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J Vessel Circ 2020, 1(1): 1-7 |
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Nadi F, Azizi-Fini I, Izadi-Avanji F S. Impact of Continuous Positive Airway Pressure (CPAP) Masks on Arterial Blood Gas Parameters and Pulmonary Side Effects after Open-heart Surgery. J Vessel Circ 2020; 1 (1) :1-7
URL: http://jvessels.muq.ac.ir/article-1-30-en.html
URL: http://jvessels.muq.ac.ir/article-1-30-en.html
1- Faculty of Nursing and Midwifery, Kashan University of Medical Sciences, دانشکده پرستاری ومامایی
2- Center of Trauma Nursing Research, Kashan University of Medical science, دانشکده پرستاری ومامایی
2- Center of Trauma Nursing Research, Kashan University of Medical science, دانشکده پرستاری ومامایی
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Table 1. Demographic and clinical variables in the two groups of control and intervention
* Independent t-test
Table 2. Frequency of demographic variables in the two groups
n (%)
*Independent t-test
**Chi-square test
Table 3. Incidence frequency of pulmonary side effects in the intervention and control groups
* Fisher’s exact test
Table 4. Mean and standard deviation of PO2, PCO2, O2 Sat, and RR in the intervention and control groups before and 10 min after each time of intervention
*Independent t-test
The results of Fisher’s exact test revealed that the two groups were significantly different in terms of atelectasis (P=0.04) and pleural effusion (P=0.01) and the incidence of these problems was lower in the intervention group, compared to the control group (Table 3). Moreover, the results of the independent t-test showed that there was a significant difference between the two groups regarding the means of PO2, PCO2, O2 Sat, and RR after each time of intervention (P<0.05). It was found that arterial O2 Sat and PO2 augmented after each time of intervention, while arterial PCO2 and RR diminished after each intervention time (Table 4).
Discussion
The present study aimed to evaluate the impact of CPAP mask on the incidence of pulmonary side effects in patients after heart surgery. Our results revealed that using a CPAP mask led to a decreased incidence of atelectasis after open-heart surgery. Some studies reported the incidence of atelectasis as 6-42% (21) and it was found as 47.2% and 22.2% in the control and test groups of this study, respectively.
Al. Mutairi et al. (2013) carried out a clinical trial aimed to investigate the influence of the early application of CPAP mask on the treatment or prevention from atelectasis following coronary artery bypass grafting. They demonstrated that the CPAP group had better results in terms of treating and preventing atelectasis, compared to the motivational spirometry group (17).
The results of other studies showed that CPAP mask can be effective in preventing atelectasis after surgery (21-23). It could be claimed that heart surgery results in reduced lung volumes, alveolar collapse, and the collapse of some parts of the lungs as atelectasis and diminished oxygenation. Consequently, the generation of continuous positive pressure in the airways and alveoli as the base of the function mechanism of CPAP masks (1) causes the alveoli to widen due to the positive pressure and the atelectasis is resolved.
Moreover, the literature indicates that improved oxygenation using CPAP mask results from the resolution of atelectasis in patients following heart surgery (23, 2). Pasquina et al. (2004) completed an investigation on 155 patients in the heart surgery ICU to compare non-invasive pressure support ventilation (NIPSV) and CPAP in terms of atelectasis treatment.
The mentioned authors concluded that CPAP was less influential than NIPSV in treating atelectasis (22). In terms of the CPAP mask, both the latter and present studies had similar findings. However, the impact of the CPAP mask in the mentioned investigation was less remarkable, in comparison with NIPSV.
Our findings revealed a significant difference in the incidence of pleural effusion between the test and control groups and the incidence rate was lower among the patients of the control group. Results of the study completed by Oliveira et al. demonstrated that CPAP mask usage led to the diminished pleural effusion in tuberculosis patients (24). Furthermore, Marti et al. reported that CPAP imposed a positive effect in individuals with heart failure due to pleural effusion (16).
Application of CPAP mask elevates the intrathoracic pressure (25) resulting in decreased liquid leakage in thoracic space. The results of Gust et al. showed that CPAP mask utilization prevents the elevation in extravascular liquid in the lungs (26). In addition, it could be stated that the improvement of heart function is among the physiological impacts of CPAP (27).
