UMEM Educational Pearls - Critical Care

Internal Jugular CVC Placement and Posterior Wall Penetration

• For a variety of reasons, many critically ill ED patients require central venous access.
• Ultrasound guidance, especially with catheters placed in the internal jugular (IJ), has become standard practice in many EDs.
• Ultrasound guidance is associated with higher success rates, reduced insertion attempts, and reduced placement failures.
• Importantly, ultrasound allows you to visualize the carotid artery which often either partially overlies or even sits direclty under the IJ.
• Recent literature, however, suggests that posterior wall penetration of the IJ, even with ultrasound guidance, may be much more common than previously thought.
• Take Home Point: Even when using ultrasound, maintain strict visualization of the needle in the IJ lumen and recognize that posterior wall penetration (into the carotid) can easily occur.

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Dexmedetomidine and the Critically Ill

• Dexmedetomidine is a newer sedative agent that is being used with increasing frequency in the critically ill
• A few pieces of information regarding dexmedetomidine:
  • highly selective alpha-2 agonist
  • produces dose-dependent sedation and anxiolysis while maintaining arousability at deep levels of sedation (hypercapnic arousal is preserved)
  • onset of action is approximately 15 minutes with peak concentration achieved in about 1 hour
  • metabolized via the liver
  • no known active or toxic metabolites
  • loading dose of 1 mcg/kg over 10 minutes followed by 0.2 - 0.7 mcg/kg/hr
• Primary side effect is bradycardia at excessive doses
• Cost is an issue when compared to propofol and midazolam

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Lorazepam Infusions

• There is some literature that propofol may be better for sedation in the mechanically ventilated patient, yet many emergency physicians still do not have access to the medication
• Lorazepam infusions are frequently used in many EDs for sedation of the mechanically ventilated patient
• Patients receiving continuous infusions of lorazepam are at risk for propylene glycol toxicity
• Propylene glycol toxicity primarily causes a metabolic acidosis and acute tubular necrosis
• Critically ill patients with renal or hepatic dysfunction are at increased risk of toxicity
• Monitoring propylene glycol levels are impractical
• Rather, check the osmol gap: a gap > 10 - 15 reflects significany propylene glycol accumulation
• Hemodialysis effectively removes propylene glycol

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The Cuff Leak Test

• As many of us have undoubtedly experienced, we are now extubating patients in the ED due to prolonged lengths of stay
• Critical to extubation is determining whether laryngeal edema may be present
• Laryngeal edema, resulting in airway obstruction, is one of the most common causes of respiratory distress following extubation
• Although shown to have moderate accuracy, many use the 'cuff leak test' to determine the iikelihood of laryngeal edema
• In most studies, performance of the cuff leak test is as follows:
  • take the average of 6 serial measurements of expired tidal volume with the ETT cuff inflated
  • take the average of 6 serial measurements of expired tidal volume with the ETT cuff deflated
  • a difference of < 110 ml between averages strongly suggests the presence of laryngeal edema
• Take Home Point: patients with a cuff leak test < 110 ml are likely to have laryngeal edema and are at high risk of airway obstruction post-extubation.  It is best not to extubate these patients in the ED.

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Coagulopathy from Acute Liver Failure

• ALF is defined as
  • absence of chronic liver disease
  • acute elevation in AST/ALT accompanied by INR > 1.5
  • any degree of mental status change (encephalopathy)
  • illness less than 26 weeks duration
• The most common cause is acetaminophen toxicity
• Regarding the coagulopathy that develops with ALF:
  • FFP transfusion is not encouraged, as the volume may exacerbate cerebral edema and it has been shown to be ineffective for improving INR elevations
  • The prophylactic transfusion of platelets for extreme thrombocytopenia is also not recommended for similar reasons

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The Maintenance Phase of Therapeutic Hypothermia

Therapeutic hypothermia (TH) has become standard in the care of patients with return of spontaneous circulation from cardiac arrest.  Although the optimal duration of TH is unknown, current literature supports 12-24 hours of cooling to 32-34^oC.  As many of our critically ill patients remain in the ED for seemingly endless lengths of stay, it is likely that most emergency physicians will be managing patients with TH during the maintenance phase of cooling.  Some pearls regarding the maintenance phase:

• Metabolic and hemodynamic homeostasis is critical
• Target volume-cycled mechanical ventilation to maintain a normal pH
• Maintain a MAP > 65 mm Hg
• Maintain blood glucose between 120 - 160 mg/dL
• Frequently check and aggressively replete potassium, magnesium, and phospate

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Acute Hyponatremia and the Critically Ill

• I just left a busy ED shift during which we had a patient with altered mental status and a serum Na of 115 mmol/L.
• Recall that severe hyponatremia may present with lethargy, disorientation, agitation, nausea/vomiting, altered mental status, abnormal respirations, and seizures.
• For severe, symptomatic hyponatremia, the treatment of choice is 3% hypertonic saline
• At a rate of 100 ml/hr, the serum Na should rise approximately 2 mmol/L per hour.
• In general, the duration of treatment with hypertonic saline is based upon sign and sypmtom improvement.
• For those with more longstanding hyponatremia, serum Na should not be increased by more than 12 mmol in the first 24 hours.

