USC IM

Informed Consent

• Found on ORCHID under “imed consent.” Use this form to obtain consent and place the signed consent in patient’s chart.

Central Venous Catheters (Central lines):

• Indications: Lack of peripheral veins (h/o IVDU, chemo, thin eldery pts), inability to cannulate peripheral veins, infusion of irritant substances, infusion of potent drugs such as pressors (dopamine can be temporarily delivered peripherally; all other pressors can be delivered peripherally but there’s risk of skin necrosis), infusion of parenteral nutrition (requires dedicated port to minimize infection risk), rapid infusion (often via Cordis) of blood products (ex: in setting of active GI bleeding), rapid replacement of electrolytes, hemodynamic monitoring, temporary cardiac pacing.
• Contraindications: No absolute contraindications. Apical emphysema or bullae precludes infraclavicular or supraclavicular subclavian approaches, carotid artery aneurysm or unclear vessel anatomy on ultrasound precludes using internal jugular vein on the same side, presence of thrombus precludes use of that vessel. If coagulopathy present, consider reversing (w/FFP, vitamin K) to INR < 1.4 & giving platelets to keep > 50K.
• Complications: Pneumothorax, hemothorax, infection, arterial puncture, hematoma, venous thrombosis, air embolism, catheter embolus, thoracic duct obstruction or injury (reduced w/ right side insertion), catheter malposition, pleural effusion, nerve injury, cardiac arrhythmias, myocardial perforation & tamponade, pericardial effusion. Infection risk: Left subclavian < Right subclavian < Right IJ < Left IJ < femoral 30

Equipment:

• Central line kit (in general, choose triple lumen catheter [TLC] over single)
• Chlorehexadine; sterile saline flushes; mask, gown, bouffant cap (2); scissors, gauze; lidocaine, site rite sleeve
• Ultrasound
• Sorbaview dressing
• Sterile Gloves
• Micropuncture kit

Preparation (general advice for all central lines):

• Obtain qualified supervisor if you have not placed the required number of supervised lines
• Obtain assistant who will complete the required Central Line Checklist. The assistant is expected to stop the procedure for any safety breach (e.g., sterile field contamination, incorrect positioning). In a true emergency, checklist is not required.
• (FOR SC & IJ LINES) Place pt in Trendelenburg & turn head away from target vessel.
• (FOR SC LINES) Roll a towel & place it between shoulder blades
• Place blue chuck lining under pt’s shoulder & head to minimize blood stains to bed (nursing will appreciate this).
• (FOR IJ LINES) Identify IJ vein w/ US [ IJ vein is LATERAL to the carotid artery & is compressible. Carotid artery is pulsating & noncompressible. ]
• Scrub procedure site w/ chlorhexidine for 30 secs (2 mins if groin site). Allow to air dry - this can take up to 2 mins.
• Angle overhead telemetry monitor so you can visualize arrhythmias or evidence of pt instability
• Open Central Line kit & bundle kit, empty saline flushes into tray, open items w/ non-sterile packaging & drop their sterile contents onto tray (including ultrasound probe cover).
• GET STERILE: Gown up w/ bouffant cap, mask, gown, & gloves.
• Set up: Attach all 3 adapters to white & blue hubs. Draw up 5cc of saline & flush white, blue, & brown ports (for TLC). You use the brown port to thread the guidewire, so put the blue hub for this port piggy-backed onto the blue hub of one of the other ports; this way the hub is easily accessible on the field & not a stretch away.
• Unsecure your guidewire; test your syringes, scalpel, & needle
• Drape pt, leaving target area exposed.
• Place equipment on pt or tray in the order you will need them.
• Have someone help you put ultrasound probe cover on.
• Order STAT CXR after IJ or subclavian to confirm placement.

