Abstract
Background
Before the chest is closed, the airtightness of the remaining lung is regularly checked after anatomical and non-anatomical lung resections. The thoracic cavity is filled with sterile water and the lungs are reventilated with a peak inspiratory pressure (Pinsp) of +25 mbar at a positive end-expiratory pressure (PEEP) of +5 mbar. The surgeon inspects the surface of the lung, especially the sutures, for leaks. In the event of a leak, air escapes in varying amounts; this can range from individual air bubbles to a massive leak of air. At this stage, the surgeon is still able to take corrective measures. Methods range from suturing to covering the leak site with a collagen fleece. An overlooked leak usually has serious consequences. Despite the leak test described above, air leaks continue to occur postoperatively. This ex vivo study on pig lungs aims to investigate whether an air leak can be better unmasked by extending the inspiration in the form of a ramp or by maintaining Pinsp for 5 seconds (“inspiratory hold”).
Methods
Heart-lung packages removed from freshly slaughtered pigs (weight: 90 kg) were connected to a ventilator via a tracheally inserted tube. Compared to the standard leak test (Pinsp = +25 mbar, PEEP = +5 mbar, frequency 10 1/min), two groups of n=15 each were examined. Group 1: inspiratory ramp 2.0 and group 2: “inspiratory hold” for 5 seconds at an inspiratory pressure of +25 mbar. Air tightness of lung lesions (diameter: 1 cm) with a depth of 0.8 and 1.8 cm was examined. A group comparison was performed using a nonparametric Mann-Whitney U test (P<0.05).
Results
The comparison of the standard group versus the ramp group was not significant at a lesion depth of 0.8 cm after 1 minute (P=0.07). This also applies to a lesion depth of 1.8 cm (P=0.09). After 5 minutes, the standard group showed significantly better recognition compared to the ramp group at both 1 and 5 minutes (P=0.03 and P=0.03). When comparing the standard group to the “inspiratory hold”, this group showed a highly significant detection of air leaks, particularly in lesions measuring 0.8 cm. This result was not as distinct for the deeper lesion. After an observation period of 5 minutes, the “inspiratory hold” group was nevertheless superior to the standard group at both lesion depths (P=0.008 and P=0.02).
Conclusions
The intraoperative detection of air leaks from the lung parenchyma can be improved by an “inspiratory hold” maneuver compared to the standard approach.
Keywords: Bronchopleural fistula, inspiratory ramp, inspiratory hold, leak test, airtightness test
Highlight box.
Key findings
• Improvement of intraoperative control for bronchopulmonary leakage with an inspiratory hold test.
• Changing the inspiratory ramp does not improve intraoperative detection of bronchopulmonary leaks.
What is known and what is new?
• Despite the currently employed intraoperative control for air leaks up to an inspiratory pressure of 25 mbar, postoperative pulmonary air leaks can occur.
• By modifying this widely employed pressure test, applying 25 mbar, the detection rate of postoperative air leaks may potentially be improved.
What is the implication and what should change now?
• The inspiratory hold test has the potential to become a routine test for intraoperative detection of air leaks. However, the results of our study require confirmation in clinical studies.
Introduction
Postoperative air leak is a common problem after lung resection procedures (1-3). According to the Society of Thoracic Surgeons General Thoracic Surgery Database (STS GTSD), prolonged air leak (>5 days postoperatively) occurred in 10.4% after resection of lung cancer (4). The consequences of a postoperative air leak are a prolonged period of time in which chest tubes are in place and a prolonged postoperative stay (5). In some cases, the chest may need to be reopened and the leak site closed. In addition, this increases the overall costs for inpatient treatment (6). The intraoperative detection of air leakage after resecting anatomical and non-anatomical surgery is very important (7). Routinely, after a lung resection is performed, a leak test is performed before the chest is closed. To do this, the chest cavity is filled with sterile water and the previously unventilated remaining lung is ventilated again with an inspiratory pressure (Pinsp) of +25 mbar at a positive end-expiratory pressure (PEEP) of +5 mbar and a frequency of 10 1/min. Similar to a leak test on a bicycle tube, the surgeon inspects the surface of the lungs and especially the seams for air leaks. As a rule, you wait a few minutes. An air leak can range from small bubbles escaping to massive air loss. If an air leak is detected, ventilation is restarted and the area is inspected. The surgeon decides whether a closure measure is necessary. For this purpose, a simple suture, gluing (8-12) or the application of a collagen fleece (8,12-14) can be carried out. The success of this measure is checked by re-ventilating the lungs after filling the chest cavity with sterile water. In individual cases, this procedure can be repeated. In any case, the chest should only be closed when you are sure that there is no longer a relevant air leak. Although the leak test carried out intraoperatively is negative, there are always cases in which a postoperative air leak becomes apparent in the further clinical course.
