Hemodynamic Monitoring in the Operating Room 

Updated: May 08, 2018
  • Author: Gregory J Blair, MD; Chief Editor: Sheela Pai Cole, MD  more...
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Practice Essentials

Key action points with regard to hemodynamic monitoring in the operating room (OR) include the following:

  • Know the indications for selecting invasive hemodynamic monitoring modalities for perioperative care
  • Understand the risks and benefits of invasive hemodynamic monitoring devices
  • Utilize an evidence-based approach to deciding between noninvasive and invasive hemodynamic monitoring
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Problem

The goal of hemodynamic monitoring in the OR is to ensure adequate tissue perfusion and oxygen delivery, as well as to predict and detect hemodynamic instability when it occurs. Invasive hemodynamic monitoring is useful for acquiring a detailed understanding of a patient's physiology; nevertheless, it is associated with certain risks, including the following [1, 2] :

  • Thrombotic or ischemic complications with device placement
  • Infection associated with indwelling devices
  • Damage to surrounding structures or nerves

Per the guidelines for basic anesthetic monitoring of the perioperative patient published by the American Society of Anesthesiologists (ASA) in 2015, [3]  blood pressure (BP) and arterial BP should be assessed at 5-minute intervals. Typically, these assessments are noninvasively achieved in the OR with the use of an automated oscillometric blood pressure cuff.

Invasive monitors (eg, arterial lines, central lines, and Swan-Ganz catheters) may provide additional data about various hemodynamic parameters (eg, preload, afterload, end-organ perfusion and cardiac output) that are useful in high-risk patients susceptible to tissue hypoperfusion. There is evidence to suggest that invasive hemodynamic monitoring and protocol-based intervention for high-risk patients may allow earlier identification of decreased tissue perfusion and earlier intervention with medications and fluids. [4, 5]

Invasive hemodynamic monitoring may be warranted for high-risk patients or for patients indergoing complex, longer procedures with anticipated derangement of hemodynamic function. Clinicians must be able to identify appropriate situations for invasive hemodynamic monitoring in the care of high-risk perioperative patients while remaining fully cognizant of the risks associated with such monitoring.

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Management

Addressing the problem

In deciding among various hemodynamic monitoring modalities, the perioperative team should follow a systematic approach.

For relatively short and simple cases performed on low-risk surgical patients, the only monitoring required may be noninvasive BP monitoring, heart rate (HR) monitoring, and end-tidal carbon dioxide (EtCO2) monitoring. [6] A sudden drop in EtCO2 without a change in ventilation status may herald a change in carbon dioxide return to the lungs as a consequence of pulmonary embolism (PE) or decreased cardiac output. [6] A combination of these three monitoring modalities should be sufficient in a low-risk case where significant hemodynamic changes are not anticipated.

In cases where hemodynamic perturbations are expected (eg, those involving blood loss or volume shifts) or for high-risk patients who may not tolerate significant derangements in hemodynamics (eg, those with heart failure or intracranial pathology), invasive hemodynamic monitoring may be beneficial. Clinicians must give appropriate consideration to both the risks and the benefits of utilizing invasive hemodynamic monitoring during operative cases.

Evidence-based recommendations

Wax et al quantified the differences between noninvasive and invasive BP monitoring, noting that noninvasive BP cuffs recorded lower pressures than arterial lines during episodes of hypertension and higher pressures than arterial lines during episodes of hypotension. [7] This discordance could lead to less therapeutic intervention by an anesthesiology team during periods of hypo- or hypertension.

Thus, using an arterial line for invasive hemodynamic monitoring may be indicated in cases where hypotension or hypertension is expected, beat-to-beat BP monitoring is useful, or cardiovascular or major vascular manipulation is expected. Arterial lines may also be useful in cases where repeated blood sampling is necessary or where placement of a noninvasive BP cuff is not possible (eg, in patients with major burns). One retrospective study documented a complication rate of 7.8 per 10,000 arterial lines placed—a low rate for this invasive procedure. [8]

