Saturation by pulse oximetry: comparison of the results obtained by instruments of different brands

Randomised crossover study on pulse oximeter readings from different sensors in very preterm infants

OBJECTIVE

In extremely preterm infants, different target ranges for pulse oximeter saturation (SpO2) may affect mortality and morbidity. Thus, the impact of technical changes potentially affecting measurements should be assessed. We studied SpO2 readings from different sensors for systematic deviations.

DESIGN

Single-centre, randomised, triple crossover study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

24 infants, born at <32 weeks' gestation, with current weight <1500 g and without right-to-left shunt via a patent ductus arteriosus.

INTERVENTIONS

Simultaneous readings from three SpO2 sensors (Red Diamond (RD), Photoplethysmography (PPG), Low Noise Cabled Sensors (LNCS)) were logged at 0.5 Hz over 6 hour/infant and compared with LNCS as control using analysis of variance. Sensor position was randomly allocated and rotated every 2 hours. Seven different batches each were used.

OUTCOMES

Primary outcome was the difference in SpO2 readings. Secondary outcomes were differences between sensors in the proportion of time within the SpO2-target range (90-95 (100)%).

RESULTS

Mean gestational age at birth (±SD) was 274/7 (±23/7) weeks, postnatal age 20 (±20) days. 134 hours of recording were analysed. Mean SpO2 (±SD) was 94.0% (±3.8; LNCS) versus 92.2% (±4.0; RD; p<0.0001) and 94.5% (±3.9; PPG; p<0.0001), respectively. Mean SpO2 difference (95% CI) was -1.8% (-1.9 to -1.8; RD) and 0.5% (0.4 to 0.5; PPG). Proportion of time in target was significantly lower with RD sensors (84.8% vs 91.7%; p=0.0001) and similar with PPG sensors (91.1% vs 91.7%; p=0.63).

CONCLUSION

There were systematic differences in SpO2 readings between RD sensors versus LNCS. These findings may impact mortality and morbidity of preterm infants, particularly when aiming for higher SpO2-target ranges (eg, 90-95%).

TRIAL REGISTRATION NUMBER

DRKS00027285.

Noninvasive Monitoring and Assessment of Oxygenation in Infants

Formerly, assessing oxygenation relied on recognizing cyanosis; however, this is unreliable. Also, in neonates, a pink color, suggesting absence of severe hypoxemia, is difficult to assess. An objective and continuous assessment of oxygenation is necessary. Currently, this is best achieved noninvasively by transcutaneous partial pressure of oxygen (PTcO₂) monitoring or pulse oximetry. Because both PTcO₂ and oxygen saturation monitors (pulse oximeters) may display erroneous measurements, thorough understanding of their operating principles is required. Also, clinicians must recognize the range of values expected in healthy neonates. In this article, data on these issues are reviewed.

Pulse Oximetry and Arterial Oxygen Saturation during Cardiopulmonary Exercise Testing

INTRODUCTION/PURPOSE

Peripheral capillary oxygen saturation (SpO2) is used as surrogate for arterial blood oxygen saturation. We studied the degree of discrepancy between SpO2 and arterial oxygen (SaO2) and identified parameters that may explain this difference.

METHODS

We included patients who underwent cardiopulmonary exercise testing at Cleveland Clinic. Pulse oximeters with forehead probes measured SpO2 and arterial blood gas samples provided the SaO2 both at rest and peak exercise.

RESULTS

We included 751 patients, 54 ± 16 yr old with 53% of female gender. Bland-Altman analysis revealed a bias of 3.8% with limits of agreement of 0.3% to 7.9% between SpO2 and SaO2 at rest. A total of 174 (23%) patients had SpO2 ≥ 5% of SaO2, and these individuals were older, current smokers with lower forced expiratory volume in the first second and higher partial pressure of carbon dioxide and carboxyhemoglobin. At peak exercise (n = 631), 75 (12%) SpO2 values were lower than the SaO2 determinations reflecting difficulties in the SpO2 measurement in some patients. The bias between SpO2 and SaO2 was 2.6% with limits of agreement between -2.9% and 8.1%. Values of SpO2 ≥ 5% of SaO2 (n = 78, 12%) were associated with the significant resting variables plus lower heart rate, oxygen consumption, and oxygen pulse. In multivariate analyses, carboxyhemoglobin remained significantly associated with the difference between SpO2 and SaO2 both at rest and peak exercise.

CONCLUSIONS

In the present study, pulse oximetry commonly overestimated the SaO2. Increased carboxyhemoglobin levels are independently associated with the difference between SpO2 and SaO2, a finding particularly relevant in smokers.

Nocturnal oxygen saturation profiles of healthy term infants

OBJECTIVE

Pulse oximetry is used extensively in hospital and home settings to measure arterial oxygen saturation (SpO2). Interpretation of the trend and range of SpO2 values observed in infants is currently limited by a lack of reference ranges using current devices, and may be augmented by development of cumulative frequency (CF) reference-curves. This study aims to provide reference oxygen saturation values from a prospective longitudinal cohort of healthy infants.

DESIGN

Prospective longitudinal cohort study.

SETTING

Sleep-laboratory.

PATIENTS

34 healthy term infants were enrolled, and studied at 2 weeks, 3, 6, 12 and 24 months of age (N=30, 25, 27, 26, 20, respectively).

INTERVENTIONS

Full overnight polysomnography, including 2 s averaging pulse oximetry (Masimo Radical).

MAIN OUTCOME MEASUREMENTS

Summary SpO2 statistics (mean, median, 5th and 10th percentiles) and SpO2 CF plots were calculated for each recording. CF reference-curves were then generated for each study age. Analyses were repeated with sleep-state stratifications and inclusion of manual artefact removal.

RESULTS

Median nocturnal SpO2 values ranged between 98% and 99% over the first 2 years of life and the CF reference-curves shift right by 1% between 2 weeks and 3 months. CF reference-curves did not change with manual artefact removal during sleep and did not vary between rapid eye movement (REM) and non-REM sleep. Manual artefact removal did significantly change summary statistics and CF reference-curves during wake.

CONCLUSIONS

SpO2 CF curves provide an intuitive visual tool for evaluating whether an individual's nocturnal SpO2 distribution falls within the range of healthy age-matched infants, thereby complementing summary statistics in the interpretation of extended oximetry recordings in infants.

Comparison of heart rate and oxygen saturation measurements from Masimo and Nellcor pulse oximeters in newly born term infants

AIM

To compare heart rate (HR) measurements from Masimo and Nellcor pulse oximeters (POs) against HR measured via a three lead electrocardiograph (ECG) (HRECG ). We also compared peripheral oxygen saturation (SpO2 ) measurements between Nellcor and Masimo oximeters.

METHOD

Term infants born via elective caesarean section were studied. ECG leads were placed on the infant's chest and abdomen. Masimo and Nellcor PO sensors were randomly allocated to either foot. The monitors were placed on a trolley, and data from each monitor screen captured by a video camera. HR, SpO2 measurements and signal quality were extracted. Bland-Altman analysis was used to determine agreement between HR from the ECG and each oximeter, and between SpO2 from the oximeters.

RESULTS

We studied 44 infants of whom 4 were resuscitated. More than 8000 pairs of observations were used for each comparison of HR and SpO2. The mean difference (±2SD) between HRECG and HRN ellcor was -0.8 (±11) beats per minute (bpm); between HRECG and HRM asimo was 0.2 (±9) bpm. The mean (±2SD) difference between SpO2Masimo and SpO2Nellcor was -3 (±15)%. The Nellcor PO measured 20% higher than the Masimo PO at SpO2 <70%.

CONCLUSION

Both oximeters accurately measure HR. There was good agreement between SpO2 measurements when SpO2 ≥70%. At lower SpO2 , agreement was poorer.

Monitoring of standard hemodynamic parameters: heart rate, systemic blood pressure, atrial pressure, pulse oximetry, and end-tidal CO2

BACKGROUND

Continuous monitoring of various clinical parameters of hemodynamic and respiratory status in pediatric critical care medicine has become routine. The evidence supporting these practices is examined in this review.