The aim of this work was to use an ex vivo model of the pig lung to investigate whether prolonging inspiration in the sense of a ramp or merely maintaining the Pinsp at +25 mbar for 5 seconds appears to be suitable for detecting possible air leaks more reliably. We present this article in accordance with the ARRIVE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1720/rc).
Methods
The heart and lung package were removed en bloc from freshly slaughtered pigs [European Union (EU) standard: 90 kg]. The specimens were inspected on site to ensure that they were intact. Packed into a cooling box at 4 ℃ they were transported to our laboratory within 10 minutes. The specimens were inspected again and endobronchial mucus was aspirated. A ventilation tube [Charriere (CH) 7.5] was inserted into the trachea and secured with a cable tie. Additionally, the tube was blocked with 10 mL of air. The preparation was placed in a tub and the tube was connected to a ventilator (Dräger EVITA 4, Dräger, Lübeck). The lungs were reventilated with a pressure of +20 mbar and inspected once more for possible injuries. In order to detect possible relevant air leaks, the tube was additionally filled with water. Lungs that were injured during the removal were no longer used for the study. Intact lungs were assigned to individual groups. In group 1 (control group) (n=15), lungs were ventilated at a Pinsp of +25 mbar and a PEEP of +5 mbar at a frequency of 10 1/min. In group 2 (n=15), a ramp 2.0 was set on the ventilator during inspiration at the same pressure. Group 3 (n=15) included all lungs in which an “inspiratory hold” of +25 mbar was continuously maintained on the ventilator for 5 seconds (Figure 1). Ramp was defined as the time to maximum inhalation pressure.
Figure 1.
Experimental setup.
On the lung surface, a circle with a diameter of 1 cm was marked in a suitable position using a template with a tissue marker. This marked circle was then cut out in cylindrical form to a depth of 0.8 or 1.8 cm. The respective depth was checked with a rod with “mm” markings. This resulted in cylindrical lesions with the respective depth (Figure 2). First, air leakage was examined by means of an underwater sample for the individual groups. The amount of escaping air was assessed visually using an established score (15). Accordingly, a score of 0= airtight, 1= leakage of individual air bubbles, 2= leakage of a continuous chain of air bubbles, and 3= massive air leakage.
Figure 2.
Preparation of defined lesions in pulmonary tissue. (A) Marking the diameter of the planned lesion. (B) Creation of a standardized lesion (0.8 cm in diameter and 1.8 cm depth).
In addition, the amount of escaped air per ventilation was quantified. For this purpose, the expired air was collected in a funnel connected to a measuring cylinder. The air rising vertically upwards displaced the water in the measuring cylinder. The amount of air expelled per ventilation was read off the measuring scale in mL (Figure 3).
Figure 3.
Measurement of the amount of air leakage (mL/ventilation) through a funnel placed over the lesions.
The amount of air per ventilation was determined after one and after five minutes. Using a tissue marker, a circle with a diameter of 1 cm was marked on a suitable spot on the lung surface employing a template.
Statistical analysis
The data obtained were analysed employing the following statistical methods: the respective mean values with their standard deviations were calculated from the measured values. The groups are compared with each other using a non-parametric Mann-Whitney U test (P<0.05). The GraphPad Prism software Version 10.0 (Boston, MA, USA) was used for statistical analysis.
Results
Comparison of groups 1–3: score values and amount of air released per ventilation (mL) at a lesion depth of 0.8 cm
In the control group, 33.3% had a score of 3. A volume of 4.73±5.9 mL of air/ventilation escaped from the lesion. Compared to group 2 (ramp), only 2.52±3.7 mL of air/ventilation escaped there. The score value of 3 was present in 26.6%. The comparison of both groups was not significant (NS) (P=0.07). In group 3, 8.80±3.4 mL of air escaped per ventilation; the comparison to the control group was highly significant (P=0.002). There was a score of 3 in 86.7%. After waiting for 5 minutes, an air volume of 10±9.1 mL air/ventilation was released in the control group. A score of 3 occurred in 93.3%. In group 2, this was only 5.13±6.5 mL air/ventilation and in 53.3% of cases, a score of 3. The difference was significant in favor of the control group (P=0.03). In group 3, 20.8±8.1 mL of air/ventilation escaped after 5 minutes. In 100% of cases, there was a score of 3. In comparison with group 1, there was a highly significant result (P=0.008). Tables 1-5 show the results at a glance.
