Correlation of lung collapse and gas exchange

Background: Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations. Methods: Shunt, PaO2 and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (Mtotal). We logarithmically transformed PaO2 (lnPaO2) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range). Results: Mtotal was 768 (715–884) g in sheep and 543 (503–583) g in pigs. Atelectasis was 26 (16–47)% in sheep and 18 (13–23) % in pigs. PaO2 (FiO2 = 1.0) was 242 (106–414) mmHg in sheep and 480 (437–514) mmHg in pigs. Shunt was 39 (29–51)% in sheep and 15 (11–20) % in pigs. Atelectasis correlated closely with lnPaO2 (R2 = 0.78) and shunt (R2 = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO2 (R2 = 0.63) and shunt (R2 = 0.34) was weaker in pigs, but R2 increased to 0.71 for lnPaO2 and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO2 and shunt. Discussion and Conclusion: In lung-healthy sheep, atelectasis correlates closely with lnPaO2 and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis

Correlation of lung collapse and gas exchange

Background: Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations. Methods: Shunt, PaO2 and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (Mtotal). We logarithmically transformed PaO2 (lnPaO2) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range). Results: Mtotal was 768 (715–884) g in sheep and 543 (503–583) g in pigs. Atelectasis was 26 (16–47)% in sheep and 18 (13–23) % in pigs. PaO2 (FiO2 = 1.0) was 242 (106–414) mmHg in sheep and 480 (437–514) mmHg in pigs. Shunt was 39 (29–51)% in sheep and 15 (11–20) % in pigs. Atelectasis correlated closely with lnPaO2 (R2 = 0.78) and shunt (R2 = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO2 (R2 = 0.63) and shunt (R2 = 0.34) was weaker in pigs, but R2 increased to 0.71 for lnPaO2 and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO2 and shunt. Discussion and Conclusion: In lung-healthy sheep, atelectasis correlates closely with lnPaO2 and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis

Correlation of lung collapse and gas exchange

Background: Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO2) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations. Methods: Shunt, PaO2 and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (Mtotal). We logarithmically transformed PaO2 (lnPaO2) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range). Results: Mtotal was 768 (715–884) g in sheep and 543 (503–583) g in pigs. Atelectasis was 26 (16–47)% in sheep and 18 (13–23) % in pigs. PaO2 (FiO2 = 1.0) was 242 (106–414) mmHg in sheep and 480 (437–514) mmHg in pigs. Shunt was 39 (29–51)% in sheep and 15 (11–20) % in pigs. Atelectasis correlated closely with lnPaO2 (R2 = 0.78) and shunt (R2 = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO2 (R2 = 0.63) and shunt (R2 = 0.34) was weaker in pigs, but R2 increased to 0.71 for lnPaO2 and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO2 and shunt. Discussion and Conclusion: In lung-healthy sheep, atelectasis correlates closely with lnPaO2 and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis

Correlation of Lung Collapse and Gas Exchange - A Computer Tomographic Study in Sheep and Pigs with Atelectasis in Otherwise Normal Lungs

<div><p>Background</p><p>Atelectasis can provoke pulmonary and non-pulmonary complications after general anaesthesia. Unfortunately, there is no instrument to estimate atelectasis and prompt changes of mechanical ventilation during general anaesthesia. Although arterial partial pressure of oxygen (PaO₂) and intrapulmonary shunt have both been suggested to correlate with atelectasis, studies yielded inconsistent results. Therefore, we investigated these correlations.</p><p>Methods</p><p>Shunt, PaO₂ and atelectasis were measured in 11 sheep and 23 pigs with otherwise normal lungs. In pigs, contrasting measurements were available 12 hours after induction of acute respiratory distress syndrome (ARDS). Atelectasis was calculated by computed tomography relative to total lung mass (M_total). We logarithmically transformed PaO₂ (lnPaO₂) to linearize its relationships with shunt and atelectasis. Data are given as median (interquartile range).</p><p>Results</p><p>M_total was 768 (715–884) g in sheep and 543 (503–583) g in pigs. Atelectasis was 26 (16–47) % in sheep and 18 (13–23) % in pigs. PaO₂ (FiO₂ = 1.0) was 242 (106–414) mmHg in sheep and 480 (437–514) mmHg in pigs. Shunt was 39 (29–51) % in sheep and 15 (11–20) % in pigs. Atelectasis correlated closely with lnPaO₂ (R² = 0.78) and shunt (R² = 0.79) in sheep (P-values<0.0001). The correlation of atelectasis with lnPaO₂ (R² = 0.63) and shunt (R² = 0.34) was weaker in pigs, but R² increased to 0.71 for lnPaO₂ and 0.72 for shunt 12 hours after induction of ARDS. In both, sheep and pigs, changes in atelectasis correlated strongly with corresponding changes in lnPaO₂ and shunt.</p><p>Discussion and Conclusion</p><p>In lung-healthy sheep, atelectasis correlates closely with lnPaO₂ and shunt, when blood gases are measured during ventilation with pure oxygen. In lung-healthy pigs, these correlations were significantly weaker, likely because pigs have stronger hypoxic pulmonary vasoconstriction (HPV) than sheep and humans. Nevertheless, correlations improved also in pigs after blunting of HPV during ARDS. In humans, the observed relationships may aid in assessing anaesthesia-related atelectasis.</p></div

