A prospective cohort study comparing monitored anesthesia care and intubated general anesthesia in cardiac surgery involving cardiopulmonary bypass | European Journal of Medical Research

Patients

The study protocol received approval from the Ethics Committee of Shuguang Hospital affiliated with Shanghai University of Traditional Chinese Medicine (SUTCM) (#2012-191-07-01). All patients provided written informed consent for the use of their clinical data for research purposes.

This prospective observational study included patients aged 18–75 years scheduled for cardiac surgery involving CPB at Shuguang Hospital of SUTCM. Inclusion criteria were: (1) New York Heart Association (NYHA) classification grade I–III; (2) anticipated aortic cross-clamp time of ≤ 120 min; and (3) body mass index (BMI) within the range of 18–30 kg/cm². Exclusion criteria included: (1) systolic pulmonary blood pressure > 70 mmHg; (2) presence of chronic obstructive pulmonary disease, obstructive sleep apnea syndrome (OSAS), or a simplified airway risk index > 3 [9]; (3) moderate (Child–Pugh grade B) or severe (Child–Pugh grade C) liver insufficiency or renal insufficiency (24-h creatinine clearance < 80 mL/min and blood urea nitrogen > 7.5 mmol/L); and (4) coagulopathy (activated partial thromboplastin time (APTT)) prolongation > 10 s compared to normal controls, prothrombin time (PT) prolongation > 3 s compared to normal controls, and international normalized ratio (INR) > 3.0).

Prior to surgery, patients received a comprehensive explanation of the potential benefits and risks associated with MAC compared to IGA. The decision on choosing either MAC or IGA was collaboratively made by the anesthesiologist, surgeon, and patient.

MAC protocol

Figure 1 provides an overview of the anesthesia protocol. Upon entering the operating room, patients were administered nasal oxygen at a rate of 2 ~ 5 L/min and were subjected to routine monitoring for cardiac surgery. Dexmedetomidine was administered intravenously with a loading dose of 0.75 ~ 1.0 µg/kg for patients younger than 65 years of age, or 0.5 ~ 0.75 µg/kg for those aged 65 years and above (completed over 10 min) and maintained at 0.2 ~ 0.5 µg/kg/h until the conclusion of the surgery. Immediately before the skin incision, remifentanil (0.05 ~ 0.08 µg/kg/min) and sufentanil (0.1 ~ 0.2 µg/kg) were administered intravenously. Local anesthesia at the incision site involved the use of 40 mL of 0.25% ropivacaine. During the sternotomy, the infusion rate of remifentanil was temporarily increased to 1.0 ~ 2.0 µg/kg/min to reduce the respiration rate to < 10/min and enhance analgesia. After the sternotomy, the remifentanil infusion rate was reduced to 0.05 ~ 0.08 µg/kg/min, and airway maneuvers (such as nasal airway, oral airway, chin lift, and bag-mask ventilation) were employed until the respiratory rate recovered to > 12/min, typically within 5 min. Arterial blood samples for gas and electrolyte analysis were obtained at 30-min intervals, and as deemed necessary by the anesthesiologists or surgeons.

The MAC protocol. ① At the site of the incision, ropivacaine (0.25% solution, 40 mL) was used to administer local anesthetic. ② A loading dose of 0.5–1.0 μg/kg of dexmedetomidine (Dex) was administered intravenously within 10 min. Subsequently, the dosage was maintained at 0.2–0.5 μg/kg/h until the conclusion of the surgical procedure. ③ Prior to skin incision, remifentanil (0.05–0.88 μg/kg/min) was administered intravenously. ④ During surgery, a bolus of intravenous sufentanil (0.1–0.2 μg/kg) was administered, with the total quantity not exceeding 35 μg. ⑤ EA stimulation was performed as follows: (1) two consecutive days prior to surgery, consisting of two 30-min sessions each; (2) on the day of surgery, from 30 min prior to the initiation of extracorporeal circulation until the conclusion of the procedure; EA was ceased upon the resumption of cardiopulmonary bypass; (3) resumed subsequent to the conclusion of the operation; (4) and (5) within two days following the conclusion of the surgical procedure (2 daily sessions of 30 min)

Electroacupuncture (EA), was administered by a licensed acupuncturist at 4.0 mA, using an alternating frequency of 2 and 100 Hz (every 1.5 s) with an LH-202 apparatus (Huawei, Beijing, China).The acupoints included bilateral Yunmen (LU2), Zhongfu (LU1), Lieque (LU7), and Neiguan (PC6), as depicted in Fig. 2. Stimulation was conducted for two consecutive days before surgery (two daily sessions of 30 min each). On the day of surgery, EA was initiated after the completion of the dexmedetomidine loading dose, temporarily suspended during the initiation of CBP (to prevent interference with electrocardiogram recording), and continued until the conclusion of the surgery.

