Fig. 11.1
CT scan of a patient who developed adult respiratory distress syndrome after thoracotomy. CT scan of a patient following thoracotomy for left upper lobectomy who subsequently developed adult respiratory distress syndrome: There is space where the lung tissue was resected, atelectatic areas in the remaining lung tissue, infiltrations in both lungs without any clinical signs of infection, and subcutaneous emphysema
A reduced functional lung volume may result from resection of parenchyma, atelectasis, lung edema, and thoracic restriction from postoperative pain.
Decreased functional residual and volume capacities, dysfunction of the diaphragm and intercostal muscles, and increased airway resistance may cause impaired ventilation.
Ventilation-perfusion mismatch and decreased minute ventilation may lead to impaired gas exchange [6].
In addition, excessive intravenous fluid infusion and blood transfusion can directly harm or exacerbate harm to the lungs.
Actually, mechanical ventilation in the PACU or ICU should be avoided if possible, since it can cause a “ventilator-associated or ventilator-related lung injury” or worsen it. Every attempt of invasive mechanical ventilation is associated with a risk of making things worse while trying to improve the patient’s condition. This risk is higher in patients after thoracotomy because the lungs (both the operated and the ventilated lung) have already been exposed to a “first hit” during the operation. In addition, clinical experience would suggest that positive pressure ventilation can injure fresh anastomoses or bronchial stump, although there is no evidence for this plausible assumption.
11.3 Practical Hints
Pragmatic rules that would help to decrease the possibility of having unwarranted events when deciding to continue mechanical ventilation after thoracic operations:
On the one hand, anesthesiologists, surgeons, and intensivists have to avoid postthoracotomy mechanical ventilation. On the other hand, the longer the patient has to deliver an increased work of breathing, the later he will recover from respiratory failure.
Spontaneous breathing is better than mechanical ventilation, and assisted ventilation is better than controlled one. However, the need for tracheal re-intubation can be considered as a worst case scenario.
The decision to ventilate should be made intraoperatively, and preoperative predictions should be continuously reevaluated.
If mechanical ventilation needs to be continued, the intraoperative double-lumen tube (DLT) should be replaced at the end of surgery with a normal single-lumen tracheal tube. However, in patients who are intended to be extubated within two hours postoperatively, the DLT may remain in place with a deflated bronchial lumen cuff.
Transition to a single-lumen tube should be performed via a tube exchanger of sufficient length (caveat: DLTs are longer than single-lumen tubes). It should be kept in mind that an “easy” intubation at the start of the operation may later become “difficult” due to various reasons such as airway edema.
In a patient, in whom postoperative ventilation is planned, the use of a bronchial blocker (BB) can be indicated because this avoids the transition from the double- to a single-lumen tube. Thus, the BB has to be removed only.
A Univent® tube (LMA North America Inc, San Diego, CA) can remain in place for postoperative ventilation, but the blocker should be pulled back into the main lumen.
Finally, weaning from mechanical ventilation is a process that should start on admission of a patient to ICU whose trachea is intubated.
11.4 Protective Lung Ventilation
Actually, the concept of “protective lung ventilation” (PLV) was defined and determined in ARDS patients [7], but this approach becomes even more important in the vulnerable lungs of patients after thoracic surgery. PLV includes:
Low tidal volumes (TV) of 6–8 ml/kg
Appropriate positive end-expiratory pressure (PEEP)
Recruitment maneuvers (RM)
Meta-analyses have found PLV to be effective and protective in both ARDS in the ICU and in OLV [8–10]. An intraoperative TV of 6–8 ml/kg has been associated with a decreased frequency of postoperative pulmonary failure [11]. Although there is no evidence that the same argument is also valid for the postoperative period, there is clear evidence for using these guidelines in general ICU patients. Moreover, this circumstance means to have a reduction of functional lung tissue that is similar to the “baby lung” in ARDS [12].
The details of this strategy are extensively discussed elsewhere in this book; the authors will only focus on some recent dilemmas:
- 1.
Is any particular component “more” important than the other? Recently, it has been reported that the driving pressure (defined as TV/respiratory system compliance) (DP) is the ventilation variable that best classifies as a risk of ALI in ARDS patients [13]. Changes in DP play a much more important role as compared to PEEP or peak inspiratory pressure (PIP). It is questionable, whether it is more appropriate to define the PLV with “low DP” (of less than approximately 20 cmH2O) rather than “low TV.”
- 2.
Is a TV of 6 mL/kg protective enough? Considering that thoracic surgery is usually associated with a reduction in lung volume, e.g., in a patient after pneumonectomy, 6 mL/kg would mean again to be too high and maybe not protective anymore. In an animal study, applying the same TV to one lung compared with two lungs has resulted in significantly greater lung injury shown in histologically assessed “diffuse alveolar damage” score [14]. On the other hand, halving the TV to 3–4 mL/kg, its size would decrease below dead space ventilation. Empirically, a TV of 4–6 mL/kg seems rational, but needs to be proven and checked on an individual basis.
- 3.
What if the DP is still high even if TV is kept low? In cases of severely decreased lung compliance and/or severe reduction effective lung volume, very high driving pressures can be necessary even for low TVs. Although it is a very rare condition, the so-called ultraprotective ventilation (application of extracorporeal lung assist (ECLA) systems) might become necessary. It has been shown in two studies (an animal study [15] and a clinical study [16]) that ECLA helps to decrease the TV to very low amounts to avoid high pressures during ALI in the postoperative period. The resulting survival rate was much higher than in the conventional setting (100 % in the animal study and 86 % (six of seven patients) in humans). ECLA is discussed in another chapter in this book.
- 4.