METHODOLOGY

A search of MEDLINE, EMBASE, PubMed, and the Cochrane Database was conducted to find controlled trials of heart rate, electrocardiography, noninvasive and invasive blood pressure, atrial pressure, end-tidal carbon dioxide, and pulse oximetry monitoring. Adult and pediatric data were considered. Guidelines published by the Society for Critical Care Medicine, the American Heart Association, the American Academy of Pediatrics, and the International Liaison Committee on Resuscitation were reviewed, including further review of references cited.

RESULTS AND CONCLUSIONS

Use of heart rate, electrocardiography, noninvasive and arterial blood pressure, atrial pressure, pulse oximetry, and end-tidal carbon dioxide monitoring in the pediatric critical care unit is commonplace; this practice, however, is not supported by well-controlled clinical trials. Despite the majority of literature being case series, expert opinion would suggest that use of routine pulse oximetry and end-tidal carbon dioxide is the current standard of care. In addition, literature would suggest that invasive arterial monitoring is the current standard for monitoring in the setting of shock. The use of heart rate, electrocardiography. and atrial pressure monitoring is advantageous in specific clinical scenarios (postoperative cardiac surgery); however, the evidence for this is based on numerous case series only.

NeOProM: Neonatal Oxygenation Prospective Meta-analysis Collaboration study protocol

BACKGROUND

The appropriate level of oxygenation for extremely preterm neonates (<28 weeks' gestation) to maximise the greatest chance of survival, without incurring significant morbidity, remains unknown. Infants exposed to lower levels of oxygen (targeting oxygen saturations of <90%) in the first weeks of life are at increased risk of death, cerebral palsy, patent ductus arteriosus, pulmonary vascular resistance and apnoea, whilst those maintained in higher levels of oxygen (targeting oxygen saturations of >90%) have been reported to have greater rates of morbidity including retinopathy of prematurity and chronic lung disease. In order to answer this clinical dilemma reliably, large scale trial evidence is needed.

METHODS/DESIGN

To detect a small but important 4% increase in death or severe disability in survivors, over 5000 neonates would need to be recruited. As extreme prematurity affects 1% of births, such a project undertaken by one trial group would be prohibitively lengthy and expensive. Hence, the Neonatal Oxygenation Prospective Meta-analysis (NeOProM) Collaboration has been formed. A prospective meta-analysis (PMA) is one where studies are identified, evaluated, and determined to be eligible before the results of any included studies are known or published, thereby avoiding some of the potential biases inherent in standard, retrospective meta-analyses. This methodology provides the same strengths as a single large-scale multicentre randomised study whilst allowing greater pragmatic flexibility. The NeOProM Collaboration protocol (NCT01124331) has been agreed prior to the results of individual trials being available. This includes pre-specifying the hypotheses, inclusion criteria and outcome measures to be used. Each trial will first publish their respective results as they become available and the combined meta-analytic results, using individual patient data, will be published when all trials are complete. The primary outcome to be assessed is a composite outcome of death or major disability at 18 months - 2 years corrected age. Secondary outcomes include several measures of neonatal morbidity. The size of the combined dataset will allow the effect of the interventions to be explored more reliably with respect to pre-specified patient- and intervention-level characteristics.

DISCUSSION

Results should be available by 2014.

Effectiveness of Cheek and Jaw Support to Improve Feeding Performance of Preterm Infants

OBJECTIVE. We examined the effects of cheek and jaw support on the feeding ability of inefficient feeders born prematurely.

METHOD. Twenty preterm infants served as their own controls. Each infant received either intervention (feeding with oral support) or control (feeding without oral support) for 2 consecutive feedings per day on 2 consecutive days.

RESULTS. Infants displayed a greater intake rate during the intervention feedings, both during the first 5 min (p = .046) and throughout the entire feeding (p = .023). The percentage of leakage during the first 5-min feeding was smaller in the intervention condition than in the control condition (p = .040). No significant differences were found between the two conditions in the sucking, physiological, and alertness variables.

CONCLUSION. Findings confirm oral support as a safe and effective strategy to improve the feeding performance of preterm infants who are poor feeders.

Oxygen titration strategies in chronic neonatal lung disease

The history of oxygen therapy in neonatology has been littered with error. Controversies remain in a number of areas of oxygen therapy, including targets and strategies in supplemental oxygen therapy in Chronic Neonatal Lung Disease (CNLD). This article reviews some of these controversies, and makes some recommendations based on the available evidence. In graduates of neonatal units who are left with CNLD, oxygen saturation should be kept above 93-95%, with levels below 90% being avoided as far as possible. Titration of oxygen should be done using oximetry recordings which include periods of different activities. Weaning of oxygen supplementation should only be done based on satisfactory recordings during a trial of a lower flow. There is insufficient evidence to say whether weaning for increasing hours a day or stepwise weaning to a continuous lower flow is a better method.

Defining the reference range for oxygen saturation for infants after birth

OBJECTIVE

The goal was to define reference ranges for pulse oxygen saturation (Spo(2)) values in the first 10 minutes after birth for infants who received no medical intervention in the delivery room.

METHODS

Infants were eligible if a member of the research team was available to record Spo(2) immediately after birth. Infants were excluded if they received supplemental oxygen or any type of assisted ventilation. Spo(2) was measured with a sensor applied to the right hand or wrist as soon as possible after birth; data were collected every 2 seconds.

RESULTS

We studied 468 infants and recorded 61650 Spo(2) data points. The infants had a mean + or - SD gestational age of 38 + or - 4 weeks and birth weight of 2970 + or - 918 g. For all 468 infants, the 3rd, 10th, 50th, 90th, and 97th percentile values at 1 minute were 29%, 39%, 66%, 87%, and 92%, respectively, those at 2 minutes were 34%, 46%, 73%, 91%, and 95%, and those at 5 minutes were 59%, 73%, 89%, 97%, and 98%. It took a median of 7.9 minutes (interquartile range: 5.0-10 minutes) to reach a Spo(2) value of >90%. Spo(2) values for preterm infants increased more slowly than those for term infants. We present percentile charts for all infants, term infants of > or = 37 weeks, preterm infants of 32 to 36 weeks, and extremely preterm infants of <32 weeks.

CONCLUSION

These data represent reference ranges for Spo(2) in the first 10 minutes after birth for preterm and term infants.

Pulse oximeter accuracy and precision affected by sensor location in cyanotic children

OBJECTIVE

Children's digits are often too small for proper attachment of oximeter sensors, necessitating sensor placement on the sole of the foot or palm of the hand. No study has determined what effect these sensor locations have on the accuracy and precision of this technology. The objective of this study was to assess the effect of sensor location on pulse oximeter accuracy (i.e., bias) and precision in critically ill children.

DESIGN

Prospective, observational study with consecutive sampling.

SETTING

Tertiary care, pediatric intensive care unit.

PATIENTS

Fifty critically ill children, newborn to 2 yrs of age, with an indwelling arterial catheter. Forty-seven of 50 (94%) patients were postcardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Co-oximeter-measured arterial oxygen saturation (Sao2) was compared with simultaneously obtained pulse oximetry saturations (Spo2). A total of 98 measurements were obtained, 48 measurements in the upper extremities (finger and palm) and 50 measurements in the lower extremities (toe and sole). The median Sao2 was 92% (66% to 100%). There was a significant difference in bias (i.e., average Spo2 - Sao2) and precision (+/-1 sd) when the sole and toe were compared (sole, 2.9 +/- 3.9 vs. toe, 1.6 +/- 2.2, p = .02) but no significant difference in bias and precision between the palm and the finger (palm, 1.4 +/- 3.2 vs. finger, 1.2 +/- 2.3, p = .99). There was a significant difference in bias +/- precision when the Sao2 was <90% compared with when Sao2 was >or=90% in the sole (6.0 +/- 5.7 vs. 1.8 +/- 2.1, p = .002) and palm (4.5 +/- 4.5 vs. 0.7 +/- 2.4, p = .006) but no significant difference in the finger (1.8 +/- 3.8 vs. 1.1 +/- 1.8, p = .95) or toe (1.9 +/- 2.9 vs. 1.6 +/- 1.9, p = .65).

CONCLUSIONS

The Philips M1020A pulse oximeter and Nellcor MAX-N sensors were less accurate and precise when used on the sole of the foot or palm of the hand of a child with an Sao2 <90%.

