Decision Support for Intraoperative Low Blood Pressure

Study Overview
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Brief Summary
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The purpose of this study is to determine whether a decision support system can improve the adherence to thresholds for low blood pressure by anesthesia providers, which in turn prevents their patients from having organ injury.

Detailed Description
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Blood pressure management is an important part of anesthesia. Many factors contribute to a change in blood pressure during a surgical procedure, such as blood loss, manipulation by surgeons, and there are several mechanisms through which anesthesia itself changes blood pressure. Although a high blood pressure also occurs during anesthesia, most of these factors lower a patient's blood pressure. When a patient's blood pressure becomes too low, the internal organs become at risk of receiving not enough blood (low perfusion or hypoperfusion). This low perfusion state can result in organ damage (ischemia) because of an insufficient supply of oxygen and glucose. Hence the important task of anesthesia providers to maintain the blood pressure of patients, using a wide range of drugs and other interventions. A big challenge in blood pressure management is to know when a low blood pressure indeed results in low perfusion of organs. There is a large variation between patients in how susceptible they are to low blood pressure, as well as a difference between the organs in how easily they are damaged because of low perfusion. Elder patients, or patients with preexisting hypertension, heart problems or other cardiovascular diseases are more prone to a low blood pressure and are more likely to develop organ ischemia when there is a low blood pressure. The kidneys, the heart and the brain are the organs that are most at risk of organ damage. As one cannot measure the perfusion states of individual organs in individual patients, it is very difficult to know 'how low to go' with a patient's blood pressure. Recent studies have used large datasets of patients to demonstrate that there is statistical association between low blood pressure during surgery and various types of organ injury. As patients are already treated for low blood pressure by anesthesia providers, this suggests that patients have low organ perfusion states despite the current treatment standards. A patient's blood pressure is not simply a dial that can be adjusted to a specific level. Finding the right level of interventions can be difficult in some patients. Consequently, lower blood pressures are common in anesthesia, even with the current standards of blood pressure management. In this proposed study the investigators will implement two forms of decision support to assist anesthesia providers in blood pressure management. The decision support aims to educate anesthesia providers about the risks of low blood pressures in direct relation to the patients that they treat. One form of decision support will provide automated notifications through pagers and through the anesthesia information management system. These automated notifications pop up when the patient's blood pressure drops below a level that is associated with a risk of organ injury, and thus alerts the anesthesia provider of the blood pressure and its associated risk. The second form of decision support will send a postoperative email the day after the procedure when the patient has had a low blood pressure for particular duration. This email then provides feedback to the anesthesia provider by informing them of the increased risks of organ injury that are associated with that low blood pressure. The study will look at both a change in patient outcome and a change in blood pressure management and will be performed at the Vanderbilt University Medical Center (VUMC). The change in patient outcome will primarily be studied through the occurrence of acute kidney injury in the first days following the procedure at the VUMC. The change in blood pressure management (provider behavior) will be studied by observing the depth and duration of low pressures during anesthesia, and the number of interventions that have been used to treat the blood pressure. Patient outcome will be studied by comparison of a baseline phase - before the decision support is implemented and uses historic data- and the intervention phase - the period during which the intervention is active. Only routinely collected clinical data will be used for these analyses: no additional data collection is required. As it is impossible to know which form of decision support will be the most effective, the first three months of the intervention period will be a 'nested cluster-randomized trial'. The anesthesia providers (not the patients) will be randomized to either the automated notifications or the feedback emails. After three months all anesthesia providers will receive both forms of decision support for the remainder of the intervention period. The reason why anesthesia providers are randomized only during the first three months is that cross-over or contamination between the two groups is expected. This contamination could make it impossible to study the effect of the decision support on patient outcome, as there will be no longer any difference between the study groups.

