UMEM Educational Pearls - By Mike Winters

Preoxygenation in Critically Ill Patients

• Achieving adequate preoxygenation and denitrogenation prior to intubating critically ill patients can be challenging.
• Critically ill patients have physiologic alterations (i.e., derangements in oxygen consumption, anemia, reduced cardiac output, air space disease) that can markedly reduce safe apnea time.
• For patients with significant air space disease and shunt physiology, noninvasive ventilation (NIV) can decrease shunt fraction, increase functional residual capacity, improve PaO2, and lengthen safe apnea time.
• Importantly, NIV should be used for at least 3 minutes to achieve improvements in alveolar recruitment.
• It is also important to remove NIV just prior to larygnoscopy, as alveoli will begin to derecruit when NIV is removed.

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Sepsis Mimics

• Emergency physicians are well versed in the resuscitation of patients with sepsis and septic shock.
• With the recent publication of the 2016 SSC Guidelines and the emphasis in meeting various quality measures, sepsis is routinely included in the differential diagnosis of critically ill patients.
• Notwithstanding, it is important to consider other disease states that can present similarly to sepsis or septic shock.  Some of these include:
  • Anaphylaxis
  • Adrenal insufficiency
  • DKA
  • Thyroid storm
  • Toxic ingestion or withdrawal

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Epinephrine in Anaphylaxis

• Delayed administration of epinephrine for patients witih anaphylaxis is associated with increased morbidity and mortality.
• Providers are often hesitant to administered epinephrine to older patients with anaphylaxis for fear of precipitating an adverse cardiovascular event.
• A recent retrospective study of almost 500 patients demonstrated that older patients were significantly less likely to receive epinephrine, despite meeting the definition for anaphylaxis.
• Furthermore, cardiovascular complications occurred in just 9 patients, 6 of which received an excessive dose via the IV route.
• Take Home Point: There are no absolute contraindications (including age) for epinephrine in patients with anaphylaxis.  Give the initial dose IM into the anterolateral thigh.

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PaCO2 and the Post-Arrest Patient

• Alterations in PaCO2 are common during the post-arrest period and have been associated with worse patient centered outcomes.
• Hypercarbia can dilate cerebral vessels, increase cerebral blood flow, and may increase intracranial pressure.
• Conversely, hypocarbia can constrict cerebral vessels and may reduce cerebral blood flow.
• Though the current evidence is primarily limited to observational trials, a recent meta-analysis found that "normocarbia" was associated with improved hospital survival and neurologic outcome. 
• Take Home: Adjust mechanical ventilation to target normocarbia (PaCO2 or ETCO2) in the post-arrest patient.

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Mechanical Ventilation in the Obese Patient

• Obesity can result in decreased lung volumes, decreased lung and chest wall compliance, and increased work of breathing.
• Unfortunately, there is very little literature to guide the emergency physician on mechanical ventilation in obese patients.
• A recent study of intubated ED patients by Goyal, et al found that over 1 in 5 patients were ventilated with potentially injurious tidal volumes.
• Importantly, obesity increased the odds of inappropriate ventilator settings.
• In the intubated obese patient, be sure to set tidal volume based on ideal body weight and consider starting with a higher PEEP setting (i.e., 10 to 15 cm H2O).

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What Matters in Cardiac Arrest?

• Approximately 500,000 adults suffer sudden cardiac arrest each year in the United States.
• The most important components of cardiac arrest care that have been shown to improve outcomes are:
  1. High-quality CPR with little to no interruptions
  2. Defibrillation for ventricular arrhythmias
  3. Optimal post-arrest care
     • Target an SpO2 of 94-98%
     • Target an ETCO2 of 35-40 mm Hg (PaCO2 of 40-45 mm Hg)
     • Targeted temperature management
     • Early cardiac catheterization