A Comparative Analysis of Arterial Oxygen Saturation among Tibetans And Han Born And Raised at High Altitude

This study compares resting arterial oxygen saturation as measured by pulse oximetry (Sp(O2)) among 818 Tibetans and 668 Han who were born and raised at altitudes between 3200 and 4300 m in Qinghai Province, Western China. Both Tibetans and Han show an increase in Sp(O2) values between the ages of 5 and 19 yr, and both groups show a decline after the third decade. However, mean, age-adjusted Sp(O2) values at rest do not differ significantly among growing Tibetans and Han aged 5 through 19 yr or among Tibetans and Han aged 20 through 51 yr. Therefore, the results of this study do not support the hypothesis that indigenous groups possess a superior arterial saturation while awake and at rest compared to lowlanders who have been born and raised at high altitude. Differences between adult Tibetan males and females approach statistical significance (females show higher values than males), while differences between adult Han males and females are not statistically significant. A review of the literature indicates that substantial interstudy variation exists in resting Sp(O2) values among Tibetans residing at high altitudes (between 2% and 4%, depending on the age of individuals measured) and may reflect differences in sample size, health of participants, instruments, probe location, and measurement protocols.

Influence of digital clubbing on oxygen saturation measurements by pulse-oximetry in cystic fibrosis patients

OBJECTIVE

To determine the influence of digital clubbing on oxygen saturation by pulse oximetry measurements (SpO2) in Cystic Fibrosis patients.

BACKGROUND

Measuring the arterial oxygen saturation at the fingertip by pulse-oximetry is commonly used in the management of CF patients. In these patients, clinical signs of hyperoxia are often observed with oxygen supplies based on digital oximetry readings. This suggests inaccuracies in the digital measurement method, which in its turn may be caused by digital clubbing. In order to study the influence of digital clubbing, measurements between fingertip and forehead sensor were compared in a clubbing and non-clubbing CF-population. The ear sensor measurements are used as a reference variable.

METHODS

Two groups were examined. Group 1 consisted of 50 CF patients without digital clubbing (DPD/IPD ratio<1.00). Group 2 consisted of 50 CF patients with digital clubbing (DPD/IPD ratio>1.00). Patients were measured at rest before any treatment and with their daily oxygen supply, if applicable. Saturation was simultaneously measured with three Criticare SpO2 T pulse oximeters, using a fingertip sensor at the right index (transmission oximetry), a forehead sensor at the forehead (reflectance oximetry) and an ear sensor at the right ear.

RESULTS

Using the Bland and Altman method no clear difference was found between the saturation measurements of right ear versus forehead sensor in the two groups. When the measurements of right ear versus fingertip sensor are compared there is still no difference for the non-clubbing group. On the contrary, for the clubbing group lower saturation scores were measured by the fingertip probe compared to the right ear measurement. The differences in saturation became greater as the saturation value at fingertip was lower.

CONCLUSION

Digital clubbing significantly influences the registrations of the SpO2 measurements by means of a fingertip probe, underestimating the saturation. It can be advised to use the ear sensor as good alternative for these patients.

Hemoglobin oxygen saturation discrepancy using various methods in patients with sickle cell vaso-occlusive painful crisis

OBJECTIVE

To evaluate agreement among various methods for measuring oxyhemoglobin (O2Hb) saturation in adult hypoxic patients with sickle cell disease (SCD) during painful vaso-occlusive crisis and to compare those results with a control group.

PATIENTS AND METHODS

The hemoglobin oxygen saturation was determined simultaneously by pulse oximetry (SpO2), co-oximetry [SO2 (functional oxyhemoglobin saturation) and FO2Hb (oxyhemoglobin fraction)] and by calculation (SaO2) using a normal O2Hb dissociation curve in 18 adult patients with SCD during vaso-occlusive crisis and 12 non-SCD patients with various cardiopulmonary diagnoses. The method proposed by Bland and Altman was used to evaluate agreement of various methods in each of the two groups.

RESULTS

Mean differences between various methods in patients with SCD were significantly larger than the control group. Limits of agreement (LOA) were also wider in the SCD group than in the control group. Mean bias between SpO2 and SO2, and SpO2 and FO2Hb in patients with SCD were -3.1 +/- 4.4 (LOA: -11.9 to 5.7) and 2 +/- 4.1 (LOA: -6.2 to 10.2) respectively, compared with -1.4 +/- 1.4 (LOA: -4.2 to 1.4) and 1.2 +/- 1.5 (LOA: -1.9 to 4.3) in the control group. A mean bias of -4.5 +/- 4 (LOA: -12.5 to 3.5) between SpO2 and SaO2 was noted in patients with SCD compared with -0.1 +/- 2.1 (LOA: -4.3 to 4.1) in the control group. The width of LOA for various methods in patients with SCD ranged from 9.8 to 17.6 compared with 1.3 to 8.4 in the control group.

CONCLUSION

Patients with SCD during vaso-occlusive crisis have discrepancies in O2Hb saturation measurements by various methods. Abnormal pulse oximetry values in these patients should be interpreted cautiously and supplemented by arterial blood gas analysis and co-oximetry.

The Australian Safe-n-Sound Baby Safety Capsule and its effect on oxygen saturation values in infants ready for discharge home

PURPOSE

To examine the effect of Australian Safe-n-Sound Baby Safety Capsule (BSC) on oxygen saturation (SpO2) values of preterm and term infants ready for discharge home.

DESIGN

A two-group pretest/protest quasi-experimental study compared the effect of the BSC on SpO2.

SAMPLE

Thirty-nine low birth weight premature newborn infants and 19 term newborn infants ready for discharge home.

MAIN OUTCOME VARIABLE

Mean oxygen saturation values and the number of oxygen desaturation events below 90 percent.

RESULTS

The mean SpO2 values for both preterm and term infants were within the normal range (>90-100 percent) for each phase of data collection (baseline, capsule, and recovery). However, mean SpO2 values decreased from baseline during the 60 minutes spent in the BSC for the preterm infants.

Reflectance pulse oximetry from core body in neonates and infants: comparison to arterial blood oxygen saturation and to transmission pulse oximetry

OBJECTIVE

To compare pulse oximetry oxygen saturation (SpO(2)) measured by a novel reflectance method from core body to arterial oxygen saturation (SaO(2)) in neonates and infants. Transmission pulse oximetry (TPO) was measured for comparison.

STUDY DESIGN

We monitored 18 infants by the two pulse oximeters simultaneously. The reflectance pulse oximetry (RPO) (PRO2, ConMed, Utica, NY) was measured on the upper back or chest, while the TPO (N395-Nellcor, Pleasanton, CA) was measured from the finger of the infant on the left hand or feet. Data from the two methods were compared to functional SaO(2) derived from blood sample drawn from arterial line for patient care and measured by a Co-oximeter (Ilex, Instrument Lab. Lexington, MA). The potential advantage of the RPO is demonstrated in a case of a premature infant with hypovolemic shock, where SaO(2) or TPO could not be obtained but oximetry was available from the RPO.

RESULTS

We used for analysis 56 RPO and 32 TPO measurements. SpO(2) obtained from the RPO was 88.3+/-9.8%, from the TPO 84.2+/-10.1%, and functional SaO(2) was 88.2+/-11.7%, with correlation coefficient of 0.93 and 0.88, respectively (p<0.0001). The mean difference (bias) and standard deviation of the differences (precision) between the RPO and the TPO compared to functional SaO(2) were -0.09+/-4.5% and 1.26+/-5.9% and the absolute errors were 3.2+/-3.1%, and 4.4+/-4.0%, respectively. The accuracy of both RPO and TPO was diminished when SaO(2) was <85%, but only the RPO remained correlated with the functional SaO(2).

CONCLUSIONS

Reflectance pulse oximetry measured from core body of neonates and infants is accurate and reliable and is comparable to the transmission SpO(2) when compared to functional SaO(2). We speculate that the reflectance method might be advantageous in cases of poor peripheral perfusion in neonates and infants.

