The effect of preoperative anxiety, hormone-induced ovarian stimulation, and prolonged face mask ventilation on gastric antrum size

doi:10.21203/rs.3.rs-1652889/v1

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The effect of preoperative anxiety, hormone-induced ovarian stimulation, and prolonged face mask ventilation on gastric antrum size

https://doi.org/10.21203/rs.3.rs-1652889/v1

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BACKGROUND: Pulmonary aspiration is a potentially lethal perioperative complication related to gastric size and contents. Several perioperative factors are believed to increase gastric size, while others are less studied. Therefore, this study aimed to investigate the effect of anxiety, hormone-induced ovarian stimulation, and prolonged face mask ventilation (FMV) on gastric size via measuring antral cross-sectional area (CSA) using ultrasound.

METHODS: This prospective observational study was conducted in Rabin Medical Center, Israel. We recruited 49 female patients undergoing hormone-induced ovarian stimulation and oocyte retrieval for in-vitro fertilization. Preoperatively, they ranked anxiety level on a visual numeric anxiety score (VNS). In the operation room, pre-and postoperative gastric ultrasound examinations were performed. Anesthesia was induced intravenously, followed by FMV with a peak inspiratory pressure of 15 cm H₂O.

RESULTS: There was no substantial correlation between pre-operative VNS anxiety and antral CSA (p=0.697). Moreover, the number of follicles, blood estradiol, and progesterone levels did not correlate with antral CSA (p=0.590, p=0.104, and p=0.511, respectively). The median duration of FMV was 13 minutes [IQR 18 to 8.5] and did not correlate with the antral CSA delta (p=0.312).

CONCLUSIONS: Neither preoperative anxiety nor extensive ovarian stimulation affects gastric size. Moreover, prolonged FMV with a peak inspiratory pressure of 15 cm H2O did not increase the gastric size by insufflation. These findings add to a growing body of literature on this topic. Furthermore, it provides new evidence that FMV is still safe even in a relatively short procedure.

TRIAL REGISTRATION: ClinicalTrials.gov (Registration number, NCT04833530; Registration date, 06/04/2021).

Anxiety

IVF

Gastric Ultrasound

Face mask ventilation

1.1 Background

Pulmonary aspiration is one of the most serious risks of general anesthesia and has been reported in as many as 1 in 4000 cases [1]. Predisposing factors include enlarged gastric antrum size and contents, increased regurgitating tendency, and laryngeal incompetence [2]. Therefore, preoperative fasting guidelines were introduced to minimize the risk of aspiration [3, 4]. However, it has been found that aspiration can occur even in fasted patients. This risk is highest in an anesthetized patient with an unprotected airway. Face mask ventilation (FMV) is particularly problematic in that there is both an unprotected airway and potential gastric insufflation due to positive pressure ventilation (PPV) [5].

Because of the disastrous consequences of pulmonary aspiration, much research has focused on identifying which patients are at risk for enlarged gastric antrum size.

Anxiety may increase gastric size because it predisposes to nausea and vomiting [6]. In addition, several studies have shown that gastric emptying in healthy females can be affected by fluctuations in ovarian sex hormones, with decreased gastric emptying reported with high estrogen levels [7]. Finally, it remains unclear to what degree gastric insufflation during FMV increases gastric antrum size as both pressure and duration influence it.

Gastric antrum size is evaluated by measuring the gastric antral cross-sectional area (CSA) using gastric ultrasound, an emerging point of care tool that provides bedside information [8]. Gastric ultrasound is increasing in popularity and has been included in recent subspecialty guidelines [9–12].

In vitro fertilization (IVF) is a standard method in infertility treatment. However, women presenting in the IVF facility are under high social and psychological stress. Moreover, this problem is exacerbated further by the hormonal manipulation occurring during IVF, which may cause increased emotional distress, including stress and anxiety [13]. General anesthesia is often required during oocyte retrieval, which forms one of the fundamental steps during the entire process [13]. The antagonist protocol with an agonist trigger almost eliminates the risk of ovarian hyperstimulation syndrome. Thus, safe recruitment of a high number of follicles is feasible and even required if fertility preservation is within the scope of the cycle. The oocyte retrieval process from these highly vascularized stimulated ovaries requires satisfactory surgical conditions, provided by minimizing breathing efforts and avoiding abdominal movements that may interfere with the process. Therefore, as acceptable in our institution, these procedures are usually performed under deep sedation with non-invasive positive pressure ventilation via a face mask.

1.2 Study objectives

We designed a study to assess various factors influencing gastric antrum size in women for oocyte retrieval.

