Can ventilation while on cardiopulmonary bypass improve post-operative lung function for patients undergoing cardiac surgery?

September 22, 2005

September 22, 2005

Hunaid A. Vohra, Adrian Levine, Specialist Registrars in Cardiothoracic Surgery (Department of Cardiothoracic Surgery, University Hospital of North Staffordshire, Stoke-on-Trent)

Joel Dunning, Department of Cardiothoracic Surgery, University Hospital of North Staffordshire, Stoke-on-Trent

In [patients undergoing cardiac surgery] is [CPAP or continued ventilation] more beneficial than lung deflation in [improving post-operative lung function].

You are about to perform four coronary arterial bypass grafts on a 78-year-old ex steel worker. He has a 60 pack per year history of smoking and his lung function tests are significantly abnormal with an FEV1 only 40% of his predicted values. His coronary arterial targets are small and you feel that an on-pump technique is the only option. You discuss the case with the anaesthetist and he asks whether he could keep ventilating while the patient is on bypass in order to improve his post-operative lung function. You have significant concerns that this may make the case even more difficult but rather than refusing this request you resolve to search the literature for evidence that this will improve post-operative lung function as your anaesthetist suggests.

Medline 1966 to Jun 2005 using the OVID interface

[exp cardiopulmonary bypass/OR cardiopulmonary by-pass.mp] AND [exp ventilation/OR ventilation.mp OR exp lung/OR lung.mp] AND [exp respiratory function tests/OR respiratory function.mp OR gas exchange.mp OR oxygenation.mp OR lung function.mp].

A total of 187 relevant papers were found from which 9 papers were selected as representing the best evidence on this topic

Seven clinical studies were found in 202 patients. The studies investigated a wide variety of ventilatory strategies during cardiopulmonary bypass (CPB) including CPAP with positive airway pressures of 5–15 cm H2O, high frequency low volume ventilation, inspired oxygen concentrations from 21% to 100% and bilateral extra-corporeal circulation using the lungs to oxygenate the blood while on bypass. In addition, two relevant animal studies were also included.
In an experimental study in pigs by Lamarche et al, ventilation during CPB prevented the occurrence of endothelial dysfunction arising after reperfusion of the pulmonary arterial tree. It also significantly improved the PaO2/FiO2 ratio. However, this model did not include aortic cross-clamping and cardioplegic arrest.

Magnusson et al, assessed the utility of continuous positive airway pressure (CPAP) in 6 pigs. Unfortunately no difference in either the intrapulmonary shunt fraction or the occurrence of atelectasis post-operatively as demonstrated by CT scanning was found.

In a non-randomised series of 34 low-risk patients undergoing conventional elective CABG patients, Massoudy et al demonstrated that the increase in extravascular thermal volume noted after conventional CPB was not observed in patients undergoing bilateral extra-corporeal circulation with continuous pulmonary perfusion and ventilation. This technique (the Drew Technique) uses the patients own lungs to oxygenate the lungs while on CPB. However, inflammatory markers, SVRI, CI, and PaO2/FiO2 ratio were not significantly improved post-surgery.

Gilbert et al performed a study comprising of 18 patients undergoing CABG. Nine patients had CPAP during CPB and 9 patients did not. However, no difference in lung resistance was noted between patients receiving CPAP and those receiving no CPAP. The authors concluded that low levels of CPAP applied during CPB did not significantly change either mechanical properties or oxygenation.

Loeckinger et al reported in an RCT of 14 patients undergoing elective cardiac surgery that CPAP at 10 cm H2O during CPB improves postoperative gas exchange. At 4 h post-surgery arterial oxygenation was improved by about 20%, the shunt fraction was halved, and blood flow to underventilated areas of lung was significantly reduced. They concluded that the simple manoeuvre of 10 cm H2O of CPAP was a simple intervention to improve post-operative respiratory function.

