Effect of Perioperative Fluid Therapy on Post-induction Hypotension

Preoperative dehydration causes severe hypotension after induction of general anaesthesia (GA). We aimed to investigate whether weight-calculated fluid therapy during the preoperative fasting period could protect against postinduction hypotension. 120 patients were included in this prospective, single-centre, randomised, controlled study. Those who received fluid therapy were referred to as Group A, those who did not were referred to as Group B, those who developed hypotension were referred to as Group H, and those who did not were referred to as Group O. Inferior vena cava diameter (dIVC), collapsibility index (CI %), perfusion index (PI) and pleth variability index (PVI) were recorded before induction and pulse pressure variation (PPV) was recorded after connection to the mechanical ventilator and compared. Mean blood pressure (MBP) \< 60 mmHg or ≤ 30% from baseline was defined as hypotension. Receiver operating characteristic (ROC) curve and regression analyses were used to evaluate the relationship between haemodynamic parameters and hypotension.

This prospective, randomized, controlled study was approved by the Ministry of Health Istanbul Medeniyet University Göztepe Training and Research Hospital Clinical Research Ethics Committee (approval number 2022/0263, dated 27 April 2022).

A total of 120 patients, aged 18 years and older and planned for gynaecological pelvic surgery with an American Society of Anaesthesiologists (ASA) physical status score of I-III, were included in this study. All participants were female patients. All patients underwent general anaesthesia. Exclusion criteria were unstable haemodynamics (persistent hypotension preventing extubation at the end of surgery, arrhythmia, ejection fraction (EF) \< 40%), valvular heart disease, cardiac pacing, obesity (BMI \>35), chronic obstructive pulmonary disease (COPD), Increased intrabdominal pressure, open wound at the US site, preoperative severe hypertension (systolic blood pressure \>180 mmHg, diastolic \>110 mmHg), use of angiotensin II receptor blockers (ARB), angiotensin coverting enzyme inhibitor (ACE-I) and refusal to participate in the study.

Randomization was performed by the sealed envelope method. The closed envelopes were randomly numbered, and each patient randomly selected the envelope that defined her group. Those who chose the envelope ending with an even number were identified as group A patients (n = 55), and those who chose the envelope ending with an odd number were identified as group B patients (n = 55).

All patients were thoroughly evaluated and medically optimised through the preoperative preparation outpatient clinic. Intra venous (IV) fluid infusion calculated according to preoperative weight and dIVC-CI measurement procedure were explained to the patient on the night of surgery and consent was obtained. Bowel cleansing procedure was performed by the gynaecological surgeon. Oral nutrition was discontinued at midnight, adhering to the routine practice of the gynaecology clinic. Group A patients were started on IV infusion of maintenance fluid (polifleks isolen-s, POLİFARMA İLAÇ SAN. VE TİC. A.Ş.) calculated according to weight. The maintenance fluid calculated according to weight was 4 mL/st for the first 10 kg, 2 mL/st for the second 10 kg and 1 mL/st for each remaining kg and infused hourly during the fasting period.

When the patient reached the operating theatre, the fasting period was questioned and recorded. 5 lead electrocardiography (ECG), pulse oximetry and non-invasive blood pressure monitoring (Fabius GS Premium Drager Anesthesia monitor, Germany) were performed. Masimo Rainbow (Adult/Neonatal Pulse CO-Oximeter Adhesive sensor, CALIFORNIA) probe was placed on the left index finger of the patients for measurement of PI and PVI values. Heart rate (HR), SBP, MBP, MBP, PI and PVI baseline measurements were recorded.

IVC ultrasonography was performed after the patient rested in the supine position in spontaneous respiration for at least 5 minutes before induction. The IVC was imaged in the paramedian long axis at the junction with the right atrium with a low (3-5 mHz) frequency convex probe (CA1-7AD Samsung brobu) using USG (Samsung Medison H60, KOREA) with a subcostal approach. In M mode, respiratory changes in the IVC were evaluated approximately 1.5-3 cm distal to the right atrium, approximately 2 cm from the point where the hepatic vein drains into the IVC. The maximum (expiratory) diameter and minimum (inspiratory) diameter of the IVC were monitored during the same respiratory cycle. IVC-CI was calculated and recorded as a percentage using the formula IVC-CI = (dIVC expiration-dIVC inspiration) ×100/dIVC expiration. The patient position and ultrasound images are shown in Figure 2.

Anesthesia management, 1 mg/kg midazolam and 1 µg/kg fentanyl IV were administered for sedation. Propofol 2 mg/kg and rocuronium bromide 0.6 mg/kg were used for induction. Sevoflurane/oxygen/air mixture with a minimum alveolar concentration (MAC) of 0.8-1 was used for resuscitation. Remifentanil infusion of 0.05-1 µg/kg/min was preferred as analgesic. Tidal volume was set as 8 ml/kg, frequency 12-16/min, positive end expiratory pressure (PEEP) 5 cm/H2O. HR (0 st min), SBP (0 st min), MBP (0 st min) measurements were repeated and recorded. For invasive blood pressure monitoring, an IV cannula was inserted into the right radial artery under aseptic conditions and PPV (0 st min) was recorded. HR, SBP, MBP, PI, PVI, PPV measurements were recorded every 10th minute.

After induction, MBP \< 60 mmHg or a decrease of more than 30% from basal value was considered as hypotension. Patients who developed hypotension (Group H) and those who did not (Group O) were recorded. Group H patients were given 3 ml/kg bolus of infused fluid, and iv 5 mg ephedrine was administered to patients whose haemodynamics did not improve despite fluid bolus and recorded. In the intraoperative period, Group A and Group B patients were administered hourly maintenance fluid (balanced solution) calculated according to weight, surgical field fluid loss, and crystalloid IV as much as the amount of diuresis. Erythrocyte replacement was performed in patients with a haemoglobin (Hb) value of 10 g/dl whose haemodynamics deteriorated due to bleeding.

Anaesthesia was terminated at the end of the surgical procedure. Neuromuscular blockade was terminated with IV sugammadex. Patients who fulfilled extubation conditions were transferred to the recovery room after extubation. They were discharged to the ward after reaching a Modified Aldrete score of 12.

Our primary outcome was a comparison of the incidence of post-induction hypotension between the two groups. Secondary outcomes included the comparison of dIVC, CI (%), PI, PVI, and PPV in predicting hypotension.

Eligibility Criteria:
Inclusion Criteria:

* Gynaecological pelvic surgery planned for patients aged 18 years and over
* Patients with an American Society of Anaesthetists score of 1-2-3

Exclusion Criteria:

* Unstable haemodynamics (persistent hypotension preventing extubation at the end of surgery, arrhythmia, ejection fraction (EF) \< 40%),
* Valvular heart disease,
* Cardiac pacing,
* Obesity (BMI \>35),
* Chronic obstructive pulmonary disease (COPD),
* Increased intrabdominal pressure,
* Open wound at the US site,
* Preoperative severe hypertension (systolic blood pressure \>180 mmHg, diastolic \>110 mmHg),
* Use of angiotensin II receptor blockers (ARB), angiotensin coverting enzyme inhibitor (ACE-I)
* Refusal to participate in the study