UMEM Educational Pearls - Critical Care

Heat stroke is hyperthermia (>41.6 Celsius / 106 Fahrenheit) plus neurologic findings (e.g., altered mental status, seizures, coma, etc.); it also causes systemic inflammation response syndrome (i.e., cytokine release), coagulation disorders (e.g., thrombosis in end organs) and tissue abnormalities (e.g., acute kidney injury and rhabdomyolysis)

Two classifications exist:

• Exertional heatstroke (young people engaged in strenuous physical activities in hot climates)
• Non-exertional heatstroke occurring in sedentary people (elderly, debilitated, or chronically-ill patients) who are unprotected from the elements (e.g., trapped in apartments during heat waves)

Treatment includes:

• Insertion of a continuous core thermometer
• Supporting ABC’s
• Cooling by at least to 0.2 degrees celsius per minute to 39 degrees (to avoid overshoot)
• Benzodiazepines for sedation, shivering, and seizures
• Antipyretics and phenytoin have not been shown beneficial
• Support and protect end-organs with particular attention to kidneys; increased risk of kidney injury from rhabdomyolysis, ischemia and systemic inflammation.

Despite the most aggressive therapy, up to 30% survivors may have permanent neurologic or multi-organ system dysfunction months to years after recovery

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Hemodynamic Optimization in the Post-Arrest Patient

• Hemodynamic instability is common in the post-cardiac arrest patient.
• While the optimal targets remain unclear, hemodynamic stabilization often consists of intravenous fluids, vasopressors, and in rare cases mechanical support, such as an intra-aortic balloon pump or left-ventricular assist device.
• Based on recent literature, current recommendations for mean arterial pressure (MAP) in the post-arrest patient range from 65-100 mm Hg.
• Depending upon the baseline blood pressure and degree of myocardial stunning, many post-arrest patients will need a higher MAP (80-100 mm Hg) in order to maintain critical perfusion pressure to vital organs such as the brain.

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Hepato-Renal Syndrome

• Hepato-renal syndrome (HRS) is the development of acute kidney injury (AKI) in patients with advanced cirrhosis.
• HRS is traditionally divided into two types based upon how quickly AKI develops:
  • Type I: a rapid decline in function in less than 2 weeks
  • Type II: a slow decline in function over weeks to months
• Type I is more likely to be seen in the ED and is often due to a precipitating event such as:
  • GI bleed
  • Spontaneous bacterial peritonitis (SBP)
  • Hypovolemia from aggressive diuresis
• In ED patients with advanced cirrhosis and new, or worsening, AKI think about HRS. 
• If suspected, look for precipitants (i.e. SBP), restore volume with IVFs, avoid nephrotoxins (IV contrast), and administer vasopressor therapy when indicated.

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Cancer patients admitted to ICUs with AKI or who develop AKI during their ICU stay have increased risk of morbidity and mortality. AKI in cancer patients is typically multi-factorial:

Causes indirectly related to malignancy

• Septic, cardiogenic, or hypovolemic shock (most common)

• Nephrotoxins:

  • Aminoglycosides

  • Contrast-induced nephropathy

  • Chemotherapy 

• Hemolytic-Uremic Syndrome

Causes directly related to malignancy

• Tumor-lysis syndrome

• Disseminated Intravascular Coagulation

• Obstruction of urinary tract by malignancy

• Multiple Myeloma of the kidney

• Hypercalcemia

Because AKI increases the already elevated morbidity and mortality in these patients, prevention (e.g., using low-osmolar IV contrast, avoiding nephrotoxins), early identification (e.g., strict attention to urine output and renal function), and aggressive treatment (e.g., early initiation of renal replacement therapy) is essential.

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AKI in the Critically Ill Cancer Patient

• Acute kidney injury (AKI) is common in the critically ill cancer patient and associated with worse outcomes.
• The incidence seems to be higher in patients with hematologic malignancies.
• Despite many different etiologies for AKI in cancer patients (tumor lysis syndrome, hypercalcemia, chemotherapeutic drugs, etc) the most common cause is sepsis, accounting for 58-65% of causes.
• Given the emphasis on early antibiotic administration in sepsis, be sure to double check the potential for nephrotoxicity of antibiotics for this patient population.  When possible, avoid nephrotoxic meds, such as aminoglycosides, that can worsen AKI.

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Bleeding associated with uremia is a spectrum, from mild cases (e.g., bruising or prolonged bleeding from venipuncture) to life-threatening (e.g., GI or intracranial bleed). The exact pathologic mechanisms are not understood, but are likely multi-factorial (e.g., dysfunctional von Willebrand’s Factor (vWF) and factor VIII, increased NO, etc.)

