2. What is the diagnosis of exclusion for all patients with postoperative hypotension?
Hypotension in the Immediate Postoperative Period
Postoperative hypotension is common and potentially serious, with a variety of underlying causes, including hypovolemia, cardiac failure, or sepsis. Because of the possibility of serious underlying pathology, the patient with postoperative hypotension should be rapidly evaluated and a diligent search for potentially life-threatening causes of hypotension should follow.
In general, a systolic blood pressure (SBP) less than 100 mm Hg or a mean arterial pressure (MAP) less than 65 mm Hg is considered hypotensive. That said, hypotension is best thought of as a decreased blood pressure rather than a low blood pressure—the difference between the patient’s current and baseline blood pressures is the most critical factor. For example, a blood pressure measurement of 95/43 mm Hg after an uncomplicated laparoscopic appendectomy in an otherwise healthy 25-year-old female whose SBP is normally no greater than 105 mm Hg is probably not hypotension. On the other hand, a blood pressure of 125/64 mm Hg after an uncomplicated laparoscopic appendectomy in a 65-year-old, homeless male who has had many years of untreated kidney disease and whose preoperative blood pressure was 212/103 mm Hg probably is hypotension. While the blood pressure reading of 125/64 mm Hg is “normal” in the conventional sense, the male patient’s tissues and peripheral vasculature have probably compensated for a long history of hypertension and therefore this blood pressure may be too low to provide adequate oxygen delivery to his tissues.
Evaluation of the hypotensive patient starts with urgently ruling out hemorrhage as a cause of the patient’s hypotension. If hemorrhage cannot be ruled out by history and physical exam, a workup including a CBC should be initiated while empiric treatment is begun.
For those patients in whom you suspect hemorrhage, proper management includes infusion of 1 L of 0.9 NS or LR. The patient’s blood pressure should respond soon after receiving the bolus, with an adequate response defined as a return to the patient’s baseline blood pressure and/or improvement in urine output. If the patient’s response is not adequate, a second 1 L bolus should be given, but suspicion for other, more life-threatening causes for the patient’s hypotension should be high and rapid escalation of care should be initiated. This would include notifying the senior resident, possibly an ICU transfer, and a more extensive workup.
Hypovolemia is common in the postoperative patient and is a result of intraoperative fluid losses, ongoing sensible and insensible fluid losses, and fluid shifts. This is the most likely cause of Mr. Patel’s hypotension. He has several factors contributing to an overall net negative fluid balance: inadequate maintenance fluids, NPO, and an open abdominal operation. The next step in managing Mr. Patel’s hypovolemia should start with a 1 L bolus of resuscitative fluid—again 0.9% normal saline or lactated Ringer’s solution. If the patient has congestive heart failure, then you should give fluid more judiciously, generally 250 to 500 cm3 at a time. An adequate response should include resolution of tachycardia and a return to the patient’s baseline blood pressure. If an adequate response is not seen after the first fluid bolus, a repeat 1 L bolus should be given. You may also consider raising the maintenance IV fluid rate.
While hypovolemia is the most common cause of postoperative hypotension, analgesia is another common cause. Narcotics cause peripheral vasodilation and may also be accompanied by a depressed mental status and decreased sympathetic tone. Proper management of this patient depends on the severity of hypotension, but withholding additional narcotic administration until the patient’s blood pressure returns to normal is the first step. In an emergency, reversal agents such as naloxone are also indicated. Epidural analgesia is another common cause of postoperative hypotension because it contains a solution of local anesthetic (eg, bupivacaine) by itself or mixed with a narcotic (eg, hydromorphone or fentanyl). These medications can anesthetize the efferent sympathetics of the spinal cord and cause peripheral vasodilation and therefore hypotension. Initial management includes decreasing or temporarily stopping the infusion of pain medication as well as judicious administration of IV fluids. You should alert your Anesthesia colleagues, who can readjust the infusion when the hypotension has resolved.
While less common, postoperative β-blockade can be yet another cause of postoperative hypotension. Note that, in contradistinction to hypovolemia and analgesics, β-blockers not only decrease blood pressure but also prevent normal reflex tachycardia. Once again, initial treatment depends on the severity of the hypotension. Options include a 1 L bolus and, in extreme cases, reversal of β-blockade with glucagon.
Lastly, you should consider a primary cardiac cause of hypotension—even if it is rarer than the other etiologies. Surgical procedures are associated with significantly increased cardiac demand, and patients with underlying coronary artery disease are at increased risk of myocardial infarction in the immediate postoperative period. If the heart attack is significant, the reduction in cardiac output will result in shock and most likely hypotension. If you suspect a cardiac cause of the hypotension, you should obtain an EKG while you begin treatment and notify your senior resident.
In summary, hypotension is a common issue in the postoperative patient and it will be something you will come across frequently. For severe cases, treatment and diagnosis should proceed in parallel, generally with the administration of fluid and collection of at least a CBC and an EKG. Most of the time, however, the cause of the hypotension will be nonhemorrhagic hypovolemia or a drug effect. In those cases, a 1 L bolus is both a therapeutic and a diagnostic maneuver and should be your initial response for all patients without underlying heart failure. You should follow up to ensure that the patient did indeed respond. If the patient’s blood pressure does not respond to this intervention, you must broaden your differential, consider escalation of care, and notify your senior resident.
3. What is the most likely cause of this patient’s hypotension?