Expiratory mechanics before and after uncomplicated heart surgery

Respiratory mechanics with volume-controlled auto-flow ventilation mode in cardiac surgery

Aim:

We aimed to investigate the changes in respiratory mechanics in adult patients undergoing open heart surgery (OHS) while using volume-controlled auto-flow (VCAF) ventilation mode.

Materials and Methods:

After obtaining ethics committee's approval and informed consent, 30 patients (17 males and 13 females; mean age: 57.3 ± 17.0 years; mean weight; 74.9 ± 13.6 kg) scheduled for OHS were enrolled. Mechanical ventilation was carried out using VCAF mode (V_T: 5–8 mL/kg, I/E: 1/2, 10 ± 2 fr/min). Values of dynamic compliance (C_dyn) and resistance (R) were obtained at six time points (TPs). Normally distributed variables were analyzed with repeated measure of analysis of variance and Bonferroni tests. For abnormally distributed variables, Friedman variance analysis and Wilcoxon signed-rank tests were used. Values were expressed as mean ± standard deviation. P value <0.05 was considered significant.

Results:

C_dyn (mL/mbar) and R (mbar/L/s) values were as follows – (1) before sternotomy (S): 49.9 ± 17.1 and 7.8 ± 3.6; (2) after S: 56.7 ± 18.3 and 7.1 ± 3.7; (3) after S and after sternal retractor placement: 48.7 ± 16.1 and 8.3 ± 4.4; (4) after weaning from cardiopulmonary bypass and following decannulation while retractor was in place: 49.6 ± 16.5 and 8.1 ± 4.0; (5) after retractor removal: 56.5 ± 19.6 and 7.4 ± 3.7; and (6) after sternal closure: 43.1 ± 14.2 and 9.6 ± 9.1, respectively. Significant differences were observed in C_dyn and R between; first and second TPs, second and third TPs, fourth and fifth TPs, and fifth and sixth TPs. Also, significant difference in C_dyn was found between first and sixth TPs, but it was not found in R.

Conclusion:

C_dyn decreases, but R remains the same in cardiac surgical patients when mechanical ventilation is performed with VCAF ventilation mode. Additionally, C_dyn is negatively affected by the presence of sternal retractor and the sternal closure in OHS.

Pulmonary pathophysiology and lung mechanics in anesthesiology: a case-based overview

Anesthesia, surgical requirements, and patients' unique pathophysiology all combine to make the accumulated knowledge of respiratory physiology and lung mechanics vital in patient management. This article take a case-based approach to discuss how the complex interactions between anesthesia, surgery, and patient disease affect patient care with respect to pulmonary pathophysiology and clinical decision making. Two disparate scenarios are examined: a patient with chronic obstructive pulmonary disease undergoing a lung resection, and a patient with coronary artery disease undergoing cardiopulmonary bypass. The impacts of important concepts in pulmonary physiology and respiratory mechanics on clinical management decisions are discussed.

Preservation of pleural integrity during coronary artery bypass surgery affects respiratory functions and postoperative pain: a prospective study

OBJECTIVE

To evaluate the role of preserved pleural integrity in postoperative pain and respiratory functional status in patients undergoing coronary revascularization.

METHODS

Two hundred forty patients undergoing on-pump coronary artery bypass grafting between March 2004 and February 2005 were included in the present study. The patients were prospectively randomized and divided into either an opened pleura (OP) group (n=120, patients with an OP) or a closed pleura (CP) group (n=120, patients whose pleural integrity was preserved). Preoperative patient characteristics were similar. Postoperative respiratory functions were compared between the groups by chest x-rays, respiratory functional tests and arterial blood gas analyses. Postoperative pain was compared by using a multidimensional pain score. All the tests were examined by the same blinded clinician.

RESULTS

The mean age of the patients was 60.4+/-8.8 years. Postoperative bleeding and the duration of hospital stay were markedly higher in the OP group than in the CP group. The incidences of atelectasis and pleural effusion were also significantly higher in the OP group (P<0.01). Respiratory functions and postoperative pain scores were better in the CP group (P<0.01 and P=0.008, respectively).

