UMEM Educational Pearls - Critical Care

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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Acute LV Dysfunction in the Critically Ill

• Approximately one-third of critically ill hospitalized patients develop acute LV dysfunction, most often due to a stress-induced cardiomyopathy.
• In these patients, up to 25% develop an acute dynamic LV outflow tract obstruction.
• Consider acute LV outflow tract obstruction in hypotensive patients with a new systolic ejection murmur in the left parasternal area.
• Aggressive IVFs is central to the management of these patients with LV outflow tract obstruction.

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The optimal hemoglobin concentration during critical illness is unknown. Although a liberal transfusion strategy (Hb 10-12 g/dL) was once believed to be beneficial for hemodynamics, evidence suggests targeting a conservative strategy (Hb 7-9 g/dL) does not increase mortality, while the unnecessary transfusion of blood products can cause harm (transfusion associated lung injury, infection, etc.) in the non-hemorrhaging patient. 

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Valproic Acid in Status Epilepticus

• In previous pearls, we have discussed the treatment of status epilepticus (SE) with first-line (benzodiazepines) and second-line agents (phenytoin/fosphenytoin).
• Refractory SE is defined as the failure to respond to both first- or second-line antiepileptic medications.
• Valproic acid is listed in many algorithms as a third-line agent for treating SE.
• Avoid valproic acid in refractory SE patients who have hepatic disease or dysfunction.
• Although rare, valproic acid can cause a fatal hepatotoxicity in these patients. 

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Dexmedetomidine for Sedation in Acute Neurologic Disease

• Critically Ill patients with acute neurologic disease are managed daily in the ED.
• Due to the need for frequent neurologic assessments, these patients can be challenging should they require sedation.
• Dexmedetomidine, a selective alpha-2 adrenergic receptor agonist, has emerged as an alternative to traditional sedatives (i.e. opioids and benzodiazepines).
• Dexmedetomidine provides sedation and anxiolysis, while producing little effect on level of arousal and cognitive function.  In essence, it reduces discomfort while permitting the patient to arouse for a neurologic examination.
   

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Posterior reversible encephalopathy syndrome (PRES) is a syndrome of visual loss, headache, altered mental status, and seizures, typically with severe hypertension. PRES usually occurs with hypertensive encephalopathy or ecclampsia, although cyclosporin and tacrolimus use have been implicated. 

PRES is due to a combination of endothelial damage, impaired auto-regulation and increased cerebral perfusion pressure. Classic CT and MRI findings are parietal-occipital, cerebellar, or brainstem cortical and subcortical edema. 

Early recognition and symptomatic treatment is key; IV anti-hypertensives (hypertensive encephalopathy), anti-epileptics (seizures), IV magnesium and emergent delivery (ecclampsia), and discontinuing offending medications (cyclosporin and tacrolimus).  

With treatment, partial to complete recovery is normal, although residual neurological and visual deficits may persist.

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Vancomycin Dosing in the Critically Ill Obese Patient

• Obesity related changes to drug metabolism and distribution can significantly impact the critically ill obese patient.
• Many meds can either be underdosed or overdosed depending on which body weight (ideal vs. actual) is used.
• With the increased incidence of MRSA infections, vancomycin is often included in the initial antibiotic selection for most critically ill ED patients.
• Importantly, vancomycin is one of the most studied antibiotics in obese patients.
• Recent guidelines recommend that an initial vancomycin dose of 25-30 mg/kg actual body weight be considered for any critically ill patient, with subsequent dosing dependent upon renal function and trough levels.

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The incidence and prevalence of thrombocytopenia in the ICU is poorly defined however, it has been found to be an independent predictor of death in the critically-ill. Increased mortality does not appear to be related to bleeding complications. On the other hand, survivors of critical illness tend to recover platelet faster as compared to non-survivors. 

Thrombocytopenia in the critically-ill is a marker for systemic inflammation/infection although the exact mechanisms are unknown. Common risk factors associated with thrombocytopenia in the ICU population are:

Sepsis

Renal failure

High-illness severity

Organ dysfunction

Bottom line:  Thrombocytopenia in the critically-ill is associated with increased mortality. 

