Consider the following scenario:

A 14-year-old boy is rushed to hospital after falling off a bike without a helmet, suffering a head injury as his head hits the road. His head is bleeding profusely upon admission despite direct pressure being applied to stop it. Blood pressure is low (90/50 mmHg) and he has a high heart rate (120bpm). His breathing is also rapid and shallow (35 breaths/min) and his body is cold (35.5°C). What should doctors do next?

Relating to the events of episodes 12 and 13, the cells are devastated by the head injury. This creates a gaping hole that sucks cells out of the body. While Neutrophil and the other white blood cells are recruited to fend off pathogens entering the body, Red Blood Cell and the others do their best to deliver oxygen to cells despite the increasingly difficult circumstances. Just as all hope is lost and Red Blood Cell collapses in a blizzard, she is saved by transfused red blood cells that deliver oxygen around the body. This gives the body time to slowly repair itself as life gradually returns to normal.

In this blog post, I will explain how the body is suffering from and responds to haemorrhagic shock, what happens if it is not promptly tended to and how the boy should be treated.

Summarising the functions of blood

At the start of episode 12, Junior Red Blood Cell summarises the functions of blood. Emerging from haematopoietic stem cells in the bone marrow, various cells contribute to the multifaceted functions of blood. These include:

• Retain moisture: blood is made up of water which is an important medium for transporting cells, nutrients and other components around the body.
• Exchange gases: red blood cells travel to the lungs where they take in oxygen and dispose of carbon dioxide in the alveoli.
• Transport nutrients: nutrients such as carbohydrates, amino acids and fats are transported to cells via the bloodstream so that they can be used to produce energy and new molecules.
• Regulate body temperature: blood carries heat around the body to maintain body temperature. During hot weather, heat can dissipate from the blood to cool down the body.
• Protect the body: white blood cells in the blood react to and eliminate pathogens to prevent infections.
• Repair wounds: when a blood vessel is broken like in a scrape wound, platelets are activated to seal and repair wounds.

What is haemorrhagic shock?

Blood has a wide array of functions to keep the body functioning, particularly in delivering oxygen and nutrients to cells and taking out carbon dioxide and wastes. Shock occurs when not enough blood is circulating around the body, reducing the amount of oxygen and nutrients that are delivered to cells. If blood flow is not restored, the cells are deprived of oxygen and nutrients while carbon dioxide and wastes continue to build up. This can damage cells which can lead to organ injury and failure, leading to death.

There are many different types of shock. The most common one which is described in the scenario and the two anime episodes is haemorrhagic shock, shock arising from haemorrhage or severe blood loss. This blood loss can come from an external injury such as a deep cut or stab wound or internal bleeding such as a fracture or a ruptured vessel or organ. Haemorrhagic shock is characterised by many symptoms that can worsen as blood loss increases. These include:

• Pale (and possibly blue) skin, particularly in the face, lips and extremities, due to reduced blood flow to these parts of the body;
• Hypothermia (low body temperature);
• Reduced urine production and increased thirst due to the need to retain fluids in the body;
• Hypotension (low blood pressure) due to reduced blood volume;
• Rapid, weak pulse;
• Shallow, rapid breathing; and
• Neurological symptoms such as anxiety (which can progress to restlessness), nausea, dizziness, confusion and fainting (which can progress to unconsciousness) due to reduced blood flow to the brain in the later stages of haemorrhagic shock.

The body’s normal responses to shock

Responses to haemorrhagic shock aim to maintain adequate blood flow to vital organs such as the brain and heart so that sufficient oxygen and nutrients can be delivered. A variety of sensors detect haemorrhage in different ways. These include baroreceptors and stretch receptors in the heart and aorta which stretch less due to reduced blood volume and chemoreceptors in the brain and blood vessels which detect the increasing acidity of blood (due to the build-up of carbon dioxide). These sensors send messages to various parts of the brain (which declare a state of emergency in the episode). In turn, the brain increases sympathetic nerve activity to different parts of the body, particularly the heart and blood vessels, to counteract the changes due to haemorrhage. The increased sympathetic nerve activity also stimulates a fight-or-flight response, producing symptoms of shock such as anxiety and cold sweats.

As described in the episodes, blood vessels to extremities such as the hands and feet and non-essential organs such as the gastrointestinal tract, skin and kidney constrict during haemorrhagic shock. This redirects blood flow to vital organs such as the brain and heart. Reduced blood flow to the skin results in less heat travelling to the skin, resulting in cold skin. The heart is directed to beat faster (which increases heart rate) and more strongly to eject more blood. This increases the amount of blood that is pumped around the body, increasing blood pressure and blood flow to essential organs.

