The Feasibility and Applications of Non-invasive Cardiac Monitoring in Obese Patients Undergoing Day-case Surgery: Results of a Prospective Observational Study

1. INTRODUCTION

2. METHODS AND MATERIALS

The current study was approved by the local Institutional Review Board and it was in accordance with the Declaration of Helsinki. Written informed consent was obtained from all patients before inclusion in this study.

We identified patients who underwent day-case surgery over the period from September 1^th, 2018 to August 31^th, 2019 in the “Day Surgery Unit” of our hospital (University of Campania “Luigi Vanvitelli” – Naples, Italy).

No prior sample size calculation was performed; however, all eligible patients were considered.

The inclusion criteria were as follows:

1. Day-case surgery procedures.

2. American Society of Anaesthesiology (ASA) ≤ 3.

3. 20 ≤ BMI ≤ 35.

4. Age of patient ≥ 18 years.

The exclusion criteria were as follows:

1. Severe cardiovascular diseases, including aortic insufficiency and thoracic aortic aneurysm.

2. External pacemakers.

3. Severe respiratory diseases.

4. Pregnancy.

5. Mental disability or other psychiatric disorder.

6. Incapacity to provide written informed consent.

The flow chart (Fig. 1) shows in detail the procedure of patient selection. 238 patients were consecutively evaluated during the preoperative examination. In our practice, it is performed about 7 days before surgery. Eighty-two patients did not meet the required inclusion criteria. From the remaining 156 patients, 104 patients agreed to participate but thirty of them did not come to the scheduled appointment. Seventy-four patients were evaluated, and all of them were finally included in the present study.

According to the obesity criteria issued by a panel of experts from the World Health Organization, patients with a BMI < 25.0 kg/m² were assigned to the non-obese group (NO group), and those with a BMI ≥ 25.0 kg/m² were assigned to the obese group (O group).

We obtained demographic (age, sex, race) and clinical (height, weight, BMI, BSA) data. The BMI was calculated as weight in kilograms divided by the square of height in meters. The Body Surface Area (BSA) was calculated using DuBois and DuBois formula based on height and weight [15, 16].

All patients underwent standard blood exams including Arterial-Blood Gas (ABG) test, Chest X-ray (CXR), electrocardiogram (ECG) and spirometry.

All procedures were classified according to the type of anesthesia (spinal vs. locoregional anaesthesia). Patients were premedicated with intravenous 50 mg ranitidine and 2 mg midazolam. Subarachnoid block was obtained with the patient in the sitting position using a 25 G pencil point spinal needle at the L2–3 vertebral inter space. After aspirating cerebrospinal fluid, patients received 8 mg hyperbaric 0.5% bupivacaine. Local anaesthesia was performed injecting lidocaine and ropivacaine mixture into the surgical area intradermally and/or subcutaneously. Spinal anesthesia was administered by the resident doctor; in case of failure, the procedure was normally repeated by the attending doctor. Local anesthesia was generally administered by the surgeon.

NICOM® device was installed as soon as the patient arrived in the operating room, at the same time when the conventional vital sign monitoring equipment was applied. Systolic Blood Pressure (SBP), Diastolic Blood Pressure (DBP), mean arterial pressure (MAP) and heart rate (HR) were monitored using Draeger® Infinity Delta monitor. Cardiac Output (CO), Cardiac Index (CI), Stroke Volume Index (SVI) and Total Peripheral Resistance Index (TPRI) were monitored using NICOM®. Four non-invasive sensor pads were applied to the thorax as per device instructions-for-use and, after calibration, all haemodynamic data were recorded and analysed offline.

Data were continuously recorded during the perioperative period. For our analysis, we collected data: 1) before surgical treatment (T0); 2) after skin incision (T1); 3) 10 minutes after the beginning of surgery (T2); 4) after the end of surgery (T3).