Besides dialysis, treatments for uremic bleeding include:

1. DDAVP (fastest)
   1. 0.3-0.4 micrograms/kg IV or SC
   2. Increases vWF and factor VIII release
   3. Advantages: Begins < 1 hour
   4. Disadvantages: Tachyphylaxis; Stored factors deplete
2. Cryoprecipitate
   1. Replaces fibrinogen, vWF, and factor VIII
   2. Advantages: Works 1-4 hours
   3. Disadvantages: transfusion reactions, infections, pulmonary edema, etc.
3. Conjugated Estrogens
   1. Unclear mechanism; possibly increases ADP and thromboxane activity
   2. 0.6 mg/kg once daily x 5 days
   3. Advantages: Short and long-term effects
   4. Disadvantages: Hot flashes (males too!)
4. Recombinant Erythropoietin (slowest)
   1. 40-150 U/kg three times weekly
   2. Multiple mechanisms
   3. Advantages: Helps anemia (common in renal failure) as well as bleeding complications.
   4. Disadvantages: Up to 7 days to observe effects

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Cardiovascular Complication of ESLD

• Patients with end-stage liver disease (ESLD) can develop a number of complications that lead to, or complicate, critical illness.
• Regarding the cardiovascular system, ESLD patients can develop:
  • Hyperdynamic vasodilated cardiovasculature: low baseline blood pressure and high cardiac output
  • "Cirrhotic cardiomyopathy": impaired systolic response to stress or altered diastolic relaxation
  • Autonomic dysfunction: reduced responsiveness to vasoconstrictors
• ESLD patients also tend to have a normal or near-normal lactate at baseline, despite lactate being cleared more slowly.
• When managing the critically ill patient with ESLD, look for signs of heart failure, expect an abnormal response to vasopressors, think about steroids for persistent shock, and don't ascribe an elevated lactate simply to impaired hepatic clearance.

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• Necrotizing enterocolitis with predilection for cecum.
• Occurs in the immunosuppressed, especially when neutropenic (<500 PMNs)
• Typically a polymicrobial infection; gram positive cocci, gram negative rods, anaerobes, and/or fungal. 
• Classically, right lower quadrant pain but can present with diffuse abdominal pain and peritoneal signs.
• CT scan with IV and PO contrast is diagnostic (see below)
• Treatment:
  • Culture and begin broad spectrum antibiotics (cover anaerobes) and antifungals (if suspected) 
  • Aggressive resuscitation
  • Surgical consult for GI perforation or clinical deterioration
• High mortality (40-50%)

TIP: Suspect when abdominal pain presents 10-14 after chemotherapy (when PMNs are lowest).

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Acute Liver Failure (ALF)

• ALF is defined as sudden and severe liver failure in a patient without preexisting liver disease.
• The clinical presentation can include altered mental status, coagulopathy, MODS, & cerebral edema.
• In the US, the most common cause of ALF is drug-induced (e.g. acetaminophen).
• Important components of the ED management of patients with ALF include:
  • Monitoring and correcting hypoglycemia (may need infusion of D20)
  • Monitoring and maintaining a normal sodium concentration
  • Volume resuscitation with isotonic crystalloids or colloids
  • Prophylactic administration of broad spectrum antibiotics (given high incidence of sepsis)
  • Consideration for continuous veno-venous hemodiafiltration (CVVHD) for severe elevations in ammonia and acidosis (even if renal function is normal)
  • Transfer to center capable of liver transplantation

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Although oral metronidazole is indicated for mild to moderate Clostridium difficile associated diarrhea, oral vancomycin should be considered first-line therapy in critically-ill patients with moderate to severe disease. Vancomycin dosing should begin at 125mg PO q6 and increased to 250mg q6 if poor enteral absorption exists. Consider adding metronidazole IV if either reduced enteral absorption or severe disease exists. 

Recently, fidaxomicin has been shown to be non-inferior to oral vancomycin in the treatment of mild to moderate C. difficile. While promising, the study population was not critically-ill and extrapolation should be avoided.

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Gastrointestinal Changes of Obesity that Complicate Critical Illness

• Obesity predisposes patients to several gastrointestinal abnormalities that can cause, or complicate, critical illness.
• Important abnormalities to keep in mind when managing a critically ill obese patient include:
  • Increased intra-abdominal pressure which predisposes to abdominal compartment syndrome
  • Increased incidence of nonalcoholic fatty liver disease which may lead to prolonged drug metabolism
  • Increased incidence of cholelithiasis which may result in pancreatitis or cholangitis

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A mortality benefit from combination antimicrobial therapy has not been clearly demonstrated in sepsis. However, when only the most severely-ill patients (i.e., septic shock) are considered in subgroup analysis, there appears to be a mortality benefit to using two antimicrobials against a suspected organism.

Combination antimicrobial therapy may reduce mortality through three mechanisms.

1. Increased probability that the causative organism will respond to at least one drug. 
2. Preventing emergence of antimicrobial resistance.
3. Two antimicrobials may act synergistically.

Always obtain appropriate cultures before initiating therapy. Although identification and susceptibility of the organism may take some time, eventually narrowing antimicrobial therapy to monotherapy in the ICU is still recommended. 

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Combination Antimicrobial Therapy for Gram (+) Bacteremia

• Bacteremia is a major cause of morbidity and mortality in the critically ill patient.
• S.aureus remains a common isolate in patients with either hospital-acquired or community-acquired bacteremia.
• In cases of suspected endocarditis due to S.aureus, traditional teaching has been to give an aminoglycoside (i.e. gentamicin) in combination with vancomycin or an antistaphylococcal penicillin.
• Importantly, there is no strong evidence to support this combination in patients with suspected S.aureus bacteremia.
• Furthermore, patients receiving the aminoglycoside combination have higher rates of renal impairment without any added clinical benefit.

