Efficacy of Low Dose Rocuronium in Reducing Induction Dose

Background

The amount of sedation and muscle relaxation of the jaw may have an impact on complications caused by laryngeal mask airway (LMA). The aim of this study is to evaluate the effect of low‑dose rocuronium on reducing the induction dose of propofol needed for LMA insertion in patients undergoing one day case surgery and its impact on LMA insertion conditions and complications.

Patients and methods: Sixty patients were included in this randomized double blind clinical study. Patients were divided into 2 groups; the control group (group I) receives intravenous fentanyl 1µg /kg and midazolam 0.05mg/kg , 5ml normal saline (placebo) and propofol (n = 30).The second (study) group (group II) receive intravenous fentanyl 1µg /kg and midazolam 0.05mg/kg , 0.15 mg / kg rocuronium diluted in 5ml normal saline and propofol ( n = 30). propofol dose was adjusted by loss of movements to maximum jaw thrust. Demographic data, ASA physical status, duration of surgery, duration of anaesthesia systolic and diastolic blood pressure, heart rate measurements (basal readings were recorded as well as immediately after induction then after one minute till the 5th minute.) induction dose of propofol, success rate of LMA insertion from first time, speed of insertion and any complications were recorded.

Results

There were no significant differences between both groups regarding demographic data, ASA physical status, duration of surgery, duration of anaesthesia, heart rate, success rate of insertion from first time and complications. On the other hand, there were significant statistical differences between both group regarding induction dose of propofol (P˂ 0.0001), Both systolic and diastolic blood pressure were noticeably lower in group II than that in group I immediately after induction (P=0.026 and 0.017 respectively ). Also time of LMA insertion was significantly lower in group II(P˂ 0.0001).

Conclusion: using low dose rocuronium(0.15 mg/kg) increases jaw relaxation, reduce propofol requirements in induction for LMA insertion, decreases the time needed for its insertion and relatively decrease postoperative complications related to LMA insertion.

Keywords: rocuronium, low dose, muscle relaxant, laryngeal mask airway, insertion conditions, propofol.

Introduction

Laryngeal mask airway( LMA) is an airway device important for both general anaesthesia and for emergency airway management, it was designed by Archie Brain in 1981 and came into clinical practice in 1988.

Correct insertion of LMA and prevention of complications need sufficient depth of anesthesia and mouth opening. Increased sedation of patients and relaxation of jaw muscle make insertion of this device easier. Although propofol is the drug of choice in induction for LMA insertion, propofol alone does not provide a good condition for it’s insertion.

Moreover administration of propofol in a fixed dose can be either insufficient or in excess resulting in undesired effects such as cough, hiccup, laryngospasm, movement of the patient and haemodynamic complications. LMA insertion without the use of muscle relaxant requires an anaesthetic depth sufficient enough to depress airway reflexes, however, the dose of propofol required to obtain that depth varies from patient to another.

Propofol 2.5-3 mg/kg is the dose frequently used for LMA insertion and it is preferred than sodium thiopental as Propofol suppresses both pharyngeal and laryngeal reflexes more than sodium thiopental. However, it frequently causes adverse hemodynamic changes.(5-8) These undesired effects can be diminished by co-induction with another anesthetic agent which is administered to reduce the total dose of propofol. These adjuvants, such as midazolam,(9) ketamine,(2) low-dose muscle relaxants,(9) opioids, (10) have been found to make the LMA insertion conditions much more easy.

On the other hand dose to targeted clinical response rather than a fixed dose allows appropriate anaesthetic depth for LMA insertion and helps in decreasing the incidence of cardiopulmonary complications. (11‑14)

Loss of verbal contact, loss of motor response to jaw thrust and apnea are the clinical indicators usually used for insertion of LMA. Forward jaw thrust is similar to the stimulus that is caused by LMA insertion. Therefore, loss of motor response to jaw thrust is considered a reliable clinical sign of appropriate anaesthetic depth for LMA insertion without complications. (15‑18)

There is controversy about using muscle relaxants for facilitation of LMA insertion. (19,20) however it is thought that the use of low doses of muscle relaxants with propofol significantly improves LMA insertion technique. (21)

One of the muscle relaxants used is rocuronium bromide with its rapid onset and intermediate duration of action and with no obvious side-effects . It is used for both standard endotracheal intubation and rapid sequence induction. (22). Recently the γ-cyclodextrin derivative sugammadex ( Bridion) has been introduced as a new agent for reversal of the action of this muscle relaxant. (23)

The aim of this study was to evaluate the effect of low dose rocuronium (0.15mg/kg) on reducing the induction dose of propofol needed for LMA insertion and its impact on LMA insertion conditions and related postoperative complications in patients undergoing one day case surgery under general anesthesia.

