One of the most intimidating things about entering the ICU for the first time is the “life support machine” – the mechanical ventilator. Although I have posted an extensive series of tutorials on Mechanical Ventilation, covering most of the modes, oxygen therapy and applied respiratory physiology, I have attempted, in this tutorial, to distill everything to the “least you have to know” in 40 minutes. Keep in mind that modern machines look more like iPhones, and are far easier to use than the devices I grew up with that looked to me, on day 1, like something in the cartoon below.
I start with a discussion about the difference between normal breathing, CPAP and Positive Pressure Ventilation (PPV). PEEP is, effectively, CPAP during PPV. I then go on to discuss pressure limited modes of ventilation; worldwide this are the most widely used modes in ICU. I limit my discussion to Pressure Assist Control, Volume Guaranteed Pressure Control (VG_PC) and Pressure Support Ventilation (PSV). VG-PC is a popular and flexible option as an ICU’s default mode. However, as it is a pressure controlled mode, there is significant variability in tidal volume and airway pressure from minute to minute.
Several important rules are emphasized: the tidal volume should, in general be lower than 6ml/kg of ideal body weight, the plateau pressure lower than 30cmH2O and the driving pressure lower than 15cmH2O. I introduce the Spontaneous Breathing Index (SBI = RR/TV in L). The magic number is 100. We use the SBI to determine the success of weaning on PSV.
Volume Controlled Ventilation is the predominant mode use in the Operating Rooms (Theatres), and Volume Assist Control is a popular mode in North America. In ICU you must set a peak inspiratory flow and be aware that this may be insufficient during assisted breaths and lead to dys-synchrony. Volume Control is often used in ARDS to “lock in” the Tidal Volume (TV) but the operator must be aware that the TV that matters is not what is dialed up on the ventilator, but what the patient exhales.
I go on to discuss how to assess the patient on invasive mechanical ventilation, by looking at whether they are breathing spontaneously, in which case we determine whether they are suitable for a Pressure Support wean or not, or whether or not there is a problem with oxygenation (increase FiO2, PEEP, Mean Airway Pressure and seriously consider Prone Positioning) or Ventilation (increase Respiratory Rate, Tidal Volume or both, reduce PEEP).
The final part of the tutorial looks at Non Invasive Ventilation (NIV), and I explain how, in general we only use 2 modes on standalone devices – CPAP and Spontaneous Timed (S/T). The latter is similar to PSV with a backup rate, but I point out that instead of PEEP+PS the breath is EPAP + IPAP and IPAP is not built upon IPAP, as is the case with PSV. If one is delivering NIV on an ICU ventilator, then “leak” adjustment or “leak sync” should be used.
This tutorial looks at the assessment of PaCO2 on the blood gas and how it interfaces with the pH and the Bicarbonate (HCO3-). The control of PaCO2 is a major physiological mechanism for maintaining homeostasis. CO2 production by the body must be balanced by CO2 elimination. PaCO2 rises when there is hypoventilation, this results in a fall in pH and an rise in HCO3 and this is called “Acute Respiratory Acidosis.” If the patient hyperventilates, the PaCO2 and the HCO3 fall and the pH rises: this is “Acute Respiratory Alkalosis.” When there is chronic CO2 retention, the body adapts by wasting Chloride in the urine, the pH normalizes and the HCO3 rises substantially.
Any patient who is intubated, or who has a laryngeal mask in situ, must undergo end tidal (end of exhalation) CO2 monitoring. The capnography waveform is worth evaluating, particularly if airway obstruction or increased resistance is suspected.
Included in this tutorial are various rules of thumb that you can use to determine the Respiratory Acid Base Status of the Patient – including the “Rule of 40.”
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.
Before approaching an critically ill patient’s bedside you should know who the patient is and why they are in the ICU. The purpose of the history is to lay out the known facts about the patient. Usually the patient in the ICU is unable to give a clear and reliable history. You need to comb through the patient’s chart to locate this information. Dig deep! Events that may have happened months ago may have an impact on the patient today. Don’t forget, you are not the only professional that is treating the patient: ask the nurse – they are excellent historians as they give and receive a concise report at the beginning and end of each shift. It is also worth talking to the primary team, physiotherapist, pharmacist and dietician about the patient. Remember, you are one member of a team: the others may have more knowledge of the patient than you. Nevertheless you need to remain a little bit skeptical about the story that you have been given: make sure the facts match the narrative
In this tutorial I will introduce the 4 Ws of clinical history: Who is this patient? Why are they in hospital and ICU. 3. What is going on with the patient (PROBLEM LIST). 4. Where are we going (what are the physiologic goals and organ based plans?).
