UMEM Educational Pearls - Critical Care

AKI and the Critically Ill

• Acute kidney injury (AKI) is an abrupt reduction in kidney function causing disturbances in electrolytes, fluids, and acid-base balance.
• AKI occurs in up to 67% of critically ill patients and is associated with a substantial increase in morbidity and mortality.
• AKI in the critically ill is often multifactorial and most commonly due to sepsis, hypovolemia, medications, and hemodynamic instability.
• Medications account for up to 20% of AKI in the critically ill.
• Common medications that cause, or exacerbate AKI, in the critically ill include:
  • NSAIDS
  • Antibiotics (aminoglycosides, amphotericin, acyclovir)
  • ACE-inhibitors
  • Radiocontrast dye
• Take Home Point:  AKI is common in our critically ill ED patients and, whenever possible, avoid nephrotoxic medications that can result in additional injury.

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Appropriate Antimicrobial Therapy for Sepsis

• In previous pearls, we have discussed the importance of early antimicrobial administration for patients with sepsis.
• In patients with septic shock, current guidelines recommend empiric antimicrobial therapy be initiated within 1 hour.
• Equally as important as early administration is the selection of appropriate antimicrobial therapy (i.e. choosing an antibiotic that is effective against the presumed or identified pathogen).
• In one of the most recent studies, investigators found a 5-fold reduction in survival (52% vs. 10.3%) between patients who received appropriate antibiotics compared to those who received antibiotics that were ineffective against the identified pathogen.
• In fact, choosing the right antibiotic is one of the strongest factors associated with patient outcome in sepsis.
• When selecting empiric antimicrobial therapy for patients with septic shock consider patient history, co-morbidities, the clinical site of infection, and local resistance data.

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Red blood cell transfusion in the critically ill patient has been and continues to be surrounded by controversy and lack of hard data.  Up to 90 percent of transfusions in the ICU are given for anemia, an indication which is least supported by the data.  The joint taskforce of EAST, ACCM and SCCM has published a clinical practice guideline which outlines recommendations and rationale.  These recommendations are summarized as follows:

• RBC transfusion is indicated for patients with evidence of hemorrhagic shock.
   
• RBC transfusion may be indicated for patients with acute hemorrhage and hemodynamic instability or inadequate DO2.
   
• Transfusion triggers for Hb<7 are as effective as those for Hb<10 in hemodynamically stable critically ill patients, except for those with AMI or USA.
   
• Hb used as a sole trigger is not advised; transfusion decisions should be based on intravascular volume status, evidence of shock, duration and extent of anemia, and cardiopulmonary physiologic parameters.
   
• Consider RBC transfusion if Hb<7 in resuscitated critically ill patients, patients who are being mechanically ventilated or critically ill patients with stable cardiac disease.
   
• RBC transfusion should not be considered as an absolute method to improve tissue oxygen consumption in critically ill patients.
   
• RBC transfusion may be beneficial in patients with acute coronary syndromes with Hb<8 on hospital admission.

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Early Recognition of Shock

• Early recognition, and thus early treatment, of shock is crucial in reducing morbidity and mortality in the critically ill ED patient.
• Traditionally, the diagnosis of shock has been based on vital sign abnormalities such as tachycardia, tachypnea, oliguria, etc.
• Vital sign abnormalities have been shown to be insensitive markers of shock in the critically ill.
• The Shock Index, although clearly not 100% sensitive, can assist in the detection of shock compared to heart rate and blood pressure alone.
• Shock Index is simply heart rate divided by systolic blood pressure.
• Values greater than 0.9 are abnormal and suggest markedly impaired cardiac output.

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Calciphylaxis is a rare disorder caused by systemic arteriolar calcification which leads to ischemia and necrosis.  It is characterized by painful ischemic necrotic lesions on adipose tissue areas such as abdomen, buttock and thighs.  This commonly occurs in patients with ESRD on hemodialysis or after transplant, but can also occur with other patients, such as those with hyperparathyroidism.

