Tuesday, March 23, 2021

Hypotension in the Post-Anesthesia Care Unit Case File

Posted By: Medical Group - 3/23/2021 Post Author : Medical Group Post Date : Tuesday, March 23, 2021 Post Time : 3/23/2021
Hypotension in the Post-Anesthesia Care Unit Case File
Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 51
A 62-year-old woman has just arrived in the post-anesthesia care unit (PACU) following an attempted declotting and subsequent revision of a left forearm arteriovenous (AV) dialysis fistula under general anesthesia. She had presented to the emergency department earlier today for evaluation after difficulty with reduced flow on her dialysis run this morning. Notably, on her first set of vital signs in the PACU, her blood pressure is 70/48 mm Hg, heart rate is 95 bpm, SaO2 is 98%, and she is afebrile. The patient is somewhat somnolent, but moaning. Intraoperatively, estimated blood loss was 500 mL and she received 1.1 L of normal saline. The patient’s medical history is significant for endstage renal disease (ESRD), chronic anemia secondary to ESRD, hypertension, coronary artery disease with several prior myocardial infarctions, type 2 diabetes mellitus, and lower extremity peripheral vascular disease. Her medications include insulin, atenolol, vitamin B complex (Nephrocaps), iron, vitamin C, and aspirin 81 mg. She has a history of smoking 1 pack/day for 30 years. She does not drink alcohol. Preoperative laboratory values were significant for Hct 24%, K 3.8 mEq/L, Cr 4.4 mg/dL, and an INR of 1.1. Her ECG showed evidence of an old inferior MI, but was otherwise normal. On examination, the patient weighs 64 kg and is 5 ft, 2 in tall. Auscultation of her heart reveals a regular heart rate, normal S1 and S2, no S3 or S4. Auscultation of her lungs reveals a few bibasilar rales, but her respiratory rate is normal.

➤ What are the three most common physiologic causes of hypotension in the PACU?

➤ How would you evaluate this patient for an acute coronary syndrome?

➤ How would you monitor this patient in the PACU?


ANSWERS TO CASE 51:
Hypotension in the Post-Anesthesia Care Unit
Summary: A 62-year-old woman with hypotension (blood pressure 70/48 mm Hg) in the PACU following a left forearm AV fistula revision. Her past medical history is remarkable for ESRD, diabetes mellitus, CAD, and peripheral vascular disease. Her estimated blood loss intraoperatively was 500 mL and she received 1.1 L of normal saline.

➤ Three most common physiologic causes of hypotension in the PACU: Hypovolemia, left ventricular dysfunction, and excessive arterial vasodilation.

➤ Evaluation for acute coronary syndrome: A history, physical examination, vital signs, 12-lead ECG, chest x-ray, troponin, creatine kinase and myoglobin, CBC, and basic chemistry panel.

➤ Monitored in PACU: The patient should receive an ECG, noninvasive blood pressure cuff, pulse oximetry, and an arterial line.


ANALYSIS

Objectives
1. Appreciate the role of the PACU following an anesthetic.
2. Understand the most common physiologic causes of hypotension in the PACU and create a working differential diagnosis.
3. Describe the evaluation and management of acute coronary syndrome.


Considerations
Interventions for the hypotension are shaped by the differential diagnosis. Our patient, described above, has multiple factors which are concerning. Her history of diabetes and CAD with prior infarctions raises the issue of acute coronary syndrome. Her preoperative anemia combined with the intraoperative blood loss, and possible recent dialysis suggest that hypovolemia may be a significant factor. Yet the rales on examination in the PACU suggest that she may have some degree of congestive failure, or alternatively, atelectasis.

The first concern is to increase the patient’s (already compromised) myocardial oxygen supply. Oxygen should be administered, if not already in progress. Second, her blood pressure should be increased. Given her previous dialysis, the fact that she was NPO, and judicious fluid administration during the procedure, the most likely diagnosis is hypovolemia. If the rales reflected hypervolemia, then some evidence of hypoxemia would quite possibly have been observed. Moreover, hypotension to this degree, in and of itself, can cause cardiac ischemia. The administration of a small amount of phenylephrine, 50 to 100 μg, should increase her blood pressure and augment both myocardial and cerebral perfusion. Once her volume resuscitation has begun, focus should turn toward evaluating the possible presence of an acute coronary syndrome. Almost simultaneously, a 12-lead ECG should be obtained to check for ischemia, and biochemical markers drawn.