Retinopathy of prematurity and pulse oximetry: a national survey of recent practices

OBJECTIVE

To determine if practices related to the use of pulse oximetry in the first 2 weeks following birth and after 2 weeks of age have a relationship to the rate of retinopathy of prematurity (ROP) and retinal ablation surgery in infants < or =1500 g.

STUDY DESIGN

A questionnaire was mailed in July 2001 to 318 neonatal intensive care units (NICUs) in the United States and information was collected regarding SpO2 guidelines and the rate of both severe ROP and retinal ablation surgery.

RESULTS

A total of 142 surveys were returned (45%). In all, 87% of the NICUs had SpO2 guidelines, and 60% of these centers maintained a different range of SpO2 for infants < or = or >2 weeks of age. The range of SpO2 was 82 to 100% with an average minimum (min) and maximum (max) of 89 and 95%, respectively. In the NICUs with an SpO2 max of >98% in the first 2 weeks following birth, the rate of retinal ablation surgery was 5.5 vs 3% in those units with a max SpO2 >98% (p<0.05). After 2 weeks of age, the rate of retinal ablation surgery was 3.3% when max SpO2 was >92 vs 1.3% when the max SpO2 was < or =92% (p<0.00001). The rate of > or =stage 3 ROP after 2 weeks of age was 5.5% when max SpO2 was >92 vs 2.4% when max SpO2 was < or =92% (p<0.0005).

CONCLUSION

NICUs in the US today have a wide range of SpO2 guidelines. The results of this survey show a "gradient of risk" towards less retinal ablation surgery when the max SpO2 is <98% in the first 2 weeks following birth (p<0.05). There was a statistically significant lower rate of > or =stage 3 ROP and retinal ablation surgery when the max SpO2 was < or =92% after the first 2 weeks of age. A randomized, controlled trial is needed to establish a safe upper limit of SpO2 in the premature infant at risk for developing ROP.

Controversy surrounding the use of home oxygen for premature infants with bronchopulmonary dysplasia

OBJECTIVE

To determine the criteria used in the current practice of neonatology for the initiation of home oxygen therapy in premature infants with bronchopulmonary dysplasia and to compare these criteria with the available literature regarding the use of home oxygen therapy.

STUDY DESIGN

Participants in the December 2000 meeting of the Vermont Oxford Network were surveyed regarding their current use of home oxygen therapy for infants with bronchopulmonary dysplasia.

RESULTS

Surveys were returned by 181 out of 297 participants. Pulse oximetry saturation (SpO2) thresholds for the initiation of home oxygen therapy varied widely from <84% to <98%. The most common threshold was <90% chosen by only 43% of the respondents. Additionally, 22% of the respondents did not initiate therapy until the oxygen saturation in room air was below 88%. Once on oxygen therapy, the target SpO2 also varied widely from >84% to >98%, with only 27% of respondents aiming for an SpO2 of >94%.

CONCLUSIONS

There is a clear lack of consensus among neonatologists regarding the initiation of home oxygen therapy for bronchopulmonary dysplasia. Furthermore, the criteria used for home oxygen therapy varies widely with the majority of neonatologists surveyed using oxygen saturation levels not supported by the literature. We speculate that a significant underutilization of home oxygen therapy exists for infants with bronchopulmonary dysplasia.

Operational evaluation of pulse oximetry in NICU patients with arterial access

OBJECTIVE

To investigate pulse oximetry in neonates who require arterial access as represented by the clinical data recorded to manage their care.

STUDY DESIGN

Analysis of simultaneous SpO(2) and SaO(2) from: 7-year historical NICU data (N=31905); 4-month prospective NICU data (N=566); verification data using two hemoximeters (N=52); and NICU data from two collaborating centers (N=95 and 168). The bias function (SpO(2)-SaO(2)) was regressed against the measured "gold" standard, SaO(2).

RESULTS

A significant negative correlation was found for each of the data sets between the bias function and SaO(2). This bias was similar for devices from several manufacturers (Datex-Ohmeda, Masimo, Nellcor, and Spacelabs). Maximum operational performance occurred with peaks between 92 and 97% SaO(2), but declined markedly above and below this narrow range. In all, 71 to 95% of patients exhibited data with significant bias(.)

CONCLUSION

These operational data suggest that with the methodology and devices currently in use, SpO(2) values in most all neonates who require arterial lines inaccurately correlate with measured arterial saturation.

Discharge and aftercare in chronic lung disease of the newborn

This article deals with the discharge planning and continuing care of babies with chronic lung disease of the newborn (CLD), especially those with a continuing oxygen requirement, with some reference to longer term outcome. The pattern of CLD has changed since early descriptions, and the most useful definition for persisting morbidity in a baby with lung disease is a continuing oxygen requirement beyond 36 weeks post-menstrual age. Long-term oxygen therapy to maintain oxygen saturation at a mean of 95% or more and prevent levels below 90% is the cornerstone of management, and with adequate oxygen therapy the excess mortality previously reported in CLD can largely be avoided. Care must be given to the method of assessing oxygen saturation: overnight monitoring using appropriate recording devices is recommended. Exposure to respiratory viruses should be minimized where possible. Metabolic requirements are increased, but if efforts are made to maintain adequate energy input the long-term outlook for catch-up growth in height is good. Respiratory morbidity is increased in early life, but this improves in later childhood, along with lung function and exercise tolerance. Although respiratory symptoms should be treated as they arise, there is no evidence for long-term benefit from any pharmacological intervention in CLD.

Oxygen monitoring in preterm babies: too high, too low?

A small randomised trial in 1952 showed that excess oxygen use might well be causing a major epidemic of retinal blindness in preterm babies. That single study of just 65 babies was enough to throw doubt on a longstanding treatment strategy of oxygen therapy and highlighted just how powerful a tool the randomised controlled trial could be. Confirmatory evidence from a co-operative trial 4 years later involving 212 babies banished all residual doubt and we should reproach ourselves that we have still not learnt after 50 years how to optimise oxygen delivery to the preterm baby, making further use of this powerful research tool. Two well-conducted trials have recently shown that avoiding subclinical hypoxaemia (a fractional SaO(2) of less than 92%) in babies more than a month old does nothing to improve later growth or development. It is now time the same question was asked of babies less than a month old. This is particularly important in babies of less than 28 weeks' gestation, who currently remain at serious risk of chronic lung disease and permanent retinal damage.

Pulse oximetry during low perfusion caused by emerging pneumonia and sepsis in rabbits

OBJECTIVE

This study tested the effects of low perfusion caused by emerging sepsis on the reliability of a new pulse oximetry technology (Masimo SET; IVY 405T) compared with a standard pulse oximeter (Nellcor N-200).

DESIGN

Randomized trial.

SETTING

University animal research facility.

SUBJECTS

Twenty-six anesthetized, ventilated (Fio, 1.0), adult rabbits.

INTERVENTIONS

Pneumonia/sepsis was induced by tracheal instillation of Escherichia coli. Oxygen saturation was measured by pulse oximetry (Spo ) and recorded continuously until death. Arterial oxygen saturation (Sao2) was measured hourly by oximetry and whenever Spo dropped to </=95%, or whenever a difference of >/=5% between devices occurred. Spo2 sensors were positioned at both forelegs and switched hourly.

MEASUREMENTS AND MAIN RESULTS

The total time of signal loss was longer with the N-200 vs. the IVY: 65 (4-299) mins vs. 7 (0-97) mins [median (range)], p < 0.001. Signal loss was more prevalent during the first 80% of the experimental time with the N-200 compared with the IVY. Nineteen of 26 animals had a total of 62 episodes of a falsely low Spo2 value with either one of the two devices associated with hemodynamic deterioration. Median bias (Spo2 - Sao2) was small, but variability of bias values increased toward the end of the experimental time with both devices.

CONCLUSIONS

The pulse oximeter equipped with Masimo SET was less prone to signal loss than the standard pulse oximeter in this sepsis model. Episodes of falsely low Spo2 readings may occur, and deviation of Spo2 from Sao2 may be increased with deteriorating hemodynamics with both devices.