Central lines are often placed for patients who are hemodynamically unstable or are undergoing major surgical procedures to allow administration of vasoactive medications, and they may be used for blood sampling or in cases where peripheral venous access is insufficient. [9] Central venous pressure (CVP) may be transduced from a central line, and measured CVP reflects a patient's right atrial (RA) pressure. [10] CVP is often used to estimate overall blood volume status (eg, in patients undergoing hepatic resection). [11]

There is a growing amount of evidence to suggest that CVP does accurately measure RA pressure but does not always accurately predict blood loss or overall blood volume status. [10, 11] Ultimately, CVP may be best used as a data point to help guide therapeutic decision-making for a patient in the OR. For example, a central line enables sampling of mixed venous oxygenation saturation (SmvO2), which can provide valuable information regarding the delivery of oxygen to end organs and tissues.

Central line placement does carry greater risks than arterial line placement—in particular, the risk of pneumothorax and the persistent risk of central line–associated bloodstream infection (BSI). [9] Thus, central line placement may not be the first-line recommendation for hemodynamic monitoring; however, CVP measurement should be considered when central lines are indicated for the other reasons listed above.

Pulmonary arterial catheters (PACs), also referred to as Swan-Ganz catheters, permit more detailed assessment of hemodynamics by allowing measurement of cardiac output and systemic vascular resistance (SVR). However, a 2006 Cochrane review found that PACs did not improve mortality outcomes for patients undergoing major surgical procedures, either from a preoperative optimization perspective or in terms of intensive care unit (ICU) admission or length of stay. [12]

Although PACs may not be helpful for every patient undergoing surgery, they may still have a role to play in the management of patients suspected of having pulmonary hypertension or right-heart failure. [13] The risks of PAC placement (eg, infection, pulmonary arterial rupture, or adverse effects of catheter malpositioning) must be considered beforehand. Mortality from PAC complications has been reported to be as high as 4%. [13]

Transesophageal echocardiography (TEE) is one of the most useful diagnostic tools available for perioperative medicine, allowing rapid assessment of hemodynamics, cardiac function, and volume status. In their 2010 practice guidelines for perioperative TEE, the ASA/Society of Cardiovascular Anesthesiologists (SCA) Task Force on Transesophageal Echocardiography made the following statement [14] :

TEE may be used when the nature of the planned surgery or the patient’s known or suspected cardiovascular pathology might result in severe hemodynamic, pulmonary, or neurologic compromise. If equipment and expertise are available, TEE should be used when unexplained life-threatening circulatory instability persists despite corrective therapy.

Esophageal injury is a risk associated with TEE placement and manipulation; accordingly, patients who have esophageal pathology or are undergoing esophageal surgery may not be candidates for evaluation with TEE. Further research is needed to define the risks associated with intraoperative TEE for noncardiac surgical patients, but reported complication rates have ranged from 0% to 1.7%. [15] The ASA/SCA guidelines for intraoperative TEE in noncardiac surgery recommended limiting it to high-risk patients and those who become hemodynamically unstable intraoperatively. [14]

Transthoracic echocardiography (TTE) is another noninvasive means of assessing cardiac function and hemodynamic instability. Its perioperative applicability and usefulness may be limited by intraoperatively sterile surgical fields, certain patient positions, the presence of operating drapes, and positive-pressure ventilation (PPV). [15] Nevertheless, if the patient's anatomy and the surgical procedure allow substantive TTE evaluation, this modality remains a valuable noninvasive tool available to the perioperative clinician.

Each of the above modalities may may be used to monitor the patient's hemodynamic status intraoperatively. Although none of the invasive approaches is without risk, invasive monitoring should still be considered for patients who are expected to lose significant amounts of blood or undergo large volume shifts, those who are hemodynamically unstable, and those who are not expected to tolerate large hemodynamic changes (eg, from congestive heart failure [CHF], coronary artery disease [CAD], or intracranial pathology).

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Case Example 1

Clinical scenario

A 63-year-old woman with a history of hypertension presents to the emergency department (ED) with 7/10 crampy abdominal pain that began approximately 6 hours previously when she woke up in the morning. Additionally, she reports two nonbloody episodes of nonbilious emesis with a sensation of bloating and further emesis after she attempted to eat a bagel for breakfast.

