Abstract
Background
Prehospital emergency airway management challenges every paramedic. Emergencies evacuated from difficult areas by armed forces need airway maintenance throughout evacuation. Effective use of supraglottic airway (SGA) devices during prehospital transfer is life saving. This study compared use of four commonly available SGAs by Armed Forces paramedics in simulated emergency situations.
Methods
This prospective observational study conducted in a tertiary care institution, included 58 volunteer paramedics. They were trained on manikins before the study in basic airway skills and insertion of the four SGA devices under study viz. Classic laryngeal mask airway (cLMA), laryngeal tube (LT), I-gel, and Combitube. SGA device insertions were performed on 474 patients scheduled for short elective surgical procedures under general anesthesia. All volunteers inserted and assessed the four SGA devices equal number of times in different patients. Overall success rate, time for successful insertion, first attempt success rate, number of attempts for successful insertion, oro-pharyngeal leak pressures, ease of insertion, durability of device, and complications were recorded.
Results
Differences among the four groups were statistically significant in all parameters. Intergroup comparison revealed that both I-gel and LT were comparable to each other, however superior to cLMA and Combitube in all outcome measures except ease of insertion and durability of device where I-gel was better and oro-pharyngeal seal pressures where Combitube was better.
Conclusion
Considering all parameters, I-gel proved superior with minimal complications compared with other SGA devices tested. I-gel may be recommended for emergency airway rescue use in patients by military paramedics.
Keywords: Military paramedics, Supraglottic devices, Simulated emergency airway management
Introduction
Prehospital airway management in emergencies is challenging for every paramedic. An ideal airway device should be easy to introduce by the prehospital paramedic, requiring minimal training and having a high success rate and minimal complications. Most of the wide spectrum of supraglottic airway (SGA) devices being used by anesthesiologists for airway management are inserted blindly, an essential difference from endotracheal intubation (ETI). The personnel of the armed forces in our country have a unique burden of being posted in difficult areas and terrain with uncongenial or extreme climatic conditions, often several hours or days from qualified medical help. The emergencies vary from battle or war causalities in the midst of active hostilities to non-battle casualties in peace areas. In either case, the importance of maintaining a patent airway before and during evacuation to higher medical echelons cannot be overemphasized. In such settings especially in field locations, the efficacy of a SGA device in maintaining a patent airway and improving ventilation during prehospital transfer can be crucial in saving lives. Tactical Combat Casualty Care Guidelines (2017)1 recommends only the nasopharyngeal airway as an airway management device. The current syllabus at the AMC Centre and College for Basic Nursing includes theory classes for nasopharyngeal airway, oropharyngeal airway, classic laryngeal mask airway (cLMA), Combitube, and ETI and their use on mannequins. This study was designed to compare the use of four commonly available SGAs by the Armed Forces paramedics in a simulated emergency situation on patients under general anesthesia (GA) who are akin to unconscious patients unable to maintain airway patency.
Materials and methods
This study was a prospective, observational study set in a tertiary care institution involved in regular training of paramedics. Institutional Ethical Committee and technical approval from the O/o DGAFMS.. The study was carried out on 58 serving paramedical personnel undergoing training who had volunteered for the study. The volunteers were excluded if they had received any training in airway management. Basic airway skills training on manikins was imparted by the author to the volunteers in batches of 4–12 before study, which included lecture cum demonstration of the basic airway maneuvers and insertion of oral/nasal airways and SGA devices. All volunteers initially observed instructive insertion and brief lecture demonstrations on each of the four SGA devices—cLMA, laryngeal tube (LT), I-gel, and the Combitube (also known as esophageal—tracheal double airway)—to be used in the study. Thereafter, they were allowed to freely insert them on manikins till they were comfortable with the procedure. Further insertions were done in the operation theatre on real patients.
For an alpha-error of 0.05 and a power of 80% the study setting required the volunteers to perform a minimum of 90 device insertions (for each SGA device) in actual patients. 54% success rate was considered as a baseline with a reference of the study by Ragazzi et al.2 In the study setting, each device group had a minimum of 114 American Society of Anaesthesiologists (ASA) I or II patients, aged 18–60 years undergoing (after informed consent) elective procedure under GA lasting less than 60 min. SGA device insertions were not done for patients with anticipated or difficult airway, restricted head and neck mobility, pulmonary disease, increased risk of aspiration, cases with cardiovascular co-morbidities, or with body mass index >35. GA was induced with a standard protocol for all patients.