Selected acupoints—bilateral Yunmen (LU2), Zhongfu (LU1), Lieque (LU7), and Neiguan (PC6)

Dosages of dexmedetomidine and remifentanil were adjusted to ensure adequate pain control (absence of observable pain response), maintain a Ramsay score of 2 ~ 4 points, ensure adequate spontaneous ventilation (PaCO₂ < 70 mmHg, SPO₂ > 95%), and uphold hemodynamic stability. Bolus administration of sufentanil (0.1 ~ 0.2 µg/kg) was provided as needed.

Conversion to IGA was preplanned under the following circumstances during the surgical procedure: (1) incidence of pneumothorax resulting in mediastinal shift and compromised hemodynamic stability; (2) anticipated aortic block duration surpassing 120 min at any point during the surgery; (3) difficulty weaning from CPB, or persistent low cardiac output [Cardiac Index (CI) 2.0 L/(min·m2)] lasting for > 10 min following resuscitation, or recurrent malignant arrhythmias; (4) anticipated blood loss > 1000 mL or uncontrollable bleeding; (5) PaCO₂ > 70 mmHg for more than 10 min despite airway interventions; and (6) Mean arterial pressure (MAP) < 60 mmHg and persistent low cardiac output [CI 2.0 L/(min·m2)] not corrected within 10 min.

Intraoperative management

Sedation

The dexmedetomidine infusion rate was adjusted based on the Ramsay score. If the Ramsay score was greater than 2 points, the infusion rate was increased in increments of 0.1 µg/kg/h until the score reached 2 points or higher. Conversely, if the Ramsay score exceeded 4 points, the infusion rate was decreased in increments of 0.1 µg/kg/h until the score was 4 points or lower.

Analgesia

In cases of insufficient pain control, as evidenced by a frowning response to painful stimuli, the remifentanil infusion rate was incrementally increased by 0.01 µg/kg/min, up to a maximum of 0.08 µg/kg/min. If pain persisted, the dexmedetomidine infusion rate was also incrementally increased by 0.1 µg/kg/h, up to a maximum of 0.5 µg/kg/h. For intense surgical procedures requiring enhanced pain management, a bolus of sufentanil at 0.1 ~ 0.2 µg/kg was administered, with the total dosage not exceeding 35 µg throughout the operation.

Hemodynamics

For increases in heart rate or blood pressure by 20% or more, the remifentanil infusion rate was increased by 0.01 µg/kg/min, up to a maximum of 0.08 µg/kg/min. If signs of persistent pain were observed, the dexmedetomidine infusion rate was incrementally increased by 0.1 µg/kg/h, up to a maximum of 0.5 µg/kg/h. If hypertension and tachycardia persisted despite remifentanil and dexmedetomidine dosage adjustments, a bolus injection of nitroglycerin (50 ~ 100 µg) or esmolol (0.3 ~ 0.5 mg/kg) was administered.

In the event of a decrease in heart rate or blood pressure by 20% or more for over 1 min despite careful titration of analgesic or sedative drugs, a rapid intravenous infusion of colloidal solution (150 mL) was initiated within 10 min. If hypotension and bradycardia persist, a bolus intravenous injection of ephedrine (5 ~ 10 mg) or atropine (0.3 ~ 0.5 mg) was administered, along with intravenous infusion of norepinephrine (0.05 ~ 0.12 µg/kg/min) or dobutamine (3 ~ 10 µg/kg/min).

Respiration

Efforts were made to maintain PaCO₂ below 70 mmHg and SPO₂ above 95%. If respiratory suppression was suspected, the remifentanil infusion rate was reduced by 0.01 µg/kg/min per step, reaching a minimum of 0.05 µg/kg/min. If abnormalities persisted, the dexmedetomidine infusion rate was decreased by 0.1 µg/kg/h per step, to a minimum of 0.2 µg/kg/h. If aberrant PaCO₂ or SPO₂ levels persisted, assisted ventilation through mask was initiated. Patients were subjected to intubation if PaCO₂ exceeded 70 mmHg or SPO₂ dropped below 95%, despite assisted ventilation.

