Desaturation events in neonates during mechanical ventilation

Accurate Measurements of Fetal Hemoglobin for Neonates with Different Gestational Ages

The purposes of this study were to examine the accuracy of fetal hemoglobin (Hb F, alpha2gamma2) as quickly measured by a hemoximeter but verified by high performance liquid chromatography [HPLC, including Hb F total (Hb Ft), acetylated Hb F (Hb F1), and non acetylated Hb F ( Hb F*)], and to predict the Hb F levels for different gestational weeks of neonates. Thirty-nine neonates of predominantly Hispanic and African American ethnicity, with gestational ages ranging from 25 to 38 weeks, were investigated. Analyses were performed on 163 blood samples that were pure neonates' blood before the transfusion of any adult blood. Two neonates had increased Hb C [beta6(A3)Glu-->Lys, GAC-->AAG] levels (1.67-2.79%) and one neonate whose mother drank alcohol during pregnancy, had elevated Hb A2 levels (0.12-0.14%). After excluding these data points, the mean Hb F were overestimated by hemoximeter, 118.4 +/- 8.77% vs. 92.6 +/- 2.77% by HPLC (mean difference: 25.8 +/- 7.71%, p = <0.001). Mean Hb F1 was 10.5 +/- 2.28%. Hb F levels decreased as gestational age increased (p <0.001 for Hb Ft and Hb F*; p = <0.05 for Hb F1). A multivariate regression model for Hb F prediction was established with the best R2. The gestational age and post birth hours in the prediction of Hb Ft was included when Hb F could be determined at the clinical settings. Future studies may be needed to account for Hb F1 when measuring Hb F levels to assess oxygenation status in (pre term) neonates.

Validation of Oxygen Saturation Monitoring in Neonates

•Background Pulse oximetry is commonly used to monitor oxygenation in neonates, but cannot detect variations in hemoglobin. Venous and arterial oxygen saturations are rarely monitored. Few data are available to validate measurements of oxygen saturation in neonates (venous, arterial, or pulse oximetric).

•Purpose To validate oxygen saturation displayed on clinical monitors against analyses (with correction for fetal hemoglobin) of blood samples from neonates and to present the oxyhemoglobin dissociation curve for neonates.

•Method Seventy-eight neonates, 25 to 38 weeks’ gestational age, had 660 arterial and 111 venous blood samples collected for analysis.

•Results The mean difference between oxygen saturation and oxyhemoglobin level was 3% (SD 1.0) in arterial blood and 3% (SD 1.1) in venous blood. The mean difference between arterial oxygen saturation displayed on the monitor and oxyhemoglobin in arterial blood samples was 2% (SD 2.0); between venous oxygen saturation displayed on the monitor and oxyhemoglobin in venous blood samples it was 3% (SD 2.1) and between oxygen saturation as determined by pulse oximetry and oxyhemoglobin in arterial blood samples it was 2.5% (SD 3.1). At a Pao2 of 50 to 75 mm Hg on the oxyhemoglobin dissociation curve, oxyhemoglobin in arterial blood samples was from 92% to 95%; oxygen saturation was from 95% to 98% in arterial blood samples, from 94% to 97% on the monitor, and from 95% to 97% according to pulse oximetry.

•Conclusions The safety limits for pulse oximeters are higher and narrower in neonates (95%–97%) than in adults, and clinical guidelines for neonates may require modification.

The measurement of accurate fetal hemoglobin and related oxygen saturation by the hemoximeter

BACKGROUND

The purposes of this study were to examine the accuracy of fetal hemoglobin (HbF) as quickly measured by the hemoximeter, verified by the high-performance liquid chromatography method, and to examine related oxygen saturation (SO(2)) measurements in neonates.

METHODS

Thirty-nine neonates with gestational ages ranging from 25 to 38 weeks were investigated (n=280 blood samples). Twenty younger premature neonates had blood transfusions (n=188 blood samples, 72 before and 116 after transfusions), and 19 older neonates did not.

RESULTS

The bias of the hemoximeter was 23% (+/-9.1) against the HPLC; 25% (+/-7.9) before, and 19% (+/-8.6) after blood transfusions (all P<0.001), for HbF measurements. A regression line (HbFt by the HPLC=8.46+0.7 x HbF by the hemoximeter) has been provided for the prediction. Oxyhemoglobin dissociation curves with the status of (before and after) blood transfusions were presented. In relation to oxygen tension values of 50-75 mm Hg, in addition to the right-shifted oxyhemoglobin dissociation curves, pulse oximeter ranged from 95 to 98% before the transfusions, but decreased to 94 to 96% after the blood transfusions.

CONCLUSIONS

Accurate HbF and related oxygen saturation measurements need to be determined, especially for premature neonates, to minimize the risk of oxygen toxicity.

Oxygen consumption monitoring by oxygen saturation measurements in mechanically ventilated premature neonates

PURPOSE

To assess oxygen consumption VO2) with arterial and venous oxygen saturation SaO2 and SvO2) from blood measurements for continuous monitoring of mechanically ventilated preterm neonates.

METHOD

Twelve preterm neonates with gestational ages ranging from 27 to 34 weeks at birth, who were mechanically ventilated and had umbilical arterial and venous lines in place, were investigated. Analyses were performed with blood samples and continuous monitoring of VO2 from SaO2 and SvO2 measurements.

RESULTS

Mean VO2 from blood samples was 3.3 mL/(kg min) (+/-2.49), and that from monitor readings was 8.8 (+/-4.49). Using curve fit analysis to predict the stability of monitor reading, the period from 8 to 28 hours following blood validation was most stable for SvO2 (cubic curve, R=0.5, P<.001). There is a considerable mix of arterial blood in the venous blood, which increased SvO2 and decreased VO2 in the blood samples during first 8 hours of monitoring following blood draws. A multivariate linear mixed model was established for VO2 measurements including related parameters. Ventilatory weaning was associated with decreased VO2.

CONCLUSIONS

These findings warrant caution against interpreting VO2 from blood SvO2 and subsequent monitoring readings during mechanical ventilation for preterm neonates.

Effects of fetal hemoglobin on accurate measurements of oxygen saturation in neonates

PURPOSE

To examine the accuracy of oxygen saturation (So(2)) in relation to blood oxyhemoglobin (Hbo(2)) measurements with the effects of fetal hemoglobin (HbF) determined and their oxyhemoglobin dissociation curves.

METHOD

Twenty neonates with gestational ages ranging from 25 to 34 weeks, who had umbilical arterial or venous lines inserted, were investigated. Analyses were performed with 169 arterial and 41 venous blood samples from these infants by employing HbF- and HbA-mode (as controls) blood analyses, using a hemoximeter.

RESULTS

Without adjusting the effects of HbF when using HbA-mode analyses, mean So(2) measurements were elevated for 5% (+/-1.38) compared with the results of HbF-mode analyses, with 3.5% elevated HbCO levels for the total blood samples. With left-shifted oxyhemoglobin dissociation curves in neonates, for the critical values of oxygen tension values between 50 and 75 mm Hg, arterial Hbo(2) ranged from 94% to 96%, Sao(2) from 97% to 98%, and Spo(2) from 96% to 97% (compared to 85%-94% in healthy adults).

CONCLUSIONS

The left-shifted oxyhemoglobin curves warrant the importance of accurate measurements of oxygenation status for neonates. Fetal hemoglobin determination is essential for accurate So(2) measurements and the assessment of proper oxygenation status in neonates.