RCRMC Anesthesia Residency Journal Club Hypoxemia During One Lung Ventilation Anesthesiology 2009: 110: 1402-11 Hiral Patel, D.O. PGY3 RCRMC Anesthesia Residency Journal Club August 26th, 2009

Review of Hypoxemia during one lung ventilation There are many procedures where one lung ventilation is indicated such as infection/bleeding to one lung, bronchopleural fistula, tracheobronchial disruption, repair of thoracic aortic aneurysm, pnuemonectomy, lobectomies, etc. Hypoxemia during one lung ventilation is a complication that we are faced with routinely and this article discusses the predictors, prevention and treatment of hypoxemia.

Background of study This article reviews and compiles results from multiple studies on the predictors of hypoxemia during one lung ventilation (OLV), prevention of hypoxemia during OLV, and treatment of hypoxemia during OLV. They also present a strategy that they use to prevent hypoxemia during OLV

Predictors Side of operation: right lung > left lung; therefore, oxygenation is better during left thoracotomy. Regression analysis used in a study found this to be an important factor in predicting hypoxemia during OLV. Lung function abnormalities: more severe the obstruction is, the less likely that the patient will experience hypoxemia during OLV. Slinger et al found the less the FEV1, the better oxygenation during OLV. The theory was due to auto peep, but other studies have not found this correlation. Another measure was capillary or ABG analysis. Low PaO2 was reliable indicator of abnormal lung function and predictor of hypoxemia during OLV. Positive correlation. Air trapping in the ventilated lung may generate auto PEEP during OLV and decrease atelectasis

Predictors continued… Distribution of perfusion: can measure preoperatively perfusion scans and help to predict hypoxemia. The less the perfusion of the nonventilated lung is, the greater the perfusion becomes of the ventilated lung resulting in higher PaO2 during OLV. One factor affecting perfusion is location of tumor (central and large tx with pneumonectomy/lobectomy vs small and peripheral tx with wedge resections). ---The authors found that pts undergoing lobectomy/pneumonectomy had better oxygenation during OLV than patients presenting for open or videoscopic metastectomy.

Distribution of perfusion cont… Other factor affecting perfusion is gravity. In supine patients, gravity affects both lungs equally. In lateral position, perfusion is better to the lower ventilated lung. Oxygenation better with lateral decubitus position than supine due to oxygenation increase as perfusion decreases to nonventilated lung. So a patient with poor oxygenation before surgery, even distribution of perfusion between lungs and is schedules to undergo surgery in supine position is very likely to develop hypoxemia!!!!

Prevention of Hypoxemia Improving preoperative lung function: not proven by published data. Improve lung function by physical therapy and drugs to dilate bronchi and loosen secretions. Monitoring lung separation: Using DLT allows easy fiberoptic access to both lungs and crucial for bleeding and secretion. Misplacement or dislodgement of DLT occurs in 12% of patients while positioning or surgical manipulation leading to hypoxemia making fiberoptic monitoring essential.

Prevention of Hypoxemia Good ventilation strategy in the dependent lung: three problems—1) Expansion of the dependent lung is impeded by weight of mediastinum, pressure of abdominal organs, etc. 2) inc of lung volume and pressure may lead to increase in perfusion of nonventilated lung and increase in venous shunting. 3) no viable means of determining best ventilation strategy

Prevention of Hypoxemia Two strategies: high tidal volume (10-12 ml/kg) without PEEP or moderate tidal volume (6-8 ml/kg) with PEEP. Their strategy: Pressure controlled dependent lung ventilation ( Peak pressure 20-30 cm H20 and a PEEP of 5 cm H2O (6-8 ml/kg)). Adjust peak pressures to have 6-7ml/kg in left lung or 7-8 ml/kg in the right lung without altering PEEP. Vent rate and I:E ratio altered to achieve expiration flow at or near 0 and EtCO2 of 30-35 mm Hg. Hypoxemia criteria was arterial desaturation below 90% found a 4% hypoxemia rate while ventilating with FiO2 > 0.5. Pulse ox saturation did not decrease below 91% in any patients.

Prevention of Hypoxemia con’t. Oxygen administration to the nondependent lung: oxygen can be administered with continued positive end expiratory pressure (CPAP) to the nondependent lung. Recent study has shown that reexpansion of nonventilated lung after OLV leads to release of oxygen radicals.

