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 Table of Contents  
ORIGINAL ARTICLE
Year : 2012  |  Volume : 2  |  Issue : 2  |  Page : 86-91

Determination of optimal dose of succinylcholine to facilitate endotracheal intubation in pregnant females undergoing elective cesarean section


1 Department of Anaesthesiology, Government Medical College, Haldwani, Uttarakhand, India
2 Department of Anaesthesiology, Sharda Medical College, Greater Noida, India
3 Department of Anaesthesiology, JNMCH, Aligarh, India

Date of Web Publication17-Dec-2012

Correspondence Address:
Mohd Asim Rasheed
Department of Anaesthesiology, Government Medical College, Haldwani, Uttarakhand
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2249-4472.104733

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  Abstract 

Aims: The study was carried out to find the optimal dose of succinylcholine for pregnant females, undergoing elective cesarean section under general anesthesia, in order to achieve excellent intubation conditions for a successful endotracheal intubation.
Materials and Methods: One hundred and twenty pregnant females aged between 20 and 35 years were randomly allocated into 4 groups of 30 patients each. Group I received Inj. succinylcholine 0.5 mg/kg, Group II received 0.6 mg/kg, Group III received 1.0 mg/kg, and Group IV received 1.5 mg/kg intravenously. The response to ulnar nerve stimulation at the wrist was recorded using the peripheral nerve stimulator. Grading of intubation conditions was done 60 s after Inj. succinylcholine administration. Peak effect, peak time, and duration of absent respiratory movement (apnea time) was noted.
Statistical Analysis: One-way analysis of variance (ANOVA) with post hoc analysis (Bonferroni test) has been applied to see significance among groups for continuous variables and the Chi-square test was performed for categoric variables. SPSS v 16 was used for statistical analysis for the study.
Results: Peak effect achieved was similar with 0.6, 1.0, and 1.5 mg/kg. There was no statistically significant difference (P >0.05) in the time taken to achieve the peak effect (peak time) between 1.0 and 1.5 mg/kg. Apnea time was 242.7 ΁ 7.1 s with 1.0 mg/kg and 377.7 ΁ 28.9 s with 1.5 mg/kg (P < 0.001). Intubating conditions were poor with 0.5 mg/kg, good with 0.6 mg/kg, and excellent with 1.0 and 1.5 mg/kg.
Conclusion: The dose of 1.0 mg/kg of succinylcholine produces excellent intubation conditions in pregnant females similar to the conventional dose of 1.5 mg/kg and is associated with a significantly shorter duration of action.

Keywords: Caesarean section, intubation conditions, pregnancy, succinylcholine


How to cite this article:
Rasheed MA, Palaria U, Bhadani UK, Quadir A. Determination of optimal dose of succinylcholine to facilitate endotracheal intubation in pregnant females undergoing elective cesarean section. J Obstet Anaesth Crit Care 2012;2:86-91

How to cite this URL:
Rasheed MA, Palaria U, Bhadani UK, Quadir A. Determination of optimal dose of succinylcholine to facilitate endotracheal intubation in pregnant females undergoing elective cesarean section. J Obstet Anaesth Crit Care [serial online] 2012 [cited 2019 Dec 10];2:86-91. Available from: http://www.joacc.com/text.asp?2012/2/2/86/104733


  Introduction Top


Most general anesthesia-related deaths occur due to hypoxemia when difficulty in securing airway is encountered. [1] The most commonly occurring adverse respiratory events are failure to intubate, failure to recognize esophageal intubation, and failure to ventilate. [2],[3] Failed end tracheal intubation is more common in pregnant females (incidence: 1:300 versus 1:2000 for all females) and is one of the major causes of maternal morbidity and mortality. [4]

There are several physiologic alterations during pregnancy that pose a challenge to the anesthesiologist in terms of a successful tracheal intubation during general anesthesia. Pregnant females have high chances for regurgitation and aspiration of gastric contents. [5],[6] Respiratory physiology is also altered in pregnant females leading to increase in tidal volume, minute ventilation volume, and oxygen consumption. [7],[8],[9] There occur changes in the upper airway, chest wall, static lung volumes, and gas exchange. [10]

Thus succinylcholine is an ideal neuromuscular blocker in pregnant females because it provides an excellent intubation conditions along with a short duration of apnea, although it has been observed that the duration of action of succinylcholine is significantly longer in pregnant women as compared with nonpregnant women. [11] Serum cholinesterase activity decreases 30% during pregnancy and remains depressed during the postpartum period. [12] Therefore, a higher proportion of females may be expected to show increased sensitivity (prolonged apnea) to succinylcholine when pregnant than when nonpregnant. This finding assumes great significance in the scenario of "cannot intubate, cannot ventilate," especially in pregnant females who are at more risk for sudden oxyhemoglobin desaturation than a nonpregnant female because of various respiratory changes and hormonal alterations.

