2Department of Cardiothoracic and vascular Surgery, All India Institute of Medical Sciences, New Delhi, India
Study design: Prospective clinical study
Setting: Tertiary health care centre
The patients were premedicated with oral diazepam 10mg at night before and 5 mg in the morning on the day of surgery. In addition they received injection morphine 0.1mg-1kg and injection phenergan 0.5mg-1kg intramuscularly one hour before being shifted to the operation theatre. Arterial blood gas was taken with room air during the preoperative visit and before administration of any sedative agents. Anaesthesia was induced with intravenous thiopentone sodium 5mgkg-1, fentanyl 5μgm- 1 kg and 1 mg kg-1 rocuronium bromide was used for muscle relaxation. Anaesthesia was maintained with midazolam, fentanyl and vecuronium bromide. All the patients were mechanically ventilated with 50% air-oxygen mixture with a tidal volume of 7-8 ml kg-1. The plateau airway pressure was kept below 30cm of H2O and end tidal carbon dioxide was maintained between 35-40 mmHg.
The surgery was performed by the same group of surgeons and anaesthesiologist. Patients underwent a median sternotomy, with harvesting of saphenous veins and internal mammary arteries as conduits. Myocardial protection was obtained with crystalloid and cold blood cardioplegia via the antegrade route, and moderate hypothermia (33°C). Haematocrit was maintained between 20% and 25%, and Cardiopulmonary Bypass (CPB) flow was maintained between 2.0 and 2.5 l -1 min -1 m2. The mean perfusion pressure was kept at 70-90 mmHg by adjusting the pump flow, hematocrit, nitroglycerin or phenylephrine infusion.
After arriving at the ICU patients were ventilated mechanically with pressure regulated volume control mode. Systolic blood pressure was maintained between 100-130 mmHg and mean arterial pressure > 60 mmHg. Weaning was started as soon as the awake and alert with cerebral function adequate for cooperation. The criteria for weaning from mechanical ventilation were as follows: spontaneous tidal volume >6mlkg- 1, no significant vasoactive infusions, chest tube drainage < 100mlhr-1, stable hemodynamic without any evidence of low cardiac output syndrome, haemoglobin > 10mg dl-1, endotracheal suctioning < once hr-1, PO2 of > 150 mmHg with an FiO2 of < 0.5 and PaCO2 between 35-45 mmHg, SaO2 > 95% and absence of life threatening arrhythmias, IABP or open chest. Throughout the weaning process and after extubation, arterial blood gas analysis and pulse oximetry were monitored closely. All the patients were monitored for the primary outcome measures that included the duration of mechanical ventilation, ICU stay and hospital stay as well as the secondary outcome measures like, requirement of inotropes, arrhythmias, requirement of IABP, cardiogenic shock, perioperative myocardial infarction, sepsis, respiratory failure , and death.
