The majority of patient who are admitted to ICU require targeted oxygen therapy during the course of their stay. This tutorial looks at how we assess oxygenation.
The easiest method for assessing oxygenation is to use the PaO2/FiO2 ratio (PFR) as a method of aligning the inspired oxygen tension (the therapy) to the PaO2 (the goal and the response). The PF ratio has been a key component of the diagnostic criteria for ARDS for decades. The PaO2 is measured by performing a blood gas. It represents dissolved oxygen in plasma rather than the oxygen content of blood that is determined by the oxyghemoglobin concentration and saturation (SaO2). The SaO2 can be helpfully estimated using non invasive pulse oximetry (SpO2).
Oxygen is taken up from the lungs continuously and carbon dioxide is excreted. Breathing is cyclical. Most gas exchange occurs during expiration, as inspiration only occupies 10 seconds or so per minute. The lungs hang down in the chest and hang out at a resting volume known as Functional Residual Capacity (FRC) at end expiration. Anything that reduces FRC, reduces the surface area for gas exchange and results in stale gas in or atelectasis of the alveoli. The consequence is ventilation perfusion mismatch and hypoxemia.
The initial treatment for hypoxemia is oxygen therapy delivered through nasal cannula. If that fails, or the patient is distressed, then high flow nasal oxygen (HFNO) is delivered. This improves oxygenation and reduces the work of breathing. If high flow fails, CPAP is delivered. CPAP applies positive pressure throughout the respiratory cycle, preventing phasic atelectasis and redistributing gas withing the lung. FRC is restored. If the patient fails HFNO, then they are intubated and ventilated.
Oxygen is assessed using FiO2, oxygen flow rate, PEEP or CPAP and mean airway pressure.
I am now going to move on, in the Introduction to Critical Care course, to a systems based assessment of the patient where you are expected to compile measurements and observations from the clinical information system, radiologic system and monitors to construct an overview of the patient’s status. This is the crux of intensive care medicine and it is not easy. I am going to visit each system sequentially, and some systems will have multiple tutorials. By the end of this process, you will have compiled all of the data, assessed and processed it, and be ready for the big presentation.
The first tutorial in this part is an overview of patient assessment. It is relatively short but essential.
The Second tutorial in this sequence is on at neurological assessment in the ICU. It contains a discussion about the Glasgow Coma Scale, The Richmond Agitation Sedation Scale and CAM-ICU. I also cover the assessment of suffering (PAID) in critical care.
You will need to assess the patients neurologic status, whether or not they appear to be suffering and what interventions, both environmental and pharmacological, that you are administering to help them.
The Critically Ill Patient should receive a systematic head to toe front to back clinical examination each day. Before you start, stand at the end of the bed and take in the scenery. An experienced ICU doctor will acquire an enormous amount of information about a patient by eyeballing the monitor, looking at the patient’s habitus, the machines, the other attached devices, infusion pumps etc.
Then INTRODUCE yourself and explain to the patient, irrespective of level of consciousness, that you are going to examine them, if that’s ok.
Does the patient have an endotracheal tube, nasogastric tube (is it on free drainage?), enteral feeding tube (yellow) or orogastric tube).
Follow the pattern of Inspection, Palpation, Percussion and Auscultation.
Start with the head and evaluate its shape and color. Then move on to the eyes, nose, lips, mouth (inside and outside) and then on to the side of the head and ears.
Move on to the neck – observe for masses, scars and lines (what type of line). Palpate the neck paying particular attention to the trachea (you may want to do a tracheostomy down the line). Feel for crepitus in the supraclavicular area.
Move on to the chest – inspect – look for recent surgical wounds and scars, chest or mediastinal drains, pacemaker wires etc. Observe the breathing pattern – is it symmetrical? Palpate the cardiac apex and the left sternal border. Auscultate for cardiac murmurs, carotid bruits and for breath sounds, looking for loss of air entry, crackles or bronchial breathing.
Move on from the chest to the arms – are they symmetrical? Is the patient moving both arms? Any redness? What color are the fingers – any mottling? Are the fingertips necrotic? Palpate the arms and hands and feel the temperature – hot or cold? Feel the brachial and radial pulses.
Move on to the abdomen: is it scaphoid or globular? If globular consider the 5 Fs: fat, fluid, flatus, feces, fetus. Are there any scars, wounds or drains? Palpate, percuss and auscultate the abdomen.
Move on to the legs. Are they moving? Are they equal in size? Are the quadriceps wasted? Is there mottling or ischemic changes? Is the patient wearing compression stockings (TED) and or sequential compression devices (SCD)? Palpate the legs, feel the pulses and then look at the ankles (pitting edema) and heels (pressure sores).
Assess the skin – are there any rashes? Are they localized or generalized? If generalized is the rash macular, maculo-papular, vesicular (one side consider herpes zoster) or – ominously purpuric. A generalized purpuric rash is either meningococcemia or thrombotic thrombocytopenia purpura until otherwise proven (both disorders are immediately life threatening).
Roll the patient on their side and look at the back – in particular look at the pressure areas and at any pain catheters and their sites (epidural). Look for the presence of a rectal tube and bowel management system.
When you have completed examination, look at the devices around the bedside sequentially. Start with the main monitor and evaluate the ECG – rate (paced?), rhythm, shape (ST segment changes?). Then the pulse oximeter, arterial blood pressure – invasive and non invasive (correlating?), then the temperature and end tidal CO2 (and waveform).
Move on to the ventilator – if one is attached and note whether the patient is breathing spontaneously or not (why?), what mode (AC, SIMV, BiLevel, PSV), rate, tidal volume, fiO2, PEEP, PFR, plateau pressure, and dynamic compliance and resistance).
Is the patient receiving continuous kidney replacement therapy – note the mode (CVVHDF or SCUF), anticoagulation strategy (citrate or heparin), and fluid removal.
Look for intravenous and enteral feed and take note of the rate and the contents. Then move on to the infusions – iv fluids and electrolyte replacement, analgesics and sedatives, vasopressors, inotropes, insulin and corticosteroids.
Before leaving the bedside look around – did you miss anything and machines or drains or infusions? Then clean up any mess that you have made, restore the bedspace to the condition it was in and inform the nurse of any changes you made or any new observations.
This tutorial has been broken up into two videos to make them easier to navigate.
ORtoICU 