The volunteer paramedics initially observed SGA device insertion in patients under GA in the OT. Thereafter, they were allowed to insert one SGA device per patient in subsequent patients with a maximum five attempts permitted per candidate per patient. All volunteer candidates assessed the four SGA devices equal number of times in different patients and recorded ease of insertion. No assistance was provided during the insertion attempts. However, a consultant anesthesiologist, who was always present to manage failures or possible complications, also noted other parameters under study. The primary outcomes evaluated were overall success rate, time to successful insertion, and ease of insertion. The secondary outcomes evaluated were first attempt insertion success rate, average number of attempts for successful insertion, leak pressures/oropharyngeal seal pressure, durability of device, and complications.
Definition of terms
Success of SGA device placement was defined as one in which successful placement was confirmed by an EtCO2 trace/chest lift with ventilation.
Time for successful insertion was measured with a stopwatch starting immediately after stopping bag-mask ventilation and picking up the SGA device (excluding SGA device preparation) till visible EtCO2trace.
Ease of insertion was assessed by the candidates on a modified Likert scale similar to the scale used by Henlin et al.3 viz. 1—very easy insertion; 2—easy insertion; 3—neither easy nor difficult insertion; 4—difficult insertion; 5—very difficult insertion.
First attempt: Any forward movement of the SGA in the oral cavity was counted as an insertion attempt. Hence, the initial forward movement was the “first attempt”, and any backward movement terminated the first attempt.
Number of attempts for successful insertion was defined as total number of forward movements till successful placement of the SGA device.
Failure of device insertion was defined as inability to achieve VTe (expired tidal volume) of at least 4 ml/kg at 5 min despite maximum insertion attempts.
Leak pressures/Oropharyngeal seal pressure was determined 5 min after successful placement of SGA device. The reservoir bag was filled with fresh gas flow and the pressure valve was closed completely. With air flow set at 3 L/min and the pressure limit at 40 cm H2O, oropharyngeal seal pressure/leak pressure was recorded as reading in the pressure gauge when the first sounds of air leak were audible above the larynx using a stethoscope.
Durability of the SGA device was defined as the average number of times it was reused before it was declared unfit for further use owing to disruption of the device anatomy.
Complications associated with insertion—signs of blood or gastric fluid staining on SGA device, bronchospasm, nausea, or vomiting or dental injuries.
Data analysis was performed using SPSS software v23. Chi-square test was used for testing between proportions. Analysis of variance was used for comparison of quantitative variables between the four groups. Post hoc Bonferroni correction was used for comparison between two groups after testing for homogeneity. Wherever homogeneity assumption was not met or for testing between medians non-parametric equivalent Kruskal-Wallis test was used.
Results
The study lasted from Mar 2013 till Sep 2015 with 58 volunteers. The study included 10 (17.24%) trainee OT matrons, 26 (44.82%) class III operation-room assistants (ORAs) and 22 (37.93%) nursing assistants (NAs). 474 patients selected for SGA device insertion were counselled, and informed consent was taken. The demographic parameters were comparable (Table 1) with no significant difference among the groups. The primary and secondary outcomes are depicted in Table 2.
Table 1.
Demography of study population.
| Demography study population | ||||
|---|---|---|---|---|
| SGA device | Demographic parameter |
|||
| Age (yrs) mean ± SD | Weight (kgs) mean ± SD | Mean duration of anesthesia ± SD | Sex distribution | |
| cLMA | 33.29 ± 0.66 | 53.65 ± 12.65 | 28.88 ± 11.56 | 35M/85F |
| LT | 34. 04 + 0.58 | 54.18 ± 10.88 | 26.92 ± 10.57 | 39M/81F |
| I-gel | 35.15 ± 0.74 | 56.19 ± 11.69 | 28.68 ± 10.20 | 37M/83F |
| Combitube | 32.93 ± 10.43 | 54.96 ± 10.13 | 27.38 ± 10.88 | 37M/77F |
| p-value | 0.46a | 0.338a | 0.445a | 0.937b |
ANOVA, analysis of variance; SGA, supraglottic airway; cLMA, classic laryngeal mask airway; LT, laryngeal tube.
