Introduction

During general anesthesia, endotracheal intubation may stimulate the sympathetic system because of the hemodynamic response to laryngoscopy, causing an increase in blood pressure, heart rate, and cardiac load due to the release of catecholamine [1]. These changes last a maximum of 1 minute after intubation and can last up to 5-10 minutes [2]. In fact, reflex vasoconstriction occurs within a few seconds, followed by sinus tachycardia, which reaches its peak within 2 minutes and lasts for 2 minutes. These changes are mostly transient and do not have any adverse consequences for the patient. However, sometimes the mentioned responses are life-threatening and could lead to the occurrence of left ventricular failure and cerebral ischemia [3]. In other words, these responses are threatening and dangerous in people who have coronary failure or high blood pressure. The induction of anesthesia causes a loss of airway control and airway protective reflexes [4]. In this context, supraglottic airway devices are often used as an alternative to tracheal intubation [5]. Laryngeal mask airway (LMA) was introduced between 1983 and 1985 for airway management when endotracheal intubation was not required. However, this method was associated with an increased risk of aspiration [6]. Nevertheless, the ProSeal laryngeal mask airway (PLMA) has a dorsal cuff in addition to the peripheral LMA cuff, which compresses the anterior mask to minimize air leakage and aspiration [7]. One of the advantages of using a laryngeal mask to create an airway is that it improves hemodynamic stability, reduces coughing during awake, and reduces postoperative sore throat [8]. LMA is the most effective supraglottic device currently used in airway management. Although LMA can be utilized in pediatric airway management, its use is contraindicated in patients at risk of aspiration of gastric contents. However, if it is properly inserted and mechanical ventilation is set to positive pressure, aspiration of gastric contents is rarely observed [9]. The LMA provides advantages over the endotracheal tube, such as less airway manipulation and easier application. Besides, it is a viable alternative to the endotracheal tube, especially in short-term procedures [10]. LMA is less invasive and causes less discomfort afterward. It causes fewer hemodynamic alterations than endotracheal tubes [11]. The present study aimed to compare respiratory parameters in patients scheduled for orthopedic surgery with general anesthesia using endotracheal intubation or a laryngeal mask. 

Materials and Methods

This randomized double-blinded clinical trial was conducted on patients planning for elective orthopedic surgery under general anesthesia at a referral hospital in Bandar Abbas, Iran, from January 2021 to December 2021. All patients aged 20 to 65 years, with the American Society of Anesthesiologists (ASA) score I to II. Those with a history of chronic obstructive pulmonary diseases, asthma, interstitial lung disease, pulmonary fibrosis with an active lung infection, left ventricular ejection fraction of less than 40%, body mass index (BMI) higher than 35 Kg/m², requiring emergency surgery, or airway malformation were all excluded from the study. The study protocol was ethically approved by the Ethics Committee of Hormozgan University of Medical Sciences (ethical code: IR.HUMS.REC.1400.344). After receiving sufficient information about the details of the study design, all patients signed a written informed consent form. This study was also registered in the Iranian Registry of Clinical Trials (code: IRCT20220612055153N1).

Using a random allocation table, the study participants were randomly assigned to two groups. Before surgery, two units of blood were reserved for each patient, and baseline routine laboratory parameters were measured. All patients received 40 mg of pantoprazole and 1 mg of lorazepam orally the day before the operation and the morning of the operation. In the operating room, all patients were monitored for heart rate, pulse oximetry, and blood pressure. Induction of general anesthesia was considered with similar planning for all participants using propofol (2 mg/Kg) and atracurium (0.5 mg/Kg). In the first study group, tracheal intubation was performed with the tube no. 7.5 for females and 8.0 for males (manufactured by Jahan Tajhiz Hakim Company, Iran), three minutes after atracurium injection and placing ventilation mask with oxygen 100% (ETT group, n=48). In the second group, a laryngeal mask (of the classic silicone type) was installed with the proper size based on the patient’s weight (LMA group, n=48). It should be noted that laryngoscopy, tracheal intubation, and the placement of a laryngeal mask were all performed by an experienced anesthesiologist. The duration of surgery for all patients (from the beginning of anesthetic induction until the time of transfer to recovery) was documented. In terms of blinding, the patient was unaware of the process used to establish their airway (blinded patient). Moreover, the person who collected the data about respiratory parameters was not involved in the airway establishment process and was unaware of the type of employed airway device (blinding of the evaluator). The study endpoint was to measure respiratory parameters including arterial oxygen saturation (SpO₂), peak airway pressure (P peak), end-tidal carbon dioxide (EtCO₂), and dynamic lung compliance (DLC) in 1, 3, 5, 10, and 15 minutes after intubation. DLC was calculated as tidal volume (mL) divided by peak pressure—PEEP (mL/cm), with the normal range of 40 to 80 mm/cmH₂O.