On initial evaluation, the patient is found to be in atrial fibrillation (AF), with an HR in the 80s; she is hemodynamically stable, with a systolic BP in the 130s and a diastolic BP in the 80s. She reports that she has no known history of cardiac arrhythmia. Her only medication is lisinopril 5 mg/day for BP control, which she has been unable to take on the day of presentation because of her nausea.

Computed tomography (CT) of the patient's abdomen raises concerns about possible small-bowel obstruction with strangulation of the small bowel. The general surgery team approaches the anesthesiology team and requests an urgent exploratory laparotomy. The anesthesiology team evaluates the patient, noting the new-onset AF, and begins preoperative planning.

In this case, is additional hemodynamic monitoring warranted in addition to ASA standard monitoring? Which modalities are appropriate for this patient?

Resolution

In this case of hemodynamically stable AF, the authors suggest placement of a preinduction arterial line. Although the patient is not hemodynamically unstable at the time of presentation, progression to hemodynamically unstable AF remains a possibility. Beat-to-beat hemodynamic monitoring for this operative case may facilitate earlier diagnosis of hypotension and thus earlier intervention to correct it. [4, 5]  

In critically ill patients with new-onset AF, reversion to sinus rhythm is often possible once the underlying pathology (in this case, small-bowel obstruction with strangulation) is suspected and addressed. [16]  Given the patient's history of vomiting, brief preoperative point-of-care TTE may be warranted to evaluate the patient's inferior vena cava (IVC) diameter and left ventricular (LV) volume status to determine whether she would benefit from administration of fluids. 

If hemodynamic instability does develop intraoperatively, the perioperative team could certainly consider placement of a TEE probe to evaluate the patient's cardiac status. However, in view of the patient's preoperative hemodynamic stability, TEE does not appear to be warranted as a part of the planned perioperative course. Rate control and vigilant hemodynamic monitoring would be a reasonable starting point for this particular case, with  further modalities added as needed, depending on the progression of the case. [16]

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Case Example 2

Clinical scenario

An 83-year-old man who underwent two-vessel coronary artery bypass grafting (CABG) 8 months previously and has a history of hypertension and osteoporosis presents to the ED after a mechanical ground-level fall. He did not lose consciousness. He is hemodynamically stable, with a BP of 128/56 mm Hg as measured with a noninvasive BP cuff.

Initial laboratory test results from the ED show hemoglobin and hematocrit values that are consistent with the patient's baseline. Notably, his 6-month follow-up visit with his cardiologist demonstrated a low-normal LV ejection fraction (LVEF) of 50%. He reports feeling significant discomfort in his right hip and has been unable to bear weight since his mechanical fall. Plain films of the right hip demonstrate an intertrochanteric fracture.

The orthopedic surgery team is consulted and informs the anesthesiology team that the plan is to perform a percutaneous intramedullary femoral nailing. The patient currently takes low-dose aspirin (81 mg/day), clopidogrel, metoprolol, and atorvastatin. The orthopedic surgeon expresses concern about the risk of intraoperative bleeding and asks whether the patient will be able to tolerate significant derangements in BP with potential intraoperative hemorrhage.

In this case, is additional hemodynamic monitoring warranted in addition to ASA standard monitoring? Which modalities are appropriate for this patient?

Resolution

Although this patient is at increased risk for bleeding because of his dual antiplatelet therapy, he is hemodynamically stable with normal hemoglobin and hematocrit values; therefore, the authors would not initially recommend invasive hemodynamic monitoring. Adequate peripheral intravenous (IV) catheterization would be preferable, in that an episode of acute intraoperative bleeding could be temporized with judicious administration of crystalloid boluses (eg, IV electrolyte solutions).

Given the nature of the procedure, the patient would most likely be in a lateral decubitus position, with the arms readily available for intraoperative placement of a radial arterial line and with the head sufficiently accessible to allow urgent placement of a TEE probe in the event of profound intraoperative hypotension. Given that the patient appears to have low-normal heart function after CABG, sudden hypotension in this case would most likely be secondary to blood loss, and treatment could be initiated while more advanced hemodynamic monitoring modalities are pursued. 