Diagnosis is made clinically, with the help of a skin biopsy as needed.  Differential diagnosis includes cholesterol embolization, warfarin necrosis, cryoglobulinemia, cellulitis and vasculitis.  There are no specific laboratory findings, although patients may manifest elevated PTH, phosphorous, calcium or calcium x phosphorous product. 

Infection is usually the cause of the high mortality rate of this condition, which has a reported mortality of 46%, or 80% if ulceration is present.

Treatment includes local wound care, trauma avoidance, electrolyte correction, increased frequency of dialysis or parathyroidectomy as needed.  Surgical debridement is controversial; as the risk of infection may outweigh the benefit in terms of outcome. 

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There is no prospective, randomized study to elucidate propofol’s effect on the critically ill patient. By definition, Propofol Infusion Syndrome (PRIS) has the following characteristics:

• acute bradycardia progressing to asystole
• lipemic plasma
• fatty liver enlargement
• metabolic acidosis with negative base excess > 10
• rhabdomyolysis or myoglobinuria

It has been thought that PRIS was limited to patients with prolonged use, but we now know that this is not necessarily true.

It has been shown that PRIS is more likely with the following risk factors:

• <19 years old
• male
• received a vasopressor
• cardiac manifestations (including Brugada Syndrome)
• metabolic acidosis
• renal failure
• hypotension
• rhabdomyolysis
• dyslipidemia

The treatment for suspected PRIS is:

• Stop infusion
• Hemodynamic stabilization
• Carbohydrate substitution
• Hemodialysis or hemofiltration
• ECMO as necessary

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Severe Acute Pancreatitis

• Patients with acute pancreatitis are considered to have severe acute pancreatitis (SAP) if they manifest signs of shock, respiratory failure, renal faliure, or GI bleeding.
• SAP is almost universally associated with pulmonary dysfunction, typically manifested as an S_pO₂ < 90% in the first few hours of illness.
• In fact, ARDS develops in at least one-third of patients with SAP.
• Take Home Point: Pay close attention to the patient with acute pancreatitis and a low pulse oximetry reading, as many will rapidly deteriorate from ARDS. In those who deteriorate, early intubation with implementation of lung protective ventilatory strategies is indicated.

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Hypoxemia in the Intubated Asthmatic

• Intubating and mechanically ventilating the asthmatic patient can be frought with potential complications that markedly increase morbidity and mortality.
• In the ventilated asthmatic who develops persistent or worsening hypoxemia, evaluate the patient for the following complications:
  • right main stem intubation
  • pneumothorax
  • ETT displacement
  • ETT obstruction
  • air leak around the ETT
  • gastric distention (decreases respiratory system compliance)
  • ventilator malfunction
  • progressive bronchospasm

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This week's pearl is courtesy of Dr. Evie Marcolini.  Thanks Evie!

Abdominal Compartment Syndrome in Burn Patients

• Patients who receive > 250 ml/kg of fluid in the the 24 hours after burn injury will most likely require abdominal decompression.
• In light of this, bladder pressure monitoring should be part of your practice in resuscitation of the patient with >30% TBSA burns.
• The simple act of placing the bladder probe will increase awareness of the possibility of ACS and prompt measurement of abdominal compartment pressures. 
• ACS can be treated with decompressive laparotomy, or in some cases, percutaneous abdominal decompression.

