A lot of people have asked what will actually happen during this upcoming surgery for Max so I will do my best to explain. He will have 2 procedures done during this surgery, the Bi-directional Glenn and the Damus-Kaye-Stansel Procedure. And once again, I am not a doctor or nurse so I know some of my terminology is incorrect and I might not explain thing perfectly but I will do my best to explain things the way I understand. Also, Max's heart is quite complicated so when I explain the procedures I will explain them in terms of a "normal" heart first and then try to relate the differences with Max's heart.
Bi-directional Glenn:
Blood circulating back to the heart is low in oxygen (blue blood) and it flows into the right Atrium through the Superior
vena cava (
SVC) or the Inferior
vena cava (
IVC). The
SVC brings blood to the heart from the head and upper extremities (arms). The
IVC brings blood to the heart from the lower extremities (legs and torso). You can see the
SVC and
IVC on the image below:

Once blood enters to the right atrium it is pumped to the right ventricle and then to the pulmonary artery which goes to the lungs. Once the blood gets to the lungs it saturates with oxygen (now it is considered red blood) and it flows back to the heart.
With the Glenn procedure the SVC will be cut and connected directly to the pulmonary artery. This means blood circulating back to the heart from the upper body will not pump through the right side of the heart, instead it will flow directly to the lungs. With blood from the SVC flowing directly to the pulmonary artery there will be less stress on the heart because it will not have to pump as much blood to the lungs. The heart diagrammed in this picture is different from Max's but you can get the general idea of the Glenn if you just look at the SVC and how it will connect to the pulmonary artery.

In a few years Max will have the Fontan procedure done which connects the IVC directly to the pulmonary artery. At that point the heart will not have any blue blood pumped through it. All blue blood flowing back to the heart from the body will go directly to the lungs. Here is a picture after the Fontan:
Max only has 1 working ventricle, his left ventricle. Right now Max's left ventricle is doing double duty because it has to pump blood to the lungs and to the body. Without any surgeries Max's left ventricle would eventually stop working because it is working way too hard. The Glenn is the first step in easing the work of the left ventricle. Like I said, in a few years Max will also have the Fontan done and that will then complete his surgeries. After the Glenn and Fontan the left ventricle will only need to pump blood to the body.
Damus-Kaye-Stansel Procedure:
For this procedure the surgeons will create a "double outlet" for the aorta. The aorta is the main artery returning blood to the body. In order to maximize that amount of blood leaving the heart with a minimal amount of effort the Damus-Kaye-Stansel (DKS) connects the pulmonary artery and aorta using a patch. That way blood can flow out of the heart directly through the aorta or through the pulmonary artery and then to the aorta. Here is a picture:
Max's aorta is connected to his non-functioning ventricle. Right now the only way blood to getting to his body is through the hole between his ventricles and then out the aorta. With the DKS Max will have blood flowing out both ventricles which again will ease the stress on his one functioning ventricle.
This surgery is pretty scary because the flow of blood in Max's heart will be redirected. Most babies his age respond well to the surgery and recover well. The hope once this surgery is complete is that Max's oxygen levels will increase and the energy required by his left ventricle will decrease. Also, if Max responds well with these 2 procedures then he will be healthy enough to wait 2-3 years at least before his next surgery, the Fontan, is needed.