On the other hand, in subjects who undergo heart surgery, the receiving and pumping actions of heart as the main function of this organ are not retrieved during the first days after the operation, which leads to elevated liquid leakage to the interstitial space. Therefore, a CPAP mask can enhance heart function (27) and reduce heart workload (28) by decreasing transmural pressure.
Results of the current study indicated that pneumothorax incidence is not significantly different between the two groups. Nonetheless, it is noteworthy that a lower number of patients were clinically affected by pneumothorax in the intervention group. There is no clinical trial concerning the influence of the CPAP mask on pneumothorax incidence or treatment. However, the results of some studies in non-surgical patients (29) and children (30) demonstrate that continuous usage of CPAP mask can cause pneumothorax. Variety in the findings might be attributed to the study groups and study duration. The literature notes that pneumothorax due to CPAP is rare (29).
Our findings revealed that PO2 and O2 Sat raised in the test group post-intervention, compared to the control group. In other words, oxygenation was improved in these individuals and PCO2 along with RR diminished in the test group, in comparison with the control group. The results of some other studies indicated that the oxygenation condition improved following CPAP mask usage, while an investigation on patients with rib fracture reported that oxygenation did not have a significant difference between the CPAP and IPPV groups (31).
A reason for this controversy might be the lack of adaptation to the CPAP mask among the patients under study. The latter point has also been mentioned in the literature (32). Enhancement in the oxygenation condition of the patients in the present study could be explained by the continuous positive pressure induced by CPAP during inspiration and expiration, which keeps airways and alveoli open leading to augmented inspiratory reserve volume and residual volume (RV).
Increased RV causes more air to remain in the lung resulting in higher rates of gas exchange. Moreover, the removal of V/Q mismatch due to the widening of alveoli and better gas emission from blood in the participants of the test group can be considered as another reason for boosted oxygenation and decreased PCO2.
In the current investigation, the CPAP mask was utilized with the purpose of preventing pulmonary sequels. According to the findings, no serious and dangerous side effect was observed and similar studies have also noted this point (22, 23). We cannot conclude from the present investigation whether CPAP mask had a treating or preventive role. Consequently, further studies regarding atelectasis treatment after heart surgery are required, which has also been mentioned in similar investigations (22).
The mask used in this study could not be tolerated by some patients because of the complete covering of the mouth and nose. As a result, some subjects could not cooperate and much time was spent on sampling by the researchers, which can be considered as a limitation for this study.
Conclusion
Results of the current study demonstrated that CPAP mask application can effectively and safely diminish atelectasis and pleural effusion along with enhancing oxygenation and ventilation in patients following open-heart surgery.
Acknowledgments
Authors of the present investigation would like to extend their gratitude to the participants in this study. In addition, they would appreciate the nurses and physicians of the heart surgery ICU of Beheshti Hospital, Kashan.
Conflict of interest
There was no conflict of interest among the authors of the present study.
Funding
This study was a part of a thesis with the code of 94116, which was completed by the financial support of Kashan University of Medical Sciences in 2015.
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Introduction
Open-heart surgery is one of the most common treatments for cardiovascular diseases that might be accompanied by various side effects, such as pulmonary sequels (1). Open-heart surgeries include coronary bypass, valves repair or replacement, congenital heart diseases, and cardiac transplant (2). According to the annual reports, 30-40 thousand open-heart surgeries are performed yearly in Iran (1). Although open-heart surgery is a reliable technique for enhancing myocardial perfusion, the operation might cause a wide range of disorders in different body organs, especially the lungs due to blood exit from the body and the cessation of the function of heart and lungs (2).
Nowadays, despite the improvements in the methods of cardiopulmonary bypass (CPB) and post-op cares, still pulmonary function defect after surgery has remained as one of the remarkable post-surgery side effects (3). Regarding the incidence of these sequels, it was stated in the literature that blood confronts a large surface of artificial materials at the first step of CPB leading to the synthesis and secretion of numerous toxic chemicals and vasoactive agents.
Next, the activation of neutrophils and their presence in pulmonary blood circulation results in deep endothelial, epithelial, and interstitial pulmonary damage. This injury may be accompanied by increased endothelial permeability, diminished pulmonary capacity, and disturbed gas exchange (4).