In the authors' opinion, optimal initial monitoring for this case would consist of automated noninvasive BP cuff monitoring, pulse oximetry, and continuous telemetry. Further monitoring could be added as needed during the procedure.

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Case Example 3

Clinical scenario

A 63-year-old man with a history of well-controlled hypertension, obesity (body mass index [BMI], 37), and osteoarthritis presents for elective right total knee arthroplasty (TKA). He refuses the offer of a spinal anesthestic, and the anesthesiology team opts for general endotracheal anesthesia with noninvasive BP cuff hemodynamic monitoring in addition to the other standard ASA intraoperative monitoring means.

The operation progresses uneventfully until the surgeon begins cementing the long stem femoral component with methylmethacrylate (MMA). Abruptly, the patient's BP drops from normal levels to the 80s/40s, and the EtCO2 decreases in a stepwise manner from 35 mm Hg to 10 mm Hg over the next three ventilatory cycles. The anesthesiology team alerts the orthopedic surgery team that they are concerned about possible PE, and the operation is paused to allow for diagnosis and resuscitation.

In this case, is additional hemodynamic monitoring warranted in addition to ASA standard monitoring? Which modalities are appropriate for this patient?

Resolution

Cardiac arrest secondary to PE from either MMA embolism or fat embolism associated with orthopedic surgery has been well described in the literature. [17, 18]  In this case involving acute hemodynamic instability of uncertain etiology, management should first focus on standard resuscitation of the patient with fluids, fraction of inspired oxygen (FiO2) set to 100%, and IV boluses of vasoactive medications as needed.

The addition of invasive hemodynamic monitoring would be warranted in this scenario, and it would be prudent to ask for help while placing additional monitoring on a hemodynamically unstable patient. To start with, an arterial line could provide beat-to-beat BP information, which would be helpful for assessing stabilization efforts. Additionally, an arterial line would allow arterial blood gas (ABG) sampling to determine the patient's acid-base status and to assess for ventilation-perfusion (V/Q) mismatch should this be an embolic event.

Echocardiography would be helpful for working up cardiogenic sources of shock. Given that this patient is already intubated and under general anesthesia, placement of a TEE probe and performance of an abbreviated examination could reveal evidence of right ventricular (RV) strain and septal bowing with PE or, conversely, a hyperdynamic RV and LV suggestive of distributive shock. If TEE examination proves not to be feasible, TTE is a noninvasive alternative.

If PE with right-heart strain is suggested, placement of a PAC could be useful in both intraoperative and postoperative management of right-heart strain and pulmonary hypertension. As previously noted (see Management above), PACs are not routinely utilized in elective noncardiac operations, because of the lack of evidence that they improve patient mortality. [12]  However, in cases involving right-heart strain with pulmonary hypertension, information from a PAC could reasonably be used to help guide management. [13]

In the scenario described above, the authors would recommend calling for help, establishing an arterial line, and performing TEE—or, at the very least, TTE—to assess for RV strain. If the findings suggest PE, the authors would advise considering the placement of a PAC to help guide management of pulmonary hypertension and RV strain both for the remainder of the operation and thereafter in the ICU.

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Case Example 4

Clinical scenario

A 24-year-old woman with no past medical history is involved in a motor vehicle collision. Emergency medical services (EMS) arrive shortly at the scene. The patient is determined to have a Glasgow Coma Scale (GCS) score of 7, is found to be hemodynamically stable, and is intubated in the field.

On arrival in the ED, the patient is found to be obtunded. HR is 114 beats/min, BP is 94/61 mm Hg, and oxygen saturation on pulse oximetry (SpO2) is 98% on an FiO2 of 60%. She is placed on volume control (VC)-assist control (AC) ventilation at 8 mL/kg of ideal body weight and started on a propofol infusion at 20 μg/kg/hr. Emergency CT shows a traumatic intracranial hemorrhage with a volume of 55 mL and narrowing of the basilar cisterns. Neurosurgery informs the anesthesiology team that craniotomy and hematoma evacuation are planned.

In this case, is additional hemodynamic monitoring warranted in addition to ASA standard monitoring? Which modalities are appropriate for this patient?