ANOVA.
Chi-square test.
Table 2.
Primary and secondary outcomes.
| SGA device | cLMA | LT | I-gel | Combitube | p-value |
|---|---|---|---|---|---|
| Overall success rate (%) | 94.16 | 95.83 | 98.33 | 85.97 | p < 0.001a |
| Time for successful insertion in seconds (Mean ± SD) | 79.11 ± 9.53 | 70.16 ± 6.73 | 66.48 ± 7.77 | 107.19 ± 28.5 | p < 0.001b |
| First attempt success rate (%) | 49.16 | 75.83 | 76.66 | 11.40 | p < 0.001a |
| Number of attempts (median with range) | 2 (1–5) | 1 (1–5) | 1 (1–5) | 3 (1–5) | p = 0.000c |
| Oropharyngeal leak pressure in cms H2O (mean ± SD) | 31.40 ± 3.88 | 32.38 ± 3.35 | 23.37 ± 2.41 | 33.53 ± 2.56 | p < 0.05b |
| Earliest damage to SGA (durability) | After 30 uses | After 15 uses | Not damaged during study | After 75 uses |
ANOVA, analysis of variance; SGA, supraglottic airway; cLMA, classic laryngeal mask airway; LT, laryngeal tube.
Chi-square test.
ANOVA.
Kruskal-Wallis test.
Overall success rate was found to be statistically significant among the four groups. However, the significance was only between cLMA/LT/I-gel vs. Combitube (p < 0.001). When cLMA vs. LT or cLMA vs. I-gel or LT vs. I-gel were compared the overall success rate was not statistically significant (p = 0.550, 0.170, and 0.440), respectively.
Time for successful insertion was least for I-gel with the difference among the four groups being statistically significant (p < 0.001). The first attempt success rate was highest for I-gel followed by the LT, cLMA, and lastly Combitube. Difference between I-gel and LT was not significant (p = 0.870).
First attempt success rate for I-gel and LT was higher than cLMA (p < 0.0001 and p < 0.0001, respectively) or Combitube device (p < 0.001 and p < 0.0001, respectively). Difference was not significant between I-gel and LT.
Average number of attempts for successful insertion were least for I-gel and LT, and the difference was not statistically significant (p = 0.82) between them. The difference was significant when comparing I-gel vs. cLMA (p < 0.001)/Combitube (p < 0.001) or LT vs. cLMA (p < 0.001)/Combitube (p < 0.001). The difference was also significant comparing cLMA vs. Combitube (p < 0.001).
Oropharyngeal seal pressure was highest with Combitube and lowest for I-gel. The remaining devices cLMA and LT devices exhibited intermediate pressures. The difference of leak pressure among the groups was statistically significant (p < 0.05).
Ease of insertion recorded by the volunteers is depicted in Table 3. The difference was compared using median scores and found to be statistically significant (p value = 0.001). 74.16% volunteers rated I-gel as very easy, whereas 58.33% 12.50%, 0.08% rated LT, I-gel, and Combitube, respectively, very easy. Hence, I-gel was the easiest to insert (median = 1), LT second (median = 1), cLMA the third (median = 2), whereas the Combitube was the most difficult (median = 4).
Table 3.
Pairwise comparison between SGA device groups.
| Pairwise comparison between SGA device groups (p-values are given) | ||||||
|---|---|---|---|---|---|---|
| SGA devices compared | cLMA vs. LT | cLMA vs. I-gel | cLMA vs. Combitube | LT vs. I-gel | LT vs. Combitube | I-gel vs. Combitube |
| Overall success rate (%)a | 0.550 | 0.170 | 0.030 | 0.440 | <0.001 | <0.001 |
| Time for successful insertion in seconds (Mean ± SD)b | <0.01 | <0.01 | <0.01 | 0.067 | <0.01 | <0.01 |
| First attempt success rate (%)a | <0.001 | <0.001 | <0.001 | 0.870 | <0.001 | <0.001 |
| Number of attempts (median with range)c | 0.00072 | 0.00044 | <0.00001 | 0.89717 | <0.00001 | <0.00001 |
| Oropharyngeal leak pressure in cms H2O (mean ± SD)b | 0.030 | <0.001 | <0.001 | <0.001 | 0.004 | <0.001 |
ANOVA, analysis of variance; SGA, supraglottic airway; cLMA, classic laryngeal mask airway; LT, laryngeal tube.
