Pulmonary aspiration is a severe complication associated with morbidity and mortality , and its risk has been linked to gastric antrum size . 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 . 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 . Additionally, the steroid hormones secreted at supraphysiological levels by the stimulated ovaries directly affect vascular permeability and gastrointestinal mobility .
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 . 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 . 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 . 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.