What is MAC anesthesia?

MAC (monitored anesthesia care) aims to put the patient in deep sedation–arousable only to painful stimuli. It may be useful in situations where the patient gets too agitated with just conscious sedation, i.e., a patient undergoing colonoscopy who has severe anxiety and “fights back” on the table. MAC utilizes a cocktail of choice of propofol, midazolam, ketamine, fentanyl, etc. to achieve deep sedation. Some studies have looked at the effect of dexmedetomidine (Precedex) and found favorable outcomes and side effect profiles. MAC requires the presence of an anesthesiologist in case of an emergency where the patient has to be intubated.

This is different from conscious sedation in that the patient is only sedated enough to stop moving around on the table–asleep, but arousable. This can be given by a trained nurse. The medications of choice are usually fentanyl/midazolam (versed).

What should I know before seeing a CABG?

CABG is an open-heart procedure that re-vascularizes the coronary arteries for people who have suffered a heart attack or are at high risk for having one. See this Medscape chart for indications for CABG.

This post is about some interesting tidbits that you might see during a CABG, or that help you understand exactly what the heck the surgeon is thinking about/doing.

What is the basic procedure?

  • Sternotomy (crack!)
  • Sewing catheters into the right atrium (a catheter pumps blood from here into the machine) and ascending aorta (a catheter pumps blood into this to perfuse the body).
  • blood flows from right atrium into the machine, and back into the ascending aorta. From: Tracy Lu, https://prezi.com/avhhcs0buz5m/cardiac-devices/
  • Usually, two surgeons will be working simultaneously to procure graft vessels. After stopping the heart, they will graft vessels onto the coronaries on the surface of the heart. (WHATTTT)
  • Test vessel flow and if everything’s good, close the patient up again.
  • 0-8 (steel cord) sutures are used to close the sternum. This is why CABG patients have metal that shows up on their chest x-rays.

Why does the patient get protamine?

  • The blood is constantly heparinized to prevent clotting during CPB. Therefore, give protamine to reverse the heparin effect. (But sometimes patients can have a reaction to protamine.)

Why are there cardioversion pads in the OR?

  • When tunneling the catheter into the right atrium, you may cause atrial fibrillation by irritating or breaking the pacemaker circuitry in that region of the heart. In the case I saw, the surgeon realized this was happening when he saw an afib rhythm on the monitor and the systolic blood pressure dropped 30 mmHg. The patient was cardioverted on the table with small pads.
  • If the surgeon decides the patient had “paroxysmal afib” the patient may be put on amiodarone or a beta-blocker after the surgery.

What will I see when cardiopulmonary bypass (CPB) is started?

A heart-lung bypass machine. From: http://www.firstheartnorth.com/
A heart-lung bypass machine. From: http://www.firstheartnorth.com/
  • CPB involves slowing the heart with potassium-loaded cardioplegia solution that is given every twenty minutes. During surgery, you can see the heart shrink in size as its pumping grows weaker and weaker. It’s humbling, really.
  • The heart rate will go to zero. The pulmonary artery pressure goes to zero. The EKG flatlines. But, the blood pressure is not zero. Why? There is steady flow determined by the CPB (BP stays around 30-50 depending on how high the flow rate is…there’s no systolic/diastolic). The central venous pressure is also not zero because you do have SOME blood flow.
  • The tubes are filled with plasmoid solution to prevent air bubbles from turning into air emboli, which could be very, very bad.

How do you pick which vessel grafts to use?

The places where grafts may come from. From: Cleveland Clinic
The places where grafts may come from. From: Cleveland Clinic
  • Classically, the great saphenous vein was used. These days, surgeons try to go with arteries if possible because they last longer and have better flow.
  • The LIMA and RIMA (left and right internal mammary) are often the arteries of choice. But you can’t take out both in a diabetic or an old person who might have a lot of complications.
  • In some younger people you can use the radial artery but again, not if they’re too old or diabetic. Furthermore you want to try to use the person’s non-dominant radial artery, but you can’t use an artery that was recently used for cath access or when the person might eventually require an AV fistula (if they have chronic kidney disease).

What complications should you be wary of?

  • MI
  • air embolism
  • atrial fibrillation
  • mediastinitis
  • tamponade
  • heart perforation (!)

When to clamp an NG tube?

Looks appropriately horrified (from youtube.com)
Looks appropriately horrified (from youtube.com)

“Clamping” an NG tube is done to determine if a patient can safely have an NG tube removed. Here’s how to decide:

When the patient has had less than 200 cc of output over an 8-hour shift, you can attempt the clamping trial!

Check on the patient in 4 hours, and release the clamp and turn on suction to see how much residue comes rushing out. If the output is less than 100-200 cc  then you can remove the NG tube and start the patient on clears.

From: Flashcard Machine