Infraclavicular Subclavian Vein Approach:

• Identify lateral margin of posterior belly of SCM muscles as it inserts into clavicle by placing middle finger of your non-dominant hand on sternal notch (medial end of clavicle) & thumb on lateral end of clavicle.
• Visually divide length of clavicle into thirds.
• Your needle insertion site is just lateral to middle 1/3 of clavicle & 1 cm inferior to the clavicle.
• Make a wheal w/ your anesthetic needle & advance needle medially & superiorly towards the sternal notch. Keep the needle parallel to the floor at all times. As you advance the needle, aspirate to make sure you’re not in a blood vessel & then inject lidocaine. Once you reach the periosteum, inject most of the lidocaine along the surface of the periosteum.
• Using your finder needle or actual needle, puncture the skin. Direct the needle medially & superiorly towards the suprasternal notch. Keep negative pressure by aspirating the syringe as you advance the needle.
• Advance the needle until it hits the clavicle & walk the needle vertically downward until you are able to pass the needle under the clavicle (keeping it parallel). As you pass the needle, point towards the suprasternal notch & you’ll hit the vein.
• Check to make sure the blood is dark & not red/pulsatile.
• Hold your position & gently unscrew the syringe.
• Insert the guidewire & advance it through the needle. W/ your nondominant hand, take some gauze & hold it at the needle insertion site w/ your non-dominant 4th finger while your non-dominant index finger & thumb slide the needle out over the guidewire. Hold onto your guidewire w/ your dominant hand & then transition the guidewire to your non-dominant index finger & thumb. Watch for ectopy on the cardiac monitor.
• Once the needle has been withdrawn over the guidewire, use your non-dominant index finger & thumb to hold the guidewire. REMEMBER to hold pressure at the needle insertion site w/ your 4th finger to minimize bleeding.
• Use the scalpel to make a slight knick in the skin at the site of the wire. This will allow more easy entry for the dilator & catheter.
• Insert the dilator over the wire, approximately 1-2cm into the skin. This is not to dilate the vessel, just the skin & subcutaneous tissue. Remove the dilator.
• W/ your dominant hand, insert the catheter over the guidewire. As you advance the catheter, you will need to use your non-dominant index finger & thumb to w/draw the guidewire into the catheter. The guidewire will come out of the brown port. Once this occurs, hold onto the guidewire as it protrudes out of the brown port & advance the catheter to the desired position/depth.
• In general, insert the catheter:
• 15 cm for a right sided subclavian
• 17 cm for the left sided subclavian.
• Now you may let go of pressure at the needle insertion site. Using both hands, w/draw the guidewire into its plastic casing.
• Check for function by aspirating each port w/ a half-filled saline syringe & flushing until the port is clear of blood.
• Secure your line w/ the white hub. Remember to stitch one side of the white hub, then place the blue hub on top & both the white & blue hub to the skin. Don’t be too tight w/ your 1st knot so as to avoid skin necrosis.
• If you hit the subclavian artery, remove the needle & hold pressure above & below the clavicle (pinch the clavicle).
• After placing IJ or Subclavian line:
• To rule out arterial placement send blood gas to stat lab.
• Call for STAT CXR to confirm placement and r/o PTX.
• Write in chart, OK to use central line.

[NEJM 2003;348:1123-33] Video at: http://content.nejm.org/cgi/content/full/348/12/1123/DC1

Internal Jugular Approach:

• The safest method for all pts is to use the Site Rite to visualize the vein. The vein will be collapsible, whereas carotid artery is pulsatile & non-collapsible. It is preferable to find a site where the IJ is not directly above the carotid.
• Make a wheal w/ your anesthetic needle & advance needle. Always aspirate before injecting any lidocaine.
• W/ your finder needle or actual needle angled ~ 60º (almost same angle as your SiteRite probe) & towards the ipsilateral nipple, puncture the skin. Keep negative pressure by aspirating the syringe as your advance the needle. W/ the Site Rite, you should be able to see your needle as you advance it. Check to make sure the blood is dark & not red/pulsatile.
• Hold your position & gently unscrew the syringe.
• Insert the guidewire & advance it through the needle. W/ your nondominant hand, take some gauze & hold it at the needle insertion site w/ your non-dominant 4th finger while your non-dominant index finger& thumb slides the needle out over the guidewire. Hold onto your guidewire w/ your dominant hand & then transition the guidewire to your non-dominant index finger & thumb.
• Once the needle has been withdrawn over the guidewire, use your non-dominant index finger & thumb to hold the guidewire. REMEMBER to hold pressure at the needle insertion site w/ your 4th finger to minimize bleeding.
• Make a slight knick in the skin w/ the scalpel (insert in & out, w/ blade pointing away from wire, to avoid cutting wire). This will allow dilator/catheter to more easily enter skin.
• Insert the dilator approximately 1-2 cm over the wire. You are not attempting to dilate the vessel, just the skin & subcutaneous tissue. Remove the dilator.
• W/ your dominant hand, insert the catheter over the guidewire. As you advance the catheter, you will need to use your non-dominant index finger & thumb to withdraw the guidewire into the catheter. Hold onto the guidewire as it protrudes out of the brown port & advance the catheter to desired position.
• In general (can adjust for height/size), insert the catheter:
• 16 cm for a right IJ
• 18 cm for a left IJ.
• If you think you have hit the carotid, remove needle & hold pressure 5-10 mins or until bleeding stops, then follow-up to ensure no hematoma. No need for ultrasound unless you have inserted the dilator
• IF PERFORMING W/O SITE RITE: Identify the triangle formed by the anterior & posterior bellies of the SCM muscle & the clavicle. Your insertion site is near the apex of this triangle.
• Palpate the carotid artery in the triangle & retract it medially.
• Insert the needle at a 45º angle to the skin into the triangle apex just lateral to the carotid pulsation, toward the ipsilateral nipple.
• After placing IJ or Subclavian line:
• To rule out arterial placement send blood gas to stat lab.
• Call for STAT CXR to confirm placement and r/o PTX.
• Write in chart “Ok to use central line”