Resolution

In the setting of traumatic brain injury and neurosurgical intervention, the perioperative team must assume that there is some inhibition of the cerebrovascular autoregulatory curve. [19]  In the areas where cerebrovascular autoregulation is impaired, cerebral perfusion becomes dependent on BP. This relation is described by the following equation:

  • Cerebral perfusion pressure (CPP) = mean arterial pressure (MAP) – CVP

With this consideration in mind, placement of an arterial line to provide beat-to-beat monitoring of BP would be desirable. Arterial lines are superior to noninvasive BP cuffs for accurately detecting hyper- and hypotension. [7]  

Placement of an arterial line allows earlier intervention and protection of cerebral perfusion while avoiding hypertension and subsequent obscuring of the surgical field with a "tight brain." Besides providing information about BP perioperatively, an arterial line allows ABG sampling to monitor arterial carbon dioxide tension (PaCO2) throughout the operation, which would aid in the detection of hypercarbia. [19]  

A central line may not be clearly indicated for this patient, who is hemodynamically stable at presentation. However, some craniotomy or cervical spine procedures are performed in the sitting position, which has been reported to be associated with a 1.6-50% incidence of venous air embolism. [20]  Most of these emboli are inconsequential with respect to the patient's hemodynamic status, but if a catastrophic air embolism does occur, a central line may be considered; successful aspiration via a central line near the RA has been reported. [20]

TEE is the most sensitive means of monitoring for intraoperative air emboli. [20]  Precordial Doppler ultrasonography (US) may also be employed for the detection of venous air emboli. [19]  In an urgent case, there may not be time to establish all of these invasive (or, in the case of precordial Doppler US, noninvasive) monitors.

In the scenario described above, the authors would recommend placing an arterial line to monitor perioperative BP. Given that the patient has already been intubated and is receiving a measure of sedation with propofol, placement of the arterial line could be accomplished in the OR while the surgical team is preparing for the craniotomy and hematoma evacuation.

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Case Example 5

Clinical scenario

A 63-year-old man with a history of type 2 diabetes mellitus and hypertension (baseline BP in the 130s/80s) presents for an elective laparoscopic cholecystectomy. He has not undergone general anesthesia in the past. Preoperative assessment by the anesthesiology team reveals no pathology of concern.

A peripheral IV line is established, and the perioperative team brings the patient to the OR. He is connected to standard ASA monitors and preoxygenated. He receives fentanyl 50 μg IV, propofol 200 mg by slow IV infusion for induction and maintenance during surgery, and subsequently rocuronium 50 mg IV.

The patient is intubated successfully, but the perioperative team notes the rapid development of urticaria over his chest, an obstructive pattern on capnography, elevated peak pressures, tachycardia (HR in the 130s), and hypotension (rapid BP decline to the 60s/30s via noninvasive BP cuff). The perioperative team begins resuscitation efforts and discusses placement of additional hemodynamic monitors.

In this case, is additional hemodynamic monitoring warranted in addition to ASA standard monitoring? Which modalities are appropriate for this patient?

Resolution

The clinical presentation suggests anaphylactic shock. Rocuronium and neuromuscular blocking agents have been implicated in the development of anaphylactic shock in the literature. [21] Invasive hemodynamic monitoring can aid in making the final diagnosis

The first priority in this case should be resuscitation with a large-volume IV bolus of crystalloid and incremental 10-μg IV boluses of epinephrine. Calling for help to establish additional hemodynamic monitoring is warranted.

An arterial line would facilitate real-time assessment of resuscitation efforts and provide access for ABG sampling to assess acid-base status. TEE would be helpful for confirming that this is not cardiogenic shock and could also facilitate volume resuscitation during this episode of distributive shock. If continued infusion of vasoactive medications should prove necessary, a central line would be warranted. CVP values could also serve as data points to help confirm volume status, though, as discussed above, CVP can be affected by many factors besides blood volume. [10]

Each of these monitors would be warranted in this scenario. The authors would recommend stabilization and resuscitation of the patient, placement of an arterial line, placement of a central venous line if continued infusions of vasoactive medications are needed, and performance of TTE or TEE as available to confirm that there are no derangements in cardiac function.

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