Study Design

Reduced Quality Factors

0 = no serious, - = serious,

- - = very serious

Positive Quality Factors

0 = none, + = one, ++ = multiple

Dichotomous Outcome Summary

Non-Dichotomous Outcome Summary

Brief description

Overall Quality

High, moderate, low,
very low, none

No of studies

Study Type

RoB

Indirectness

Imprecision

Inconsistency

Large Effect

Dose-Response

Confounder

# Intervention with Outcome

# Control with Outcome

RR (95% CI)

Outcome: Survival to discharge

1

OB

- -

- -

-

0

0

0

0

Very low

Outcome: ROSC

1

OB

- -

- -

0

0

0

0

0

Very low

Outcome: Correct intubation – species, poor NPV (imprecision?)

10

OB

0

-

-

0

0

0

0

Very low

1

EXP

0

-

-

0

0

0

0

Very low

Outcome: Time to start CPR, Complications - none

0

0

0

0

0

0

0

0

0

None

Introduction

Timely airway management is essential to maximize successful recovery efforts for patients experiencing CPA. Confirmation of endotracheal intubation can allow the rescuer to quickly support ventilation and oxygenation during CPR. There are several studies in which high EtCO2 concentrations have a high sensitivity and specificity to confirm endotracheal intubation; however, many investigators warn that low perfusion states like those encountered in CPA may result in lower sensitivity of the technique, and that the clinician may need other methods to confirm correct intubation.1–7

Consensus on science

Outcome 1: Survival to discharge

One observational study in people was identified (very low quality of evidence, downgraded for very serious risk of bias, very serious indirectness, and serious imprecision) that addresses the PICO question. This registry study of 176,054 people experiencing IHCA found an association between documentation of EtCO2 or esophageal detection device (EDD) to confirm ETT placement and survival to discharge (adjusted OR 1.093, 95% CI 1.033, 1.157) when compared to no documented method to determine correct ETT placement. Survival to discharge was 18.2% (7800 / 42,955) for patients with correct intubation confirmed by capnometer or EDD compared to 17.2% (3339 / 19,464) when confirmation was done only by auscultation and compared to 17.3% (5674 / 32,712) for the pool of patients that either did not have any documentation of correct intubation or when confirmation was done by auscultation alone. No statistical comparison was made between capnometry and confirmation of intubation via other means.8

Outcome 2: ROSC

One observational study in people was identified (very low quality of evidence, downgraded for very serious risk of bias, very serious indirectness, and serious imprecision) that addresses the PICO question. This registry study of 176,054 people experiencing IHCA found an association between documentation of EtCO2 or EDD to confirm ETT placement and ROSC (adjusted OR 1.229, 95% CI 1.179, 1.282) when compared to no documented method to determine correct ETT placement. ROSC was achieved in 53.6% (23,061 / 43,034) of patients with correct intubation confirmed by capnometer or EDD compared to 48.7% (9489 / 19,480) when confirmation was done only by auscultation and compared to 48.9% (16,002 / 32,743) for the pool of patients that either did not have any documentation of correct intubation or when confirmation was done by auscultation alone. No comparison was made between capnometry and confirmation of intubation via other means.8