[NEJM 2003;348:1123-33] Video at: http://content.nejm.org/cgi/content/full/348/12/1123/DC1

Helpful Femoral Vein Line Hints:

• Identify the pulsation of the femoral artery & pull it laterally.
• Needle insertion is just medial to the pulsation, 1 cm inferior to the inguinal ligament. Insert the catheter to the hub.
• To rule out arterial placement, one of the following must be performed: transduce CVP, estimate CVP by fluid column, or send blood gas to stat lab.

Radial Arterial Line Insertion (ICU, CCU) Equipment:

• Basic tray, Arrow-ART line (get several just in case)
• Suture (2.0 or 3.0), needle–driver, scissors (sterile)
• Chlorhexidine scrub (1 or 2), blue chuck, +/- 1% or 2% lidocaine
• Tape & arm board to stabilize/immobilize pt’s hand, +/- kerlex roll to help extend wrist
• Sterile gloves, face shield, bouffant cap
• Gauze
• Sorbaview for dressing
• Ask nurse in advance to “set up for an A-line”

Procedure:

• Perform Allen’s test to assure collateral flow. Nml response < 7 secs. Inadequate collateral flow ≥14 secs.
• Place blue chuck lining below arm. Use kerlex roll or rolled towel to place under the pt’s wrist to hyperextend the wrist & hand (may have to tape down their thumb to rail). Chloroprep wrist & get sterile, draping wrist w/ drape form basic tray.
• Palpate the radial artery w/ 2 fingertips placed 2 cm apart. If unable to palpate, consider using a Doppler
• Delineate a line between the fingertips, & insert the angiocatheter along this line at approximately a 45º angle from the skin.
• Once you get a flash of blood in the needle hub, drop the angle & advance the guidewire until you cannot go further. If you notice resistance, re-angle (as far as 90º) or carefully reposition.
• Slowly, in a twisting/pushing motion, advance the white catheter over the wire.
• W/draw the guidewire, & leave the catheter in place. REMEMBER to quickly place your thumb over the white catheter once the guidewire is removed completely to prevent arterial blood from projecting across the room!
• Attach the catheter to the transducer (nurse will often hand it to you). If good waveform, suture the catheter securely to the skin (around hub of art line).
• [NEJM 2006;354:e13] http://content.nejm.org/cgi/video/354/15/e13

Femoral Arterial Line Insertion: Equipment:

• Single lumen central line kit
• Basic tray
• Suture
• Needle driver, scissors
• Chlorhexidine (several)
• Sterile gloves
• Ask Nurse to “set up for an A-line”

Procedure:

• Identify the pulsation of the femoral artery.
• This is your insertion site. Continue as if you were inserting a central line. Requires maximum barrier, including mask, sterile gloves, sterile gown & large sterile drape.
• Attach catheter to the transducer & suture the site down.

