Week 3 - Circulation and Head Injury

What is circulation?

movement of blood through the body for the purpose of oxygen delivery and waste removal

What are the two main circuits of the circulatory system?

1. system

2. pulmonary

What is the pathway of systemic circulation?

heart → body → lungs

What is the pathway for pulmonary circulation?

heart → lungs → heart

What are the three major parts of circulation?

1. pump (the heart)

2. pipes (the blood vessels)

3. fluid (the blood)

On which side of the body does systemic circulation take place?

left

On which side of the body does pulmonary circulation take place?

right

What is cardiac output

how much blood the heart pumps in 1 minute

Which side of the heart (which circuit) is a low pressure system

right side; pulmonary circuit

What happens when the lung alveolar air pressure becomes greater than the capillary blood pressure in the lungs

the capillaries close and there is no blood flow

What is Wests Zone 1 of the lung

the uppermost region (apex) where alveolar pressure exceeds pulmonary arterial and venous pressures, causing capillaries to collapse and suspending blood flow

arises during hypotension (positive-pressure ventilation) creating alveolar dead space

What is alveolar dead space

• the volume of inhaled air that reaches the alveoli (air sacs) but doesn't participate in gas exchange because those alveoli lack blood flow (perfusion)

• the portion of "wasted" ventilation beyond the normal anatomical dead space (conducting airways)

What is Wests Zone 2 of the lung

• pulmonary arterial pressure exceeds alveolar pressure

• alveolar pressure exceeds pulmonary venous pressure

• blood flow is therefore dependent on the gradient between alveolar and pulmonary arterial pressure

  • changes throughout the respiratory cycle

• in diastole, particularly in conditions of hypovolemia, pulmonary arterial pressure may also be lower than the alveolar pressure, which means flow would only occur during systole

What is Wests Zone 3 of the lung

• both pulmonary arterial and pulmonary venous pressure exceeds alveolar pressure

• flow is proportional to the gradient between pulmonary arterial and pulmonary venous pressure

  • alveolar pressure does not play much of a role unless it exceeds pulmonary venous pressure

• blood flow to this zone exceeds the blood flow to all other zones

What region of the lung is Zone 4

• the bulk of atelectatic or oedematous lung at the very base of the chest cavity

• interstitial fluid pressure exceeds pulmonary or alveolar venous pressure

• blood flow is governed by the gradient between arterial and interstitial pressures

What can increase the size of Zone 1

• haemorrhagic shock (or hypovolemia generally)

• positive pressure ventilation

  • increased positive alveolar pressure can push blood out of the lung, creating a Zone 1)

• positive pressure ventilation of a volume depleted patient

What would an increase in the size of Zone 1 present as clinically

• worsening hypoxia with increased PEEP

• improving hypoxia with supine positioning

• improved hypoxia with fluid resuscitation

What are Wests zones

on the basis of its perfusion (the interplay between alveolar pressure, arterial pressure, and venous pressure), the lung can be divided into four discrete areas

What is special about Zone 1

• under normal circumstances, Zone 1 (a poorly perfused region containing a lot of dead space) does not exist

• only manifests during

  • positive pressure ventilation

  • hypovolaemia (e.g., haemorrhage)

What does PEEP stand for

positive end-expiratory pressure

What is positive end-expiratory pressure

• PEEP

• the pressure maintained in the lungs at the end of exhalation during mechanical ventilation to keep air sacs open

What clinical findings must we establish during a circulation assessment

1. pulse

2. blood pressure

3. skin check

4. Glasgow Coma Scale

What are the components of a circulation assessment

1. clinical findings

2. determination of degree of perfusion

3. BITFT algorithm

What is the BITFT algoritm

1. bones + bleeds

2. intravenous access

3. tranexamic acid (TXA)

4. fluids

5. tourniquet re-assessment

What are the different classifications when determining degree of perfusion

• good perfusion

• poor peripheral perfusion

• poor central perfusion

What are the indicators of good perfusion

• warm extremities, dry skin

• capillary refill (less than 2 seconds)

• strong peripheral pulse

• normal heart rate

• normal blood pressure

• relaxed, alert, and oriented

What are the indicators of poor peripheral perfusion

• cool extremities

• slow capillary refill (more than 2 seconds)

• weak or absent peripheral pulse

• tachycardia

• cool, pale skin

• anxiety, restlessness

• MAP around 65mmHg

• systolic BP around 90-100mmHg

What are the indicators of poor central perfusion

• peripheral perfusion is comprised and,

• altered GCS
  or

• hypotensive

What are arteries

• blood vessels that carry blood away from the heart

• high pressure system = thick, muscular walls

What are veins

• blood vessels that carry blood back to the heart

• low pressure system

• contains valves to prevent backflow

Which artery does not carry oxygenated blood

pulmonary artery

What is the significance of capillaries

site of gas exchange (perfusion happens here)

