UMEM Educational Pearls - Critical Care

Treating ischemic strokes with interventional therapies (e.g., clot retrievers, stents, intra-arterial tPA, etc.) is nothing new, but there has never been a randomized control trial demonstrating benefit until recently.

The prospective MR CLEAN trial evaluated whether interventional therapies (i.e., either mechanical intervention or intra-arterial tPA) would confer benefit; patients were included if there was an acute occlusion within the proximal intracranial portion of the anterior cerebral circulation.

90% of patients received alteplase prior to randomization; there were 233 patients in the intervention group (alteplase + intraarterial intervention) and 267 patients in the usual care care arm (alteplase only); all patients were treated within 6 hours of symptoms onset

The primary outcome was functional independence at 90 days; an absolute difference of 13.5 percentage points favoring the intervention group was found. There were no significant differences in mortality or symptomatic intracerebral hemorrhage.

Despite these exciting results, we must pause and ask why this was this the first randomized trial demonstrating benefit when previous trials could not? Here are three blogs posts that deep dive this question and raise even more questions:

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How does it present?

  • Fever, cough, sore throat, runny nose, muscle aches, headaches, fatigue, diarrhea (in children especially)

Who cares…I got my vaccine! Does the vaccine work this year?

  • There has been some antigenic drift this year in the influenza A (H3N2) type virus.
  • 52% are anti-genically different than the H3N2 vaccine virus.
  • So the vaccine is less effective this year but it can give some cross-protection (in addition to protection against the other strains used in the vaccine)
  • CDC recommends still getting the vaccine  (http://www.cdc.gov/flu/protect/vaccine/vaccines.htm)
  • 91% of samples reported to the CDC have been influenza A this year

Can I test for this?

  • Rapid influenza diagnostic tests check for antigen detection
  • Pooled sensitivity of 62%; specificity of 98%
  • False negatives are common
  • Good technique during sample collection is important

The CDC is recommending treatment...wait I thought we were done with Tamiflu?

  • Benefits: shortens the duration of symptoms (day or less), reduces the risk of complications, reduces the risk of death among hospitalized patients
  • Risks: side effects (see below)
  • A recent Cochrane review revealed that treatment did not really help reduce complications and most of the data on anti-viral agents is biased (Roche funded) and hotly debated

Who is at risk/who deserves consideration for treatment?

  • Hospitalized patients with influenza 
  • Old people (>65)
  • Children
  • Pregnant women
  • Chronic medical conditions (asthma, COPD, diabetes, or heart disease)
  • American Indians and Alaskan natives
  • Chronic immunosuppression
  • Institutional outbreaks (nursing homes, correctional facilities)

Pearls of treatment

  • Treat as early as possible (<48hours from symptom onset)
  • 5 days of treatment; twice daily dosing. Wt based for children. Renally dosed.
  • Oseltamivir: used for more severe influenza cases
  • Zanamivir: 7 years or older; IV Zanamivir is currently in Phase III clinical trials

What are the side effects of anti-viral agents?

  • Don’t use zanamivir in patients w/ pulmonary disease
  • Transient neuropsychiatric events for oseltamivir
  • Nausea, vomiting, diarrhea are common both both

 

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The Critically Ill Patient with Ebola Virus Disease

  • The current outbreak of Ebola Virus Disease (EVD) is the largest ever recorded and has been declared "a public health emergency of international concern" by the WHO.
  • Pearls regarding critically ill patients within the current EVD outbreak include:
    • Clinical Features
      • Tachycardia, tachypnea, oliguria, and alterations in mental status are common and generally seen about 7-12 days after symptom onset.
      • Shock is often due to profound hypovolemia from GI losses.
      • Hemorrhage is a late finding and most often manifests as lower GIB.
    • Labs
      • Common lab abnormalities include hypokalemia, hypocalcemia, hypoalbuminemia, and lactic acidosis.
    • Treatment
      • The mainstay of treatment is aggressive fluid resuscitation and electrolyte repletion (especially potassium).
      • Blood products can be administered for those with coagulopathy and hemorrhage.
      • Empiric antibiotics and antimalarial medications should be considered while awaiting confirmatory testing for EVD.

