Pocketbook of Clinical IR (eBook)

1 The Basics of IR

Alex Lionberg, Shantanu Warhadpande, and Joshua Pinter

Being a trainee in IR can be intimidating. The specialty sees a wide variety of pathology, and performs over a hundred different procedures. The equipment and imaging techniques used require some time to get acclimated to. All of this can be overwhelming. However, with some fundamental knowledge and the tips outlined in this book, you can hit the ground running on your first IR rotation.

When it comes to learning IR procedures, there’s no substitute for getting your feet wet and participating in cases. While it is important to get as much procedural experience as you can, you’ll also need to be attentive to the clinical responsibilities expected of you as a trainee on the service. This includes answering the phone, fielding consults, and interfacing with other clinical teams. You should take full ownership of patients scheduled for procedures during the day, postprocedure patients, and the new consults as they come in.

Your day starts with reviewing the scheduled cases. This includes reviewing the indication for the procedure, any relevant imaging available, and any pertinent progress notes. You’ll learn quickly that IR is a fast-paced specialty. Preparing ahead of time will make the day run much smoother.

Consults for IR can come at any time; some are urgent or emergent, while others may be routine. A good habit to get into is to follow the same set of steps for each new consult so that you don’t overlook any important details (▸Table 1.1).

1.1 The IR Consult

What Is the Reason for the Consult?

Determine the nature of the clinical problem and the expectations of the referring service. There should be a conversation where you gather from the referring team the underlying clinical problem, the interventions that have been performed thus far, and the urgency. You’ll need to make sure you understand what they are hoping to gain from the IR procedure. If the consult is for a diagnostic procedure, what information is being sought? Good communication will ensure that both the IR team and the referring service have an understanding of what will be done.

Does the Patient Need to Be Seen Immediately?

If an urgent consult is requested, gather the bare bones information (clinical history, hemodynamic status, laboratory values, imaging), but don’t delay in notifying your attending. He or she may decide to bring the patient straight to IR. If the consult is nonurgent, you have time to perform a more thorough work-up before staffing the case. An ideal presentation will include the clinical history, imaging findings, your final assessment, and a proposed plan of action.

Table 1.1 Consult checklist

Are There Alternatives to IR Treatment That Are More Appropriate, and Have They Already Been Attempted?

It is important to have some foundational knowledge of the diseases commonly treated by IR, and how the IR procedure fits into the bigger picture. Unfortunately, this is not always cut and dry. Many IR procedures do not fall neatly into an algorithm. A good understanding of the clinical context is required to determine if and when IR should get involved.

Is the Procedure Technically Feasible?

If an IR intervention is potentially indicated, review the relevant imaging available to you. As radiologists, our expertise in imaging interpretation allows us to learn a great deal about the patient before we even meet them. We can plan out a procedural approach, identify anatomic variants, and look for potential pitfalls. As a trainee, you may not have a strong foundation in imaging, so it’s okay to ask your senior residents or an attending for help.

Are There Any Safety Concerns That Need to Be Addressed?

If the conditions above are met, the next step is completing a basic preprocedure work-up. This can be time consuming, but it is important to review before officially approving a procedure. This is part of what separates clinicians from technicians.

Bleeding Risk

Bleeding risk should be assessed for any patient undergoing an interventional procedure. Society of Interventional Radiology (SIR) guidelines stratify procedures into low, moderate, and high risk of bleeding. Low-risk procedures are those which are either minimally traumatic with small access devices, or those in which access is obtained into a space in which bleeding would be easily detected and controlled. Examples include paracentesis, drainage catheter exchange, superficial biopsies, peripherally inserted central catheter (PICC) placement, and IVC filter placement. Moderate-risk procedures include the majority of interventional procedures, including most arterial and venous interventions, and tunneled line placement. High-risk procedures are those in which a solid organ is traversed, including transjugular intrahepatic portosystemic shunt (TIPS), biliary interventions, and nephrostomy access.

The two laboratory tests that are most important in determining the bleeding risk are platelets and international normalized ratio (INR). For all procedures, platelets need to be greater than 50,000. For low-risk procedures, the INR needs to be below 2. For moderate- and high-risk procedures, the INR needs to be below 1.5 (▸Table 1.2).

The number of patients on long-term anticoagulation has increased in recent years, and there are now a wide variety of medications used for this purpose (see Chapter 9). The preprocedural assessment should look into any history of bleeding or clotting disorders, as well as review use of warfarin, heparin, antiplatelet agents, or the newer factor Xa or direct thrombin inhibitors. Screening laboratory tests should include INR, partial thromboplastin time (PTT), and platelets (+/− anti-Xa levels). Note that PTT/INR takes into account only a portion of the overall clotting cascade.

Thromboelastography (TEG) is a relatively quick blood test that measures the functionality of the entire blood clotting cascade (platelet function, clot formation, fibrin cross-linking, etc.). TEG is presented as a graph of clot formation and fibrinolysis (called a TEG tracing), with several parameters measured, each corresponding to different parts of the coagulation cascade. In IR, the two patient populations that you’ll see getting a TEG include bleeding patients, (especially in the setting of traumatic or obstetric bleeds), and cirrhotics. In the setting of trauma, coagulopathy is one of the components of the “deadly triad” (along with hypothermia and metabolic acidosis). In cirrhotics, poor synthetic function of the liver leads to low levels of coagulation factors. Abnormal PTT/INR in these patients only tells one part of the story. By identifying the specific dysfunctional components of the coagulation cascade, a TEG study can determine which types of blood products should be transfused. The details of interpreting TEGs is beyond what you need to know. For now, simply know when and how it can be used.

For those patients on anticoagulation, reversal agents may be necessary in order to expedite an IR procedure. These include protamine sulfate for heparin, idarucizumab for dabigatran, and vitamin K for warfarin. In some cases, reversal is accomplished with the use of blood products. Options include fresh frozen plasma (FFP), prothrombin complex concentrate (PCC), platelets, and cryoprecipitate (▸Table 1.3).

Table 1.2 IR procedure risk stratification based on the bleeding risk

Table 1.3 Reversal agents for common anticoagulants