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Plethysmography variability index for prediction of spinal induced hypotension.
Abstract Number: F-04
Abstract Type: Original Research
Background: Hypotension occurs commonly following spinal anesthesia for cesarean delivery. The incidence of hypotension can be significantly reduced with a prophylactic phenylephrine infusion with rapid fluid co-loading. This strategy can be associated with reactive hypertension and reflex bradycardia. The hemodynamic response and dose requirements also vary among individual patients. Identifying women at greater risk for spinal induced hypotension might allow targeting prophylactic vasopressor therapy to those who need it. The plethysmography variability index (PVI), a continuous noninvasive measure of the respiratory variations in the pulse oximetry waveform, has been validated to predict fluid responsiveness in mechanically ventilated patients. Although PVI has not been validated in spontaneously breathing patients, it might predict hemodynamic changes induced by passive leg raising (PLR). Studies assessing PVI to predict spinal induced hypotension during cesarean delivery have yielded conflicting results. We performed this study to assess if baseline PVI and PVI/cardiac output (CO) changes induced by PLR can predict hypotension following spinal anesthesia for cesarean delivery.
Methods: Women scheduled for cesarean delivery under spinal anesthesia were enrolled in this study. Baseline blood pressure (BP) was obtained by taking the mean of 3 blood pressure readings 2 minutes apart. Baseline PVI and CO were measured using the Masimo Radical-7 device and PhysioFlow over 6 minutes. A PLR test was performed and the change of PVI and CO to PLR was recorded after 3 minutes. Patients received a standardized spinal anesthetic. BP was measured at 1-minute intervals and SBP decreases >20% were treated with phenylephrine boluses. Fluid therapy was standardized and consisted of 2 L crystalloid coload administered before delivery.
Results: 39 patients were included in the analysis. Mean (SD) baseline PVI was 25.8 (9.9) and 27.1 (10.5) after PLR (P=0.50). Baseline CO was 6.7 (2.3) and 7.0 (2.7) after PLR (p=0.63). Blood pressure decreased significantly after spinal (p<0.0001). Spinal induced hypotension occurred in 28 (72 %) patients before delivery and 19 (49%) after delivery. Overall, 33 (85%) patients needed phenylephrine. Mean (SD) PVI at baseline [35 (12) vs. 23 (8)] and after PLR [34 (13) vs. 25 (8)] were significantly higher in those who developed hypotension (p<0.05). There was however no significant correlation between baseline PVI, PVI change after PLR or CO change after PLR and change in SBP after spinal until delivery (Spearman correlation=0.31, p=0.058, 0.02, p=0.9 and -0.27, p=0.09 respectively) or after delivery. There was also no significant correlation between baseline PVI, PVI change after PLR or CO change after PLR with occurrence of hypotension, need for vasopressors or dose of phenylephrine given.
Conclusion: PVI and change in CO induced by PLR did not predict hypotension in women undergoing cesarean delivery under spinal anesthesia.