In an RCT of 30 patients undergoing elective myocardial revascularization, Cogliati et al showed that lung inflation with air (static inflation with PEEP=5 cm H2O and FiO2=0.21) during CPB, effectively preserved respiratory system mechanics as compared to deflated lungs or lungs inflated with 100% O2. While all groups showed a deterioration in lung function post-operatively, this deterioration was least significant in the CPAP group with FiO2 of 21%.

Berry et al randomised 61 patients to no CPAP, CPAP at 5 cm H2O ventilating with air or CPAP at the same level with 100% oxygen. They found that alveolar-arterial oxygen partial pressure difference (PAO2-PaO2) was improved for the CPAP groups at 30 min post-surgery but not at 4 or 8 h. The time to extubation and early extubation were also not affected by the use of CPAP. In addition, there were several cases where the surgeon demanded that the lungs be deflated due to difficult surgical access.

Zabeeda et al studied 75 patients who were split into 5 groups receiving CPAP, and high frequency ventilation with either 21% or 100% inspired oxygen. The alveolar-arterial oxygen gradient was lower and the PaO2 was higher 5 min after bypass in patients receiving CPAP (100% O2), but this difference disappeared on chest closure and post-operatively. No other differences were found between groups in this study.

Berry et al studied 90 patients undergoing CABG using a range of CPAP, continuous ventilation and non-ventilated techniques. There was an increase in extravascular lung water in all groups, and decrease in post-operative oxygenation, being most pronounced in patients with 15 cm H2O of CPAP as compared to those with 5 cm H2O of CPAP or controlled mechanical ventilation. No significant improvements compared with no ventilation were demonstrated.

A wide range of ventilatory strategies while on cardiopulmonary bypass have been attempted including CPAP with positive airway pressures of 5–15 cm H2O, high frequency low volume ventilation (100 breaths per min), inspired oxygen concentrations from 21% to 100% and bilateral extra-corporeal circulation using the lungs to oxygenate the blood while on bypass. While some small and transient benefits for CPAP with 10 cm H2O have been demonstrated no convincing clinical benefits for any of these strategies have been shown and thus ventilation while on Cardiopulmonary bypass cannot be supported as a strategy to improve post-operative lung function.

1. Lamarche Y, Gagnon J, Malo O, Blaise G, Carrier M, Perrault LP.. Ventilation prevents pulmonary endothelial dysfunction and improves oxygenation after cardiopulmonary bypass without aortic cross-clamping.
2. Magnusson L, Zemgulis V, Wicky S, Tyden H, Hedenstierna G.. Effect of CPAP during cardiopulmonary bypass on postoperative lung function. An experimental study.
3. Massoudy P, Piotrowski JA, van de Wal HCJM, Giebler R, Marggraf G, Peters J, Jakob HG.. Perfusing and Ventilating the patient's lungs during bypass ameliorates the increase in extravascular thermal volume after coronary bypass grafting.
4. Gilbert TB, Barnas GM, Sequeira AJ.. Impact of pleurotomy, continuous positive airway pressure, and fluid balance during cardiopulmonary bypass on lung mechanics and oxygenation.
5. Loeckinger A, Kleinsasser A, Lindner KH, Margreiter J, Keller C, Hoermann C.. Continuous positive airway pressure at 10 cm H(2)O during cardiopulmonary bypass improves postoperative gas exchange.
6. Cogliati AA, Menichetti A, Tritapepe L, Conti G.. Effects of three techniques of lung management on pulmonary function during cardiopulmonary bypass.
7. Berry CB, Butler PJ, Myles PS.. Lung management during cardiopulmonary bypass: is continuous positive airways pressure beneficial.
8. Zabeeda D, Gefen R, Medalion B, Khazin V, Shachner A, Ezri T.. The effect of high-frequency ventilation of the lungs on postbypass oxygenation: A comparison with other ventilation methods applied during cardiopulmonary bypass.
9. Boldt J, King D, Scheld HH, Hempelmann G.. Lung management during cardiopulmonary bypass: influence on extravascular lung water.