All these events after surgery can cause atelectasis, pneumonia, pleural effusion, and reduced pulmonary capacity leading to decreased oxygen delivery to the tissues (5). Some studies reported the incidence of post-operation atelectasis and pleural effusion as 15-98% (6) and 63% (7), respectively. Considering the extent and importance of changes in pulmonary function after open-heart surgery, these patients require suitable interventions.
There is no consensus in the existing literature concerning the best intervention for the rehabilitation and improvement of respiratory system function in patients under open-heart surgery (8). However, there are some techniques for the prevention and treatment of these side effects (9), among which respiratory physiotherapy (10), post-op positioning, and pain management could be noted (11, 12).
One of the recommended methods for decreasing the incidence of pulmonary sequels is to apply continuous positive airway pressure (CPAP) masks (13, 14). These masks non-invasively enhance the respiratory condition of the patients with spontaneous respiration during inspiration and expiration by inducing a continuous positive pressure in airways at inspiration and expiration (15). The CPAPs can be used easily for respiratory support, cost low, are well-tolerated, and prevent repetitive intubation (16).
Studies regarding the application of CPAP have revealed controversial results. Zarbock et al. reported that the long-term utilization of non-invasive CPAP following heart surgery improves arterial blood oxygenation and reduces pulmonary side effects, such as pneumonia, repeated intubation, and return to the Intensive Care Unit (ICU) (2)
The results of another study showed that CPAP masks can be useful for treating or preventing atelectasis in patients after open-heart surgery (17). Furthermore, another study revealed that arterial blood gases remarkably get enhanced in patients receiving CPAP mask after open-heart surgery (18). On the other hand, Altmay et al. found no influence regarding invasive CPAP application during CPB on post-op pulmonary function (19).
Considering the mentioned contradictions, different methodologies in using this technique, and the importance of preventing pulmonary sequels after heart surgery, we aimed to evaluate the impact of CPAP mask on arterial blood gases and the reduction of pulmonary side effects after heart surgery. The results of the present study might be useful in promoting care services after heart surgery, which leads to the sooner discharge of the patient from the ICU. Moreover, some sequels, including a long stay in hospital and high costs for the patients and health organizations might decline.
Materials and Methods
This double-blind randomized clinical trial (blind for both patient and statistician) was carried out on the study population of all patients referring to the heart surgery ICU of Shahid Beheshti Teaching Hospital of Kashan in 2015. A total of 72 patients who were candidates for open-heart surgery were selected through the continuous sampling method and were assigned to the two groups of test (n=36) and control (n=36) by random placement using a coin. The sample size was calculated utilizing the following formula based on the results of the previous studies (the mean of heart rate difference; d=7 and σ=14) (20):
The inclusion criteria entailed 1) being over 18 years old, 2) having elective surgery under CPB pump, 3) having an ejection fraction of over 40%, 4) having at least one evacuation drain in the pleural region, 5) receiving mechanical ventilation post-operation for less than 12 h, 6) not requiring inotropic agents at the beginning of the study (e.g., epinephrine, dopamine, dobutamine), and 7) not having any history of chronic obstructive pulmonary disease or asthma. The exclusion criteria were 1) need for repeated intubation during the study, 2) hemodynamic instability, 3) need for bronchodilator or inotropic medications, and 4) not tolerating CPAP mask.
Data Collection Tools
The data collection instrument entailed three parts, the first of which addressed age, gender, smoking history, surgery type, drainage type, background disease, BMI, ejection fraction, aortic cross-clamping time (XCT), CPB time, left-side drainage, and right-side drainage. The second part was about arterial blood gases, including PO2, PCO2, oxygen saturation (O2 Sat), and respiratory rate (RR) that were recorded 10 min pre- and post-intervention from the arterial blood gas (ABG) description of the patients checked by GEM premier3000 system.
In addition, the third part evaluated the pulmonary side effects, namely atelectasis, pneumothorax, and pleural effusion, which were diagnosed 24 h after the removal of drains using a chest X-ray by a radiologist. The face and content types of the validity of the instrument were assessed and confirmed by ten members of the scientific committee of Kashan University of Medical Sciences. In order to examine the reliability, the checklist was completed for five patients by two separate assessors and the agreement coefficient was obtained as 0.92.
