To Study the Effect of Noninvasive Ventilation on Hemodynamics and Respiratory Parameters in Postoperative CABG Patients.

Background and Aim: Bilevel positive airway pressure (BIPAP) is emerging as a useful modality in prevention as well as the management of postoperative respiratory dysfunction in patients undergoing coronary artery bypass graft (CABG). Materials and
Methods: A total of 50 patients who underwent CABG were managed using BIPAP during postoperative period. Acid-base gas parameters, electrolyte levels, respiratory and hemodynamic parameters, and 24 h urine output before and after BIPAP application were measured. Data were analyzed using SPSS 21.0 version. Paired "t"-test was used to compare the changes in different parameters.
Results: The mean age of patients was 57.72 ± 9.67 years (range: 36-85 years), majority were males (84%). Mean body mass index and mean left ventricular ejection fraction of patients were 24.26 ± 3.74 kg.m -2 and 52.77 ± 10.26%, respectively. Mean pO2, pCO2, and respiratory rate before BIPAP application were 90.62 ± 12.90 torr, 40.26 ± 5.39 torr, and 25.64 ± 6.21/min, respectively, which became 158.52 ± 50.43 torr, 37.77 ± 6.98 torr, and 21.78 ± 4.79/min, respectively, after BIPAP application, thus showing a significant change (P < 0.05). No significant change in other parameters was observed. No other adverse effect was noted.
Conclusion: BIPAP application helped in improving ventilatory parameters without any adverse impact on hemodynamics and other parameters. Its application was a safe method to prevent respiratory disturbances following cardiac surgery. Copyright:

INTRODUCTION

Postoperative respiratory complications are commonly encountered in patients undergoing cardiac surgery and result in prolonged duration of hospital stay, increased costs, and increased morbidity and mortality. Post-operative respiratory complications have been attributed to a number of factors primary being general anesthesia, duration of surgery, duration of mechanical ventilation, extent of pleural opening, surgical route and regions involved and use of surgical drains, age, comorbid conditions, nutritional status.[1] Noninvasive ventilation (NIV) has emerged as a useful modality for postoperative management of pulmonary complications among cardiac surgery patients. The main effect of NIV is seen on the pulmonary and cardiovascular systems. NIV can be successfully employed for the prevention and treatment of acute respiratory failure and has been utilized for the transition of patients from mechanical ventilation.[2] However, despite these reported benefits, the success of postoperative NIV in cardiac surgery patients is not well established in view of inconsistent results.[1] Thus, there is a need to establish its usefulness through further studies in different environments.

Bilevel positive airway pressure (BIPAP) is a commonly employed NIV modality which has shown to be beneficial in different high-risk situations and can be employed without causing discomfort to the patient.[34] Moreover, it also helps to avoid intubation, reduces complications such as ventilator-associated pneumonia, does not require deep sedation, and offers better oxygenation.[56] Some previous studies have also shown it to be useful in postoperative airway management among cardiac surgery patients.[789] Hence, the present study was carried out to evaluate the usefulness of BIPAP during immediate postoperative period among patients having undergone off-pump coronary artery bypass graft surgery (CABG).

MATERIALS AND METHODS

This prospective observational study was carried out at a 700-bedded tertiary care hospital having a 6-bedded cardiac surgery unit. The study was conducted from January 2019 to March 2020 after obtaining approval from the Institutional Ethics Committee and informed consent from the patients.

The sample size was based on the study by Takami and Ina[10] and determined on the basis of the effect on one of the variables, PaO2:FiO2 ratio. Changes in the hemodynamic, BIPAP parameters, SaO2, PaO2, PaCO2, heart rate (HR), mean blood pressure (BP), and central venous pressure (CVP) were calculated from relative changes from the baseline. A sample size of 50 achieved 90% power to detect a 20% and above mean paired difference with an estimated standard deviation of the difference being 20, with a significance level (alpha) of 0.01 using a paired t-test.

A total of 143 patients underwent off-pump CABG during the study period. Post-CABG patients who were in respiratory distress (respiratory rate >30 and paO2:FiO2 ratio of <200 and oxygen saturation (SpO2) of <92%) were included in the study. A total of 61 patients satisfied the abovementioned criterion and were invited to participate in the study. Patients’ refusal, preexisting pulmonary disease, emergency surgery, those with postoperative complications such as pneumothorax, hemorrhage, cardiac tamponade, and those with postoperative cognitive decline were excluded from the study. A total of 11 patients satisfied the exclusion criterion. Finally, a total of 50 patients were enrolled in the study [Consort Flow Diagram].