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Transient Hypotension and Mortality in Sepsis

• Not surprisingly, septic ED patients with persistent hypotension despite fluid resuscitation have increased mortality.
• What about the more common scenario of septic ED patients who have a transient drop in their BP?
• Recent evidence suggests that ED patients with sepsis who have non-sustained decrease in their BP (SBP < 100 mm Hg) have a 3-fold increased risk of in-hospital mortality compared with those who maintain arterial pressure.
• Take Home Point: Any drop in BP in a septic patient, even if it responds to fluids, portends a higher mortality.  Be vigilant and aggressively resuscitate these patients.

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Heparin for Maintaining Arteral Catheter Patency ?

• Arterial catheter placement is common in many critically ill ED patients.
• Typically, a heparin solution is used in arterial catheters based on the belief that it helps to maintain catheter patency.
• In one of the most recent studies (referenced below), the use of a heparinized solution did not improve the functionality, or increase the duration of patency, of arterial catheters when compared to a saline solution.
• As the incidence of heparin-induced thrombocytopenia (HIT) continues to increase, it is worth noting that the routine use of heparin to maintain arterial catheter patency is not well supported by the literature.

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NICE-SUGAR and Glucose Control in the Critically Ill

• Hypergycemia is associated with increased morbidity and mortality in hetergeneous populations of critically ill patients.
• Over the past few years there has been great interest in aggressively controlling glucose through the use of continuous insulin infusions.
• Results of recent trials and meta-analyses, however, question the benefit of tight glucose control and highlight the marked increase in severe hypoglycemia rates.
• Recently, the results of the NICE-SUGAR study were published, the largest trial to date (6000 patients)evaluating intensive vs. conventional glucose control in the critically ill.
• Investigators found an INCREASED mortality among adults randomized to intensive glucose control
• Given the lack of benefit, potential harm, risks of severe hypoglycemia, and resource utilization, intensive glucose control should not be a therapy routinely implemented in the ED.

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Platelet Transfusions and the Critically Ill

• Current literature suggests that platelets are given too frequently and inappropriately
• Recall that approximately 50% of platelet transfusions fail to increase counts
• In addition, bacterial contamination of units is a special concern, with sepsis occurring 10x more frequently than with PRBCs
• In general, platelet transfusions in nonbleeding patients can be withheld untl the count reaches 10 x 10³/mm³
• A transfusion trigger of 50 x 10³/mm³ should be used for invasive procedures

Ultrasound of the IVC for Volume Assessment

• In a recent pearl, I discussed that a 15% variation in IVC collapsibility could be used as a marker of hypovolemia
• As a follow up and since % variation is sometimes difficult to calculate at the bedside, consider the following numbers:
  • The normal diameter of the IVC is 1.6 - 1.75 cm
  • Patients with hypovolemia typically have an IVC diameter < 0.8 - 1.0 cm
  • In general, the IVC diameter should increase 1 mm for every 100 ml of isotonic fluid

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New Perspectives on Clostridium difficile

• In the past 5 years, C.difficile infection rates have doubled and the overall disease severity appears to be worsening.
• Particularly concerning is the increase in community acquired infections in young patients without antibiotic or nosocomial exposure.
• These epidemiologic changes are likely due to a new strain of C.difficile characterized by increased virulence and quinolone resistance.
• Importantly, the efficacy of metronidazole has waned in recent years.  In fact, > 25% of patients with moderate to severe disease do not respond to metronidazole therapy.
• As a result, vancomycin has become first-line therapy for any critically ill patient with C.difficile.

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Acute Cor Pulmonale and Ventilation In the critically ill,

Acute cor pulmonale (ACP) is usually observed in the setting of massive pulmonary embolism or acute respiratory distress syndrome (ARDS). As we manage more and more critically ill patients in the ED, it is likely that you will manage patients who develop ARDS.

We have discussed in previous pearls that, especially in ARDS, using a low tidal volume and monitoring plateau pressure are key components to mechanical ventilation.