Official Title
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Decision Support for Intraoperative Low Blood Pressure

Conditions
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Hypotension

Intervention / Treatment
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* Procedure: Attending real-time decision support
* Procedure: In-room real-time decision support
* Procedure: Attending feedback emails
* Procedure: In-room provider feedback emails
* Device: Anesthesia Information Management System (AIMS)
* Device: Perioperative Data Warehouse (PDW)
* Procedure: General anesthesia
* Device: Pager system
* Procedure: Central neuraxial anesthesia
* Procedure: Non-cardiac surgery
* Drug: Propofol
* Drug: Sevoflurane
* Drug: Desflurane
* Drug: Isoflurane
* Drug: Ephedrine
* Drug: Phenylephrine
* Drug: Norepinephrine
* Drug: Epinephrine
* Drug: Dobutamine
* Drug: Dopamine
* Drug: Isoproterenol
* Drug: Milrinone
* Drug: Atropine
* Drug: Glycopyrrolate
* Drug: Vasopressin
* Drug: Terlipressin
* Drug: Sodium Chloride 0.9%
* Drug: Ringer's lactate
* Drug: Hydroxyethyl starch solutions
* Drug: Fresh Frozen Plasma
* Drug: Packed Red Blood Cells
* Drug: Albumin solutions
* Drug: Plasma-Lyte
* Drug: Lidocaine
* Drug: Bupivacaine
* Drug: Levobupivacaine
* Drug: Ropivacaine
* Drug: Mepivacaine
* Drug: Tetracaine
* Drug: Prilocaine
* Drug: Procaine
* Drug: Chloroprocaine
* Drug: Benzocaine
* Drug: Articaine


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: 60 years and older Inpatients Scheduled for a non-cardiac surgical procedure under general or central neuraxial anesthesia Exclusion Criteria: Pre-existing end-stage renal disease: operationalized as a preoperative need for dialysis The following surgical procedures: renal surgery, cardiac surgery, organ transplantation, ophthalmic surgery, endoscopic gastrointestinal procedures, and (interventional) radiologic procedures. small non-invasive or minimally-invasive procedures will also be excluded, operationalized as excluding procedures with a surgical time of less than twenty minutes.

Ages Eligible for Study
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Minimum Age: 60 Years
Maximum Age: 100 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Prevention
Allocation: Non-Randomized
Intervention Model: Sequential Assignment
Interventional Model Description: It is an interrupted time-series of a decision support package intervention that aims to study the the effect of the decision support package on patient outcome. The effects of the individual decision support components of the package on healthcare provider behavior will be studied in a nested cluster-randomized trial: in the first month the attending anesthesiologists will be randomized to near-realtime notifications or feedback emails; in the second month in-room providers will be randomized to near-realtime notifications or feedback emails. Starting month four all providers will receive both near-realtime notifications and feedback emails.
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Hypotension decision support<br>The intervention period. Several decision support elements are implemented to notify anesthesia providers: attending anesthesiologists and in-room anesthesia providers of intraoperative hypotension (threshold of a mean arterial pressure below 60 mmHg). Two types of decision support will be implemented: near real-time decision support and feedback emails. Near real-time decision support elements will notify the anesthesia providers of a blood pressure drop below the threshold and display the associated increased risk of acute kidney injury. The notification is presented through the pager system for attending anesthesiologists and through the anesthesia information management system for the in-room anesthesia provider. All providers will be notified through email within 24 hours after the end of an anesthetic case, when the patient had an episode of intraoperative hypotension that is associated with an increased risk of organ injury due to organ ischemia. | Procedure: Attending real-time decision support<br>* Near real-time decision support elements will notify the attending anesthesiologists of a blood pressure drop below the threshold for intraoperative hypotension (mean arterial pressure below 60 mmHg). The notification is presented through the pager system. The page will also display the associated increased risk of organ injury due to organ ischemia.<br>Procedure: In-room real-time decision support<br>* Near real-time decision support elements will notify the in-room anesthesia provider of a blood pressure drop below the threshold for intraoperative hypotension (mean arterial pressure below 60 mmHg). The notification is presented through the anesthesia information management system. The decision support system will display the associated increased risk of organ injury due to organ ischemia.<br>Procedure: Attending feedback emails<br>* Attending anesthesiologists will be notified through email within 24 hours after the end of an anesthetic case, when the patient had an episode of intraoperative hypotension (mean arterial pressure below 60 mmHg or lower for a particular duration) that is associated with an increased risk of organ injury due to organ ischemia.