Therefore, the objective of our study was to find out the optimal dose of succinylcholine for getting the best intubation conditions in pregnant females undergoing cesarean section.


  Materials and Methods Top


This prospective, randomized study was approved by the ethical committee of Government Medical College, Haldwani. After obtaining written informed consent, 120 pregnant females of ASA grade I aged between 20 and 35 years, posted for elective cesarean section over a period of 11 months were selected.

Females with cardiac, hepatic, pulmonary, and renal disease were excluded from the study. Females with neuromuscular disease or those taking medications known to interfere with neuromuscular transmission were also excluded from the study with the help of history taking and clinical investigations. Females with a documented or family history of abnormal response to succinylcholine, with a history of difficult intubation during previous surgery or with modified Mallampati grades III and IV were also excluded from the study. Actual body weight of the females was taken for the calculation of the dose of succinylcholine to be administered.

Random allotment of pregnant females into various groups was done by asking them to pick a sealed envelope containing cards specifying the dose to be given.

Females in Group I received Inj. succinylcholine 0.5 mg/kg. IV, Group II received dose of 0.6 mg/kg IV, Group III received 1.0 mg/kg IV, and Group IV received the dose of 1.5 mg/kg IV.

In the operating theater, the patients were monitored with an electrocardiogram, pulse oximetry, and noninvasive blood pressure monitoring using multichannel monitor (Drager model no. ms 18986 E539U). All females were premeditated with ranitidine 1 mg/kg IV and metoclopramide 0.15 mg/kg IV.

Patients were preoxygenated with 100% oxygen through a facemask for more than 3 min. Anesthesia was then induced with thiopentone sodium (5 mg/kg IV). After loss of eyelash reflex, we calibrated our peripheral nerve stimulator (TOF Watch S Organon IPXO CE 0543). The designated dose of succinylcholine (volume of the injection being 10 mL in each group) was then administered to the patient via a free running IV line on the contralateral arm. The patient was unaware of the dose to be administered as this was a single-blinded study.

A size 3 Macintosh blade was used for the laryngoscopy in each case. One minute after succinylcholine administration, laryngoscopy and tracheal intubation was performed by an anesthesiologist with more than 2 years of experience, who was unaware of the dose of succinylcholine administered and tracheal intubation conditions were graded using Copenhagen Consensus Conference Criteria [Table 1].
Table 1: Copenhagen consensus conference criteria

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If tracheal intubation proved impossible because of inadequate relaxation, respiration was supplemented by a face mask and the patient was given a supplemented dose of 0.5 mg/kg of succinylcholine, and another attempt was made 1 min later. These patients who received supplemental dose were excluded from the study. Correct tracheal tube placement was confirmed by EtCO 2 measurement and bilaterally equal air entry on auscultation.

After proper placement and confirmation of endotracheal tube by capnograph, cesarean section was started to keep the induction-delivery time as short as possible. Maintenance of anesthesia was done with FiO 2 of 0.5 (with nitrous oxide) in 0.6% isoflurane. The patient's lungs were ventilated to target EtCO 2 concentration of 35-40 mmHg using open circuit with fresh gas flow of 8 L/min.

Following parameters were recorded using a peripheral nerve stimulator:

  1. Peak effect (maximal twitch depression achieved)
  2. Peak time (time taken to achieve peak effect)


Duration of absence of respiratory effort (apnea time) was recorded as the time taken from the correct placement of the endotracheal tube until the appearance of patient's first respiratory effort as shown by the first visible reservoir bag movement.

Statistical analysis

One-way analysis of variance (ANOVA) with post hoc analysis (Bonferroni test) has been applied to see significance among groups for continuous variables and the Chi-square test was performed for categoric variables. SPSS v 16 was used for statistical analysis for the study.