For the statistical analysis, the statistical SPSS software version 23.0 for Windows (IBM, Armonk, New York) was used. The results were presented as mean±standard deviation (SD) for quantitative variables and frequency (%) for categorical variables. When there was a violation of the assumption of equal variances among the research groups or when the data did not seem to have a normal distribution, continuous variables were compared using the t-test or Mann-Whitney test. The Chi-Square test or Fisher’s exact test was used to compare the categorical variables. The Repeated Measure ANOVA test was used to assess the changes in study parameters. General linear modeling was used to examine the difference in the trend of parameter changes between the ETT and EMA groups after considering baseline factors such as sex, age, and length of operation. P values of less than 0.05 were considered statistically significant.

Results

The mean age of the patients in the ETT and LMA groups was 36.08±14.94 years and 42.04±15.16 years, respectively (p=0.095). There was similarity between the two groups, with 58.3% and 66.7% of the population being male (p=0.399). The mean body weight was also 70.50±9.66 and 68.88±5.63 Kg, with no significant difference (p=0.321). Table 1 shows that the mean operation time in the ETT and LMA groups was 1.66±0.70 hours and 1.15±0.52 hours, respectively, which was significantly higher in the ETT group (p=0.001).

Table 2 summarizes the respiratory parameters of the two studied groups. First, there was no significant difference in the trends of changes in arterial oxygen saturation and EtCO₂ between the two groups. In terms of changes in P peak, both groups indicated a significant decrease in the mean of this parameter during the first 15 minutes after airway management. Furthermore, at all-time points, the average of the P peak parameter in the ETT group was significantly higher than in the EMA group. With regard to the values of the P plateau, although the value of this index in the ETT group was higher than the EMA group at all-time points, there was no difference in the trend of the changes in this index between the two groups during the first 15 minutes. In terms of DLC changes, the LMA group had significantly higher values than the ETT group in all considered time periods. However, the upward trend in the value of this index was only significant in the LMA group.

When the trend of changes in study parameters (including P peak, P plateau, and DLC) was compared between the LMA and ETT groups, after adjusting the background variables such as sex, age, and duration of surgery, there was a significant difference between the two groups. Indeed, the trend of the changes in pointed parameters was independent of baseline variables (Tables 3-5).

Discussion

Supraglottic airway devices are now considered routine and standard techniques for airway management. Such devices, such as tracheal tubes and face masks, can provide a suitable gastight airway to provide proper hemodynamic stability before, during, and after procedural interventions [12]. However, one of the main limitations of some of these devices is poor pulmonary compliance due to setting positive pressure ventilation, particularly in obese patients. Therefore, certain modifications have been proposed to address this issue [13]. In this regard, some modifications have been made to the cuff and drain tube in the new generation of these devices known as PLMA, which could protect against gastric contents regurgitation, while also improving ventilatory mechanical characteristics, reducing the risk of sore throat, lowering hemodynamic upset during induction, and maintain proper oxygenation within emergent conditions []14, 15]. Today, the aforementioned designed tools have replaced the older ones including the endotracheal tube; nevertheless, it is still not clear how much the new tools affect the respiratory parameters compared to the previous ones [16]. Moreover, applying LMA instead of a tracheal tube could significantly reduce the risk of tracheal intubation-related morbidities, reduce stress during intubation, and result in faster recovery [17]. As indicated in the present study, although no difference was found in the status of arterial oxygen saturation and EtCO₂ between the two techniques, including LMA and ETT; the LMA technique was superior to ETT in terms of providing DLC and establishing proper conditions for P peak and P plateau. Remarkably, the marked advantage was completely independent of age, BMI, and time of operation. Ultimately, it seems that using LMA could result in less stress reaction and could be utilized with higher safety. It has been clearly shown that applying ETT might lead to serious postoperative complications, including pharyngalgia, pharyngeal pain, and tachycardia mainly due to the need for using a laryngoscope in the ETT technique [18, 19]. In other words, employing LMA instead of a laryngoscope reduces the risk of damaging the tracheal mucosa or regional circulation system. In addition, LMA can be easily installed, even by non-professional and non-specialist personnel, and does not require specific training, lowering the risk of airway failure [20].