Given her persistent hypotension and the need for closely monitoring blood pressure during medication interventions, an arterial line should be considered. If fluid is required, the resuscitation fluid of choice in this patient is cross-matched blood, as she began the case anemic and lost an additional 500 mL intraoperatively.


APPROACH TO
Patients in the Post-Anesthesia Care Unit

CLINICAL APPROACH
The post-anesthesia care unit (PACU) is a relatively recent development in the history of anesthesia and surgical care. Prior to the Second World War, patients were often managed either back on their hospital ward or in the intensive care unit following an anesthetic. As surgical volume and complexity increased, the need for a specialized area for patients to recover from anesthesia became critical. Issues following anesthetic emergence, including airway management and hemodynamic changes, are managed in the PACU by a specialized group of nursing staff working in conjunction with the anesthesiologists (Feeley and Macario, 2005).

Upon admission to the PACU, patients emerging from anesthesia are placed on standard ASA monitors identical to the operating room. These include pulse oximetry, ECG, and blood pressure monitors. Oxygen and suction are available for each patient. Resuscitation equipment is available, including a “crash cart” with medications, a defibrillator, and airway management devices.

Once the initial vital signs have been obtained, the anesthesiologist must provide a full report of the anesthetic to the PACU nurse. Details from the surgery as well as the patient’s pre-existing medical conditions, medications, allergies, fluids and blood administered, and any complications that may have been encountered should be included. The anesthesiologist should also provide the nurse with areas of concern specific to the particular patient’s recovery.

Patients are monitored in the PACU until they are stable for transfer to a regular medical/surgical ward, the intensive care unit, or the day surgery discharge unit for patients having ambulatory surgical procedures. A number of scales exist for determining a patient’s readiness for discharge from the PACU. The most common scale used is the Modified Aldrete Score (Table 51–1), which consists of five items, each with a possible score of 0, 1, or 2. Patients achieving a score of 8 or higher are suitable for discharge to a ward, while those with scores of 7 or less should either be observed longer or transferred to an intensive care unit.


Hypotension
During the recovery period, hypotension is a common urgent issue to be encountered, second only to airway management. It is important to quickly recognize the various factors that may contribute to hypotension, develop a differential diagnosis, and enact appropriate management. The general approach for evaluation of hypotension involves evaluating preload, contractility, and afterload. To expedite the creation of a differential, knowledge of the patient’s pre-existing medical conditions along with the intraoperative events and anesthetic management must all be considered.

Table 51–1 THE MODIFIED ALDRETE SCORE

Activity

Able to move four extremities on command

Able to move two extremities voluntarily or on command

Unable to move extremities voluntarily or on command

2

1

0

Respiration

Able to breathe deeply and cough freely

Dyspnea or limited breathing

Apneic

2

1

0

Circulation

BP ± 20% of pre-anesthetic level

BP ± 20%-49% of pre-anesthetic level

BP ± 50% of pre-anesthetic level

2

1

0

Consciousness

Fully awake

Arousable on calling

Not responding

2

1

0

O2 saturation

Able to maintain O2 saturation >92% on room air

Needs O2 inhalation to maintain O2 saturation >90%

O2 saturation <90% even with O2 supplementation

2

1

0

From Aldrete, 1995.

Hypovolemia is a common finding in patients following anesthesia and frequently contributes to a diminished preload. Patients typically present for elective surgery having fasted for at least the preceding 8 hours. Intraoperative fluid management focuses on repleting the pre-existing deficit, meeting maintenance fluid requirements, and finally replacing losses. These losses take two forms: insensible fluid losses and frank bleeding. Patients lose fluid volume from insensible losses, either through evaporation from large tissue exposures or third spacing of fluid into the extracellular compartment of the body. Bleeding may be easy to appreciate in large incisions such as cardiac operations, but can be quite difficult to assess in other settings such as transurethral prostate resections. Pneumothorax, pulmonary embolus, or cardiac tamponade are less frequent causes of a reduced preload.

Left ventricular dysfunction may have a variety of causes. Hypoxia, hypercarbia, and hypothermia can worsen myocardial function. Arrhythmias may lead to poor filling of the ventricle (with supraventricular arrhythmias) versus intrinsic ventricular dysfunction, such as polymorphic ventricular tachycardia. Acute coronary ischemia can impair myocardial left ventricular contraction. Volume overload may worsen an impaired ventricle, by exceeding the optimal point on the Starling curve. Medications such as beta blockers and calcium channel blockers, can reduce cardiac output by reducing heart rate. Inhalation agents, in particular older agents such as halothane, also had myocardial depressant effects.