For patients with ARDS who develop ACP, consider lower plateau pressure thresholds (< 26 cm H20) and minimizing PEEP to < 8 cm H2O.

If ACP persists despite lower plateau pressures and low PEEP, consider prone position ventilation as a last resort.

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Assessing Volume Status in the Critically Ill

• In previous pearls we have discussed the many limitations of central venous pressure as an accurate marker of volume status.
• Importantly, the focus of volume assessment should be on determining which patients are likely to augment their cardiac output in response to additional IVFs, i.e. 'preload responsive'.
• Ultrasound can be used in the ED to assist in identifying which patients are preload responsive.
• In general, a 15% variation in the inferior vena cava diameter with respiration predicts response to additional fluids.

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Mechanical Ventilation and Obesity

• Obesity is defined as a BMI of 30 - 34.99 kg/m2, with class II obesity defined as 35 - 39.9 kg/m² and extreme obesity as > 40 kg/m²
• In obese patients:
  • oxygen consumption is increased with a high proportion going to the work of breathing
  • lung volumes are abnormal with reduced expiratory reserve
  • the alveolar - arterial oxygen difference is increased
  • respiratory system compliance is markedly reduced
• These changes are futher exacerbated in the supine position
• To overcome the effects of reduced compliance, higher levels of PEEP are generally needed
• In addition, higher plateau pressures may be necessary to achieve adequate tidal volumes

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Ventilation in the Brain-injured Patient

• As we have discussed in previous pearls, the ARDSnet trial forms the basis for ventilatory management in the ICU.  A primary component to current ventilatory management is the focus on maintaining lower and safer distending pressures through the use of lower tidal volumes.
• Similar to last week's pearl on the obstetric patient, these ventilatory settings may not be applicable to all patients.
• Recall that the use lower tidal volumes results in lower minute ventilation.  This leads to the accumulation of CO₂, termed permissive hypercapnia.  In general, we tolerate higher levels of CO₂ in favor of lower plateau pressures.
• For the brain-injured patient, however, increases in CO₂ may increase intracranial pressure (ICP) causing adverse effects.
• Current recommendations for mechanical ventilation in the brain-injured patient include maintaining a P_aCO₂ between 35 - 40 mm Hg.  Thus, you need to be more vigilant at following P_aCO₂ in this patient population.

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Mechanical Ventilation of the Obstetric Patient

• In previous pearls, we have discussed ventilatory settings to avoid excessive volumes and limit plateau pressures to < 30 cm H₂O
• Importantly, these settings have not be extensively evaluated in pregnant patients
• Some important pearls when ventilating the pregnant patient:
  • Avoid hyperventilation, as this adversely affects uterine blood flow
  • Optimize oxygenation to ensure adequate fetal oxygen delivery (us 100% F_iO₂)
  • In the presence of adequate oxygenation, P_aCO_s values <= 60 mm Hg do not appear to be detrimental to the fetus

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Critical Illness-Related Corticosteroid Insufficiency (CIRCI)

• CIRCI is defined as inadequate corticosteroid activity for the severity of illness of a patient
• CIRCI arises due to steroid tissue resistance and inadequate circulating levels of free cortisol
• Hypotension refractory to fluids and requirement of vasopressors is the primary manifestation of CIRCI
• In contrast to chronic adrenal insufficiency, hyponatremia and hyperkalemia are uncommon
• Consider CIRCI in all critically ill patients requiring vasopressor support

So, which critically ill patients do you treat with steroids?  Current literature suggests the indications for steroid treatment include vasopressor dependent septic shock and persistent ARDS despite supportive therapy and lung protective ventilation.  A patient who requires only an hour or two of a vasopressor while being fluid resuscitated is unlikely to benefit.  An accepted dosing schedule is hydrocortisone 50 mg IV every 6 hours.

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Early Critical Care Management of Aneurysmal SAH

• 30,000 patients per year have an SAH
• Early ED management certainly should focus on airway assessment, emergent CT scanning, continuous caridac monitoring, and serial neurologic exams
• A few other pearls regarding management:
  • Volume management - maintain euvolemia with an isotonic crystalloid fluid
  • Anticonvulsants - routine use is associated with cognitive impairment and is not recommended
  • Steroids - once used to reduce meningeal irritation, however, there is no convincing evidence of a beneficial effect.  As such, corticosteroids are no longer recommended.
  • Rebleeding - risk of rebleeding is highest in first 24 hours after initial SAH.  Definitive prevention is done by repair via surgery or endovascular coiling.  A large, prospective study found outcome was better with endovascular coiling.

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