Our findings indicated that LMA could achieve appropriate DLC more successfully than ETT devices. Almost all previous studies emphasized the superiority of the LMA method over the ETT in terms of establishing DLC [21-23]. As shown by Wei et al., no significant PaCO₂ change was noted in either group 5 minutes after Time Zero. However, there was a significantly lower PaO₂ in the ETT Group at that time point [21]. Additionally, coughs and snores were far more frequent in the ETT group, necessitating more interventions to maintain adequate respiratory function. Xu et al., also reported that the LMA group had a shorter anesthetic recovery time, indwelling days of chest catheter, and postoperative hospital stay as well as a considerably higher intraoperative partial pressure of CO₂ [22]. In their study, the arterial blood gas analysis after the operation showed no significant difference between the two groups. Regarding the difference in respiratory mechanics and similar to the findings of the present study, Mahdavi et al., found that using an LMA increased pulmonary dynamic compliance more than using an ETT. However, their study was conducted on young people [23]. Finally, Brimacombe conducted an extensive systematic review and reported that the main advantages of LMA over traditional ETT devices included ease of LMA placement by inexperienced personnel, improved hemodynamic stability, reduced airway tolerance, as well as lower rate anesthetic requirements for overcoming this resistance, and reduced the rate of sore throat [24]. Considering the obtained results, especially in providing optimal pulmonary acceptance, the LMA method could still be superior in providing an airway in major surgeries. However several other confounding factors, such as the performer’s experience or the tracheal tube cuff pressure, might affect outcome [25].

In conclusion, the findings of the present study indicated that using LMA instead of ETT in airway management was completely preferable due to optimal acceptance of lung dynamics and stabilization of peak pressure and pulmonary plateau, as well as maintaining respiratory oxygen and carbon dioxide pressure. In this regard, it seems that the use of LMA could be used successfully for different age groups, both sexes and even regardless of the patient’s weight status.

Declaration

Ethics approval and consent to participate: All patient information was anonymized to maintain confidentiality. The study adhered to the ethical principles of the Helsinki Declaration. Additionally, it received approval from the Ethics Committee of Hormozgan University of Medical Sciences (code: IR.HUMS.REC.1400.344). It was also registered in the Iranian Registry of Clinical Trials (code: IRCT20220612055153N1).

Consent for publication: All the authors, collectively, grant consent for the publication of this content.

Conflict of Interest: The authors declared that they had no conflict of interest.

Funding: This study was financially supported by the Hormozgan University of Medical Sciences (grant number: 4000415)

Acknowledgment: The research presented in this paper has been made possible through generous funding support from Shahid Mohammadi Hospital. The financial support provided by the hospital has played a crucial role in facilitating the necessary resources, equipment, and personnel required for the successful execution of our study. We extend our sincere appreciation to Shahid Mohammadi Hospital for its commitment to advancing research initiatives and contributing to the dissemination of valuable knowledge in the medical field.

Moreover, the authors would like to thank the Clinical Research Development Unit of Peymanieh Educational and Research and Therapeutic Center of Jahrom University of Medical Sciences for editorial assistance.

Authors’ Contribution: MM and MV were primarily responsible for the conception and design of the study, as well as the acquisition and analysis of data. NK, PA, ET, and TZ played key roles in drafting and critically revising the manuscript for intellectual content. HJ contributed significantly to the interpretation of data and provided valuable insights throughout the research process. TZ and MS participated in the statistical analysis and data interpretation. All authors have read and approved the final version of the manuscript, demonstrating a collaborative effort in the development of this research work.