Fetal blood lactate concentration

Abstract

To the editors:Kruger et al (Kruger K, Hallberg B, Blennow M, Kublickas M, Westgren M. Predictive value of fetal scalp blood lactate concentration and pH as markers of neurologic disability. Am J Obstet Gynecol 1999;181:1072-8) derived optimum cutoff values of fetal scalp blood pH and lactate concentration during labor for the prediction of 6 short-term outcomes by means of receiver-operating characteristic curves. Values for pH ranged from 7.26 to 7.20, and values for lactate concentration ranged from 4.0 to 6.5 mmol/L. Moderate to severe hypoxic-ischemic encephalopathy was associated with the highest lactate value (6.5 mmol/L) and the lowest pH value (7.20). However, Kruger et al recommended a fetal scalp blood lactate concentration of 4.8 mmol/L as a suitable cutoff value to indicate asphyxia. This value was the 75th percentile of the total range of lactate values in their study. We wonder why the 90th percentile value (6.1 mmol/L) was not considered more appropriate, because that value is closer to the cutoff value for hypoxic-ischemic encephalopathy.Lactate concentration and pH values were obtained from the same sample in a subgroup of 326 labors. The area under the receiver-operating characteristic curve for lactate concentration was significantly greater than that for pH for 2 outcomes, a low 5-minute Apgar score (P =.03) and moderate to severe hypoxic-ischemic encephalopathy (P =.015). These observations support the use of a lactate concentration cutoff value derived from the receiver-operating characteristic curves for these outcome measures. Metabolic acidemia is the clinical concern. Lactate concentration represents a better measure of metabolic acidemia because, unlike pH, it is not influenced by respiratory acidemia. If a low pH value has a significant contribution from respiratory acidemia, the lactate concentration will still be low. A lactate concentration cutoff derived from cases in which pH was used for management might produce a higher number of false-positive results and lead to a greater intervention rate. It would be interesting to know the lactate concentrations equivalent to scalp blood pH values of 7.15, 7.20, and 7.25.We are hopeful that the microsample technique used by Kruger et al may prove useful in the future. Their group has already shown in a previous study that the success rate for obtaining a fetal scalp blood lactate concentration reading is significantly greater than that for obtaining a fetal scalp blood pH value.1Westgren M Kruger K Ek S Grunevald C Kublickas M Naka K et al.Lactate compared with pH analysis at fetal scalp blood sampling: a prospective randomised study.Br J Obstet Gynaecol. 1998; 105: 29-33Crossref PubMed Scopus (109) Google Scholar Clearly, an appropriate cutoff value for lactate concentration needs to perform only as well as pH in terms of identifying need to deliver for the technique to become preferable. We note that the previous study in Sweden used a lactate concentration cutoff value of 4.2 mmol/L, and it seems that determination of an optimal lactate value to use in place of a pH of 7.20 may be difficult.6/8/107464 To the editors:Kruger et al (Kruger K, Hallberg B, Blennow M, Kublickas M, Westgren M. Predictive value of fetal scalp blood lactate concentration and pH as markers of neurologic disability. Am J Obstet Gynecol 1999;181:1072-8) derived optimum cutoff values of fetal scalp blood pH and lactate concentration during labor for the prediction of 6 short-term outcomes by means of receiver-operating characteristic curves. Values for pH ranged from 7.26 to 7.20, and values for lactate concentration ranged from 4.0 to 6.5 mmol/L. Moderate to severe hypoxic-ischemic encephalopathy was associated with the highest lactate value (6.5 mmol/L) and the lowest pH value (7.20). However, Kruger et al recommended a fetal scalp blood lactate concentration of 4.8 mmol/L as a suitable cutoff value to indicate asphyxia. This value was the 75th percentile of the total range of lactate values in their study. We wonder why the 90th percentile value (6.1 mmol/L) was not considered more appropriate, because that value is closer to the cutoff value for hypoxic-ischemic encephalopathy.Lactate concentration and pH values were obtained from the same sample in a subgroup of 326 labors. The area under the receiver-operating characteristic curve for lactate concentration was significantly greater than that for pH for 2 outcomes, a low 5-minute Apgar score (P =.03) and moderate to severe hypoxic-ischemic encephalopathy (P =.015). These observations support the use of a lactate concentration cutoff value derived from the receiver-operating characteristic