It varies depending on the metabolic rates of local areas of the brain.
The electrical potential for an individual ion, helping to predict how each ion affects the cell membrane potential.
In the thoraco-lumbar regions.
Polar molecules move across the cell membrane via transmembrane protein complexes such as pores, channels, and gates.
Em = 61.5 × log10([ion]out/[ion]in)
Excretion of K+ and secretion of H+.
In the craniosacral regions.
Em = RT/ZF × ln([ion]out/[ion]in)
To separate CSF proteins electrophoretically and detect CSF immunoglobulin.
135–145 mmol/L
Sodium (Na+) and potassium (K+) ions.
Adrenaline (E) and Noradrenaline (NE).
It describes the vicious cycle that develops if there is a reduction in cerebral perfusion pressure (CPP), leading to vasodilatation, a rise in ICP, and an increase in cerebral blood volume.
Vm = (RT/F) × ln((P[Na+]out + P[K+]out + P[Cl-]in) / (P[Na+]in + P[K+]in + P[Cl-]out))
Body compartment volumes are estimated using dilutional techniques, where an indicator dye is injected, and its concentration is measured to calculate the volume.
Volatile anaesthetics increase CBF and reduce cerebral metabolic oxygen requirements (CMRO2), uncoupling CBF from CMRO2. N2O increases both CBF and CMRO2. NMBA do not affect CBF. Most induction drugs reduce CMRO2, CBF, and ICP, except ketamine, which increases ICP.
It consists of a single pre-ganglionic fibre that terminates on the adrenal medulla, which then releases neurotransmitters/hormones into the bloodstream.
It consists of more non-contractile connective tissue.
WBC counts increase to 12 × 10^9/L by term, with a further increase to 30 × 10^9/L during labor.
The membrane potential will fall away from zero and become more negative as the K+ equilibrium is re-established, and no action potential (AP) will be generated.
In neonates, the larynx is at the level of C2/3, whereas in adults it is at C5/6.
The depolarisation above threshold potential and subsequent repolarisation of a nerve axon resulting in the propagation of a nerve impulse along that axon.
Less than 0.45 g/L.
Short pre-ganglionic fibers (cholinergic) and long post-ganglionic fibers (cholinergic).
It describes the treatment of reduced CPP, involving a rise in mean arterial pressure (MAP), a rise in CPP, vasoconstriction, a fall in ICP, and reduced cerebral blood volume.
A reduction in cerebral perfusion pressure (CPP).
CSF is the clear, colorless fluid that bathes the brain and spinal cord, acting as a protective fluid layer for the central nervous system (CNS).
CBF increases linearly between a PaCO2 range of 3 and 10 kPa. Outside this range, CO2 reactivity is lost. Hypocapnia can cause intense cerebral vasoconstriction and ischaemia, while hypercapnia can increase intracranial blood volume and ICP. CBF increases below a PaO2 of 8 kPa due to hypoxic vasodilatation.
The curve is shifted to the right.
Cerebral vasoconstriction occurs, keeping CBF constant.
CSF flows from the lateral ventricles through the foramen of Monro into the third ventricle, then via the aqueduct of Sylvius into the fourth ventricle. It leaves the ventricular system via the midline foramen of Magendie and lateral foramen of Lushka, entering the subarachnoid space of the brain and spinal cord. CSF is absorbed into the dural venous sinuses via arachnoid villi and granulations that project into the dural sinuses.
-70 mV.
The movement of Na+ ions into the cell.
Depolarisation is when the inside of the cell becomes more positive, while hyperpolarisation is when the inside of the cell becomes more negative.
70 mL/100 g/minute.
The ANS is a collection of nerves and ganglia involved in the involuntary control of homeostasis and the stress response.
The maintenance of constant blood flow despite changes in cerebral perfusion pressure (CPP).
Approximately 70–80 mmHg.
The diffusion of water molecules (solvent) across a semi-permeable membrane, from a dilute solution to a concentrated solution.
By applying pressure to the more concentrated solution.
The PNS ganglia are known as terminal ganglia and are located close to or within the wall of the target tissue.
CPP should be maintained at >70–80 mmHg.
−55 mV.
Properties of solutions that depend on the number of solute particles, including lowering of vapor pressure, elevation of boiling point, depression of freezing point, and osmotic pressure.
The relatively large liver in neonates restricts diaphragmatic movement.
Aortic compression increases afterload, decreases cardiac output, and reduces utero-placental blood flow. This can be mitigated by avoiding the supine position and using at least a 15° lateral tilt.
