Shock in neonates

Source

1. Cloherty and Stark’s manual of neonatal care

definition

one or more of the following of

• Poor central or peripheral pulses
• tachycardia
• mottled appearance
• pale color
• prolonged CRT (>3 sec)
• core-periphery difference of 3^o C
• low blood pressure

Additional features includes (to strengthen the diagnosis)

• urine output <0.5 ml/kg/hour in the last 6 hours
• serum lactate >5 mmol/L
• low PH (<7.25)
• base deficit of >-5mEq/L

Hypotension in neonates

• Mean blood pressure less than 5th percentile for the postnatal age in days
• British Association of perinatal medicine - working Definition MBP less than gestational age or <30 mm Hg whichever is higher
• MPB of 20 mm Hg isacceptable if CrCP (Cerebral critical closing pressure) is maintained - undermines the importance of organ perfusion rather than blood pressure alone
• Bedside capnography can be a surrogate marker for organ perfusion

Classification of neonatal shock

4 types irrespective of the etiology

features	type of shock
low CO + normal BP	compensated shock
low CO + low BP	decompensated shock
normal to high CO + low BP	hyperdynamic shock
normal CO + low BP	transitional circulation

Assessment of circulation

clinical signs

• pulses - especially femoral and brachial pulses
• heart rate - tachycardia denotes early phase of shock
• capillary refill time - unreliable in hypothermia, rapid CRT may denote septic shock
• cold peripheries - core-peripheral difference of 3^o C
• SpO₂ - pre-post ductal difference of 3%

Blood pressure

• Systolic BP - myocardial contractility
• Diastolic BP - basal vascular tone, low blood volume
• cuff width to arm ratio should be between 0.45 - 0.55
• invasive BP(iBP) can be considered in extremely low birth weight babies as oscillometric method can overestimate BP if MBP is less than 25 mm Hg
• in iBP, dampening of waveform can happen which can be due to introduction of air bubbles or use of small depth catheters
• it can under-read systolic and over-read diastolic pressures

Echo

• various parameters of echo helps in the assessment of shock

parameter	inference	Cut-off for abnormality	Caveats
IVC collapsibility	IVC collapsibility	IVC collapsibility	IVC collapsibil
Left ventricular output	systolic function and contractility	< 150 ml/kg/min	affected by PDA shunt
Right ventricular output	systolic function and contractility	< 150 ml/kg/min	affected by ASD / PFO
ejection fraction	systolic function and contactility	- 41-55% (mild reduction) - 31- 40% (moderate) - < 30% (severe)	affected by preload and after laod
shortening fraction	systolic function and contactility	< 25% to sd	affected by preload and after load
superior vena cava flow	cerebral blood flow return (surrogate for organ blood flow)	< 40 ml/kg/min in first 24-48 hrs	difficult to measure Only measure cerebral blood flow

other methods of assessment

• chest x ray -helpful to diagnose cardiomegaly, pulmonary oligemia or plethora, pleural effusion, pneumothorax
• ECG - to diagnose myocardial injury and structural heart diseases
• Perfusion index (PI) - ratio of pulsatile and non-pulsatile blood flow
• plethysmograph variability index - derived from PI reflecting its dynamic change during one respiratory cycle
• Electrical bio-impedance and bio-reactance - continuous cardiac output measurement by measuring electrical impendence over thorax
• cerebral and somatic oxygenation ( near infra-red spectrometry)

Causes of shock

sepsis perinatal asphyxia left to right shunt

sepsis and shock

• vasodilation and vasoparesis leading to capillary vascular leak
• initially can be compensated with increased heart rate
• LV contractility deteriorate quickly with increase in SVR, leading to compromised blood flow, MODS and death

features of septic shock

• low DBP and hyperdynamic left ventricle in early stages
• low SBP in late stages
• state of relative adrenaline insufficiency (RAI)
  • < 5 μg/dL of plasma cortisol is suggestive of adrenocortical insufficiency
  • <15 μg/dL in a stressed neonate is suggestive of RAI

Diagnosis of shock

• confirmed sepsis - blood culture or sepsis screen positive
• Probable sepsis - blood culture and sepsis screen negative, but strongly suggestive of sepsis like sclerema or refractive metabolic acidosis

Perinatal asphyxia

• shock in initial 48 hours due to myocardial ischemia
• reduced stroke volume and low SBP,
• mimics
  • cardiogenic shock - arrhythmias, cardiomyopathy
  • pneumothorax, pleural effusion

Management of shock

Management of early signs of shock

• TABC - Temperature, airway, breathing and circulation
• administer antibiotics in the 1st hour if sepsis is suspected
• initial administration of 10 ml/kg of 0.9% saline over 30-60 mins
• permissive hypotension not advised
• withhold enteral feeds in acute phase of shock for the risk of redistribution of mesenteric circulation and gut ischemia
• monitor blood sugar, ionized calcium and electrolytes
• intubate if needed

Volume expansion

• 10 ml/kg of NS initially
• upto 20-30 ml/kg in cases of proven blood loss and distributive shock
• caution should be used to give fluid in PDA associated shock, post-asphyxia cardiogenic shock and shock during transitional circulation and POCE (point of care Echo) should always be used as a guide
• choice of agents
  • crystalliods
  • NS >>> RL
• Infants operate at the higher end of frank-starling curve, so they may not have enough left ventricular reserve for volume expansive. volume expansion helps cardiac output but not blood pressure
• start initially with one bolus, plan expansion with the help of POCE and BP

Choice of drugs

• should be decided based on POCE/ BP

<img src=https://i.ibb.co/1J2xs5ns/4SxOo6Y.jpg>

condition	seen in	drug to use
low DBP	low afterload (more common), low preload. seen in left to right shunts like PDA, vasodialatory shock	dopamine, vasopressin, norepinephrine
low SBP	low myocardial contractility	doubutamine, epinephrine

• adrenal insufficiency - use hydrocortisone
• pulmonary artery hypertension - pulmonary vasodilator
• refractory to two inotropes - consider hydrocortisone
• rule out pneumothorax, cardiac tamponade, pleural collections
• use of two separate lines to provide maintenance fluids and inotropes is preferred
• avoid using inotropes with vasculocorrosive drugs like calcium gluconate <img src=https://i.ibb.co/fYcRHfdR/EzDwCEW.jpg alt=“algorithm for shock management”>

End-points of shock and weaning

<img src=https://i.ibb.co/RGdHt3vf/x5ar56V.jpg>

• first in, first out principle should be used in weaning
• if BP more than 75th percentile, faster weaning should be planned
• trophic feeds at 10 to 20 ml/kg/day may be initiated once the therapeutic end points are met