3. RESULTS

Seventy-four patients were included in the study. 34 were overweight or obese (weight 84 ± 10 kg, height 160 ± 10 cm, BMI ≈ 30 kg/m²), 40 were normal weight (weight 63 ± 15 kg, height 160 ± 10 cm, BMI ≈ 22 kg/m²). The age of the patients was 52.75 ± 10 years in the NO group, and 55.76 ± 10 years in the O group. The patients’ clinical and demographics characteristics are presented in Table 1. There were no significant demographic differences between the groups, except for weight, BSA and BMI. The distribution of patients based on BMI is shown in Fig. (2).

The surgical procedures performed in day surgery were: skin lesion removal (13.5%), breast-conserving surgery (lumpectomy) (15%), varicocelectomy (13.5%), phimosis surgical treatment (circumcision) (11%), trans urethral removal of bladder tumour (TURBT) (12%), carpal tunnel surgery (12%), inguinal hernia surgery (9.5%), and lipofilling in breast cancer patients (13.5%). All these procedures were performed in locoregional (76%) or spinal anaesthesia (24%). Table 2 shows the patients’ distribution in the various interventions and the types of anesthesia used.

In the control group, eight procedures (20%) were performed under spinal anaesthesia; in the obese group spinal anaesthesia was performed ten times (29.5%). Other procedures were carried out under locoregional anaesthesia. General anesthesia was not administered, being normally not provided at our institution in day-case surgery. No failure was reported in the administration of the anesthesia techniques; in the cases in which spinal anesthesia was used, five procedures (1 in the control group and 4 in the obese group) were performed on the second attempt by the attending doctor.

NICOM® electrodes were placed on the intended anatomic location in every case. In three cases, we observed displacement of the electrodes due to sweat, chest hair, or manipulation of the electrodes by a patient. In addition, a temporary signal loss occurred for unknown reasons in a case. Except for these incidents, the device recorded all parameters continuously.

We recorded a variation in SBP, DBP, MAP and CO during surgery in the obese group (p < 0.05). This data returned to baseline at the end of surgery.

The CI measured by NICOM® in the NO group was 3.49 ± 0.81 l/min at T0, 3.34 ± 0.72 l/min at T1, 3.27 ± 0.77 l/min at T2, 3.06 ± 0.76 l/min at T4. In the O group was 3.19 ± 0.47 l/min at T0, 3.00 ± 0.84 l/min at T1, 2.81 ± 1.13 l/min at T2, 2.94 ± 0.82 l/min at T3. Data analysis shows a statistically significant change (p = 0.047) in CI over time during the operation (Fig. 3), (p < 0.05). This variation is greater in the O group than in the NO one, although this difference is not statistically significant (p = 0.24).

In the same way, the difference in the cumulative averages of SVI was 0.048 (Fig. 4), (p < 0.05). The SVI measured by NICOM® in normal weight group was 45.7 ± 9.8 ml/m²/beat at T0, 43.6 ± 11.8 ml/m²/beat at T1, 42.1 ± 9.6 ml/m²/beat at T2, 42.3 ± 12.1 ml/m²/beat at T3. In the obese group it was 40.3 ± 4.5 ml/m²/beat at T0, 38.8 ± 8.7 ml/m²/beat at T1, 37.4 ± 11.7 ml/m²/beat at T2, 37.7 ± 12.1 ml/m²/beat at T3.

Otherwise, HR data do not show statistical significance (Fig. 5), (p > 0.05).

Concerning TPRI, the averages between the obese and normal weight groups do not show a significant change during operation under spinal anaesthesia (Fig. 6), (p > 0.05). Among the obese patients, TPRI is similar to the one in the NO group under spinal anesthesia. When local anesthesia was performed, we recorded an important difference in T0 (p = 0.0076), T1 (p = 0.0019) and T2 (p = 0.045); no significant difference was recorded in T3 (p = 0.10) (Fig. 7).

4. DISCUSSION

The goal of this observational study was to assess the impact of the BMI and anaesthesia technique during day-case surgery, as well as to evaluate the feasibility of using the non-invasive cardiac output monitoring NICOM® for the evaluation of haemodynamics in obese patients during these procedures.

Intraoperative haemodynamic perturbations are determined by the effects of anaesthetic agents and techniques, surgical manipulations, and the patient's medical comorbidities.

