Our definition of “Firehose fistula”
A “Firehose fistula” is our term for a fistula that carries more flow than is desirable for the average patient. On the bottom end, a fistula must deliver at least 600 cc per minute of flow to allow effective dialysis, and probably closer to 1000 cc/min to prevent recirculation. We know that access flows less than 600 cc/min are associated with a greater than 50 percent chance of clotting within a month. Generally, we are comfortable with fistulas that carry 1200 to 1500 cc per minute – enough to allow good dialysis, enough to keep the access patent without clotting, and low enough that they do not cause complications.
A “Firehose fistula”
“Firehose fistula” image #2
Flow measurements during a fistulogram
“Firehose fistula” image #3
Hypertrophy in the feeding artery
“Firehose fistula” image #4
Arterial hypertropy in a 110 lb patient
“Firehose fistula” image #5
An anastomosis as large as the artery allows arterialization of the fistula
We expect the veins to grow after connecting them to an artery, giving them supranormal pressures and flows, so that they will become big enough to support dialysis. Unfortunately, we do not know how to tell them to stop growing. Some fistulas grow big enough, and carry enough flow, that they cause problems (see “Firehose fistula” image #1). Flows over 2000-3000 cc/min are worrisome. Flows over 3000 cc/min deserve detailed consideration. Flows of over 4000-5000 cc/min are seen less frequently, but most often associated with symptoms. These are sometimes called “Mega-fistulas”, and when they cause obvious cardiorespiratory compromise, “Vampire fistulas”, sucking the life out of the unfortunate patient.
The diagnosis is made by clinical suspicion and ultrasound findings and confirmed by measuring the flow (“Firehose fistula” image #2).
Problems related to excessive flows
Symptoms relating to excessive flow may be due to digital or extremity ischemia, or due to the cardiovascular effects of a high-volume shunt. Classic digital ischemia (“steal”) may be present, or a more subtle and vague arm achiness or weakness.
Effects on the heart may include high output heart failure, or pulmonary hypertension, and may be hard to uncover. Many dialysis patients assume they are supposed to feel lousy, or may be unwilling to discuss their problems. Careful questioning may uncover symptoms of digital ischemia in the hand or arm, loss of vitality, exercise intolerance, fatigue, shortness of breath, or sexual dysfunction. Many patients are in denial, or unwilling to disclose their problems. The surgeon must be patient, understanding, and thorough if the truth is to be found.
Etiology of excessive flows
“Firehouse fistulas” occur when three conditions coincide:
- The feeding artery hypertrophies – normal 4-6mm brachial arteries may dilate to 8mm, 1 cm, or larger. The amount of blood that can be delivered to the fistula through these dilated arteries is huge (“Firehose fistula” images #3 and #4). Pulsatile and tender “lumps” in the arm representing kinks and hairpin turns in a hypertrophied artery may cause undue concern about “aneurysms” in the arm.
- The anastomosis is generally larger than desirable, allowing the fistula to be excessively arterialized. When the diameter of the anastomosis approaches the diameter of the feeding artery, the resistance of the anastomotic suture line is lost, and the fistula becomes an extension of the artery (“Firehose fistula” image #5). If the artery is hypertrophied, you have a “Firehose”.
- The fistula itself grows large enough to carry three, four or five liters a minute.
Most often, “Firehose fistulas” are found after a complaint of elevated venous pressures, or for complaints of aneurysmal changes.
Frequently, the narrative is that an aneurysmal and pulsatile fistula is sent to the “Access Center” for elevated venous pressures, and repeated outflow venoplasties are done over-and-over again without a durable result. An outflow stent may be placed, but it does not solve the problem. The venous pressures remain high, the fistula remains aneurysmal, and bleeding is a problem. The patient and family become frustrated. The problem is not the relative narrowing in the outflow, but excess inflow.
A routine venoplasty for excessive venous pressure would reveal unappreciated excessive inflows, only if you measure flows during the procedure. Most often, since the extra cost of measuring flows (approximately $100 per case) is not covered by Medicare or any of the other insurance companies, flows are routinely NOT measured, and patients have repeated procedures to address the complaint of elevated venous pressures without identifying the real problem. In such cases, when we re-do the fistulogram and measure the flows, flows of three, four and five liters a minute in fistulas are seen.
Sometimes, a fistula with an outflow stenosis is noted to have a high normal flow (over 1500 cc/min) at first. After venoplasty of the outflow stenosis, resistance to outflow drops and flow increases (Ohms Law – flow is proportional to inflow pressure divided by resistance. If resistance goes down, flow increases). The “after venoplasty” flow may double.
Treatment of “Firehose fistulas”
When the diagnosis is made, the patient may not be symptomatic, and not anxious to have additional procedures. In that case, the common problems are discussed, and the patient is cautioned to remember that conditions may change, and to seek advise if they do. They are also advised to discuss the condition with their cardiologist, or primary medical provider.
If they are symptomatic, a flow reduction procedure is indicated. More on flow reduction in a future post.
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