Did you know? The blood vessels to the brain are not constricted during shock. This allows normal blood flow to the brain to be maintained despite continual blood loss.

The episodes also depict the turbines in the lungs operating very rapidly. This represents the increased breathing rate and ventilation that occurs during haemorrhagic shock. As carbon dioxide builds up in the organs due to insufficient blood flow, acids build up in the blood and fluids around the brain. These increase the firing rate of chemoreceptors which prompts the brain to increase the firing rate to the respiratory muscles. The respiratory muscles contract more often to increase breathing rate, leading to rapid, shallow breathing. This restores ventilation and gas exchange in the lungs, allowing oxygen to be inspired and carbon dioxide to be expired.

Fluids must be retained in the body to conserve blood volume during haemorrhagic shock. As explained in a previous blog post, this involves stimulating thirst to elevate fluid intake and releasing aldosterone and ADH to increase water and salt reabsorption from the kidney into the body. While the amount of urine excreted is reduced, these responses maintain blood volume to ensure enough blood is pumped around the body, maintaining sufficient oxygen and nutrient delivery to organs. As the reduced blood pressure pushes less plasma from the blood into tissues, fluids from cells and tissues are transported into the blood vessel. This contributes to the maintenance of blood volume.

How does shock worsen over time?

These responses to haemorrhage can only be sustained for a short period of time. If blood loss still persists, blood pressure will continue to fall. This can be exacerbated by the release of various chemicals (like adrenaline and β-endorphin) in the body which relax smooth muscle cells on blood vessels. This reverses the constriction of blood vessels which further reduces blood pressure and hence blood flow. Further reductions in blood pressure can occur when the heart does not receive enough oxygen and nutrients to continue functioning. As the heart cannot effectively pump enough blood to other organs, blood pressure and flow further decrease.

Decreased blood flow around the body reduces heat distribution around the body, resulting in hypothermia (depicted by the blizzard in the image above). As blood flow to various organs falls, cells do not receive enough oxygen and nutrients to function properly while wastes and carbon dioxide continue to accumulate. These factors damage cells which leads to various organs failing, producing downstream effects on the body. For example, when the kidneys fail, the body cannot reabsorb salts and water to maintain blood volume and dispose wastes to prevent them building up. Eventually, blood flow to the brain will be reduced, injuring parts of the brain which can lead to neurological symptoms such as confusion and unconsciousness. The damage and failure of these organs due to insufficient blood flow is what kills the person in haemorrhagic shock.

How is shock treated?

Haemorrhagic shock is a medical emergency that requires prompt first aid and medical treatment. Just after the boy falls off the bike, first aid would focus on treating the cause of shock (in that case, bleeding from the head) and the shock itself. Initially, while calling for help, the boy would be laid down on the ground and encouraged to stay still. Bleeding to the head, which would otherwise worsen shock, would be stemmed by applying direct pressure on the wound with a clean cloth or pad. If possible, the boy should be covered in a blanket to keep him comfortable and warm due to reduced heat distribution around the body.

As the boy is taken to hospital, treatment would aim to restore blood circulation and oxygen delivery to the organs. Ideally, bleeding to the head would be stopped first which would be done by an operation. At the same time, blood volume would be replenished by replacing fluids and blood before organs start to fail. This would be done via an intravenous (IV) line of fluids such as saline, plasma or, in severe cases, blood (as is the case in the episode). These fluids allow blood to be retained to alleviate the symptoms and responses of shock. Red blood cells from a blood transfusion would also replace those lost during haemorrhage to deliver oxygen around the body, stopping cell and organ damage.

In addition, drugs such as dopamine, dobutamine, adrenaline and noradrenaline would be given to increase blood pressure. These drugs act to restore or retain vasoconstriction to maintain blood pressure as well as boost heart function to increase the amount of blood that is pumped around the body.

Conclusion

Haemorrhagic shock is a serious medical condition driven by reduced blood flow to organs due to severe blood loss. The body initiates some responses to maintain blood pressure and blood flow to different organs despite the bleeding. If the bleeding is not tended to; though, these responses can falter, damaging cells which can lead to organ failure and death. Treating haemorrhagic shock consists of stopping the bleeding via an operation and maintaining blood volume via intravenous administration of fluids such as saline, plasma and blood.

As a footnote to the scenario, the boy’s condition stabilised after being treated and he stayed in hospital for two weeks before going home. Having fully recovered, he is told by doctors to wear a helmet next time he goes on a bike.

In the last blog post of the season, we will look at a very common viral infection that appears most frequently in autumn and winter (the answer is not influenza as that is already covered). See you then!