  Results Top


Of the 120 patients who underwent randomization, all the patients agreed to participate in the study. The baseline characteristics of the patients in the 4 groups were similar [Table 2]. Comparison of peak effect (maximal twitch depression achieved) and peak time (time taken to achieve peak effect) is compared in [Table 3]. Peak time (mean ± SD) was 78.3 ± 3.8 s in Group I (0.5 mg/kg); 69 ± 4.0 s in Group II (0.6 mg/kg); 59.7 ± 1.8 s in Group III (1.0 mg/kg); and 59.7 ± 3.1 s in Group IV (1.5 mg/kg).
Table 2: Distribution of females in the study according to age (years), height (cm), and weight (kg)

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Table 3: Peak time, peak effect, and intubation condition during laryngoscopy according to copenhagen consensus conference criteria

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The difference of peak time between group IV (1.5 mg/kg) and Group III (1.0 mg/kg) was statistically insignificant (P = 1) [Table 3], whereas it was statistically significant (P value < 0.001) between Group IV (1.5 mg/kg) and Group II (0.6 mg/kg) and between Group IV (1.5 mg/kg) and Group I (0.5 mg/kg). Peak time was inversely related to the dose of succinylcholine given. Maximal twitch depression achieved was 96% with the dose of 0.5 and 0.6 mg/kg but all pregnant females achieved full muscular relaxation with the dose of 1.0 and 1.5 mg/kg.

Intubation conditions were graded and the results are shown in [Table 3]. In females receiving the dose of 0.5 mg/kg, 13 females were graded as poor (vocal cord was closed in 7 females and 6 females had movement of limbs), 12 were graded as good, and 5 were graded as having excellent intubation conditions.

With 0.6 mg/kg, 11 females were graded as having good and 19 were graded as having excellent intubation condition, whereas all the females receiving the dose of 1.0 and 1.5 mg/kg were graded as having excellent intubation condition.

(Out of 23 females having good intubation conditions, 21 females had slight movement of the limbs especially lower limbs and 2 had vocal cord in intermediate position due to which they were graded as having good intubation condition.)

The mean apnea time was recorded and is shown in [Table 4]. In Group I (0.5 mg/kg), the apnea time (mean ± SD) was 162.1 ± 7.6 s; in Group II (0.6 mg/kg) it was 215.6 ± 20.3 s; in Group III (1.0 mg/kg) it was 242.7 ± 7.1 s, and in Group IV (1.5 mg/kg) the apnea time was 377.7 ± 28.9 s.
Table 4: Mean apnea time

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  Discussion Top


Succinylcholine is a unique drug in anesthetic practice, primarily because of its pharmacodynamic profile. Although rocuronium has rapid onset of action similar to succinylcholine when given in the dose of 0.9 and 1.2 mg/kg, it is associated with long duration of action. [13] Recently it was found that despite its very short duration of action, functional recovery of succinylcholine takes a longer time after the conventional dose of 1.0 mg/kg in a healthy adult human being. [14]

Therefore, finding the optimal dose of succinylcholine during general anesthesia for cesarean section is of paramount importance: firstly, because of various physiologic and anatomic changes during pregnancy; and secondly, because most of the general anesthesia-related deaths in pregnancy is because of hypoxemia and airway catastrophe. [15],[16]

Although succinylcholine has a short duration of action because of its rapid hydrolysis by plasma cholinesterase, it was found that the critical oxyhemoglobin desaturation occurred before return to an unparalyzed state following 1 mg/kg intravenous dose. [17] They found that 0.6 mg/kg dose was ideal in terms of providing excellent intubation conditions as well as keeping the apnea time as short as possible to prevent any oxyhemoglobin desaturation. In addition, succinylcholine produced desaturation below 80% in 50% of females receiving conventional dose of 1.5 mg/kg. [18]

The present study was aimed at finding the optimal dose of succinylcholine, in pregnant females undergoing cesarean sections, so as to produce excellent intubation conditions, and at the same time producing an apnea time as short as possible to prevent oxyhemoglobin desaturation in cases of cannot-ventilate and cannot-intubate scenario.

The results of our study show that satisfactory tracheal intubation conditions in pregnant females could be achieved 1 min after succinylcholine administration, with doses much less than the traditionally recommended dose of 1.5 mg/kg

and the dose of 0.6 mg/kg do not always provide the satisfactory intubation condition as produced in a normal healthy nonpregnant female and male patients.

We selected four groups in our study to determine the optimal dose required for intubation; 1.5 mg/kg was the traditionally recommended dose and 0.6 mg/kg was the dose as suggested for normal healthy nonpregnant female and male patients and 1.0 mg/kg was taken as a group because the dose calculation was easy. Although the difference between 0.5 and 0.6 mg/kg was small it nevertheless found whether intubation was possible with such small doses or not.

The present study also recorded the peak time and peak effect of various doses of succinylcholine using the peripheral nerve stimulator.

Peak time (time taken to achieve peak effect) was not statistically significant between groups IV and III, whereas it was statistically significant (P value < 0.001) between groups IV and II and between groups IV and I.