WHO? Who is this patient? How old are they? Where do they come from and what is their occupation? How long has this patient been in the ICU – is this a recent admission (the patient is acutely critically ill and likely still being resuscitated)? Has the patient been in the ICU for more than 7 days? In that case the patient may be slow to recover or chronically critically ill.
What type of patient are we dealing with? Surgical or Medical? Postoperative or Critically Ill?
There are three types of critically ill patients: 1. Medical patients with an acute medical syndrome that may have occurred in the setting of low physiologic reserve. These may be children or adults. 2. Surgical patients – who have had complex elective surgery (e.g. cardiac or neurosurgery), emergency surgery or trauma. The patient may have originated as a surgical patient but now has medical problems (e.g. hospital acquired pneumonia). 3. Obstetric patients who may be currently pregnant, recently pregnant and be in ICU as a consequence of pregnancy (pre-eclampsia, post partum hemorrhage) or co-incidental with pregnancy (trauma, bowel obstruction etc.).
WHY?
It is absolutely CRITICAL that you understand the dynamics around the patient’s ICU admission. The patient may have come directly from the emergency room or operating room to ICU, or may have been transferred from a ward or other hospital. In the latter case you will need to ensure that you know exactly what went on there. These are the questions that you must ask, up front about the patient.
Why was the patient admitted to hospital? Why was the patient admitted to ICU? What happened in between?
What was the patient’s admission problem (MAJOR ADMISSION PROBLEM)?
This is the patient’s presenting problem (although it may not be the patient’s main current problem). It is the symptoms and diagnosis that led the patient to come into the hospital originally – e.g. chest pain, shortness of breath, confusion. This may be clarified as “pneumonia” “septic shock” etc.
Between the patient arriving in the hospital and being admitted to ICU clinical episodes may have occurred – you need to know these. Was there a delay with the diagnosis? Was a wrong pathway chosen? Did the patient deteriorate or have a cardiac or respiratory arrest on the ward?
What was the patient’s indication for ICU ADMISSION
This is a remarkably limited list because patients are admitted to ICU for life sustaining therapy consequent of single or multi organ failure. Those injuries can be summarized as follows:
Neurological – Low GCS, Seizures
Cardiovascular – Hypotension, Arrhythmias, Blood Loss
Some patients, for example those with septic shock, may have multiple system problems: confusion, hypotension, hypoxemia, oliguria – AKI.
What complications followed?
Prolonged admission to intensive care is characterized by “second and third hits” – organ injuries such as hospital acquired pneumonia, line sepsis, myocardial ischemia, acute kidney injury, bed sores etc. It is important that you are aware of these problems even if they have now resolved, as complete recovery of organ function at this stage is unlikely, and those organs remain vulnerable (for example, it is important that you do not prescribe non steroidal anti inflammatory agents (NSAIDS) to a patient who has recently recovered from acute renal failure).
What is the patient’s age and baseline health status (BACKGROUND)?
What background medical problems does the patient have? We know that patients with major organ dysfunction (such COPD, pulmonary fibrosis, heart failure (EF<40%), chronic kidney disease, cirrhosis or chronic hepatitis, previous myocardial infarction or active ischemia, connective tissue disease, inflammatory bowel disease, cancer, cerebrovascular disease, carotid arterial disease) have diminished physiologic reserve, and have a worse prognosis when admitted to intensive care. The greatest determinant of outcome, however, is the patient’s age: young patients do better in intensive care than older ones. You also need to know what medications the patient was taking pre-admission: antihypertensives, statins, SGL2 inhibitors, GLP-1 receptor agonists etc. If the patient is taking anti-coagulants you need to know why? Pulmonary embolism, stroke, atrial fibrillation, arterial obstruction, heart valve etc. All of this is relevant.
WHAT?
What PROBLEMS are keeping this patient in intensive care (CURRENT PROBLEMS)?
The patient may remain in ICU for a problem wholly unrelated to the original presenting complaint – failure to liberate from mechanical ventilation, failure to emerge from sedation etc). This is the patient’s main current problem, and it needs to be addressed. In addition, it is important to enumerate the other problems, even if they are apparently trivial.
If you don’t have a precise diagnosis don’t invent one – just list the problems, these can be padded out later
So a patient may be admitted with Hypoxic Respiratory Failure That might evolve to Ventilator Dependent Respiratory Failure That Becomes Acute Respiratory Distress Syndrome Clarified as Community Acquired Pneumonia, secondary to culture positive Staphylococcus Aureus
To identify the problems you need to evaluate the patient’s organ systems in an organized, precise and systematic way. The way I go through the systems is as follows:
NEUROSYSTEM
•The patient has a “Low GCS secondary to….” traumatic brain injury (specify), stroke, encephalopathy, encephalitis, meningitis, cause uncertain etc.
