Module 2 Shock and i/v fluids Flashcards
Define shock and the physiological causes
Shock is inadequate tissue metabolism to support healthy tissue function. This is usually generated by inadequate perfusion. Perfusion relies on blood pressure, cardiac volume, systemic vascular resistance, oxygenation.
Physiological causes of shock:
a) Hypoxaemia-eg impaired lung or impaired/reduced haemoglobin
b) Circulatory eg reduced blood volume or impedance to blood flow/distribution
c) Metabolic-impaired or decreased cellular metabolism ie hypoglycaemia, toxins, sepsis.
Explain circulatory shock in terms of hypovolaemic, cardiogenic, distributive, obstructive shock
(how shock manifests)
HYPOVOLAEMIC SHOCK; reduced blood volume eg haemorrhage, v+, d+, polyuria, burns etc.
Clinical signs: pallor, increased crt, tachycardia (cats may be bradycardic or tachycardic, possibly more likely bradycardic especially if also hypothermic), hypothermia, pulses initially hyperdynamic then hypodynamic, reduced mentation. May have haemoconcentration or very low pcv.
(hypothermia can interfere with usual vasoconstrictive efforts aimed at counteracting hypovolaemia)
CARDIOGENIC SHOCK; an issue arising with the heart, eg cardiomyopathy, arrhythmia, valvular dz.
DISTRIBUTIVE SHOCK;inappropriate vasodilation or inadequate ability to vasoconstrict. eg pro inflammatory state (eg severe pancreatitis, SIRS, severe burns, neoplasia), sepsis, anaphylaxis, hypoglycaemia, addisons (or illness induced corticosteroid insufficiency).
Clinical signs:injected mucous membranes, bounding pulse, tachycardia, hyperthermia or normothermia.
Tx may include vasopressor meds.
OBSTRUCTIVE SHOCK;reduced venous return eg GDV, pericardial effusion, peritoneal effusion, pulmonary thromboembolism, tension pneumothorax.
Clinical signs are similar to hypovolaemic shock.
Outline the stages of shock
STAGES OF HYPOVOLAEMIC SHOCK;
1.Compensatory; initially, the body responds to reduced circulating blood volume by baroreceptors triggering sympathetic nervous system, thus releasing catecholamines which increases cardiac output and maintains blood pressure (tachycardia and peripheral vasoconstriction). A slower response may also occur via the renin angiotensin-aldosterone system such that the kidneys retain fluid. if can tx at this stage, outcome will likely be very good.
2.Decompensatory shock ;(cats only seem to present in stage 2) there is continued loss of fluid, the SNS is overwhelmed, blood is directed to brain and heart with inadequate supplies to rest of body. Rest of body switches to anaerobic metabolism, ATP and glucose is depleted and cells are damaged, releasing free radicals, inflammatory stimulators and activation of clotting cascade. Need aggressive therapy here if going to win.
3.End stage shock: ongoing extensive organ hypoxia and organ failure. Death is inevitable despite best treatment.
Describe the principles of fluid therapy
Based on theory of water distribition, and water / electrolytes movement.
BODY WATER DISTRIBUTION;(60 40 20 rule).
Total body water is 60% of body weight.
Intracellular fluid is 40% of body weight.
Extracellular fluid is 20% of body weight and comprises intravascular fluid and interstitial fluid (3/4 of the extracellular fluid is interstitial). The intravascular volume of a dog is 77-78ml per kg body weight and for a cat 62-66ml per kg body weight.
MOVEMENT OF WATER AND SOLUTES; Water can move freely between divisions, but the electrolytes rely mainly on transport systems in order to enter cells. Albumin is in the plasma but usually does not pass into the interstitium (unless problems of leaky vessels).
Used to be thought of as vessels, interstitium (between cells and vessels) and cells. Now thought there is also a glycocalyx matrix on the endothelium of the vessels. The glycocalyx comprises proteoglycans and glycoproteins. Exact composition varies from organ to organ. This makes it harder for water to transfer through from vessels to interstitium, and resists most macromolecules. It is unlikely that water would move from interstitium into vessels.
Discuss the goals of fluid therapy
Goals of fluid therapy are to correct fluid/molecule/blood/plasma deficits, provide for ongoing losses and daily requirements. Also used for parenteral nutrition.
Demonstrate how to assess the degree of dehydration
<5% dehydrated; no signs but history suggests.
5% dehydrated (mild);slight skin tent, slight tacky membranes.
7-9% dehydrated (moderate);skin tenting, tacky membranes, maybe sunken eyes.
