Time course of systolic and diastolic blood pressure decreases during the preintubation period of anesthesia induction: modeling with a logistic function

Study ObjectiveTo investigate whether systolic (SBP) and diastolic blood pressure (DBP) decreases during the preintubation period could be expressed as 4-parameter logistic and cubic functions giving S-shaped curves.DesignProspective, clinical study.SettingOperating room of a metropolitan general hospital.PatientsSeven ASA physical status I and II patients scheduled for elective spinal surgery during general anesthesia.InterventionsAnesthesia was induced with fentanyl, propofol, and vecuronium injection followed by inhalation of sevoflurane.MeasurementsThe SBP and DBP data were recorded at all beats from fentanyl injection to direct laryngoscopy. The respective changes were analyzed using a logistic function: P(t) = pL + (qL − pL)/(1 + exp{[4 mL/(qL − pL)][kL − t]}) and a cubic function: P(t) = at3 + bt2 + ct + d, where parameter pL is the upper asymptote, qL is the lower asymptote, mL is the slope at the inflection point, and kL is the time to the inflection point and where a, b, and c are coefficients, and d are constants. Goodness of fit of the two functions was compared using a correlation coefficient and residual mean squares. Each parameter was compared with the corresponding observed data.Main ResultsLogistic correlation coefficient values for SBP and DBP decreases were larger than the cubic correlation coefficient values (0.990 [Z transformation: 2.64 ± 0.32] vs 0.981 [Z: 2.32 ± 0.37] and 0.977 [Z: 2.22 ± 0.33] vs 0.967 [Z: 2.05 ± 0.34], respectively; P < 0.05). Logistic residual mean squares values for SBP and DBP decreases were smaller than cubic residual mean squares values (20.6 vs 41.0 and 9.2 vs 13.7 mmHg2, respectively; P < 0.05). There were significant correlations between pL and SBP or DBP after anesthesia induction, between qL and SBP or DBP before endotracheal intubation, and between kL and time to maximal rate of the SBP or DBP decrease (dP/dtmin), but no significant correlation between mL and dP/dtmin for SBP or DBP.ConclusionsTime courses of SBP and DBP decreases during the preintubation period of anesthesia induction are modeled effectively by a logistic function.