Three Essentials for Rapid Assessment: Blood, Oxygen, and Glucose

Three Essentials for Rapid Assessment: Blood, Oxygen, and Glucose

What might it mean to walk into any medical emergency and know where to begin?
Not in an abstract, theoretical way. In an actual shift, with an actual person in front of you.

This question has guided SkillStat for more than three decades. Our answer always comes back to three elements that sit at the center of how the body produces energy: blood, oxygen, and glucose. When these three are working, life has what it needs. When one falters, things change quickly.

This is the starting point for everything that follows.

 

 

Energy for life: looking at the essentials

Each of us runs on ATP. Every cell, every organ, every function depends on it. To make ATP, the body needs blood, oxygen, and glucose in the right places, at the right time.

This is why these three show up so often in emergency care. Not because they are complicated. Because they are reliable. They tell you what is happening faster than almost anything else.

Imagine someone arrives and something is clearly off. You take a quick look. They are not quite themselves. So you begin where most of us begin: vital signs.

Blood pressure 120/80.
Oxygen saturation 90%.
Glucose low.

Right away, you have a direction – glucose

Another person arrives.
Blood pressure is steady.
Glucose looks fine.
Oxygen saturation is 64%.

That number alone tells you where to go first – oxygen

Another arrives.
Saturation looks good.
Sugar looks good.
Blood pressure is 60/40.

Again, direction is clear – blood

You are essentially asking one question:
Which of these three is the main issue?

And from there, things unfold naturally.

 

 

Where the earliest signs appear

Some parts of the body burn through energy faster than others. The brain is one of them. Even though it is only a small percentage of body weight, it uses a large amount of oxygen. When something limits blood, oxygen, or glucose, the brain tends to be the first to speak up. A person becomes confused, drowsy, slow to respond, or simply “not right.” That is often the earliest sign that energy is dropping somewhere upstream.

The heart is another high-demand organ. When its supply is limited, a person might feel chest pressure, shoulder tension, jaw or back discomfort, abdominal symptoms, or unexplained fatigue. The body sends signals in many forms.

The gut, liver, and skin respond in their own ways too. Nausea, cool skin, mottled skin, delayed cap refill — each reflects a shift in energy.

The pattern repeats: look at blood, oxygen, and glucose. One of them is affecting the rest.

 

 

Blood: amount, flow, and where it all ends up

Blood sounds simple, although it carries a lot inside it. Three things matter most: how much there is, how well it moves, and where it is going.

Amount

Adults usually have around six litres of blood. Losing about a litre quickly can trigger a cascade of physiological responses. You see it in the pulse, the skin, the level of alertness.

Infants have far less volume, so even a small loss creates significant change. A few dozen millilitres in a newborn can shift the entire picture.

If amount is the issue, volume replacement becomes central. Blood when available. Crystalloids when indicated. The goal is straightforward: restore circulating volume so the system has what it needs to keep going.

Flow

Flow depends on heart rate and stroke volume. Both work together. When the heart races too quickly, it does not fill well. When it slows too much, total output drops. When the ventricle weakens, output falls even if the rate is ideal.

And then there are sudden events: a rhythm that produces no output, a tension pneumothorax shifting the mediastinum and compressing return flow, a tamponade limiting filling, or a pulmonary embolus blocking forward movement.

In these situations, things can change in seconds. Being on a monitor helps because an alarm picks up the change before anyone has time to call for help. Flow matters.

Where the blood ends up

Sometimes the body has enough blood. The heart is trying, yet blood is not reaching the organs that need it. This happens in sepsis, anaphylaxis, and neurogenic shock, each for different reasons. Blood moves toward the periphery or becomes less available to vital organs.

In each case, the intention is the same: restore adequate perfusion and address the root cause, whether that is infection, an allergic reaction, or loss of sympathetic tone.

 

 

Oxygen: airway, alveoli, and breathing

Oxygen is just as central. Most people feel changes in oxygen quickly — shortness of breath, altered level of consciousness, cyanosis, fatigue.

To understand oxygen problems, consider three areas: the upper airway, the lower airway, and the breath.

If the upper airway is obstructed — by decreased consciousness, swelling, or anatomical blockage — oxygen cannot enter effectively. Simple adjustments like positioning or basic airway adjuncts can make a dramatic difference.

If the lower airway is the issue — pneumonia, pulmonary edema, collapsed alveoli — oxygen cannot exchange well. PEEP often supports alveolar recruitment and improves saturation once the airway is open.

If the problem is breath — low respiratory rate, low tidal volume, or irregular effort — oxygen cannot reach the alveoli in adequate amounts. This is common in opioid overdose, where respiratory rate drops significantly and airway tone decreases. Assisted ventilation and opioid antagonists become important here.

When you identify which part of the oxygen pathway is limited, the next step becomes clear.

 

 

Glucose: fuel and access to fuel

Glucose is an essential part of energy production, especially for the brain. When glucose is low or cannot reach the cells that need it, neurological function changes quickly.

Three things matter: whether glucose is available, whether it can enter the cell, and how quickly the body is using it.

Infants and neonates have limited stores and can become hypoglycemic quickly, especially if feeding is interrupted. Adults have more reserve, although they can still become hypoglycemic under certain conditions.

In other situations, glucose is present in high amounts, although cells cannot access it. This occurs when insulin is insufficient or ineffective. Transport becomes the limitation, not availability.

Use rate increases with infection, fever, and metabolic stress. Vulnerable patients may not be able to meet increased demand.

Whether the next step is dextrose, insulin, circulatory support, or nutritional support depends on which part of this system is limited.

 

 

Conclusion: clarity in fast-changing situations

When you step back from all the scenarios, the same questions appear in every emergency:

Where is energy limited?
Which system — blood, oxygen, or glucose — is not meeting the body’s needs?
What is the most effective next step?

This way of thinking reduces the noise in moments that can feel complicated. It directs attention to what matters most and supports decisions that match the physiology in front of you. It also offers a reliable way to evaluate whether an intervention has worked. When perfusion improves, mental status changes. When oxygenation improves, saturation changes. When glucose improves, responsiveness often changes.

These three areas are the foundation of every assessment because they shape everything else. They help clinicians respond with accuracy. They help learners gain confidence. They help teams coordinate their actions based on shared understanding.

Blood. Oxygen. Glucose.
Three essentials that support timely, informed, and effective care in emergencies.