10-12% dehydrated (severe); dry mm, pronounced skin tent, prolonged crt, tachycardia, depression, weakness.
12-15% dehydrated (major, life threatening);as per previous, with signs of hypovolaemic shock and obtunded.
Discuss types of intravenous fluids and their indications
2 classification systems:
a) CRYSTALLOID (water plus electrolytes/ soluble molecules). Cheap. Will not trigger immune response.
COLLOIDS (contain large insoluble molecules such as proteins). Have high osmotic pressure. Expensive. May trigger an immune response. (some regard blood products as colloids and whilst they are, some classify as “blood products” distinct from colloids)
b) COMPARE OSMOTIC PRESSURE TO PLASMA ie usually in regards to crystalloids. ie might be hypotonic, isotonic, hypertonic compared with plasma.
FLUID INDICATIONS;
1. Hartmanns;isotonic. used extensively for hypovolaemic shock, correction of many acid base issues, dehydration and maintenance. Even when concerned re hyperkalaemia, usually the effect of isotonic fluids is to dilute the potassium.
2. Hypertonic crystalloid such as 7% NaCl useful for low volume resuscitation, good for head trauma or cardiac issues, but only used short term then switch to isotonic. Do Not use if severely dehydrated or if hyponatraemic or hypernatraemic.
3.Colloids used for rapid volume expansion (1 ml colloid approx = 3ml crystalloid). Avoid constant rate infusion, avoid large doses, monitor aptt and pt, contraindicated in sepsis.
4. Blood transfusion.
Construct a fluid plan to correct hypovolaemia, dehydration, ongoing losses and maintenance
- Correct for perfusion deficits
- Correct dehydration
- Provide for maintenance
- Provide for ongoing losses
- Reassess
PERFUSION DEFICITS;
Aims to correct plasma volume, restore cardiac output and allow for normal aerobic metabolism. This is done via monitoring to specific endpoints which are;
alert mentation, HR 90-140 (dogs), 180 (cat), pink mm, normal crt, temp >37.4, mean arterial pressure 70-80mm Hg, systolic bp > 100mmHg, lactate normalised, urine output >1ml/kg/hour.
Always do boluses and re-assess. Constant rate infusion is only recommended once perfusion deficits have been corrected.
DOSES TO CORRECT PERFUSION DEFICITS;(eg hypovolaemic shock doses)
a) isotonic crystalloids; eg Hartmanns 5-10 ml/kg over 5 minutes. Repeat as required to maxium total of 40ml/kg (dog) or 30ml/kg (cat). If no response, reconsider cause of shock (some are unresponsive to fluid therapy) and different fluid eg colloid, blood, or hypertonic saline if not contraindicated.
b) hypertonic saline; 2-5ml/kg over 5 minutes.NOT if hypo or hypernatraemic, NOR if severely dehydrated and MUST use isotonic crystalloids after but only up to 5ml/kg boluses
c) Colloids: 2-5ml/kg over 5 minutes. Repeat crystalloid/colloid bolus intermittently until end point of fluid resuscitation.
d) blood products (whole blood if severely haemorrhaging ie v low pcv and low total protein, fresh frozen plasma if haemorrhaging without severe anaemia. and packed red blood cells if severely anaemic but normal total protein). as per requirement. If half the calculated dose has been administered without improvement, reassess.
CORRECTIONS FOR DEHYDRATION;
Based on assessment of physical exam. Correct 25-50% of the fluid deficit over 4-6 hours, and the remainder over the next 18-24 hours.
PROVISION FOR MAINTENANCE;
CATS; 80ml/day x body weight (kg) x 0.75.
DOGS; 132 ml /day x body weight (kg) x 0.75.
COVERAGE FOR ONGOING LOSSES;
eg from v+ or d+. Weigh fluid loss for accuracy. 1gram approx =1ml
REASSMENT; frequent patient checking and regular repeats of electrolyte readings.
Explain indications for bolus and shock fluid rates
Shock rates = 60-90ml/kg/hr crystalloid or 10-20ml/kg/hour colloid. NOT recommended to do via fluid pumps as too easy to not closely monitor patient and have complications.
Bolus is giving a set amount over 5 minutes and observing.
Describe monitoring and end points for fluid therapy
see above
List the potential complications of fluid therapy
Over correction or dilution of electrolytes, adverse reaction to colloids/blood products, catheter issues eg phlebitis, delivery extravascular, haemolysis if given too quickly, increased circulating blood volume, overhydration, increased cardiac load.
List considerations in perioperative fluid therapy
Consider need, type of surgery, pre-exisiting conditions, possible adverse effects, availability, client wishes/costs.
