Critical Care

Ventilator Settings and Management

Most physiologic ventilator mode?
Iron lung (Negative Pressure Ventilation)
Ventilator induced lung injury
Volume
Pressure (Barotrauma)
Oxygen Toxicity
Oxygenation vs Ventilation
Oxygenation affected by:
Fi02, PEEP, Mean Airway Pressure
Ventilation affected by:
RR, Tidal Volume
RR x TV = Minute Ventilation
Peak pressure - reflects pressure in large airways
Plateau pressure - must do inspiratory pause . This allows pressures to equilibrate and better reflects alveolar pressure
What if there is large differential between peak and plateau pressure (e .g . Peak 50, Plateau 30)?
Large airway obstruction
Bronchospasm
What if peak and plateau are both high?
Alveolar lung disease (e .g . ARDS)
Negative inspiratory Force (NIF) - Must do expiratory pause to check this .
Vent Modes
Continuous mandatory ventilation (CMV)/Assist Control (AC)
Respiratory Rate (RR) and Volume are set
Every breath is fully supported
Problems: Volume is set regardless of pressure and can result in barotrauma; hyperventilation if patient RR is high .
Pressure Support (PS)
Pressure is set
Advantages: Limits barotrauma
Disadvantages: Hypoventilation
Synchronized Intermittent Mandatory Ventilations (SIMV)
RR and Volume set
Spontaneous breaths above set rate are not fully supported
Delivered breaths are synchronized - typically a more comfortable mode of breathing
Problems: Patients can tire out
Extubation criteria
Spontaneous Breathing Trial (SBT) should be done every day
Follows commands (i .e . neurologically able to protect airway)
Minimal Vent Settings for extubation (in general):
Fi02 50% or less
PEEP <10
Rapid shallow RR/TV < 100 (Best Predictor)
NIF > 20 (Good predictor of who will fail if <20; However >20 is poorly predictive of who will do well) Acute Respiratory Distress Syndrome (ARDS)
Definition: Within 1 week of insult, characteristic radiographic finding, not cardiogenic
Mild: P:F ratio = 200-300
Moderate: P:F ratio = 100-200
Severe: P:F ratio = <100
Ventilator strategies for ARDS
Lung protection ARDSNET protocol - Low tidal volume (4- 6cc/kg)
Permissive hypercapnia
Generally, as long as pH above 7 .20 it is recommended to allow hypercapnia as long as the patient is oxygenating . This avoids further lung injury .
Strategies for ARDS patients that are failing
Airway Pressure Release Ventilation (APRV)
Long inhalation period with short extubation
Set P-high (Pressure High) and P-Low (Pressure Low) as well as T-high (Time High) and T-Low (Time Low)
Want long T-high and short T-low
Patient can breathe spontaneously throughout
Proning
Nitrous Oxide, NM blockade
Proning and neuromuscular blockade have proven benefits for ARDS in prospective RCTs Sepsis
Old definition - Focused on inflammation (SIRS Criteria)
Sepsis = SIRS + infection source
Severe Sepsis = SIRS + source + end organ dysfunction
Septic Shock = SIRS + end organ dysfunction + hypotension/pressor requirement
New Definition - Focuses more on organ dysfunction with infection (SOFA Score)
SOFA = Sequential Organ Function Assessment
Sepsis = If SOFA score increases by 2 or more points, or a score of 2 or more on a patient initial presentation
Septic Shock = Pressor requirement AND lactate of 2 or more despite resuscitation
Diagnostic adjuncts
Procalcitonin - when normalizes can be a guide to stop antibiotics
Better at ruling out sepsis if negative; More sensitive than specific
1,3 beta-d-glucan assay for fungal infections
Mannan antigen and anti-mannan antibody for invasive candidiasis
Sepsis management
Send cultures before starting antibiotics
Within 3 hours → Start antibiotic (send cultures prior), bolus with 30cc/kg crystalloid if lactate >4
Within 6 hours → Start pressors (norepinephrine recommended over dopamine, vasopressin added as secondary) if needed to maintain MAP, repeat lactate
Activated protein C is no longer recommended (Never choose as an answer)
Adrenal insufficiency in Septic Shock?
Generally do not do a stimulation test - if refractory shock and suspect adrenal insufficiency, you should empirically treat with hydrocortisone
Glucose control in the ICU
Tight glucose control is associated with worse outcomes; shoot for <180 Vasoactive agents
Dopamine
Receptors:
Low dose: Dopamine receptors in kidney
Medium dose: Beta 1
High dose: Alpha
Norepinephrine (Levophed)
Receptors:
Alpha and some Beta 1
Epinephrine
Receptors:
Alpha and Beta 1
Phenylephrine
Receptors:
Purely alpha
Used in neurogenic shock from spinal cord injury
Vasopressin
Receptors:
V1 receptor
Dobutamine
Receptors:
Beta 1
Increases cardiac output
Can have vasodilatory effects
Milrinone
Phosphodiesterase inhibitor
Increases cardiac output
Increases cAMP
Inotropic, Vasodilatory Pulmonary Embolism (PE)
Most common vital sign change?
Tachycardia, Tachypnea
Respiratory alkalosis
Most common EKG findings with PE?
Sinus tachycardia
Classic S1Q3T3 finding is uncommon
Diagnosis
CT Pulmonary Arteriogram is study of choice
Role of D-Dimer?
Sensitive – Good for ruling out PE . High false positive rate .
