Intraoperative Ventilation Strategies for Thoracic Surgery

Abstract

Ventilatory strategies for one-lung ventilation (OLV) should take into account preventing intraoperative hypoxemia, intraoperative alveolar stress, and postoperative ventilator-induced lung injury (VILI). A lung-protective strategy utilizing low tidal volumes (< 6 mL/kg of predicted body weight) and limited plateau inflation pressures (<25 cm H₂O) is clearly indicated for patients at high risk for developing postoperative acute respiratory distress syndrome (ARDS) or acute lung injury (ALI). Based on this recent data, the use of low tidal volumes and inflation pressures during OLV is appropriate as long as high breathing frequencies are not required and permissive hypercapnia is not contraindicated. With appropriate use of pressure and tidal volume alarms, either pressure- or volume-controlled ventilation may be used. Intrinsic positive end-expiratory pressure (PEEP) is common with OLV (utilizing a double-lumen endotracheal tube), and caution is warranted when high respiratory rates (short exhalation times) are utilized.

The addition of external PEEP does not consistently improve oxygenation and has not been shown to reduce the incidence of VILI.

A lung-opening procedure (LOP) utilizing several breaths of high inspiratory and expiratory pressures may improve oxygenation, but the hemodynamic consequences of the maneuver must be considered. While no evidence-based specific recommendations can be made for OLV, the growing body of OLV research does help the anesthesiologist select the best strategy for an individual patient and surgery.

Recognition of Denham S. Ward, MD, author of the first edition chapter and on whose work this edit is based.

Clinical Case Discussion

A 72-year-old woman, with weight = 98 kg, height = 168 cm (BMI = 34.7, PBW = 60.3 kg), and a 43 pack-year smoking history (stopped smoking 2 weeks ago), presents for left upper lobectomy for small cell carcinoma via a left VATS. Past medical history includes hypertension, type 2 DM, and obstructive sleep apnea (CPAP at 10 cm H₂O nightly).

Preoperative pulmonary function testing showed:

• FVC = 2.82 L (57% predicted).

• FEV₁ = 1.58 (42% predicted).

• FEV₁/FVC = 56%.

• DLCO = 23.9 mL/min/mmHg (79% predicted).

A left 37 French DLT was placed without difficulty, and its correct position was confirmed via fiber-optic bronchoscopy. Two-lung ventilation was initiated, while the patient was supine with VCV incorporating a 10% end-inspiratory pause with a tidal volume of 550 mL and a rate of 10 breaths/min. Peak airway pressures were 22 cm H₂O and the P_ETCO₂ was 45 mmHg. SpO₂ = 98% on 100% oxygen.

• (a) What mode of ventilation and inspiratory gas concentration would you use for initiating OLV? What tidal volume would you use?

  Either PCV or VCV would be acceptable. Initial tidal volume should be set based on the PBW, typically at 4–6 mL/kg. 6 mL/kg × 60.3 kg PBW = 361 mL, so initial tidal volume should be reduced and the OLV peak and plateau pressures noted.

• (b) After setting the tidal volume to 361 mL with a rate of 14 and 0 end-expiratory pressure (ZEEP), the peak inspiratory pressure is 28 cm H₂O, and the P_ETCO₂ is 49 mmHg. Is any further adjustment of the ventilator required? Would other clinical measurements be useful?

  With the peak inspiratory pressure less than 30 mmHg (presumable if VCV is being used, the plateau pressure, which is more reflective of the alveolar distending pressure, will be less than the peak) and the end-tidal CO₂ at an acceptable level, no further adjustments are needed. Initially observing the end-tidal CO₂ (P_ETCO₂) can guide the respiratory rate setting, but a blood gas would be helpful because the increased alveolar dead space associated with this patient’s COPD may result in a significant arterial to end-tidal gradient.

• (c) What would your recommendation for PEEP be after making these adjustments?

  At low tidal volumes and in patients with ALI, PEEP may help reduce the opening and closing of atelectatic regions of the lung, improving oxygenation and possibly prevent further lung injury. However, a high PEEP may also reduce oxygenation during OLV by forcing more blood flow to the unventilated lung. PEEP up to 5 cm H₂O may be used but higher levels should be instituted cautiously.

• (d) Thirty minutes after the start of OLV, S_pO₂ falls to 88%. What maneuvers could be employed to stabilize the S_pO₂?

  Whenever there is an acute decrease in the S_pO₂, after increasing the FiO₂, the position of the DLT must be carefully checked with a fiber-optic bronchoscopy. In this case entry of the left bronchial lumen into the left lower lobe orifice could result in the tracheal opening of the DLT to abut the carina and result in a decrease in right lung ventilation.

A lung opening procedure (LOP) with a few breaths of high PEEP and inspiratory pressure may also be of benefit, but caution must be exercised if there is any indication of hemodynamic instability.

If hypoxemia still persists after optimal positioning of the DLT and a LOP, then CPAP to the unventilated lung is the most reliable way of decreasing the venous admixture; however, this is unlikely to provide acceptable operating conditions for a VATS. Switching to PCV or increasing the end-inspiratory pause with VCV may be useful. With a large DLT and a respiratory rate of only 14, significant intrinsic PEEP is unlikely, but a reduction in the inspiratory rate (with perhaps an increase in the tidal volume) can be tried.

A blood gas should be obtained and the surgeon notified that it may be necessary to return to two-lung ventilation intermittently if the saturation falls any lower. Since a low cardiac output will cause hypoxemia during OLV, interventions to increase the cardiac output may be of value.