Beat-to-beat tracking of systolic blood pressure using noninvasive pulse transit time during anesthesia induction in hypertensive patients.

BACKGROUND: Pulse transit time (PTT) has been reported to show good agreement with arterial blood pressure (BP) in awake humans. We evaluated whether noninvasive beat-to-beat PTT accurately correlated with invasively measured continuous arterial BP during anesthesia induction in hypertensive patients.
METHODS: Twenty-three hypertensive patients who were scheduled for kidney transplant were enrolled. Radial arterial BP, electrocardiogram, and finger pulse oximetric plethysmography were simultaneously recorded. PTT was measured as the time interval from the R-wave peak on the electrocardiogram to the maximal upslope of the photoplethysmogram. Relationships between beat-to-beat PTT and BP were evaluated by correlation and receiver operating characteristic (ROC) curve analysis.
RESULTS: During anesthesia induction, changes in PTT were directly proportional to changes in BP: when BP decreased, PTT lengthened, and vice versa. The inverse of PTT demonstrated significantly better correlation with systolic BP than with mean BP (r = 0.81 ± 0.11 vs r = 0.72 ± 0.17; P < 0.001) or diastolic BP (r = 0.81 ± 0.11 vs r = 0.52 ± 0.24; P < 0.001). The inverse of PTT was more highly correlated with decreasing than with increasing changes in systolic BP (r = 0.83 ± 0.12 vs r = 0.68 ± 0.20; P = 0.001). The ROC curve analysis revealed that a 15% increase in PTT during anesthesia induction could detect a ≥30% decrease in systolic BP, with an area under the ROC curve of 0.85.
CONCLUSION: Beat-to-beat PTT was fairly well correlated with invasive systolic BP and could predict a reduction in systolic BP during anesthesia induction. Beat-to-beat PTT may show potential as a useful noninvasive index of systolic BP when invasive BP is unavailable in high-risk hypertensive patients.