Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC335
Relationship between serum pH and seizure onset following birth asphyxia in the newborn.
R. Delahunty1, N. E. Lynch1, G. Boylan1
1. Neonatology, University College Cork, Cork University Maternity Hospital, Cork, Ireland.
Hypoxic-ischemic encephalopathy (HIE) is due to perinatal asphyxia causing morbidity and mortality. It affects 2-3 newborns per 1000 live births.(1) Asphyxia is characterized by hypoxia around birth leading to an increase in [H+] in the blood, and acidosis.(2) HIE can be graded depending on the severity and the physiological effects. Grade 1 is mild, Grade 2 moderate and Grade 3 severe.(3) Seizure activity is detected using continuous video EEG monitoring.(4) Studies in rat models suggest that a rapid restoration of pH from acidic levels following asphyxia to alkalotic levels leads to enhancement of neuronal excitability resulting in an increase in seizure activity.(5) The aims were; i. To establish the range of serum pH values at seizure onset in the human newborn. ii. To examine the time to normalisation of serum pH between newborns with and without seizures. A retrospective chart review of newborns with HIE was undertaken. The pH results, seizures, medications, and EEG results were recorded for each newborn. The range of normal pH was considered to be 7.35-7.45 where acidosis was <7.35 and alkalosis was >7.45. Statistical analysis was performed using PASW Statistics 18.0, using the Mann-Whitney U test. A p-value <0.05 was considered to be statistically significant. Twenty four full term newborns; 12 with seizures and 12 with no seizures. Seizure newborns had an initial pH value that was in the range of 6.902-7.396. EEG seizure activity was recorded within the 7.35-7.45 range for ten newborns while one newborn had a seizure at 7.17 and the other had a seizure at 7.465. Eight suffered a Grade 2 HIE and four suffered a Grade 3 HIE. All newborns survived. The non-seizure group had an initial pH range of 6.32 to 7.326. From this group, there were eight newborns with Grade 2 HIE and four with Grade 3 HIE. Two newborns died. The initial median pH value of the non-seizure group was 7.03 (IQR;6.74-7.19) while the seizure group had a median pH value of 7.15 (IQR;7.03-7.21). The median initial pH values between the groups was not statistically significant (p=0.141). The non-seizure group had a median time to pH normalisation of 4.47 hours (IQR;3.09-8.58) while the seizure group had a median time of 10.23 hours (IQR;4.75-21.75) but the time to normalisation was statistically significant (p=0.039). The time to the first normal pH had a median value of 10.27 hours (IQR;4.91-21.69) and the time to first EEG seizure onset had a median value of 17.97 hours (IQR;12.2-25.5). The time to pH normalisation and seizure onset in the seizure group was not statistically significant (p=0.158). Seizure newborns remained acidotic for longer compared to non-seizure and subsequent seizures were seen with the onset of pH normalisation. The onset of seizures occurs at the same time as pH normalisation. This implies that the normalisation of pH to normal values leads to seizure activity.
Where applicable, experiments conform with Society ethical requirements