Table 1. Results for group 1 (n=15).
| Depth of lesion | Score after 1 min | Air volume (ml/ventilation) after 1 min | Score after 5 min | Air volume (ml/ventilation) after 5 min |
|---|---|---|---|---|
| 0.8 cm | 33.3% Score 3 | 4.73±5.9 | 93.3% Score 3 | 10.00±9.1 |
| 1.8 cm | 93.3% Score 3 | 27.67±32.2 | 100% Score 3 | 48.93±38.6 |
Group 1: ventilation with an inspiratory pressure of +25 mbar and a PEEP of +5 mbar at a frequency of 10 1/min. Lesion scores (0= airtight, 1= leakage of individual air bubbles, 2= leakage of a continuous chain of air bubbles and 3= massive air leakage) for different lesion depths are expressed as percentages. The volume of air is presented as leaked in mL/ventilation ± standard deviation after 1 and 5 minutes. PEEP, positive end-expiratory pressure.
Table 2. Results for group 2 (n=15).
| Depth of lesion | Score after 1 min | Air volume (ml/ventilation) after 1 min | Score after 5 min | Air volume (ml/ventilation) after 5 minutes |
|---|---|---|---|---|
| 0.8 cm | 26.6% Score 3 | 2.52±3.7 | 53.3% Score 3 | 5.13±6.5 |
| 1.8 cm | 80% Score 3 | 11.03±11.7 | 86.7% Score 3 | 24.80±33.2 |
Group 2: a ramp 2.0 was set on the ventilator during inspiration. Lesion scores (0= airtight, 1= leakage of individual air bubbles, 2= leakage of a continuous chain of air bubbles and 3= massive air leakage) for different lesion depths are expressed as percentages. The volume of air is presented as leaked in mL/ventilation ± standard deviation after 1 and 5 minutes.
Table 3. Results for group 3 (n=15).
| Depth of lesion | Score after 1 min | Air volume (ml/ventilation) after 1 minute | Score after 5 min | Air volume (ml/ventilation) after 5 minutes |
|---|---|---|---|---|
| 0.8 cm | 86.7% Score 3 | 8.80±3.4 | 100% Score 3 | 20.80±8.1 |
| 1.8 cm | 100% Score 3 | 29.80±8.5 | 100% Score 3 | 87.53±13.1 |
Group 3: an inspiratory hold of +25 mbar was continuously maintained for 5 seconds. Lesion scores (0= airtight, 1= leakage of individual air bubbles, 2= leakage of a continuous chain of air bubbles and 3= massive air leakage) for different lesion depths are expressed as percentages. The volume of air is presented as leaked in mL/ventilation ± standard deviation after 1 and 5 minutes.
Table 4. Group comparisons of statistical significance after 1 minute.
| Depth of lesion | P value (group 1 vs. group 2) |
P value (group 1 vs. group 3) |
|---|---|---|
| 0.8 cm | 0.07 NS | 0.002** |
| 1.8 cm | 0.09 NS | 0.08 NS |
**P<0.01. Group 1: ventilation with an inspiratory pressure of +25 mbar and a PEEP of +5 mbar at a frequency of 10 1/min. Group 2: a ramp 2.0 was set on the ventilator during inspiration. Group 3: an inspiratory hold of +25 mbar was continuously maintained for 5 seconds. NS, not significant; PEEP, positive end-expiratory pressure.
Table 5. Group comparisons of statistical significance after 5 minutes.
| Depth of lesion | P value (group 1 vs. group 2) |
P value (group 1 vs. group 3) |
|---|---|---|
| 0.8 cm | 0.03* | 0.008** |
| 1.8 cm | 0.03* | 0.02* |
*P<0.05, **P<0.01. Group 1: ventilation with an inspiratory pressure of +25 mbar and a PEEP of +5 mbar at a frequency of 10 1/min. Group 2: a ramp 2.0 was set on the ventilator during inspiration. Group 3: an inspiratory hold of +25 mbar was continuously maintained for 5 seconds. PEEP, positive end-expiratory pressure.
