SpO2 are not easily available at all centres. World Health Organization has published recommendations for hospital management of pneumonia in developing countries suggesting that with limited availability of oxygen, only children with cyanosis or inability to drink should be given oxygen[4] Our finding in a essence confirm and validate the WHO criteria for provision of oxygen when oximetry is not readily available.

A number of physical signs were highly significantly associated with hypoxemia but the sensitivity of each signs was low. Besides chest indrawing, nasal flaring, recessions, inability to feed and crepitations on auscultation were found to be other clinical sign that could help identification of hypoxemia but none of these signs could independently do so. None of combinations of clinical signs could predict hypoxemia very well. The signs with high sensitivity had poor specificity and vice versa. Cyanosis is invariably considered to be associated with hypoxemia[4],[18] but the difficulty of its detection, especially in dark skinned children, makes it an insensitive marker.[3],[13] None of infants under 12 months in our study had cyanosis. We believe that in a setting where oxygen is delivered in cylinders a pulse oximeter would be a cost effective tool as it would allow precise identification of children with hypoxemia; delivery of oxygen to children who do not actually need it can be avoided, thus avoiding oxygen wastage. Teaching of clinical signs (which predict hypoxemia) to health professionals in a more peripheral set up can help children in need of supplemental oxygen to be referred to bigger hospitals, thus decreasing the morbidity due to hypoxemia. We therefore recommend routine delivery of oxygen to children who present with respiratory illness with chest wall retractions, nasal flaring, inability to feed and or cyanosis, if SpO2 values cannot be measured.

Studies that examined relationship between chest indrawing and hypoxemia has given conflicting results [3],[13],[18],[19],[20]. One of the studies at high altitude found chest indrawing as highly sensitive (88%) but poorly specific[3] while other found it having low sensitivity (35%) and high specificity.[13] Auscultatory finding of either ronchi or crepitations had good sensitivity and specificity. At high altitude presence of either ronchi or crepitations had a 96% sensitivity and 47% specificity to predict hypoxia.[13] Can health care workers can be trained in auscultation?

Oxygen therapy not only improves the survival, but it may also be preventing substantial morbidity that may occur from prolonged hypoxemia in children who survive.[21],[22],[23] Since supplemental oxygen in children with respiratory distress has no serious adverse effects, a sign with high sensitivity for detection of hypoxemia such as chest retraction may be preferable as an indicator of need for oxygen therapy. On the other hand it is possible that supplemental oxygen to these children with chest indrawing who have not yet progressed to hypoxemia may offer several advantages. It may prevent exhaustion from rapid respiratory efforts by improving arterial oxygenation and by decreasing acidosis. However this aspect needs further study.

Our data suggest that using only a few physical signs, hypoxemia will be missed in certain children or oxygen will be wasted in children who do not really need it. In resource poor countries where oxygen has to be brought in cylinders, pulse oximeters might be a cost effective and objective option to assess hypoxemia, it will allow precise identification of children in need of oxygen. The cost of oxygen and logistics of transporting cylinders are major public health hazards in developing countries. In more peripheral centres where hypoxemic children have to be screened by using physical signs as an aid for referral to higher centres, teaching of these signs to health professionals can enable faster and accurate referral. There is a need for more evidence about the prevalence of hypoxemia at sea level, children with ALRI who may benefit from oxygen therapy and the best ways to predict hypoxemia in remote settings to come to a definite conclusion.

We would have liked to study various predictors of hypoxemia with stratification by age and disease category but it cannot be complied at this time , it is planned for a latter stage when the sample size reaches a reasonable number within each age group namely neonate, infants 2-11 months, and 1-5 years and diagnostic categories. Nonetheless, we would like to point out that categorization of respiratory illness in URI, non-severe pneumonia, severe pneumonia and very severe pneumonia is based on clinical signs that have been individually studies (respiratory rate, chest indrawing, cyanosis and inability to feed). An analysis based on diagnostic category is needed to further define the variables associated with hypoxemia with respect to specific diseaese.

To conclude, at present it appears unlikely that we agree on a specific set of clinical signs that consistently indicate hypoxemia in children with ALRI in different regions and altitude. Pulse oximeter remains gold standard to detect hypoxemia in children presenting with respiratory symptoms and signs to an emergency room.Clinical signs such as chest wall retraction, inability to feed and cyanosis that may be used by health workers to allow rational use of oxygen in places where pulse oximeter is not available.

