Physiology in Anaesthesia Part 2 Flashcards
(32 cards)
pH 7.0 = how many hydrogen ions
100nmol/L
what is the effect of alkalosis on calcium ions
encourages calcium to bind with proteins;
lowers free ionised fraction of calcium;
may lead to tetany
What is myoglobin
A single ferroprotein chain, can bind only one molecule of oxygen, releasing it at only extremely low PO2 levels.
Factors in the neonate that can cause dilation of the ductus arteriousus
hypoxia
hypercarbia
acidosis
pulmonary vasoconstriction
Causes of persistent pulmonary hypertension in neonates
prematurity
diaphragmatic hernia
meconium aspiration
infection
congenital heart disease
polycythaemia
Neonatal myocardium is more sensitive to (inotrope);
and less sensitive to (inotrope);
because:
noradrenaline;
dopamine;
sympathetic innervation of the myocardium is incomplete
Neonatal haemotocrit should be maintained at ____% or higher;
because:
30%;
neonates have a marginal cardiovascular reserve, and the foetal haemoglobin dissociation curve is left-shifted.
Conducting airways are fully developed at ____ weeks of gestation;
but alveoli begin to develop from distal saccules at ____ weeks.
16;
24-28
Complete alveolar maturation occurs at:
8-10 years
The primary neonatal respiratory muscle:
diaphragm
Production of surfactant begins at ____;
and reaches maturity at ______.
23-24 weeks gestation;
35 weeks gestation
Cause of ventilation-perfusion mismatch in the neonate:
distal airway closure during normal tidal breathing
Prevention of respiratory distress syndrome in preterm infants:
- maternal coritcosteroids before delivery;
- intratracheal exogenous surfactant
Why does the neonatal lung have a greater tendency to collapse
- greater compliance;
less outward recoil
Neonatal active mechanisms to maintain normal lung volumes
- rapid breathing rate shortens duration of expiration;
- utilises intercostal muscle activity during expiration to stabilise the chest wall;
- exhalation through a partially closed glottis in order to slow expiratory flow and maintain an end-expiratory lung volume.
Explain the rapid wash-in and wash-out of inhaled gases in neonates
high ratio of minute ventilation to FRC
Why does the neonate have an altered response to hypoxia and hypercarbia
immature function of peripheral chemoreceptors
Respiratory differences in neonates (cf. adults)
- decreased ratio of alveolar surface area to body surface area;
- alveolar minute ventilation is doubled;
- diaphragm has fewer high-oxidative muscle fibres and his more fatiguable;
- increased alveolar-arterial oxygen tension gradient;
- chest wall is more compliant and has less outward recoil;
- greater V/Q mismatch;
- greater tendency for airway collapse;
- altered response to hypoxia and hypercarbia;
- low airway resistance;
- narrow airways more vulnerable to obstruction.
Neonatal thermogenesis relies on:
non-shivering;
chemical thermogenesis by brown fat metabolism
Define: thermoregulatory range
the ambient temperature range;
within which an unclothed subject;
can maintain a normal body temperature
What stimulates thermogenesis in brown fat
sympathetic system: noradrenaline
What is the lower limit of the thermoregulatory range in:
1. term infant
2. preterm infant
- 23C
- 28C
Causes of accelerated heat loss in the paediatric patient
- decreased thermoregulatory threshold due to anaesthesia;
- low ambient temperature in the OR;
- cold skin preparation solutions;
- infusion of cold solutions;
- anaesthesia-induced vasodilatation;
- dry gases at high flows in nonrebreathing systems
Measures to prevent loss of heat in paediatric anaesthesia
- raising OR temperatures to 28-30C;
- radiant heat lamps;
- wrapping peripheries in insulating material;
- warmed, non-volatile skin preparation solutions;
- warmed IV fluids/blood products;
- heated and humidified inhaled gases;
- forced-air warmers