Giving small babies oxygen: 50 years of uncertainty

A small landmark trial in 1952 showed that excess oxygen use might well be causing a major epidemic of retinal blindness in preterm babies. That a single study of just 65 babies was enough to throw doubt on a long-standing treatment strategy revealed just how powerful a tool the randomized controlled trial could be. Confirmatory evidence from a cooperative trial involving a further 212 babies banished all residual doubt just 4 years later, and it remains a major reproach that we have still not learnt, after 50 years, how to optimize the delivery of oxygen to the preterm baby with further help from this powerful tool. Two well-conducted trials have recently shown that avoiding subclinical hypoxaemia (fractional SaO(2)<92%) in babies more than a month old does nothing to improve later growth or development. It is now time the same question was asked of babies less than a month old, because we might reduce their need for ventilatory support. This is particularly important in babies of less than 28 weeks' gestation, who remain, currently, at serious risk of chronic lung disease and permanent retinal scarring.

Functional versus fractional oxygen saturation readings: bias and agreement using simulated solutions and adult blood

The purpose of this study was to examine the bias and agreement between functional oxygen saturation (SO2) and fractional oxyhemoglobin (HbO2) using simulated quality control (QC) solutions and adult blood. Using a hemoximeter, 5 analysts performed at least 5 tests each on QC solutions with 3 different hemoglobin (Hb) levels and on adult blood samples of various oxygen saturation levels representing venous or arterial samples. Bias and the limits of agreement were determined using the technique of Bland and Altman. Using QC solutions with low, normal, and high Hb levels, the bias for SO2 against HbO2 was 20.82 +/- 0.50 (n = 66), 19.14 +/- 0.56 (n = 81), and 19.59 +/- 0.43 (n = 79), respectively, with SO2 reading consistently higher. The correlation between SO2 and HbO2 was -0.49, -0.69, and -0.68, respectively. Using adult blood, the bias for SO2 against HbO2 was 1.29 +/- 0.48 for venous samples (n = 62) and 1.9 +/- 0.19 for fully oxygenated samples (n = 36), and the correlation between SO2 and HbO2 was 1.0 and 0.68, respectively. These findings suggest that the consistency between the measurements of SO2 and HbO2 may be dependent on hemoglobin levels and oxygenation status. Thus, caution is warranted when assuming that the measurements of SO2 and HbO2 are interchangeable.

Desaturation events in neonates during mechanical ventilation

This study examines the accuracy of oxygen saturation measured by Nellcor N200 pulse oximetry (SpO2) compared with arterial oxygen saturation (SaO2) measured through a three-wavelength fiberoptic umbilical catheter in 10 neonates who needed mechanical ventilation. Real-time SaO2 was validated with a reference method every 4 hours. Oxygen saturation readings (SaO2 and SpO2), along with pulse rate and pulsation, were recorded continuously every second through a computer. Concurrent care events and neonatal responses were recorded. Data were completed on 10 neonates who had an umbilical arterial catheter. Desaturation events (<90%) as measured by both SaO2 and SpO2 were described and compared. A total of 959 desaturation events occurred during an average of 51 hours of monitoring per subject. Of these events, 63% were associated with frozen SPO2 readings, and 18% of frozen readings occurred when SaO2 was <90%. Bias for SpO2 compared with SaO2 was +5.03%, with 5.6% of the readings outside the range of two standard deviations. However, 67% of the readings exceeded the 4% difference criterion between measurements. Future studies need to examine the desaturation events in relation to oxygenation status as measured by different methods.

Automatic detection of distorted plethysmogram pulses in neonates and paediatric patients using an adaptive-network-based fuzzy inference system

Despite the fact that pulse oximetry has become an essential technology in respiratory monitoring of neonates and paediatric patients, it is still fraught with artefacts causing false alarms resulting from patient or probe movement. As the shape of the plethysmogram has always been considered as a useful visual indicator for determining the reliability of SaO(2) numerical readings, automation of this observation might benefit health care providers at the bedside. We observed that the systolic upstroke time (t(1)), the diastolic time (t(2)) and heart rate (HR) extracted from the plethysmogram pulse constitute features, which can be used for detecting normal and distorted plethysmogram pulses. We developed a technique for classifying plethysmogram pulses into two categories: valid and artefact via implementations of fuzzy inference systems (FIS), which were tuned using an adaptive-network-based fuzzy inference system (ANFIS) and receiver operating characteristics (ROC) curves analysis. Features extracted from a total of 22,497 pulse waveforms obtained from 13 patients were used to systematically optimise the FIS. A further 2843 waveforms obtained from another eight patients were used for testing the system, and visually classified into 1635 (58%) valid and 1208 (42%) distorted segments. For the optimum system, the area under the ROC curve was 0.92. The system was able to classify 1418 (87%) valid segments and 897 (74%) distorted segments correctly. The calculations of the system's performance showed 87% sensitivity, 81% accuracy and 74% specificity. In comparison with the 95% confidence interval (CI) thresholding method, the fuzzy system showed higher specificity (P=0.008,P<0.01), and no significant difference was found between the two methods in terms of sensitivity (P=0.720,P>0.05) and accuracy (P=0.053,P>0.05). We therefore conclude that the algorithm used in this system has some potential in detecting valid and distorted plethysmogram pulse. However, further evaluation is needed using larger patient groups.

A fuzzy system for detecting distorted plethysmogram pulses in neonates and paediatric patients

Pulse oximetry is a useful, quick, non-invasive and widely used technology for monitoring oxygen saturation (SaO2) for neonates and paediatric patients. However, pulse oximetry is fraught with artefacts, causing false alarms resulting from patient or probe movement. The shape of the plethysmogram is a useful visual indicator for determining the reliability of SaO2 numerical readings. If certain features could be defined that tag valid plethysmogram pulses, then automatic recognition of valid SaO2 values can be attained. We observed that the systolic upstroke time (t1), the diastolic time (t2) and heart rate (HR) extracted from the plethysmogram pulse constitute features which can be used for detecting normal and distorted plethysmogram pulses. Therefore, we developed a knowledge-based system using fuzzy logic for classifying plethysmogram pulses into two categories: valid and artefact. A total of 22,497 pulse waveforms were used to define the system parameters. These were obtained from 13 patients with heart rates ranging between 62 and 209 beats min-1. A further 1420 waveforms obtained from another four patients were used for testing the system, and visually classified into 833 (59%) valid and 587 (41%) distorted segments. The system was able to classify 679 (82%) valid segments and 543 (93%) distorted segments correctly. The calculations of the system's performance showed 82% sensitivity, 86% accuracy and 93% specificity. We, therefore, conclude that the algorithm used in this system can be implemented in its present from for real-time SaO2 monitoring in intensive care for detecting valid and distorted plethysmogram pulses.

Pulse oximetry, severe retinopathy, and outcome at one year in babies of less than 28 weeks gestation

AIM

To determine whether differing policies with regard to the control of oxygen saturation have any impact on the number of babies who develop retinopathy of prematurity and the number surviving with or without signs of cerebral palsy at one year.

METHODS

An examination of the case notes of all the 295 babies who survived infancy after delivery before 28 weeks gestation in the north of England in 1990-1994.

RESULTS

Babies given enough supplemental oxygen to maintain an oxygen saturation of 88-98%, as measured by pulse oximetry, for at least the first 8 weeks of life developed retinopathy of prematurity severe enough to be treated with cryotherapy four times as often as babies only given enough oxygen to maintain an oxygen saturation of 70-90% (27.2% v 6.2%). Surviving babies were also ventilated longer (31.4 v 13.9 days), more likely to be in oxygen at a postmenstrual age of 36 weeks (46% v 18 %), and more likely to have a weight below the third centile at discharge (45% v 17%). There was no difference in the proportion who survived infancy (53% v 52%) or who later developed cerebral palsy (17% v 15%). The lowest incidence of retinopathy in the study was associated with a policy that made little use of arterial lines.

CONCLUSIONS

Attempts to keep oxygen saturation at a normal "physiological" level may do more harm than good in babies of less than 28 weeks gestation.

