Mr. Jones is a 65-year-old man with a history of smoking, type 2 diabetes mellitus, and poorly controlled hypertension. He underwent an uncomplicated Whipple procedure 3 days ago and was transferred to the floor from the surgical ICU this morning. You are the night-float intern, and shortly after receiving sign-out, the nurse pages you to the patient’s bedside stating that she is concerned about how he is doing. On arrival, you find him sitting up in bed and leaning forward. He states that he feels a bit anxious and is having trouble catching his breath. You ask the nurse to obtain a pulse oximetry reading that demonstrates an O2 saturation of 88%. He is in obvious respiratory distress. You call for an EKG and CXR and proceed with your physical exam.
1. What are the two most likely causes of this patient’s acute decompensated heart failure?
2. Which findings in the patient’s preoperative evaluation might suggest that he would be at increased risk of postoperative CHF?
Acute Postoperative Heart Failure
Like many other things in surgery and medicine, one of the best approaches to understanding and managing a clinical condition is to go back to the underlying physiology and basic science. In heart failure, one must think about the pathophysiology of cardiogenic shock that is essentially the result of inadequate cardiac output. Cardiac output is the product of stroke volume and heart rate. While heart rate is essentially dependent on autonomic tone and underlying rhythm, stroke volume is more complex and affected by preload, afterload, and contractility. In certain situations, rhythm may affect preload. Most causes of postoperative heart failure can be attributed to a problem or imbalance in one or more of these factors (see Figure 29-1).
- Preload: This should be thought of as the amount of volume in the heart at the end of diastole, right before the heart contracts. In the case of postoperative heart failure, too much preload can overdistend the myocardium and push cardiac function to the far end of the Starling curve (see Figure 29-2). The most common cause of this is overly aggressive fluid resuscitation in the immediate postoperative period. Often, patients undergoing large operations will have a postoperative systemic inflammatory response syndrome (SIRS) response that will result in third spacing of fluid. This fluid tends to “mobilize” back into the vascular space around postoperative day 3 resulting in sudden intravascular fluid overload. Rhythm can also affect preload. This is discussed separately in the section below.
- The Frank-Starling relationship (see Figure 29-2): As preload increases, the myocardium stretches and cardiac output subsequently increases to a point where the myocardium becomes overstretched and stroke volume and cardiac output begin to decline. The #1 arrow represents the point on the curve where additional intravascular volume (preload) will augment cardiac output. ...