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Extracorporeal Membrane Oxygenation

• In last week's pearl pertaining to critically ill patients with H1N1, I mentioned the use of ECMO as a potentially life-sustaining treatment for refractory respiratory failure.
• Essentially, ECMO removes blood from the patient and circulates it through an artificial lung with a pump.  For patients with respiratory failure, this is usually accomplished via cannulation of the femoral and internal jugular veins.
• General guidelines to consider ECMO in severe, refractory respiratory failure include:
  • P_aO₂ / F_iO₂ ratio < 100 on 100% F_iO₂ or A-a gradient > 600 mm Hg
  • Age < 65 years
  • No known contraindication to anticoagulation
  • Lack of significant co-morbidities (due to prolonged recovery after weaning from ECMO)

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Critically Ill Patients with H1N1

• Three recent reports published online in the Journal of the Americal Medical Association (JAMA) detail the potential problems of H1N1 infection in the critically ill.
• The three studies (Mexico, Canada, Australia/New Zealand) seem to have recurring themes:
  • shock and multisystem organ failure were common
  • many were healthy, young adults who developed rapid respiratory failure
  • hypoxemia was prolonged and often refractory to conventional modes of mechanical ventilation
• Newer modes of ventilation and therapies were required to treat refractory hypoxemia.  These included high frequency oscillatory ventilation, prone positioning, neuromuscular blockade, nitric oxide, and extracorporeal membrane oxygenation.
• Take Home Point: Involve your intensivist early in the management of ED patients with respiratory failure and suspected H1N1 infection, as non-conventional methods of ventilation may be needed to treat hypoxemia.

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Damage Control Resuscitation

• "Damage control resucitation" is a term that is used to describe the resuscitation strategy of damage control surgical techniques and the tolerance of moderate hypotension, prevention of hypothermia, temporization of acidosis, and the correction of coagulopathy in the severly injured trauma patient.
• In terms of the "lethal triad", it is important to avoid interventions that may cause, or worsen, acidosis.
• A preventable and easily correctable cause of acidosis is hypoventilation.
• In the intubated trauma patient, pay close attention to the minute ventilation to avoid hypoventilation and the accumulation of CO₂.

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Mechanically Ventilated ED Patients and Secretion Mobilization

• As more of our intubated ED patients remain in the ED for longer periods of time, some may develop problems with secretion management (thick/copious amounts of sputum).
• The preferred method of secretion mobilization is heated humidification.
• If you anticipate the duration of intubation to be at least 96 hours, have your respiratory therapist set up a heated humidifier.
• Commonly, clinicians and nurses will instill 5-10 ml of isotonic saline to thin secretions.
• The use of saline to thin secretions is unsupported by the literature and carries a small risk of dislodging the bacterial laden biofilm that covers the endotracheal tube.

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Complications of Resuscitation

• CPR, defibrillation, endotracheal intubation, and cannulation of peripheral and central veins are common procedures during resuscitation of cardiac arrest patients
• Although not obvious immediately, complications from these procedures can develop and manifest several hours after successful return of spontaneous circulation
• Not surprisingly, the most common complications are rib and sternal fractures
• Additional complications to recall include:
  • tracheal mucosal lesions (almost 20%)
  • retropharyngeal bleeding
  • liver/spleen injuries
  • rhabdomyolysis (post-defibrillation)
  • air embolism (central venous access)
  • gastric rupture (very rare; due to continuous air insufflation into the stomach)

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The Supraclavicular Subclavian Central Venous Cathetherization

• Central venous catheters (CVCs) are routinely placed in critically ill ED patients.
• The literature has clearly demonstrated that CVCs placed in the subclavian vein have lower risks of infection and thrombosis when compared to the femoral and internal jugular vein routes.
• Although we routinely teach the infraclavicular approach, don't forget the subclavian vein can also be cannulated via the supraclavicular approach.
• Some pearls on the supraclavicular approach:
  • Identify the clavisternomastoid angle: formed by the lateral head of the sternocleidomastoid muscle (SCM) and the clavicle
  • Insert the needle 1 cm lateral to the lateral head of the SCM and 1 cm posterior to the clavicle
  • Direct the needle at a 45-degree angle aimed at the contralateral nipple
  • The right side is preferred due to a more direct route to the SVC and a lower pleural dome (decreasing the incidence of pneumothorax)
  • Place the patient in Trendelenburg position and aim the bevel of the needle downward