Treatment
Anticoagulation - Heparin bolus followed by drip for goal PTT 60-90
Indications for thrombolytics with PE?
Hemodynamic instability
Right heart strain on echocardiogram
Pulmonary embolectomy (Trendelenburg Procedure)
Uncommon
Surgical option if there is a contraindication for lytics Cardiovascular physiology
Central Venous Pressure (CVP) - surrogate for end diastolic right ventricular volume
Pulmonary Wedge Pressure (PWP) - surrogate for end diastolic left ventricular volume
Cardiac Output (CO)= Stroke volume x Heart Rate
Cardiac index (CI)= Cardiac Output/Body Surface Area
Swan Ganz Patterns - Less commonly used but good to know principles
Hemorrhagic shock
Low CO, High Systemic vascular resistance (SVR), Low filling pressures (CVP/PWP)
Septic shock
High CO (may be low in late septic shock), Low SVR, Low/ Normal filling pressures (CVP, PWP)
Cardiogenic shock
Low CO, High SVR, High filling pressures (CVP, PWP)
Formulas you need to know
Oxygen Delivery = CO x [Hb x 02 Saturation x 1 .34 + (Pa02 x 0 .003)]
Oxygen Consumption = CO x (Arterial-Venous 02 difference)
Extraction Ratio = O2 Consumption/O2 Delivery
What decreases the Extraction Ratio?
Sepsis, cardiac failure, anemia/hypoxia, fever, seizure can affect extraction ratios Anticoagulation Agents and reversal
Coumadin - Inhibits Vit K dependent factors
Reversal:
FFP, Vit K
If emergent reversal needed → PCC
Less volume than FFP
Reversal is faster and more predictable than FFP
Dabigatran (Pradaxa) - Direct Thrombin inhibitors
Reversal:
Dialysis
Praxbind - New monoclonal antibody against Pradaxa
Apixaban (Eliquis), Rivaroxaban (Xarelto) - Factor Xa inhibitors
Reversal:
PCC will give partial reversal Nutrition
Metabolic Cart (Indirect Calorimetry)
Measures 02 Consumption and C02 production
Respiratory Quotient (RQ) = C02 production/02 consumption
RQ is useful to identify carbohydrate overfeeding in intubated patients, which results in higher C02 production and difficulty weaning from the ventilator.
Fat 0 .7
Protein 0 .8
Carb 1 .0
Nitrogen balance
Requires 24-hour collection and measurement of urine Nitrogen
Nitrogen Balance = Protein intake /6 .25 - (Urine nitrogen + 4)
Negative Nitrogen Balance = Catabolic State
Positive Nitrogen Balance = Anabolic State
Caloric contents
Carb: 4 kcal/g
Should make up 75% of non-protein calories
Toxicity: C02 production, hyperglycemia, immunosuppressant
Dextrose: 3 .4kCal/g
Lipids: 9 kcal/g
Should make up 25% of non-protein calories
Essential Fatty Acids
Linoleic acid
Alpha-Linolenic acid
Toxicity: pro-inflammatory (Omega 3 Fatty Acids are less inflammatory and immunogenic)
Protein: 4 kcal/g
1-2 g/kg/day requirement
Always prefer enteral nutrition over TPN if possible
Start enteral nutrition within 24-48hrs (after resuscitation/ stabilization)
If unable to tolerate enteral nutrition, start TPN at day 5-7
Nutritional Deficiencies
Thiamine - Beri Beri
Folate - Macrocytic anemia
Vit D - Rickets
Vit C- Scurvy
Vit K - Coagulopathy
Zinc - rash, alopecia, vision changes
Copper - Microcytic anemia, pancytopenia, osteopenia
Nutrition in pancreatitis patient
Classic teaching is to avoid gastric feeds and provide enteral nutrition with distal feeding access . More and more evidence showing gastric or small bowel enteral feeds generally acceptable . Trend is towards early enteral feeding .
Immunonutrition - Contain Omega 3 fatty acids, Glutamine, Arginine
Associated with lower infectious complications QUICK HITS
Hemoptysis after Swan Ganz Balloon Inflation?
Ruptured pulmonary artery
Treatment: Angioembolization
Tachyarrhythmia, Torsades de Pointes on EKG?
IV Magnesium
No brainstem reflexes, fixed and dilated pupils, normotensive, normothermic. What’s next to declare brain death?
Apnea Test
Who should discuss organ donation with a brain dead patient’s family?
The organ donation representative, not the physician .
Hyperacute rejection of a transplanted organ is mediated by?
Antibodies
Acute rejection of a transplanted organ is mediated by?
T-cells
Cyclosporine/Tacrolimus mechanism of action?
Calcineurin inhibitor, blocks IL2
Post Op Day 2 CABG patient with decreased chest tube output followed by PEA?
Cardiac Tamponade
Treatment: Cut wires and open chest in ICU
Frequent IV Haldol doses for ETOH withdrawal followed by arrhythmia?
Prolonged QT
Patient with positive UA with MAP of 60 and lactate of 4 .5?
Septic Shock
5yo trauma patient with bradycardia during attempted intubation?
Atropine
Post Op CABG patient with hypotension with CVP and wedge pressure of 20?
Cardiac Tamponade
Critically ill patient in sudden drop in end tidal CO2?
Decreased cardiac output or cardiac arrest
Large volume paracentesis for ascites in a cirrhotic patient followed by oliguria and elevated Cr, Urine Na is less than 10?
Hepatorenal syndrome
Treatment: Albumin and vasopressin; transplant