Fluid Management And Blood Transfusions Flashcards
What else stimulates the release of ADH?
Stress and pain
How is ADH regulated in the heart?
By stretch receptors in low-pressure system of the heart and great vessels = baroreceptors
How do baroreceptors work?
Tonic firing from these receptors inhibit ADH release. In response to a decrease in filling of the RA, the rate of firing decreases =increasing ADH
What is ANP, and what role does it play?
Stretch of the right artrium releases atrial natriuretic peptide (ANP), which stimulates the excretion of sodium in the kidney. Fall in atrial filling inhibits release of ANP
What is the thirst mechanism?
Osmoreceptors sense an alter in osmotic concentration of the plasma and trigger the thirst mechanism releasing ADH from the post pituitary.
This stimulates water intake and re-absorption of water in the kidney
What is the circulatory response?
Central catecholamine release due to sympathetic stimulation in BRAINSTEM, and inhibition of parasympathetic response.
Increased HR and maintained BP(with decreased blood vol)
What does adrenaline do? And which organs are involved?
It had dominant B-agonist effects on CO and vasodilation of blood vessels in heart and skeletal mm
Brain heart and skeletal mm are predominately responsive to B-adrenergic stimulation
What does noradrenaline do?
Vasoconstriction via alpha agonist effect in all organs expect fight or flight
How is the kidney involved in shock?
Increased sympathetic tone reduced global renal blood flow, and redistributes plasma flow from cortical to JM nephrons
- retention of Na and H2O
- reduced ruins output
- decreased urea clearance
Why are Juxtamedullary nephrons at high risk of renal tubular ischaemia, ATN, and AKI?
They have a tenuous oxygen supply and reductions in renal plasma flow puts them at risk
What is the diabetes of trauma?
Hormones released during shock = catecholamines, glucocorticoids, thyroid hormone and growth hormone. All anti- insulin hormones (insulin secretion and response is inhibited).
This causes increased glucose from liver
First glycogen breakdown
Gluconeogenesis
Suppression of insulin limited glucose use to fight/flight organs. Other organs are fat-adopted.
Rely on FFA and ketones for energy
In an inactive patient the metabolic response is inappropriate and results in elevated blood sugar
What are the fluid consequences of shock?
Maximal Na and water retention, dilutions like hyponatraemia, hypokalamia (Met. Alkalosis) diminished blood flow- risk of renal failure and hyperglycemia
What is the objective of fluid therapy?
Early and complete restoration of tissue blood flow and O2 supplies, reducing biochem disturbance and preservation of organ function (kidney and gut) and avoidance of transfusion complications
What are fluids used for?
Replacement of pre-operative losses
in-theatre resus
postop maintenance
Purpose of intra-operation fluids?
Rehydration
Maintenance
Replacement
What is the fluid replacement of pre-operative starvation losses according to normal hourly maintenance rate?
1-2ml kg hr
What should rehydration and maintenance fluids be replaced with?
Crystalloid solutions
Maintenance for adults?
1-2ml kg hr
How is blood loss replaced?
Isotonic crystalloid initially but once it exceeds 1litre all further replacement should be with colloids and then blood to maintain the appropriate haematocrit
Why should high sodium containing solutions be used?
To avoid hyponatraemia that results from the retention of water in excess sodium as part of the stress response
Should one use glucose containing products and why?
No, physiological response will ensure that blood sugar rises regardless of glucose admin and they are hypotonic not isotonic (don’t expand intravasculature space)
Where do crystalloid expand to and what is its consequences?
They expand the ECF and are redistributed between the intravascular as extracellular compartments in a 1:4 ration (1ml intravascular and 4ml in the ECF)
Consequently, full volume expansion after blood loss requires 3-4times the volume lost to be replaced
What is the ideal crystalloid resus solution?
One that resembles the electrolyte content of the plasma
What does normal saline contain that make it slightly hypertonic?
High levels of Na and Cl (154mmol). Osmolality is 308mosml
High levels of Cl can cause a metabolic acidosis
USE WITH CAUTION!
What does Ringer’s lactate contain?
Higher Cl (115) the Na is lower than plasma but still high (131) and osmolality is 273mosml
That does the lactate in ringer’s lactate result in and what is the consequences thereof?
Lactate is metabolized to CO2 and water and leads to metabolic alkalosis even though pH is 6,5
Compensatory Respiratory acidosis and post-op resp depression
What should be avoided when in diabetics on metformin?
Ringer’s lactate