UMEM Educational Pearls - Critical Care

Propofol Infusion Syndrome

• Many of us are now using propofol for sedation in our critically ill patients
• Although a great drug, it is important to be aware of "propofol infusion syndrome" (PIS)
• Risk factors for PIS include young age, severe CNS or pulmonary illness, and exogenous catecholamine administration
• Clinical features include: unexplained metabolic acidosis, rhabdomyolysis, hyperlipidemia, hepatomegaly, and cardiovascular instability
• Pearl: It is reported that the development of coved ST elevations in V1-V3 (similar to Brugada syndrome) may be the first sign of cardiac instability with PIS

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Intra-aortic balloon pump counterpulsation

• It is possible that at some point in your career you may need to place an intra-aortic balloon pump (IABP) to temporarily stabilize a patient wth cardiogenic shock
• Optimal performance of the IABP is dependent upon proper positioning in the thoracic aorta
• Traditional teaching has been to insert the IABP via the femoral artery and advance to the level of the aortic knob (via CXR)
• A recent study suggests that using the aortic knob to position the IABP may result in occlusion of the left subclavian artery in a substantial portion of patients (16% in the study)
• Placing the IABP 2 cm above the carina may be a more reliable landmark that using the aortic knob

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Bedside Glucometry in the Critically Ill

• Hyperglycemia is common in critically ill patients
• Depending on the underlying condition (e.g. DKA), you may be instituting an insulin drip and following frequent fingersticks in the ED
• A recent study indicates that bedside glucose values may not accurately reflect serum values in approximately 15% of critically ill patients
• This is more likely to occur in patients with poor peripheral perfusion
• Take Home Point: Interpret bedside glucose readings with caution especially in hypotensive critically ill patients

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Vasopressin for Sepsis

• The VASST trial was recently published in NEJM comparing vasopressin vs. norepinephrine for septic shock
• Unfortunately, there are some issues with the study which I will clarify/expand upon in the next Critical Care Literature Update
• There was a trend towards improved mortality in the vasopressin group receiving low doses of norepinephrine (5 - 14 mcg/min)
• Take Home Point: If you are thinking about adding vasopressin to norepinephrine in patients wtih refractory septic shock, do it early.  In other words, add vasopressin when you find yourself titrating norepinephrine doses to 6, 7, 8 mcg/min

ACTH Stimulation Test

• With the recent publication of the CORTICUS study (along with others), it is becoming clear that the ACTH stimulation test is not reliable in identifying patients with adrenal insufficiency
• In fact, the test is no longer recommended in the evaluation of patients with severe sepsis/septic shock
• Furthermore, if you decide to give steroids to the patient with severe sepsis/septic shock, there is no need to use dexamethasone for fear of "disrupting the ACTH stim test" (hydrocortisone is the preferred agent)

Dialysis Disequilibrium Syndrome (DDS)

• Although typically seen in ESRD patients who are being initiated on hemodialysis, DDS can be seen in the critically ill
• Critically ill patients at risk for DDS include recent CVA, head trauma, subdural hematoma, hyponatremia,, hypertensive emergency, and hepatic encephalopathy
• Mild cases are characterized by restlessness, nausea, vomiting, headache, disorientation, and tremors
• More severe symptoms include seizures and coma
• The exact pathogenesis is debated but centers around acute cerebral edema
• Treatment of DDS primarily centers around manipulation of hemodialysis
• For the EP: patients with DDS presenting with seizures can be treated by rapidly increasing plasma osmolality with either hypertonic saline or mannitol (12.5 gms)  

Guidewire length for central venous catheterization

• 18 cm should be considered the upper limit of guidewire insertion during internal jugular or subclavian central venous catheterization (16cm for right IJ)
• There is the Peres Nomogram for determining guidewire length, which is based on patient height
• However, height is less reliable in predicting safe guidewire length

Potassium Phosphate ("K-phos")

Over the weekend, I had a patient with Dr. Scott that had a phosphate of 0.8 mmol/L.  Phosphate < 1.0 mmol/L is an indication for IV repletion.  IV repletion involves giving potassium phosphate.  An important clinical question, therefore, is how much potassium does the patient actually get?