Patients and methods

This randomized double blind clinical study was performed in Zagazig University Hospitals. After obtaining the approval from the hospital ethics committee, written informed consents were obtained from 60 patients who were scheduled for one day case surgery under general anesthesia. Patients were aged between 18 and 60 years old of both sexes, with American Society of Anesthesiologists (ASA) physical status I or II. Exclusion criteria were as follows: Patients with predicted difficult intubation, predicted difficult mask ventilation, pregnancy, allergy to any of the used drugs, BMI more than 30, gastro esophageal reflux disease or other risk of aspiration and presence of respiratory tract pathology . Patients were divided randomly using closed envelopes into two groups. The anesthetist nurse who prepared the medications opened the envelopes before induction of anesthesia and was not involved in data collection.

Discussion

The optimal depth of anaesthesia needed for LMA insertion should provide a relaxed jaw, sufficient mouth opening with suppression of airway reflexes to avoid coughing, gaging, and laryngospasm. (24)

Jaw thrust imitates the stimulus caused by insertion of LMA. Thus, loss of motor response to jaw thrust may indicate a level of anaesthesia deep enough to allow easy insertion of LMA. (15)

Drag et al.(15)showed that easy LMA insertion conditions could be obtained in 87% of patients who had loss of motor response to jaw thrust with propofol dose of 2.55mg/kg with rate of propofol infusion of 10 ml /minute.

Dutt et al.(25) found that combination of propofol in a dose of 2.5mg/kg. with fentanyl in a dose of 1micg/kg. provide more hemodynamic stability for LMA insertion.

Furthermore, the addition of midazolam reduce induction dose of propofol for LMA insertion. (26-28). To our knowledge, thus far, no studies comparing the effect of adding low dose muscle relaxant on induction dose of propofol for LMA insertion. However, there was significant decrease in propofol dose when low dose rocuronium(0.15mg/kg) was used in this current study.

This study was designed to compare the optimal insertion conditions with or without low dose rocuronium(0.15mg/kg)and its effect on induction dose of propofol judged by loss of motor response to jaw thrust as an ideal end point for LMA insertion. The results of this study revealed that using a low doses of rocuronium before propofol injection produce better relaxation of the jaw, reduce propofol requirements and facilitate faster LMA insertion.

Chui and Cheam compared the effect of two different doses of mivacurium with normal saline for LMA insertion with propofol induction. They found that both doses of mivacurium significantly facilitated LMA insertion in a similar manner in comparison with normal saline.(29)

Other studies revealed that a single intu¬bating dose of non-depolarizing muscle relax¬ant with an intermediate duration of action increase the recovery time and cause residual muscle paralysis after surgery (30-32). But in comparison with the standard intubating dose (0.6 mg/kg), low-dose rocuronium (0.45 mg/kg) could decrease the patient’s recovery time (33).

In this study, 0.15 mg/kg rocuronium was used in study group and patient’s recovery time was comparable to those of control group. This suggests that low-dose of rocuronium rather than standard intubating dose is safe in short surgery with LMA.

On the other hand, Monem and Chohan compared the effects of succinylcholine and atracurium with thiopental for LMA insertion, and they found that succinylcholine provides better conditions for LMA insertion in comparison with atracurium which is in agreement with this current study. However, they found that succinylcholine was accompanied with high incidence of postoperative myalgia.(34)

Nevertheless, van Vlymen et al. (35) revealed the need for injecting muscle relaxant for endotracheal intubation by the intubating LMA (ILMA). They divided the patients into 3 groups. a placebo group(normal saline) and two study groups in which rocuronium was used in doses of 0.2, and 0.4 mg/kg for muscle relaxation respectively. they did not find any relationship between the use of rocuronium and the required time for insertion and fixing of the endotracheal tube.

Their results don’t concur with the results of this current study. The possible causes of the difference between both studies is the time of giving the muscle relaxant as they give the muscle relaxant after ILMA insertion and before tracheal intubation, the other cause is the type of LMA used ( a Classic LMA was used in this current study, while ILMA was used in their study).

The results of our study demonstrated that the use of rocuronium for muscle relaxation significantly decreases the time needed for LMA insertion. According to the results in both groups, LMA was inserted in an average time of 10-12 seconds. However this time was lesser in another study in which the average time was less than 6 seconds (36)

Nevertheless, in other studies of Chauhan et al., Hayashi et al. and Oh et al., this time was 15, 16, and 38 second, respectively. (37-39)

The exact cause of different insertion time in this current study in comparison to other studies is not exactly obvious. Possible causes can be attributed to differences in pretreatment, the method of calculating the time of insertion, and experience of the person who carried out the insertion.