NU656 Unit 3 Hemodynamic Data After Colectomy Example

Will Another Bolus Raise His Stroke Volume? A Hemodynamic Data Interpretation Ten Hours After Open Right Hemicolectomy in a 72-Year-Old Man

[Student Name]

Purdue University Global

NU656: AGACNP Critical Care Management

Unit 3 Hemodynamic Data Interpretation

[Instructor Name]

[Date]

The patient is composite; every value and time is bracketed.

The Question and the Data

Mr. [N.], [72], had an open right hemicolectomy for a cecal cancer, ending at [15:30]. He was extubated in the operating room and has a thoracic epidural with bupivacaine running at [8] mL an hour. He has received [3.5] liters of crystalloid since the start of surgery. The overnight clinician is asking whether to give another [500] mL bolus.

1. [18:00]. Mean arterial pressure [72]; heart rate [88]; pulse pressure variation [11] percent; central venous pressure [7]; lactate [2.4]; central venous oxygen saturation [74] percent; urine [45] mL an hour.

2. [20:00]. Pressure [66]; heart rate [92]; variation [10]; venous pressure [8]; lactate [1.9]; saturation [76]; urine [35].

3. [22:00]. Pressure [63]; heart rate [90]; variation [9]; venous pressure [9]; lactate [1.6]; saturation [77]; urine [30].

4. [00:00]. Pressure [61]; heart rate [88]; variation [9]; venous pressure [9]; lactate [1.8]; saturation [78]; urine [28].

5. [02:00]. Pressure [60]; heart rate [86]; variation [8]; venous pressure [10]; lactate [2.2]; saturation [78]; urine [25].

6. [04:00]. Pressure [61]; heart rate [88]; variation [9]; venous pressure [10]; lactate [2.6]; saturation [77]; urine [22].

Step One: Can the Arterial Line Be Trusted?

Before any number from the arterial line is used, the trace must be checked. A fast-flush test at [00:10] showed one or two oscillations before the trace returned to baseline, which indicates adequate damping. An overdamped line would have flattened both the pressure and the variation, and any reading built on it would rest on artifact. The cuff pressure on the other arm matched within [5] mmHg. The line can be trusted.

Step Two: Which Numbers Can Answer the Question?

Central venous pressure is a static measure, and a systematic review found that it predicts the response to fluid little better than chance (Marik et al., 2008). His value of [9] neither supports nor rules out a bolus, and the interpretation sets it aside openly rather than using it quietly.

Pulse pressure variation is a dynamic measure, and in the original study of septic patients on mechanical ventilation, a variation above 13 percent separated patients whose cardiac output rose with fluid from those whose output did not (Michard et al., 2000). But that finding depends on conditions: controlled mechanical ventilation with an adequate tidal volume and a regular heart rhythm. Mr. [N.] is breathing on his own. A pulse pressure variation of 9 percent in a spontaneously breathing man is not a low number; it is an unreadable one.

Step Three: Testing Fluid Responsiveness Directly

When pulse pressure variation cannot be used, a passive leg raise can test fluid responsiveness without giving any fluid, by returning about [300] mL of the patient's own blood from the legs to the heart. Its value depends on measuring a change in cardiac output or a surrogate in real time, not blood pressure alone (Monnet et al., 2016). At [04:10], with bedside echocardiography measuring the velocity-time integral in the left ventricular outflow tract, a leg raise increased the integral from [18.2] to [19.1] cm, a rise of [5] percent, below the [10 to 15] percent usually taken to indicate a response. He is not likely to raise his stroke volume with another bolus.

Step Four: What Is Lowering His Pressure?

If he is not short of volume, something else is lowering his pressure. His central venous oxygen saturation of [77 to 78] percent is not low, which argues against low cardiac output. His heart rate is not high. The most likely cause is vasodilation from the thoracic epidural, which blocks sympathetic nerves to the vessels of the abdomen and lower body. His urine output has fallen slowly as his pressure has, which fits a low perfusion pressure rather than a low volume.

The rising lactate needs its own explanation, because vasodilation alone rarely raises lactate. After a colectomy, an anastomotic leak or bowel ischemia can cause a rising lactate before other signs appear. His abdomen was examined at [04:15]: soft, appropriately tender at the incision, with no distension. The team decided to repeat the lactate after the pressure was corrected and to request a CT if it continued to rise.

Why Not Simply Give the Bolus?

A [500] mL bolus is a familiar answer to a low pressure after surgery, and it can feel harmless. In Mr. [N.]'s case it would not have been. He had already received [3.5] liters, and fluid given to a patient who does not respond to it stays in the tissues. After bowel surgery, extra fluid is associated with swelling of the bowel wall and anastomosis, slower return of bowel function and a higher risk of complications. Fluid would also have diluted the information in the data: a pressure that rose briefly after a bolus might have been read as proof of a volume problem, delaying recognition of the epidural's effect. The test that answered the question, a leg raise with an echocardiographic measurement, took ten minutes and cost him nothing.

There is also the question of what a mean pressure of [61] means for this man. He has long-standing hypertension, and his kidneys may need a higher pressure than a general target. His falling urine output suggested they did. The plan sets a target of at least [65] and asks the team to consider a higher target if his urine output does not improve once it is reached.

Interpretation and Plan

1. No further fluid bolus.

2. Reduce the epidural infusion to [5] mL an hour after discussion with the acute pain service, checking his pain score and sensory level.

3. Start norepinephrine at [0.03 to 0.05] mcg/kg per minute through the central line to restore a mean pressure of at least [65].

4. Repeat lactate at [06:00]; CT of the abdomen if it has risen or if his examination changes.

5. Hourly urine measurement, aiming for [40] mL an hour or more once his pressure recovers.

What the Data Could Not Tell

Numbers from the monitor answered the fluid question but not the lactate question. That part of the plan depends on the surgeon's examination and, if needed, imaging. Hemodynamic data are best at telling a team what the circulation is doing; they are less able to say why an organ is struggling. By [06:00], on low-dose norepinephrine and a lower epidural rate, his mean pressure was [69], his urine output [40] mL an hour and his lactate [1.9].

References

Marik, P. E., Baram, M., & Vahid, B. (2008). Does central venous pressure predict fluid responsiveness? A systematic review of the literature and the tale of seven mares. Chest, 134(1), 172-178. https://doi.org/10.1378/chest.07-2331

Michard, F., Boussat, S., Chemla, D., Anguel, N., Mercat, A., Lecarpentier, Y., Richard, C., Pinsky, M. R., & Teboul, J.-L. (2000). Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure. American Journal of Respiratory and Critical Care Medicine, 162(1), 134-138. https://doi.org/10.1164/ajrccm.162.1.9903035

Monnet, X., Marik, P. E., & Teboul, J.-L. (2016). Prediction of fluid responsiveness: An update. Annals of Intensive Care, 6, Article 111. https://doi.org/10.1186/s13613-016-0216-7