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Dynamic LVOT Obstruction

• Recent literature has indicated that dynamic LVOT obstruction can occur in critically ill patients without hypertrophic cardiomyopathy. In fact, a recent study found that this condition may be present in many patients with septic shock.
• Risk factors for  LVOT obstruction include any condition that decreases afterload, decreases preload, or increases heart rate.
• Consider LVOT obstruction when your ultrasound demonstrates close approximation of the lateral wall and septum plus systolic anterior motion of the anterior mitral leaflet.
• The treatment of patients with dynamic LVOT obstruction includes:
  • Increasing preload with aggressive IVFs
  • Increasing afterload (phenylephrine may be a good choice)
  • Avoiding inotropes
  • Decreasing heart rate (often with esmolol)

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Takeaways

Oxygen-ICU Trial

• Recent observational trials have demonstrated an association between hyperoxia and worse outcomes in select critically ill patient populations.
• The Oxygen-ICU Trial was just published online in JAMA, and was an RCT to assess whether a conservative protocol for oxygen supplementation could improve outcomes in critically ill ICU patients compared with usual care.
• A total of 236 patients were randomized to the conservative oxgyen group (PaO2 target 70-100 mm Hg, SpO2 94-98%), whereas 244 were randomized to the usual care group (PaO2 up to 150 mm Hg, SpO2 97-100%).
• The results demonstrated that ICU mortality was lower in patients treated witih a conservative oxygen strategy, with an absolute risk reduction of 8.6%.
• Take Home Point: Be careful with the tiration of oxygen therapy and avoid hyperoxia in many of your critically ill patients.

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Pitfalls with PLR

• The passive leg raise (PLR) test has become a popular method to assess volume responsiveness in critically ill patients.
• PLR mobilizes a volume of approximately 150-300 mL and can be used in spontaneously breathing patients, those receiving positive pressure ventilation, or those with various arrhythmias. 
• In order to properly perform the PLR, you must have a method to monitor cardiac output. (See previously pearl on 7/26/16).
• Pitfall: Simply monitoring arterial blood pressure alone is not a sufficient method to assess a positive PLR.
• Pitfalls:Risks of performing a PLR include increased intracranial pressure, reduced cerebral blood flow, and decreased pulmonary compliance.

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Ketamine for RSE?

• Up to 43% of patients with status epilepticus may progress to refractory status epilepticus (RSE).
• Propofol, midazolam, and barbituates are often recommended for patients with RSE.
• Importantly, all of these medications may be limited by hypotension and respiratory depression.
• Ketamine is emerging as adjuvant therapy for patients with RSE.
• The loading dose of ketamine ranges from 0.5 to 3 mg/kg, followed by a maintenance infusion of 0.3 to 4 mg/kg/h.

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Zika Virus-associated GBS

• Zika virus has been shown to trigger Guillain-Barre Syndrome (GBS) at a rate similar to Campylobacter jejuni infections.
• In patients with Zika virus-associated GBS, neurologic deterioration has been rapid, with approximately 33% of patients developing respiratory distress.
• For patients who have required intubation, the duration of mechanical ventilation and length of ICU stay has been very long.
• Consider Zika virus-associated GBS in patients with muscle weakness, facial palsy, or paresthesias in the setting of a travel or exposure history to the virus.

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Predicting Fluid Responsiveness with ETCO2

• It is well known that almost 50% of critically ill patients do not respond to fluid resuscitaiton. For those that do not respond, indiscriminate fluid administration may be harmful.
• There is increasing emphasis on the use of dynamic markers of fluid responsiveness, namely passive leg raise (PLR), pulse pressure variation, respirophasic changes in the IVC, and many others.
• ETCO2 can also be used to assess fluid responsiveness in mechanically ventilated patients with no spontaneous respiratory effort.
• An increase in ETCO2 of at least 5% with a PLR has been shown to outperform arterial pulse pressure as a measure of fluid responsiveness.

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LVADs and RV Failure

• Acute RV failure can be seen in up to 10% of patients after LVAD implantation.
• The treatment of RV failure in the LVAD patient consists of the following:
  • Fluids: avoid aggressive fluid administration, as this can displace the septum and impair LVAD function
  • Inotropes: consider early initiation of dobutamine, milrinone, or epinephrine to augment RV function
  • Vasopressors: target a MAP higher than 60 to 70 mmHg to maintain RV perfusion pressure
• If intubated, avoid hypoxia, hypercarbia, high PEEP, and high ventilator pressures.  These can increase pulmonary vascular resistance and further worsen RV function.