Afterload reduction in the form of vasodilation must also be considered. Residual anesthetic, either from a neuraxial block or a general anesthetic, may continue to cause hypotension into the recovery period. Intraoperative medications should be considered, especially antihypertensives or opioids that may have been given in response to surgical stimulus. There is a case report of a patient with persistent postoperative hypotension after this surgeon placed 2% nitroglycerin ointment along wound edges to promote vascular blood flow for wound healing (Siddiqi, 2004). Anaphylaxis should also be considered as it may occur as a result of a reaction to one of the intraoperative medications or as a result of contact with latex or other allergens. Lastly, sepsis can cause severe vasodilatation and result in significant hypotension.

The likelihood of whether each of the above items is going to rise or fall on the differential diagnosis is based on the patient’s history combined with the type of surgery and their immediate postoperative state. An otherwise healthy lymphoma patient who underwent a tunneled central venous catheter that complains of new shortness of breath and rapidly worsening hypotension will have a very different differential than a patient with heart failure who just underwent a 4-hour bowel resection.


Acute Coronary Syndrome
Acute coronary syndrome (ACS) describes a wide spectrum of heart diseases ranging from stable coronary disease without angina to unstable angina, acute myocardial infarction, and even sudden death. Awake patients may describe anginal symptoms in the recovery room, but in the diabetic patient, these symptoms may be absent. Other symptoms such as nausea, dyspnea, or alteration in mental status may be present.

After performing a physical examination, one should consider other diagnostic tools. Continuous ECG monitoring is performed in both the operating room and the PACU. ST-segment or T-wave changes may be early signs of ACS. A 12-lead ECG should be obtained for greater diagnostic resolution since the detection of ST-T wave changes is unreliable on a monitor. A chest radiograph should be obtained to exclude other intrathoracic causes of hypotension and ECG changes, and to also evaluate the cardiac size and silhouette. Serum biochemical markers of myocardial injury should be assayed with an order for troponin, myoglobin, and CK-MB.

If the ACS is quite early on, a single negative result from a single marker does not exclude the diagnosis. The markers should be followed over the next 6 to 12 hours. Using these three markers in combination was shown to have 100% sensitivity and 100% negative predictive power for acute myocardial infarction in the emergency department setting (Ng, 2001). Echocardiography provides a very sensitive measure of regional wall motion abnormalities, which may correspond to any underlying ischemia.

The initial management of ACS focuses on increasing oxygen supply to the myocardium and reducing myocardial metabolic requirements. The patient should be given oxygen. Aspirin should be given either orally or rectally depending on the patient’s surgery and mental status. Nitrates should be considered, though in the setting of profound hypotension, they may not be well-tolerated. Untreated pain, either from the surgery or from angina, should be treated to reduce catecholamine stress response. Likewise, beta blockade may be considered, though its use may be relatively contraindicated in the setting of severe congestive failure, profound bradycardia, or severe hypotension. Patients with a history of severe asthma may also be poor candidates for beta-blocker therapy. A cardiologist should be contacted as soon as ACS is suspected, as studies have shown that better outcomes are associated with an earlier revascularization intervention, either via thrombolytics or percutaneous coronary intervention (PCI). Patients that are in the immediate postoperative state are generally not candidates for thrombolytic therapy due to the risk of bleeding from the surgical sites. The final focus should be stabilizing the patient for potential transfer to the cardiac catheterization laboratory for PCI.


Comprehension Questions

51.1. A 33-year-old healthy man presented for ACL reconstruction following a skiing injury. He received a femoral nerve block and an uneventful general anesthetic with an LMA. Following his 2-hour operation, he was transferred to the PACU, where he was observed for 45 minutes. His nurse reports that his oxygen saturation is 98% on room air. His blood pressure is 130/79 mm Hg (preoperation 145/80 mm Hg). He is awake and asking questions about his operation. His respiratory rate is normal an unlabored. He is unable to extend his lower leg at the knee. Which of the following is his Aldrete score?
A. 1
B. 4
C. 7
D. 9