curves for these outcome measures. Metabolic acidemia is the clinical concern. Lactate concentration represents a better measure of metabolic acidemia because, unlike pH, it is not influenced by respiratory acidemia. If a low pH value has a significant contribution from respiratory acidemia, the lactate concentration will still be low. A lactate concentration cutoff derived from cases in which pH was used for management might produce a higher number of false-positive results and lead to a greater intervention rate. It would be interesting to know the lactate concentrations equivalent to scalp blood pH values of 7.15, 7.20, and 7.25.We are hopeful that the microsample technique used by Kruger et al may prove useful in the future. Their group has already shown in a previous study that the success rate for obtaining a fetal scalp blood lactate concentration reading is significantly greater than that for obtaining a fetal scalp blood pH value.1Westgren M Kruger K Ek S Grunevald C Kublickas M Naka K et al.Lactate compared with pH analysis at fetal scalp blood sampling: a prospective randomised study.Br J Obstet Gynaecol. 1998; 105: 29-33Crossref PubMed Scopus (109) Google Scholar Clearly, an appropriate cutoff value for lactate concentration needs to perform only as well as pH in terms of identifying need to deliver for the technique to become preferable. We note that the previous study in Sweden used a lactate concentration cutoff value of 4.2 mmol/L, and it seems that determination of an optimal lactate value to use in place of a pH of 7.20 may be difficult.6/8/107464 Kruger et al (Kruger K, Hallberg B, Blennow M, Kublickas M, Westgren M. Predictive value of fetal scalp blood lactate concentration and pH as markers of neurologic disability. Am J Obstet Gynecol 1999;181:1072-8) derived optimum cutoff values of fetal scalp blood pH and lactate concentration during labor for the prediction of 6 short-term outcomes by means of receiver-operating characteristic curves. Values for pH ranged from 7.26 to 7.20, and values for lactate concentration ranged from 4.0 to 6.5 mmol/L. Moderate to severe hypoxic-ischemic encephalopathy was associated with the highest lactate value (6.5 mmol/L) and the lowest pH value (7.20). However, Kruger et al recommended a fetal scalp blood lactate concentration of 4.8 mmol/L as a suitable cutoff value to indicate asphyxia. This value was the 75th percentile of the total range of lactate values in their study. We wonder why the 90th percentile value (6.1 mmol/L) was not considered more appropriate, because that value is closer to the cutoff value for hypoxic-ischemic encephalopathy. Lactate concentration and pH values were obtained from the same sample in a subgroup of 326 labors. The area under the receiver-operating characteristic curve for lactate concentration was significantly greater than that for pH for 2 outcomes, a low 5-minute Apgar score (P =.03) and moderate to severe hypoxic-ischemic encephalopathy (P =.015). These observations support the use of a lactate concentration cutoff value derived from the receiver-operating characteristic curves for these outcome measures. Metabolic acidemia is the clinical concern. Lactate concentration represents a better measure of metabolic acidemia because, unlike pH, it is not influenced by respiratory acidemia. If a low pH value has a significant contribution from respiratory acidemia, the lactate concentration will still be low. A lactate concentration cutoff derived from cases in which pH was used for management might produce a higher number of false-positive results and lead to a greater intervention rate. It would be interesting to know the lactate concentrations equivalent to scalp blood pH values of 7.15, 7.20, and 7.25. We are hopeful that the microsample technique used by Kruger et al may prove useful in the future. Their group has already shown in a previous study that the success rate for obtaining a fetal scalp blood lactate concentration reading is significantly greater than that for obtaining a fetal scalp blood pH value.1Westgren M Kruger K Ek S Grunevald C Kublickas M Naka K et al.Lactate compared with pH analysis at fetal scalp blood sampling: a prospective randomised study.Br J Obstet Gynaecol. 1998; 105: 29-33Crossref PubMed Scopus (109) Google Scholar Clearly, an appropriate cutoff value for lactate concentration needs to perform only as well as pH in terms of identifying need to deliver for the technique to become preferable. We note that the previous study in Sweden used a lactate concentration cutoff value of 4.2 mmol/L, and it seems that determination of an optimal lactate value to use in place of a pH of 7.20 may be difficult. 6/8/107464