Shock Recognition and Treatment

Question 1

what is shock?

Answer 1

1. inadequate cellular energy production resulting from insufficient oxygen or nutrient delivery to meet cellular energy requirements
   -inability to meet energy requirements; cellular needs exceeds delivery of oxygen/nutrients

Question 2

what are the 5 categories of shock?

Answer 2

1. hypovolemic- MOST COMMON
2. distributive-septic
3. cardiogenic
4. obstructive
5. metabolic

Question 3

describe hypovolemic shock

Answer 3

1. low effective circulating volume
2. mechanism:
   -low blood volume reduces preload and thus decreases cardiac output
3. causes: all with inadequate fluid intake to meet the losses!
   -hemorrhage
   -fluid loss via: vomiting, diarrhea, polyurea, third space pooling of fluids into the abdomen or chest
   -evaporative losses (burns)
   -severe dehydration (but hypovolemia does NOT EQUAL dehydration)

Question 4

describe distributive shock

Answer 4

1. state of relative hypovolemia due to vasodilation (also called vasodilatory shock)
2. mechanism: blood volume does not filler the larger (arterial) vascular system, vasodilation also cases reduced afterload
3. causes:
   -anaphylaxis
   -mast cell tumor degranulation
   -toxic doses of vasodilatory drugs
   -neurologic causes: brain or spinal injury/trauma affecting autonomic nervous system
   -hypoadrenocorticism
4. septic shock:
   -specific subcategory of distributive shock
   -begins with an infection which leads to release of inflammatory mediators that cause vasodilation

Question 5

describe cardiogenic shock

Answer 5

1. low forward flow of blood due to heart-related problems/failure of the heart to pump blood to the periphery
   -NOT the same as congestive heart failure
2. causes:
   -poor contractility (DCM, late stage valvular disease/leaky valves, hypertrophic/restrictive cardiomyopathy, myocardial depression from sepsis or drug-induced)

-reduced preload (hypertrophic cardiomyopathy causing poor relaxation or tachycardia/sustained tachyarrhythmias)

-decreased heart rate (sustained bradyarrhythmias)

-cardiac damage from trauma or toxins
–monensin in horses, avocados in birds, selenium in pigs, plants containing cardiac glycosides, grayanotoxins (in azaleas), doxorubicin (chemotherapy)

Question 6

describe obstructive shock

Answer 6

1. caused by a physical obstruction impeding blood flow/primarily a preload problem affecting central circulation (the great arteries/veins of the heart)
2. causes:
   -pericardial effusion: impairs cardiac filling (cardiac tamponade), especially of right side
   -thromboembolic disease (vascular blood clots)
   -masses impeding blood flow
   -kinked or compressed vessels (with GDV or colonic torsion)

Question 7

describe metabolic shock

Answer 7

1. caused by inadequate delivery of substrates needed to make energy
2. causes:
   -decreased O2 carrying capacity of blood
   –severe anemia, hypoxemia (low PaO2), hemoglobinopathies
   -increased oxygen demand (sepsis or heat stroke) elevates metabolic rate past body’s ability to deliver substrate
   -inability to utilize oxygen properly (cyanide, hypoglycemia, sepsis)

Question 8

what types of shock can occur at the same time with GDV or colonic torsion?

Answer 8

1. hypovolemic
2. obstructive
3. possibly distributive

Question 9

what types of shock can occur at the same time with sepsis?

Answer 9

1. distributive
2. hypovolemic
3. metabolic

Question 10

describe physical exam and the continuum of shock

Answer 10

1. neuro: mentation
2. resp system: rate and effort, pattern
3. cardiovascular system: MM color, CRT, pulse quality, relative rate, rhythm
4. urinary: can it urinate?

Question 11

describe compensatory shock

Answer 11

1. occurs when compensatory mechanism are adequate to continue to meet metabolic oxygen demands of cells and tissues
2. clinical signs:
   -increased resp rate
   -increased HR/tachycardia and pulse quality (sometimes bounding)
   -rapid CRT
   -normal to dark pink mucous membranes
   -normal mentation
   -normal blood pressure
3. the clinical signs result when epinephrine and other catecholamines are released in response to a decrease in pressure detected by aortic baroreceptors leaving the heart, increasing the strength of cardiac contraction, increasing heart rate, and increasing BP by increasing systemic vascular resistance via vasoconstriction, resulting in an improved effective circulating volume