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Dynamic Measures of Intravascular Volume Assessment

The resuscitation of a patient in shock often requires the administration of intravenous fluid.  Excessive fluid resuscitation can lead to worsening pulmonary edema, systemic edema, acid-base disturbances, as well as many other complications. There are a myriad of techniques to try and figure out if the patient needs more intravascular volume, but each has it’s pitfalls.

Recently, experts have recommend that we move away from using static measures of preload assessment such as central venous pressure (CVP) and instead focus on using dynamic measures for volume responsiveness.

Volume Responsiveness Defined: An increase of stroke volume of 10-15% after a 500 mL IV crystalloid bolus over 10-15 minutes.

Below is a chart describing key values, requirements, and contraindications for each of these dynamic measures of non-invasive intravascular volume assessment. 

Important notes:  PPV and SVV require the patient to be intubated with controlled tidal volumes.  Arrhythmias and right heart failure make many of these measures invalid (except for PLR).  Other methods of assessment not discussed include systolic pressure variation, left ventricular outflow track velocity time integral (LVOT VTI), and end-expiratory occlusion pressure (EEO).

Bottom Line: None of these measures are perfect and shouldn't be used in isolation to determine if the patient’s “tank is full”.  Combine clinical judgment with these measures to get a best estimate of whether or not to give that next fluid bolus.  

 

Reference

1. Enomoto TM, Harder L. Dynamic indices of preload. Crit Care Clin. 2010;26(2):307-21, 

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Running a successful resuscitation not only means doing everything right, but also remembering all the things that can go wrong. A.E.I.O.U. is a simple mnemonic that can help you remember the simple things that are sometimes forgotten during a medical resuscitation.

AAdvanced airway equipment to bedside, as well as checking the correct placement of the Airway if a patient is intubated in the field. Also consider adding another A, for Arterial line; early placement can help with pulse checks and an accurate assessment of blood pressure should there be return of spontaneous circulation (ROSC); the femoral site is fast and accurate.

EEnd-tidal CO2 (ETCO2) helps detect ROSC. Ask for the ETCO2 monitor to be set up right after you receive notification of an arrest in transit; ETCO2 requires time to set-up / calibrate

IIntraosseous line(s); compared to peripheral or central venous access, IO’s are faster, safer, and any medication can be administered through it, including vasopressors / inotropes.

OOrder (i.e., “who’s who in the Resus room?); You may be the team leader or you may be assisting, but it is important that you, and everyone else in the room, know their role prior patient arrival. If you are leading the resus, be sure everyone knows who you are, and assign everyone in the room a specific task (e.g., chest compressions, IO placement, etc.). If you are assisting and have not been assigned a task, ask the resus leader what you can do to help. If there is nothing immediate for you to do then take the initiative to de-clutter the room and step outside; be nearby and ready to help, if needed.

UUltrasound; can help prognosticate and detect reversible causes (e.g., pericardial tamponade). Have the ultrasound machine in the room prior to patient arrival. It should be powered on, with the proper probe connected, and in the proper mode. The most experienced ultrasonographer should scan the patient during a pulse check; experience is vital because hands-off time should be minimized.

 

*Tips for the Resuscitationist (#TFTR) is a new series to help you to better manage your critically ill patients. Do you have an idea for a topic or do you have a tip you would like to share? Send it to us via twitter @criticalcarenow (use (#TFTR)). You can also email us here

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Tips for the inpatient management of community acquired pneumonia

