The Impact of Sevoflurane and Propofol Anesthetic Induction on Bag Mask Ventilation in Surgical Patients with High Body Mass Index.

BACKGROUND AND AIMS: Obesity is associated with restrictive ventilatory pattern which causes rapid oxygen desaturation. Although obesity is considered as a risk factor for difficult airway management, failure to achieve effective bag mask ventilation (BMV) can be catastrophic. This study tried to assess the effect of both propofol and sevoflurane on the efficacy of BMV during anesthetic induction in obese patients. PATIENTS AND METHODS: A total of 200 cases were included, and they were randomly divided into two equal groups; Group S which included 100 cases who underwent sevoflurane induction, and Group P which included the remaining 100 cases who underwent propofol induction.
RESULTS: No statistically significant difference was detected between the two groups regarding patient and air way characteristics (P > 0.05). Difficult BMV (DBMV) was encountered in 19% and 37% of cases in Groups S and P, respectively. The incidence of DBMV was significantly increased in the P group (P = 0.005). Furthermore, the severity of difficulty was more marked in the P group. Logistic regression analysis revealed that thyromental distance, presence of macroglossia, presence of beard, lack of teeth, history of snoring, as well as propofol induction were risk factors for DBMV.
CONCLUSION: Sevoflurane can facilitate BMV and provide better intubation conditions in comparison to propofol during anesthetic induction in morbidly obese patients. Moreover, decreased thyromental distance, presence of macroglossia and beard, lack of teeth, and history of snoring are considered preoperative indicators of DBMV. Copyright:

INTRODUCTION

Anesthetists encourage to understand the impact of obesity on anesthetic practice as obesity has become an international epidemic over the past decades.[1] Obesity is associated with restrictive ventilatory pattern which decreases the chest wall compliance and impair diaphragm descent, especially when patient position changed from sitting to supine.[234] Added to that, obese patients have high oxygen consumption due to their high metabolic rate with more basal lung atelectasis when compared to lean patients.[5]

As a result, with inadequate preoxygenation, oxygen desaturation may occur within 1–2 min following anesthetic apnea.[6789] This shorten the time for airway management, especially in “can’t intubate, can’t ventilate” situations.[1011]

Yet, obesity has been considered as a risk factor for the possibility of difficult airway management, especially difficult bag mask ventilation (DBMV).[1213]

Failure to achieve effective BMV can be catastrophic. It may lead to permanent brain damage or death particularly if associated with difficult intubation.[14] Effective BMV can indeed minimize or reverse hypoxia, particularly if timely successful intubation is impossible.[1516]

Propofol and sevoflurane are common anesthetic agents used for induction and maintenance of anesthesia. Both cause rapid changes in the depth of anesthesia, a favorable emergence profile, and minimal postoperative morbidity.[17] Studies comparing propofol with sevoflurane in intubated adults have shown them to be similar in terms of cardiorespiratory effects, emergence times, and monitor. However, emergence is more rapid and excitatory phenomena more common with sevoflurane.[18] Although both propofol and sevoflurane are common anesthetic agents, their impact on BMV efficiency during induction of anesthesia was not assessed before.

Aim

In this prospective, randomized, double-blinded study, the primary aim was to compare the effect of both propofol and sevoflurane on the efficacy of BMV during anesthetic induction in obese patients with low physiological reserve to ensure preparation of appropriate airway choices. In addition, risk factors and the incidence of DBMV in obese patients were assessed.

PATIENTS AND METHODS

This prospective randomized study was conducted at Mansoura University main hospital in collaboration with general surgery unit during the period between June 2020 and January 2021. An informed written consent was obtained from all cases after the explanation of the benefits and drawbacks of each technique of induction. Furthermore, the study was approved by the Institutional Research Board (IRB number R.20.06.879), Mansoura University on June 15, 2020. This study was done according to the Declaration of Helsinki and good clinical practice (Brazil, 2013).

All patients with high body mass index (BMI) (>30 kg.m−2), aged between 18 and 60 years, having American Society of Anesthesiologists (ASA) physical status Classes I and II, and predicted to be difficult for BMV (defined as the presence of two or more signs of difficult BMV including: age >55 years, BMI >26 kg.m−2, presence of beard, history of snoring, or lack of teeth[19]) and scheduled for elective operations using general anesthesia were enrolled in the current study.

Patients with severe systemic comorbidities, ASA physical status classes >II, history of difficult intubation, or refuse to participate in the study were excluded from the study.