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Heat Stroke

• Heat stroke is critical illness defined as a core body temperature greater than or equal to 40^oC and altered level of consciousness.
• Mortality from heat stroke can be as high as 30%.
• Numerous methods exist to rapidly cool patients below 39^oC.
• Of these methods, ice-water immersion cools patients the fastest and is highly effective in young patients with exertional heat stroke.
• There is currently insufficient evidence to routinely recommend antipyretic agents, intravascular cooling devices, body cavity lavage, or the use of ice packs in the groin/axilla/neck. In addition, dantrolene is not recommended in the treatment of heat stroke.

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Situations Where ECMO Will Likely Fail

• As many EDs and ICUs begin to develop protocols for the use of ECMO, it is important to note select conditions when this therapy is unlikely to be succesful.
  • Chronic respiratory or cardiac disease with no hope of recovery
  • OHCA with prolonged no blood flow
  • Severe aortic regurgitation
  • Type A aortic dissection
  • Refractoroy septic shock with preserved LV function
  • Stem cell transplant patients
  • Advanced age with ARDS
  • Prolonged pre-ECMO mechanical ventilation (> 7 days)
  • Center inexperienced with ECMO

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Can NIV be Used in ARDS?

• Mechanical ventilation can cause lung injury and increase patient morbidity and mortality.
• Noninvasive ventilation (NIV) is well-known to decrease intubation rates and improve patient outcome in select disease states (i.e., COPD, acute CHF).
• For patients with acute respiratory distress syndrome (ARDS), NIV may reduce the work of breathing by opening collapsed alveoli, increasing FRC, and improving oxygenation.
• To date, there are only a few RCTs that have evaluated the use of NIV in ARDS.
• Unfortunately, these trials have failed to demonstrate improved patient outcome or decreased intubation rates in patients with ARDS.
• Clinical Bottom Line: Intubate patients with ARDS who are difficult to oxygenate with standard oxygen therapy.

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Cerebral Venous Thrombosis

• Approximately 25% of patients with cerebral venous thrombosis (CVT) will experience neurologic deterioration.
• This is most commonly due to an increase in ICP that results in transtentorial herniation.
• While heparin remains the treatment of choice for CVT, consider the following alternative strategies in the acutely decompensating patient:
  • Endovascular thrombolysis
  • Mechanical thrombectomy
  • Decompressive hemicraniectomy

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Sepsis-3

• After nearly 2 decades, the definitions for sepsis and septic shock have been updated.
• Key findings from the Task Force convened by SCCM and ESICM include:
  • Sepsis
    • Definition: life-threatening organ dysfunction due to a dysregulated host response to infection
    • ICU patients: organ dysfunction is defined as an increase of 2 points or more in the Sequential Organ Failure Assessment (SOFA) score
    • ED patients: 2 or more of the following new qSOFA (quickSOFA) score may identify patients with increased mortality
      • SBP less than or equal to 100 mm Hg
      • RR greater than or equal to 22
      • Altered mental status
  • Septic Shock
    • Definition: a subset of patients with sepsis and profound circulatory, cellular, and metabolic abnormalities
    • Clinical Criteria:
      • Persistent hypotension requiring vasopressors to maintain MAP greater than or equal to 65 mm Hg despite adequate volume resuscitation
      • Lactate greater than or equal to 2 mmol/L
  • The term "severe sepsis" is no longer used

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Shock Index

• The shock index (SI) is calculated as the ratio of heart rate to systolic blood pressure and is often used in the assessment of critically ill patients.
• A SI > 0.8 has been shown to be an independent predictor of post-intubation hypotension during emergency airway management.
• Kristensen and colleagues performed a retrospective review in a single-center in Denmark to evaluate the ability of SI to predict 30-day mortality.
• In over 110,000 patients, they found a weaker association of SI with 30-day mortality in patients > 65 years of age, those taking a beta-blocker or calcium channel blocker, or those with a history of hypertension.
• Notwithstanding, a SI > 1 was a significant predictor of mortality across all patient populations and should be considered a warning of serious illness.

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