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

Study Objective: To 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. Design: Prospective, clinical study. Setting: Operating room of a metropolitan general hospital. Patients: Seven ASA physical status I and II patients scheduled for elective spinal surgery during general anesthesia. Interventions: Anesthesia was induced with fentanyl, propofol, and vecuronium injection followed by inhalation of sevoflurane. Measurements: The 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) = p_L + (q_L - p_L)/(1 + exp{[4 m_L/(q_L - p_L)][k_L - t]}) and a cubic function: P(t) = at³ + bt² + ct + d, where parameter p_L is the upper asymptote, q_L is the lower asymptote, m_L is the slope at the inflection point, and k_L 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 Results: Logistic 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 p_L and SBP or DBP after anesthesia induction, between q_L and SBP or DBP before endotracheal intubation, and between k_L and time to maximal rate of the SBP or DBP decrease (dP/dt_min), but no significant correlation between m_L and dP/dt_min for SBP or DBP. Conclusions: Time courses of SBP and DBP decreases during the preintubation period of anesthesia induction are modeled effectively by a logistic function.