Pink blood pressure Monitor

I'm not an ICU doctor or nurse, and, if you are then I'd suggest you stop reading now and ask an experienced colleague. I've spent a modicum of time in intensive care units but the following is really an "Idiot's Guide". And, by that, I mean it's written by an idiot. Don't be surprised if the comments section quickly fills with corrections by experts.

Before getting to the monitor screen I'd like to highlight that despite the variety of numbers, colours and lines that litter this complicated monitor it is nothing but a piece of information. It provides information to a doctor or nurse that they combine with the patient's history and examination to guide diagnosis and management.

The monitor is not a diagnostic test. You can't look at a screen and determine what is wrong with the patient. Often you can't tell whether something is wrong or not. The numbers could be very good, or very bad, depending on what is happening to the patient. For example, a septic patient with a high blood pressure is not as worrying as that same blood pressure in a stroke patient. For the same reasons, an alarm on one of these monitors could be nothing to worry about or a job for the emergency trolley. It all depends - and often is obvious by looking at the patient rather than the monitor.

So ... the underlying message is that a layperson can't tell much from a ICU monitor without knowing a lot about the patient and what we want all the numbers to be. And this varies depending on the individual patient. Please don't pretend you can tell the ICU staff when something is wrong with your loved one simply by looking at the screen. They're pretty good at knowing when to panic.

With those warnings out of the way, let's look at an ICU monitor screen. This one was the first to pop up on Google images. I know nothing about the patient.

Let's read it like a book - from left to right. Top to bottom.

The top left spiked lines are ECG/ EKG traces.

These are two leads of a 12 lead . You can choose which two leads, of the available 12, you want to look at. Nobody would try to gather too much information from this small panel - they'd use a full 12 lead ECG instead. However, by monitoring these couple of lines you can monitor the heart rate, spot cardiac arrhythmias and detect ischaemia (heart attacks).

Which leads us to the top right of the monitor.

The big "80" is the heart rate. It provides exactly the same information as your doctor counting the pulse in your wrist. It's how mant times the heart is beating per minute. Normal pulse is between 60 to 100 per minute. Too fast and too slow are bad - unless we want them to be slow or fast.

The bar to the left of the "80" is a graphic of the pulse over the recent past. We can see a couple of spikes in the heart rate. Is this worthy of panic? Unlikely ... but it depends on what was happening at the time.

The lower bar (labelled ST-II) is monitoring changes to the ST segment (the flat bit between the S wave and the T wave in the image below) of lead II (one of the 12 leads) of the ECG.

If the ST segment deviates above or below baseline (the lines between the T wave and the next p wave) then it's usually bad. It's often a sign of cardiac ischaemia (the heart running out of oxygen) - which is bad.

On the screen, the letters and numbers next to this bar, under the 80, is the current ST deviation of different leads. Lead I has ST elevation of 0.3mm. Lead aVR has ST depression of 0.4mm. Less than 1mm is less panicky than more than 1mm.

The next section of the monitor deals with blood pressure. Actually, the red, yellow and pink (at the bottom) sections all deal with blood pressure. Blood carries oxygen to your brain and other vital organs. Maintaining oxygen to these important organs is a large part of critical care medicine. Therefore, monitoring blood pressure is an important job for this machine.

Blood pressure is simply the pressure of blood pushing on the walls of an artery at two points in time. The first number (systolic) is the pressure exerted by blood against the artery walls when the heart pumps. The lower number (diastolic) is when the heart relaxes.

The reason there are 3 different measurements of blood pressure is because the normal pressure is very different depending on which artery you are looking at. This monitor demonstrates this very nicely.

When your GP pumps up that cuff around your arm they are obtaining an estimate of the pressure in your brachial artery. This same process is occuring in this patient - but the machine is pumping, deflating and measuring without human assistance. The results are recorded in the pink section.

The most recent reading is 97/73mmHg. 79 represents the mean pressure. Note that at 1502 the blood pressure was 93/60. 3 minutes later it shot up to 161/125. Is that bad? Dunno. Maybe an attractive nurse walked past. Maybe someone stuck them with a needle. Maybe someone turned up their intravenous vasoconstrictor or gave them a bolus of fluids. Can't tell by looking at the monitor.

The problem with those BP cuffs is that there's a lot of things that can affect their accuracy - like improper size, placement and movement. We can get a much better measurement of the pressure in your artery if we stick a probe into your artery (arterial line) and measure the pressure directly. This arterial blood pressure is the red section of the monitor. It's currently 119/79. The waves on the left are how the pressure is changing in real time - rising with each contraction of the heart and falling as it relaxes. The bars beside it are how the top and bottom pressures have varied over time.

The final piece of the blood pressure puzzle is that the heart actually has two outputs. One half of the heart pumps blood to your brain, and the pulse in your wrist. The blood pressure in this system is the red and pink sections. However, the other half of the heart pumps blood to the lungs - to collect the all important oxygen.

We can measure the pressure in the lung half of the system by inserting a special type of measuring instrument - a Swan-Ganz catheter.

It may looked complicated but they're pretty simple to insert. You just ask an Intensive Care doctor to put one in for you. Usually there's some residents around eager to have a go.

Once properly inserted, and lying somewhere around the heart, this instrument allows us to measure the pressure in the vessels pumping to the lungs (called pulmonary artery pressure or PAP). This is the yellow part of the screen and you can see the pressures are dramatically different compared to the other half of the system. This is good. The current PAP is 29/14. Again the waves are real time and the bars are the readings for the recent past.