The primary outcome was the impact of anxiety on pre-operative antral CSA. Secondary outcomes were the effect of ovarian stimulation on pre-operative antral CSA and the effect of prolonged FMV on antral CSA delta (the difference between pre-and postoperative antral CSA).

2.1 Ethics

Ethical approval

for this study was provided by the institutional review board of Rabin Medical Center (Trail number, RMC 21 − 0010; Chairperson, Prof. Ran Tur-Kaspa; Registration date, 21/03/2021). In addition, the study was registered with the U.S. National Institutes of Health ClinicalTrials.gov(Registration number, NCT04833530; Registration date, 06/04/2021). All included patients gave informed written consent. All methods were carried out in accordance with the relevant guidelines and regulations of Rabin Medical Center, Beilinson Hospital.

2.2 Study design

Prospective observational study.

2.3 Settings

We consecutively recruited women between April 7th and August 9th, 2021. The study was performed in a tertiary medical center (Rabin Medical Center-Beilinson Hospital, Petah Tikva, Israel).

2.4 Participants

Women undergoing general anesthesia for oocyte retrieval, aged ≥ 18 years, ASA physical status of I or II.

Exclusion criteria were: patient refusal, morbid obesity (Body Mass Index ≥ 40 kg m^− 2), diabetes mellitus, depressive disorders, and history of bariatric surgeries.

2.5 Study protocol and variables

Anxiety

Upon enrolment, participants were asked to fill out a verbal numeric anxiety score (VNS) to rank their anxiety level on a scale of 0–10 (i.e., 0: no anxiety, 10: highest anxiety). This measurement was validated [14] and used in three previous studies in our institution measuring pre-operative anxiety [15–17].

Ovarian stimulation

All patients underwent ovarian stimulation for IVF utilizing a short antagonist protocol. The follicle stimulation hormone dose was set according to individual clinical parameters. Oocyte maturation was triggered using human Chorionic Gonadotropin 250 µg (Ovitrelle ®, Merck Serono, Germany), combined with Triptorelin 0.2 mg (Decapeptyl ®, Ferring, Germany), administered 36–38 hours prior to the oocyte retrieval procedure.

Facemask ventilation

Before induction of anesthesia, all participants were premedicated with 1 g of Paracetamol (Fresenius Kabi, Germany) intravenously. Then, anesthesia was induced intravenously with propofol (Fresenius Kabi, Germany) 2 mg kg^− 1 and fentanyl (Rafa Laboratories, Israel) 75 µg. Neither halogenated anesthetics nor neuromuscular blocking agents were administered. Once eyelash reflex loss had occurred, a Guedel oropharyngeal airway (Besmed Health Business Corp., Taiwan) and a well-fitting disposable facemask (#5 Inflatable Air Cushion Mask, Besmed Health Business Corp., Taiwan) were placed sequentially. Afterward, FMV was carried out using a two-handed jaw-thrust technique followed by head-tilt. Pressure Control Ventilation was delivered by a Fabius® GS premium ventilator (Dräger Medical, Lübeck, Germany) with an inspiratory pressure of 15 cm H₂O, I:E ratio of 1:2, frequency of 15 breaths min^− 1, and FiO₂ of 0.5. No positive end-expiratory pressure was added. FMV was continued until the end of the procedure. Anesthesia was maintained with small boluses of Propofol 20–30 mg (Ripol ®, CordenPharma, Italy) as needed.

Gastric ultrasound

An initial pre-operative gastric ultrasound examination was performed in the operating room using a SonoSite EDGE portable ultrasound machine (SonoSite, Inc., Bothell, WA, USA), fitted with a 5 − 2 MHz probe. The ultrasound examination was performed in the supine position on the operating table, and the antral CSA was measured as per standard protocol [18].

In addition, the ultrasound image quality was assessed according to a previous study [19]. This score ranks quality from 1 to 3 (i.e., “1” is poor, “2” is average, and “3” is good image quality).

Immediately following the procedure, a second gastric ultrasound was performed. An example of pre and postoperative gastric sonograms with the relevant anatomic landmarks and antral CSA measurements is shown in (Fig. 1).

2.6 Data collection

The following data were collected: demographics (i.e., age, height, weight, and BMI); medical history (i.e., comorbidities, concomitant medications, smoking status, and history of PONV or motion sickness); peri-operative data (i.e., pre-operative VAS anxiety, duration of procedure, postoperative VAS pain score, nausea, and vomiting); gynecological profile and extent of ovarian stimulation (i.e., indication for IVF, number of the current cycle, length of ovarian stimulation, number of follicles > 14mm, number of oocytes retrieved, and the blood levels of estradiol and progesterone prior to triggering of oocyte maturation); intraoperative data (i.e., vital signs, ventilation parameters, and duration of procedure); and gastric ultrasound parameters (i.e., pre-operative and postoperative: antral CSA, and image quality score).

