The SLUScore: A Novel Method for Detecting Hazardous Hypotension in Adult Patients Undergoing Noncardiac Surgical Procedures. 

Anesthesia and Analgesia 2017;124(4):1135–1152. 

Presented by: Dr T. Newton

Background

  • Adequate blood pressure control is one of the major concerns in an intra-operative setting.
  • Increasing evidence that extended periods of severe hypotension may effect long-term outcomes.
  • Patients currently categorised in binary fashion- intervention either unnecessary or already too late.
  • Hypothesis: adverse outcomes affected by severity of hypotension and duration accumulated below thresholds commonly encountered during anaesthesia.

Design and Setting

  • 3 centre retrospective cohort study
  • Approval from institutional ethics bodies
  • Databases searched for adult patients undergoing non-cardiac procedures. Data collected on demographics, Charlson comorbidity score, type of anaesthetic, case duration, blood loss, minute to minute MAP values, all-cause 30 day mortality.
  • Development of score:
    • N=33904
    • Multivariable logistic regression to identify risks associated with increased 30 day mortality including time spent below 31 commonly encountered MAP thresholds
    • % increase in odds of 30d mortality calculated for each minute spent below each of the MAP thresholds
    • Number of minutes calculated for each threshold required to produce identical increases in 30d mortality from 5-30%
    • 20% set used to determine SLUScore- each increment of score corresponds to +5%compounding progression of odds of 30d mortality
  • Validation of score with 3 centre study, n=116,541

Results

  • Independent factors affecting 30 day mortality: age, Charlson comorbidity score, cumulative blood loss. All adjusted for.
  • Dropping below progressively lower MAP thresholds à greater increase in 30d mortality per unit time below that threshld.
  • Preoperative diagnosis of hypertension means time needed below each threshold for same increase in risk.
  • Increase in mortality depended on number of exposure limits exceeded.
  • 30 day mortality approximately doubled in patients with SLUScore >0.
  • Less time may be spent at lower MAP to accrue same risks (analogous to diving charts).

Strengths

  • Large sample size for creation of score, larger size across multiple sites for valifation.
  • 5 year duration at one site.
  • Accounts for some confounding factors, separate scores for pre-existing hypertension.

Weaknesses

  • Does not account for severity/risk of procedure- increased risk of procedure vs MAP, or does procedure cause drop in MAP?
  • Minute to minute measurements taken from extrapolation of 5 minute NIBPs.

Impact

  • Too complex to calculate in real time intra-op.
  • Relies on assumptions with 5 minute NIBPs in most cases.
  • May be useful in future generations of monitors/anaesthetic machines as in-built function.
  • Potential for litigation- if any patient has morbidity from renal function/sepsis etc and has had a GA, anaesthetist may be targeted using SLUScore.