Intervention Procedure
At the beginning of the study (before surgery), a mask for mouth and nose with a suitable size was applied to all patients. The subjects were requested to breathe with the mask for 1 min to understand the study conditions and decide for participation in the investigation. The selected mouth and nose mask for each patient was kept at the ICU until transfer from the operation room.
In the test group, the mask connected to the CPAP system with the pressure of 5 cmH2O was located and fixed on the mouth and nose of the participants so that air could not exit the edges of a mask when entered the pathways with pressure. The masks were used for the patients five times after open-heart surgery immediately after extubation and then every 8 h for 30 min (2). The subjects of both intervention and control groups received the routine care of the unit.
Ethical Considerations
The researchers selected the samples based on the inclusion criteria after receiving approval from the Ethics Committee of Kashan University of Medical Sciences and the authorities of the hospital and ICU. First, individuals who were a candidate for heart surgery were selected and the aims of the study were explained to all the participants.
Following receiving written informed consent, the subjects were told that continuing or leaving the study will not affect the treatment procedure and will not have any expenses. Moreover, the participants were assured regarding the confidentiality of the data and the researchers explained that they could leave the study anytime they desired. The present study was approved by the University with the code of IRCT138902013146N2 and the ethical code of IR.KAUMS.REC.1394.116.
Statistical Analysis
All the data were analyzed by descriptive statistics, independent t-test, and Chi-square test using the SPSS software version 13. Moreover, the Kolmogorov-Smirnov test was utilized to evaluate the normality of the data showing that all the data had a normal distribution.
Results
A total of 72 patients under open-heart surgery participated in this study. Our findings showed that the mean age of people was 61.38±9.08 years in the control group and 59.72±12.25 years in the test group without a significant difference between the two groups (P=0.51).
Furthermore, ejection fraction, left-side drainage, aorta clamp right-side drainage, and XCT were not significantly different between the two groups (P>0.05) (Table 1). According to the results of this study, 33.3% and 30.6% of the subjects in the control and test groups were male, respectively. Therefore, the two groups did not have a significant difference regarding gender (P=0.05) (Table 2).
Nowadays, despite the improvements in the methods of cardiopulmonary bypass (CPB) and post-op cares, still pulmonary function defect after surgery has remained as one of the remarkable post-surgery side effects (3). Regarding the incidence of these sequels, it was stated in the literature that blood confronts a large surface of artificial materials at the first step of CPB leading to the synthesis and secretion of numerous toxic chemicals and vasoactive agents.
Next, the activation of neutrophils and their presence in pulmonary blood circulation results in deep endothelial, epithelial, and interstitial pulmonary damage. This injury may be accompanied by increased endothelial permeability, diminished pulmonary capacity, and disturbed gas exchange (4).
All these events after surgery can cause atelectasis, pneumonia, pleural effusion, and reduced pulmonary capacity leading to decreased oxygen delivery to the tissues (5). Some studies reported the incidence of post-operation atelectasis and pleural effusion as 15-98% (6) and 63% (7), respectively. Considering the extent and importance of changes in pulmonary function after open-heart surgery, these patients require suitable interventions.
There is no consensus in the existing literature concerning the best intervention for the rehabilitation and improvement of respiratory system function in patients under open-heart surgery (8). However, there are some techniques for the prevention and treatment of these side effects (9), among which respiratory physiotherapy (10), post-op positioning, and pain management could be noted (11, 12).
One of the recommended methods for decreasing the incidence of pulmonary sequels is to apply continuous positive airway pressure (CPAP) masks (13, 14). These masks non-invasively enhance the respiratory condition of the patients with spontaneous respiration during inspiration and expiration by inducing a continuous positive pressure in airways at inspiration and expiration (15). The CPAPs can be used easily for respiratory support, cost low, are well-tolerated, and prevent repetitive intubation (16).