<br>Procedure: In-room provider feedback emails<br>* In-room anesthesia providers will be notified through email within 24 hours after the end of an anesthetic case, when the patient had an episode of intraoperative hypotension (mean arterial pressure below 60 mmHg or lower for a particular duration) that is associated with an increased risk of organ injury due to organ ischemia.<br>Device: Anesthesia Information Management System (AIMS)<br>* The anesthesia electronic record keeping system<br>Device: Perioperative Data Warehouse (PDW)<br>* The data warehouse that is used to gather perioperative data and create user reports. In this instance the PDW will be used to send the postoperative feedback emails.<br>Procedure: General anesthesia<br>* Any anesthetic drugs that are used to induce general anesthesia above the level of sedation.<br>Device: Pager system<br>* The mobile pager system through which alerts can be sent<br>Procedure: Central neuraxial anesthesia<br>* Regional anesthesia effectuated through the placement of local anesthetics around the nerves of the central nervous system, e.g. spinal anesthesia and epidural anesthesia.<br>* Other names: Central neuraxial blockade;Procedure: Non-cardiac surgery<br>* Any surgical intervention that is not aimed at surgical correction of the heart<br>Drug: Propofol<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Sevoflurane<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Desflurane<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Isoflurane<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Ephedrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Phenylephrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Norepinephrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Epinephrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Dobutamine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Dopamine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Isoproterenol<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Milrinone<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Atropine<br>* Cardiovascular drugs used to treat intraoperative hypotension<br>Drug: Glycopyrrolate<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Vasopressin<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Terlipressin<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Sodium Chloride 0.9%<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Ringer's lactate<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Hydroxyethyl starch solutions<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Fresh Frozen Plasma<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Packed Red Blood Cells<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Albumin solutions<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Plasma-Lyte<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Lidocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>* Other names: Lignocaine;Drug: Bupivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Levobupivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Ropivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Mepivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Tetracaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Prilocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Procaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Chloroprocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Benzocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Articaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>|
| Active Comparator: Usual care group<br>The 'before' period - or historic control group - during which no decision support for intraoperative hypotension was being used, also known as 'usual care'. This is the three year period prior to the intervention period (the 'Intraoperative hypotension decision support' arm). | Procedure: General anesthesia<br>* Any anesthetic drugs that are used to induce general anesthesia above the level of sedation.<br>Procedure: Central neuraxial anesthesia<br>* Regional anesthesia effectuated through the placement of local anesthetics around the nerves of the central nervous system, e.g. spinal anesthesia and epidural anesthesia.<br>* Other names: Central neuraxial blockade;Procedure: Non-cardiac surgery<br>* Any surgical intervention that is not aimed at surgical correction of the heart<br>Drug: Propofol<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Sevoflurane<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Desflurane<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Isoflurane<br>* Anesthetic drug used to maintain general anesthesia<br>Drug: Ephedrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Phenylephrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Norepinephrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Epinephrine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Dobutamine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Dopamine<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Isoproterenol<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Milrinone<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Atropine<br>* Cardiovascular drugs used to treat intraoperative hypotension<br>Drug: Glycopyrrolate<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Vasopressin<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Terlipressin<br>* Cardiovascular