External Jugular Line: Equipment:

• IV start kits from Clean utility (EtOH swabs, gauze, tubing, flushes)
• Chlorhexidine
• Angiocath – several 18 or 20 gauges
• Blue chuck lining

Procedure:

• EJ’s are all about prepping & positioning. It isn't a central line, so sterility isn’t required, but it’s important to keep the field clean & well lit.
• Move bed away from wall, lock it, elevate it to its highest position, & then lower head down (Trendelenberg). Wait a few secs as external jugular vessels engorge.
• Ask pt to turn their head all the way to 1 side & relax the neck muscles as much as possible. To engorge the vessels more (if pt awake), ask pt to bear down.
• Divide the distance from jaw to above clavicle & work in the middle. Don’t go too far toward the lung as any error ruins the vessel for further attempts.
• When the vessel is spotted, clean the field w/ a Chloraprep. Get the angiocath ready, get the tubing ready (flush w/ saline), leave the flush attached to the tubing (unless about to draw blood), have the Sorbaview ready, have the adherent tape ready, have gauze ready, make sure the pt is positioned on a chuck (clean bed after procedure).
• Approach the vessel w/ the 18 gauge at a 45º angle. Hold the angiocath like a pencil between your thumb & forefinger. Advance using your fingers, not the whole hand. Holding the skin tight w/ the non-dominant hand, aim for the middle of the vessel, & pierce the skin & vessel w/ the needle. If you have blood return, lower the angle of the angiocath, & using the index finger of the hand holding the needle, advance the tubing over the needle into the vessel. Hub the tube.
• Disconnect the angiocath from the assembly. Blood should spill out. Quickly grab the tubing & connect it to the hubbed angiocath tube. Flush & attempt to draw back blood.
• Secure the tubing using the adherent tape in the IV starter kit, cover the EJ w/ the sorbaview, & clean up the remaining field. You have just obtained IV access! Now write for q6h 10cc saline or 6cc heparin flush.

Ultrasound-Guided Peripheral IV: Equipment:

• IV start kits from Clean utility (EtOH swabs, gauze, tubing, flushes)
• Sorbaview dressing
• Clorhexidine (optional)
• Arrow radial artery catheters (2-3)
• SiteRite Ultrasound
• Sterile ultrasound gel
• Blue Chucks

Procedure:

• The following method is designed to access deep peripheral veins not readily accessible by traditional means. The technique does not require complete sterility (sterile gowns & gloves are NOT required).
• Raise the bed & position the pt such that you can comfortably view the supinated upper extremity both above & below the antecubital fossa.
• Prep for the IV by connecting the tubing to the 10 cc saline syringe & flushing it. Open one of the arrow catheters.
• Place a tourniquet on the proximal upper extremity & identify the veins & artery in the antecubital fossa via the ultrasound (the veins should compress, the artery pulsates).
• Track the veins proximally & distally from the fossa w/ ultrasound & identify a site where the vein does not overly the artery. It is generally easier to place the IV distal to the fossa; however, proximal works as well.
• When a suitable target vein has been found, clean the area w/ either EtOH or chlorhexidine. Apply sterile U/S gel once the site has been cleaned & confirm your position w/ the ultrasound.
• Insert the catheter into the skin at a 70º angle. Use the SiteRite to guide your needle (you should be able to see the needle enter the vein).
• Once you see the flash of venous blood, drop the angle of the arrow catheter to 30º. Unlike when placing an arterial line, do not advance the wire further than the length of the white catheter.
• While holding the remainder of the catheter stable, advance the white catheter sheath w/ a gentle twisting motion. Remove the needle & wire once the catheter sheath is hubbed. Blood should spill out of the catheter once the wire/needle assembly is removed. Quickly connect the IV tubing to the catheter. You should be able to drawback & flush the IV.
• Secure the tubing using the adherent tape in the IV starter kit, cover the PIV w/ the sorbaview, clean up the remaining field. You have just successfully placed an ultrasound-visualized, wire-guided deep peripheral IV!

Lumbar Puncture: Contraindications:

• Evidence of uncal/cerebellar herniation, markedly increased intracranial pressure, or obliteration of the 4th ventricle or basal cisterns. Usually cranial nerve abnormalities (blown pupil, papilledema) are hints. LP may be done in these pts if bacterial meningitis is strongly suspected. When in doubt & bacterial meningitis is suspected treat w/o LP. Do not wait for CT & reading!
• Platelets < 50,000, unless there is a pressing reason. For counts of <20,000, platelet transfusion is recommended prior to LP.
• When the pt is anticoagulated, anticoagulation needs to be stopped & measures of anticoagulation must be nl for at least one hour prior to the procedure. Vitamin K or Protamine should be used in anticoagulated pts. If it must be done, use a 22 gauge spinal needle.
• Back or spinal local infections as organisms can be introduced into the CSF.

