Brazilian Journal of Pulmonology

ISSN (on-line): 1806-3756 | ISSN (printed): 1806-3713

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Current Issue: 2018 - Volume 44 - Number 6 (November/December)

LETTERS TO THE EDITOR

Near-fatal pulmonary embolism: capnographic perspective

Embolia pulmonar quase fatal: perspectiva capnográfica

 

Marcos Mello Moreira1; 2; a; Luiz Claudio Martins3; b; Konradin Metze4; c; Marcus Vinicius Pereira2; d; Ilma Aparecida Paschoal1; e

 

1. Disciplina de Pneumologia, Departamento de Clínica Médica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas - Unicamp - Campinas (SP) Brasil.
2. Programa de Pós-Graduação em Ciências da Cirurgia, Faculdade de Ciências Médicas, Universidade Estadual de Campinas - Unicamp - Campinas (SP) Brasil.
3. Disciplina de Medicina Interna e Semiologia, Departamento de Clínica Médica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas - Unicamp
- Campinas (SP) Brasil.
4. Departamento de Patologia Clínica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas - Unicamp - Campinas (SP) Brasil.
a. http://orcid.org/0000-0002-2148-5479; b. http://orcid.org/00000-0002-2920-2162; c. http://orcid.org/0000-0003-0742-8846;
d. http://orcid.org/0000-0002-7195-0404; e. http://orcid.org/0000-0002-0539-4243


 

 

 

DEAR EDITOR,

Massive pulmonary embolism (MPE) is a condition that causes sudden changes to the cardiopulmonary system(1-5) and is associated with high morbidity and mortality. Methods that detect those changes in real time, especially noninvasive ones, can be very useful. They can also indicate whether the MPE is likely to improve or not.

To address the clinical scenario of MPE, one may make use of noninvasive devices with software that monitors respiratory mechanics and volumetric capnography (VCap) data, online and offline, providing information that may indicate ventilation-perfusion mismatch, in MPE or in other diseases.

The respiratory profile monitor (CO2SMO PLUS DX-8100; Respironics, Murrysville, PA, USA) provides and records variables such as end-tidal partial pressure of CO2 (PetCO2), CO2 output (VCO2), the phase II slope of the capnogram (SII), the phase III slope of the capnogram (SIII)―also known as the alveolar plateau, respiratory rate (RR), inspiratory tidal volume (VTi), expiratory tidal volume (VTe), inspiratory time, expiratory time, alveolar minute volume (MValv), peak inspiratory flow, and peak expiratory flow.

This was an observational study of pigs induced to MPE through the injection of autologous clots, during spontaneous ventilation (FiO2 = 0.21). Our aim was to record, observe, and analyze the behavior of respiratory mechanics parameters, especially VCap data.

We evaluated numerical variables (Table 1) and curves (Figures 1A, 1B, and 1C).









This study was conducted in conjunction with the work published by Pereira et al.,(3) which has been approved by the Ethics Committee on the Use of Animals of the State University at Campinas Institute of Biology (Reference no. 2298-1).

At baseline (T0, before the clots were injected), all of the variables were measured. The clots were injected in increments of 5 mL until a borderline (i.e., "near-fatal") mean pulmonary artery pressure (the primary endpoint) was reached. The mean quantity of clots injected was 24.7 ± 4.3 mL, and the mean clot injection time was 45 min. As can be seen in Table 1, gas exchange (PaCO2) and hemodynamic changes (cardiac output) were evaluated at three different time points: T1 (the endpoint), T2 (30 min after T1), and T3 (1 h after T1).

For the comparison between hemodynamic, gas exchange, and respiratory variables at T0, T1, T2, and T3, we used repeated-measures ANOVA (Winstat, version 3.1). Values of p < 0.05 were considered statistically significant.

PetCO2, MValv, and the alveolar dead space volume presented significant differences among the various time points evaluated, whereas RR did not. It is well known that MPE leads to an increase in RR and in lung volumes. The increase in RR and in lung volumes can be evidenced by a significant increase in MValv, which, in turn, leads to alveolar washout and, as a consequence, to a significant decrease in PetCO2. Another factor that contributed to the reduction in PetCO2 was a significant decrease in pulmonary perfusion (resulting from a decrease in cardiac output). There was a significant increase in the volume of the alveolar dead space, which does not take part in gas exchange. Following the rationale of this variable behavior, the volumes of VCap phases I and II were obtained in mL and per respiratory cycle. Those volumes increased significantly over the study period.

Other variables were provided by VCap or associated with other variables: VCO2; SII; SIII; VCO2/VTe; alveolar VCO2/VT; SII/exhaled CO2 partial pressure (SII/PECO2); SIII/PECO2; SIII/PetCO2; and SIII/VTe. The expected decrease in VCO2 at T1 (p < 0.001 vs. T0) can be attributed to the increase in MValv, as well as to a significant reduction in pulmonary blood flow (resulting from a decrease in cardiac output). There were also significant reductions in other metabolic variables, such as VCO2/VTe, and alveolar VCO2/VT.