Procedure

A full face mask was used to cover the mouth and nose and then attached with a portable BIPAP machine (VPAP III STA QuickNav®; ResMed, Bangalore, India). It delivers a positive pressure through a single air circuit with the exhaled air exiting through a mask exhaust vent. Initial settings of inspiratory pressure 12 and expiratory pressure of 6 were applied and gradually increased accordingly. No attempt was made to wean off during the study period. The patient was monitored for mask intolerance, gastric distension, and facial skin laceration. All data were recorded on a pro forma, which included demographics, reason for application, SaO2 at the time of first application, time it started, total duration of application, initial settings, range (minimum and maximum), and outcome of BIPAP application. Data were collected by an investigator blinded to the nature of the study.

All statistical analyses were performed using the Statistical Package for the Social Sciences version 19 (SPSS Inc., Chicago, IL, USA). Frequency and percentage were computed for categorical observation, while mean and standard deviation were estimated for continuous variables. Pre-BIPAP and post-BIPAP effects on dependent variables were analyzed by paired t-test. “P”< 0.05 was considered statistically significant.

RESULTS

The age of patients enrolled in the study ranged from 36 to 85 years. The mean age of patients was 57.72 ± 9.67 years. Majority of the patients were males (84%). The sex ratio (M: F) of the study was 5.25. The body mass index of patients ranged from 18.26 to 31.77 kg.m−2 with a mean of 24.26 ± 3.74 kg.m−2. Mean left ventricular ejection fraction (LVEF) of patients was 52.77 ± 10.26% [Table 1].

Table 1

Demographic profile and characteristics of patients

Characteristic	Statistic
Mean age±SD (range) in years	57.72±9.67 (36-85)
Sex (%)
Male	42 (84.0)
Female	8 (16.0)
Mean BMI±SD (range) kg/m2	24.26±3.74 (18.26-31.77)
Mean LVEF±SD (range) %	52.77±10.26 (30-65)

SD=Standard deviation, BMI=Body mass index, LVEF=Left ventricular ejection fraction

Pre-BIPAP mean values of PaO2 and PaCO2 levels were 90.62 ± 12.90 and 40.26 ± 5.39 torr, respectively. Pre-BIPAP mean values of pH were 9.31 ± 10.23, HCO3 – 27.98 ± 5.48 mEq/L, and SaO2 level – 98.22 ± 9.87%. Mean Na+, K+, and Ca2+ levels were 138.70 ± 3.78 mE/L, 3.69 ± 0.42 mEq/L, and 0.85 ± 0.45 mg/dl, respectively. The mean platelet count was 2.71 ± 1.55 lakhs/mm3 and the mean hemoglobin (Hb) level was 9.76 ± 2.29 g/dl. Mean pulse rate, systolic BP (SBP), diastolic BP (DBP), and CVP were 94.12 ± 13.12 bpm, 129.44 ± 17.18 mmHg, 65.28 ± 11.10 mmHg, and 5.06 ± 1.92 cmH2O, respectively. The mean respiratory rate was 25.64 ± 6.2 1/min and mean SpO2 was 99.94 ± 0.42%. Mean urinary output was 145.10 ± 76.36 ml. Post-BIPAP mean values of PaO2 and PaCO2 values were 158.52 ± 50.43 torr and 37.77 ± 6.98 torr, respectively, thus showing a significant increase in PaO2 (P < 0.001) and a significant decline in PaCO2 levels (P = 0.030). Mean pH, HCO3, and SaO2 levels were 7.38 ± 0.06, 31.94 ± 28.34 mEq/L, and 97.52 ± 7.81%, respectively, thereby showing no significant difference from pre-BIPAP application values. Mean Na+, K+, and Ca2+ levels were 138.72 ± 8.82 mEq/L, 3.66 ± 0.49 mEq/L, and 0.91 ± 0.64 mg/dl, respectively, thus showing no significant difference from pre-BIPAP application values. Mean platelet count was 2.57 ± 3.32 lakhs/mm3, Hb level was 9.90 ± 1.90 g/dl, pulse rate was 92.60 ± 13.14 bpm, and mean SBP and DBP were 125.76 ± 19.58 mmHg and 65.66 ± 10.50 mmHg, respectively, thereby not showing a significant difference from pre-BIPAP application values. Mean CVP was 4.98 ± 1.60 cmH2O which again did not show a statistically significant change from pre-BIPAP application value. However, the mean respiratory rate which was 21.78 ± 4.79/min showed a significant decline from pre-BIPAP application status. Mean SpO2 was 99.96 ± 0.28% and mean urinary output was 152.20 ± 61.45 ml. Both these parameters did not show a significant change from pre-BIPAP application status (P > 0.05) [Table 2]. No adverse event or need of intubation was reported in any of the patients.