Equipment:

• LP kit
• Betadine or chlorhexidine (can use either)
• Extra CSF tubes

Minimal CSF volumes needed:

• Cell count & differential 1.0 cc
• Fungal cx/Crypto Ag 0.5 cc
• Oligoclonal bands 5.0 cc
• Bacteriology 0.5 cc
• Glucose 0.3 cc
• Virology 0.5 cc
• Mycobacteria/AFB 5.0 cc
• Immuno/Meningitis 1.0 cc
• Protein 0.4 cc
• VDRL 0.5 cc
• IgG Index (for MS) 0.5 cc
• Cytopath (variable) ~3 cc
• You can often combine several of these tests together in one tube: e.g. tube #1 & tube #4 (1 cc each) for cell count & diff; tube #2 (1 cc) for protein/glucose; tube #3 (8 cc) for all of the microbiology which will later be distributed among the labs, except for VDRL which needs a separate tube. Always remember to collect 1-2 extra tubes for second thought tests & keep in fridge. Make sure all labs are ordered “STAT” so labels will print immediately. CSF for cytopath needs to be dropped off within an hour or so of the tap

Procedure:

• Position the pt either sitting on the edge of the bed leaning over a table (only if you do not need an opening pressure), or lying on their side in a tight fetal position. The key to a champagne LP is POSITIONING & a little bit of luck.
• Palpate the superior edge of the iliac crests & create a line between it & the L4-L5 area. - When performing an LP on an overweight pt in whom the iliac crest cannot be identified, ask the pt “Put your hand on your hips.” This will be the level of the top of the iliac crest. No matter how obese, people always know where their hips are. The L4-5 interspace is a common location for osteophytic disease. It is also quite a small interspace. We often use the L3-4 space (just count one space above) which is usually larger & easier to get a needle in between the spinous process.
• After prep (supplies, chlorhexidine to back, draping, etc.) & local anesthesia, insert the needle deeper, anesthetizing the periosteum.
• Now, using spinal needle, advance between the spinous processes, angling towards the umbilicus. Keep the needle parallel to the floor at all times. Keep the bevel of the needle parallel to the fibers; if pt is upright, this means bevel to the side; if pt is lying on his/her side, this means bevel up toward the ceiling.
• As you advance (usually a little more than 1/3 of the needle), w/draw the stylet periodically to check for spinal fluid. As you pass the dura, you will often feel a “pop”.
• video: http://content.nejm.org/cgi/video/355/13/e12/

Abdominal Paracentesis: Contraindications:

• Bleeding diathesis/anticoagulation. This must be considered a relative contraindication, since most pts w/ hepatic cirrhosis have an acquired coagulopathy. Consider using FFP and/or platelet transfusions if severe coagulopathy or DIC exists.
• Pregnancy, especially sec or third trimester because of the danger of puncturing the uterus.
• Known pneumoperitoneum

Equipment: Diagnostic only:

• 30 cc syringe
• Basic Tray
• Lidocaine
• Chlorhexidine
• Red top, lavender or green top tube
• Port-a-cult vial/tube

Therapeutic:

• Either
  • Caldwell (Paracentesis) needle
  • Basic tray
  • Lidocaine
  • 10 or 20cc syringe
  • Angio-cath tubing
  • Lavender or green top tube
  • Red top tube
• Or
  • Thoracentesis Kit +
  • Chlorhexidine
  • Vacuum bottles/containers

For all:

• Sterile gloves, face shields, nonsterile gowns
• Diagnostic +/- therapeutic paracentesis fluid should be sent for:
• (1) Cell count & differential (green top or lavender top, or tube from thora kit minimum 1 cc)
• (2) Gram stain & bacterial culture, as well as fungal & AFB when indicated (port-a-cult culture bottle/tube, or specimen cup)
• (3) Albumin (& send serum sample for albumin to calculate serumascites albumin gradient) (red top or tube from thora kit, min 1 cc)
• (4) Consider total protein, LDH, amylase (if you suspect pancreatitis), cholesterol (if you suspect chylous ascites) (red top or tube from thora kit)
• (5) Consider cytopath (any container, the more the better).