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Pulse Pressure Variation and Volume Responsiveness

• Assessing volume status in the critically ill is extremely challenging, as up to 50% of patients do not respond to a fluid challenge (i.e. increase their stroke volume/cardiac output with additional IVFs).
• As highlighted in previous pearls, traditional measurements such as blood pressure, heart rate, and urine output are extremely variable and inaccurate in determining volume status.
• Pulse pressure variation is an emerging method of volume assessment that, to date, seems even better than ultrasound measurements of the IVC.
• To calculate PPV, print out a tracing from an arterial line that captures both inspiration and expiration use the following formula:
  • ΔPP = 100 × (PPmax - PPmin)/[(PPmax + PPmin)/2]
• Values > 13% indicate that the patient is likely on the ascending portion of their Starling Curve and will augment their cardiac output with additional IVFs.
• Note that arrhythmias and spontaneous breathing can affect measurements, thus patients should be mechanically ventilated and well sedated when measuring PPV.

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High Frequency Oscillatory Ventilation (HFOV)

• Although traditionally used in neonates, HFOV is becoming increasingly popular for select adult patients with ALI/ARDS.
• Benefits of HFOV include:
  • use of smaller tidal volumes than conventional ventilation
  • maintains alveoli open at a relatively constant airway pressure thereby preventing atelectrauma
  • improves ventilation/perfusion
• Indications for use of HFOV are when:
  • conventional ventilator settings require an F_iO₂ > 70% and PEEP > 14 cm H₂O OR
  • pH < 7.25 despite higher tidal volumes and plateau pressures > 30 cm H₂O
• Key variables, along with suggested initial settings, for HFOV include:
  • Frequency: 4 - 7 Hertz
  • Amplitude: 70 - 90 cm H₂O
  • Mean airway pressure: 5 cm H₂O greater than last plateau pressure measured on conventional setting
  • Bias flow: 40 L/min
  • Inspiratory time: 33%
  • F_iO₂: 100%

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Airway Pressure Release Ventilation (APRV)

• As emergency physicians manage mechanically ventilated patients for longer periods of time, it is important to be familiar with newer, alternative modes of ventilation
• APRV is an open-lung ventilation strategy designed to provide oxygenation benefits while augmenting ventilation for patients with low compliance lung disease
• APRV has been described as CPAP with brief, regular, intermittent releases in airway pressure - essentially cycling between two CPAP levels
• The degree of ventilatory support is determined by the duration at each of the 2 CPAP levels and the distending pressure
• The 5 major parameters of APRV, along with suggested initial settings include:
  • P_high (high pressure): set at desired plateau pressure
  • T_high (time spent at the high pressure): 4-6 seconds
  • P_low (low pressure): 0 cm H₂O
  • T_low (time spent at the low pressure): 0.6-0.8 seconds
  • F_iO₂: 100%
• The pressure gradient between P_high and P_low, T_low, and the patient's spontaneous minute ventilation are the primary determinants of alveolar ventilation
• When using APRV, be sure to optimize intravascular volume to offset the decrease in venous return that results from prolonged positive intrathoracic pressure

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Antibiotic Dosing in the Critically Ill Septic Patient

• Current international guidelines recommend that intravenous antibiotics begin within one hour for those with severe sepsis and septic shock.
• Equally as important as choosing the right antimicrobial is choosing the correct dose at the right dosing schedule.
• In fact, there is evidence to suggest improved outcomes in patients given continous antimicrobial infusions (over hours) rather than intermittent bolus dosing (over minutes).
• An important cause of underdosing in critically ill patients, especially those with sepsis, is hypoalbuminemia.
• It is believed that by increasing the unbound fraction, hypoalbuminemia promotes more extensive distribution and greater renal clearance, thereby increasing the risk of underdosing.
• Take Home Point: Critically ill septic patients with hypoalbuminemia require higher dosages, or alternative regimens, to ensure appropriate antimicrobial coverage.

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