How do I know if my patient needs ICU admission?
  • The best scoring system is the Pneumonia Severity Index (PSI) for deciding on ICU admission and inpatient treatment. You can also use the CURB-65 score or the SMART-COP score but these are less sensitive.
  • In general, PSI score of 4 or 5 tends to require ICU admission
Do I still need to treat within 4 hours?
  • No, not really. Just try to do it as fast as you reasonably can do without over-treating
What do I use for general inpatient treatment?
  • Beta-lactam plus a macrolide or a quinolone alone. These work pretty well, cure rate around 90% or so
What about ICU admission treatment?
  • You can stick with a beta-lactam plus a macrolide or quinolone in some cases but should be aware of certain issues
  • Consider influenza now that we have entered the flu season
  • Consider Staph aureus coverage for patients with influenza or those on chronic glucosteroids. Use linezolid or vancomycin for this.
  • Consider P. aeruginosa coverage in patients with COPD or bronchiectasis.
How long do I treat for?
  • This can vary based on clinician preference but there is good data to support treating for around 5-7 days
  • Longer treatment for Staph aureus or gram negative bacilli.   
What if there is no response?
  • Consider correct dosage of medications, possible antibiotic resistance, empyema, noninfectious cause etc. 

 

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Aminoglycosides in Critically Ill Patients

  • Aminoglycosides remain an important class of antibiotics in critically ill patients, especially those infected with multidrug-resistant organisms (i.e., Klebsiella  and Pseudomonas spp.).
  • Importantly, aminoglycosides are concentration-dependent antibiotics and a greatly affected by the increased volume of distribution and altered elimination commonly seen in the critically ill.
  • As a result, recommended doses are often too low to be effective. 
  • Initial doses of aminoglycosides should, therefore, be higher in critically ill patients.
    • Amikacin: 25-30 mg/kg
    • Gentamicin: 7-9 mg/kg
    • Tobramycin: 7-9 mg/kg
  • Subsequent doses are based on drug level monitoring.

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Category: Critical Care

Title: Back 2 Basics Series: Your Simple RSI Checklist - SOAP ME

Keywords: Airway, critical care, RSI, rapid sequence intubation (PubMed Search)

Posted: 11/3/2014 by John Greenwood, MD (Emailed: 11/4/2014) (Updated: 11/4/2014)
Click here to contact John Greenwood, MD

Back 2 Basics Series: Your Simple RSI Checklist - SOAP ME

The use of a checklist during high stress medical procedures is often recommended.  Rapid sequence intubation (RSI) is a classic situation where having a checklist can ensure adequate preparation however, if you don’t have a checklist – this simple mnemonic will make sure you are well prepared for a successful intubation.

 

Mnemonic – “SOAP ME”  
Suction
  • Yankauer suction placed under the mattress on the right side, head of bed (x2 if GI bleed, vomiting, or lots of secretions)
Oxygen
  • Bag valve mask (with PEEP valve) ready
  • Non-rebreather mask on patient (O2 wide open)
  • Nasal cannula on the patient (with 15L O2) during RSI
Airways
  • Oral, nasal airways
  • 2 ETT (expected size & one size below) w/ balloons checked, & stylet straight to cuff
  • 1 ETT ready for video laryngoscopy (curved stylet needed)
  • Rescue devices (Laryngeal mask airway, scalpel, etc.)
Positioning
  • Ear-to-sternal notch position
  • Ramped if obese
Monitors & Meds
  • Continuous monitoring devices
  • RSI Meds: Drawn up in carefully considered doses, labeled syringes
    • Sedative (Ketamine, etomidate, etc.)
    • Paralytic (rocuronium, succinylcholine)
  • Post intubation sedation meds (Propofol, fentanyl, etc)

EtCO2 & other Equipment

  • Continuous EtCO2 or at least color-change device to confirm successful intubation
  • Bougie placed under the mattress next to yankauer suction
  • 2 laryngoscopes (MAC 3 & 4) with lights checked.
  • Video laryngoscope plugged in & turned on

 

The SOAP ME mnemonic is a quick and useful technique to remember only the basics of airway management and preparation.  Always remember to also assign roles to team members and communicate clearly to maximize your chances of success.  