Calibration of near-infrared frequency-domain tissue spectroscopy for absolute absorption coefficient quantitation in neonatal head-simulating phantoms

Frequency-domain tissue spectroscopy is a method to measure the absolute absorption coefficient of bulk tissues, assuming that a representative model can be found to recover the optical properties from measurements. While reliable methods exist to calculate absorption coefficients from source-detector measurements less than a few centimeters apart along a flat tissue volume, it is less obvious what methods can be used for transmittance through the larger tissue volumes typically associated with neonatal cerebral monitoring. In this study we compare the use of multiple distance frequency-domain measurements processed with (i) a modified Beer-Lambert law method, (ii) an analytic infinite-medium diffusion theory expression, and (iii) a numerical finite element solution of the diffusion equation, with the goal of recovering the absolute absorption coefficient of the medium. Based upon our observations, the modified Beer-Lambert method provides accurate absolute changes in the absorption coefficient, while analytic infinite-medium diffusion theory solutions or finite element-based numerical solutions can be used to calculate the absolute absorption coefficient, assuming that the data can be measured at multiple source-detector distances. We recommend that the infinite-medium multi-distance method or the finite element method be used across large tissue regions for calculation of the absolute absorption coefficient using frequency-domain near-infrared measurements at multiple positions along the head.

Measurement of hemoglobin saturation by oxygen in children and adolescents with sickle cell disease

Pulse oximetry is a noninvasive method of measuring oxyhemoglobin saturation. The validity of pulse oximetry in sickle cell disease (SCD) has been questioned. We evaluated pulse oximetry, arterial blood gas analysis, and co-oximetry in patients with SCD, and we assessed the effect of dyshemoglobin and altered blood-oxygen affinity on their accuracy. Sixteen patients with SCD aged 7-21 years had arterial and venous blood drawn and transcutaneous pulse oximetry performed. Oxyhemoglobin dissociation curves were plotted from the venous blood of 15 patients. Oxyhemoglobin saturation estimated by arterial blood gas analysis (SaO(2)) and measured by pulse oximetry (SpO(2)) were both higher than the saturation by co-oximetry (FO(2)Hb) (mean +/- SD = 96.3 +/- 1.6%, 94 +/- 3.1%, and 89.1 +/- 3.8%, respectively). There was a significant, positive correlation between SpO(2) and FO(2)Hb (r = 0.7, P = 0.002). The patients had elevated levels of methemoglobin (MetHb) and carboxyhemoglobin (COHb) (2.3 +/- 1.4% and 4.7 +/- 1.3%, respectively). The oxyhemoglobin dissociation curves were frequently shifted to the right with oxygen tensions elevated when hemoglobin was 50% saturated with oxygen (P(50)) (32.5 +/- 4.5 mm Hg). There was a strong correlation between the amounts of dyshemoglobin (MetHb + COHb) and the difference between SaO(2) and FO(2)Hb (r = 0.7, P = 0.002). There was no correlation between the difference between SaO(2) and FO(2)Hb and the P(50) (r = 0.27, P = 0.33) There was also a strong positive correlation between SaO(2)-SpO(2) and dyshemoglobin fraction (r = 0.77, P = 0.001). We conclude that pulse oximetry and arterial blood gas analysis overestimate oxygen saturation when compared to co-oximetry, but that SpO(2) is consistently closer than SaO(2) to FO(2)Hb. SpO(2) is partially affected by MetHb and COHb. The discrepancy between SaO(2) and FO(2)Hb is due to the presence of dyshemoglobin and a shifted oxyhemoglobin dissociation curve, but the effect from dyshemoglobin predominates.

Longitudinal assessment of hemoglobin oxygen saturation in healthy infants during the first 6 months of age. Collaborative Home Infant Monitoring Evaluation (CHIME) Study Group

Limitations in home monitoring technology have precluded longitudinal studies of hemoglobin oxygen saturation during unperturbed sleep. The memory monitor used in the Collaborative Home Infant Monitoring Evaluation addresses these limitations. We studied 64 healthy term infants at 2 to 25 weeks of age. We analyzed hemoglobin oxygen saturation by pulse oximetry (SpO(2)), respiratory inductance plethysmography, heart rate, and sleep position during 35, 127 epochs automatically recorded during the first 3 minutes of each hour. For each epoch baseline SpO(2) was determined during >/=10 s of quiet breathing. Acute decreases of at least 10 saturation points and <90% for >/=5 s were identified, and the lowest SpO(2) was noted. The median baseline SpO(2) was 97.9% and did not change with age or sleep position. The baseline SpO(2) was <90% in at least 1 epoch in 59% of infants and in 0.51% of all epochs. Acute decreases in SpO(2) occurred in 59% of infants; among these, the median number of episodes was 4. The median lowest SpO(2) during an acute decrease was 83% (10th, 90th percentiles 78%, 87%); 79% of acute decreases were associated with periodic breathing, and >/=16% were associated with isolated apnea. With the use of multivariate analyses, the odds of having an acute decrease increased as the number of epochs with periodic breathing increased, and they lessened significantly with age. We conclude that healthy infants generally have baseline SpO(2) levels >95%. The transient acute decreases are correlated with younger age, periodic breathing, and apnea and appear to be part of normal breathing and oxygenation behavior.

Alarm settings for the Marquette 8000 pulse oximeter to prevent hyperoxic and hypoxic episodes

OBJECTIVE

To determine safe and appropriate alarm limits for the Marquette 8000 pulse oximeter to prevent hyperoxic and hypoxic episodes in neonates. It is necessary to define these limits for each brand of oximeter because of the variance in nonuser adjustable calibration algorithms used in pulse oximeters.

METHODOLOGY

Oxygen saturation values obtained from a Marquette 8000 pulse oximeter (SpO2) were compared with simultaneous arterial blood gas PaO2 values obtained from blood gas analysis, for 322 samples in 24 consecutive neonates (median 30 weeks' gestation).

RESULTS

In order to prevent 95% of hyperoxic episodes (PaO2 > 90 mmHg), the upper alarm limit was 95% SpO2. Similarly, to prevent 95% of hypoxic episodes (PaO2 < 40 mmHg), the lower alarm limit was 95% SpO2. A sensitivity lower than 95% had to be accepted to develop an alarm range which prevented both hyperoxic and hypoxic episodes. To maintain PaO2 values between 40 and 90 mmHg, an appropriate alarm range of 94-97% SpO2 (90% sensitivity, 28% specificity) was established.

CONCLUSIONS

The relative merits of high sensitivity versus high specificity should be considered when determining appropriate alarm limits. Alarm limits which represent a balance between sensitivity and specificity will minimise false alarms and provide a clinically practical range. It would be useful for this type of information to be available for each brand of oximeter, to assist the user in determining appropriate alarm settings.

Pulse oximetry saturations in the first 6 hours of life in normal term infants

The pulse oximetry saturation values and the average percentage of time that normal newborns spend at different saturation ranges in the first 6 hours of life were determined in a cross-sectional study. Pulse oximetry saturation values were measured for a single 20-minute period in 101 normal term newborns between 20 minutes and 6 hours of age. The 25th percentile saturation values in the first postnatal hour (range 91%-100%) were lower than those from the second postnatal hour (range 96%-100%) onward. There was no significant difference between the 50th percentile (range 96%-100%) and the 75th percentile (range 97%-100%) saturation values in all postnatal hours. The babies spent a majority of time with saturations > or = 96% in all postnatal hours. A newborn more than 20 minutes old who does not achieve a pulse oximetry saturation value of 96% over several minutes of observation may need evaluation or continuous monitoring.

When do infants need additional inspired oxygen? A review of the current literature

There is considerable uncertainty regarding the oxygen saturation threshold below which additional inspired oxygen should be given to infants with acute or chronic lung disease. In the absence of data from controlled studies, recommendations can only be based on reference values for healthy infants and on observational studies regarding the pathophysiological effects of acute and chronic hypoxia. Reference values for pulse oximeter saturations (SpO2) in term and preterm infants show that during normal breathing 95% of infants maintain SpO2 at or above 93-97%, depending on age. Studies of infants with chronic lung disease (CLD) show that (1) when SpO2 was kept at > or =93% by administration of home oxygen, rates of sudden infant death were reduced; (2) weight gain was significantly better when SpO2 was maintained at > or =93-95%, (3) increasing SpO2 from 82 to 93% by delivering low-flow oxygen resulted in a 50% reduction in pulmonary artery pressure, (4) O2 administration to mildly hypoxemic infants (SPO2 89%) caused a 50% decrease in airway resistance, and (5) low-flow oxygen reduced the frequency of intermittent hypoxemic episodes, even in infants who had values of > or =90% at rest. Based on these data, it is recommended that oxygen therapy should be considered in infants whose baseline SpO2 is <93%, and that SpO2 should be maintained at > or =95% when infants are managed at home.