drug used to treat intraoperative hypotension<br>Drug: Sodium Chloride 0.9%<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Ringer's lactate<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Hydroxyethyl starch solutions<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Fresh Frozen Plasma<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Packed Red Blood Cells<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Albumin solutions<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Plasma-Lyte<br>* Intravenous fluid used to treat intraoperative hypotension<br>Drug: Lidocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>* Other names: Lignocaine;Drug: Bupivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Levobupivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Ropivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Mepivacaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Tetracaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Prilocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Procaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Chloroprocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Benzocaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>Drug: Articaine<br>* Local anesthetic used for central neuraxial anesthesia.<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Postoperative Acute Kidney Injury | Postoperative Acute Kidney Injury (AKI), Stage I or higher according to the KDIGO criteria (Kidney Disease: Improving Global Outcomes). The staging will be based on serum creatinine values, as documentation of urine output is probably not sufficiently accurate. This will be the primary outcome for the Vanderbilt University Medical Center. The creatinine measurements are part of routine clinical care. Therefore, absence of creatinine postoperative measurements are considered to be 'no suspicion of kidney injury'. KDIGO defines AKI as any of the following: Increase in serum creatinine by 0.3mg/dL or more within 48 hours or Increase in serum creatinine to 1.5 times baseline or more within the last 7 days or Urine output less than 0.5 mL/kg/h for 6 hours. Stage 1 is 1.5-9x baseline or >0.3 increase; Stage 2 is 2-2.9x baseline; Stage 3 is 3x baseline, or increase to > 4, or initiation of renal replacement therapy. | Within 7 days after surgery | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| 30-day Mortality | Vanderbilt University Medical Center: combination of in-hospital mortality and 'alive-index' (which checks for visits to the hospital in the electronic healthcare record as indication of being alive at 30 days) | 30 days after surgery | 
| In-hospital Mortality | Hospital mortality rate during a single hospital admission after the surgery | All postoperative days during a single hospital admission, expected median of 5 days | 
| Postoperative Acute Kidney Injury Stage 2 | Postoperative Acute Kidney Injury (AKI), Stage II or higher according to the KDIGO criteria (Kidney Disease: Improving Global Outcomes). The staging will be based on serum creatinine values, as documentation of urine output is probably not sufficiently accurate. The creatinine measurements are part of routine clinical care. Therefore, absence of creatinine postoperative measurements are considered to be 'no suspicion of kidney injury'. KDIGO defines AKI as any of the following: Increase in serum creatinine by 0.3mg/dL or more within 48 hours or Increase in serum creatinine to 1.5 times baseline or more within the last 7 days or Urine output less than 0.5 mL/kg/h for 6 hours. Stage 1 is 1.5-9x baseline or >0.3 increase; Stage 2 is 2-2.9x baseline; Stage 3 is 3x baseline, or increase to > 4, or initiation of renal replacement therapy. | Within 7 days after surgery | 
| Postoperative Rise in Creatinine Levels | Absolute values for serum creatinine before and after surgery will be compared. When multiple postoperative creatinine measurements are made, the maximum difference is reported. | Within 7 days after surgery | 
| Incidence of a MAP < 60 mmHg | Incidence of a mean arterial pressure (MAP) < 60 mmHg during anesthesia for 1 minute or more. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 55 mmHg | Incidence of a mean arterial pressure (MAP) < 55 mmHg during anesthesia for 1 minute or more. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 50 mmHg | Incidence of a mean arterial pressure (MAP) < 50 mmHg during anesthesia for 1 minute or more. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 60 mmHg for > 10 Minutes | Incidence of a mean arterial pressure (MAP) < 60 mmHg for a cumulative duration of all hypotensive episodes of more than 10 minutes during the anesthetic phase of the procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 55 mmHg for > 10 Minutes | Incidence of a mean arterial pressure (MAP) < 55 mmHg for a cumulative duration of all hypotensive episodes of more than 10 minutes during the anesthetic phase of the procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 50 mmHg for > 10 Minutes | Incidence of a mean arterial pressure (MAP) < 50 mmHg for a cumulative duration of all hypotensive episodes of more than 10 minutes during the anesthetic phase of the procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 60 mmHg for > 20 Minutes | Incidence of a mean arterial pressure (MAP) < 60 mmHg for