CONCLUSIONS

Preserving pleural integrity has beneficial effects on the respiratory functions and postoperative pain after coronary revascularization. The preservation of pleural integrity results in better respiratory function, decreased hospital stay and cost, and as a consequence, a better surgical outcome.

Evaluation of respiratory mechanics and lung histology in a model of atelectasis

To develop a reproducible model of atelectasis, 15 mechanically ventilated Wistar rats were wrapped around the thorax/abdomen with a sphygmomanometer. The cuff was inflated to transpulmonary pressures (PL) of -4 cmH2O (group A) and -8 cmH2O (group B) for 5 sec. Group C was not compressed. Airflow, volume, tracheal and oesophageal pressures were registered. Respiratory system (rs), lung (L), and chest wall resistive (DeltaP1), viscoelastic/inhomogeneous pressures (DeltaP2), DeltaPtot (=DeltaP1 + DeltaP2), static (Est) and dynamic (Edyn) elastances, and DeltaE (=Edyn - Est) were determined before and after compression. In A, respiratory mechanics remained unaltered. In B, Est,rs (+99%), Est,L (+111%), DeltaE,rs (+41%), DeltaE,L (+73%), DeltaP1,rs (+45%), DeltaP1,L (+44%), DeltaP2,rs (+41%), DeltaP2,L (+69%), DeltaPtot,rs (+40%), and DeltaPtot,L (+58%) increased after compression. Mean alveolar diameter and bronchiolar lumen decreased in A, and were even smaller in B. In conclusion, chest wall compression with PL of -8 cmH2O yielded a reproducible alveolar collapse, which resulted in increased elastic, resistive and viscoelastic/inhomogeneous pressures.

Changes in respiratory mechanics during cardiac surgery

We investigated the role of cardiopulmonary bypass (CPB) in compromised lung function associated with cardiac surgery. Low-frequency respiratory impedance (Zrs) was measured in patients undergoing cardiac surgery with (n = 30; CPB group) or without (n = 29; off-pump coronary artery bypass [OPCAB] group) CPB. Another group of CPB patients received dopamine (DA) (n = 12; CPB-DA group). Extravascular lung water was determined in five CPB subjects. Zrs was measured before skin incision and after chest closure. Airway resistance and inertance and tissue damping and elastance were determined from Zrs data. Airway resistance increased in the CPB group (74.9% +/- 20.8%; P < 0.05), whereas it did not change in the OPCAB group (11.8% +/- 7.9%; not significant) and even decreased in the CPB-DA patients (-40.6% +/- 9.2%; P < 0.05). Tissue damping increased in the CPB and OPCAB groups, whereas it remained constant in the CPB-DA patients. Significant increases in elastance were observed in all groups. There was no difference in extravascular lung water before and after CPB, suggesting that edema did not develop. These results indicate a significant and heterogeneous airway narrowing during CPB, which was counteracted by the administration of DA. The mild deterioration in tissue mechanics, reflecting partial closure of the airways, may be a consequence of the anesthesia itself.

IMPLICATIONS

We observed that cardiopulmonary bypass deteriorates lung function by inducing a heterogeneous airway constriction, whereas no such effects were observed in patients undergoing cardiac surgery without bypass. The impairment in parenchymal mechanics, which was obtained in both groups, may result from peripheral airway closure and/or be a consequence of mediator release.

Effects of off-pump coronary surgery on the mechanics of the respiratory system, lung, and chest wall: Comparison with extracorporeal circulation

OBJECTIVE

To compare the effects of cardiac surgery with and without extracorporeal circulation on the mechanics of the respiratory system, lung, and chest wall. We also determined the time course of those effects.

DESIGN

Prospective, controlled study.

SETTING

An eight-bed, cardiac-surgical intensive care unit at a university hospital.