“How to apply ‘PEEP’?” PEEP is “good” not only for the improvement of oxygenation but also (and maybe more importantly) for the improvement of the V/Q relationship in the dependent lung and for prevention of alveolar collapse at end expiration by increasing the functional residual capacity (Fig. 11.2) [17]. However, excessive PEEP can also lead to an unnecessary and harmful rightward shift of the ventilation in pressure-volume curve (Fig. 11.3). Moreover, although it is not evidence based and may even sound irrational, “clinical experience” would suggest that positive pressure ventilation can injure fresh anastomoses or bronchial stumps. An approach to keep PEEP “as high as necessary” and “as low as possible” can help to overcome both atelectasis and alveolar overdistension [18]; but practically, this issue is more complicated than at first sight. A “decremental trial” following a recruitment maneuver (RM) (stepwise decline of PEEP from 20 cm H2O) to adjust the best compliance appears to be appropriate [19].
Fig. 11.2
Relationship of FRC (functional residual capacity) and CC (closing capacity) in different ventilatory settings. Right: FRC falls below CC during mechanical ventilation; a larger tidal volume (TV) can obtain a better gas exchange (note the larger area above the CC line); however, a cyclic recruitment cannot be avoided. Left: Applying PEEP during keeping the TV low: PEEP obtains an FRC above the CC. Cyclic recruitment is avoided; and the ventilation (now the area above the “new” FRC) is still better than the one without PEEP (Adapted from [17] (with permission))
Fig. 11.3
Relationship of PEEP and LIP (lower inflection point). Note that LIP can differ in each individual and can sometimes be zero. A, B, and C are possible points for total (intrinsic + external) end-expiratory pressure. The level of external PEEP should be adjusted to get closer to LIP, e.g., if the external PEEP brings the total PEEP from A to B, oxygenation gets better, but if the external PEEP brings the total PEEP from B to C, oxygenation gets impaired; if the LIP is 0, the best oxygenation is obtained by A (Adapted from [17] (with permission))
- 5.
How to recruit? While PEEP can keep the lung open, it is not capable of opening an atelectatic lung. To open collapsed regions, a recruitment maneuver (RM) is necessary [20]. However, in patients with air leak, RM is contraindicated; moreover, in patients without an air leak (or with a small one), there is a common “fear” of the high pressure generated by RM, and PEEP may disrupt bronchial stumps and anastomoses. RM after thoracic surgery is an issue, of which pros and cons have to be examined in the individual clinical setting.
11.5 Permissive Hypercapnia
Clinicians tend to compensate the reductions in TV by an increase in frequency to maintain the minute ventilation volume. However, this might be wrong:
- 1.
The price of shorter inspiration can be a higher airway pressures, and the consequence of shorter expiration can be air trapping and auto-PEEP.
- 2.
Physically, it is the “power” that plays a role in the lung injury (rather than “work”), and therefore “the number of the hammer hits per time” is also important (quote of Luciano Gattinoni). Increasing the respiratory rate (=hits with the hammer) increases the energy that causes the lung injury.
- 3.
More importantly, mild hypercapnia is not only something that can be permitted in many cases [21], it can also be even therapeutic for several hours [22]. Permissive hypercapnia may protect the lung and improve the tissue oxygenation as a result of the increased cardiac output and the resulting right shift of the oxygen (O2) saturation curve [23].
- 4.
On the other hand, it should be kept in mind that hypercapnia exacerbates hypoxic pulmonary vasoconstriction, and therefore, it is contraindicated in pulmonary hypertension, which is more frequent in patients after thoracotomy. In the remaining population, permissive hypercapnia can be considered as a standard procedure of protective lung ventilation.
11.6 Inspired Oxygen Fraction
Increased O2 consumption in postoperative patients has led to a routine administration of supplemental O2. However, it has been shown that this approach could be more harmful than beneficial [24]. Although this study was performed in medical emergencies, the mechanism of the damage from high FiO2 can be viewed as valid for patients after thoracic surgery. These are the postulated pathways of possible damages caused by hyperoxia:
- 1.
Coronary and systemic vasoconstriction leading to a decreased stroke volume.
- 2.
Even a short period of preoxygenation with an FiO2 of 1.0 can lead to atelectasis as a result of collapsed alveoli because of the replacement of nitrogen [25].
Obviously, hypoxemia of the postoperative patient should be treated, but one still has to avoid hyperoxia: Hypoxemia should be treated with stepwise increases in FiO2 as high as necessary to avoid hyperoxia [24].
Recently, increasing the FiO2 prior to application of the bundle of “low TV-PEEP-RM” has been advocated: the so-called permissive atelectasis. Although this suggestion was limited to mechanical ventilation during anesthesia of the “healthy” lungs, the extrapolation to postthoracotomy patients should be examined [18].
11.7 Ventilation Mode
Considering that it is the “driving pressure” (DP) that is the principle reason for lung injury, it appears to have less or even no meaning whether to apply the same DP with pressure-controlled (PCV) or volume-controlled way (VCV). Previous studies advocating PCV because of its “descending flow pattern” that resembles more to physiologic spontaneous breathing in OLV [26] have not been confirmed in more recent studies with similar settings [27]. The effects during postoperative period can be considered to be similar.
The only difference between these ventilation modes is probably the lower peak (not the plateau) airway pressures, which contributes less (if any) to ALI. Recently it has been shown in OLV that PCV was more associated with an improvement in right ventricular function than VCV.[28] Right ventricular function is crucial for patients after thoracic surgery; however, whether the reported advantage can also be extrapolated for the postoperative period also remains to be examined.
Physiological breathing is irregular in all its components (TV, frequency, sighs, etc.). It has been shown in an experimental ALI study that a so-called “noisy” pressure support ventilation was associated with an improvement in oxygenation and also a redistribution of pulmonary blood flow [29].
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