a cumulative duration of all hypotensive episodes of more than 20 minutes during the anesthetic phase of the procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 55 mmHg for > 20 Minutes | Incidence of a mean arterial pressure (MAP) < 55 mmHg for a cumulative duration of all hypotensive episodes of more than 20 minutes during the anesthetic phase of the procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Incidence of a MAP < 50 mmHg for > 20 Minutes | Incidence of a mean arterial pressure (MAP) < 50 mmHg for a cumulative duration of all hypotensive episodes of more than 20 minutes during the anesthetic phase of the procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Depth and Duration of Intraoperative Hypotension - Threshold MAP 75 mmHg | Depth and duration of intraoperative hypotension will be modeled by calculating areas under the threshold for mean arterial pressures (MAPs). Thresholds will vary from 75 mmHg to 50 mmHg in 5 mmHg decrements. Together these variables represent the depth and duration of intraoperative hypotension. To optimize goodness of fit of these variables, the decremental steps may be increased to 10 mmHg and more restrictive lowest and highest thresholds may be chosen for the statistical analysis. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Depth and Duration of Intraoperative Hypotension - Threshold MAP 70 mmHg | Depth and duration of intraoperative hypotension will be modeled by calculating areas under the threshold for mean arterial pressures (MAPs). Thresholds will vary from 75 mmHg to 50 mmHg in 5 mmHg decrements. Together these variables represent the depth and duration of intraoperative hypotension. To optimize goodness of fit of these variables, the decremental steps may be increased to 10 mmHg and more restrictive lowest and highest thresholds may be chosen for the statistical analysis. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Depth and Duration of Intraoperative Hypotension - Threshold MAP 65 mmHg | Depth and duration of intraoperative hypotension will be modeled by calculating areas under the threshold for mean arterial pressures (MAPs). Thresholds will vary from 75 mmHg to 50 mmHg in 5 mmHg decrements. Together these variables represent the depth and duration of intraoperative hypotension. To optimize goodness of fit of these variables, the decremental steps may be increased to 10 mmHg and more restrictive lowest and highest thresholds may be chosen for the statistical analysis. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Depth and Duration of Intraoperative Hypotension - Threshold MAP 60 mmHg | Depth and duration of intraoperative hypotension will be modeled by calculating areas under the threshold for mean arterial pressures (MAPs). Thresholds will vary from 75 mmHg to 50 mmHg in 5 mmHg decrements. Together these variables represent the depth and duration of intraoperative hypotension. To optimize goodness of fit of these variables, the decremental steps may be increased to 10 mmHg and more restrictive lowest and highest thresholds may be chosen for the statistical analysis. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Depth and Duration of Intraoperative Hypotension - Threshold MAP 55 mmHg | Depth and duration of intraoperative hypotension will be modeled by calculating areas under the threshold for mean arterial pressures (MAPs). Thresholds will vary from 75 mmHg to 50 mmHg in 5 mmHg decrements. Together these variables represent the depth and duration of intraoperative hypotension. To optimize goodness of fit of these variables, the decremental steps may be increased to 10 mmHg and more restrictive lowest and highest thresholds may be chosen for the statistical analysis. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Depth and Duration of Intraoperative Hypotension - Threshold MAP 50 mmHg | Depth and duration of intraoperative hypotension will be modeled by calculating areas under the threshold for mean arterial pressures (MAPs). Thresholds will vary from 75 mmHg to 50 mmHg in 5 mmHg decrements. Together these variables represent the depth and duration of intraoperative hypotension. To optimize goodness of fit of these variables, the decremental steps may be increased to 10 mmHg and more restrictive lowest and highest thresholds may be chosen for the statistical analysis. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Estimated Intraoperative Blood Loss | The estimated blood loss in mL during the surgical procedure | During the surgical procedure: an expected average of 2 hours | 
| Time to Discharge Readiness at the Postanesthesia Care Unit (PACU) | The time from arriving at the postanesthesia care unit (PACU) until the time the patient is considered ready for discharge (in minutes). | A specific time frame on the day of surgery: from the start of admission to the PACU to discharge from the PACU, an expected average of 4 hours | 