Furthermore, obesity produces a variety of haemodynamic alterations including elevated CO, low peripheral vascular resistance, and increased left ventricular end-diastolic pressure [18]. HR is normal or mildly elevated in obesity [18].

In our study, the obese show an increase in SBP, DBP and MAP with a return to baseline values at the end of surgery. These results are in accordance with those of preceding studies, which demonstrate that obesity is closely related to blood pressure [19].

CO shows a similar trend, whereas HR is normal. Indeed, the CO raise in obesity is due mainly to the augmentation of left ventricular stroke volume [18].

To attenuate the effects of BMI, we indexed haemodynamic measurements to BSA. A reduction in CI during operation was noticed in both groups, the one in obese patients being greater. In the same way, SVI was lower in the obese during surgery. Indexing haemodynamic data to BSA helps to remove any uncertainty regarding the interpretation of CO and SV at the extremes of body size [20].

We also evaluated the haemodynamic status after spinal and loco-regional anesthesia in the obese patients. In spinal anesthesia, TPRI was not statistically different between the groups of study. As for the TPRI in obese patients, we reported values similar to non-obese patients in spinal anesthesia. In local anesthesia, TPRI was higher in obese patients than in non-obese ones.

Spinal anesthesia induces sympathetic blockade with subsequent reduction in myocardial contractility, heart rate, and change in cardiac loading conditions [21]. It leads to a decrease in venous return due to increased compliance of the venous system, vasodilatation and, finally, decreased blood pressure [21]. Concerning local anesthesia, it may cause stress leading to blood pressure change, haemodynamic and cardiovascular reactions [23]. Pain causes an alarm reaction with an increase in systemic arterial pressure and pulse rate due to the release of endogenous catecholamine [22].

NICOM® was easy to use: installation, operation, and monitoring could be performed by one person. Problems with the device were the detachment of the electrodes and the temporary loss of the signal due to the displacement of the electrode or unknown reasons. This device did not affect the standard of care in the operating room, including anesthesia and all surgery procedures.

NICOM® is deployable in a wide variety of clinical settings, and has demonstrated clinical utility with diverse patient populations, and for a wide range of clinical conditions. Common clinical sites for non-invasive cardiac monitoring are the operating room and the Critical Care, such as the Intensive Care Unit (ICU) and the Emergency Department (ED).

Critical care patient populations are often haemodynamically unstable and only 50% of these patients respond to fluid administration by increasing CO and perfusion. NICOM® provides the ability to rapidly and noninvasively test fluid responsiveness, allowing critical care clinicians to make more informed decisions, guiding effective fluids, vasopressors and inotropes administration [24-26].

According to Enhanced Recovery after Surgery (ERAS), an accurately administration of fluids and vasoactive agents throughout the entire perioperative period has been shown to improve patient outcome [27]. ERAS protocols have resulted in a length of hospital stay 30% to 50% shorter and similar reductions in complications, while readmissions and costs are reduced. This is particularly important in day-case surgery, where patients are admitted to hospital, have the operation or treatment and go home the same day. Until recently, haemodynamic evaluation required invasive monitoring, which was unsuitable in awake patients for day-case surgery. NICOM® provides a continuous, non-invasive haemodynamic measurement. This device does not bring inconvenience to patients making it clinically suitable for monitoring awake patients having loco-regional anesthesia.

CONCLUSION

Obesity produces a variety of haemodynamic alterations with greater risk of morbidity and perioperative mortality. Cardiovascular alterations related to obesity include an increase in blood pressure, CO and SV. Among the risk factors for perioperative complications there is the inadequate and insufficient monitoring of haemodynamic parameters. Especially in day-case surgery invasive monitoring is difficult to apply. NICOM® is often presented as a monitoring system that is easy to use, non-invasive, able to better evaluate and guide the correct anaesthetic plan for this type of patients. Further research is needed to confirm the clinical value of NICOM® monitoring and how this technology might help to further reduce postoperative morbidity and mortality in obese patients scheduled for day-case surgery.

REFERENCES