Background

After traumatic brain injury (TBI), the ability of cerebral vessels to appropriately react to changes in arterial blood pressure (pressure reactivity) is impaired, leaving patients vulnerable to cerebral hypo- or hyperperfusion. Although, the traditional pressure reactivity index (PRx) has demonstrated that impaired pressure reactivity is associated with poor patient outcome, PRx is sometimes erratic and may not be reliable in various clinical circumstances. Here, we introduce a more robust transform-based wavelet pressure reactivity index (wPRx) and compare its performance with the widely used traditional PRx across 3 areas: its stability and reliability in time, its ability to give an optimal cerebral perfusion pressure (CPPopt) recommendation, and its relationship with patient outcome.

Methods and findings

Five hundred and fifteen patients with TBI admitted in Addenbrooke’s Hospital, United Kingdom (March 23rd, 2003 through December 9th, 2014), with continuous monitoring of arterial blood pressure (ABP) and intracranial pressure (ICP), were retrospectively analyzed to calculate the traditional PRx and a novel wavelet transform-based wPRx. wPRx was calculated by taking the cosine of the wavelet transform phase-shift between ABP and ICP. A time trend of CPPopt was calculated using an automated curve-fitting method that determined the cerebral perfusion pressure (CPP) at which the pressure reactivity (PRx or wPRx) was most efficient (CPPopt_PRx and CPPopt_wPRx, respectively).

There was a significantly positive relationship between PRx and wPRx (r = 0.73), and wavelet wPRx was more reliable in time (ratio of between-hour variance to total variance, wPRx 0.957 ± 0.0032 versus PRx and 0.949 ± 0.047 for PRx, p = 0.002). The 2-hour interval standard deviation of wPRx (0.19 ± 0.07) was smaller than that of PRx (0.30 ± 0.13, p < 0.001). wPRx performed better in distinguishing between mortality and survival (the area under the receiver operating characteristic [ROC] curve [AUROC] for wPRx was 0.73 versus 0.66 for PRx, p = 0.003). The mean difference between the patients’ CPP and their CPPopt was related to outcome for both calculation methods. There was a good relationship between the 2 CPPopts (r = 0.814, p < 0.001). CPPopt_wPRx was more stable than CPPopt_PRx (within patient standard deviation 7.05 ± 3.78 versus 8.45 ± 2.90; p < 0.001).

Key limitations include that this study is a retrospective analysis and only compared wPRx with PRx in the cohort of patients with TBI. Prior prospective validation is required to better assess clinical utility of this approach.

Conclusions

wPRx offers several advantages to the traditional PRx: it is more stable in time, it yields a more consistent CPPopt recommendation, and, importantly, it has a stronger relationship with patient outcome. The clinical utility of wPRx should be explored in prospective studies of critically injured neurological patients.

中文翻译：

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应用小波分析监测脑外伤患者的脑血管压力反应性：一项回顾性研究

背景

脑外伤（TBI）后，脑血管对动脉血压的变化做出适当反应的能力（压力反应性）受损，使患者容易遭受脑灌注不足或灌注过高。尽管传统的压力反应性指数（PRx）已证明压力反应性受损与患者预后不良相关，但PRx有时不稳定，在各种临床情况下可能都不可靠。在这里，我们介绍了一个更强大的基于变换的小波压力反应性指数（wPRx），并将其性能与3个领域中广泛使用的传统PRx进行了比较：其稳定性和及时性，提供最佳脑灌注压力的能力（CPPopt）推荐及其与患者预后的关系。

方法和发现

回顾性分析了英国Addenbrooke医院（2003年3月23日至2014年12月9日）收治的515例TBI患者，这些患者连续监测动脉血压（ABP）和颅内压（ICP），以计算传统PRx和一种新颖的基于小波变换的wPRx。通过采用ABP和ICP之间的小波变换相移的余弦来计算wPRx。使用自动曲线拟合方法计算CPPopt的时间趋势，该方法确定压力反应性（PRx或wPRx）最有效的大脑灌注压力（CPP）（分别为CPPopt_PRx和CPPopt_wPRx）。

PRx和wPRx之间存在显着正相关（r = 0.73），并且小波wPRx在时间上更可靠（小时间方差与总方差之比，相对于PRx，wPRx为0.957±0.0032，对于PRx，wPRx为0.949±0.047，p = 0.002）。wPRx的2小时间隔标准偏差（0.19±0.07）小于PRx的2小时间隔标准偏差（0.30±0.13，p <0.001）。wPRx在区分死亡率和存活率方面表现更好（wPRx的受试者工作特征[ROC]曲线[AUROC]下面积为0.73，而PRx为0.66，p = 0.003）。两种计算方法的患者CPP与CPPopt之间的平均差异与结局有关。2个CPPopts之间存在良好的关系（r = 0.814，p<0.001）。CPPopt_wPRx比CPPopt_PRx更稳定（患者标准偏差为7.05±3.78对8.45±2.90；p <0.001）。

主要限制包括该研究是一项回顾性分析，仅将TPR患者队列中的wPRx与PRx进行了比较。需要事先进行前瞻性验证才能更好地评估此方法的临床效用。

结论

wPRx与传统PRx相比具有以下优点：时间更稳定，产生更一致的CPPopt建议，并且重要的是，它与患者预后之间有着更强的联系。在严重受伤的神经系统患者的前瞻性研究中应探索wPRx的临床用途。