Other Flashcards
Interthreshold Range
Range of core temperatures over which no autonomic thermoregulatory responses occur.
36.7-37.1 (+/- 0.2) in non-anaesthetised stated.
- Sweating begins at upper end
- Vasoconstriction begins at lower end
Thermoneutral zone
Range of ambient temperatures which the body can maintain core temperature with minimal O2 consumption. Core body temp can be maintained by changes in vasomotor activity to skin blood vessels alone.
Lower end is the critical temperature - point at which heat production requirement -> incr O2 consumption.
Clothed adult = 22-28
Naked adult = 27-31
Neonate clothed = 32-34
Radiation
40%
Transfer of heat by infrared electromagnetic radiation from one object to another at different temperature with which it is not in contact
Convection
30%
Transfer of heat by the circulation or movement of the heated parts of a liquid or gas
Conduction
5%
Heat exchanged between object at different temperatures that are in direct contact with one another
Evaporative loss
15% + resp loss (15%)
Loss of latent heat of vaporisation when a substance (water) changes phase from liquid to gas
Latent heat of vapourisation
Heat absorbed when a substance changed phase from liquid to gas
GA effects on thermoregulation
Increases interthreshold range from 0.2C to 4C
- Decr threshold to cold by 2.5C
- Incr threshold to warmth by 1.3C
Active thermoregulatory responses absent. The only thermoregulatory responses available to anaesthetised and paralysed are vasoconstriction and non-shivering thermogenesis
Hypothermia
Endocrine and metabolic consequences
Decreased metabolism and oxygen consumption
Decreased carbohydrate metabolism and hyperglycaemia
Essentially unchanged electrolytes
Haematological consequences
Increased hematocrit and blood viscosity
Neutropenia and thrombocytopenia
Coagulopathy and platelet dysfunction
Respiratory consequences
Decreased respiratory rate and medullary sensitivity to CO2
Acid-base changes: alkalosis and hypocapnea
Rise of pH with falling body temperature
Fall of PCO2 with falling body temperature
Increased oxygen solubility and O2-haemoglobin affinity
Pharmacological consequences
Delayed absorption
Decreased drug metabolism, especially hepatic metabolism
Delayed hepatic and renal clearance
Poorer affinity of receptors (eg. for catecholamines)
Cardiovascular consequences
Decreased cardiac output and bradycardia
QT prolongation and the J wave
Arrhythmias - classically AF and VF
Resistance to defibrillation
Vasoconstriction
Renal consequences
“Cold diuresis” due to decreased vasopressin synthesis
Central nervous system effects
Confusion and decreased level of consciousness
Shivering
Increased seizure threshold
Immunological consequences
Decreased granulocyte and monocyte activity
ACF anatomy
My Brother Throws Rad Parties (Med -> Lat)
M: median nerve
B: brachial artery
T: tendon of biceps
R: radial nerve
P: posterior interosseous branch of radial nerve
Internal jugular vein
IJV course
- Origin - sigmoid sinus + inferior petrosal sinus
- Emerges - jugular foramen at base of skull
- Travels - down either side of neck in vertical direction
- Terminates - joins subclavian v to form brachiocephalic v
Relationships
- Ant - ICA, vagus nerve
- Post - C1, sympathetic chain, dome of pleura, thoracic duct (on left)
- Med - carotid arteries (both internal then common), cranial nerves
Surface anatomy
Sonoanatomy
Subclavian vein
- Continuation of the axillary vein as it crosses the upper surface of the first rib
- Travels post to the clavicle and subclavian muscle
- Separated from the subclavian artery by the anterior scalene
- Joins with the IJV to form the brachiocephalic vein behind SC joint
- Left subclavian receives termination of thoracic duct
Borders
- Ant by clavicle, subclavius muscle + pec major
- Post by ant scalene + subclavian artery
- Inf by first rib + lung apex
- Sup by skin, subcut tissue + platysma
- Med joins brachiocephalic vein
- Lat fed by axillary vein
Surface anatomy
- Needle placed in the deltopectoral groove, inferior and lateral to the middle third of the clavicle
- Inserted at shallow angle
- Pass under the middle third of the clavicle aiming at the sternal notch
Complications
- If artery cannulated, applying pressure difficult
- Left side approaches incr risk of thoracic duct damage
- Incr risk PTX
Lymphatic systemic
Consists of lymphatic capillaries which arise in the tissues and drain lymph through lymph node. In almost all tissues except cartilage, bone marrow + CNS.
Blind ending and possess flap valves. Unidirectional flow
Thoracic duct originates from cisterns chyli at T12.
Drains into systemic circulation via the thoracic duct (which drains into the circulation at the junction of the L) subclavian and IJV - L brachiocephalic), and the R) lymphatic duct
Composition
- Lymph, protein, all coag factors, low levels of fibrinogen, fat, lymphocytes, macrophages, electrolytes, CHO
- 8-12l/day produced, 4L returned to circulation. Incr with exercise, peristalsis, elevated capillary filtration
Functions
- Return of protein + excess fluid
- Transport fat from small intestine
- Immunological roles
Emergency surgical airway
Cricothyroid membrane
- Runs between thyroid and cricoid cartilage
- Mainly elastic tissue
- Thyroid cartilage superiorly
- Cricoid cartilage inferiorly
- Cricothyroid muscle laterally on both sides
Surface anatomy
- Laryngeal prominence (palpable notch) forms sup edge of thyroid cartilage. Usually at C4
- Cricothyroid membrane 2cm inferior to laryngeal prominence
Cricothyroid arteries - branches of sup thyroid arteries running along both sides of cricothyroid membrane, anastome in the midline closer to the superior border - therefore should ideally be performed in inferior part.