Accuracy of two pulse oximeters at low arterial hemoglobin-oxygen saturation

OBJECTIVE

To evaluate the performance of two pulse oximeters in the measurement of arterial hemoglobin saturation in hypoxemic children.

DESIGN

Prospective, repeated-measures observational study.

SETTING

A 16-bed pediatric intensive care unit in a children's tertiary hospital.

PATIENTS

Sixty-six patients with arterial saturation of <90%.

INTERVENTIONS

Three arterial blood samples were taken from each subject during a 48-hr period. Pulse oximeter measurements of arterial saturation were compared with arterial saturation determined by cooximetry.

MEASUREMENTS AND MAIN RESULTS

Arterial saturation was measured using one or both pulse oximeters (SpO2) and compared with the arterial hemoglobin saturation determined by cooximetry (SaO2). Sixty-two subjects were studied, using the Ohmeda pulse oximeter giving 185 data points (78 with saturations <75% [defined by the average of pulse oximeter and cooximeter]); 53 subjects were studied, using the Hewlett-Packard pulse oximeter yielding 155 data points (60 with saturations <75%). SpO2 ranged from 24% to 94%. Bias and precision of the Ohmeda pulse oximeter were -2.8% and 4.8% >75% and -0.8% and 8.0% <75%. Bias and precision of the Hewlett-Packard pulse oximeter were -0.5% and 5.1% >75% and 0.4% and 4.6% <75%. Intrapatient regression coefficient (r) for the differences between pulse oximeter and cooximeter was 0.58 for the Ohmeda and 0.59 for the Hewlett-Packard. Regression coefficients for predicting change in cooximeter value given a change in the Ohmeda pulse oximeter were 0.59 and 0.71 <75% and >75%, respectively. Similar coefficients for the Hewlett-Packard pulse oximeter were 0.50 and 0.70, respectively.

CONCLUSION

The performance of the Ohmeda pulse oximeter deteriorated below an SpO2 of 75%. The Hewlett-Packard pulse oximeter performed consistently above and below an SpO2 of 75%. The ability of both pulse oximeters to reliably predict change in SaO2 based on change in pulse oximetry was limited. We recommend measurement of PaO2 or SaO2 for important clinical decisions.

Clinical predictors of hypoxaemia in children with pneumonia

A prospective study to determine which clinical factors identified children with acute lower respiratory infection who were hypoxaemic and at risk of death was done over a 9-month period on children under 5 years of age admitted to a district hospital in rural Zambia. Of 158 children studied, 55 (35%) were found to be hypoxaemic and 23 (14.6%) died. For the subgroup of children under 1 year of age, a respiratory rate of > 70 was the only significant predictor of hypoxaemia (p < 0.001, sensitivity 63%, specificity 89%). In older children, only the presence of crepitations/bronchial breathing was predictive (p = 0.018, sensitivity 75%, specificity 57%). The likelihood of death was increased in those children with low oxygen saturation (p = 0.021) and poor nutrition (p = 0.007). It is concluded that, on the basis of raised respiratory rate, the WHO guidelines are likely to identify children under 1 year of age who are hypoxaemic. However, it may be necessary to include auscultatory findings in the guidelines to recognize hypoxaemia in older children in order to ensure that they receive appropriate treatment with oxygen. This study demonstrates that hypoxaemia and malnutrition are risk factors for death.

Comparison of two different pulse oximeters in monitoring preterm infants

OBJECTIVE

The aim of the study was to test the reliability and variation in the readings of two widely used pulse oximeters in preterm infants.

DESIGN

Two different pulse oximeters and a transcutaneous PO2 monitor were used to record the data continuously on a cotside computer database.

PATIENTS

Sixteen preterm infants were studied in the Neonatal Unit, Simpson Memorial Maternity Pavilion, Edinburgh, UK.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Approximately one fifth of the time, the pulse oximeter readings could be established as artifactual. Study of the remaining four fifths of the data showed that, on average, the Nellcor pulse oximeter recorded saturation percentages 2.2% higher than the Ohmeda oximeter.

CONCLUSIONS

We recommend that all neonatal units adopt a policy of using different saturation alarm limits for these two instruments. We further recommend that other pulse oximeters be tested by a methodology similar to the one we present in this paper, before their use in monitoring oxygenation in preterm infants.

Retinopathy of prematurity in infants less than 29 weeks' gestation: 3 1/2 years pre- and postsurfactant

OBJECTIVE

To determine the effects of surfactant on retinopathy of prematurity (ROP).

DESIGN

We compared infants for 3 1/2 years both before and after the introduction of surfactant in our neonatal intensive care unit (NICU) using prospectively collected data. Exogenous surfactant (Exosurf) was introduced into our NICU on July 1, 1991.

METHODS

We compared the incidence and severity of ROP in two groups of infants born at less than 29 weeks' gestation who required cryo- or laser therapy. Premature infants born during the first 3 1/2 years following the introduction of surfactant were compared with those born during the 3 1/2-year period prior to its introduction. The infants were examined by one ophthalmologist (J.K.) and classified according to the International Classification of ROP.

RESULTS

A total of 124 infants born presurfactant and 152 infants born postsurfactant were examined for the presence of ROP. No significant difference between the two groups regarding any stage of ROP or the necessity for treatment was found. In infants of less than 27 weeks' gestation, a significant reduction in the number requiring cryo- or laser therapy was noted (12 of 48 examined [25.0%] vs 6 of 62 examined [9.7%], respectively; P < 0.05). This decreased need for treatment, however, was found in infants without hyaline membrane disease who did not receive surfactant.

CONCLUSION

Exosurf has had no significant impact on the incidence or severity of ROP. Due to its effect on improved survival rates, the surfactant produces a larger proportion of infants at risk of developing ROP. Other changes in NICU protocol may be causing a reduction in the incidence of severe ROP.

[Pulse oximetry in pediatrics]

Pulse oximetry has become the leading technique for monitoring hemoglobin oxygen saturation whenever a risk of hypoxia exists. It is based upon the principle of light absorbance of pulsatile arterial blood. Since it uses 2 wavelengths, it can only measure oxyhemoglobin and reduced hemoglobin. Thus, in case of increased methemoglobin or carboxyhemoglobin, pulse oximetry values are not reliable. Low tissue perfusion can also be responsible for inaccurate values. Nevertheless pulse oximetry is a reliable and easy-to-use technique in most of the clinical situations. This article reviews the physical basis, the reliability, the pediatric aspects, and the limitations of the technique.

Do cardiac output and serum lactate levels indicate blood transfusion requirements in anemia of prematurity?

BACKGROUND

Whether and when to transfuse in anemia of prematurity is highly controversial. Some authors suggest transfusions simply if the hemoglobin (Hb) level is below a defined normal range. Others propose the use of clinical or laboratory parameters in anemic patients to decide whether to transfuse or not.

HYPOTHESIS

A decreasing amount of circulating Hb should cause a compensatory increase in cardiac output (CO) and an increase in arterial serum lactate.

MATERIALS AND METHODS

In 56 anemic preterm infants (not in respiratory or hemodynamic failure) we analyzed CO after the first week of life using a Doppler sonographic method. At the same time serum lactate levels, Hb levels and oxygen saturation were registered. Nineteen of these patients were given transfusion when they demonstrated clinical signs of anemia by tachycardia > 180/min, tachypnea, retractions, apneas and centralization (group 2). The remaining 37 patients were not transfused (group 1). Serum lactate, CO, heart rate (HR), oxygen delivery, respiratory rate, capillary refill and Hb were analyzed in both groups and in group 2 before and 12-24 h after transfusion. Data between groups 1 and 2 and in group 2 before and after transfusion were compared.