Prevention of Hypoxemia Modulation of Perfusion: studies have been conducted on use of drugs such as nitric oxide to increase perfusion of the ventilated lung or decrease perfusion to the nonventilated lung. In concentration of 5 to 40 ppm, nitric oxide not beneficial. Almitrine decreases perfusion to nonventilated lung by augmenting HPV ( dec shunt fraction and improve oxygenation). Has shown to improve oxygenation.

Prevention of Hypoxemia continued… Type of anesthesia: does not affect oxygenation during OLV (General with volatiles vs TIVA vs. local anesthetic with thoracic epidural anesthesia) Hemoglobin levels: study showed that shunt fraction increases and oxygenation decreases with low hemoglobin levels. Factors leading to decrease in oxygenation: shunted (venous) blood, an increased oxygen extraction (low cardiac output or increased oxygen expenditure) and low hemoglobin levels.

Treatment of Hypoxemia during OLV Two strategies must be applied at the same time: Hypoxemia must be effectively and immediately treated. Also cause of hypoxemia should be addressed. Increasing FiO2: effective immediately. Cannot improve oxygenation if shunt fractions > 40%. This article did show that increasing FiO2 from 0.3 to 0.5 and to 1.0 does improve oxygenation but Fi02 at 1.0 can increase risk of atelectasis. It also states that this can help with hypoxemia until cause of decreased oxygenation is determined.

Treatment of Hypoxemia during OLV Reexpansion of the nonventilated lung: if Fi02 increase does not improve hypoxemia, surgeon must be notified and expansion of nonventilated lung with CPAP must be used. CPAP in 3 – 10 cm H20 is more effective way of improving oxygenation. Must note that pressure of 5-10 cm H20 will not immediately inflate an already collapsed and atelectatic lung and may not be very helpful in increasing oxygenation right away. Therefore, its necessary to reinflate lung with higher airway pressure and then using CPAP to kepp lung at constant level of inflation. High frequency jet ventilation is another method and keeps lung almost immobile helping with operating conditions. Problem is expense of equipment, expertise, and danger of barotrauma

Treatment of Hypoxemia “The most common treatable causes of hypoxemia during OLV are dislodgement of the DLT, inadequate ventilation strategy leading to atelectasis in the ventilated lung, and occlusion of major bronchi of the ventilated lung with secretions or blood.” This article suggest some of the problems can be corrected with fiberoptic monitoring. Expansion of ventilated dependent lung with high pressures to open up atelectasis and increases PEEP and or TV to keep lung open. Recruitment strategies on oxygenation has shown to improve Pa02/Fi02 ratio but also depend on other factors such as if primary ventilation was tailored to avoid atelectasis.

Treatment of hypoxemia Conclusion: hypoxemia may occur in 5-10% of patients undergoing OLV.

So what do we do now? This study does a really good job of breaking down the three concepts. The article has strong points on predictors of hypoxemia as it guides us in practice to look at certain tests and also patient function preoperatively. The article talks about physical therapy to optimize surgical condition but most patients undergoing the procedure are ill and cannot wait to have the procedure done.

Application The authors makes a strong case on using fiberoptic monitoring for such cases as dislodgement or obstruction from the double lumen tube is common. Problem: expertise of the anesthesiologist is necessary and also requires time during the procedure. Different strategies for ventilation during the procedure to prevent hypoxemia were also offered. The problem is that there is not a concrete approach as many of them work and many do not depending on the background of the patient.

Application cont… Size of tumor and type of resection was mentioned as likely predictor of perfusion, which for the anesthesiologist could be critical not just for hypoxemia during the procedure but on managing the airway prior. The study mentions arterial desaturation as the criteria for data collection on hypoxemia yet in clinical practice we are to rely on the pulse oximeter.

Application continued… The biggest problem with this study is that the population used is not indicative of the patients we encounter on a routine basis. The greatest benefit is to use the information offered in this study and tailor your approach for your patient as you see fit.

Current use We encounter VATS, pneumonectomies, lobectomies, wedge resections, etc on a daily basis. This study outlines and breaks down the issues encountered in a systematic way. This article helps us to troubleshoot the problem encountered during thorascopic procedures and gives us a guideline on how to approach and even prevent hypoxemia.