It is relatively more permeable to K+ than Na+, so the resting membrane potential approaches the equilibrium potential of K+.
Short pre-ganglionic fibers (cholinergic) and long post-ganglionic fibers (adrenergic).
50 mL/100 g brain tissue/minute.
The overall membrane potential, taking into account the permeabilities and concentration gradients of each ion.
Vm: membrane potential, R: universal gas constant, T: absolute temperature, F: Faraday’s constant, P: permeability of the ion.
The three main types are continuous, fenestrated, and sinusoidal capillaries.
CSF is produced at a rate of approximately 0.3 ml per minute.
A pre-ganglionic fibre, an autonomic ganglion, and a post-ganglionic fibre.
85 ml/kg in neonates compared to 70 ml/kg in adults.
The concentration of osmotically active particles in solution.
200 ml/kg/min.
ADH stimulates V2 receptors on collecting ducts, increasing adenylate cyclase activity, which causes fusion of pre-formed water channels on the apical membrane, increasing water permeability. Other effects include stimulating thirst, releasing factor VIII, platelet aggregation and degranulation, arteriolar vasoconstriction, glycogenolysis in the liver, acting as a brain neurotransmitter, and secreting ACTH from the anterior pituitary gland.
Cholinergic (they release acetylcholine).
Furosemide (0.25–1.0 mg/kg), mannitol (0.25–1.0 g/kg), or hypertonic saline.
Adrenaline (80%) and noradrenaline (20%).
80%.
Acetylcholine (Ach).
-55 mV.
Nicotinic acetylcholine receptors, muscarinic acetylcholine receptors, and adrenoceptors.
The capillary wall consists of a single layer of simple squamous epithelium and a basement membrane.
CBF and cerebral metabolism are coupled, meaning regional CBF varies with metabolic activity. Products of metabolism (H+, K+, adenosine, nitric oxide) cause vasodilatation, matching CBF to metabolic requirements.
Between 50 and 150 mmHg.
The pressure required to prevent solvent migration by osmosis across a semi-permeable membrane.
Cerebral vascular smooth muscle relaxes, causing vasodilatation and maintaining CBF.
1 osmole.
Anterior to the vertebral column next to the major arteries.
MAP should be maintained at around 90 mmHg.
Using the formula: (2 × Na+) + glucose + urea, which adds up to approximately 290 mosmol/kg H2O.
Stroke volume and heart rate increase, leading to a cardiac output increase of up to 60% by term (8 L/min).
Neonates primarily use diaphragmatic breathing, whereas adults use intercostal breathing.
Vena caval compression reduces venous return and preload, decreasing cardiac output and blood pressure, and causing engorged vertebral veins.
Adrenergic receptors (either α or β).
Water balance governs the ICF, and sodium balance regulates the ECF compartments.
Hyperosmolarity, volume depletion, angiotensin II, and factors like pain, exercise, stress, emotion, nausea, vomiting, standing, nicotine, morphine, barbiturates, and carbamazepine.
[ion]out: extracellular concentration of the ion, [ion]in: intracellular concentration of the ion, Em: membrane equilibrium potential, R: universal gas constant, T: absolute temperature, Z: valency, F: Faraday’s constant.
Reabsorption of NaCl with a 30–90 minute latent period.
50 mL/minute (20% of total body oxygen requirements).
Because the plasma glucose concentration must be known to interpret the CSF glucose level properly.
CPP = mean arterial pressure (MAP) – [intracranial pressure (ICP) + central venous pressure (CVP)].
The 7% increase in plasma volume is detected by baroreceptors, leading to reduced ADH secretion.
The three determinants of intracranial pressure are CSF, brain tissue, and blood volume.
RBC mass increases, but plasma volume increases more, causing physiological anemia.
Oncotic pressure is the pressure exerted by plasma proteins, contributing less than 1% to plasma osmolality and osmotic pressure, amounting to 25–28 mmHg. It is significant as it is the major determinant of fluid retention within the capillaries.
Albumin concentration decreases, increasing the free active proportion of plasma-bound drugs.
Water intake is stimulated by an increase in plasma osmolality, which activates osmoreceptors in the anterior hypothalamus, leading to thirst and ADH release. Extracellular fluid volume depletion stimulates the renin–angiotensin system, with angiotensin II acting on receptors in the diencephalon. Baroreceptors, dryness of the pharyngeal mucous membranes, and psychological and social factors also play a role.
