Effect of Perinatal Hypoxia ✅ Flashcards
What happens to the foetal gases during normal labour?
There is a gradual decrease in fetal pO2 and increase in pCO2
What accompanies the increase in fetal pCO2 and decrease in pO2 during a normal labour?
A gradual increase in base deficit
Why is there a decrease in fetal pO2 during normal labour?
As uterine contractions strengthen, there are periods of decrease placental perfusion which temporarily impairs as exchange. Subsequent uterine relaxation allows the fetus to recover, at least partially
What is respiratory adaptation to extrauterine life influenced by?
Mode of delivery
What is C-section associated with, with regarding to respiratory adaptation to extrauterine life?
- Retained fetal lung fluid
- Relatively impaired lung function during first hours of life
What has been theorised to cause the relatively impaired lung function following C-section?
Absence of mechanical pressure on the thorax to squeeze lung fluid from the respiratory tract experienced by infants delivered vaginally
What is the limitation of the theory that relatively impaired lung function post C-section is caused by the absence of mechanical pressure on the thorax?
Animal studies and improved understanding of the pathophysiology of respiratory disorders in neonates has shown that the clearance of fetal lung fluid is largely dependent on reabsorption of alveolar fluid via sodium channels in the lung epithelium
What influences the reabsorption of fetal alveolar fluid through the lung epithelium?
Circulating catecholamines in the newborn
How can alveolar fluid reabsorption being influenced by circulating catecholamines explain why C-section delivery is associated with relatively impaired lung function?
Newborns delivered by C-section have lower concentrations of circulating catecholamines
In what situation do C-section babies have even lower levels of circulating catecholamines?
If there is delivery without prior labour
What changes must a neonate undergo in a short period of time at birth to survive independently of the placenta?
- Breathe and rapidly establish a functional residual capacity (FRC)
- Circulation to the lung
- Clear lung fluid
Why does a newborn baby rapidly need to establish a FRC?
To act as a gas reservoir and allow gas exchange to continue between breaths
Why must the circulation to the lungs change immediately after birth
To ensure the lungs, which were preferentially not perfused, are now perfused sufficiently to allow adequate gas exchange and tissue oxygen delivery
How much lung fluid needs to be cleared in a term baby?
About 100ml
Why is it important to clear lung fluid quickly at birth?
To allow establishment of a functional residual capacity
What process helps the baby clear lung fluid at birth?
For the few days before onset of spontaneous labour, alveolar fluid production and therefore lung fluid volume deceases markedly
When is the majority of lung fluid absorbed?
Within the first few breaths
What facilitates the absorption of lung fluid in the first few breaths?
Generating positive end expiratory pressure
How is PEEP generated with the first few breaths?
Exhaling against a partially closed glottis, usually by crying
What does the development of PEEP in the newborn lungs lead to?
- Development of FRC
- Distribution of gas throughout the lungs
- Release of surfactant
Why does the generation of PEEP lead to the release of surfactant?
Due to lung stretching
What is the result of the release of the surfactant caused by the generation of PEEP in newborn lungs?
Lowers alveolar surface tension
What happens to a fetus immediatey in acute, severe asphyxia?
- Breathing movements become more rapid and deeper
- Rise in heart rate
- pO2 falls rapidly to virtually 0
What happens after a few minutes of acute, severe asphyxia?
A period of ‘primary apnoea’
What happens in primary apnoea?
- Breathing ceases
- Heart rate falls markedly, but is maintained at a lower rate
- Cardiac output and systemic blood pressure particular maintained
What maintains the heart rate at a lower rate during primary apnoea?
- Vagal nerve stimulation
- Onset of less efficient myocardial anaerobic respiration
What enables anaerobic respiratory of the myocardium in primary apnoea?
Glycogen stores in the heart
What maintains cardiac output and systemic blood pressure in primary apnoea?
- Increased stroke volume
- Rise in systemic vascular resistance from peripheral vasoconstriction
What is protected to a degree in primary apnoea?
The blood supply to vital organs such as the brain and heart
What happens after a few minutes of primary apnoea?
Primitive spinal centres start to produce whole body gasps
What allows primitive spinal centres to produce whole body gasps?
They are released from the inhibition of the respiratory centres
At what rate do primitive spinal centres being to produce whole body gasps?
10-12/minute
Is cardiac output maintained during the stage of acute severe asphyxia where primitive spinal centres cause whole body gasping?
Yes
What eventually happens to the gasping produced by primitive spinal centres in acute severe asphyxia?
It stops due to increasing acidosis
What causes the acidosis in acute severe asphyxia?
- Rising pCO2
- Rising metabolic acids from anaerobic respiration in the tissues
Does the fetus have any buffering capacity to counteract the acidosis in acute severe asphyxia?
It has some buffering capacity, but it is soon overwhelmed
Why does the fetus have some buffering capacity to overcome acidosis?
To overcome the mildly asphyxial process of normal labour
What does the acidosis in acute severe asphyxia eventually lead to?
Changes in synaptic functions, which stops the gasping
What is it called when the baby enters the phase where acidosis stops the gasping produced by primitive spinal centres?
Secondary apnoea, or terminal apnoea
How long does the whole process of onset of acute severe asphyxia to terminal apnoea take?
20 minutes
What does recovery at the stage of secondary apnoea require?
Resuscitation with lung expansion
When might episodes of acute total asphyxia occur?
- Placental abruption
- Ruptured uterus
- Cord compression from shoulder dystocia or cord prolapse
What scenario of fetal hypoxia occurs much more commonly than acute total asphyxia?
Gradual development of fetal hypoxia and academia in utero
What are the potential outcomes of babies with chronic in-utero partial asphyxia?
- Some survive and make full recovery
- Some develop further hypoxic damage around birth
- Some will have developed severe neurological damage before onset of labour
Why are babies with chronic in-utero partial asphyxia more susceptible to hypoxia around birth?
They have limited energy stores before labour commences, and so will be less able to tolerate the mild asphyxia of normal labour, and unable to tolerate a more severe acute hypoxic event
Why is it not always immediately apparent if a child with chronic in-utero partial asphyxia has developed significant neurological damage?
They can appear fine at birth, as they may have made a full biochemical recovery
What can develop from asphyxia in utero or at birth?
Hypoxic-ischaemic encephalopathy
What can result from hypoxic-ischaemic encephalopathy?
- Death
- Neurodevelopmental impairment
What monitoring can be used to reduce the risk of hypoxic-ischaemic encephalopathy?
Fetal scalp pH
How can fetal scalp pH monitoring reduce the risk of hypoxic-ischaemic encephalopathy?
It can identify significant academia and expedite delivery before damage has occurred