 

References
  1. Dr. Richard Levitan
  2. Dr. Ken Butler

Follow me on Twitter @JohnGreenwoodMD

 



Category: Critical Care

Title: Choosing Wisely in the ICU

Keywords: choosing wisely, icu, critical care (PubMed Search)

Posted: 10/21/2014 by Feras Khan, MD (Updated: 4/24/2024)
Click here to contact Feras Khan, MD

Choosing Wisely in the ICU

  • There is a general overuse of medical tests and treatments
  • This wastes healthcare resources
  • The Choosing Wisely Campaign was developed to have providers of different specialties choose medical services that should be questioned

The Critical Care Societies Collaborative came up with this list for ICU providers

1.     Don’t order diagnostic tests at regular intervals (such as every day) but rather in response to specific clinical questions. Do you really need a daily INR check or CBC check in all ICU patients? Really?

2.     Don’t transfuse red blood cells in hemodynamically stable, non-bleeding ICU patients with a hemoglobin concentration greater than 7 g/dl. See last week’s Pearl!

3.     Don’t use parental nutrition in adequately nourished critically ill patients within the first seven days of an ICU stay. TPN is the Cinnamon Toast Crunch of fungi.

4.     Don’t deeply sedate mechanically ventilated patients without a specific indication and without daily attempts to lighten sedation. Use as little as possible when you can.

5.     Don’t continue life support for patients at high risk for death or severely impaired functional recovery without offering patients and their families the alternative of care focused entirely on comfort. Engage families early in the hospital stay regarding aggressive life-sustaining treatments. Get palliative care involved in the ED!

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Hemoglobin Threshold in Septic Shock

  • Numerous trials have demonstrated the benefit of lower hemoglobin thresholds for blood transfusion in critically ill patients.
  • The recently published Transfusion Requirements in Septic Shock (TRISS) trial evaluated the effects on mortality of a lower versus higher hemoglobin threshold in ICU patients with septic shock.
  • The TRISS trial randomized 1005 patients to a lower hemglobin threshold (7 g/dL) or a higher hemoglobin threshold (9 g/dL). 
  • Overall, there was no difference in 90-day mortality between groups.
  • Patients randomized to the lower threshold received significantly fewer units without any increase in ischemic or adverse events.
  • Take Home Point: A hemoglogin threshold of 7 g/dL for blood transfusion appears effective for most patients with septic shock.

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The ARISE Trial

Early, aggressive resuscitation and attention to detail are essential element of managing critically ill patients.  This past week the ARISE trial was published - a 2nd large, randomized control study to examine the benefit of protocolized vs. usual care in patients with severe sepsis and septic shock. 

What were the main findings?  After enrolling 1,600 patients who presented to the ED in severe sepsis or septic shock:

  • They found no difference in mortality between the control (usual care) and treatment arm (early goal-directed therapy)
  • Mortality was 18.6% vs. 18.8% at 90 days
  • No evidence that continuous ScVO2, Hgb target > 10 mg/dL (check out the TRISS trial), or use of inotropes with a normal cardiac index improved mortality

Bottom Line:  Resuscitation goals for the patient with septic shock should include:

  • Early antibiotics (source control)
  • Adequate volume resuscitation (preferably balanced, crystalloid solution)
  • End-organ perfusion (lactate normalization)

Additional therapeutic goals should be made on a patient by patient basis.  Reassess your patient frequently, pay attention to the details, and you will improve your patient’s mortality.

 

Suggested Reading

  1. The ARISE Investigators and the ANZICS Clinical Trials Group.  Goal-Directed Resuscitation for Patients with Early Septic Shock. N Engl J Med. 2014. [PubMed Link]
  2. Wessex ICS: The Bottom Line Review

Follow Me on Twitter: @JohnGreenwoodMD



The last Back to the Basics post discussed the use of vasopressors to improve hemodynamics by increasing arterial (and venous) tone. This time we’ll discuss the use of agents to increase inotropy for patients with severe systolic dysfunction / failure.

Dobutamine: a direct b1 and b2-receptors agonist. It has no peripheral vasoconstrictor properties, so if blood pressure increases it occurs secondary to increased cardiac output. Unfortunately, blood pressure may be decreased in some patients due to its peripheral vasodilatory effects; in these cases it may need to be used with a vasopressor.