By positioning the patient at a 30° head-up tilt and using tape instead of endotracheal tube ties to avoid obstructing venous drainage.
Deuterium oxide and Antipyrine.
By using infusions of propofol or midazolam, or in certain situations, thiopentone to induce a 'thiopentone coma'.
Radiolabelled albumin and Evan’s blue dye.
Long pre-ganglionic fibers (cholinergic) and short post-ganglionic fibers (cholinergic).
Fat-soluble molecules can easily diffuse across the cell membrane.
There is no initial rise in ICP due to compensatory mechanisms such as a reduction in intracranial venous blood volume and an increase in CSF absorption combined with CSF movement into the spinal compartment.
Endocytosis is a form of active transport where the cell membrane creates a vesicle to capture and internalize substances.
An oligoclonal pattern of immunoglobulin synthesis, detectable in 90% of patients with MS.
To rapidly amplify a defined region of DNA or RNA and detect the presence of bacterial (e.g., syphilis, TB) and viral pathogens (e.g., HIV) in the CSF.
The total volume of CSF is approximately 150 ml, which equates to about 10% of intracranial volume.
Brain injury can lead to loss of cerebral autoregulation in affected areas, resulting in pressure-dependent perfusion. A fall in CPP may lead to secondary ischaemic brain injury.
10–15 mmHg is normal, while above 20 mmHg is considered elevated ICP.
The paravertebral ganglia (sympathetic trunk) and the prevertebral ganglia.
Osmoreceptors are cells of the anterior hypothalamus, located outside the blood-brain barrier. They respond to changes in osmolality and stimulate thirst and the secretion of vasopressin.
It increases the risk of edema.
Until 6 months of age.
Systemic vascular resistance reduces, leading to a reduction in diastolic blood pressure (DBP) and systolic blood pressure (SBP), resulting in increased pulse pressure.
At L3 (L1 by age 2 years).
Neonates have a higher alveolar ventilation of 100–150 ml/kg/min compared to 60 ml/kg/min in adults.
The closing volume is larger than FRC in neonates until 6–8 years of age, resulting in airway closure at end-expiration. Consider the use of IPPV and PEEP.
Due to their higher basal oxygen consumption, higher risk of apnoea, and all the other anatomical and physiological differences, hypoxaemia occurs more rapidly in neonates.
Any further small increase in intracranial volume results in a large increase in ICP, indicating decompensation.
1. Secondary to an increase in plasma immunoglobulin (e.g., multiple myeloma), 2. Impairment of the blood-brain barrier, 3. Local synthesis in the CNS (e.g., multiple sclerosis).
Atrial stretch due to ECF expansion from high NaCl intake or IV infusion of saline.
The PNS is involved in 'rest and digest' processes.
Approximately 450 ml of CSF is produced per day, and the CSF volume is replaced three times every 24 hours.
The skull is a rigid box containing brain tissue (80%), blood (12%), and CSF (8%). The volume of the box is constant, so an increase in volume of any one constituent must be accompanied by a reduction in another to keep ICP constant.
The ABC approach stands for Airway, Breathing, and Circulation.
The BBB prevents plasma constituents from passing freely into the CSF. It is maintained by tight junctions and fenestrated choroidal capillaries within the brain, and a specialized bidirectional transport system for ions, glucose, and amino acids.
Neonates have a relatively larger head, short neck, large tongue, narrow nasal passages, high anterior larynx (C2/3), large U-shaped floppy epiglottis, narrowest point of the larynx at the cricoid cartilage, equal angles of mainstem bronchi, and are obligate nasal breathers.
Hypoxia, acidosis, hypercapnia, or hypothermia.
16–20 g/dl.
Using the equation P = nRT/V, where n is the number of particles, R is the universal gas constant, and T is temperature.
Due to their immature central nervous system.
Neonates increase their minute ventilation by increasing their respiratory rate due to a relatively fixed tidal volume.
TBV = Plasma volume × 100 / (100 - haematocrit).
30 ml/min at term, increasing to 110 ml/min by age 2 years.
Muscarinic acetylcholine receptors (mAChR).
1.2–1.5 mmol/L
10–15 cm H2O
TB meningitis, fungal meningitis, or chronic bacterial meningitis.
The cell membrane consists of a phospholipid bilayer with hydrophobic heads on either side and hydrophilic tails facing inwards.
Infection, blood contamination, and chronic inflammatory disorders of the CNS (e.g., TB, syphilis, Guillain–Barré).
20 mL/100 g/minute.