With similar pathophysiologies, SII and SIII variables also presented significant variations (p < 0.0001). The SII represents removal of CO2 from the alveoli, which are the most distal elements of the small airways. The SIII represents the elimination of CO2 from most alveoli and, in normal organisms, its shape is similar to a plateau, with a slight upward slope. Higher SIII/VTe and SIII/PetCO2 values suggest structural damage in the peripheral and distal part of the lungs, which promotes this heterogeneous distribution of ventilation.(5,6) The same principle applies to the significant drop in the normalization of SII/PECO2, SIII/PECO2, SIII/PetCO2, and SIII/VTe (p < 0.0001 for all). Negative SIII values seem to be associated with vascular damage,(2,5) whereas an excessive increase in these values may be associated with airway damage (such as that occurring in bronchiectasis, cystic fibrosis, and COPD).(7,8)

It was necessary to normalize VCO2/VTe, SII/PECO2, SIII/PECO2, SIII/PetCO2, and SIII/VTe, in order to allow them to be compared to the equivalent CO2 excretion rates (PECO2, PetCO2, and VTe, respectively).(9)
Other variables that are not usually described in the literature are intercept Y2 and intercept Y3 (both in mmHg), which indicate an increase or a decrease in the caliber of the conducting airways. These variables refer to the intersection of SII and SIII with the y axis of the VCap curve and represent a mathematical increase of the inclination of the slopes. Scheffzek et al.(10) were able to verify that. In the present study, there was a significant variation in those two variables (p < 0.0001 for both).
In conclusion, recording, observing, and analyzing the behavior of the parameters of respiratory mechanics, especially VCap, made it possible to identify MPE. When carefully applied and analyzed, our results can make a major contribution to decreasing morbidity and mortality in patients presenting with a clinical profile suggestive of MPE.

Further studies of MPE, either experimental or clinical, are still needed. Such studies could broaden our knowledge of the disease and of its implications for the cardiopulmonary system.

REFERENCES

1. Ferreira JH, Terzi RG, Paschoal IA, Silva WA, Moraes AC, Moreira MM. Mechanisms underlying gas exchange alterations in an experimental model of pulmonary embolism. Braz J Med Biol Res. 2006,39(9):1197-204.
2. Moreira MM, Terzi RGG, Paschoal IA, Martins lC, Oliveira EP, Falcão Al. Thrombolysis in massive pulmonary embolism based on the volumetric capnography. Arq Bras Cardiol. 2010;95:e97-e99. https://doi.org/10.1590/S0066-782X2010001400025
3. Pereira DJ, Moreira MM, Paschoal IA, Martins lC, Metze K, Moreno Junior H. Near-fatal pulmonary embolism in an experimental model: hemodynamic, gasometric and capnographic variables. Rev Bras Cir Cardiovasc. 2011;26(3):462-8. https://doi.org/10.5935/1678-9741.20110023
4. Moreira MM, Terzi RG, Pereira MC, Grangeia Tde A, Paschoal IA. Volumetric capnography as a noninvasive diagnostic procedure in acute pulmonary thromboembolism. J Bras Pneumol. 2008;34(5):328-32. https://doi.org/10.1590/S1806-37132008000500013
5. Schreiner MS, leksell lG, Gobran SR, Hoffman EA, Scherer PW, Neufeld GR. Microemboli reduce phase III slopes of CO2 and invert phase III slopes of infused SF6. Respir Physiol. 1993;91(2-3):137-54. https://doi.org/10.1016/0034-5687(93)90095-R
6. Schwardt JD, Gobran SR, Neufeld GR, Aukburg SJ, Scherer PW. Sensitivity of CO2 washout to changes in acinar structure in a single-path model of lung airways. Ann Biomed Eng. 1991;19(6):679-97. https://doi.org/10.1007/BF02368076
7. Veronez l, Pereira MC, da Silva SM, Barcaui lA, De Capitani EM, Moreira MM, et al. Volumetric capnography for the evaluation of chronic airways diseases. Int J Chron Obstruct Pulmon Dis. 2014;9:983-9. https://doi.org/10.2147/COPD.S62886
8. da Silva SM, Paschoal IA, De Capitani EM, Moreira MM, Palhares lC, Pereira MC. COPD phenotypes on computed tomography and its correlation with selected lung function variables in severe patients. Int J Chron Obstruct Pulmon Dis. 2016;11:503-13. https://doi.org/10.2147/COPD.S90638
9. Scherer PW, Gobran S, Aukburg SJ, Baumgardner JE, Bartkowski R, Neufeld GR. Numerical and experimental study of steady-state CO2 and inert gas washout. J Appl Physiol (1985). 1988;64(3):1022-9. https://doi.org/10.1152/jappl.1988.64.3.1022
10. Scheffzek S, Mosing M, Hirt R, Iff I, Moens Y. Volumetric capnography curves as lung function test to confirm bronchoconstriction after carbachol challenge in sedated dogs. Res Vet Sci. 2012;93(3):1418-25. https://doi.org/10.1016/j.rvsc.2012.04.010

 

 


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