Neonatal General 7: NICU Practices 1
Hussein Elmufti, MD
University of Tennessee Health Science Center College of Medicine
Memphis, Tennessee, United States
Blood gas pH is an important factor in determining eligibility for therapeutic hyperthermia. Among other criteria, a cord pH of ≤ 7.0 is used to guide the decision to initiate hypothermia. In the absence of cord blood pH, suggested algorithms would use a 1st hour gas pH ≤ 7.0 or use a 1st hour gas pH between 7.01-7.15 with additional criteria including 10 min Apgar ≤ 5, acute perinatal event, or findings of moderate to severe encephalopathy on physical exam.
During the first hour of life, a significant improvement on the blood gas pH may develop that may affect the eligibility and the decision to initiate therapeutic hypothermia. We hypothesized that in term and near-term infants with a cord pH of ≤ 7, a substantial number of these infants will have a significant improvement in their 1st hour gas pH from their cord pH enough to be misleading and make them ineligible for therapeutic hypothermia.
To describe changes in gas pH between cord arterial sample and first hour infant arterial blood gas.
A 10-year retrospective chart review of infants with gestational age ≥35 weeks and cord gas < 7.0 and an admission 1st hour arterial blood gas were included. Hypocarbia was defined as PaCo2 ≤35. A normal blood gas defined with pH >7.3 and PaCO2 >35.
102 infants had a cord pH < 7.0 with a mean gestational age of 38.8 ±1.9 and median 5-minute Apgar score of 6 (5,8). As a group 92/102 infants had 1st hour pH >7.0 and 78/102 >7.15. A significant number of infants had hypocarbia, table 1. This did not differ with age of blood draw. Only 5/102 of blood gas met the definition of normal blood gas
Conclusion: In infants with cord pH < 7.0, a significant number of 1st hour blood gas pH was already above 7.0 and 7.15. A 1st hour blood gas pH > 7.0 or 7.15 may miss a significant number of infants with initially low cord blood gas pH. These limits should be used with caution in deciding on the need for therapeutic hypothermia. However, a 1st hour blood gas with pH >7.3 and PaCo2 >35 may reflect an absence of cord gas pH of 7.0. Similarly, this should be factored in when deciding on initiating therapeutic hypothermia. Hypocarbia on 1st hour blood gas is common and leads to an improved pH. This needs to be also factored in when deciding on initiating therapeutic hypothermia.