Milrinone: augments contractility by increasing intracellular Ca levels via cellular phosphodiesterase inhibition. Because it does not work on beta-receptors, it might be preferred for patients taking beta-blockers requiring inotropic support. It may cause peripheral vasodilation and hypotension, but this may be a benefit if pulmonary artery pressure is elevated as reductions in pulmonary artery pressure lead to improvements in right ventricular function. It has a long-half life and should be avoided in patients with renal impairment.

Dopamine: chemical precursor to norepinephrine and technically a vasopressor. At moderate doses (3-10 mcg/kg/min) it works on beta-receptors to increase myocyte contractility. At higher doses works primarily as a vasopressor, which may reduce cardiac output due to higher afterload.

Norepinephrine/epinephrine: has alpha and beta properties that lead to increased peripheral vasoconstriction, but also increases inotropy and chronotropy (faster heart rate)

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Category: Critical Care

Title: Massive Transfusion Protocols

Keywords: massive transfusion, bleeding (PubMed Search)

Posted: 9/23/2014 by Feras Khan, MD (Updated: 4/24/2024)
Click here to contact Feras Khan, MD

What is a massive transfusion?

  • Can be institution dependent but usually means greater than 10 Units of blood products transfused within 24hrs.
  • Most hospitals have this as a protocol that a physician can order to notify the blood bank that a large volume of blood products may be required rapidly.

When would I use this?

Indications:

-Systolic Blood pressure < 100

-Unable to obtain blood pressure

AND

-Penetrating torso trauma

-Positive FAST

-External blood loss

-Plans to go to the OR

How do I give it?

  • The transfusion ratio is usually 1:1:1 or 2:1:1
  • Give 1 unit PRBC, then 1 U FFP, and alternate until 6 units of each have been given and then 1 bag of apheresis platelets (6 equivalent units). Can repeat as needed.

Does this apply for just traumatic bleeding?

  • Although this data was based on soldiers in the recent Iraq Wars, it has been used for medical patients as well.
  • Therefore, consider using in upper GI bleeds, post-partum hemorrhage, etc.

Are there other agents I can use?

  • There is some data to give tranexamic acid early (less than three hours from injury) in trauma patients who are hypotensive and are having severe bleeding.

What am I trying to do with this protocol?

  • Control hemorrhage
  • Use the best products possible
  • Prevent hypothermia
  • Prevent hemodilution
  • Treat coagulopathy

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Infectious Risks Associated with TTM

  • Targeted temperature management (TTM) is commonly used in the care of patients resuscitated from cardiac arrest.
  • Despite improving neurologic outcomes, TTM can increase the risk of infection, bleeding, coagulopathy, arrhythmias, and electrolyte derangements.
  • Infectious complications of TTM are associated with increases in ICU length of stay, along with increases in the duration of mechanical ventilation.
  • Pneumonia and bacteremia are the two most common infectious complications of TTM, with S.aureus the most common single pathogen isolated in cases of infection.
  • Since TTM may suppress normal signs of infection, it is important to be vigilant for these two infectious complications.
  • At present, evidence does not support prophylactic antibiotics for all patients receiving TTM.

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Category: Critical Care

Title: Goal-Directed Resuscitation During Cardiac Arrest

Posted: 9/8/2014 by John Greenwood, MD (Emailed: 9/9/2014) (Updated: 9/9/2014)
Click here to contact John Greenwood, MD

 

Goal-Directed Resuscitation During Cardiac Arrest

Focusing on high-quality CPR is by far one of the most effective methods to ensure your arrested patient has the best chance to survive.  However, emerging evidence suggests that there are additional goals that we should try and accomplish during our resuscitation.

 As we continue to move toward goal-directed resuscitation strategies, optimizing coronary perfusion pressure (CPP) may be our next target in “personalizing” the care we provide to those in cardiac arrest.

A recent AHA consensus statement recommended the following physiologic goals during cardiac arrest care:

  • CPP > 20 mmHg: Estimated by diastolic BP [DBP] – [CVP] using an arterial line & central line.
  • DBP > 25 mmHg: When an a-line is present without an appropriate CVC.
  • EtCO2 > 20 mmHg: When an a-line & CVC are not present.