Chi-square test.
ANOVA.
Kruskal-Wallis test.
Complications encountered during the study are shown in Table 4. The commonest was airway trauma seen maximally with the Combitube. Nausea and vomiting was maximal with LT, whereas in other groups, it was negligible. All SGA devices had equal incidence of bronchospasm. Combitube had a high incidence of dental injuries, but analysis revealed that these patients had preexisting loose teeth.
Table 4.
Ease of insertion score.
| Ease of insertion score (% of participants) | |||||
|---|---|---|---|---|---|
| Ease of insertion score | 1 | 2 | 3 | 4 | 5 |
| cLMA | 12.50 | 43.33 | 30.83 | 8.33 | 5.00 |
| LT | 58.33 | 24.17 | 8.33 | 4.17 | 4.17 |
| I-gel | 74.16 | 13.33 | 6.66 | 4.16 | 1.66 |
| Combitube | 0.08 | 13.15 | 32.46 | 32.46 | 21.92 |
cLMA, classic laryngeal mask airway; LT, laryngeal tube.
The Combitube exhibited good durability lasting more than 75 usages before rupture. Both the LT and cLMA exhibited poor durability suffering damage within an average 15 uses and 30 uses, respectively. Though the manufacturer has mentioned 50 uses, LT exhibited maximum cuff rupture which was usually during extraction of the device. I-gel did not suffer any damage and was reusable even after 120 uses. However the stem of the device became successively stiffer with prolonged use.
Interoperator variability analysis: All volunteer candidates were allowed to insert and assess the four SGA devices equal number of times. No interoperator variability was assumed because all 58 were trained by the author. However, operator-wise analysis of the data was carried out for limited number of variables and is presented in Table 5. There was no significant difference among the operators for the time for successful insertion or the number of attempts taken except in the cLMA group, where the NA group showed a significantly lesser time than Nursing Officers (NO) or ORAs. This was surprising as the category of NAs are exposed to airway management much lesser than the NO or the ORA (Table 6).
Table 5.
Complications.
| Complication |
Blood staining | Nausea/vomiting | Bronchospasm | Dental injuries | Rupture of cuff (No.) | Total |
|---|---|---|---|---|---|---|
| SGA device | ||||||
| cLMA | 22 (18.33%) | 1 (0.83%) | 6 (0.5%) | 0 | 2 (1.66) | 31 (25.83%) |
| LT | 15 (12.5%) | 6 (5.0%) | 8 (0.67%) | 0 | 5 (4.16%) | 34 (28.33%) |
| I-gel | 13 (10.83%) | 1 (0.83%) | 6 (0.5%) | 0 | 0 | 20 (16.67%) |
| Combitube | 70 (61.40%) | 1 (0.87%) | 9 (0.79%) | 5 (4.39%) | 2 (1.75%) | 87 (76.31%) |
| Total | 120 (25.32%) | 9 (1.90%) | 29 (6.12%) | 5 (1.05%) | 9 (1.90%) | 172 (36.29%) |
SGA, supraglottic airway; cLMA, classic laryngeal mask airway; LT, laryngeal tube.
Table 6.
Interoperator variability analysis.
| Paramedic Gp | cLMA | LT | I-gel | Combitube |
|---|---|---|---|---|
| Time for insertion (Mean +SD) | ||||
| NO | 81.37 + 9.35 | 70.14 + 6.27 | 67.27 + 5.98 | 113.00 + 16.17 |
| ORA | 81.58 + 9.66 | 71.23 + 6.93 | 67.6 + 8.93 | 110.87 + 18.43 |
| NA | 74.81 + 8.13 | 69.18 + 7.39 | 63.96 + 7.22 | 101.28 + 18.63 |
| p-value | 0.003 | 0.44 | 0.122 | 0.06 |
| Average no of attempts for insertion (Mean + SD) | ||||
| NO | 2.1 + 1.42 | 1.23 + 0.82 | 1.03 + 0.18 | 3.25 + 1.42 |
| ORA | 2.02 + 1.09 | 1.46 + 0.91 | 1.35 + 0.87 | 3.13 + 1.15 |
| NA | 1.61 + 0.88 | 1.25 + 0.44 | 1.11 + 0.42 | 2.5 + 0.92 |
| p-value | 0.2 | 0.34 | 0.07 | 0.12 |
cLMA, classic laryngeal mask airway; LT, laryngeal tube; ORA, operation-room assistants; NA, nursing assistants.