Studies regarding the application of CPAP have revealed controversial results. Zarbock et al. reported that the long-term utilization of non-invasive CPAP following heart surgery improves arterial blood oxygenation and reduces pulmonary side effects, such as pneumonia, repeated intubation, and return to the Intensive Care Unit (ICU) (2)
The results of another study showed that CPAP masks can be useful for treating or preventing atelectasis in patients after open-heart surgery (17). Furthermore, another study revealed that arterial blood gases remarkably get enhanced in patients receiving CPAP mask after open-heart surgery (18). On the other hand, Altmay et al. found no influence regarding invasive CPAP application during CPB on post-op pulmonary function (19).
Considering the mentioned contradictions, different methodologies in using this technique, and the importance of preventing pulmonary sequels after heart surgery, we aimed to evaluate the impact of CPAP mask on arterial blood gases and the reduction of pulmonary side effects after heart surgery. The results of the present study might be useful in promoting care services after heart surgery, which leads to the sooner discharge of the patient from the ICU. Moreover, some sequels, including a long stay in hospital and high costs for the patients and health organizations might decline.
Materials and Methods
This double-blind randomized clinical trial (blind for both patient and statistician) was carried out on the study population of all patients referring to the heart surgery ICU of Shahid Beheshti Teaching Hospital of Kashan in 2015. A total of 72 patients who were candidates for open-heart surgery were selected through the continuous sampling method and were assigned to the two groups of test (n=36) and control (n=36) by random placement using a coin. The sample size was calculated utilizing the following formula based on the results of the previous studies (the mean of heart rate difference; d=7 and σ=14) (20):
The inclusion criteria entailed 1) being over 18 years old, 2) having elective surgery under CPB pump, 3) having an ejection fraction of over 40%, 4) having at least one evacuation drain in the pleural region, 5) receiving mechanical ventilation post-operation for less than 12 h, 6) not requiring inotropic agents at the beginning of the study (e.g., epinephrine, dopamine, dobutamine), and 7) not having any history of chronic obstructive pulmonary disease or asthma. The exclusion criteria were 1) need for repeated intubation during the study, 2) hemodynamic instability, 3) need for bronchodilator or inotropic medications, and 4) not tolerating CPAP mask.
Data Collection Tools
The data collection instrument entailed three parts, the first of which addressed age, gender, smoking history, surgery type, drainage type, background disease, BMI, ejection fraction, aortic cross-clamping time (XCT), CPB time, left-side drainage, and right-side drainage. The second part was about arterial blood gases, including PO2, PCO2, oxygen saturation (O2 Sat), and respiratory rate (RR) that were recorded 10 min pre- and post-intervention from the arterial blood gas (ABG) description of the patients checked by GEM premier3000 system.
In addition, the third part evaluated the pulmonary side effects, namely atelectasis, pneumothorax, and pleural effusion, which were diagnosed 24 h after the removal of drains using a chest X-ray by a radiologist. The face and content types of the validity of the instrument were assessed and confirmed by ten members of the scientific committee of Kashan University of Medical Sciences. In order to examine the reliability, the checklist was completed for five patients by two separate assessors and the agreement coefficient was obtained as 0.92.
Intervention Procedure
At the beginning of the study (before surgery), a mask for mouth and nose with a suitable size was applied to all patients. The subjects were requested to breathe with the mask for 1 min to understand the study conditions and decide for participation in the investigation. The selected mouth and nose mask for each patient was kept at the ICU until transfer from the operation room.
In the test group, the mask connected to the CPAP system with the pressure of 5 cmH2O was located and fixed on the mouth and nose of the participants so that air could not exit the edges of a mask when entered the pathways with pressure. The masks were used for the patients five times after open-heart surgery immediately after extubation and then every 8 h for 30 min (2). The subjects of both intervention and control groups received the routine care of the unit.
Ethical Considerations
The researchers selected the samples based on the inclusion criteria after receiving approval from the Ethics Committee of Kashan University of Medical Sciences and the authorities of the hospital and ICU. First, individuals who were a candidate for heart surgery were selected and the aims of the study were explained to all the participants.
Following receiving written informed consent, the subjects were told that continuing or leaving the study will not affect the treatment procedure and will not have any expenses. Moreover, the participants were assured regarding the confidentiality of the data and the researchers explained that they could leave the study anytime they desired. The present study was approved by the University with the code of IRCT138902013146N2 and the ethical code of IR.KAUMS.REC.1394.116.