Procedure:

• 1) The lower quadrant approach is most often used. Place the pt in a supine position. If splenomegaly &/or hepatomegaly are present on physical exam, you should perform the paracentesis w/ ultrasound guidance.
• 2) Percuss to find the level of dullness to identify pocket of ascites. You can also send pt for an ultrasound mark, but be sure to tap as soon as possible, as ascites fluid moves. Perform paracentesis in same position pt was in when marked.
• 3) Locally anesthetize the skin w/ a wheal, then as you advance the needle, aspirate & inject lidocaine (particularly near peritoneum).
• 4) To decrease draining of fluid after removal of angiocath, you can elect to use the “Z” method in which you insert the Caldwell needle into the skin, then pull the skin caudally, then advance the needle until to you reach the ascitic fluid. REMEMBER TO KEEP NEGATIVE PRESSURE AS YOU ADVANCE THE NEEDLE. Sometimes you
• 5) Insert the needle along the anterior axillary line, lateral to the rectus sheath (halfway between umbilicus & anterior superior iliac spine) or 1-2 cm below the level of percussed dullness.
• 6) Once needle is in the fluid pocket, attach the angio-cath tubing to the needle.
• 7) Insert the other end of the angio-cath into the vacuum bottles.
• *If the fluid stops draining, try spiking another bottle (sometimes the vacuum seal is depleted) or repositioning the needle.
• Video: http://content.nejm.org/cgi/video/355/19/e21/
• Post-paracentesis albumin infusion: It is generally recommended, in large-volume paracentesis (i.e. ≥ 4L), to give 25cc of albumin (25% solution) for every 2L of ascitic fluid removed.

Thoracentesis: Indications:

• Fever w/ a pleural effusion (“Never let the sun set on an infected pleural effusion”)
• 1 cm thick effusion on US or lateral decubitus CXR w/o known cause;
• Unilateral effusion in CHF exacerbation;
• Effusions in CHF that don't resolve in 3 days w/ dieresis (75% of CHF effusions resolve w/in 48h of diuresis);
• Poor oxygenation due to unresolving effusion(s).

Equipment:

• Thoracentesis kit
• Chlorhexidine
• ABG syringe,
• Sterile gloves
• Face shield
• Gowns.
• (Thora kit tubes okay to send samples in instead of red, green & portacult)

Pre-procedure Imaging:

• Get a decub film (lie on the side of the effusion) to make sure it layers; also consider U/S to mark the tap

Post-procedure Imaging:

• Chest Xray

Laboratory Tests:

• Cell count & diff
• Gram stain +/- culture (bacteriology, virology, mycology, AFB)
• Glucose, protein*, LDH*, albumin, cholesterol, (if you suspect chylous effusion)
• pH (draw in ABG syringe & place in ice) - walked to critical care lab ASAP
• Cytopath, depending on your diagnostic concern (in any container: the more the better)
• *Send corresponding serum tests to calculate pleural fluid:serum ratios.

Procedure:

• View the CXR or thoracic CT so you know the area of interest. 46
• Place the pt in a sitting position, leaning over a table.
• Percuss out the effusion, noting the superior edge of dullness on the posterior chest wall.
• Confirm w/ auscultation / Site Rite.
• Sterilize the area & drape.
• Insert the needle at the middle of the rib just below the superior edge of the dullness in the posterior axillary line. Aim for the SUPERIOR aspect of the rib (the neuro-vascular bundle runs under the rib).
• Anesthetize the periosteum. Remember to aspirate as you inject. You will likely get pleural fluid while anesthetizing.
• Exchange the needle for thoracentesis catheter, & proceed in the same manner. Remember to keep negative pressure in your syringe as you advance the needle. If you are performing a therapeutic tap, attach the syringe & bag to the tubing. Never use vacuum bottles for thoras. Obtain an opening pressure by removing the syringe & seeing at what vertical level the fluid stops dripping. Use constant pressure on the syringe to drain fluid, then push into the bag (it’s a one way valve.) Remember to estimate pleural pressure after every 4 syringes of fluid drained. Stop before -20 cm to avoid PTX & reexpansion pulm edema.
• Tell the pt to hum as you remove the needle.
• Video: http://content.nejm.org/cgi/video/355/15/e16/