The characteristics of 141 CABG patients are shown in Table 1. Patients were divided into two groups. Group1: PaO2/FiO2 ratio<300, Group 2:PaO2/FiO2 ratio >300.Group 1 constituted of 34 patients and Group 2 constituted of 107 patients. A significant positive correlation was found between PaO2/FiO2 ratio and intubation period (r = -0.5607, p = 0.001) (Figure 1, Table 4) and ICU stay period (r = -0.2564, p = 0.002) , (Figure 2, Table 4) .Furthermore, the PaO2/FiO2 ratio also correlated with the use of inotropes (dopamine and noradrenaline ) and the frequency of death in patients undergoing CABG (Table 3 and Table 4)
In 1983, Covelli, et al demonstrated that oxygen tensionbased indices, including both (a/A) PO2, and PaO2 /FiO2, were highly reliable, even in critically ill patients [8]. In a recent study to determine the effects of diabetes on pulmonary gas exchange in patients undergoing CABG, Seki, et al [5,9] concluded that the PaO2 / FiO2 ratio was a reliable predictor of the (a / A) PO2 ratio during early postoperative management. In the present study,
Variables |
Mean |
SD |
||
Demographic attributes |
Age (yrs) |
58.3 |
8.2 |
|
Sex (M/F) |
125/16 |
122.3/118.1 |
||
Weight (kg) |
73.6 |
11.9 |
||
Clinical Profile |
Haemoglobin( gm/dl) |
12.5 |
1.9 |
|
DOE |
81(57.4%) |
|
||
AOE |
88(62.4%) |
|
||
Chest pain |
41(29.1%) |
|
||
Diabetes |
64(45.4%) |
|
||
Hypertension |
79(56.0%) |
|
||
Hypothyroidism |
3(2.1%) |
|||
Hyperlipedemia |
35(24.8%) |
|
||
Positive family history |
38(26.9%) |
|
||
Smoking |
52(36.9%) |
|
||
alcohol |
11(7.8%) |
|||
b-blocker |
118(83.7%) |
|
||
Anticholestrol drugs |
111(78.7%) |
|
||
ACE-I |
40(28.4%) |
|
||
CCB |
27(19.1%) |
|
||
Digoxin |
9(6.4%) |
|||
Diuretic |
19(13.5%) |
|
||
Antioxidant |
94(66.7%) |
|
||
No of disease coronary branches : |
||||
Three: |
15(10.63%) |
|
||
Four: |
110(78.01%) |
|
||
Five |
16 (11.34%) |
|
DOE: Dyspnoea on Exertion; AOE : Angina on Exertion; ACE-I :
Angiotensin Converting Enzyme Inhibitor; CCB: Calcium Channel Blocker
|
Factors |
Mean |
SD |
Perioperative Factors |
CPB duration(mins) |
84.1 |
22.5 |
AOx CL(mins) |
50.8 |
15.6 |
|
ACT (secs) |
152.1 |
44.9 |
|
EtCO2 |
79.1 |
|
|
PaO2/FiO2 ratio |
412.7 |
121.4 |
|
Intubation period(hrs) |
21.8 |
6.85 |
|
Pacing |
14(9.9%) |
|
|
ICU stay (hrs) |
50.4 |
19.6 |
|
Dopamine |
52(36.8%) |
|
|
Dobutamine |
3(2.1%) |
|
|
Adrenaline |
17(12.1%) |
|
|
Noradrenaline |
7(4.9%) |
|
|
Nitroglycerine |
42(65.3%) |
|
|
Sodium nitroprusside |
8(5.7%) |
|
|
Amiodarone |
14(10%) |
|
|
IABP use |
5(3.5%) |
|
|
Post op drainage (ml) |
673.3 |
20.4 |
|
Blood and blood products(ml) |
1061 |
584.2 |
|
Reexploration |
1(0.7%) |
|
|
Hospital stay (days) |
9.3 |
4.45 |
|
Death |
3(2.1%) |
|
CPB: Cardio Pulmonary Bypass; AOxCL: Cross Clamp Time; ACT:
Activated Clotting Time; EtCO2: End Tidal Carbondioxide; IABP: Intra Aortic Ballon Pump
The PaO2/FiO2 ratio has been recognized as a good index for predicting mortality and the need for endotracheal intubation in patients suffering from trauma [14]. It has also been suggested to be a reliable predictor of the arterial/alveolar oxygen tension ratio and of pulmonary dysfunction in patients undergoing CABG [15]. In addition, arterial blood gas analysis is routinely performed just after returning to the ICU in most hospitals and the PaO2/ FiO2 ratio is the simplest of the oxygen tension-based indices to calculate. The normal range of PaO2/FiO2 ratio is 350–500. In the