Sample size was calculated based on a previous study which compared tidal volume between patient with or without history of sleep breathing disorders, based on the tidal volume. The calculated sample size was 84 patients in each arm with α = 0.05 (two tailed) and β = 0.8 (Sigma Plot 12.0; Systat Software Inc., USA). Accordingly, total sample size will be 186 cases. We intentionally increased the number of participants to 200 to compensate for dropout and missed cases.[20]

A total of 200 cases were included, and they were divided using a computer-generated randomization software and numbered sealed envelopes into two equal groups; Group S which included 100 cases who underwent sevoflurane induction, and Group P which included the remaining 100 cases who underwent propofol induction.

All patients were evaluated preoperatively for tolerability of the surgery according to our local protocol. Airway assessment included: Mallampati pharyngeal classification, interincisor gap, thyromental distance, sternomental distance with the neck fully extended, dentition status, neck circumference at the thyroid cartilage level, facial or neck trauma, presence of facial hair, nasal deficiencies, and neck mobility grade. Furthermore, diagnosis of OSA was done according to patient history, and BMI was measured for all cases.

Patients were asked to fast for 6 h for solids 2 h for clear fluids. In the operative theater, patients were placed in supine position with oxford pillow below their head and chest. Basic monitoring was attached including noninvasive blood pressure, heart rate, pulse oximetry, electrocardiography, bispectral index (BIS), and capnography (connected to face mask). Intravenous (i.v.) access was established in the nondominant hand. Crystalloid lactated Ringer's solution was infused (1 mg.kg−1 of the ideal body weight).

Preoxygenation was started with 100% O2 until the expired oxygen saturation was >98%. Induction of anesthesia was performed using either i.v. 1.5–2.5 mg.kg−1 propofol in Group P or inhalation of 8% sevoflurane through a face mask connected to semi-closed breathing circuit after priming the circuit with 8% sevoflurane with a fresh gas flow of 6.0 L/min in Group S.

After confirming loss of consciousness, verbal contact, eyelash reflex, and BIS value <60, face mask was firmly applied to the patient face by one-handed maneuver using best airway opening technique. After that, ventilation was manually performed for 2 min at rate 12 cycle/min, trying to maintain an inspiratory pressure of 15 cmH2O (the adjustable pressure limiting valve was settled at 15 cmH2O), with observation of synchronized bilateral expansion of the chest, auscultation, and capnography. Rocuronium 1 mg.kg−1 bodyweight was injected after that to facilitate the endotracheal intubation.

We used the ASA task force definition of difficult mask ventilation established when it is not possible for the unassisted anesthesiologist to maintain the oxygen saturation (SpO2) >90% by 100% oxygen and positive pressure mask ventilation in a patient whose SpO2 was >90% before anesthetic intervention; and/or it is not possible for the unassisted anesthesiologist to prevent or reverse signs of inadequate ventilation during positive pressure mask ventilation.[21]

A severity score was used to grade difficult BMV; Grade 0 = easy, Grade 1 = use of oral airway, Grade 2 = need for two handed ventilation, and Grade 3 = requirement of supraglottic device. True DBMV was identified if considered true DBMV if it was graded as 2 or 3, and false DBMV was identified if the grade was 0 or 1.[22]

Statistical analysis

The collected data were analyzed through the SPSS version 24 (SPSS Inc., Chicago, IL, USA). The normality of data was tested using the Kolmogorov–Smirnov test. Chi-square or Fisher's exact test was used for categorical data analysis. Continuous normally distributed data were analyzed using independent sample t-test. Nonparametric data were analyzed using Kruskal–Wallis and post hoc Wilcox on rank sum t-tests, when appropriate. Data were expressed as mean ± standard deviation, median and range, and number (%). P < 0.05 was considered statistically significant.

RESULTS

Starting with demographics, the mean age of the included cases was 59.51 and 60.13 years in the S and P groups, respectively. Females represented 50% and 53% of cases in the study groups, respectively, whereas the remaining cases were males. BMI had mean values of 39.97 and 39.75 kg.m−2 in both groups, respectively. Neither of the previously mentioned demographic variables was significantly different between the two groups (P > 0.05). Table 1 illustrates these data.

