Duration of Surgery and Intraoperative Blood Pressure Management Are Modifiable Risk Factors for Postoperative Neurocognitive Disorders After Spine Surgery: Results of the Prospective CONFESS Study

Abstract

Study design: Prospective quasi-experimental observational study.

Objective: The objective of this study was to evaluate whether duration of surgery is a modifiable risk factor for postoperative delirium (POD) after spine surgery and explore further modifiable risk factors. In addition, we sought to investigate the association between POD and postoperative cognitive dysfunction and persistent neurocognitive disorders.

Summary of background data: Advances in spine surgery enable technically safe interventions in elderly patients with disabling spine disease. The occurrence of POD and delayed neurocognitive complications ( e.g. postoperative cognitive dysfunction/persistent neurocognitive disorder) remain a concern since these contribute to inferior functional outcomes and long-term care dependency after spine surgery.

Materials and methods: This prospective single-center study recruited patients aged 60 years or above and scheduled for elective spine surgery between February 2018 and March 2020. Functional (Barthel Index, BI) and cognitive outcomes [Consortium to Establish a Registry for Alzheimer's Disease (CERAD) test battery; telephone Montréal Cognitive Assessment] were assessed at baseline, three (V3), and 12 months postoperatively. The primary hypothesis was that the duration of surgery predicts POD. Multivariable predictive models of POD included surgical and anesthesiological parameters.

Results: Twenty-two percent of patients developed POD (n=22/99). In a multivariable model, duration of surgery [OR adj =1.61/h (95% CI, 1.20-2.30)], age [OR adj =1.22/yr (95% CI, 1.10-1.36)], and baseline deviations of intraoperative systolic blood pressure [25th percentile: OR adj =0.94/mm Hg (95% CI, 0.89-0.99); 90th percentile: OR adj =1.07/mm Hg (95% CI, 1.01-1.14)] were significantly associated with POD. Postoperative cognitive scores generally improved (V3, ΔCERAD total z -score: 0.22±0.63). However, this positive group effect was counteracted by POD [beta: -0.87 (95% CI, -1.31 to 0.42)], older age [beta: -0.03/yr (95% CI, -0.05 to 0.01)], and lack of functional improvement [ΔBI; beta: -0.04/point (95% CI, -0.06 to 0.02)]. Cognitive scores at twelve months remained inferior in the POD group, adjusted for baseline cognition/age.

Conclusions: This study identified distinct neurocognitive effects after spine surgery, which are influenced by perioperative risk factors. Potential cognitive benefits are counteracted by POD, rendering its prevention critical in an aging population.

Figure 1

Illustration of how the ORs for developing POD change with age and duration of surgery, which was the primary hypothesis. The odds for a patient being 60 years of age and undergoing surgery for about 60 minutes were defined as baseline, i.e. OR=1. One can see that the risk for a 60-year-old patient being exposed to 600 minutes of surgery equals the risk of a 85-year-old patient undergoing 120 minutes of surgery (both OR=1.7). The risk increases exponentially with age and duration of surgery.

Figure 2

Illustration of how the ORs for developing POD change with age, duration of surgery and intraoperative blood pressure management. Color coding is similar to Figure 1. The illustration of the four-factor multivariable model includes a box for each of four representative age groups. The z-axis represents an increasing duration of surgery, and x-/y-axes depict intraoperative changes of systolic blood pressure (sBP) compared with baseline values before surgery (25th percentile, i.e. lowest proportion, and 90th percentile, i.e. highest proportion, of intraoperative sBP changes). ORs for an episode increase with age and duration of surgery in line with Figure 1. The model based on this study’s data reveals that either lowering or increasing intraoperative sBP beyond baseline sBP values increases the risk for POD, i.e. blood pressure management should be even more meticulously taken care of in older patients undergoing longer surgery. BP indicates blood pressure.

Figure 3

Illustration of how CERAD-NP total scores (z-score) change from the preoperative to the postoperative period (V0 vs. V3) depending on the delirium status during the postoperative period (top = nondelirious; bottom = delirious), age (x-axis) and functional improvement/deterioration after surgery as assessed by the Barthel Index (y-axis). Color coding indicates either postoperative cognitive dysfunction (POCD; toward red) or cognitive improvement (POCI; toward green), while yellow indicates no change. The model based on this study’s data reveals that no patient, irrespective of age, would be affected by POCD (defined as a z-score change of ≤−1) if neither POD nor deterioration of functional abilities were present. In contrast, almost any age group would develop POCD if they were affected by POD, unless they functionally improved by about 10 (70 years of age or below) to 30 (90 years of age or above) points on the Barthel scale after surgery. The notion of POCI in patients improving by ≥1 z-score is difficult to interpret and may be either subject to enhanced cognitive abilities due to improved physical abilities or retest training effects (see Discussion for a more elaborate discussion).

Figure 4

Trajectories of cognitive scores (mean, 95% CI) at baseline, three and 12 months postoperatively. Cognitive scores are normalized (z-score) and represent the CERAD-NP total score (baseline, 3 mo; straight line) and telephone MoCA sum score (12 mo; dashed line), respectively. Scores are furthermore given unadjusted (left), adjusted for age at baseline (center), and additionally for baseline cognitive performance (right). Color coding indicates patients without (green) and with an episode of POD (red). Patients suffering an episode of PSD tended to have lower cognitive scores at baseline, which was not significant since 95% CI overlap. Postoperative scores were significantly lower in the POD group at three and 12 months, which was more pronounced in the age-adjusted analysis and remained significant after adjusting for baseline cognitive abilities.