RESULTS

In the 56 patients studied no linear correlation between Hb and CO or between Hb and serum lactate was found. Nor could any correlation be demonstrated between the other variables studied. Examining the subgroups separately, a negative linear correlation was demonstrated between serum lactate and oxygen delivery in group 2. No other significant correlations were detected. However, when the pre- and post-transfusion data were compared in group 2 (increase of Hb from 9.45 (SD 3.44) to 12.5 (SD 3.8) g/100 ml), the CO decreased from 281.3 (SD 162.6) to 224 (SD 95.7) ml/kg per min (p < 0.01) and serum lactate decreased significantly from 3.23 mmol/l (SD 2.07) before to 1.71 (SD 0.83) after transfusion. Oxygen delivery was 35.8 (+/- 0.19) ml/kg per min group 1, 27.8 (+/- 0.05) pre- and 43.4 (+/- 0.07) post-transfusion in group 2 (p < 0.01).

CONCLUSIONS

CO measurements and serum lactate levels add little information to the decision-making process for blood transfusions, as neither CO nor serum lactate levels correlate with HB levels in an otherwise asymptomatic population of preterm infants. In infants where the indication for blood transfusion is made based on traditionally accepted clinical criteria, serum lactate is an additional laboratory indicator of impaired oxygenation, as it correlates significantly with oxygen delivery. A significant lower oxygen delivery in patients in whom blood transfusion is indicated and an increase in oxygen induced by transfusion demonstrate the value of these criteria in identifying preterm infants who benefit from transfusion.

Prediction of early outcome in resolving chronic lung disease of prematurity after discharge from hospital

In an attempt to identify those infants with resolving chronic lung disease of prematurity (CLD) at greatest risk of sudden infant death syndrome or acute life threatening event (SIDS/ALTE), or readmission to hospital following discharge, recordings of arterial oxygen saturation were made on 35 infants. Recordings were collected while the infants were breathing room air. Movement artefact was excluded and the data analysed to provide the mean individual arterial oxygen saturation (MSaO2), and the variability of the mean individual oxygen saturation (delta MSaO2). These data were related to clinical outcome recorded over the three months following investigation. A MSaO2 less than 90% on discharge predicted hospital admission within three months with a sensitivity of 1 and a specificity of 0.76, and SIDS/ALTE with a sensitivity of 1 and a specificity of 0.75. A delta MSaO2 greater than 6% predicted SIDS/ALTE with a sensitivity 0.88 and specificity of 1. Infants with resolving chronic lung disease of prematurity who are at risk of increased morbidity and mortality can be assessed by accurate measurement of mean arterial saturation.

From oxygen content to pulse oximetry: completing the picture in the newborn

In recent years clinicians caring for sick preterm infants have come to depend on pulse oximetry to avoid hyperoxia, which means assuming saturation values for critical levels of oxygen tension. This prediction is made difficult by the shape of the haemoglobin-oxygen dissociation curve at critical values for arterial pO2 and by the effects of changes in acid-base balance on p50. Combined blood gas and co-oximetry measurements can be used to determine critical limits for pulse oximetry. Fetal haemoglobin has slightly different light absorption characteristics from adult haemoglobin. To adjust for this, adult and fetal matrices are available in the OSM 3 HEMOXIMETER (Radiometer Medical A/S, Denmark) but the measurement requires an extra preliminary step to estimate fetal haemoglobin concentration. We sought to determine the importance of this extra procedure for measuring the saturation of newborn blood, and to determine whether the adult or fetal mode should be used for determining saturation for comparison with pulse oximeters. We measured the effect of the correction for fetal haemoglobin by obtaining absorbances from the co-oximeter and multiplying them by the adult and fetal matrices. We demonstrated that, at 90% saturation, failure to use the fetal correction in the presence of high levels of fetal haemoglobin result in a 4% overestimate of saturation, with resultant underestimation of the safe range for pulse oximetry. Published values for extinction coefficients for fetal and adult blood at wavelengths used by pulse oximeters are inconsistent, but it appears that fetal haemoglobin does not bias pulse oximetry readings. Determining saturation limits by co-oximetry for use with pulse oximeters in preterm infants requires the description of the haemoglobin-oxygen dissociation curve with the correction for fetal haemoglobin.

Pulse oximetry in ventilated preterm newborns: reliability of detection of hyperoxaemia and hypoxaemia, and feasibility of alarm settings

The aim of our study was to evaluate the reliability of pulse oximetry in detecting both hyper- and hypoxaemic states and to create clinically feasible alarm limits. A total of 792 readings of a pulse oximeter and corresponding values of arterial oxygen tension from 146 (79M, 67F) artificially ventilated preterm newborns with indwelling umbilical artery catheters were compared. Predictive value analysis of pulse oximeter readings related to arterial oxygen tension confirmed the ability of the pulse oximeter to identify both hypoxaemia and hyperoxaemia. However, a clinically feasible and safe range of alarm limits for maintenance of arterial oxygen tension of 40-90 mmHg (5.3-12 kPa) could only be established at a sensitivity level less than 0.9. At a level of 0.85, the alarm range on the pulse oximeter was 92.5-95%. Based on these findings, we are concerned about using pulse oximetry as the sole means of oxygen monitoring for preterm infants receiving supplementary oxygen. A combination of the pulse oximetry with other methods of blood-gas monitoring seems mandatory.

Near-patient measurements of methemoglobin, oxygen saturation, and total hemoglobin: evaluation of a new instrument for adult and neonatal intensive care

OBJECTIVES

a) To evaluate the performance of a compact, new instrument that uses disposable cuvettes to measure total hemoglobin concentration, oxygen content, and the relative concentrations of oxy- and methemoglobin in 50-microL blood samples; b) to determine whether the instrument can be used for near-patient assessment of methemoglobinemia; and c) to ascertain whether problems commonly encountered in neonatal blood samples affect the instrument's performance.

DESIGN

Prospective study, in which the test instrument was compared with a standard method. Samples of whole blood with and without bilirubin, fetal hemoglobin, and hemolysis were analyzed on the new (test) instrument and on a widely used cooximeter (OSM3 hemoximeter, Radiometer; reference instrument).

SETTING

In vitro analyses of blood samples in clinical and university laboratories.

MEASUREMENTS AND MAIN RESULTS

There was a close linear correlation between the methomoglobin measurements of the test instrument and those measurements of the reference instrument (slope = 0.989; r2 = .989). The average difference in mean assay values between the reference instrument and the test instrument was -0.59%, i.e., < 1% methemoglobin. Repeated measurements indicated the precision was 0.5% methemoglobin. Complete hemolysis of the sample reduced the methemoglobin reading by only 0.40%. Adding bilirubin (10 to 11 mg/dL [171 to 188.1 mumol/L]), increased the methemoglobin reading by 0.23%, increased the oxyhemoglobin reading by 0.45%, and increased total hemoglobin by 0.21 g/dL. Fetal hemoglobin also had minimal effects on the readings.

CONCLUSIONS

The test instrument is fast and easy to operate. No sample preparation or pipetting is required. To operate the instrument, the user simply connects a syringe containing the blood sample to one of the disposable cuvettes, injects 50 microL of blood into the cuvette, and inserts the cuvette into the instrument. The test instrument automatically detects the presence of the cuvette, analyzes the sample, and displays the results in < 10 secs. The findings in this study indicate that the test instrument has sufficient accuracy for near-patient testing in intensive care units. The errors introduced by hemolysis, fetal hemoglobin, and bilirubin were too small to be of clinical importance. Thus, the test instrument is essentially unaffected by complications commonly encountered in neonatal blood. The capacity of the test instrument to measure methemoglobin makes it particularly useful if inhaled nitric oxide therapy becomes a standard clinical practice.

Comparison of oxygenation measurements in pediatric patients during sickle cell crises

Measurements of the saturation of arterial blood with oxygen (SaO2) were compared in 24 children during sickle cell crises. Simultaneous pulse oximetry (Nellcor N-100 pulse oximeter) and arterial blood analysis showed that SaO2 measured by pulse oximetry overestimated cooximeter-measured SaO2 (mean bias, 6.9%; p < 0.001). The blood gas machine-calculated SaO2 also overestimated cooximeter-measured SaO2 (p < 0.001). The bias increased with increasing age (p = 0.002) and carboxyhemoglobin level (p = 0.005) but was not related to methemoglobin, total hemoglobin, percentage of hemoglobin S, or percentage of hemoglobin F.