Our study was approved by the Ethics Committee of Fuyang District First People's Hospital, and followed the principles of the Helsinki Declaration. Written informed consents were obtained from patients. The study was a two-part prospective, clinical trial. We obtained the IVCci threshold for patients with post-IGA hypotension due to lack of blood volume in Part I. We increased the liquid infusion step for elderly patients with hypovolemic blood to verify the effect of hypovolemic state before induction on the post-IGA hypotension incidence in elderly patients in Part II. Informed consent was obtained from the patients or their families.
The subjects were older adult patients (n=126) who underwent general anesthesia for surgery between March 2017 and June 2017 in the Department of Anesthesia, Fuyang District First People's Hospital, Hangzhou. We included female or male patients aged 65-94 years with an American Society of Anesthesiologists grade of I-III. Exclusion criteria were: mental disorder, obesity, severe peripheral vascular disease, thoracic disease, pleural effusion/increased intrapleural pressure, heart valve disease, unstable angina, cardiac dysfunction,presence of valvuler pathologies and presence of cardiac dysfunction autonomous nervous system disorder, pacemaker/cardioverter, hypertension, respiratory distress, pulmonary hypertension(the diagnosis of these diseases was made by echocardiography or by medical history), patients who used drugs that affect the cardiovascular system, potentially difficult airway, abdominal effusion/increased intra-abdominal pressure, uncooperative patients, and unsuccessful ultrasonographic scanning of the IVC. Patients were preoperatively fasted for 12 h, with fluid deprivation for 4 h.
Part I (group T). An intravenous trocar was preoperatively placed in 60 older adult patients who underwent general anesthesia for surgery between March 2017 and April 2017 in the preparation room, followed by intravenous infusion of compound sodium chloride at 10 ml/kg/h. After entering the operation room, patients were sedated with intravenous midazolam (0.01 mg/kg, Jiangsu Enhua Pharmaceutical Co., Ltd., China). A nasal catheter was used to deliver oxygen at 2 L/min. Local anesthesia was applied to enable catheterization of the radial artery. The ambient temperature in the operation room was maintained at 25°C. Before IGA, the following measurements were taken: electrocardiographic monitoring, systolic BP, diastolic BP, mean arterial pressure (MAP), heart rate (HR), and bispectral index. Patients were placed in supine position for 5 min to stabilize their hemodynamics. An ultrasound machine (Sonosite, Inc., Bothell, WA, USA) with a 3.5 MHz probe (L25x, 3.5 MHz; SonoSite) was used to locate the posterior hepatic IVC vertically along the right costal margin. The internal IVC diameter (IVCD) was measured at a position 2 cm from the entrance to the right atrium. Ultrasound images were synchronized. The maximum and minimum ICVD (IVCmax and IVCmin) were measured at end inspiration and end expiration, respectively. Measurements were performed in triplicate, and the mean was used to calculate the IVC collapsibility index (IVCci = (IVCmax - IVCmin)/IVCmax×100%), the IVC distensibility index (IVCdi = (IVCmax - IVCmin)/IVCmin × 100%), and the IVC respiratory variation rate (IVCrvr = (IVCmax - IVCmin)/[0.5 × (IVCmax + IVCmin)] × 100%). All IVCD measurements were performed by one physician (T.W.) who was fully trained and experienced in echocardiography. Systolic BP, diastolic BP, and MAP were then measured every 20 s for a total of three times just before IGA. Mean BPs were calculated and used as baseline BP values. Five minutes after IVCD measurements were performed, IGA was initiated via intravenous administration of sufentanil (0.5 µg/kg, Yichang Renfu Pharmaceutical Co., Ltd., China) for 60 s, propofol (1.8 mg/kg, Beijing Fresenius-Kabi Pharmaceutical Co., Ltd., China) at a rate of 40 ml/10 s, and cisatracurium besilate (0.2 mg/kg, Shanghai Dongying Pharmaceutical Co., Ltd., China). Mask ventilation was provided following jaw thrust with tidal volume at 8-10 ml/kg, respiratory rate at 18–20 breaths/min, and end-tidal carbon dioxide partial pressure at 34–45 mmHg (1 mmHg = 0.133 kPa). Bispectral index was maintained at 40–60. Tracheal intubation was performed 5 min after IGA to enable mechanical ventilation.
Part II. An intravenous trocar was placed in 66 patients who underwent general anesthesia for surgery between May 2017 and June 2017 in the preparation room, followed by intravenous infusion of compound sodium chloride at 10 ml/kg/h. The operation room ambient temperature, hemodynamic monitoring, midazolam sedation, and IVCD measurements were performed as described in part I. IVCD measurements were used to calculate the most sensitive index (MSI). The optimal cutoff value (OCV) of the MSI from part I was used to divide the patients in part II into two groups: group B (MSI ≥ OCV), and group S (MSI < OCV). Prior to IGA, group B were administered an intravenous bolus of compound sodium chloride (8 ml/kg) over a period of 30 min to maintain sufficient body fluid volume. Group S were administered an intravenous infusion of compound sodium chloride injection at 10 ml/kg/h for 30 min for volumetric maintenance. IGA was started after 30 min of infusion in both groups. IGA was performed as described in part I. Sevoflurane (1–2%) was used to maintain anesthesia after tracheal intubation. We recorded the pre- and post-infusion MAP and HR of both groups, and the lowest MAP and HR in the period between IGA and surgery commencement.
Those who did not have hypotension were observed for at least 10 min between IGA and surgery commencement. Hypotension was defined as a MAP decrease of ≥ 20% from baseline, and bradycardia was defined as a HR of < 40 beats/min. If hypotension occurred, phenylephrine (50 µg, Shanghai Hefeng Pharmaceutical Co., Ltd., China) was administered intravenously. If bradycardia occurred, atropine 0.5 mg was administered intravenously. These two medications were re-administered as necessary until MAP was ≥ 20% of the baseline value and HR was ≥ 40 beats/min. The number of patients who received phenylephrine and/or atropine was recorded during IGA.
Statistical analysis.
Quantitative values were expressed as the mean ± SD. The paired-sample t-test was used to compare paired samples. Comparisons between groups were carried out with the independent sample t-test, and correlation analysis was carried out using Pearson’s coefficient. The receiver operating characteristic (ROC) curve of the observed results was generated, and the area under the ROC curve was calculated. One-way analysis of variance (ANOVA) was used for multi-group comparisons, followed by Bonferroni’s correction. Replicate measurements were analyzed using ANOVA, and numerical data were analyzed using the chi-squared test, with p<0.05 considered statistically significant. The statistical analysis was performed with SPSS 22.0 (SPSS Inc., Chicago, IL, USA).