|
Factor |
PaO2/FiO2<300 (n=34) |
PaO2/FiO2>300 (n=107) |
P value |
Preoperative Factors |
Age (yrs) |
57 ± 7.7 |
58.6 ± 8.3 |
0.39 |
Weight (kg) |
71.2±14.2 |
74.3±11.0 |
0.20 |
|
Haemoglobin(gm/dl) |
12.2±2.5 |
12.5±1.6 |
0.47 |
|
hypothyroidism |
2 (5.7%) |
1(0.9%) |
0.152 |
|
DOE |
21(60%) |
60(56.6%) |
0.725 |
|
AOE |
18(51.4%) |
70(66.0%) |
0.122 |
|
Chest pain |
10(28.6%) |
31(29.2%) |
0.939 |
|
Diabetes |
20(57.1%) |
44(41.5%) |
0.107 |
|
Hypertension |
21(60%) |
58(54.7%) |
0.585 |
|
Hyperlipedemia |
9(25.7%) |
26(24.5%) |
0.888 |
|
Smoking |
17(48.6%) |
35(33.0%) |
0.09 |
|
Alcohol |
4(11.4%) |
7(6.6%) |
0.46 |
|
b-blocker |
28(80%) |
90(84.9%) |
0.49 |
|
Anticholestrol drugs |
26(74.3%) |
85(80.2%) |
0.45 |
|
CCB |
8(22.8%) |
19(17.9%) |
0.52 |
|
ACE-I |
10(28.6%) |
30(28.3%) |
0.98 |
|
Digoxin |
1(2.9%) |
8(7.5%) |
0.45 |
|
Diuretic |
6(17.1%) |
13(12.3%) |
0.46 |
|
Antioxidant |
26(74.3%) |
68(64.2%) |
0.27 |
|
|
|
|
|
|
Perioperative Factors |
CPB Time (mins) |
83.4±24.5
|
84.4±21.7 |
0.32 |
ACC time (mins) |
49.9 ±21.7 |
51.3±15.1 |
0.20 |
|
No of disease coronary branches : Three: Four: Five |
4 (11.74%) 27 (79.57%) 3 (8.82%)
|
11(10.28%) 83(77.57%) 13(12.14%) |
0.81 0.8 0.59 |
|
Number of grafts Three Four Five |
4(11.74%) 25(73.52%) 1(2.94%) |
11(10.28%) 79(73.83%) 5(4.67%) |
0.81 0.97 0.66 |
|
Complete revascularization |
89.88±7.5 |
86.63±13.52 |
0.18 |
|
Duration of intubation (hrs) |
28±7.7 |
18.99±4.0 |
0.001 |
|
Dopamine |
16(55.7%) |
36(33.9%) |
0.03 |
|
Dobutamine |
1(2.9%) |
2(1.9%) |
1.00 |
|
adrenaline |
6(17.1%) |
11(10.4%) |
0.28 |
|
Noradrenaline |
4(11.4%) |
3(2.8%) |
0.042 |
|
NTG |
21(60%) |
71(66.9%) |
0.45 |
|
SNP |
2(5.7%) |
6(5.7%) |
1.00 |
|
Arrhythmia requiring treatment |
6(17.1%) |
8(7.6%) |
0.10 |
|
Amiodarone |
6(17.1%) |
8(7.6%) |
0.10 |
|
IABP use |
2(5.7%) |
3(2.8%) |
0.59 |
|
Pacing |
3(8.6%) |
11(10.4%) |
0.75 |
|
ICU stay (hrs) |
60.9±24.9 |
45.6±14.5 |
0.002 |
|
Reexploration |
1(2.9%) |
0 |
0.24 |
|
|
|
|
|
|
Cardiogenic shock |
3(8.6%) |
0 |
0.014 |
|
Respiratory failure |
0 |
0 |
|
|
Death |
3(8.6%) |
0 |
0.014 |
IABP: Intra Aortic Ballon Pump
|
Factor |
Correlation |
Demographic factors |
Age (yrs) |
0.15 |
Weight (kgs) |
0.02 |
|
Haemoglobin (gm/dl) |
-0.02 |
|
CPB(min) |
-0.34 |
|
AOxCL (min) |
-0.02 |
|
ACT(sec) |
0.01 |
|
EtCO2 |
-0.55 |
|
Intubation period(hrs) |
-0.56 |
|
ICU stay (hrs) |
-0.25 |
|
Postop drainage (ml) |
0.09 |
|
Blood and blood products used (ml) |
0.14 |
The number of inotropes administered during the immediate postoperative period (a gross index of myocardial function) has also been found by previous investigators [19-21] to be an independent determinant of outcome in patients undergoing CABG. According to Michalopoulos and colleague the combination of inotropic drug therapy and excessive blood transfusions is significantly associated with hospital death following CABG[18]. Results of our present study also suggest that the incidence of death was higher in the group with PaO2/FiO2 ratio < 350 which also had a higher requirement of inotropes.
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