PATIENTS

Two groups of patients scheduled for elective coronary bypass surgery were studied: ten patients with extracorporeal circulation and 13 patients without extracorporeal circulation.

INTERVENTIONS

Measurement of esophageal pressure after insertion of an esophageal balloon catheter to separate respiratory system mechanics into lung and chest wall components. Measurements were performed preoperatively after induction of anesthesia (control), immediately postoperatively at arrival in the intensive care unit (time 1), and after 3 hrs (time 2). In 12 of the 23 patients, measurements were also performed 6 hrs postoperatively (time 3).

MEASUREMENTS AND MAIN RESULTS

No significant differences concerning demographics or surgical procedure were noticed between the two groups. Respiratory system, chest wall, and lung mechanics were obtained using the technique of rapid airway occlusion during constant-flow inflation. In both the group with and without extracorporeal circulation there was a significant increase in static and dynamic elastance of the respiratory system and lung at times 1 and 2, which tended to decrease again at time 3; chest wall elastance significantly increased at times 2 and 3 in the group without extracorporeal circulation, whereas the increase in chest wall elastance in the group with extracorporeal circulation occurred earlier (also at time 1). Additional resistance of the respiratory system and lung remained unchanged; chest wall resistance, however, significantly increased in both groups. Work of breathing significantly increased in both groups at times 1 and 2. There was a significant reduction in the Pao2/Fio2 ratio in both groups at times 2 and 3. No significant differences between the groups at any moment were noticed.

CONCLUSIONS

Coronary bypass surgery with and without extracorporeal circulation results in dramatic impairment of respiratory system mechanics. Based on respiratory system mechanics, early extubation after coronary artery bypass grafting should be performed with caution, no matter whether the off-pump or cardiopulmonary bypass technique is used.

Time-course of impairment of respiratory mechanics after cardiac surgery and cardiopulmonary bypass

OBJECTIVE

Cardiopulmonary bypass (CPB) is associated with abnormalities of lung function characterized by an increase in static elastance of the respiratory system. We examined the following: a) the effects of CPB on the total inspiratory volume-pressure (V-P) relationship of the respiratory system; b) the relative contribution of the chest wall and lung to the impairment of respiratory system mechanics; and c) the time-course of such impairment.

DESIGN

Prospective, interventional study.

SETTING

Surgical and medical intensive care units in a teaching hospital.

PATIENTS

Eight adult patients scheduled for elective open heart surgery to correct valvular dysfunction.

INTERVENTIONS

V-P curves (interrupter technique) of the respiratory system were partitioned between the chest wall and lung by measurements of esophageal pressure. Measurements were obtained before sternotomy (control), immediately after, 4 hrs after, and 7 hrs after separation from CPB.

MEASUREMENTS AND MAIN RESULTS

Control V-P relationships of the respiratory system and lung showed lower inflection points (Pflex) at pressure values of 5.9+/-2.3 and 4.3+/-2.5 cm H2O, respectively. Immediately after and 4 hrs after separation from CPB, both curves had sigmoid shapes because of lower Pflex and formation of upper inflection (UIP) points. The pressures corresponding to the Pflex increased significantly (p < .001) by 56%+/-3% and 78%+/-4%, whereas the UIP corresponded to a pressure value of 42.34+/-8.5 and 35.6+/-7.8 cm H2O in the respiratory system and lung, respectively. A linear V-P relationship of the chest wall was observed during the control condition and after separation from CPB. Four hours later, no further increases in the pressure values corresponding to Pflex were observed on the inspiratory V-P curves of the respiratory system and lung, whereas the UIP occurred at a pressure of 35.6+/-9.1 and 29.7+/-8.4 cm H2O, respectively. A UIP was present on the V-P curve of the chest wall at a volume of 0.77+/-0.02 L. Seven hours after separation from CPB, the inspiratory V-P curves of the respiratory system, chest wall, and lung returned to normal.