Statistical Analysis
All the data were analyzed by descriptive statistics, independent t-test, and Chi-square test using the SPSS software version 13. Moreover, the Kolmogorov-Smirnov test was utilized to evaluate the normality of the data showing that all the data had a normal distribution.
Results
A total of 72 patients under open-heart surgery participated in this study. Our findings showed that the mean age of people was 61.38±9.08 years in the control group and 59.72±12.25 years in the test group without a significant difference between the two groups (P=0.51).
Furthermore, ejection fraction, left-side drainage, aorta clamp right-side drainage, and XCT were not significantly different between the two groups (P>0.05) (Table 1). According to the results of this study, 33.3% and 30.6% of the subjects in the control and test groups were male, respectively. Therefore, the two groups did not have a significant difference regarding gender (P=0.05) (Table 2).
Table 1. Demographic and clinical variables in the two groups of control and intervention
| *P-value | Group | Variable | |
| Control Mean±SD |
Intervention Mean±SD |
||
| 0.51 | 61.38±9.08 | 59.72±12.25 | Age (years) |
| 0.35 | 27.73±5.36 | 26.63±4.67 | BMI |
| 0.06 | 52.91±6.58 | 55.55±5.03 | Ejection fraction (%) |
| 0.41 | 168.05±127.98 | 199.3±188.36 | Left-side drainage (cc) |
| 0.75 | 29.16±87.52 | 35.41±84.17 | Right-side drainage (cc) |
| 0.19 | 34.86±7.69 | 38.61±15.35 | Aorta clamping (min) |
| 0.16 | 64.66±12.03 | 70.08±19.63 | Pump time (min) |
Table 2. Frequency of demographic variables in the two groups
| Variable | Group | P-value | ||
| Intervention | Control | |||
| Gender | Male | 11(30.6) | 12 (33.3) | 0.5* |
| Female | 25 (69.4) | 24 (66.7) | ||
| Smoking history | No | 24 (66.7) | 23 (63.9) | 0.5** |
| Yes | 12 (33.3) | 13(36.1) | ||
| Type of surgery | CABG | 33 (91.7) | 36 (100) | 0.2** |
| Valve | 1(2.8) | 0 | ||
| Both | 2 (5.6) | 0 | ||
| Type of drain | Mediastinal and left plural | 24 (66.7) | 30 (83.3) | 0.2** |
| Mediastinal and right plural | 1 (2.8) | 0 | ||
| All three | 11 (30.6) | 6 (16.7) | ||
| Gender | No | 30 (83.3) | 30 (83.3) | 0.2** |
| Yes | 6 (16.7) | 6 (16.7) | ||
*Independent t-test
**Chi-square test
Table 3. Incidence frequency of pulmonary side effects in the intervention and control groups
| Variable | Group | P-value | ||
| Intervention n (%) |
Control n (%) |
|||
| Atelectasis | Yes | 8 (22.2) | 17 (47.2) | 0.04* |
| No | 28 (77.8) | 19 (52.8) | ||
| Pleural effusion | Yes | 2 (8.3) | 11 (30.6) | 0.01* |
| No | 34 (91.7) | 25 (69.4) | ||
| Pneumothorax | Yes | 1 (2.8) | 4 (11.1) | 0.35* |
| No | 35 (97.2) | 32 (88.9) | ||
Table 4. Mean and standard deviation of PO2, PCO2, O2 Sat, and RR in the intervention and control groups before and 10 min after each time of intervention
| Intervention time | First | Second | Third | Fourth | Fifth | |||||||||||
| Group | Intervention | Control | *P-value | Intervention | Control | P-value | Intervention | Control | P-value | Intervention | Control | P-value | Intervention | Control | P-value | |
| RR | Before | 17.8±3.61 | 16.4±2.26 | 0.05 | 18.3±3.98 | 17.7±2.09 | 0.43 | 18.5±4.57 | 17.6±2.45 | 0.3 | 18.7±4.8 | 19.1±2.51 | 0.71 | 18.6±4.56 | 19.6±2.59 | 0.28 |
| After | 13.8±3.3 | 15.8±2.54 | 0 | 14.4±3.01 | 16.7±2.98 | 0 | 15.3±3.96 | 17.0±3.11 | 0.04 | 15.2±3.93 | 19.3±2.42 | 0 | 16.9±4.12 | 19.6±2.56 | 0.002 | |