• 1 mmol of IV phosphate delivers 1.46 mEq of potassium
• Recommended infusion rate is 5 mmol/hr
• Rapid infusion may lead to severe hypocalcemia, hypotension, acute renal failure, hypomagnesemia, and hypernatremia

Coagulopathy and Trauma

• When resuscitating a trauma patient recall that the "lethal triad" consists of acidosis, hypothermia, and coagulopathy
• Coagulopathy is induced by the combination of direct loss of clotting factors, consumption in clot formation, dilutional due to crystalloid administration, acidosis, and hypothermia
• When giving PRBCs in trauma resuscitation, don't forget to give FFP
• The ratio to remember is 1U of FFP for every 2U PRBCs

Aspiration Pneumonitis

• Aspiration pneumonitis is an acute lung injury resulting from the aspiration of gastric contents
• It is an inflammatory condition rather than infectious
• Despite the inflammation, corticosteroids have been shown to have no effect on mortality
• Aspiration pneumonitis is self limited
• Antibiotics are generally held for 24 to 48 hours
• When to consider empiric broad spectrum antibiotics in the ED:  Gastric contents are sterile in most patients.  Patients who may have colonization/contamination of gastric contents are more likely to progress from pneumonitis to pneumonia.  Consider empiric antibiotics for aspiration pneumonitis in the patient with SBO, gastroparesis, those receiving enteral feeds through a G- or J-tube, and those on chronic PPI's/antacids.

D-Dimer in the Critically Ill

• Diagnosis of VTE in the critically ill can be challenging and these patients are at high risk for the disease
• Only 3.6% - 16% of critically ill patients have a negative d-dimer, regardless of the presence or absence of VTE
• Even in patients with low pretest probability, d-dimer in the critically ill is of limited utility

Crowther MA, et al. Neither baseline tests of molecular hypercoagulability nor D-dimer levels predict deep venous thrombosis in critically ill medical-surgical patients. Intensive Care Med 2005;31(1):48-55.

• The use of central venous pressure as a monitor of volume status remains very controversial in the critical care literature
• Remember that CVP can be affected by many conditions
• Important conditions that affect the accuracy of CVP include: 
  • right ventricular disease
  • tricuspid valve disease
  • pericardial disease
  • changes in intrathoracic pressure (PEEP, positive pressure ventilation) 
  • arrhythmias
  • reference level of the transducer

Spontaneous Pneumomediastinum

• Spontaneous pneumomediastinum is largely a benign disease typically seen in young males ages 18-21 years
• It is typically caused by activities that increase alveolar pressure such as coughing, sneezing, vomiting, inhalational drug use, and Valsalva maneuver
• The most common symptoms include chest pain and dyspnea; chest pain is usually centrally located, may radiate to the neck, and may be worse with inspiration
• CT scan is the "gold standard"; CXR is a good place to start but it is normal in up to 30% of cases
• The vast majority of patients do not require admission or supplemental O₂
• Advise patients to avoid strenuous activity until after symptom resolution (typically takes about 2 weeks)
• Any patient with a fever, elevated WBC count, hemodynamic instability, severe dysphagia or odynophagia should first be evaluated for infectious mediastinitis or esophageal perforation (spont. pneumomediastinum is a diagnosis of exclusion in these patients)

Invasive Arterial Pressure Monitoring - Complications

In critically ill patients with hemodynamic instability we often place arterial catheters to continuously monitor mean arterial pressure.  Since we frequently use the radial artery for cannulation, it is important to know the complications associated with these catheters.  Scheer et al performed, perhaps, the largest review of complications of peripheral arterial catheters.  The results:

• Radial arterial catheters
  • 19,617 cannulations reviewed
  • temporary occlusions - 19.7%
  • hematoma - 14.4%
  • serious ischemic damage - 0.09%
  • pseudoaneurysm - 0.09%
  • sepsis - 0.13%

Pearl: Although permanent ischemic damage is rare, when placing a radial artery catheter use the non-dominant hand.

Scheer BV, Perel A, Pfeiffer UJ. Clinical review: Complications and risk factors of peripheral arterial catheters used for haemodynamic monitoring in anaesthesia and intensive care medicine. Crit Care 2002;6:198-204.

