Cerebral Oxygenation After Lung Resection

Surgery remains the treatment of choice for patients with resectable lung cancer. However, a significant proportion of patients undergoing lung resections have the associated condition COPD,1 which increases the risk of perioperative complications and death. New techniques in anesthesiology and critical care have enabled patients with COPD to have better outcomes following lung resections. Nowadays, patients with limited lung function, who would have been denied surgery according to the criteria proposed in the past, may undergo pulmonary resection with a low mortality rate.2

Lung resection results in loss of lung parenchyma including residual healthy lung tissue and in reduction in the pulmonary vascular bed. A decrease in residual pulmonary vascular bed after lung resection causes an increase in the right heart afterload, and in others, it would be associated with an increase in the right heart preload.3

The removal of lung parenchyma from patients with carcinoma of the lung, may lead to cardiopulmonary failure or death. A predicted postoperative forced expiratory volume in one second (FEV1) less than 0.8 to 1.0 liter is considered an indicative of a high risk of postoperative chronic ventilatory insufficiency. After pneumonectomy, FEV1 decreases by 29-35% and forced vital capacity (FVC) decreases by 27-44%. After lobectomy, FEV1 and FVC decrease to12-23% and 10-30%, respectively.4

After lobectomy in patients with normal pulmonary functions, there is a transient good maintenance of gas exchange for only 6-12hours, then it is followed with progressive deterioration in oxygen delivery and intra-pulmonary shunt fraction because of peripheral atelectasis 4-13 days after surgery.5 Other investigators reported a significant decrease in maximal oxygen uptake (VO2-Max) and maximal work rate (WR-Max) by 27% and 42%, respectively, 3 months after pneumonectomy, and by13% and 2%, respectively after lobectomy.

In patients with moderate-to-severe pulmonary dysfunction there is significant worsening of pulmonary gas exchange; especially during one-lung ventilation (OLV) which is the mandatory technique to facilitate thoracic surgery. This worsening is more marked in patients undergoing right thoracotomies after lung resection.6

Postoperative lung function changes in the elderly followed the similar trend as in patients with pulmonary dysfunction. The mean postoperative decrease in FEV 1 was 14.16% in the elderly, compared with a 29.23% decrease in patients with normal lung function ( P < 0.05). However, the operative morbidity in the elderly group was significantly lower than in patients with pulmonary dysfunction (23.3% vs. 60%).7

The potential for postoperative neurocognitive dysfunction and its impact on the postoperative course has gained recent attention over the past few years.8 There is an interesting study for the changes in brain tissue oxygenation (rSO2) during OLV for thoracic surgery using near infrared spectroscopy (NIRS), otherwise known as cerebral oximetry, is a non-invasive device that uses infrared light to estimate brain tissue oxygenation which may occur during OLV. The investigators reported significant changes in rSO2 occur during OLV for thoracic surgical procedures without changes in hemodynamic or ventilatory parameters. They recommended future studies to determine the impact of such changes on the postoperative course of these patients.9

According to the above evidences, the changes in oxygen delivery, oxygen uptake and intrapulmonary shunt after lung resection will be reflected on the cerebral blood flow and oxygen delivery and jugular bulb oxygen saturation in patients with impaired pulmonary functions rather than those with healthy lung functions.

Oxygenation of cerebral venous outflow has been investigated as a neuro-monitor for more than 50 years.10-12 Currently, jugular venous oxygen saturation (SjVO2) provides an indirect assessment of cerebral oxygen use and is used to guide physiologic management decisions in a variety of clinical paradigms.13-14 This is simply can be achieved through introducing of an intravascular catheter, similar to those used for central venous pressure monitoring, may be placed retrograde, via the internal jugular vein, into the jugular bulb at the base of skull.15

Jugular venous oxygen is an indirect assessment of cerebral oxygen use. Simplistically, when demand exceeds supply, the brain extracts greater oxygen, resulting in decreased jugular bulb oxygen saturation. If cerebral blood flow (CBF) decreases, a point is eventually reached at which the brain can no longer completely compensate for decreased CBF by a further increase in oxygen extraction. At this point, oxygen consumption decreases and anaerobic metabolism with lactate production ensues. When cerebral oxygen supply exceeds demand, oxygen saturation of jugular bulb blood is increased.15

To our knowledge there is no any study was done on the changes in cerebral oxygenation after lung resections, especially in the high-risk group with pulmonary dysfunction.

Project Objectives:

We hypothesize that the lung resection would be associated with lower jugular bulb oxygen saturation in the patients with severe pulmonary dysfunction than in the patients with healthy lung functions.