What is perfusion

the delivery of oxygen to tissues at the cellular level

What is required for good perfusion

adequate circulation

What are the determinants of perfusion

1. heart

2. blood volume

3. blood vessels

note: if any of these three fail → decreased perfusion → SHOCK

What must we pay attention to regarding the heart and perfusion

• heart rate (HR)

• rhythm

  • is it organized

• strength

  • SV (stroke volume)

What must we pay attention to regarding blood volume and perfusion

• is there enough blood in the system

• if patient is bleeding andor dehydrated = decreased blood volume

What must we pay attention to regarding blood vessels and perfusion

• dilated vessels

• constricted vessels

What is the pressure like in dilated vessels

low pressure

What is the pressure like in constricted vessels

high pressure

What are the common types of shock in trauma

1. hemorrhagic (hypovolemic)

2. neurogenic (distributive)

3. obstructive

What is hemorrhagic shock also called

hypovolemic

What is hemorrhagic shock

• 15–20% or more loss of total blood or body fluids

• prevents the heart from pumping enough blood to meet body needs

• immediate treatment → stopping fluid loss and replacement of lost volume with intravenous fluids or blood

What is neurogenic shock

• spinal cord injury to the cervical and upper thoracic spinal cord levels

• disruption of sympathetic tone

  • results in dilation of capillaries in the lower extremities → decreased cardiac filling → hypotension → shock

  • bradycardia from unopposed vagal nerve

What is another name for neurogenic shock

distributive

What is obstructive shock

• physical obstruction prevents proper blood flow into (or out of) the heart

• similar to cardiogenic shock, but this is caused by non-cardiac, external, mechanical issues

What are the primary causes of obstructive shock

• tension pneumothorax

• cardiac tamponade

• pulmonary embolism

• aortic diessection/stenosis

• abdominal compartment syndrome (ACS)

How might neurogenic shock present in a patient

• decline in sympathetic tone (loss of autonomic function) prompts the dilation of capacitance blood vessels in the lower extremities → decreased cardiac filling → hypotension and SHOCK

• bradycardia due to unopposed vagal cardiac influence

• pink, warm skin from dilation of subcutaneous blood vessels

• midline spinal tenderness or step-offs

What is tension pneumothorax

air trapped in the chest cavity that compresses the heart

What is cardiac tamponade

fluid build-up in the pericardium that restricts heart movement

What is an aortic dissestion/stenosis

• when the intima (inner layer) tears → blood forces the intima and media (middle layer) apart

• this blood-filled space (false lumen) compresses the "true" lumen (normal channel) → resulting in stenosis (narrowing)

What is abdominal compartment syndrome (ACS)

• sustained intra-abdominal pressure (IAP) of less than 20mmHg = organ dystention

• trauma (e.g., blunt, penetrating, or retroperitoneal hematoma) causes rapid blood/fluid accumulation and tissue edema → increasing abdominal pressure → which compresses organs and veins → inhibiting blood return

What are the symptoms of obstructive shock

• tachycardia

• hypotension

• tachypnea

• distended neck veins

• cold and clammy skin

What are the symptoms of abdominal compartment syndrome (ACS)

• tight, distended abdomen

• decreased urine output

• significant difficulty with ventilation

  • increased peak airway pressures

What is abdominal compartment syndrome (ACS) most commonly associated with

severe injury followed by massive fluid resuscitation, which exacerbates bowel swelling and edema

What is the technical difference between an aortic dissection and stenosis

• while an aortic dissection is the tear itself, the narrowing of the aorta that occurs as a result of the pressure from that tear is the stenosis

• In some cases, a focal dissection can lead to significant localized stenosis, sometimes long after an initial injury

What is sympathethic tone

• sympathetic signals typically cause increased activity in tissues (like constriction or contraction)

• mediated by signals sent from the spinal cord

• arteries in the body depend on a constant baseline sympathetic tone to maintain a certain level of constriction → supports tissue perfusion

What is the primary cause of neurogenic shock

severe, traumatic spinal cord injury above T6 (the cervical or upper thoracic level)

When should tranexamic acid (TXA) be considered

whenever there is suspsted major external or internal bleeding with major trauma patients

How does TXA work

it prevents the breakdown of fibrin clots

What are the perfusion interventions

• stop blood volume loss

• slow down blood volume loss

• replace blood volume loos

• reverse obstructive shock pathology

• CPR (if cardiac output has decreased to the point of losing palpable pulses)