| PO2 | Before | 89.6±17.21 | 94.8±25.82 | 0.31 | 88.9±23.27 | 97.0±35.25 | 0.25 | 80±21.79 | 76.5±15.81 | 0.44 | 74.2±18.79 | 78.5±24.45 | 0.4 | 72.9±15.57 | 72.1±16.06 | 0.83 |
| After | 141.7±47.35 | 114.6±37.31 | 0.009 | 117.6±36.96 | 94.9±31.54 | 0.006 | 103.8±29.47 | 78.1±17.93 | 0 | 102.3±21.07 | 74.5±18.6 | 0 | 94.7±26.32 | 75.1±18.06 | 0 | |
| PCO2 | Before | 38±3.87 | 36.9±3.78 | 0.22 | 40.1±4.15 | 38.7±3.79 | 0.13 | 37.9±3.01 | 37.8±3.64 | 0.88 | 39.9±5.58 | 37.9±3.74 | 0.08 | 36.5±5.43 | 37.9±5 | 0.25 |
| After | 36±3.49 | 39.1±4.28 | 0.001 | 41.0±7.15 | 37.7±3.97 | 0.01 | 37.3±5.56 | 40.6±5.58 | 0.01 | 36.1±5 | 40.9±5.22 | 0 | 35.6±5.34 | 38.4±5.59 | 0.03 | |
| O2 Sat | Before | 95±2.98 | 95.4±2.86 | 0.49 | 96.1±2.56 | 96.6±2.24 | 0.4 | 95.1±2.95 | 94.8±3.3 | 0.68 | 94.3±2.67 | 95.1±2.74 | 0.22 | 94.3±2.81 | 94.3±2.49 | 0.96 |
| After | 97.7±2.11 | 95.5±3.52 | 0.003 | 97.6±2.11 | 96.4±2.29 | 0.02 | 96.2±2.5 | 94.3±3.02 | 0.006 | 96.3±2.64 | 94.6±2.2 | 0.004 | 95.9±2.72 | 94.8±2.26 | 0.07 | |
The results of Fisher’s exact test revealed that the two groups were significantly different in terms of atelectasis (P=0.04) and pleural effusion (P=0.01) and the incidence of these problems was lower in the intervention group, compared to the control group (Table 3). Moreover, the results of the independent t-test showed that there was a significant difference between the two groups regarding the means of PO2, PCO2, O2 Sat, and RR after each time of intervention (P<0.05). It was found that arterial O2 Sat and PO2 augmented after each time of intervention, while arterial PCO2 and RR diminished after each intervention time (Table 4).
Discussion
The present study aimed to evaluate the impact of CPAP mask on the incidence of pulmonary side effects in patients after heart surgery. Our results revealed that using a CPAP mask led to a decreased incidence of atelectasis after open-heart surgery. Some studies reported the incidence of atelectasis as 6-42% (21) and it was found as 47.2% and 22.2% in the control and test groups of this study, respectively.
Al. Mutairi et al. (2013) carried out a clinical trial aimed to investigate the influence of the early application of CPAP mask on the treatment or prevention from atelectasis following coronary artery bypass grafting. They demonstrated that the CPAP group had better results in terms of treating and preventing atelectasis, compared to the motivational spirometry group (17).
The results of other studies showed that CPAP mask can be effective in preventing atelectasis after surgery (21-23). It could be claimed that heart surgery results in reduced lung volumes, alveolar collapse, and the collapse of some parts of the lungs as atelectasis and diminished oxygenation. Consequently, the generation of continuous positive pressure in the airways and alveoli as the base of the function mechanism of CPAP masks (1) causes the alveoli to widen due to the positive pressure and the atelectasis is resolved.
Moreover, the literature indicates that improved oxygenation using CPAP mask results from the resolution of atelectasis in patients following heart surgery (23, 2). Pasquina et al. (2004) completed an investigation on 155 patients in the heart surgery ICU to compare non-invasive pressure support ventilation (NIPSV) and CPAP in terms of atelectasis treatment.
