Other physiology Flashcards
Hormone
Hormone is chemical secreted by a gland, transported in the circulatory system to transmit a message to a distant cell or other gland
Four classes of hormones
- Amine derived e.g. catecholamines
- Peptide - short chain e.g. ADH, long chain e.g. insulin
- Steroid e.g. cortisol
- Eicosanoids e.g. leukotrienes
Innate immune system
Immune system complex network of cells and organs designed to fight infection
Innate: first line, no prior exposure, non-specific rapid response to threat
- Anatomical - skin, mucociliary escalator, acidic stomach acid
- cellular
- neutrophils - phagocytosis
- monocytes - become macrophages in tissue
- NK cells - destroy virus infected cells
- mast cells - inflammatory mediators
- proteins
- compleement
Inflammation
non-specific response to
- trauma - mechanical damage causes vessel disruption and mast cell activation and haemostasis
- infection - macrophage phagocytose organisms and release cytokines il-1 il-6 TNF
Symptoms - pain, redness, swelling, heat
series of events
- vasodilation (histamine)
- capillary leak (TNF, histamine)
- Migration of phagocytes
- microorganism killing, removal of debris
Complement
Plasma proteins activated
- contact with bacterial cell wall
- exposure to antibody-antigen complex
Once activated
- bacterial cell lysis (membrane attack complex)
- opsonisation - coat microorganism, binding site for phagocytes
- chemotaxis - attract phagocytes
Peri-operative period and immune function
Disruption of barriers - site of surgery, endotracheal intubation
Exposure to allergens
Depression of immune system
- stress response - depress lymphocyte
- opioids impair macrophages
- transfusion related immunomodulation
- preoperative hypothermia
Normal nutritional requirements for healthy adult
25kcal/kg/day (Harris-Benedict equation estimates BMR)
Critical illness recovery - 30kcal/kg/day
- Protein 1.5g/kg/day
- lipids 40%
- Carbohydrates rest
Electrolytes
- 1-2mmol/kg/day sodium
- 1mmol/kg/day potassium
Malnutrition
Condition of insufficient vitamins, minerals and other nutrients to maintain health.
In ITU can lead to
- poor wound healing
- increased risk of infection
- muscle weakness - delayed ventilation and mobilisation
Refeeding syndrome
Metabolic disturbances occurring after reinstitution of nutrition to a patient who has been malnourished for a prolonged period. Characterised by severe hypophosphataemia. complications include rhabdomyolysis, cardiac failure, seizures.
Sudden shift from fat to carbohydrate metabolism leading to sudden increase in insulin –> massive cellular uptake of phosphate, Na, K, Mg –> low serum levels and fluid shifts
Management
- Slow nutrition 10kcal/kg/day
- aggressive treatment of electrolyte abnormalities
- careful fluid balance
Pathophysiology of alcoholic liver disease
Steatosis
- metabolism of alcohol leads accumulation of lipids
Alcoholic hepatitis
- alcohol metabolism generates reactive oxygen species which trigger inflammation
Cirrhosis
- prolonged hepatocellular damage generates my-fibroblast like cells that produce collagen
- as hepatocytes are destroyed and liver architecture changes, hepatic function falls and there is increased resistance to portal blood flow
Hepatorenal syndrome
Advanced liver disease causing reduced GFR
Creatinine > 133 in patient with ascites when all other pathologies excluded
Generalised vasodilation causes AngII, SNS, ADH, subjecting kidney to reduced perfusion
HRS 1 - rapid and severe progressive renal failure (< 2 weeks). precipitated by infection, GIB etc
HRS 2 - slowly progressive moderate deterioration in renal function
Hepatic encephalopathy
Confusion, altered level of conscious and coma due to liver failure (neuro toxins)
1 - confused
2 - drowsy
3 - stupor, rowsable, agitated
4 - coma
Child - Pugh
prognosis, necessity for transplant
1 / 2 / 3 points
- Encephalopathy grade none / 1-2 / 3-4
- Ascites none / easy controlled / poor control
- Bili
- Albumin
- PT
Anaesthetic implications for end-stage liver disease
Preop
- assessment / MDT
- optimise fluid, electrolytes, nutrition, coagulopathy
- consider paracentesis
- delayed gastric emptying
Intraop
- drugs - altered handling, reduced metabolism, increase Vd
- neuraxial caution due to coagulopathy
- invasive monitoring but caution ODM
- glycemic control
- thermoregulation
- abx prophylaxis
Haemostasis
- Vessel injury - vasoconstriction, expose collagen, TF with platelet binding via VwF
- Initial platelet activation by binding to collagen. initial activation of V and VII to generate small amounts of thrombin. forms procoagulant surface
- Next cohort of platelet activation via ADP receptors causing release of numerous molecules (TXA2, ADP, thrombin, Ca) and crosslinking fibrinogen via GPIIb/IIIa receptors to make soft platelet plug
- Massive generation of thrombin - amplification phase
- Thrombin catalyses fibrinogen to fibrin and formation of firm scaffold - propagation phase
- Anticoagualant pathways - Protein C, S, fibrinolysis. Fibrinogen cleaves by plasmin (formed from plasminogen). FDP, d-dimer. TXA inhibit action of plasminogen
Initiation, amplification, propagation
Clotting tests
PT - test of extrinsic pathway (VII, II, X of common). TF added to sample. INR is ratio of PT to average PT of control sample. Prolonged by warfarin, liver disease, DIC
APTT - intrinsic (VIII, IX, XI, XII) and common pathway. Prolonged by UFH, haemophilia, VWF, DIC
Hypothermia definitions
Temp < 35
Mild 32-35
mod 28-32
sev < 28
Physiological consequences of severe hypothermia
CVS
- Bradycardia
- Reduced CO
- Peripheral vasoconstriction
- J waves and arrhythmias
- Increased blood viscosity
RS
- Apnoea below 24
- reduced O2 delivery - reduce CO, left shift oxyHb dissociation curve
Neuro
- confusion < 35 unconscious < 30
- Reduced MAC
Other
- diuresis
- acidosis
- reduced BMR
methods of rewarming
Passive
- blankets, remove wet clothing, increase ambient temperature
Peripheral Active
- forced air warmer
- Chemical heat pad
Central Active
- warmed fluids 42C
- warm bladder irrigation
- warm inspired gases if intubated
- RRT / ECMO
In cardiac arrest - VF shock 3x below 30 then wait until 30
No adrenaline until 30 then every 10 mims
Rewarming and IV fluid ++ as vasodilation causes expansion of IV space
IOP
- increased or decreased volume of globe content e.g. aq / vit humour, haemorrhage
- external pressure - retrobulbar haematoma, prone position
regulation by control aq humour
Aqueous humour
- ciliary bodies - active secretion and untrafiltreation
- flows from posterior chamber over lens through iris and into anterior chamber
- drained via trabecular network and canal of schlemm (between cornea and lens)
- reabsorption depends on IOP and venous pressure
- raised in IOP can be compensated by increased drainage. production is constant
- glaucoma reduces draiange
- prone position increases episcleral venous pressure
