INTRA OPERATIVE HYPOTENSION MATTERS?
Intraoperative hypotension may be an important factor in the development of postoperative complications.
Data1 from 27,381 patients undergoing 33,330 noncardiac surgeries were studied to determine the durations of various mean arterial pressures (MAP) that were associated with acute kidney injury and myocardial injury. Acute kidney injury occurred after 7.4% of surgeries while myocardial injury occurred after 2.3% of surgeries and 1.5% of patients died within 30 days of surgery. Any time spent with a MAP of less than 55 mmHg during noncardiac surgery was independently associated with an increased risk of acute kidney injury and myocardial injury. As the time with a MAP of less than 55 mmHg increased so too did the risk for acute kidney injury and myocardial injury. Thirty-day mortality was associated with more than 20 min of MAP less than 55 mmHg. Optimizing intraoperative hemodynamics may improve patient outcomes.
Even short durations of an intraoperative MAP less than 55 mmHg are associated with AKI and myocardial injury.
In a retrospective study2 of 5,127 patients undergoing noncardiac surgery, an increased risk of postoperative acute kidney injury (defined as >50% or 0.3 mg/dl increase in serum creatinine concentration) was found when “Intraoperative mean arterial pressure was less than 60 mmHg for more than 20 min and less than 55 mmHg for more than 10 min”
The authors3 tested the hypothesis that blood pressure variability, independent from absolute blood pressure, is associated with increased 30-day mortality. Baseline and intraoperative variables plus 30-day mortality were obtained for 104,401 adults having noncardiac surgery lasting 60 min or longer. In confounder-adjusted models, the authors evaluated the associations between 30-day mortality and both time-weighted average intraoperative mean arterial pressure (TWA-MAP) and measures of intraoperative MAP variability—including generalized average real variability of MAP (ARV-MAP) and SD of MAP (SD-MAP). Mean ± SD TWA-MAP was 84 ± 10 mmHg, and ARV-MAP was 2.5 ± 1.3 mmHg/min. TWA-MAP was strongly related to 30-day mortality, which more than tripled as TWA-MAP decreased from 80 to 50 mmHg. ARV-MAP was only marginally related to 30-day mortality (P = 0.033) after adjusting for TWA-MAP.
Average mean arterial pressure and mean pressure variability were nonlinearly related to 30-day mortality in noncardiac surgical patients. After adjusting for time-weighted average mean arterial pressure and other important covariables, low blood pressure variability as measured by an improved formula was still associated with higher 30-day mortality, but the differences were not clinically important. Anesthesiologists might thus pay more attention to overall trends in the mean blood pressure for a case than in the minute-to-minute variation.
In a study4 conducted by the Cleveland Clinic, researchers found that intraoperative hypotension is associated with clinical outcomes after noncardiac surgery.
Mean arterial pressure (MAP) below absolute thresholds of 65 mmHg or relative thresholds of 20% or more below baseline were progressively related to both myocardial and acute kidney injury (AKI). At any given threshold, prolonged exposure was associated with increased odds.
Absolute and relative MAP thresholds had comparable ability to discriminate patients with myocardial or kidney injury from those without. The results suggest that maintaining intraoperative MAP greater than 65 mmHg may reduce the risk of AKI and myocardial injury.
The associations based on relative mean arterial pressure thresholds were no stronger than those based on absolute thresholds. Furthermore, there was no clinically important interaction with preoperative pressure. These data suggest that anesthetic management can thus be based on intraoperative pressures without regard to preoperative pressure.
PHYSIOLOGY OF PERFUSION: PRESSURE AND FLOW s (Edwards Lifesciences)
Adequate perfusion requires adequate arterial pressure and cardiac output (CO)
Cardiac Output (CO) = Stroke Volume x Heart Rate:
Managing the flow component of perfusion
Maintaining patients in the optimal volume range is key. Using dynamic and flow-based parameters to guide fluid administration helps maintain patients in the optimal volume range.
Insufficient volume administration is associated with:
- GI dysfunction (postoperative ileus, PONV, upper GI bleeding, anastomotic leak)2
- Infectious complication (tissue hypoperfusion)3
- Acute renal insufficiency or failure
Excessive volume administration is associated with:
- Pulmonary edema
- GI dysfunction (abdominal compartment syndrome, ileus, anastomotic leak)
Individualizing volume management
Preload: the tension of myocardial fibers at the end of diastole, as a result of volume in the ventricle:
Stroke Volume (SV): volume of blood pumped from the left ventricle per heartbeat:
When managing perfusion, stroke volume can be optimized using the patient’s own Frank-Starling curve — a plot of stroke volume (SV) vs. preload.
The patient’s location on his or her Frank-Starling curve can be determined by measuring ∆SV in response to change in preload using:
Bolus fluid challenge:
Passive leg raise (PLR):
Dynamic and flow-based parameters are more informative than conventional parameters in determining fluid responsiveness and may help you avoid excessive and insufficient fluid administration.
Clinical studies have shown that conventional volume management methods, based on conventional parameters, are misleading and insensitive.
Advanced hemodynamic parameters such as stroke volume (SV) and stroke volume variation (SVV), are key to optimal fluid administration.
SVV has been proven to be a highly sensitive and specific indicator for preload responsiveness when managing perfusion. As a dynamic parameter, SVV has been shown to be an accurate predictor of fluid responsiveness in loading conditions induced by mechanical ventilation.
Reducing fluid variability using Perioperative Goal-Directed Therapy (PGDT)
PGDT is a treatment protocol using dynamic and flow-based parameters with the objective of making the appropriate volume management decisions (e.g. fluid only when needed).
PGDT can be implemented in a single procedure or as part of a larger initiative such as Enhanced Recovery After Surgery pathways.
Perioperarive goal-directed algorithm5:
s Source: Edwards Lifesciences.
- Michael Walsh, Philip J. Devereaux, Amit X. Garg, Andrea Kurz, Alparslan Turan, Reitze N. Rodseth, Jacek Cywinski, Lehana Thabane, Daniel I. Sessler; Relationship between Intraoperative Mean Arterial Pressure and Clinical Outcomes after Noncardiac Surgery: Toward an Empirical Definition of Hypotension. Anesthesiology 2013;119(3):507-515. doi: 10.1097/ALN.0b013e3182a10e26.
- 2. Louise Y. Sun, Duminda N. Wijeysundera, Gordon A. Tait, W. Scott Beattie; Association of Intraoperative Hypotension with Acute Kidney Injury after Elective Noncardiac Surgery. Anesthesiology 2015;123(3):515-523. doi: 10.1097/ALN.0000000000000765.
- Edward J. Mascha, Dongsheng Yang, Stephanie Weiss, Daniel I. Sessler; Intraoperative Mean Arterial Pressure Variability and 30-day Mortality in Patients Having Noncardiac Surgery. Anesthesiology 2015;123(1):79-91. doi: 10.1097/ALN.0000000000000686.
- Vafi Salmasi, Kamal Maheshwari, Dongsheng Yang, Edward J. Mascha, Asha Singh, Daniel I. Sessler, Andrea Kurz; Relationship between Intraoperative Hypotension, Defined by Either Reduction from Baseline or Absolute Thresholds, and Acute Kidney and Myocardial Injury after Noncardiac Surgery: A Retrospective Cohort Analysis. Anesthesiology 2017;126(1):47-65. doi: 10.1097/ALN.0000000000001432.
- Perioperative goal-directed therapy and postoperative outcomes in patients undergoing high-risk abdominal surgery: a historical-prospective, comparative effectiveness study. Critical Care201519:261