The mentioned authors concluded that CPAP was less influential than NIPSV in treating atelectasis (22). In terms of the CPAP mask, both the latter and present studies had similar findings. However, the impact of the CPAP mask in the mentioned investigation was less remarkable, in comparison with NIPSV.
Our findings revealed a significant difference in the incidence of pleural effusion between the test and control groups and the incidence rate was lower among the patients of the control group. Results of the study completed by Oliveira et al. demonstrated that CPAP mask usage led to the diminished pleural effusion in tuberculosis patients (24). Furthermore, Marti et al. reported that CPAP imposed a positive effect in individuals with heart failure due to pleural effusion (16).
Application of CPAP mask elevates the intrathoracic pressure (25) resulting in decreased liquid leakage in thoracic space. The results of Gust et al. showed that CPAP mask utilization prevents the elevation in extravascular liquid in the lungs (26). In addition, it could be stated that the improvement of heart function is among the physiological impacts of CPAP (27).
On the other hand, in subjects who undergo heart surgery, the receiving and pumping actions of heart as the main function of this organ are not retrieved during the first days after the operation, which leads to elevated liquid leakage to the interstitial space. Therefore, a CPAP mask can enhance heart function (27) and reduce heart workload (28) by decreasing transmural pressure.
Results of the current study indicated that pneumothorax incidence is not significantly different between the two groups. Nonetheless, it is noteworthy that a lower number of patients were clinically affected by pneumothorax in the intervention group. There is no clinical trial concerning the influence of the CPAP mask on pneumothorax incidence or treatment. However, the results of some studies in non-surgical patients (29) and children (30) demonstrate that continuous usage of CPAP mask can cause pneumothorax. Variety in the findings might be attributed to the study groups and study duration. The literature notes that pneumothorax due to CPAP is rare (29).
Our findings revealed that PO2 and O2 Sat raised in the test group post-intervention, compared to the control group. In other words, oxygenation was improved in these individuals and PCO2 along with RR diminished in the test group, in comparison with the control group. The results of some other studies indicated that the oxygenation condition improved following CPAP mask usage, while an investigation on patients with rib fracture reported that oxygenation did not have a significant difference between the CPAP and IPPV groups (31).
A reason for this controversy might be the lack of adaptation to the CPAP mask among the patients under study. The latter point has also been mentioned in the literature (32). Enhancement in the oxygenation condition of the patients in the present study could be explained by the continuous positive pressure induced by CPAP during inspiration and expiration, which keeps airways and alveoli open leading to augmented inspiratory reserve volume and residual volume (RV).
Increased RV causes more air to remain in the lung resulting in higher rates of gas exchange. Moreover, the removal of V/Q mismatch due to the widening of alveoli and better gas emission from blood in the participants of the test group can be considered as another reason for boosted oxygenation and decreased PCO2.
In the current investigation, the CPAP mask was utilized with the purpose of preventing pulmonary sequels. According to the findings, no serious and dangerous side effect was observed and similar studies have also noted this point (22, 23). We cannot conclude from the present investigation whether CPAP mask had a treating or preventive role. Consequently, further studies regarding atelectasis treatment after heart surgery are required, which has also been mentioned in similar investigations (22).
The mask used in this study could not be tolerated by some patients because of the complete covering of the mouth and nose. As a result, some subjects could not cooperate and much time was spent on sampling by the researchers, which can be considered as a limitation for this study.
Conclusion
Results of the current study demonstrated that CPAP mask application can effectively and safely diminish atelectasis and pleural effusion along with enhancing oxygenation and ventilation in patients following open-heart surgery.
Acknowledgments
Authors of the present investigation would like to extend their gratitude to the participants in this study. In addition, they would appreciate the nurses and physicians of the heart surgery ICU of Beheshti Hospital, Kashan.
Conflict of interest
There was no conflict of interest among the authors of the present study.
Funding
This study was a part of a thesis with the code of 94116, which was completed by the financial support of Kashan University of Medical Sciences in 2015.
Type of Study: Research |
Subject:
vascular surgery
Received: 2019/12/2 | Accepted: 2020/01/4 | Published: 2020/01/30
Received: 2019/12/2 | Accepted: 2020/01/4 | Published: 2020/01/30
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