Comparison of groups 1–3: amount of air released per ventilation (mL) at a lesion depth of 1.8 cm
In 93.3% of cases, there was a score of 3. In the control group, 27.67±32.2 mL of air escaped after 1 minute per ventilation. In group 2 (ramp), this was only 11.03±11.7 mL air/ventilation. Only 80% had a score of 3. The comparison of both groups was NS (P=0.09). In group 3, 29.8±8.5 mL of air/ventilation leaked from the lesion. A score of 3 was present in 100%. There was a non-significant difference compared to the control group (P=0.08). After 5 minutes, an air volume of 48.93±38.6 mL/ventilation escaped in group 1.
A score of 3 was 100%. In group 2, 24.8±33.2 mL of air/ventilation leaked. Only 86.7% had a score of 3. If you compare both groups, the difference is significant in favor of the control group (P=0.03). Looking at group 3, 87.53±13.1 mL of air/ventilation escaped from the lesion after 5 minutes. A score of 3 occurred in 100% of cases. Compared to the control group, there was a significant difference in favor of group 3 (P=0.02). Tables 1-5 show the results at a glance.
Discussion
The intraoperative search for a possible air leak after a resecting lung procedure is of great clinical importance. The standard test of ventilation with a Pinsp of +25 mbar at a PEEP of +5 mbar and a frequency of 10 1/min, which has so far been routinely carried out, cannot detect a relevant air leak in every case. A possible cause could be incomplete re-expansion of the operated lung. The work dealt with two alternative ventilation modes with the aim of better detecting air leaks. On the one hand, the inspiratory ramp was significantly lengthened. And in the other group, the Pinsp was maintained at +25 mbar for 5 seconds. Our results suggest that extending inspiration in the form of a ramp does not provide any advantage over the standard approach. This was also evident in the observation of the amount of air escaping. The differences in both lesion depths were not significantly different from the control group. It is possible that the extension of the Pinsp no longer created enough pressure at the lesion sites to detect a significant difference. This situation was still observed even after waiting 5 minutes. At this longer observation period, detection of relevant leaks in the control group was even better. The same was observed with the greater lesion depth of 1.8 cm.
The situation is different for the group in which a so-called “inspiratory hold” maneuver was performed. At the lesion depth of 0.8 cm, the difference between the control group and this group was significant after both 1 minute and after 5 minutes. This means that the inspiratory hold group shows the air leaks more clearly than the control group. Looking at the lesion depth of 1.8 cm, the difference after ventilation of one minute is less distinct, but the “inspiratory hold” maneuver was not inferior to the control group. After 5 minutes of observation, the difference between the two groups was still significant. The “inspiratory hold” group had significant air loss with a lesion depth of 1.8 cm.
Unfortunately, relevant information from the available literature on this topic is missing. Dealing with a modification of a leak test, therefore, makes perfect sense.
We consider the model we used of a ventilated pig lung to be realistic. The lesions were created in a reproducible and comparable manner. By collecting escaping air in a funnel combined with a riser tube, we were able to determine exactly the amount of air that had escaped. In addition, we estimated the amount of air leaked using a standard score. Ventilation was carried out using a ventilator that is also used in clinical practice. It should be noted, however, that the initial assessment of the removed lungs needs to be carried out extremely meticulously to sort out any existing injuries or bleeding so as not to falsify the results. During our investigation, we discarded approximately 20% of the lungs removed for these reasons.
Our results indicate that a simple “inspiratory hold” maneuver effectively improved relevant air leaks intraoperatively. It appears to enhance detection, particularly in more superficial lung parenchymal lesions. This result is certainly of great clinical interest since superficial lung lesions are much more common than deep lesions. They are often clinically underestimated. In our opinion, it would make sense to conduct a prospective randomized clinical study comparing the standard procedure with the “inspiratory hold” maneuver in this regard.
Conclusions
Compared to the mostly employed standard procedure, an intraoperative “inspiratory hold” maneuver can improve the detection of air leaks, especially in superficial lung lesions.
Supplementary
The article’s supplementary files as
Acknowledgments
None.
Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. As our experiments were performed on cadaveric porcine lungs obtained from commercially slaughtered pigs (nutritional purposes, EU-standard 90 kg), there is no ethical concern.
Footnotes
Reporting Checklist: The authors have completed the ARRIVE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1720/rc
Funding: None.
Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1720/coif). The authors have no conflicts of interest to declare.
Data Sharing Statement
Available at https://jtd.amegroups.com/article/view/10.21037/jtd-24-1720/dss
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