| Intravenous Anesthetic Drug Use During Intraoperative Hypotension: MAP < 65 mmHg | Average concentrations of propofol infusion rates during MAP < 65 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Intravenous Anesthetic Drug Use During Intraoperative Hypotension: MAP < 60 mmHg | Average concentrations of propofol infusion rates during MAP < 60 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Intravenous Anesthetic Drug Use During Intraoperative Hypotension: MAP < 55 mmHg | Average concentrations of propofol infusion rates during MAP < 55 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Intravenous Anesthetic Drug Use During Intraoperative Hypotension: MAP < 50 mmHg | Average concentrations of propofol infusion rates during MAP < 50 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Average Use of Cardiovascular Drugs: Ephedrine | Cardiovascular drugs as defined under interventions. Average use for each drug will be calculated. Cardiovascular drugs that were given in <1% of cases are not reported, as the average dosages would be meaningless. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Average Use of Cardiovascular Drugs: Phenylephrine | Cardiovascular drugs as defined under interventions. Average use for each drug will be calculated. Cardiovascular drugs that were given in <1% of cases are not reported, as the average dosage would be meaningless. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Average Use of Cardiovascular Drugs: Glycopyrrolate | Cardiovascular drugs as defined under interventions. Average use for each drug will be calculated. Cardiovascular drugs that were given in <1% of cases are not reported, as the average dosage would be meaningless. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Average Use of Cardiovascular Drugs: Epinephrine | Cardiovascular drugs as defined under interventions. Average use for each drug will be calculated. Cardiovascular drugs that were given in <1% of cases are not reported, as the average dosage would be meaningless. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Average Use of Cardiovascular Drugs: Norepinephrine | Cardiovascular drugs as defined under interventions. Average use for each drug will be calculated. Cardiovascular drugs that were given in <1% of cases are not reported, as the average dosage would be meaningless. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Timing of Cardiovascular Drugs for MAP < 65 mmHg | Cardiovascular drugs as defined under interventions. Time of first administration of cardiovascular drug relative to the time at which the mean arterial pressure (MAP) drops below 60 mmHg. Per patient the average time to first administration of all hypotensive episodes was calculated. That average time is used as the outcome variable. A negative value indicates that administration occurred before the drop in MAP. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Timing of Cardiovascular Drugs for MAP < 60 mmHg | Cardiovascular drugs as defined under interventions. Time of first administration of cardiovascular drug relative to the time at which the mean arterial pressure (MAP) drops below 60 mmHg. Per patient the average time to first administration of all hypotensive episodes was calculated. That average time is used as the outcome variable. A negative value indicates that administration occurred before the drop in MAP. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Timing of Cardiovascular Drugs for MAP < 55 mmHg | Cardiovascular drugs as defined under interventions. Time of first administration of cardiovascular drug relative to the time at which the mean arterial pressure (MAP) drops below 55 mmHg. Per patient the average time to first administration of all hypotensive episodes was calculated. That average time is used as the outcome variable. A negative value indicates that administration occurred before the drop in MAP. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Timing of Cardiovascular Drugs for MAP < 50 mmHg | Cardiovascular drugs as defined under interventions. Time of first administration of cardiovascular drug relative to the time at which the mean arterial pressure (MAP) drops below 50 mmHg. Per patient the average time to first administration of all hypotensive episodes was calculated. That average time is used as the outcome variable. A negative value indicates that administration occurred before the drop in MAP. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Intraoperative Administration of Intravenous Fluids | Total amount (mL) of intravenous fluids (as defined under interventions) administered during the surgical procedure. | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Inhaled Anesthetic Drug Use During Intraoperative Hypotension: MAP < 65 mmHg | Average concentrations of inhalational anesthesia during MAP < 65 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Inhaled Anesthetic Drug Use During Intraoperative Hypotension: MAP < 60 mmHg | Average concentrations of inhalational anesthesia during MAP < 60 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Inhaled Anesthetic Drug Use During Intraoperative Hypotension: MAP < 55 mmHg | Average concentrations of inhalational anesthesia during MAP < 55 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 
| Inhaled Anesthetic Drug Use During Intraoperative Hypotension: MAP < 50 mmHg | Average concentrations of inhalational anesthesia during MAP < 50 mmHg episodes | During the anesthetic phase of the surgical procedure: an expected average of 2.5 hours | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Decision support, Decision Support Systems, Clinical, Decision Support Techniques, Hypotension, Intraoperative Hypotension, Acute Kidney Injury, Postoperative Mortality, Blood Pressure