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The Importance of Antibiotic Timing for Sepsis and Septic Shock

• Septic shock is perhaps the most common critical illness that emergency physicians manage.
• In several studies, delays in initiating antibiotics for patients with septic shock were the strongest predictor of mortality.
• Broad spectrum antibiotics should be administered ASAP (preferably within 60 minutes) to patients with septic shock. 
• Selection of antibiotics should be based on the presumed source, the antibiogram at your institution, and the patient's risk factors for resistant organisms.
   

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Linezolid is used for gram-positive infections resistant to conventional therapy (e.g., Vancomycin-resistant enterococcus and Methicillin Resistant Staph Aureus). Linezolid is an oxazolidinone, but more importantly it is a weak monoamine oxidase inhibitor (MAOI) and serotonin syndrome (e.g., altered mental status, neuromuscular abnormalities, autonomic instability) may occur when combined with selective serotonin re-uptake inhibitors (SSRIs) or with recent discontinuation of SSRI. 

Be aware that the following drugs can precipitate serotonin syndrome when combined with Linezolid:

Mirtazpine       Buproprion       Fentanyl

Trazodone       Buspirone         Bromocryptine

Levodopa        Lithium               Amphetamines

Cocaine           Codeine            Reserpine

Ergots               MAOI's

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Beware Trendelenburg Positioning in the Critically Ill Obese Patient

• When inserting a central venous catheter (CVC) into the internal jugular or subclavian vein, clinicians often place patients in the Trendelenburg position to increase the size of the vein.
• When possible, avoid Trendelenburg position for CVC placement in the morbidly obese patient.
• These patients can quickly deteriorate in this position due to reduced lung volumes, increased right heart pressures, decreased cardiopulmonary reserve, and the effects in intra-abdominal pressure.

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Non-Convulsive Status Epilepticus (NCSE) is generally under reported. An ICU study found 10% admissions for altered mental status (AMS) were eventually diagnosed as NCSE.

Pearls:

- Include NCSE in the AMS differential

- NCSE may occur with or without convulsive seizures

- Difficult to distinguish from a post-ictal state (14% of convulsive seizures convert to  

  NCSE)

- Reported mortality is up to 44%

Consider NCSE when:

- Seizure history / recent seizures

- Post-ictal period >1 hour

- Odd behaviors (e.g., chewing, blinking, personality change) and abnormal eye 

  movements (86% specific)

- AMS without structural, metabolic or traumatic etiology

- Patient intubated for status epilepticus 

If you are unsure but suspicious of NCSE order a STAT EEG.  Treat NCSE like a convulsive status.

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Positioning for Ventilated, Critically Ill Obese Patients

• Up to one-quarter of patients in the ICU are obese, as defined by a BMI > 35 kg/m²
• Obesity can significantly alter pulmonary physiology causing
  • reduced lung volumes
  • decreased compliance
  • abnormal ventilation to perfusion relationships
  • respiratory muscle inefficiency
• For intubated obese patients, body position can affect ventilatory management
• In the supine position, obese patients can have collapse of lung segments along with increased impedance of the diaphragm
• Elevating the head of the bed to 30-45 degrees in intubated obese patients has been shown to improve tidal volumes and lower respiratory rates.

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Ocular sonography is a fast, simple, and non-invasive tool to detect elevated intracranial pressure (ICP) by measuring the optic nerve sheath diameter (ONSD). Several studies have shown a positive correlation between increased ONSD (>5.7mm) and elevated ICP (>20mmHg).  Although ultrasound may not replace CT or MRI to diagnose the cause of the increased ICP, its use as a triage tool can expedite these tests.

The technique:

1. Use linear probe on closed eyelid.
2. Identify the optic nerve sheath.
3. Measure the optic nerve sheath, 3mm behind globe.
4. Rotate probe 90 degrees and measure again.
5. Average both diameters.

Please see the references below for more information and, as with any new technique please consult local experts prior to making clinical decisions. 

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Ventilation Pearls in the Post-Cardiac Arrest Patient

• Some ventilation pearls from the recently released 2010 AHA guidelines include:
  • Set the tidal volume to 6-8 ml/kg ideal body weight
  • Titrate minute ventilation to achieve a P_aCO₂ between 40-45 mm Hg or P_ETCO₂ between 35-40 mm Hg
  • Reduce the F_iO₂ to maintain S_pO₂ > 94%

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