2.7 Study size

No studies have been performed on the relationship between anxiety and antral CSA. A moderate correlation coefficient of 0.4 was considered of clinical importance to justify the sample size calculation.

Therefore, a correlation coefficient of 0.4, with an alpha level of 0.05 and power of 80% was used to calculate the required sample size using the ‘pwr’ package in R (R Foundation for Statistical Computing, Vienna, Austria), yielding the need of 46 participants. With an expected attrition rate of 30%, a sample of 60 participants was planned for recruitment.

2.8 Statistical methods

Before the performance of linear regression models, statistical assumptions (i.e., linearity, independence) were tested. Spearman-rank correlation coefficients and linear regression models were generated. Nonlinear relationships were assessed visually and using loess-smoothing.

The dependent variable was the antral CSA, while other variables were independent.

All the continuous variables were tested for normality of distribution using histograms and Q-Q plots. Due to nonnormality, variables are presented as median [IQR]. All statistical analyses have been performed in R (R Foundation for Statistical Computing, Vienna, Austria) and IBM SPSS® Statistics version 22 (IBM Corp., Armonk, NY, USA).

We screened 77 patients, and after the exclusions, we included 49. The enrollment flow diagram is presented in (Fig. 2). Examples of gastric sonograms of excluded patients are presented in (Fig. 3–4). Patient characteristics and peri-operative data are listed in (Table 1).

3.1 Primary outcome

Preoperative anxiety

The median VNS Anxiety was 4 [IQR 1 to 6)]. There was no substantial correlation between pre-operative VNS anxiety and pre-operative antral CSA (r = 0.057, p = 0.697). Linear regression with pre-operative VNS anxiety as the independent and pre-operative antral CSA as the dependent variable did not result in a good model (p-value of β coefficient 0.216, and R² = 0.012).

3.2 Secondary outcomes

Ovarian stimulation

The IVF cycle data are listed in (Table 2). The number of follicles, pre-trigger estradiol (pmol l^− 1) and progesterone (nmol l^− 1) levels did not correlate with pre-operative antral CSA (r=-0.079, p = 0.590; r=-0.096, p = 0.511; and r=-0.235, p = 0.104, respectively). Univariable linear regression with the number of follicles, estradiol (pmol l^− 1), and progesterone (nmol l^− 1) levels as independent variables and pre-operative antral CSA as the dependent variable also showed no association between these variables and pre-operative antral CSA (p values of β coefficients all > 0.1, and R² all < 0.015). In contrast, the number of oocytes retrieved showed a weak correlation with pre-operative antral CSA (r=-0.316, p = 0.027). A univariable linear regression model with the number of oocytes as an independent variable and pre-operative antral CSA as the dependent variable did not result in a good linear model (p-value of β coefficient in linear regression 0.444, and R² = 0.013). Therefore, there is likely no association between the number of oocytes and pre-operative antral CSA.

Facemask ventilation

Gastric ultrasound data are listed in (Table 3). The median duration of FMV was 13 minutes [IQR 18 to 8.5] and did not correlate with delta antral CSA (r=-0.151, p = 0.312). Moreover, the duration of FMV did not increase the delta antral CSA (p-value of β coefficient in linear regression 0.273, and R² = 0.005).

Pulmonary aspiration is a severe complication associated with morbidity and mortality [1], and its risk has been linked to gastric antrum size [2]. Currently, there are a few factors that have been identified as contributing to an increase in gastric antrum size, such as delayed gastric emptying and gastroparesis in diabetes mellitus [20]. While other peri-operative variables, such as pre-operative anxiety, the extent of ovarian stimulation, and the duration of FMV, have received less attention in the literature in specific populations.

The oocyte retrieval procedure during IVF was selected to evaluate the impact of all these peri-operative variables on gastric size. IVF is a standard procedure in the gynecological arena. Female patients with a tendency to anxiety and those under hormonally induced ovarian stimulation undergo a relatively short period of general anesthesia with PPV via face mask [13]. Additionally, the steroid hormones secreted at supraphysiological levels by the stimulated ovaries directly affect vascular permeability and gastrointestinal mobility [7].

Peri-operative anxiety is related to increased anesthetic requirements, augmented pain during the postoperative period, and an elevated incidence of nausea and vomiting [15, 16, 21, 22]. Nevertheless, no data were found on the association between anxiety and gastric size.

