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Waveform capnography: an alternative to physician gestalt in determining optimal intubating conditions after administration of paralytic agents
  1. Anthony Scoccimarro,
  2. Jason R West,
  3. Marc Kanter,
  4. Nicholas D Caputo
  1. Department of Emergency Medicine, Lincoln Medical Center, New York City, New York, USA
  1. Correspondence to Dr Nicholas D Caputo, Department of Emergency Medicine, Lincoln Medical Center, New York NY 10451, USA; ncaputo.md{at}gmail.com

Abstract

Purpose We sought to evaluate the utility of waveform capnography (WC) in detecting paralysis, by using apnoea as a surrogate determinant, as compared with clinical gestalt during rapid sequence intubation. Additionally, we sought to determine if this improves the time to intubation and first pass success rates through more consistent and expedient means of detecting optimal intubating conditions (ie, paralysis).

Methods A prospective observational cohort study of consecutively enrolled patients was conducted from April to June 2016 at an academic, urban, level 1 trauma centre in New York City. Nasal cannula WC was used to determine the presence of apnoea as a surrogate measure of paralysis versus physician gestalt (ie, blink test, mandible relaxation, and so on).

Results One hundred patients were enrolled (50 in the WC group and 50 in the gestalt group). There were higher proportions of failure to determine optimal intubating conditions (ie, paralysis) in the gestalt group (32%, n=16) versus the WC group (6%, n=3), absolute difference 26, 95% CI 10 to 40. Time to intubation was longer in the gestalt group versus the WC group (136 seconds vs 116 seconds, absolute difference 20 seconds 95% CI 14 to 26). First pass success rates were higher in the WC group verses the gestalt group (92%, 95% CI 85 to 97 vs 88%, 95% CI 88 to 95, absolute difference 4%, 95% CI 1 to 8).

Conclusion These preliminary results demonstrate WC may be a useful objective measure to determine the presence of paralysis and optimal in tubating conditions in RSI.

  • anaesthesia - RSI
  • airway
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Introduction

Paralysis is the hallmark of rapid sequence intubation (RSI). RSI has been the preferred method among emergency providers due to the advantage of neuromuscular blockade in providing optimal intubating conditions and minimising the risk of complications.1 Despite the common and critical nature of this procedure, there is a paucity of data regarding the objective determination of the presence of paralysis. There are some recommendations to wait for 45–60 s before attempting laryngoscopy depending on the agent administered or other non-validated means such as the eyelash-blink test.2 The presence of apnoea may be one of the earliest signs of muscle paralysis if it can be objectively measured.

Waveform capnography (WC) has been validated as an objective means for monitoring respiratory depression and apnoea during procedural sedation. We sought to evaluate the utility of WC in detecting paralysis, by using apnoea as a surrogate determinant, as compared with clinical gestalt during RSI. Additionally, we sought to determine if this improves the time to intubation and first pass success (FPS) rates through more consistent and expedient means of detecting optimal intubating conditions (ie, paralysis).

Methods

A pilot prospective observational cohort study of consecutively enrolled patients was conducted from April to June 2016 at an academic, urban, level 1 trauma centre in New York City. Patients were enrolled in a consecutive and alternating fashion to each arm of the study (ie, one to WC then one to gestalt). The study was done at a hospital with an emergency medicine (EM) residency training programme. All intubations were supervised by attending EM physicians and over 80% were done by credentialed senior residents (ie, postgraduate year (PGY)-3s and PGY-4s). All patients requiring endotracheal intubation were included. Exclusion criteria were patients in cardiac, traumatic arrest or where awake intubation was the procedure performed. As there are no prior data published on the utility of WC to determine paralysis by means of apnoea in RSI, we performed a pilot study utilising a convenience sample of 100 patients (50 waveform, 50 gestalt).

In the gestalt group, paralysis was determined by physician judgement utilising measures such as blink test, muscle fasciculation and mandible relaxation. The medications used for paralysis were rocuronium (at a minimum dose of at least 0.6 mg/kg, ~50 mg) or succinylcholine (also at a minimum dose of at least 0.6 mg/kg, ~50 mg). Physicians were allowed to determine the dosing based on the individual patient, but were not to give doses of less than 0.6 mg/kg for either rocuronium or succinylcholine.

For the WC group, apnoea (flat line on the capnography monitor) was used as a surrogate marker for the presence of paralysis. Flat line was determined present by the supervising physician when present for at least 10 s. A need to wait longer or redose neuromuscular blocker (NMB) after initial attempt at laryngoscopy was considered failure to detect paralysis. Time to intubation was defined as from administration of NMB to confirmation of tube placement by EtCO2. This was measured by an observer using our timed ED intubation checklist and is defined as time of blade insertion to confirmation by WC. FPS rate and first pass success rates with hypoxia (FPS-H) were reported as rates.