51.2. A 44-year-old woman presents for elective total abdominal hysterectomy. She has a history of migraines, GERD, and significant uterine fibroids. She exercises four to five times each week. She
received a spinal anesthetic and light sedation during the operation. Operative events were notable for an estimated blood loss of 1 L. She received 1.5 L of crystalloid intraoperatively. On arrival in
the PACU, the RN notes a blood pressure of 78/33 mm Hg with a heart rate of 118 bpm. Which of the following is the most likely cause of her hypotension?
A. Hypovolemia from her preoperative fast and intraoperative blood loss
B. Persistent spinal anesthesia-mediated autonomic dysfunction
C. Acute myocardial infarction
D. Persistent postoperative bleeding

51.3. Which of the following is the first therapeutic intervention for a patient with possible acute coronary syndrome in the PACU following a colon resection?
A. Give aspirin.
B. Start nitroglycerin.
C. Administer oxygen.
D. Administer alteplase.


ANSWERS
51.1. D. The Aldrete score was developed to help determine which patients may be safely transferred from the recovery room to the ward or the day surgery unit. The score contains five components: activity, respiration, circulation, saturation, and consciousness. Each of the five components receives a score of 0 to 2 with 2 being best. The 33-year-old patient received a femoral nerve block, which will impair movement of his lower extremity and result in an activity score of 1. All of his other components received a 2, thus giving a score of 9. He is ready for discharge.

51.2. A. When approaching a patient with hypotension in the recovery room, it is important to quickly form an accurate differential diagnosis to avoid spending time on issues that are unlikely to be responsible for the problem. One must consider the patient’s preoperative condition as well as intraoperative events when developing the differential. The 44-year-old woman was on fast since the night before surgery, had a significant intraoperative blood loss, and received a minimal amount of fluids. She also received a spinal anesthetic, which can have persistent autonomic effects into the recovery period. However, by the recovery period, the spinal is beginning to recede, and is not a likely explanation for newly found hypotension. Postoperative bleeding is always a possibility and early contact with the surgeon should be considered. But this is not “first” on the list. The appropriate treatment for this patient is fluid resuscitation and pressors. In this otherwise active patient with few comorbidities, option C, an acute coronary syndrome would be quite unlikely.

51.3. C. Acute coronary syndrome can present in the immediate postoperative period and require immediate management by the anesthesiologist and PACU nurse. The initial treatment for suspected acute coronary syndrome emphasizes promotion of myocardial oxygen supply and reduction in myocardial oxygen demand, so oxygen is administered. Next, restoring any abnormal hemodynamics also facilitates maintenance of coronary perfusion. Hypotension can reduce myocardial blood flow; while conversely, hypertension and tachycardia increase the heart’s demand for oxygen. Nitroglycerine should be considered, although it may be poorly tolerated in a patient who is hypertensive. Option D, alteplase is a tissue plasminogen activator produced by recombinant DNA technology. It is indicated for acute myocardial infarction, acute ischemic stroke, and pulmonary embolism. Alteplase is contraindicated in the setting of recent major surgery due to the risk of massive hemorrhage.


Clinical Pearls
➤ The PACU is a specialized unit designed for the recovery of patients following anesthesia and surgery. Patients are observed until they have recovered their mental status, achieved hemodynamic stability, and are achieving adequate oxygenation with minimal supplementation.

➤ The Modified Aldrete Score is a common scale from 0 to 10 used to determine whether a patient meets criteria for discharge from the PACU to the ward or the day surgery unit. Scores of 8 to 10 suggest the patient will do well outside of the PACU setting.

➤ Acute coronary syndrome (ACS) describes a wide range of cardiac events ranging from stable coronary artery disease without angina to acute myocardial infarction or even sudden cardiac death.When ACS is encountered in the PACU, the anesthesiologist must focus on therapies to improve myocardial oxygen supply.However, a cardiologist should be contacted as early as possible for the potential need for percutaneuos coronary intervention as postsurgical patients are not candidates for intravenous thrombolytics.

References

Aldrete JA. The post-anesthesia recovery score revisited. J Clin Anesthesiol. 1995;7:89-91. Feeley TW, Macario A. The postanesthesia care unit. In: Miller RD, ed. Miller’s Anesthesia. 6th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2005. 

Ng SM, Krishnaswamy P, Morissey R, et al. Ninety-minute accelerated critical pathway for chest pain evaluation. Am J Cardiol. 2001;88:403. 

Siddiqi M, Marco AP, Gorp CV. Postoperative hypotension from topical use of 2% nitroglycerin ointment after a total knee replacement procedure. J Clin Anesthesiol. 2004;16(1):77-78.

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