Table 1

Demographic characteristics in the studied groups

	Mean±SD		95% CI	P
	Group S (n=100), n (%)	Group P (n=100), n (%)
Age (years)	59.51±4.72	60.13±3.72	−1.80-0.56	0.303
Gender
Male	50 (50.0)	47 (47.0)	−0.17-0.11	0.671
Female	50 (50.0)	53 (53.0)
Height (cm)	167.70±7.12	168.76±7.74	−3.04-1.10	0.357
Weight (kg)	112.59±12.18	113.21±11.93	−3.98-2.74	0.717
BMI (kg/m2)	39.97±2.72	39.75±2.72	−0.54-0.98	0.572

Data are expressed as mean±SD, n (%). CI=Confidence interval of the mean difference between both groups, BMI=Body mass index, SD=Standard deviation

As regard Mallampati score, score I was present in 51% and 61% of cases in the study groups, respectively, while the remaining cases had score II. Mouth opening had mean values of 45.2 and 46.48 mm in the same groups. Furthermore, the mean values of thyromental distance were 84.47 and 81.80 mm in the same groups, respectively. Macroglossia was present in 5% and 7% of cases, whereas receding mandible was detected in 21% and 27% of cases in both groups, respectively. Beard was present in 6% and 9% of cases, while snoring was reported by 56% and 57% of the included cases in both groups in order of speech. There was no significant difference between the two groups regarding any of the previously mentioned variables (P > 0.05), Table 2.

Table 2

Predictors of difficult bag mask ventilation in the studied groups

	Group S (n=100), n (%)	Group P (n=100), n (%)	95% CI	P
Mallampati
I	51.0 (51)	61.0 (61)	−0.04, 0.24	0.154
II	49.0 (49)	39.0 (39)
Mouth opening (cm)	45.20±5.79	46.48±6.61	−3.01, 0.45	0.147
Thyromental distance (cm)	84.47±12.59	81.80±11.80	−0.73, 6.07	0.123
Presence of macroglossia	5.0 (5)	7.0 (7)	−0.05, 0.09	0.552
Receding mandible	21.0 (21)	27.0 (27)	−0.06, 0.18	0.321
Lack of teeth	18.0 (18)	23.0 (23)	−0.06, 0.16	0.381
Presence of beard	6.0 (6)	9.0 (9)	−0.04, 0.1	0.421
History of snoring	56.0 (56)	57.0 (57)	−0.13, 0.15	0.887

Data are expressed as mean±SD, number and %. 95% CI: 95% confidence interval of the mean difference between both groups. SD=Standard deviation

DBMV was encountered in 19% and 37% of cases in Groups S and P, respectively. There was a significant increase in DBMV in the P group (P = 0.005). All difficult cases in the S group were managed either by oral airway or two-handed ventilation, while in the other group, difficult cases were managed wither by oral airway, two-handed ventilation, or supraglottic device. These data are illustrated in Table 3.

Table 3

Incidence of difficult bag mask ventilation and its severity in both groups

	Group S (n=100), n (%)	Group P (n=100), n (%)	95% CI	P
DBMV	19 (19.0)	37* (37.0)	0.06-0.3	0.005
Severity
Oral airway	15 (78.9)	16 (43.2)	-	0.027
Two handed ventilation	4 (21.1)	19* (51.4)
Supraglottic device	0	2 (5.4)

Data are expressed as n (%). CI=Confidence interval of the mean difference between both groups. *P is significant when <0.05. DBMV=Difficult bag mask ventilation

Logistic regression analysis revealed that thyromental distance, presence of macroglossia, presence of beard, lack of teeth, history of snoring, as well as propofol induction were risk factors for DBMV. Table 4 illustrates these data.

Table 4

Univariable logistic regression for the incidence of difficult bag mask ventilation

	OR	95% CI	P
Age	1.020	0.948-1.097	0.601
Female gender	0.891	0.480-1.654	0.715
BMI	1.028	0.917-1.152	0.637
Mallampati II	1.611	0.852-3.045	0.143
Mouth opening	1.016	0.967-1.068	0.527
Thyromental distance	0.734	0.669-0.805*	<0.001
Presence of macroglossia	5.833	1.681-20.242*	0.005
Lack of teeth	10.077	4.647-21.853*	<0.001
Presence of beard	12.818	3.460-47.489*	<0.001
History of snoring	3.986	1.945-8.165*	< 0.001
Propofol induction	2.504	1.315-4.766*	0.005

*P is significant when <0.05. CI=Confidence interval, OR=Odds ratio, BMI=Body mass index

DISCUSSION

Facemask ventilation is an essential element of airway management during anesthetic induction; however, the prediction of airway management difficulties remains a challenge. Better prediction may reduce morbidity and mortality by adequate preparation of relevant personnel and appropriate equipment.[23]

To the best of our knowledge, there is a lack of studies which have discussed the induction method (i.v. or inhalational) implication on BMV. Most of the existing studies compared the same drugs in laryngeal mask airway not face mask ventilation.[2425]

Our data showed that DBMV occurred in both propofol and sevoflurane groups, although, there was a significant increase in DBMV in P group (P = 0.005) when compared to sevoflurane group. DBMV was encountered in 19% and 37% of cases in Groups S and P, respectively.