Reduction in intracranial venous blood volume, increase in CSF absorption, and movement of CSF into the spinal compartment.
Natriuresis, reduction in blood pressure, and reduced secretion of aldosterone, ADH, renin, and consequently angiotensin II.
CSF is produced by the four choroid plexuses located in the third, fourth, and lateral ventricles.
Chemoreceptors, baroreceptors, mechanoreceptors, and regions within the central nervous system.
A change in perfusion pressure results in a myogenic response in the cerebral vascular smooth muscle to maintain constant CBF.
Within the lateral grey horns of the first to twelfth thoracic segments and the first to third lumbar segments.
To prevent hypoxia, which can cause cellular ischemia and raise ICP through vasodilatation.
Because their cardiac output is largely rate-dependent.
Because it is not influenced by temperature.
Trauma to the small airway can easily lead to oedema and airway obstruction. A 1 mm oedema can narrow an infant’s airway by 60% (resistance ∝ 1/radius).
Only those innervating sweat glands.
740.7 kPa or 7.33 atm (5629.3 mmHg).
Nicotinic acetylcholine receptors (nAChR).
The process where the action potential jumps from node to node in a myelinated axon, increasing the action potential's velocity.
Rest and digest.
Thoracolumbar tract.
0.15–0.45 g/L
The two main types are passive transport (osmosis and diffusion) and active transport.
Relative Refractory Period and Absolute Refractory Period.
Infection (local metabolism by white cells) or hypoglycemia.
It leads to a rise in cerebral perfusion pressure (CPP), vasoconstriction, a fall in intracranial pressure (ICP), and reduced cerebral blood volume.
It causes ECF expansion, diuresis, and natriuresis, with sodium and water confined to the ECF, leading to plasma expansion and reduced ADH secretion.
Cerebral metabolic requirement for oxygen (CMRO2) falls by 7% per 1°C decrease in core body temperature, and CBF parallels this reduction in CMRO2.
Within the nuclei of III, VII, IX, and X cranial nerves and in the lateral grey horns of the second to fourth sacral segments.
Osmometers capable of detecting temperature changes of 0.002°C are used. They utilize one or more of the colligative properties of water, such as the depression of the freezing point by 1.86°C per mole of solute added to 1 kg of water.
The movement of the membrane potential towards zero causes the opening of voltage-gated Na+ channels.
CPP = MAP − ICP.
A positive feedback effect occurs on the Na+ channels, causing large numbers of them to open, leading to an explosive influx of Na+ and raising the membrane potential above 0 to +35 mV.
The membrane either reaches the threshold level or does not, and the size of the action potential is fixed and not dependent on the size of the stimulus.
Neonates have a compliant chest wall with horizontal ribs.
A period following each action potential where the nerve cell cannot be excited, no matter how large the stimulus.
Because they can increase brain edema as they cross the disrupted blood-brain barrier.
Neonates are born with only 10% of the total number of alveoli as adults. Alveoli develop over the first 8 years.
Fight or flight.
Low osmolarity, increased ECF volume, and alcohol.
CSF chloride and magnesium levels are higher than plasma.
TB meningitis.
Exocytosis is the process where a vesicle fuses with the plasma membrane to expel its contents into the extracellular environment.
Small molecules cross the capillary wall through the space between cells (paracellular transport).
The parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS).
The SNS is involved in 'fight-or-flight' processes.
Increased ANP secretion, natriuresis, and inhibition of the renin–angiotensin–aldosterone system.
Plasma volume increases by 50% by term, increasing preload and volume of distribution (Vd) of polar drugs.
CSF-related causes include hydrocephalus. Brain-related causes include tumours, oedema, and contusions. Blood-related causes include haematoma and cerebral aneurysm.
Platelet counts reduce due to consumption.
Asystole.
Grey rami communicantes.
Neonates have equal angles of mainstem bronchi, while in adults, the right main bronchus is more vertical.
The process where K+ channels remain open after Na+ channels have closed, allowing the resting membrane potential to be re-established.
ICF = TBW - ECF.
Muscarinic acetylcholine receptors (mAChR).
The diffusion of permeable ions across a semipermeable membrane down their concentration gradient is balanced by the electrostatic attraction of impermeable ions trapped on the inside of the membrane.
Due to a large body surface area/volume ratio and high heat loss.
Dietary sodium intake, ECF volume (baroreceptors) and ADH secretion, GFR and tubuloglomerular feedback, and the renin–angiotensin–aldosterone system.