Table 2

Evaluation of change in different study parameters between pre- and post-bilevel positive airway pressure application intervals (n=50)

Parameter	Before BiPAP application		After BiPAP application		Statistical significance (Paired t-test)
	Mean	SD	Mean	SD	t	P
PaO2 (torr)	90.62	12.90	158.52	50.43	10.06	<0.001
PaCO2 (torr)	40.26	5.39	37.77	6.98	2.240	0.030
pH	9.31	10.23	7.38	0.06	1.338	0.187
HCO3 (mEq/L)	27.98	5.48	31.94	28.34	0.969	0.337
SaO2 (%)	98.22	9.87	97.52	7.81	0.384	0.703
Na+ (mEq/L)	138.70	3.78	138.72	8.82	0.016	0.987
K+ (mEq/L)	3.69	0.42	3.66	0.49	0.372	0.712
Ca2+ (mg/dl)	0.85	0.45	0.91	0.64	0.703	0.486
Platelet count (lakhs/mm3)	2.71	1.55	2.57	3.32	0.313	0.755
Hb (g/dl)	9.76	2.29	9.90	1.94	0.365	0.717
Pulse rate (bpm)	94.12	13.17	92.60	13.14	0.851	0.399
SBP (mmHg)	129.44	17.18	125.76	19.58	1.026	0.310
DBP (mmHg)	65.28	11.10	65.66	10.50	0.204	0.839
CVP (cm H2O)	5.06	1.92	4.98	1.60	0.271	0.788
RR (/min)	25.64	6.21	21.78	4.79	4.015	<0.001
SpO2 (%)	99.94	0.42	99.96	0.28	0.275	0.785
Urine output (ml/24 h)	145.10	76.36	152.20	61.45	0.553	0.583

BiPAP=Bilevel positive airway pressure, Hb=Hemoglobin, SBP=Systolic blood pressure, DBP=Diastolic blood pressure, CVP=Central venous pressure, RR=Respiratory rate, SpO2=Oxygen saturation

DISCUSSION

The present study showed a significant improvement in PaO2 and a significant decline in PaCO2 levels following the application of BIPAP. A significant decline in respiratory rate was also observed. The hemodynamic stability of the patients was maintained and no adverse effect on acid–base gas profile, serum electrolyte levels, and hematological parameters was seen. Adverse events such as acute respiratory failure, ventilator-associated pneumonia, and atelectasis were not observed. The BIPAP application was thus uneventful and was helpful in ensuring a better ventilatory performance. Similar to the present study, Hamid et al. also reported an improvement in respiratory parameters with the maintenance of hemodynamic stability.[7] However, in their study, reintubation was needed in 18.2% of patients. In the present study, we did not observe any need for reintubation probably owing to the inclusion of only CABG patients as compared to their study in which patients undergoing different types of cardiac surgery were enrolled. Similar to the present study, they also did not report any adverse events such as respiratory failure, ventilator-associated pneumonia, and atelectasis. Similar to the present study, where PaO2 levels showed a significant improvement and respiratory rate showed a significant decline following BIPAP application. Sağıroğlu et al. also observed a significant improvement in PaO2 levels and respiratory rate following BIPAP application;[8] however, they also observed a significant improvement in HR and SpO2 which was not observed in the present study. Sağıroğlu et al. also reported reintubation in 5.5% of patients in BIPAP group as compared to 11% in control group. They also reported other adverse effects such as pneumonia, cerebrovascular events, arrhythmias, and pleural effusion in 0.8%–12.5% of patients who were managed using BIPAP. They also reported mortality in 5% of the cases.[8] In the present study, reintubation was not reported in any of the patients. Moreover, our study did not record any other adverse events and there was no mortality. The reason for this could primarily be a relatively lower mean age of the patients (57.72 years) in the present study as compared to theirs (63 years). Older age might affect ventilatory performance and other outcomes.

The usefulness of BIPAP application for the management of respiratory distress in post-CABG patients with poor left ventricle function was also reported by Vats et al. although adverse events such as atelectasis and pneumonia were observed in 10% and 5% of patients, respectively.[9] They did not observe re-intubation but had mortality. Poor outcomes in their study could be attributed to poor left ventricular function in the study population. Better outcomes in our study could be attributed to an average LVEF value of 52.77% in our patient population.

The present study thus was able to record beneficial effects of BIPAP application in post-CABG patients without adverse effects as recorded by Takami and Ina in their study,[10] who observed that the BIPAP application was effective in improving lung oxygenation in post-CABG patients without any adverse event.

CONCLUSION

The findings of the present study thus show that BIPAP application is a noninvasive measure to ensure respiratory function improvement in patients undergoing cardiac surgery. One of the limitations of the present study was its noncomparative nature. A comparison of outcomes with a control group or any other noninvasive or invasive ventilation method could help in assessing the relative performance of BIPAP application. Nevertheless, within the limitations of the present study, BIPAP application could be recommended as a safe method for airway management in patients undergoing airway management. Further studies on a larger sample size with inclusion of other contemporary comparative measures are recommended.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.