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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