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) = at(3) + bt(2) + 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 mmHg(2), 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.