USS identification
Ion concentrations + Nernt potential
Intracellular (mM)
- K = 150
- Na = 15
- Cl = 10
Extracellular (mM)
- K = 5
- Na = 145
- Cl = 125
Nernst Potential (mV)
- K = -90
- Na = +60
- Cl = -70
Ion with greater membrane permeability -> Nernst potential has greater contribution to total RMP (K+)
Resting Membrane Potential
RMP = voltage difference across cell membrane when the electrical and chemical gradients are in equilibrium
RMP - generated by uneven distribution of charge particles across membrane, due to
- Cell membrane having different permeability do diff charge particles
- Gibb-Donan effect - presence of impermeable charge molecules on one side of semi-permeable membrane results in asymmetric distribution of permeable charged ions
- Ion channels and transporters (e.g Na/K ATPase plays important part in maintaining RMP)
RMPs of cells
- Axon -70mV
- Skeletal muscle -90mV
- Cardiac myocyte -80mV
- Cardiac pacemaker -60mV
- Smooth muscle wandering -40 to -60mV
Nernst potential
Voltage difference generated by the electrochemical gradient of an ion across the cell membrane (assuming complete permeability)
Calculated using the Nernst equation
K -90mV (greatest permeability so contributes most)
Na +60mV
Cl -70mV
Smooth muscle
Involuntary non-striated muscle
- Single nucleus
- Not striated - irregular actin/ myosin distribution
- No fixed tension-length relationship
- Does not require nerve AP to stimulate contraction (automaticity)
- Poorly developed SR -> require EC Ca2+ for contraction
- No troponin
- Can maintain sustained contraction with minimal energy consumption ‘latched bridge’ mechanism
- Dense bodies instead of Z-line
- No end plate, instead multiple nerve endings with varicosities
- Poorly developed T-tubules
Recurrent laryngeal nerve
Innervates all intrinsic laryngeal muscles except cricothyroid.
Sensory innervation to larynx below vocal cords
Cough reflex
Aim:
- Prevent aspiration of foreign substances
- Clear secretions from airways
Reflex arc:
Afferent
- Irritant receptors (rapidly adapting) located on wall of pharynx, trachea (esp carina) and bronchi
- Absent beyond resp bronchioles
- Sensitive to chemical and mechanical stimuli
- Receptor stimulation -> impulse travels along vagus nerve (internal laryngeal n) and glossopharyngeal (pharynx) -> diffusely synapse in medullae (NTS)
- Slowly adapting stretch receptors - mechanical forces, participate in Hering-Breuer
- C-fibres (J receptors) - nociceptors, responds to noxious chemical and mechanical stimuli
Central pathway
- Central coordinating region for coughing is located in the upper brainstem and pons (no cough centre)
Efferent
- Impulse from brainstem -> vagus, phrenic, spinal motor nerves -> laryngeal, diaphragm, abdo wall muscles -> cough
Efferent mechanism
- Sensory, inspiratory, compressive and expulsive phases
- Rapid inspiration of large volumes of gas
- Epiglottis + larynx close -> gas trapped within lungs
- Exp muscles contract forcefully -> incr trans pulmonary pressure
- Sudden opening of epiglottis + larynx -> rapid expulsion of gas from lungs
- Strong compressive forces on lung partially collapse non-cartilaginous parts of bronchi + trachea -> rapid moving turbulent gas flow expels foreign material adhered
Complement system
Part of innate immunity
Main functions
- Membrane pore -> cell lysis
- Opsonisation for phagocytosis by neutrophils, macrophages
- Chemotaxis
- Mast cell degranulation
Pathways
- Classic (activated by antibody-ag complex, IgG or IgM)
- Alternate - LPS bacterial cell wall
- Lectin - mannose binding lectin
Common pathway
- Cleaves C3 -> C3a + C3b
- C3b cleaves C5 -> C5a + C5b
- C5b binds C6/7/8/9 -> MAC -> cell lysis and destruction
C5a/C3a
- Release of mediators via degranulation of mast cells
- Local VasoD
- Neutrophil aggregation
- Chemotaxis
Order of fibre blockade
- B - preganglionic autonomic
- C + AD - pain, temp + touch
- AG - motor
- AB - touch, pressure
- Aa - proprioception
Cold receptors in skin
Krause bulbs
- Via AD fibres and spinothalamic tract
- Become active <25oC
Warm receptors in skin
Ruffini endings
- Via C-fibres and spinothalamic tracts
- Becomes active >30oC. max 40oC, cease 46oC
Viscosity
Measure of a fluid’s internal resistance to flow
Ratio of shear stress (dyn/s) to shear rate (cm/s/cm), hence units = dyn/s/cm-2
SI unit = Pa.s
Incr temp = incr viscosity gas, decr viscosity fluid
Density
Mass of a substance per unit volume
kg/m3
Incr temp = decr density in both gas and fluid