Discussion
Despite numerous studies on SGA devices as alternatives to ETI, the optimal technique for out of hospital cardiac arrest (OHCA)4 remains unclear. Previous studies demonstrated improved outcomes when paramedics had been trained for early use of SGA devices.5 The Fouche meta-analysis compared Basic Airway Intervention and Advanced Airway Intervention by out of hospital paramedics in OHCA patients and found decreased survival (long-term and short-term) as the primary outcome. However, user-dependent factors were not considered and the meta-analysis was limited by paucity of data from prospective clinical trials.6
The study took into account the fact that paramedical staff is usually the first responders. The focus of this study has been comparison of novice user dependent factors between four SGA devices. The anesthetized patient created a well-controlled simulated airway management scenario where novice paramedics inserted the SGA devices in real patients. The beneficiaries in armed forces from this study would be Medical Officers and paramedical staff, including the Battle Field Nursing Assistants who are vital to Combat Casualty Care.
In our study, the overall success rate was highest for I-gel but only significantly different from Combitube. Success rates in other studies for cLMA,7,8 LT,9,10,11,12 I-gel13,14,15, and Combitube16,17,18 were comparable to our study. The shortest time for insertion was with I-gel and LT, whereas the longest time was seen with the Combitube. These values are comparable to the study carried out by Henlin et al.,3 but much higher than those quoted in other studies.7,8,14 Analysis revealed this difference emerged because of the definition of insertion time. The insertion time defined in our study more closely matches the time a paramedic would take in real-life OHCA situations. In most of the other studies, the definition included the time from the start of device insertion till achieving chest rise/EtCO2 trace. Though clinically a large difference was appreciable only between the cLMA/LT/I-gel vs. Combitube (>40s), the statistically significant difference between cLMA vs. LT of 9s, cLMA vs. I-gel of 13.3s and LT vs. I-gel of 4.3s assumes significance considering the 2015 AHA guidelines for resuscitation, which emphasize no interruption to chest compressions exceeding 10 s.19,20 Subjectively, the volunteers reported the easiest insertion with I-gel which was comparable to the study by Larkin et al.14 The LT was the second easiest SGA device to insert which is at a variance with Henlin study3 who found (S)LMA the easiest and the LTS(D) most difficult. In our study, the volunteers ranked cLMA third and Combitube fourth. The first-attempt success rate was also highest for the I-gel and LT, which is comparable to the study by Larkin et al.14 The cLMA and Combitube had significantly lesser first attempt success rates compared with the LT annd I-gel.
Literature did not reveal the use of the parameter of “average number of attempts” for successful insertion nor was the criterion of an attempt at insertion clearly defined. The average number of attempts is a parameter which closely correlates to both the time for successful insertion and the ease of insertion. Likewise, durability of the devices has not been addressed in any study but is of vital importance to the armed forces. Unless a device has high durability, it is unlikely to survive routine use by novice operators with an elementary training and will be difficult to replace in remote locations. We recorded oropharyngeal seal pressures similar to other studies3, 21. The limitation of this study was its conduct in a simulated environment and the need for its validation in real life scenarios such as casualty management. However, conducting studies on these patient populations has obvious limitations.
Conclusions
I-gel exhibited a combination of highest overall success rate, highest first attempt success rate, shortest insertion time, least complication rate, and best durability and is also (though not included as part of the study) the lowest in cost (Rs. 1500–2500); however, it also had the lowest oropharyngeal seal pressure. The LT had a comparable overall success rate, first attempt success rate, but high incidence of nausea and vomiting, longer insertion time, and very poor durability in addition to the highest cost (though not part of the study) of about Rs 8000–20,000/-. cLMA and Combitube did not exhibit satisfactory user dependent factors. Thus, for the armed forces, I-gel can be recommended as a reliable and effective rescue device for airway maintenance by paramedical staff as has been validated during simulated emergency scenario in this study.
Disclosure of competing interest
The authors have none to declare.
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