Pitfalls in pulse oximetry in the critically ill

• Pulse oximeters are calibrated by manufacturers using data collected from healthy volunteers
• In general, pulse oximeters are accurate  within +/- 2% for sats > 70%
• In the critically ill, however, the accuracy of pulse oximetry diminishes when sats drop below 90%
• Also, there may be a significant lag time between a hypoxic event and the actual display of the event - most commonly seen in low flow states, hypotension, mild hypothermia, and when using vasoactive medications
• Prolonged lag times are more common with finger probes
• Pitfall - pulse oximetry does not provide any assessment regarding ventilation (P_aCO₂) or acid-base status (pH) - it is simply an estimate of arterial oxgyen saturation
• Pearl: anemia does not affect the accuracy of pulse oximetry

Mean Arterial Pressure

• Arterial pressure is the input pressure for organ perfusion
• Mean arterial pressure (MAP) is the best physiologic estimate of perfusion pressure
• MAP is less subject to measurement variability than SBP and DBP
• MAP remains relatively constant when measured at different sites throughout the arterial circuit
• MAP of 60 mmHg is considered the autoregulatory threshold below which perfusion becomes compromised
• Goal: maintain MAP > 65 mmHg
• There is no proven value to achieving a MAP higher that 65 mmHg.  In fact, there is some literature to support that if you try and drive the MAP higher, patients do worse

Pulmonary Hypertension Pearls

We are beginning to see more and more patients with pulmonary hypertension (PAH),  many of whom are on continuous IV infusions of new medications.  With that in mind, here are a few pearls:

• The most common causes of rapid deterioration in patients with PAH are: catheter occlusion/pump malfunction, pneumonia, indwelling catheter infection, RV ischemia, PE, and GI bleeding
• Hypotension is usually due to worsening RV failure and less likely to hypovolemia
• If a catheter occlusion or pump failure is found, the drug should be restarted as soon as possible through an alternative access (including peripheral)
• Calcium channel blockers, a prior treatment for PAH, are no longer indicated and should not be given

Adrenal Insufficiency in the Critically Ill

• Adrenal insufficiency (AI) is estimated to occur in up to 30% of critically ill patients
• The most common causes of AI in the critically ill are SIRS and sepsis
• In most cases of critically ill patients, AI is functional (i.e relative) - the adrenal response is insufficient to respond to the degree of stress
• Diagnostic clues include hyponatremia, hyperkalemia, hypoglycemia (rare), and hemodynamic instability despite IVFs and vasopressors
• Although still controversial, most feel that AI is present in critically ill patients with either a basal cortisol < 15 mcg/dl, an increase in < 9 mcg/dl after ACTH stimulation, or a random cortisol < 25 mcg/dl
• IV hydrocortisone, methylprednisolone, and dexamethasone are the 3 glucocorticoids most commonly administered
• Hydrocortisone is usually the preferred agent because it is the synthetic equivalent of cortisol (and has both glucocorticoid and mineralocorticoid activity)

Critical Care Monitoring - End-Tidal CO₂

• End-tidal CO₂ (ETCO₂) monitoring is used to verify ETT placement, monitor procedural sedation, traumatic brain injury, and to estimate prognosis during cardiopulmonary resuscitation
• ETCO₂ concentration typically underestimates P_aCO₂ by 4-5 mmHg in healthy non-intubated patients
• This relationship is less reliable in critically ill patients secondary to shunt, altered alveolar dead space, and inadequate ventilation
• While a low ETCO₂ value is less useful in the critically ill, a high value almost always correlates with an equal or higher P_aCO₂ value
• This can be useful when monitoring conditions such as status asthmaticus, CHF, or increased ICPs in which a high ETCO₂ may signal the need for additional aggressive treatment

Unilateral Pulmonary Edema

• unilateral pulmonary edema is a well recognized and well documented entity
• although there are several causes, the most likely scenarios for EPs are severe mitral valve insufficiency, aortic dissection (with compression of the pulmonary artery), airway obstruction, and heroin use
• even though radiology will read the xray as likely pneumonia, if the story/exam fit with edema then treat as such