•The patient has “Severe Delirium with a RASS score of…..being treated with…..
•The patient is in “Status Epilepticus being treated with…..with a know or no known history of Epilepsy”
•The patient has “Guillain Barre Syndrome, requiring mechanical ventilation being treated with plasma exchange”
RESPIRATORY SYSTEMPROBLEMS
Problems with the respiratory system are usually 1. problems with the lung parenchyma (gas exchange) or 2. problems with the airway (particularly airway obstruction)
Parenchymal Problems
Acute Hypoxic (AHRF) or Hypercarbic Respiratory Failure
Although rhythm disturbances causing hypotension are technically “cardiogenic shock” nobody really uses that term, generally we describe the problem
•Complete Heart Block requiring external pacing
•Fast Atrial Fibrillation requiring an amiodarone infusion
•Runs of Non Sustained Ventricular Tachycardia requiring……
KIDNEY PROBLEMS
•The patient has “Acute Kidney Injury secondary to (sepsis or rhabdomyolysis or prolonged hypotension) requiring Continuous Kidney Replacement Therapy”
•You might also qualify this with “on a background of CKD”
•“Dialysis Dependent AKI – he receives intermittent hemodialysis for 3 hours each day”
•“AKI no longer requiring Kidney Replacement Therapy”
The patient may have been admitted with a hematology issue e.g. thrombotic thrombocytopenia purpura (TTP) or a complication of chemotherapy or bone marrow transplantation Otherwise
•Anemia, Polycytemia, Thrombocytopenia
INFECTIOUS PROBLEMS
The infection may be the primary problem or it may be secondary
•Wound contaminated with VRE or Pseudomonas
•Patient may have acquired MRSA
•Patient may be isolated due to CPE
RESOLVED PROBLEMS
•If the patient was admitted with sepsis – source control may have resolved the problem
•An underlying cardiac problem may have been fixed by a stent
•An obstructed bowel or leaking aneurysm may have been surgically repaired.
•Acute kidney injury may have resolved
•Is anything ever fully resolved?
WHERE?
We can’t determine where we are going if we don’t know where we are now! From the outset, the physiological parameters under your control must be targeted: level of sedation, heart rate, Blood pressure, PaO2, PaCO2, pH, urinary output, enteral feeding, fluid balance, mobilization etc.
What physiologic targets have we set for this patient?
•Neurological – RASS score (or GCS) target with sedation
You don’t need notes to present a quick history, summary, problem list and goals of therapy. This should be drawn from memory as often the history is presented several times a day at handovers, rounds etc. Keep the narrative succinct – don’t stray off track – we are interested in the FACTS the FACTS and nothing but the FACTS.
Follow the system in the image below:
This Mr Eddie Chambers he is a 73 year old retired farmer from Mayo He is a medical patient He has been in the ICU for 4 Days………having originally been admitted with acute hypercarbic respiratory failure secondary to pneumoni He was admitted to ICU for intubation and mechanical ventilation He subsequently developed septic shock and acute kidney injury, requiring pressors and RRT He has a background history of hypertension treated with calcium channel blockers. His current problems are: ventilator dependent respiratory failure, pressor dependent septic shock and dialysis dependent acute kidney injury He is also malnourished, due to gastroparesis, hypoalbuminemic, anemic and has a hyperchloremic metabolic acidosis and stress hyperglycemia He also has an early sacral pressure sore
Our goals are to: Sedate to a RASS score of minus 2 Reduce the ventilator settings Keep the PaO2 above 8kPa (60mmHg) Keep the PaCO2 between 5.3 and 6kPa (40-45mmHg) A MAP of 70mmHg Fluid balance of -1000ml today on Kidney Replacement Therapy We are starting TPN today, and targeting a Blood glucose below 10mmol/L (180mg/dl) Sit him out in a chair today
REVIEW
This Tutorial Looked at Getting a History in the ICU. It is not easy because the patient is usually not able to communicate effectively. Significant detective work may be required.
Who – who the patient is
Why – the patient came to hospital and why they needed to be admitted to ICU
What is currently wrong with the patient (Problems)
Tutorials 2 and 3 in the Introduction the Critical Care Series.
The first is titled “What is Critical Illness” and it covers the concept of Physiologic Reserve.
The third tutorial looks at the problem that many healthcare providers encounter: how do I identify the critically ill patient. In this tutorial I discuss the type of scenarios in which you might be called to the patients bedside. I principally discuss Early Warning Scores (EWS) and why I think they are helpful. I also mention the SOFA score.
ORtoICU 