We defined hypoxia as SpO2<90% at time of endotracheal tube confirmation by WC.

Ninety-five per cent CIs and p values are reported; descriptive statistics and comparative statistics using Student’s t-tests for outcomes. All statistical analyses were performed using the XLSTAT (Addinsoft, New York, NY) statistical software package. The study was approved by the institutional review board with waiver of consent, as this was considered minimal risk as standard of care treatment was not withheld from any patient.

WC is already used to determine the presence of apnoea in other areas of medicine (eg, procedural sedation and analgesia). The study design generally conformed to the recommendations of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) statement.3

Results

One hundred patients were enrolled. There was no difference in baseline demographics (table 1). There were significantly more failures to determine optimal intubating conditions in the gestalt group versus the waveform group (32%, 95% CI 20 to 45 vs 6%, 95% CI 2 to 16, respectively, absolute difference 26, 95% CI 10 to 40). Table 2 demonstrates the main outcomes between the two groups. Time to intubation was longer in the gestalt group versus the WC group (136 s vs 116 s, absolute difference 20 s, 95% CI 14 to 26). On average, those patients where gestalt failed to detect paralysis added 35 s to the total time. The absolute difference between the WC group and the gestalt group for FPS rate was 4% (95% CI 1 to 8). The absolute difference between the gestalt group and the WC group for lowest SpO2 was 3 (95% CI 0 to 5). The absolute difference between the gestalt group and the WC group for FPS-H was 16% (95% CI 2 to 29).

Table 1

Patient demographics

Table 2

Difference in outcomes between the two groups

Discussion

WC has long been used by anaesthesiologists. Since 1998, the monitoring of expired carbon dioxide has been a mandatory component of the standards of basic anaesthetic monitoring.4 Similarly, there are guidelines instituted by the American College of Emergency Physicians recommending the use of WC as an adjunct to pulse oximetry during procedural sedation in order to detect respiratory depression/apnoea at its earliest point to prevent adverse events.5 There have been several studies that have demonstrated 100% sensitivity of WC in detecting respiratory depression/apnoea during procedural sedation when compared with traditional means including pulse oximetry and physician gestalt.6 7 WC has been reported to recognise respiratory depression/apnoea 18 times more than standard means during procedural sedation.8

Our study applied this principle of using WC to detect respiratory depression/apnoea during procedural sedation to RSI in order assess for the same. The difference, however, is that in procedural sedation WC is used to prevent adverse events from respiratory depression/apnoea whereas in RSI, we propose, it can be used objectively to detect it in order to determine the presence of optimal intubation conditions at its earliest point. This is evident in that there were much fewer failures in recognising paralysis as defined by apnoea when using WC compared with a 33% failure rate using gestalt alone. The failure rate of the gestalt group was also associated with a delay in tube placement and confirmation (gestalt, when failing to detect paralysis, added 35 s to the total time to intubation). This may be a clinically significant amount of time as the critically ill may desaturate to <90% in a few as 23 s.9 In addition, the prolonged time to intubation is also compounded by the perceptual disturbance of the operator to recognise hypoxic events and also the passage of time itself.10 Interestingly, we found that patients in the gestalt group had lower oxygen saturation rates with a trend towards a lower rate of FPS when using gestalt compared with WC as well as higher rate of FPS-H.

There were several limitations in our study. This was a pilot study performed at a single centre. We also did not perform an analysis to determine if there was a difference in the neuromuscular blockade between the two groups, which also may have contributed to the failure rate by increasing the rate of redosing. Finally, the study was not powered to analyse the effect of using WC on patient-oriented outcomes such as the rate of complications and hypoxic events.

Conclusion

WC may be useful as an objective means to determine paralysis in patients requiring endotracheal intubation and may reduce premature attempts at laryngoscopy requiring further waiting time or redosing of NMB. A larger study randomised and blinded in design is warranted in order to test these preliminary findings.

References

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Footnotes

  • Contributors AS, JW, MK and NDC all contributed to the study design,patient enrollment and data collection. NDC and JW were responsible for data analysis and statistics. AS, JW, MK and NDC all contributed to the initial drafting and subsequent revisions of the manuscript.

  • Competing interests None declared.

  • Patient consent Detail has been removed from this case description/these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.

  • Ethics approval Lincoln IRB.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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