Ischaemia and Hypoxia Overview

Time is Tissue

• Prolonged tissue deprivation of oxygenated blood increases the risk of cell death and permanent damage.
• Early intervention is crucial to minimize tissue loss and improve patient outcomes.

Ischaemia

• Reduced oxygen in the atmosphere does not automatically result in ischaemia.
• Ischaemia is caused by obstructed blood flow, reduced blood volume, low oxygen levels, or external pressure on blood vessels.

Hypoxia and Ischaemia

• Hypoxia and ischaemia are the most common causes of cell death.
• Some cells can regenerate, but others are permanently lost upon death.
• Proper assessment and airway management/oxygenation can reduce or avoid hypoxic cell injury/death.
• Ischaemia is time-critical in situations such as strokes and heart attacks.

Reperfusion Injury

• Restoring blood flow to a cell can lead to further injury known as ischaemia-reperfusion injury.
• This occurs because oxygen molecules interact with reactive oxygen species (ROS) during reperfusion, causing ROS to multiply and damage cells.

Paramedic Considerations

• Some paramedic treatments resolve ischaemia, potentially leading to ischaemia-reperfusion injury.
• Reperfusion in myocardial ischaemia may cause temporary cardiac dysrhythmias like ventricular fibrillation or tachycardia.

Total Body Water

• Total body water is divided into intracellular fluid (ICF) and extracellular fluid (ECF).
• ICF comprises two-thirds of total body water.
• ECF comprises the remaining third and is further divided into interstitial fluid and intravascular fluid.

Water Loss

• Under normal conditions, most water loss occurs through urine, breathing, sweat, and faeces.
• The majority of water loss is through urine.

Osmosis

• Osmosis is the movement of water through a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration.
• In cells, water moves across the lipid bilayer through aquaporins, which are protein water channels.

Hydrostatic Pressure

• Hydrostatic pressure is the pressure inside of vessels.
• Fluid under pressure is pushed out of vessels, primarily water.
• Hydrostatic pressure is highest in arteries due to higher pressure in the arterial system.

Oncotic Pressure

• Oncotic pressure, also called osmotic pressure, is the pull of fluid back into vessels due to osmosis.
• This pull is caused by the higher concentration of proteins like albumin inside the vessel.
• Under homeostatic conditions, any fluid not drawn back in by oncotic pressure is collected by the lymphatic system.
• Oncotic pressure is highest in the veins because of lower pressure in the venous system and less hydrostatic pressure.

Fluid Pressure

• Fluid pressure is highest in arteries.

Osmotic Movement

• The osmotic movement of fluid back into a blood vessel is due to oncotic pressure.

Oedema

• Oedema is the accumulation of fluid in the interstitial space.
• The four main causes of oedema are:
  • Increased hydrostatic pressure
  • Reduced oncotic pressure
  • Increased capillary permeability
  • Lymphatic obstruction

Case Study - Phyllis

• Phyllis presents with significant pitting oedema in her right foot and leg, swollen up to the thigh.
• This suggests increased hydrostatic pressure in the lower extremity, potentially due to venous insufficiency or heart failure.

Electrolytes

• Electrolytes are molecules with either a positive or negative charge.
• The main positive electrolytes in the body are sodium, potassium, calcium, and magnesium.
• The main negative electrolytes are chloride, bicarbonate, phosphate, and sulfate.

Sodium

• Sodium (Na+) is the main extracellular cation, responsible for regulating water balance and extracellular volume.
• Its concentration is maintained by the kidneys, neural, and hormonal processes.

Chloride

• Chloride (Cl-) is the main extracellular anion and balances the charge of sodium.
• Its transport is passive and is proportionately related to sodium movement.

Sodium Concentration

• The normal sodium concentration is 135-145 mEq/L.