CPB

During CPB, perfusion pressure was maintained between 70 and 80 mmHg, and core body temperature was kept between 30 and 32 °C. Patients primarily depended on extracorporeal circulation to ensure adequate perfusion, maintaining a perfusion pressure within the specified range. Oxygenation was supported by the artificial lung, keeping oxygen saturation between 95 and 100%. Nasal oxygen was administered at a flow rate of 2–5 L/min, with mask ventilation used as necessary. After CPB, upon the resumption of spontaneous breathing, assisted ventilation was used to ensure adequate ventilation. Patients were instructed to cough before the termination of CPB to prevent atelectasis.

IGA protocol

Anesthesia induction involved the administration of propofol (2.0 ~ 3.5 μg/ml) via target-controlled infusion (TCI) and 0.3 ~ 0.5 μg/kg sufentanil. Rocuronium (1.0 mg/kg) was used to facilitate tracheal intubation. Anesthesia maintenance involved the use of isoflurane at 0.7 ~ 1.0 minimal alveolar concentration in an oxygen and air gas mixture. Additionally, remifentanil (administered at a rate of 0.05 ~ 0.2 μg/kg/min) was delivered via an intravenous injection pump. The total amount of sufentanil administered ranged from 2.5 ~ 4.0 μg/kg. Muscle relaxation was maintained with 1/3 ~ 1/4 of the induction dose every 40 ~ 60 min, guided by train-of-four (TOF) monitoring. Mechanical ventilation with 80% oxygen in air was employed, and tidal volume (7 ~ 8 mL/kg) and respiratory rate (10 ~ 12/min) were adjusted based on PetCO₂ levels to achieve normal ventilation (PetCO₂ within 35 ~ 45 mmHg).

Outcomes

Demographic data encompassed age, gender, body mass index (BMI), smoking history, comorbidities, procedural details, New York Heart Association (NYHA) class, ejection fraction, durations of cardiopulmonary bypass (CPB), and durations of aortic cross-clamping.

Safety outcomes were assessed in terms of:

1. 1)

   Major complications, categorized as: (i) respiratory-related malignant complications (e.g., pneumothorax, bronchospasm, upper airway obstruction, apnea, severe hypercapnia); and (ii) circulatory complications (e.g., malignant arrhythmia, cardiac arrest).

2. 2)

   Incidence of confirmed awareness events during the surgery.

3. 3)

   Perioperative Vasoactive-Inotropic Score (VIS).

Perioperative opioid consumption included the use of sufentanil, remifentanil, and pethidine. Sufentanil and remifentanil were administered for intraoperative analgesia, whereas pethidine was used for analgesia during the first 72 h post-surgery.

Postoperative recovery outcomes included:

1. 1)

   Time to oral intake of liquids after surgery.

2. 2)

   ICU LOS.

3. 3)

   Cardiac function recovery, as indicated by perioperative VIS at 24 and 48 h after ICU arrival.

4. 4)

   Myocardial injury, measured through serum cardiac troponin I levels (TnI).

5. 5)

   Urine volume 24 h after surgery.

Statistical analysis

The normality of the distribution for each continuous variable was assessed using the Shapiro–Wilk test and visual inspection of Q-Q plots. Continuous variables adhering to a normal distribution are presented as mean ± standard deviation (SD), while those not conforming to normal distribution are presented as median (interquartile range [IQR]). Categorical variables are expressed as numbers and percentages.

Mann–Whitney U test and Fisher’s exact test were conducted for non-normally distributed continuous variables and categorical variables, respectively. Student’s t-test was used to assess differences in normal variables of demographic, baseline characteristics, and operative features between the two groups.

One-way analysis of covariance (ANCOVA) adjusting for age and BMI was used to assess differences in normal perioperative parameters. For repeated measures data, like VIS and TnI, differences among groups were analyzed using repeated measures ANCOVA. All tests were two-tailed, with a significance level of α = 0.05. The statistical analyses were conducted using SPSS program V.21.0 (SPSS Inc., Chicago, IL, USA).

To ensure a robust scientific conclusion, patients in the MAC group were matched to those in the IGA group in an approximate 1:1 ratio. Manual methods were used for matching, with MAC set as the dependent variable. The independent variables included 10 confounders: age, gender, BMI, smoking history, comorbidities, procedure, NYHA classification grade, ejection fraction, durations of CPB, and durations of aortic cross-clamping. The matching criteria involved setting boundaries, such as a maximum 5-year difference in age, a maximum 1-point difference in BMI, and not more than a 15-min difference in CPB time and aortic cross-clamp time. The remaining confounding factors, including gender, smoking history, comorbidities, and procedure, were also sought to be essentially similar between the groups.