Airway compromise during procedural sedation has the potential to result in clinically important complications, predominantly involving the upper respiratory tract structures [1]. Among the sedative agents routinely administered for moderate sedation in various diagnostic and therapeutic interventions across India, midazolam and propofol are most frequently utilized. Therefore, selecting an appropriate sedative, particularly for individuals with existing comorbidities, becomes crucial [2].

One of the useful physiological markers for assessing dynamic pulmonary function is the Peak Expiratory Flow Rate (PEFR), also referred to simply as peak expiratory flow. PEFR is indicative of the airflow through the larger airways and is influenced by numerous factors in healthy individuals. These determinants include sex, thoracic cavity dimensions (both intra- and extrathoracic), alveolar compliance, elastic recoil capability of the lungs, voluntary respiratory effort, and the contractile strength of the respiratory musculature [3].

Accordingly, measurement of PEFR before and after surgical procedures can serve as a valuable parameter to evaluate the impact of general anesthesia on respiratory mechanics and lung performance. The peak expiratory flow—alternatively termed peak flow or PEFR—represents the highest airflow rate achieved during a forceful expiration and is commonly measured using a compact handheld device called a peak flow meter. This instrument quantifies bronchial airflow in liters per minute (L/min), offering a non-invasive method to monitor expiratory capacity and detect airway obstruction [4].

The primary aim of this study is to assess and compare the effects of two commonly used sedative agents—midazolam and propofol—on post-anesthetic pulmonary function, specifically focusing on peak expiratory flow rate (PEFR). The objectives include evaluating PEFR in patients recovering from anesthesia induced with midazolam, as well as in those administered propofol. Furthermore, the study seeks to compare the mean PEFR values between these two groups to determine any significant differences in respiratory performance following the use of either agent. In addition to these primary goals, the secondary objective is to analyze the incidence and severity of respiratory obstruction during the recovery period and to compare the associated risks between midazolam and propofol in the context of post-anesthetic respiratory outcomes.

This study included adult participants of both sexes, ranging in age from 20 to 50 years. Only those individuals scheduled for general anesthesia and exhibiting completely normal findings on pre-anesthetic respiratory assessment were considered eligible. Subjects presenting with musculoskeletal deformities, unstable vital parameters, or a history of recurrent cardiopulmonary issues were excluded.

The objective of this research was to compare post-anesthetic peak expiratory flow rate (PEFR) between patients administered midazolam and those who received propofol for induction. A total of 30 participants, fulfilling all eligibility criteria and providing informed written consent, were enrolled in the study. Detailed explanations of the study protocol were provided in the local language to ensure comprehension.

PEFR measurements were performed six hours following the administration of anesthesia, once the subjects were fully awake, alert, oriented to person, place, and time, and capable of sitting upright and following instructions. The evaluation utilized the Mini-Wright Peak Flow Meter. The procedure entailed inserting the mouthpiece into the device and adjusting the indicator to the baseline. Each subject was asked to hold the instrument without obstructing any of its air passages. While seated, participants were instructed to inhale deeply and then exhale forcefully and rapidly into the meter. Subjects were advised to occlude both nostrils during exhalation to ensure accurate measurement. This process was repeated three times, and the mean of the three readings was recorded for analysis.

The induction dosage of midazolam administered ranged from 3 to 4 mg, while for propofol it varied between 100 and 130 mg. The study population was evenly divided into two groups based on the sedative agent used. Subsequent statistical evaluation was performed using SPSS 24 software, and intergroup comparisons were carried out utilizing the unpaired t-test.

In the present study, PEFR measurements were evaluated to compare the effects of two commonly used induction agents, propofol and midazolam. A statistically significant difference was observed in the mean PEFR values between the two groups. Patients who received propofol demonstrated higher post-induction PEFR compared to those who received midazolam, indicating a more favorable respiratory profile with propofol administration (Table 1).

Table 1: Comparison of PEFR values between the study groups

Further subgroup analysis was performed to assess gender-wise variations in PEFR within each group. Among patients receiving propofol, male participants exhibited significantly higher PEFR values as compared to females, suggesting a potential gender-based differential response to the agent (Table 2). A similar trend was observed in the midazolam group, where male participants showed higher PEFR readings than their female counterparts (Table 3). In both cases, the differences were statistically significant, indicating consistent gender-related differences across induction agents.

Table 2: Gender wise PEFR in Propofol group

Table 3: Gender wise PEFR in Midazolam group

Previous studies [5,6] explored the comparative effects of midazolam and propofol on upper airway collapsibility using a dynamic negative airway pressure technique. Upon achieving equivalent depths of sedation, findings ny Norton et al [1] indicated no significant difference in the tendency to develop upper airway obstruction (UAO) between the two agents at mild to moderate sedation levels. In contrast, the present study observed a noteworthy reduction in peak expiratory flow rate (PEFR) among female patients compared to males, regardless of whether midazolam or propofol was administered, with a highly significant p-value (<0.001). This disparity may be influenced by physiological and anatomical differences such as variations in body mass index, thoracic dimensions, voluntary respiratory effort, respiratory muscle strength, and gender-specific thoracic anatomy.

In an earlier investigation by Montravers et al. [7], the effects of intravenous midazolam on upper airway resistance were assessed by measuring supraglottic pressure through a balloon-tipped catheter and airflow via pneumotachography. Although their methodology differed from the present study, their conclusion aligned with our findings, identifying midazolam as a potent depressant of respiratory function. They attributed this to a reduction in pharyngeal muscle tone, contributing to elevated upper airway resistance. The more pronounced respiratory depression observed with midazolam in the current study is likely a consequence of similar mechanisms [8,9].

Furthermore, Molliex et al. [10] evaluated the impact of midazolam on respiratory muscles in healthy individuals. Their results suggested minimal alterations in dynamic pulmonary function, with only a slight increase in large airway resistance noted during sleep. These findings may reflect the limited influence of midazolam under resting conditions in healthy subjects, in contrast to its more substantial impact observed in perioperative settings [11,12].

Supporting our observations regarding propofol, Liu et al. [13] examined its effects on respiratory drive and patient-ventilator synchrony during pressure support ventilation in postoperative patients. Their study demonstrated that deeper levels of sedation were associated with a reduction in respiratory drive, peak inspiratory effort, and minute ventilation, although tidal volume remained unaffected. This aligns with our data, which showed a less pronounced decline in PEFR following propofol administration compared to midazolam, indicating that propofol may exert a relatively milder effect on expiratory airflow dynamics.

Midazolam significantly impairs respiratory recovery compared to propofol, suggesting propofol as the preferred induction agent in patients with respiratory conditions, particularly asthma and COPD. As PEFR was consistently lower in female patients, careful dose monitoring of both drugs is recommended in this group. The study emphasizes the need for further research on anesthetic agents using dynamic lung function tests to reduce post-anesthetic respiratory morbidity.

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