  • ensure other perfusion interventions are iniated again ASAP in parallel with CPR)

How do we stop blood volume loss in perfusion interventions

early appropriate massive hemorrhage management

How do we slow down blood volume loss in perfusion interventions

• flat palmar pressure on abdominal bleeds

• prevention of hypothermia

• TXA administration

• bind pelvis if unstable

How do we replace blood volume loss in perfusion interventions

• ideally with blood

  • carried by all hospitals and some ORNGE units

• controversially with normal saline fluid bolus

Why is normal saline fluid bolus controversial in perfusion interventions

How do we reverse obstructive shock pathology in perfusion interventions

• 3-sided occlusive dressing for open pneumothorax

• support spontaneous ventilations by NOT having patient supine

• ensure adequate oxygenation to support accessory muscle function

What is a traumatic brain injury (TBI)

• any disruption in normal brain function caused by an external mechanical force

• may result in temporary or permanent neurological impairment

• distinct from non-tramautic brain injuriesacquired brain injury (strokes, infection, tumour)

What is secondary brain injury

ongoing physiological damage after the inital insult (e,g,, edema, hypoxia, hypoperfusion, ischemia)

What are the factors that case secondary brain injury

• hypoxia

• hypotension

• hypercapnia

• hypocapnia

• hypoventilation

What are the factors that case secondary brain injury collectively referred to

the H bombs

What is hypoxia

What is hyperventilation

How can we prevent hyperventilation of TBI patients

• using ETCO₂ RR reading as a guideline

• metronome

What is Cushings triad

1. widening pulse pressure

   • systolic climbs high, diastolic dives low

2. bradycardia

   • usually early on there is tachycardia

   • widening pulse pressure causes bradycardia over time

3. irregular respirations

   • as pressure mounts, the brainstem is squeezed and autonomic breathing control breaks

note: happens in this order as the intracranial pressure increases and the brain herniates

How should intravenous (IV) access be incorporated into patient scenarios

• IV access considered to help expedite blood transfusions in hospital

• en-route is likely appropriate

  • if trapped at scene, can be done on scene since there is a wait anyways
    

note: most strong pain meds can be given by alternate routes (like TXA, can be given intramuscularly)

What are the downsides of normal saline fluid bolus in trauma situations

• cold = expedites onset of hypothermia

• acidotic = worsens coagulation

  • blood vessels dilate more when blood becomes more acidic

• carries no beneficial components (does not contribute to oxygen carrying capacity like RBCs and other clotting factors)

note: general consensus = we should be much more conservative with its use

When should normal saline fluid boluses be considered

suspected massive hemorrhage + hyptotension

note: generally reserved for patients who also have an altered GCS

When should normal saline fluid boluses be strongly considered

moderate to severe TBI + hypotension

note: benefits by maintaining normal brain perfusion (helps keep them normotensive)

What clinical findings must we establish during a head injury assessment

• check for instability andor crepitus

  • observation and palpation of entire skull and facial bones

• check ears and nose for cerebrospinal fluid (CSF) or blood

• assess pupils for equality, size, reactivity, accommodation

What are indicators of a moderate to severe traumatic brain injury in head injury patients

• increasing confusion

• GCS less than 12

• seizures

• ineffective breathing

• hypoxia

What is brain herniation

What is decorticate posturing

What is decerebrate posturing?

What are the signs of brain herniation?

• dilated and unreactive pupils

• asymmetric pupullary response

• posturing (decorticate or decerebrate)

How can the H bombs be avoided?

• good airway, respiratory, and circulation assessment and interventions

• intentional re-assessments of supplemental oxygen and circulation interventions

  • are they working

  • is SPO₂ above 92%

  • did a 3-sided occlusive help reverse hypotension

  • is the head of the bed elevated 30 degrees

• remember that hyperventilation causes harm

What should be done if a CSF leak is suspected

apply a loose, sterile dressing over the source opening

What should be done if protruding brain tissue is present

cover it with non-adherent material

How many degrees should the head of head injury patients be elevated

30 degrees

What things should a paramedic prepare for when dealing with a head injury patient

• respiratory distress or arrest

• seizures

• decreasing level of consciousness

• agitation or combativeness

What should be done if eyelids are swollen shut

nothing, leave them alone

If there is a severe injury or pain in one eye, what should be done to the other eye

cover both eyes, not just one

What should be done if there is obvious or suspected rupture of the globe of the eye

avoid any kind of:

• manipulation

• palpation

• irrigation

• direct pressure

What should NOT be done if an eye is avulsed

replace it back inside the socket

What should be done if an eye is avulsed

• cover the eye with a moist, sterile dressing

• protectstabilize as if it is an impaled object