Outcome 3: Correct intubation

For the critical outcome of correct intubation, there were 10 observational studies in people (very low quality of evidence, downgraded for serious indirectness and serious imprecision)1–4,7,9–13 and 1 experimental study in dogs (very low quality of evidence, downgraded for serious indirectness and serious imprecision)14 that address the PICO question. All included studies were in pulseless people and animals, because they were considered adequately direct to our population of interest (dogs and cats in CPA). The largest study most directly applicable to the PICO question12 included 246 adults with OHCA intubated in the field; this study found that capnometry was 100% specific (if CO2 was detected, the tube was in the trachea rather than the esophagus) and 88% sensitive (occasionally no CO2 was detected even though the tube was in the trachea) for tracheal intubation. The positive predictive value of auscultation (99%) and capnometry (100%) were similar to confirm proper ETT placement (if breath sounds were heard or CO2 was detected, respectively, these were highly predictive of tracheal placement). However, the negative predictive value of auscultation (100%; the absence of breath sounds confirmed improper tube placement) was significantly better than that of capnometry (13%; that the absence of CO2 reflected improper tube placement; P < 0.05).12 Takeda et al. (2003) showed that in people in CPA, lung auscultation and EtCO2 measurement had sensitivities of 92.6% and 67.9% (P < 0.0001) for tracheal intubation, respectively.[ 1056] The negative predictive value of auscultation in this study (60%; the absence of breath sounds accurately identified improper tube placement 60% of the time) was statistically equivalent to the negative predictive value of ETCO2 measurement (25.7%; the absence of CO2 correctly identified improper tube placement).13 The remaining 8 observational studies in people in CPA had similar results: that the confirmation of CO2 presence is uniformly consistent with tracheal ETT placement while the absence of detection of CO2 may indicate either tracheal or extra-tracheal intubation; these other studies were either small or did not consistently compare to other methods of confirmation.1–4,7,9–11 In the single experimental study in dogs in CPA, tubes were pre-placed in either the esophagus or the trachea prior to fibrillation and placement confirmed by fiberoptic scope. While the ETCO2 was significantly higher in the correctly intubated dogs during CPR (P = 0.001), the ETCO2 from esophageal tubes was not zero (median, 3 mmHg, range 2 to 11

mmHg).14

Outcome 4: Time to start CPR

No studies were identified that addressed the outcome of Time to start CPR for this PICO question.

Though there is human literature to support that colorimetric CO2 detection devices may allow for earlier confirmation of endotracheal intubation over capnography or lung auscultation.5,15,16

Outcome 5: Complications

No studies were identified that addressed the impact of ETCO2 measurement at time of intubation on complications.

Treatment recommendation

In dogs and cats in CPA, detection of ETCO2 using a waveform capnograph attached to the breathing circuit is adequate to confirm proper ETT placement if a waveform is present and CO2 is consistently detected.(strong recommendation, very low quality of evidence)

In dogs and cats in CPA with a CO2 detection device in place, an ETCO2 ≥ 12 mmHg likely indicates proper ETT placement, while an ETCO2 < 12 mmHg should lead the rescuer to confirm tracheal intubation by other means.(strong recommendation, very low quality of evidence)

In intubated dogs and cats undergoing CPR that are instrumented with any CO2 detection device, when ETCO2 is 0 or very low (e.g., < 5 mmHg) despite high quality chest compressions, we recommend confirmation of tracheal intubation by other means (e.g., direct visualization of the tube passing through the arytenoid cartilages, lung auscultation during the pause between CC cycles) and reintubation if indicated.(strong recommendation, very low quality of evidence)

Justification of treatment recommendation

All available evidence shows that higher ETCO2 concentration at intubation likely predicts correct tracheal intubation; however, in poor perfusion states such as CPA, low ETCO2 concentrations do not rule out tracheal intubation and may instead indicate the need for improved circulation (e.g., improved chest compression technique). Other methods were more accurate to confirm esophageal intubation in human studies, such as lung auscultation (which likely requires a pause in CCs), confirming chest wall excursions during ventilation (challenging to assess during CC), and laryngoscopy (which is often unavailable). Considering the ease with which the larynx can be visualized in most dogs and cats, the committee recommends confirmation of ETT placement in the case of low ETCO2 by direct visualization when possible – this can be done during CCs with adequate staff. When visualization is not possible, the evidence suggests that auscultation of breath sounds during a scheduled 2-minute cycle pause may be more reliable than absence of CO2 at detecting correct tube location.

Knowledge gaps

There is no clinical evidence in dogs or cats to evaluate successful endotracheal intubation using ETCO2 with or without other clinical verification methods.

It is unknown at this time whether use of colorimetric devices in dogs and cats will allow faster or more accurate confirmation of tube placement within the trachea, as there are no studies published on the use of colorimetric CO2 detection devices in dogs and cats experiencing CPA.

Experimental data in dogs with cardiac arrest suggest a possible benefit of capnography over capnometry to confirm ETT placement, though further study is necessary.

This search did not identify any laboratory or clinical studies evaluating the use of esophageal detection devices, which may be of particular interest in brachycephalic dogs and other animals in which direct visualization of the glottis is impossible.