Assessment of heart rate changes during positive pressure ventilation in asphyxia induced bradycardia porcine model of neonatal resuscitation

Abstract

Abstract BACKGROUND The Neonatal Resuscitation Program (NRP) states that if positive pressure ventilation (PPV) was started because a baby had a low heart rate (HR), the baby’s HR should begin to increase within the first 15sec of PPV. However, this recommendation has not been examined in either an animal models nor in the delivery room. OBJECTIVES To assess changes in HR in piglets with asphyxia induced bradycardia. DESIGN/METHODS Term newborn piglets (n=30) were anesthetized, intubated, instrumented, and exposed to 40min normocapnic hypoxia followed by asphyxia. Asphyxia was achieved by clamping the endotracheal tube until the piglet had bradycardia (defined as HR 25% of baseline); at that time CPR was initiated. As per NRP protocol PPV was immediately started for 30sec followed by chest compression. HR was continuously recorded using an ECG during the whole duration of the experiment. Changes in HR during PPV were assessed and divided into four epochs (0-10sec, 5-15sec, 10-20sec and 20-30sec, respectively) after start of PPV. RESULTS The median (IQR) duration of asphyxia was similar between the groups with 189 (128–291)sec, 126 (70–197)sec, 118 (66–250)sec for 3:1C:V, SI+90 and SI+120 respectively (p=0.37; oneway ANOVA with Bonferroni). At time of start of PPV the mean (SD) HR was 35 (13)/min. An increase in HR >100/min was observed in 6/30 (5%) at 30 seconds of PPV. None achieved changes in HR at the epochs 0-10sec, 5-15sec, or 10-20sec. After 15sec of PPV 13/30 (43%) had a decrease in HR and 11/ 30 (36%) had no change in HR. CONCLUSION Adequate PPV does not increase HR in piglets with asphyxia induced bradycardia. This is contrary to the current NRP, which recommends that after 15 sec of PPV HR should be assessed.