NLS: Fetal Life

NLS Fetal life Alveolar fluid exerts pressure on capillaries à R pressure > L FLOW • 80% through foramen ovale • 10% through ductus arteriosus • 10% through lungs • NO MURMER as non turbulent system O2 Tensions • pO2 umbilical vein = 6.5kPa • pO2 to fetal brain = 5.5kPa (due to mixing with flow through lungs) • pO2 to fetal body = 5.0kPa (due to mixing with PDA flow) • pO2 in umbilical veins & through lungs = 4.0 kPa • HbF carries & releases O2 at lower O2 tension Low O2 in pulmonary vessels à vasoconstriction à vasoconstriction As R & L ventricles work in parallel fetus can survive with 1 ventricle = Hypoplastic left heart At Birth Air into lungs Bubbles exert negative pressure on their surroundings (try to collapse) = decreases pressure on capillaries à Decreased pulmonary resistance à Foramen ovale closes à Increased flow à Increased O2 in blood to system à Ductus closes at PO2 7-8kPa (initial spasm, lumen obstructs fully in 3/52, muscle gone by 3/12) Also increased local lung vasodilators (e.g. Nitric oxide) à Baby turns pink Because system is now running in series needs 2 ventricles therefore hypoplastic left heart manifests. NB: raised pulmonary vascular resistance is favoured by: • Hypoxia • Hypercarbia • Acidosis • Poor lung expansion i.e. all features of asphyxia Persistent Fetal Circulation Caused by: • Hypoxia, hypercarbia, metabolic acidosis • Failure of lung expansion • = raised pulmonary vascular resistance Results in: • Duct & FO stay open • à decreased systemic O2 • à decreased ventilation • à worsening fetal circulation • à blue baby, worsening hypoxia, acidosis & rising CO2 (late sign as easily transported across membranes) Neonate Resus Activity (muscle tone) Pulse Grimace Appearance (skin colour) Respiration 0=flaccid 0=0 bpm 0=no response 0=white 0=absent 1=some flexion 1= <100 1=grimace 1=blue / pink trunk 1=gasping 2=normal 2= >100 2=cry 2=pink hands / feet 2=regular Term Baby Dry & wrap Stimulation (flick feet) Facial O2 Inflation breaths as req Ventilation La Place’s Law P=2T/r P = pressure, r = radius, T = surface tension • • • At first breath radius is low therefore high pressure (30cmH2O in term infant) As lungs expand with progressive breaths à becomes more compliant à better volumes for given pressure (i.e. moves from pre (non-compliant / stiff) to post (compliant)) Surfactant will reduce surface tension à increase residual volume Intubation Closed vocal cords require O2 to brain = protective mechanism Wait for O2 levels to fall to enable non traumatic intubation Fluid expelled from lungs by pressure / absorbed to lymphatics. If fluid fails to be expelled from lungs à TTN Breathing - @ 20/30 / min <30cm H2O Circulation – If HR < 60 à massage Drugs Adrenaline 1:10,000 = 1g in 10,000ml = 100mg/L = 100microg / ml Dose – 10mcg / kg = 0.1ml/kg of 1:10,000 Route – UVC or ET (no evidence for ET tube) NB: can’t bind to receptors at low pH therefore give bicarb & try again at 30mcg/kg If giving via ET tube need to give 100mcg/kg = 1ml/kg Sodium Bicarbonate 4.2% (or 8.4% diluted 1:1 with 5% or 10% dextrose) Dose 1-2mmol/kg = 2-4ml/kg of 4.2% Via UAC / UVC f.b. flush & chest compressions Aim – to reverse intra-cardiac acidosis Should work within a few minutes Dextrose 10% = 10g in 100mls = 100mg / ml Dose – 250mg/kg = 2.5ml/kg of 10% Route – UVC If no response to Bicarb & adrenaline Volume correction 0.9% saline (or other balanced salt e.g. hartmanns) Dose 10mls/kg initially Route UVC Blood 20-40mls/kg Naloxone Maternal pethidine babies are active only if cold (wrap warm à apnoea) High risk if doses < 3 hrs apart (t1/2 in adult), IV rather than IM, < 3 hrs pre delivery. Manage as non breathing baby Naloxone is NOT an emergency drug. Dose – 200micrograms IM LINES Placing a Umbilical line Start with either flushed line & syringe OR empty line & syringe TIE – the cord ligature / tape about the cord base. Vessels unlikely to bleed in collapsed baby but will once recovered CUT – the cord approx 1cm from skin with clean scalpel slice IDENTIFY - the 3 vessels. Vein = thin walled & should be RUQ. 2 Arteries – stiff, string like at 2 lower quadrants GRASP – the cord with the artery forceps near the vein & insert catheter ADVANCE – until resistance felt at vascular ring, apply gentle pressure until passes through. Ideal position for UVC is just outside RA in IVC. Length = umbilicus to inter-nipple line DRAW – back on the syringe & blood should flow easily FLUSH – with saline to avoid clotting TAPE – or fix in other way GIVE – drugs as required INTUBATION Size = internal diameter Most term babies need 3.5, If 1.8-1kg need 3.0, If < 1kg need 2.5 Length – 1kg baby = 7cm, 2kg baby 8cm, 3kg baby 9cm