Sevoflurane can improve BMV by different mechanism. Sevoflurane decreases lung resistance with moderate bronchodilation, even in subjects without hyperreactive airway disease.[2627] The bronchodilator effect of sevoflurane is a result of either indirect inhibition of the neural reflex pathways or by direct effects on airway smooth muscle cells.[28] The direct airway smooth muscle relaxation induced by sevoflurane is linked to a reduction in the intracellular concentration of free Ca ions which acts as a key second messenger inside these cells.[2930] Moreover, sevoflurane slightly but significantly increases the dynamic compliance without changing the lung resistance.[26]

Propofol can facilitate BMV through its effect on laryngeal muscle tone. Propofol can attenuate laryngospasm incidence on induction of anesthesia by suppressing the laryngeal reflex[3132] through inhibition of upper airway muscle activity either by central or peripheral reflex pathways inhibition together with its significant inhibiting effects on phasic genioglossus muscle activity. This contributes to its ability to maintain the upper airway patency and BMV facilitation.[3334]

Added to that, propofol has an inhibitory effect on diaphragmatic contractility and relaxation. It acts either presynaptically to inhibit neuromuscular transmission or at the muscle membrane to inhibit muscular contraction.[35] This can result in a fall in lung volume based on suggestions from previous studies.[3637]

The superiority of sevoflurane on propofol in facilitating BMV according to our study results may be attributed to the fact that both propofol and sevoflurane have different inhibitory effects on genioglossus muscle, hence affecting upper airway patency. These differences are mostly related to the differential inhibitory effects of both agents on neural drive to the genioglossus muscle. Potential sources of such inhibition are the inhibitory neurotransmitters – aminobutyric acid (GABA) and glycine.[38] Propofol can act mainly on the GABA receptor[3940] and sevoflurane-like isoflurane acts on both the glycine and GABA receptors.[4142] As a results sevoflurane-like isoflurane inhibits genioglossus muscle activity more profoundly than propofol.

According to the current study, more patients in propofol group required additional doses to obtain adequate BMV. This finding demonstrates the better quality of conditions for BMV placement given by sevoflurane. In similar study by Molloy et al., additional doses of propofol were required to obtain suitable insertion condition for LMA like those obtained with sevoflurane induction of anesthesia.[43]

The previous study was conducted to estimate the risk factors for DBMV reported that the rate of DBMV was 5%.[15] Other results reported different rates ranging between 0.07% and 1.4%.[444546] These studies reported lower rates compared to ours and that could be explained by the fact that all of these studies included patients with BMI lower than our study. Increased BMI has been known to be a significant risk factor for DBMV.[1547] This could be also due to different definitions existing for DBMV.

The results obtained in our study could be explained by the fact that propofol causes relaxation of upper air way muscles and loss of air way reflexes. Furthermore, its dose is guided by patient weight.[48] On the other hand, sevoflurane does not express that strong inhibitory effect on respiratory muscles and reflexes.[4950] Moreover, its dose is guided by patient inhalation. Therefore, if obstruction is going to happen, partial airway collapse will decrease sevoflurane intake, leading to decrease in drug uptake to prevent further collapse.

Ryken TC have reported that the incidence of apnea was significantly higher in the propofol group compared to sevoflurane group (9/36 vs. 2/36 – P = 0.049).[51]

In the current study, we identified decreased thyromental distance, presence of macroglossia, lack of teeth, presence of beard, history of snoring, along with propofol induction as independent risk factor for DBMV.

Langeron et al. reported that age >55 years (P = 0.002), the presence of beard (P = 0.006), BMI >26 kg.m − 2 (P < 0.001), lack of teeth (P = 0.006), and history of snoring (P = 0.02) were significant predictors of DBMV.[44]

Another study reported that a history of snoring (P = 0.004) and thyromental distance <6 cm (P = 0.04) were the only independent factors for DBMV.[52]

Sachs reported that increased neck circumference, male gender, sleep apnea, presence of beard, snoring, BMI >26 kg.m−2, along with lack of teeth were significant risk factors for DBMV.[53]

Although studies in the literature agree on some risk factors, there is a heterogenicity regarding others and that could be explained by different sample size, patient, or air way characteristics.

Our study has some limitations; first of all, it is a single-center study. Furthermore, the incidence of difficult intubation should have been assessed as well. Furthermore, we did not conduct polysomnography in our patients such that obstructive sleep apnea cannot formally be excluded.

CONCLUSION

Sevoflurane can facilitate BMV and provide better intubation conditions in comparison to propofol during anesthetic induction in morbidly obese patients. Moreover, decreased thyromental distance, presence of macroglossia and beard, lack of teeth, and history of snoring are considered preoperative indicators of DBMV.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.