  »   References   Top

1. Chretein J, Holland W, Macklem P, Murray J, Woolock A. Acute Respiratory infection in children : A global public health problem. N Engl J Med 1984;310:982-4.  Back to cited text no. 1    
2. Duke T, Frank D, Mgone J. Hypoxemia in children with severe pneumonia in Papua New Guinea. Int J Tuberc Lung Dis 2000;5:511-9.  Back to cited text no. 2    
3. Onyango FE, Steinhoff MC, Wafula EM, Wariua S, Musia J, Kitonyi J. Hypoxaemia in young Kenyan children with acute lower respiratory infection. BMJ 1993;306:612-5.  Back to cited text no. 3  [PUBMED]  
4. WHO Technical basis for the WHO recommendation on the management of pneumonia in children at first level health facilities Geneva: WHO/ARI/91.  Back to cited text no. 4    
5. Duke T, Blaschke AJ, Sialis S, Bonkowsky JL. Hypoxaemia in Acute Respiratory and non respiratory illnesses in neonates and children in a developing country. Arch Dis Child 2002;86:108-12.   Back to cited text no. 5  [PUBMED]  [FULLTEXT]
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7. Lozano JM, Steinhoff M, Ruiz JG. Meza ML, Martinez N, Dussan B. Clinical predictors of acute radiological pneumonia and hypoxaemia at high altitude. Arch Dis Child 1994;71:323-7.  Back to cited text no. 7    
8. Usen S, Weber M, Mullholand K, et al. Clinical predictors of hypoxaemia in Gambian children with acute lower respiratory tract infection : prospective cohort study. BMJ 1999;318:86-91.  Back to cited text no. 8    
9. Singhi S, Jain V, Gupta G. Pediatric admissions at a tertiary care hospital in India. J Trop Pediatr 2003;49:00-00 (In Press).  Back to cited text no. 9    
10. Lozano JM. Epidemiology of hypoxaemia in children with acute lower respiratory infection. Int J Tuberc Lung Dis 2001;5:496-504.  Back to cited text no. 10  [PUBMED]  
11. Rajesh VT, Singhi S, Kataria S. Tachypnoea is a good predictor of hypoxia in acutely ill children. Arch Dis Child 2000;82:46-9.  Back to cited text no. 11  [PUBMED]  [FULLTEXT]
12. Singhi S, Bharti B. Response to Duke, et al. Hypoxaemia in acute respiratory and non-respiratory illnesses in neonates and children in a developing country. Arch Dis Child 2003;88:364-5.   Back to cited text no. 12  [PUBMED]  [FULLTEXT]
13. Reuland DS, Steinhoff MC, Gilman RH, Oliveres EG, Jabra A, Finkelstein D. Prevalence and prediction of hypoxemia in children with respiratory infections in the Peruvian Andes. J Pediatr 1991;119:900-6.  Back to cited text no. 13    
14. Nicholas R, Yaron M, Reeves J. Oxygen saturation in children living at moderate altitude. J Am Board Fam Pract 1993;6:452-6.  Back to cited text no. 14  [PUBMED]  
15. Gamponia MJ, Babaali H, Yugar F, Gilman RH. Reference values for pulse oximetry at high altitude. Arch Dis Child 1998;78:461-5.  Back to cited text no. 15  [PUBMED]  [FULLTEXT]
16. Huicho L, Pawson IG, Leon-Velarde F, Rivera-Ch M, Pacheco A, Muro M, et al. Oxygen saturation and heart rate in healthy school children and adolescents living at high altitude. Am J Hum Biol 2001;13:761-70.  Back to cited text no. 16    
17. Wang EL, Milner RA, Navas L, Maj H. Observer agreement for respiratory signs and oximetry in infants hospitalized with lower respiratory infections. Am Rev Respir Dis 1992;145:106-9.  Back to cited text no. 17    
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21. Stadie WC. The treatment of anoxemia in pneumonia in an oxygen chamber. J Exp Med 1922;35:337-60.  Back to cited text no. 21    
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23. Binger CAL. Therapeutic value of oxygen in pneumonia. NY State J Med 1925;25:953-8.  Back to cited text no. 23    

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