Each of these variables can give the provider valuable feedback about how their patient is responding to their resuscitation.  Some argue that the DBP target should be much higher (>35 mmHg), with the caveat that pharmacologic optimization can only occur once high quality CPR is confirmed.  The goal should always be to minimize the use of epinephrine whenever possible!

Bottom Line:  During your next cardiac arrest resus, consider using a goal-directed strategy by monitoring the patient’s CPP, DBP, & EtCO2 to determine the effectiveness of your resuscitation.

 

 

Suggested Reading

  1. Meaney PA, Bobrow BJ, Mancini ME, et al. Cardiopulmonary resuscitation quality: [corrected] improving cardiac resuscitation outcomes both inside and outside the hospital: a consensus statement from the American Heart Association. Circulation. 2013;128(4):417-35.
  2. Sutton RM, Friess SH, Maltese MR, et al. Hemodynamic-directed cardiopulmonary resuscitation during in-hospital cardiac arrest. Resuscitation. 2014;85(8):983-6.

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Vasopressors are used in shock-states to increase mean arterial pressure (MAP) and improve distal tissue perfusion. Additionally, some agents have effects on the heart to augment cardiac output.

Receptors that vasopressors work on include: 

  • Alpha-1: increase arterial tone (increases MAP) and venous tone to reduce venous pooling and augment cardiac preload 
  • Beta-1: increase inotropy and chronotropy on heart muscle; also increases arterial tone
  • Beta-2 and Dopamine: cause vasodilation but may actually be beneficial because this increases perfusion to cardiac, renal, and GI tissues.
  • V1: arterial vasoconstriction to increase MAP
  • The chart below is a summary; please note that quoted receptor effects vary depending on the source reviewed

Norepinephrine (NE): excellent vasopressor for most types of shock and recommended as a first-line agent in the Surviving Sepsis Guidelines.

  • Works on alpha-1, beta-1, and beta-2 receptors. 
  • Initial dosing 0.05 mcg/kg/min with a maximum dose often cited as 0.5 mcg/kg/min (though there is technically no maximum dose).

Epinephrine (a.k.a. Adrenaline): in several countries the first-line agent for shock (including sepsis).

  • Works similarly to NE on alpha-1, beta-1 and beta-2; it is a more potent inotrope than NE.
  • One downside is the production of lactic acid, which can sometimes lead to confusion when following serial lactates during resuscitation. 

 

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Category: Critical Care

Title: Enteral Nutrition in Critical Care

Keywords: immunonutrition, enteral feeding (PubMed Search)

Posted: 8/26/2014 by Feras Khan, MD (Updated: 4/24/2024)
Click here to contact Feras Khan, MD

Background

  • Artificial nutrition is a staple of critical care
  • Patients who are unable to eat, require enteral nutrition (preferred over parental nutrition)
  • There are some formulas that are called "immunonutrition" which try to alter the inflammatory response seen in critical illness
  • They may contain omega-3 fatty acids and essential amino acids such as arginine or glutamine, and anti-oxidants.

Data

  • A recent trial (MetaPlus) was designed to see if immunonutrition could decrease the development of infections in the critically ill
  • Compared to regular high protein formulas, there was no difference in mortality, duration of ventilation, or hospital length of stay

What to do

  • Immuno-nutrition formulas cannot be routinely recommended
  • Use regular high protein formulas
  • Start within 48 hours of identifying a need

 

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Sepsis Pearls from the Recent Literature

  • Sepsis remains one of the most common critical illnesses managed by emergency physicians and intensivists.
  • Recent publications and meta-analyses (i.e., ProCESS, ALBIOS, SEPSISPAM) have further refined the management of these complex patients.
  • A few pearls from the recent literature:
    • Early broad-spectrum antibiotics remains the most important factor in reducing morbidity and mortality.
    • Appropriate fluid resuscitation with a balanced crystalloid solution targeting 30 ml/kg. Use a dynamic measure of volume responsiveness to determine if additional fluid needed (i.e., PLR with a minimally invasive or noninvasive cardiac output monitor)
    • Maintain adequate tissue perfusion with IVFs and vasopressors (norepinephrine) targeting a MAP > 65 mm Hg.  Patients with chronic HTN may benefit from a higher MAP goal.  If the diastolic BP is < 40 mm Hg upon presentation, start vasopressors concurrent with IVF resuscitation.