The peak effect (maximal twitch depression achieved) was recorded and was found to be 96% in groups I and II, whereas it was 100% in groups III and IV. We recorded apnea time from the time of placement of tracheal tube until the first visible movement in the reservoir bag. When compared statistically, we found that there was statistically significant difference (P value < 0.001) between the apnea time in groups IV and III. Similarly, the apnea time between groups IV and II and between groups IV and I was also statistically significant (P value < 0.001).

Intubation conditions were compared in 4 groups using Copenhagen consensus conference criteria. In females receiving the dose of 0.5 mg/kg, intubation condition was graded as poor and with 0.6 mg/kg, intubation condition was graded as good, whereas all the females receiving the dose of 1.0 and 1.5 mg/kg were graded as having excellent intubation condition.

When compared statistically, we found that the difference in intubation conditions were not statistically significant between groups IV and III, whereas the difference in intubation conditions were statistically significant between groups IV and II and between groups IV and I (P value < 0.001). There was also a statistically significant difference in intubation conditions between groups III and II between groups III and I and between groups II and I (P value < 0.001). Naguib et al. had found that the calculated dose of succinylcholine (and their 95% confidence intervals) required to achieve excellent intubation conditions in 50% and 80% of nonpregnant females and male patient at 60 s to be 0.39 (0.29-0.51) mg/kg and 1.6 (1.2-2.0) mg/kg, respectively. [19]

We have not taken the body mass index (BMI) of the pregnant females into consideration in our study as a high BMI is a weak predictor for difficult and failed tracheal intubation. [20] Thus we cannot comment on the dose and intubation conditions in obese females, although it has been found that for complete neuromuscular paralysis and predictable laryngoscopy conditions, succinylcholine 1 mg/kg total body weight was appropriate in morbidly obese females with BMI of >40 kg/m 2 . [21]

We found that the dose of 0.5 and 0.6 mg/kg did not often result in satisfactory intubation conditions at 60 s, and therefore cannot be recommended for routine endotracheal intubation in pregnant females. The conditions after 0.6 mg/kg were clinically acceptable, although not ideal, whereas the intubation conditions after 1.0 mg/kg were identical to those obtained after 1.5 mg/kg dose.

The effectiveness of small doses of succinylcholine in achieving adequate tracheal intubation conditions 60 s after administration has been reported previously but they were not appreciated because there was no clearly defined relationship between the apnea time and oxyhemoglobin desaturation. [22],[23]

Although in our study the onset of action was dose dependent, there was no statistically significant difference between 1.0 and 1.5 mg/kg groups. This suggests that there is no benefit in terms of peak time in giving doses of succinylcholine larger than 1.0 mg/kg in pregnant females.

All the doses administered produced nearly complete abolition of the twitch response. The peak effect was 100% in groups III and IV.

The apnea time, was also dose dependent. It increased with the increase in dose of succinylcholine. It was 242.7 ± 7.1 s with 1.0 mg/kg (Viby-Mogensen had reported an apnea time of 348 min with the dose of 1 mg/kg in nonpregnant female and male patients. [24] The apnea time increased to 377.7 ± 28.9 seconds with the dose of 1.5 mg/kg which was statistically significant (P value < 0.001).

In our study we found that respiration began in most of the pregnant females, even before any muscular activity at the thumb, as recorded by the peripheral nerve stimulator. Although initial spontaneous and regular breathing may not reflect full functional recovery, this may still prevent oxyhemoglobin desaturation that would ensue if the patient remained apneic.

This study had few limitations. Firstly, the apnea time which was measured as the first visible reservoir bag movement after muscular relaxation was sometime effected by the pressure, which was applied on the abdomen by the surgeon. This limitation was removed by asking the surgeon to remove the pressure from the abdomen temporarily to determine the accuracy of reservoir bag movement.

Secondly, the duration of absence of respiratory effort (apnea time) was not very accurate for it was measured in between the IPPV given to the patient but the inaccuracy was reduced by diligent observation by the same observer in each case.

Thus, we can say that succinylcholine in the dose of 1.0 mg/kg provides excellent intubation conditions similar to the conventional dose of 1.5 mg/kg and is associated with shorter apnea time.

Alternatively, the more rapid return of neuromuscular function after smaller doses of succinylcholine could negatively affect intubation conditions by narrowing the window of opportunity for successful tracheal intubation.


  Conclusion Top


The dose of 1.0 mg/kg of succinylcholine produces excellent intubation conditions during pregnancy, and is associated with a shorter apnea time as compared with the conventional dose of 1.5 mg/kg.

 
  References Top

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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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