We thought that it would affect gastric emptying and consequently increase antral CSA. However, our study results showed no substantial correlation between anxiety and antral CSA. In fact, none of the patients experienced postoperative vomiting, but the lack of vomiting may have been due to propofol’s antiemetic effect. This result may suggest that anxiety, although causing nausea, does not affect gastric emptying in a way that standard fasting guidelines cannot overcome.

Concerning the extent of ovarian stimulation, evidence from the literature suggests that fluctuations in ovarian sex hormone levels affect gastric emptying, mainly when estrogen levels are high [7]. Nevertheless, no data were found regarding the association between the number of follicles aspirated or oocytes retrieved and antral CSA. Surprisingly, neither estradiol and progesterone levels nor the number of follicles aspirated demonstrated a significant correlation with antral CSA. In contrast, the number of oocytes retrieved exhibited a modest correlation with pre-operative antral CSA, but this did not result statistically in a satisfactory linear model. Thus, our study results showed no association between stimulated ovaries and pre-operative antral CSA following recommended fasting guidelines. Furthermore, considering that the number of aspirated oocytes is associated with the cumulative outcome of the oocyte aspiration [23]. Thus, this study demonstrates that a more extensive ovarian stimulation aimed to recruit and retrieve a higher number of oocytes is not associated with a higher degree of increased pre-operative gastric size.

Regarding FMV, several authors have previously shown that high airway pressures may increase the risk of gastric insufflation during FMV [5, 24, 25]. However, to the best of our knowledge, no previous study verified the effect of prolonged FMV in the setting of an unprotected airway on antral CSA. Recently, Bouvet et al. measured gastric insufflation at an inspiratory pressure of 10, 15, 20, and 25 cm H₂O [26]. Thus, according to ultrasonography, they reported significant increases in gastric insufflation with inspiratory pressure from 19% (group 10 cm H₂O) to 59% (group 25 cm H₂O). Therefore, they conclude that 15 cm H₂O provided the best balance between the probability of sufficient pulmonary ventilation and the likelihood of absence of gastric insufflation. Note that their work only focused on the induction, and therefore the duration of FMV was limited to 120 seconds. Moreover, in group 15 cm H₂O only 17 participants were enrolled.

Unlike Bouvet et al., the present study was conducted on 49 participants, with a median duration of 13 minutes [IQR 18 to 8.5] of FMV with peak inspiratory pressure of 15 cm H₂O. Interestingly, this prolonged duration of FMV did not increase the delta antral CSA. Therefore, this study reinforces the previous evidence and emphasizes the safety of this method not only as a bridge for definitive airway but also as an alternative method for relatively short procedures in a selected patient population such as nonobese non paralyzed fasted patients.

Strengths and limitations

This study has two significant strengths. First, the investigators have completed a training program to enhance internal validity and quality control, including dedicated teaching and a portfolio of live scans. Moreover, one of the investigators with experience in gastric ultrasound (C.A) assessed, reviewed, and verified all measurements before beginning the statistical analysis.

Second, the gastric ultrasound examiners were blinded to the preoperative VNS anxiety score and the level of ovarian stimulation.

We need to consider two limitations. First, the dynamic nature of the organ is an inherent limitation of any research utilizing gastric ultrasound. Despite following a strict ultrasound scanning protocol, the peristaltic contractions may have added an element of variability between successive measurements.

Second, the study selected population was homogenous, with no known risk factors for perioperative aspiration, since all the patients were admitted for elective cases while fasting for at least 6 hours. A more heterogeneous group with higher risk factors for perioperative aspiration may yield different results.

Neither preoperative anxiety nor extensive ovarian stimulation affects gastric size. Moreover, prolonged FMV with a peak inspiratory pressure of 15 cm H₂O did not increase the gastric size by insufflation. These findings add to a growing body of literature on this topic. Furthermore, it provides new evidence that FMV is still safe even in a relatively short procedure.

BMI, body mass index; CSA, cross-sectional area; GA, general anesthesia; HTN, hypertension; IBS, irritable bowel syndrome; IQR, interquartile range; IVF, in-vitro fertilization; LMA, laryngeal mask airway; PGT, pre-gestational testing; PONV, postoperative nausea and vomiting, PPV, positive pressure ventilation; SLE, systemic lupus erythematosus; VAS, visual analog scale; VNS, visual numeric scale.

Acknowledgements

We would like to thank Mrs. Atara Davis for her technical assistance with this manuscript.

Authors’ contributions

All authors contributed to the study conception and design. Material preparation and data collection were performed by KA, AF, SOZ. Formal analysis were performed by PH. The first draft of the manuscript was written by KA, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

N/A

Availability of data and materials

The data used to support the findings of this study are available from the corresponding author upon reasonable request.