Question 12

describe early decompensatory shock

Answer 12

1. clinical signs:
   -tachycardia (most species) or bradycardia in cats
   -prolonged CRT
   -pale mucous membranes EXCEPT vasodilatory/distributive shock (red or inappropriately pink like in the face of hypotension but cats DONT do this)
   -decreased pulse quality
   -hypotension in some animals
   -decreased body temperature (in small animals)
   -depressed mentation
2. signs are the result of redistribution of blood flow to vital organs (heart and brain) with subsequent decreased blood flow to other organs
   -reduced oxygen delivery to non-vital organs leads to onset of anaerobic metabolism and lactic acidosis

Question 13

describe late decompensatory shock

Answer 13

1. clinical signs:
   -bradycardia, decreased cardiac sounds
   -low cardiac output, weak or nonpalpable pulses
   -severe hypotension in all
   -pallor or cyanosis
   -markedly prolonged to absent CRT
   -hypothermia in all
   -oliguria to anuria
   -stupor or coma, cardiopulmonary arrest is imminent
2. clinical signs are a result of failure or normal compensatory mechanisms due to ongoing lack of oxygen and nutrient delivery
3. this form of shock is NOT responsive to even the most intensive therapy! (also called terminal shock, too much damage to cells to respond)

Question 14

describe septic shock

Answer 14

1. unique clinical signs:
   -marked or hyperemic (red) or inappropriately pink (pink in the face of hypotension)mucous membranes; except in cats
2. any animal in shock presenting with red mucous membranes should have sepsis as a top differential
   -except in cats, who show pallor
   -horses develop toxic line at top of teeth/gums

Question 15

describe other general signs of shock

Answer 15

related to decreased oxygen delivery to specific tissues

1. bloody diarrhea and/or vomiting
2. acute renal failure
3. arrhythmias from poor perfusion of coronary arteries
4. leaky alveoli that fill with fluid (acute respiratory distress syndrome) from lung damage

Question 16

describe treatment for shock (generally)

Answer 16

1. main goals: restoration of oxygen delivery and improving effective circulating volume

-circulating volume is determined by blood pressure and cardiac output
-BP = CO x SVR
-CO = HR x SV
-stroke volume (SV) is determined by strength of cardiac contraction and circulating volume of blood

-manipulate any of the above parameters to improve effective circulating volume

Question 17

describe the use of oxygen to treat shock

Answer 17

1. oxygen administration is implemented when physically possible
2. will increase PaO2, mainstay of treatment for metabolic shock caused by hypoxemia

Question 18

describe fluid therapy to treat shock

Answer 18

1. other than cardiogenic, fluids are the first step in treatment for most types of shock!
2. quickly administer large quantities of IV crystalloid fluids or smaller quantities of hypertonic solutions or colloids
3. fluid therapy improves stroke volume, which improves cardiac output and therefore blood pressure
4. type and amount of fluids used depends on underlying problem and type and severity of shock
   -isotonic colloids, hypertonic saline, and colloids can be used for fluid resuscitation
5. treatment of compensatory shock can often be accomplished with isotonic replacement cyrstalloids alone

Question 19

describe sympathomimetics (inotropes and vasopressors) to treat shock

Answer 19

1. for patients that remain hypotensive despite intensive fluid therapy and adequate vascular volume
2. positive inotropic drugs (beta agonists) increase strength of cardiac contraction, improving CO and BP
   -also increase heart rate
   -examples: dobutamine, mid-dose dopamine, epinephrine
3. vasopressors (alpha agonists: phenylephrine, high-dose dopamine, epinephrine, norepinephrine) or V1 agonists (vasopressors): increase systemic vascular resistance by causing vasoconstriction which will increase BP
4. inotropes and vasopressors may be used for cardiogenic shock, esp due to myocardial failure

Question 20

describe treatment of metabolic shock

Answer 20

aimed at treating the specific underlying cause

Question 21

describe other treatments for shock

Answer 21

1. rewarming:
   -animals in shock are often hypothermic, especially cats and exotics
   -aggressive fluid resuscitation prior to rewarming can lead to fluid overload once cats are normothermic
2. antibiotics
   -always indicated in states of septic shock or if animal has a documented infection
   -also indicated if evidence or suspicion of breach of normal body defenses
3. corticosteroids
   -generally not indicated for shock except:
   a. patients with relative or absolute adrenal insufficiency
   b. patients in anaphylaxis (in conjunction with epinephrine)

Question 22

describe the endpoints of shock resuscitation

Answer 22

1. restoration of an effective circulating volume: evidenced by pink mucous membranes with normal CRT, normal temp and heart rate, strong pulse quality and normal BP, improved mentation, adequate urine output
2. once achieved, institute additional fluid therapy to maintain intravascular volume and perfusion and to address dehydration and ongoing losses
3. then continue monitoring parameters of perfusion and lactate