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Category: Critical Care

Title: Should I Give My Patient with Septic Cardiomyopathy Fluids?

Keywords: cardiomyopathy, sepsis, septic shock, pressors, inotropes, epinephrine, norepinephrine, dobutamine (PubMed Search)

Posted: 8/12/2014 by John Greenwood, MD
Click here to contact John Greenwood, MD

 

Should I Give My Patient with Septic Cardiomyopathy Fluids? 

 

The incidence of acute LV dysfunction in septic shock is estimated to occur in 18 - 46% of patients within the first 24 hours of shock.  Unlike the "classic" pattern of cardiogenic shock where LV filling pressure is high, in septic shock there are normal or low LV filling pressures.

Three therapeutic options should be strongly considered in the patient with a septic cardiomyopathy [CM]:

  • FLUIDS:  Most patients with septic CM need fluids to restore adequate preload/afterload.  Severe vasoplegia requires volume resuscitation - even if the bedside ECHO suggests reduced contractility. Give fluids generously.
  • Vasopressors: Catecholamine supplementation (norepi) improves patient's preload & afterload, but can often unmask septic CM. Consider epinephrine as a second line agent (over vasopressin) for inotropic support.
  • Inotropes: Consider adding epinephrine (1 to 5 mcg/min) or dobutamine (start at 1-5 mcg/kg/min) to target an improved cardiac index (>2.5 L/min/m2) or ScVO2 > 70%.

 

 

 

 

 

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There are many ventilator modes to choose from, but almost every mode can be distilled down to its basic principles by understanding the “Three T's of Mechanical Ventilation”

Trigger: You must determine whether the vent or patient will trigger a mechanical breath. For example, machine-triggered breaths (a.k.a. control mode of ventilation) are used for paralyzed patients and will deliver a breath after a period of time has elapsed (e.g., if RR is 10/min, then a breath is given every 6 seconds). On the other hand, if a patient’s respiratory drive is intact (a.k.a. assist-mode) than the patient triggers the breath when the vent detects a patient induced change in airflow or airway pressure. These two modes can also be mixed together.

Target: Mechanical breaths must have a specific target, either a target airway pressure or a tidal volume. Because pressure and volume are directly related, pick the variable you want to target and the other parameter will vary depending on the patient’s intrinsic physiology. For example, if you choose to target a specific tidal volume, we may get one plateau pressure in a patient with normal lungs, but a higher plateau pressure in another patient with stiffer lungs.

Terminate: You must decide when the mechanical breath (i.e., inspiration) terminates and expiration begins. Termination occurs: 1) after a set inspiratory time has elapsed in certain pressure-targeted modes, 2) when a predefined target volume has been achieved (i.e., volume-cycled modes), or 3) when airflow has been reduced by a certain percentage (as in pressure-support ventilation; to be discussed separately)

Let’s put this all together by looking at an example: pressure control ventilation (rate = 12/min and target pressure 20cm H20). Trigger: Because this is a “control”, not assist mode, the machine will trigger a breath 12 times per minute or every 5 seconds. Target: Here we chose to have pressure be the target, so when the ventilator triggers a breath it will deliver a constant airway pressure of 20 cmH2O until we tell the vent terminate that breath. Terminate: the constant airway pressure will be turned off after a fixed period of time has elapsed; for this example we will set the inspiratory time as 1 second, then expiration begins. Now, after a few vent breaths we will observe the results of our settings and reassess; if the resulting tidal volume is lower than what we wanted, we will increase the target pressure to increase the tidal volume. If the tidal volume is higher than what we wanted, we will reduce the target pressure to reduce the tidal volume. We can also tweak the inspiratory time to manipulate the tidal volume, but this does so to a lesser degree.

Try to break down your favorite modes of ventilation using the Three T’s and see if this helps you understand vent modes better. 

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