280–300 mmol/L
1.1–2.4 mmol/L
CSF calcium levels are approximately 50% that of plasma.
It can provide important diagnostic information.
It is a hypotonic solution that gets distributed equally throughout all fluid compartments, minimally increasing intravascular volume and decreasing plasma osmolarity, which stimulates osmoreceptors and decreases ADH secretion.
Sodium diffuses from high to low concentration areas, followed by water, with 75% in the ISF and 25% in the plasma.
CSF is derived from plasma filtration and subsequent secretion by the choroid plexuses.
In situations of raised intracranial pressure, CSF production remains relatively constant, but CSF absorption increases, thereby reducing total CSF volume.
Because stroke volume is relatively fixed.
2 osmoles.
White rami communicantes.
Because hypercapnia and hypoxia increase cerebral blood volume and ICP according to the Monroe-Kellie doctrine.
Noradrenaline (they are adrenergic).
CMRO2 decreases by 7% for every 1°C fall in temperature, paralleled by a fall in CBF.
Using radiolabelled red cells.
Functional residual capacity (FRC) reduces by up to 20%, and closing volume encroaches on FRC, leading to airway closure and increased risk of hypoxia. Tidal volume (Vt) increases, but total lung capacity (TLC) and vital capacity (VC) remain unchanged.
Antidiuretic hormone (ADH/vasopressin).
Release of factor 8 by the endothelium (V2), platelet aggregation and degranulation (V1), and arteriolar vasoconstriction (V1).
On either side of the vertebral column from the base of the skull to the coccyx.
The number of osmoles (or mosmoles) of solute in 1 liter of solution, osm/L.
All clotting factors increase except XI and XIII, leading to shortened bleeding time (BT), prothrombin time (PT), and activated partial thromboplastin time (aPTT), increasing the risk of thromboembolic complications.
Myelination is incomplete in the first year of life.
Left ventricular mass increases, and ECG may show left axis deviation, ST depression, and even a flat or inverted T-wave. A systolic murmur is almost universal at term.
The action potential moves like a wave; local currents spreading in front of the action potential cause a change in membrane potential and bring the membrane to threshold potential to spark propagation.
Sweat glands, arrector pili muscles, adipose cells, kidneys, and most blood vessels (SNS only); lacrimal glands (PNS only).
Neonates have a higher basal oxygen consumption of 6 ml/kg/min compared to 3.5 ml/kg/min in adults.
Increased water permeability in cortical collecting tubule (V2 receptors), increased water and urea permeability in medullary collecting tubule, increased retention of water, and reduced urine volume.
Efferent arteriolar vasoconstriction to maintain GFR, direct sodium reabsorption, secretion of aldosterone from adrenal cortex, increased ADH, increased thirst (water retention), and negative feedback on renin release.
Plasma cholinesterase reduces, but the effect of suxamethonium is offset by the increased volume of distribution (Vd).
K+ ions move out of the cell to restore the resting membrane potential, facilitated by the opening of voltage-gated K+ channels.
Inulin, Thiocyanate, and Thiosulphate.
A period following the absolute refractory period where another action potential can be generated with a supra-maximal stimulus.
Due to increased extracellular fluid (ECF).
6% of cardiac output at birth, rising to 18% at 1 month.
32°C for a term infant compared to 28°C for an adult.
115–125 mmol/L
3.0–6.5 mmol/L
Capillary enlargement and mucosal congestion can lead to voice changes and difficulty breathing. The diaphragm is elevated by 4 cm, thoracic circumference increases, and breathing becomes largely diaphragmatic by term.
Neonates have a sinusoidal respiratory pattern with no end-expiratory pause and an inspiratory/expiratory ratio of 1:1.
By utilizing non-shivering brown fat thermogenesis.
1.00–1.40 mmol/L
Raised intracranial pressure.
Meningeal infiltration by hematological malignancy.
Renal immaturity resulting in poor handling of water excess or excess sodium.
WISE: Water regulates Intracellular; Sodium regulates Extracellular.
7.28–7.40
CSF proteins are approximately 1% that of plasma.
Interstitial fluid = ECF - Plasma volume.
Craniosacral tract.
50–110 μmol/L
CSF glucose levels are approximately 60% that of plasma.
20–30 cm H2O
Bacterial meningitis, cerebral abscess, seizures, or CNS hemorrhage.
2.6–3.0 mmol/L
2.8–4.4 mmol/L
Viral meningitis, TB, syphilis, fungal and parasitic infections, or degenerative CNS diseases like multiple sclerosis.
