There are two tutorials on pulse oximetry. The first looks at the SpO2 and how it is measured. The second looks at the pleth waveform and problems that we commonly encounter with pulse oximetry in general. I guarantee you’ll learn something.
This is a longer version of the lecture that I delivered at the 2025 College of Anaesthesiologists of Ireland Annual Scientific Meeting.
This is the second tutorial in the nutrition series. Previously I looked at metabolism in critical illness. In this tutorial I start to answer many of the questions that arise on rounds principally: how many calories does the patient need? How much protein? What are the routes of food administration? Is there a benefit to post pyloric feeding tubes? Should I feed the stomach continuously or by bolus? Should I check gastric residual volumes? I provide you with the answers to these questions using the best available evidence.
Hypovolemic shock is one of the major problems we encounter in acute critical illness. This tutorial explains the mechanisms by which the body compensates for hemorrhage/hypovolemia, why the blood pressure and hemoglobin saturation are unhelpful and what tools may be useful at the bedside to assess the patient.
I also briefly discuss resuscitation of the bleeding patient and compartment syndromes.
This tutorial looks at the problems of Hypotension and Shock. I define the difference between the concepts – not all hypotensive patients are shocked and not all shocked patients are hypotensive. I then go through a system for exploring the hypotensive or shocked patients’ status to determine the underlying problem – illustrated by a series of clinical scenarios.
This tutorial looks at the pulse, what it is, the waveform and how that reflects systole and diastole. I then go on to look at the pulse waveform on pulse oximeters and the pulsatility index. Finally, I discuss the essential topic of Pulse Pressure Variability.
I feel like I have been working on this tutorial for several years. I actually have. When one encounters a modern chest drain unit in ICU for the first time or the 50th time it can be quite daunting. How much is draining? Is it oscillating? What does “bubbling” imply? When do you use suction? Why do some nurses leave a meniscus of fluid in the tubing but others don’t? What is the little red cap supposed to do?
This tutorial starts with a discussion of the physiology of pneumothorax and hemothorax, and then progressively visits one bottle, two bottle and three bottle systems. I then go on to explain how relatively modern chest drainage systems work, and how they need to be modified to apply suction – wet and dry. Finally I explain how very modern digital chest drainage systems work.
If you have struggled with understanding chest drains, I guarantee you’ll learn something.
This is the final tutorial on the basics of Chest Imaging in the ICU. It includes a discussion about the extrapulmonary tissues – pleural and mediastinal and lung diseases (pneumonia, ARDS, PJP etc.).
One of the reasons that we perform portable AP chest x-rays (CXR) in the ICU is to confirm the correct positioning of hardware: endotracheal tubes, central lines, feeding tubes, pulmonary artery catheters, pacemaker wires and chest tubes. This tutorial discusses the correct position of each of these devices and looks at malplacement and complications.
The ideal location of the tip of the endotracheal tube is 3 to 5cm above the carina, below the clavicles and at the level of the T4 spinous process. If tube is too far in, there is a risk of endobronchial intubation and atelectasis of an entire lung (usually the left lung, but not infrequently the right upper lobe also).
The ideal location of a central line, placed in the SVC distribution (internal jugular, subclavian or PICC) is at the junction of the Superior Vena Cava and the Right Atrium. Although inadvertent arterial puncture is less likely, these days, due to ultrasound guided insertion, the tip of a central line can end up can end up in all kinds of places. The tip placement, for prolonged infusions in critical care (for example – pressors or TPN), needs to be confirmed by chest x ray. The major complication of central lines is pneumothorax due to inadvertent pleural puncture during placement.
The pulmonary artery catheter is floated through the right heart and lodged into a peripheral branch of the pulmonary artery, aided by a balloon. The ideal location of the tip is in the lower zone of the lung, and the appearance of the catheter may be a V – the tip is in the left pulmonary artery or a B – the tip is in the right pulmonary artery. It should not be curled up in the RV or, worse, in the inferior vena cava.
Intra-aortic balloon pumps are inserted in cardiology, to manage cardiogenic shock, and following cardiac surgery. The balloon inflates in diastole to increase diastolic pressure, increasing coronary artery perfusion pressure and improving cardiac performance. The tip of the IABP should be distal to the left subclavian artery as it comes off the thoracic aorta. If the tip is too proximal, there is a risk of ischemia to the left arm, if it is not high enough, then it doesn’t function as required and may injure the kidneys.
Chest drains are typically placed to drain air and fluid from the pleural cavity. The tip of the chest tube needs to be where the “stuff” that you wish to drain is located: in the lung apices for air (if the patient is erect or semi erect), in the bases for fluid. There are two “eyes” on each chest tube – both need to be located inside the pleura or air will leak into the subcutaneous tissues.
Finally you need to be able to identify single lead and dual lead pacemakers, implantable defibrillators (ICD) and loop recorders on chest x-ray.
When patients arrive in the ICU, as soon as they are settled, an AP portable chest x-ray (CXR) is ordered. That x-ray will look different from one done in the radiology department, as the patient is likely semi-recumbent, may be in expiration and the projection is different than from an CXR taken from the back.
The lung has 5 lobes – three on the right and two on the left (the left lung is smaller to accommodate the heart). Each one of these lobes is connected to the trachea by one major airway, that may become plugged off, resulting in atelectasis or collapse of the lobe. As we often need to remove mucus plugs or other material causing these obstructions, it is imperative that you are able to identify the particular lobe that has collapsed. I sequentially go through each lobe of the lungs.
To identify a collapsed lung lobe I suggest that you follow the “Ds” listed in the image below.
In addition, radiologists often report lung units as being “consolidated.” This is a catch all phrase that identifies the presence of liquid or semisolid material in airspaces – infectious exudate, blood, mucus, water-fluid, gastric contents etc. You should be able, with you anatomical knowledge, to identify which lung lobe is affected, in particular if you are planning on performing a broncho-alveolar lavage. @ccmtutorials
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