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Vancomycin is often started empirically for gram-positive and MRSA coverage. Although effective and generally well-tolerated, emerging resistance and side-effect profiles limit its use in some patients. Two alternatives are Linezolid and Daptomycin.

Linezolid

• 600 mg IV every 12 hours
• No renal dosing
• Better lung penetration in pneumonia (compared to Vancomycin)
• Side effects: Serotonin Syndrome (w/ concurrent MAOIs), hypersensitivity reaction, and myelosuppresssion

Daptomycin

• 4 mg/kg IV once daily (skin/subcutaneous tissues infection), 6 mg/kg IV once daily (bacteremia or endocarditis), or 6-8mg/kg IV once daily (bacteremia with intravascular line)
• Renally dosed by altering administration frequency; no change in dose.
• NEVER use for pneumonia; pulmonary surfactant binds and inactivates drug.
• Side effects: Reversible rhabdomyolysis (requires weekly CPK levels)

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Emergency Medicine physicians are gaining experience with non-invasive ventilation (i.e., Bi-level ventilation and continuous positive-pressure ventilation) in managing respiratory distress and failure. Although NIV is commonly used across a variety of pathologies, the best data exists for use with COPD exacerbation and cardiogenic pulmonary edema (CHF, not an acute MI) 

Although other indications for NIV have been studied, the data is less robust (eg., smaller study size, weak control groups, etc.). If there are no contraindications, however, many experts still support a trial of NIV in the following populations:

• Asthma
• Severe community acquired pneumonia
• Acute lung injury / Acute Respiratory Distress Syndrome
• Chest trauma (lung contusion, rib fractures, flail chest,etc)
• Immunosuppression with acute respiratory failure
• Neuromuscular respiratory failure (eg., Myesthenia Gravis)
• Cystic Fibrosis
• Pneumocystis Jiroveci Pneumonia
• “Do not intubate” status

Failure to clinically improve during a NIV trial should prompt invasive mechanical ventilation.

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Aspiration Pneumonitis and Pneumonia

• Aspiration of low pH gastric fluid or food matter is common in critically ill patients and often underdiagnosed.
• Patients with aspiration initially develop a pneumonitis that, in some, can be complicated by bacterial pneumonia.  Up to 33% develop severe ALI/ARDS, with an associated 30% mortality rate.
• Aspiration pneumonitis presents with hypoxia and a CXR demonstrating infiltrates in the dependent portion of the lungs.  Often, the degree of respiratory distress is worse than the CXR appearance.
• Since it is challenging to differentiate aspiration pneumonia from aspiration pneumonitis, current recommendations suggest initiating empiric antibiotics with agents that have adequate Gram-negative coverage.  Routine coverage against anaerobic bacteria is not currently recommended, except in patients with severe periodontal disease and those with a lung abscess on CXR or CT.
• Despite the initial inflammatory response, steroids are not indicated for patients with aspiration.

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Many changes in pulmonary physiology occur during pregnancy. These changes are generally well tolerated but can become problematic when pathologic states arise.

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The Severely Hypoxemic ED Patient

• Most define hypoxemia as a P_aO₂ < 60 mm Hg.
• Perhaps a better definition of hypoxemia is a P_aO₂ that is associated with continued tissue hypoxia (rising lactate, low S_cvO₂), the need for vasopressor medications, or severe metabolic acidosis.
• For ED patients that remain hypoxemic despite increased F_iO₂ and high levels of PEEP, consider the following rescue therapies:
  • Recruitment maneuvers - brief periods of high PEEP (35-50 cm H₂O) or pressure-controlled breaths to reopen collapsed alveoli
  • High-frequency oscillatory ventilation - employs a high airway pressure to recruit closed alveolar segments
  • Prone positioning - believed to improve oxygenation through a redistribution of ventilation and perfusion
  • Extracorporeal membrane oxygenation

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Hemodynamic Monitoring in the Ventilated Patient

• Consider pulse pressure variation (PPV) as a method to monitor volume responsiveness in your mechanically ventilated ED patients.
• The theory behind PPV:
  • When a positive pressure breath is delivered via the ventilator, pleural pressure rises and causes a decrease in venous return, right heart filling, and right heart output.
  • Simultaneously, the positive pressure breath causes an increase in left heart filling and a decrease in left heart afterload.  This is reflected clinically as an increase in blood pressure.
  • Within a few beats, the decreased right heart output is transmitted to the left heart resulting in a decrease in blood pressure during expiration.
• Patients who are volume depleted can have significant differences in blood pressure between inspiration and expiration - i.e. a large variation in pulse pressure.
• PPV values > 12% have been shown to identify patients who are volume responsive.
• Importantly, PPV works best in vented patients who have no spontaneous respiratory effort, are in sinus rhythm, and receiving 8 ml/kg tidal volumes.

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