Correlation between changes of oxygenation, shunt and atelectasis in pigs.

<p>The differences (deltas) between the two measurement points in pigs (atelectasis in otherwise normal lungs and 12h after induction of ARDS) for PaO₂, lnPaO₂, shunt and atelectasis were calculated. These repeated measurements were available only for pigs (N = 19). Linear regression of delta-PaO₂ (ΔPaO₂, left panel), delta-lnPaO₂ (ΔlnPaO₂, central panel) or delta-shunt (Δshunt, right panel) on the changes in atelectasis (Δatelectasis) was performed. Blood gases were obtained after short-term ventilation with pure oxygen for five minutes. In this figure, atelectasis refers to real atelectasis as well as to the non-aerated lung tissue after induction of ARDS and was quantified as percentage of Mtotal (-100 to 100 HU in computer tomography). Intrapulmonary (Berggren’s) shunt was calculated according to [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135272#pone.0135272.ref028" target="_blank">28</a>]. We transformed PaO₂ values logarithmically (lnPaO₂) to linearize the relationship between PaO₂ and atelectasis.</p

Correlation between atelectasis, oxygenation and shunt.

<p>Linear regression of raw PaO₂ (upper row), ln-transformed PaO₂ (lnPaO₂, second row) and intrapulmonary (Bergren’s) shunt (lower row), respectively, on the amount of atelectasis (percentage of total lung mass). Only data points from the “atelectasis” columns in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135272#pone.0135272.t001" target="_blank">Table 1</a> were used. Berggren’s shunt was calculated according to [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0135272#pone.0135272.ref028" target="_blank">28</a>]. We transformed PaO₂ values logarithmically (lnPaO₂) to linearize the relationship between PaO₂ and atelectasis.</p

Results from quantitative computer tomography and blood gas analysis.

<p>Values are given as median (interquartile range). Data for sheep were obtained for atelectatic (first column) and recruited lungs. Data in the second column were obtained after applying a recruitment manoeuvre (RM) and subsequent ventilation with PEEP of 10 cm H₂O for 10 minutes. Data in the third column were obtained after applying another RM and ventilation with PEEP of 20 cm H₂O for 10 minutes. Pigs were studied during baseline conditions (atelectasis in otherwise normal lungs) and 12 hours after induction of acute respiratory distress syndrome (ARDS). The PEEP in the ARDS column was chosen according to different lung protective ventilation strategies. N, number of animals studied; V_total, total lung volume; M_total, total lung mass; M_hyper, mass of the hyperaerated (-901 to -1000 HU); M_normal, mass of the normally aerated (-501 to -900 HU); M_poor, mass of the poorly aerated (-101 to -500 HU); M_atelectasis, mass of the atelectatic lung compartment (-100 to +100 HU). Weights of differently aerated lung compartments were calculated as percentage of M_total. Atelectasis was also calculated as volume and expressed as percentage of V_total. All blood gases were obtained after short-term ventilation with pure oxygen for five minutes. We transformed PaO₂ values logarithmically (lnPaO₂) to linearize the relationship between PaO₂ and atelectasis. Shunt was calculated using Berggren’s approach. As the effects of PEEP or RM on lung aeration were no endpoints of the present study and subgroups were very small, statistical between-group comparison was omitted.</p