Ethics approval and consent to participate

Ethical approval for this study was provided by the institutional review board of Rabin Medical Center (Trail number, RMC 21-0010; Chairperson, Prof. Ran Tur-Kaspa; Registration date, 21/03/2021). In addition, the study was registered with the U.S. National Institutes of Health ClinicalTrials.gov (Registration number, NCT04833530; Registration date, 06/04/2021). All included patients gave informed written consent. All methods were carried out in accordance with the relevant guidelines and regulations of Rabin Medical Center, Beilinson Hospital.

Consent for publication

N/A

Competing interests

The authors declare that they have no competing interests.

Author details

¹ Department of Anesthesiology, Rabin Medical Center, Beilinson Hospital, Petah Tikva, Israel. ² Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel. ³ Faculty of Medicine, University of Zurich, Zurich, Switzerland. ⁴ Infertility and IVF Unit, Helen Schneider Hospital for Women, Rabin Medical Center, Beilinson Hospital, Petah Tikva, Israel. ⁵ Department of Anesthesiology and Pain Medicine, Mount Sinai Hospital, University of Toronto, Toronto, Canada. ^* Equal co-last authors

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Table 1. Patient characteristics and peri-operative data.

Continuous variables are presented as median [IQR]. Categorical variables are presented as n (%).

Variable				n=49
Demographics
	Age (years)			36	[33 to 39.5]
	BMI (kg m^-2)			23.7	[21.1 to 28]
Medical history
	Comorbidities
		None		32	(65%)
		Hypothyroidism		5	(10%)
		Asthma		3	(6%)
		IBS		2	(4%)
		Epilepsy		1	(2%)
		Fibromyalgia		1	(2%)
		HTN		1	(2%)
		SLE		1	(2%)
		Others ^a		5	(10%)
	Smoking			5	(10%)
	Previous PONV			9	(18%)
	Motion sickness			13	(27%)
Peri-operative data
	Pre-operative
			VNS anxiety	4	[1 to 6]
	Intraoperative
			Duration of procedure (min)	13	[18 to 8.5]
	Postoperative
			Nausea	5	(10%)
			Vomit	0	(0%)
			VAS pain	0	[0 to 2]

^a Other diseases: Thrombophilia, neurofibromatosis type I, thalassemia minor, chronic spontaneous urticaria, and antiphospholipid syndrome.

BMI, body mass index; IBS, irritable bowel syndrome; HTN, hypertension; SLE, systemic lupus erythematosus; PONV, postoperative nausea, and vomiting; VNS, visual numeric scale; VAS, visual analog scale.

Table 2. IVF cycle data.

Continuous variables are presented as median [IQR]. Categorical variables are presented as n (%).

Variable			n=49
Gynecological profile
	Indication for IVF
		Unexplained infertility	3	(6%)
		Mechanical	1	(2%)
		Age related	8	(16%)
		Fertility preservation	13	(27%)
		Male factor	8	(16%)
		PGT	16	(33%)
	Number of the current cycle		3	[1 to 5]
	Days of ovarian stimulation		9	[8 to 10]
	Number of follicles>14 mm		7	[4 to 11.5]
	Oocytes aspirated		8	[5.5 to 16]
	Pre-trigger blood Estradiol (pmol l^-1)		3151	[2015 to 6300.5]
	Pre-trigger blood Progesterone (nmol l^-1)		1.5	[0.8 to 2.5]

IVF, in vitro fertilization; PGT, pre-gestational testing.

Table 3. Peri-operative gastric ultrasound data.

Continuous variables are presented as median [IQR].

Variable	Gastric Ultrasound
	Pre-operative	Postoperative	Delta
US quality	3 [3 to 3]	3 [3 to 3]	0 [0 to 0]
Gastric antral CSA (cm²)	3.8 [3 to 4.4]	4 [4.9 to 3.2]	0.2 [-0.3 to 0.5]

CSA, cross-sectional area.

No competing interests reported.

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The effect of preoperative anxiety, hormone-induced ovarian stimulation, and prolonged face mask ventilation on gastric antrum size

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Abstract

Figures

1. Introduction

1.1 Background

1.2 Study objectives

2. Materials And Methods

2.1 Ethics

2.2 Study design

2.3 Settings

2.4 Participants

2.5 Study protocol and variables

2.6 Data collection

2.7 Study size

2.8 Statistical methods

3. Results

3.1 Primary outcome

3.2 Secondary outcomes

4. Discussion

5. Conclusions

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