CONCLUSIONS

Sternotomy and CPB produced immediate changes in lung mechanics. Chest wall mechanics were affected only 4 hrs after sternotomy. Seven hours after disconnection from CPB, all mechanics had returned to normal.

Effect of internal thoracic artery preparation on blood loss, lung function, and pain

BACKGROUND

Postoperative blood loss, respiratory distress, and pain after coronary artery operation were assessed in a prospective, randomized, clinical study comparing two techniques of internal thoracic artery preparation.

METHODS

In group A (n = 57) the internal thoracic artery was dissected with the entire surrounding connective tissue after opening the pleura, using routine lateral pleural drainage. In group B (n = 55) a venoarterial pedicle was prepared without surrounding muscle leaving the pleura intact. We assessed blood loss, clinical outcome, lung function, location, intensity, and quality of pain 6 days and 3 months after the operation.

RESULTS

Significantly higher blood loss was observed in group A (A, 608+/-58 mL; B, 470+/-48 mL; p = 0.027). Forced expiratory volume in 1 second was significantly decreased in group A 6 days after surgery (A, 76.0%+/-1.6%; B, 83.2%+/-1.6%; p = 0.020). The forced expiratory volume in 1 second correlated to inspiratory vital capacity, which confirmed the advantage of the venoarterial technique (A, 0.771+/-0.021; B, 0.832+/-0.020; p = 0.003). Vital capacity was significantly higher in the venoarterial group at 3 months (A, 85.2%+/-2.1%; B, 98.5%+/-1.2%; p = 0.009), but not on postoperative day 6. The incidence of pleural effusion and atelectasis was significantly higher in group A (effusion: A, 52.6%; B, 23.6%; p = 0.002; atelectasis: A, 42.1%; B, 20.0%, p = 0.015). Sternal pain (A, 36.8%; B, 9.1%; p = 0.001) and suspenders pain (A, 33.3%; B, 7.3%; p = 0.001) occurred more often in group A. When using a multidimensional pain score, patients in group A experienced significantly sharper (6 days: A, 6.7+/-0.3; B, 3.3+/-0.2; p = 0.018; 3 months: A, 3.5+/-0.3; B, 1.4+/-0.3; p = 0.046) and more annoying pain (6 days: A, 7.6+/-0.2; B, 2.7+/-0.1; p = 0.036; 3 months: A, 6.6+/-0.3; B, 2.3+/-0.2; p = 0.040).

CONCLUSIONS

These results demonstrate that the venoarterial preparation technique is superior to conventional internal thoracic artery preparation regarding postoperative blood loss, lung function, and pain.

Effects of thoracotomy on respiratory system, lung, and chest wall mechanics

Nineteen rats were sedated, anesthetized, paralyzed, and mechanically ventilated. The respiratory, lung, and chest wall elastances (Est-rs, Est-L, Est-w); respiratory system, pulmonary, and chest wall total resistances (Rtot-rs, Rtot-L, Rtot-w); respiratory system, pulmonary, and chest wall initial resistances (Rinit-rs, Rinit-L, Rinit-w); and respiratory system, pulmonary, and chest wall difference resistances (Rdiff-rs, Rdiff-L, Rdiff-w) were determined before and after thoracotomy using the end-inflation occlusion method. Rinit reflects the Newtonian resistances and Rdiff represents the viscoelastic/inhomogeneous pressure dissipations in the system. Rtot = Rinit+Rdiff, ie, total resistance. The animals were submitted to either anterolateral thoracotomy (group A, n = 7), median sternotomy (group B, n = 6), or median sternotomy under PEEP while the lungs were exposed (group C, n = 6). In groups A and B, statistically significant increases in Rdiff-rs significantly augmented Rtot-rs. The former results were entirely secondary to significant increases in Rdiff-L, which naturally raised Rtot, L. Resistance was not altered in group C rats. Thus, anterolateral thoracotomy and median sternotomy increases Rtot-rs as a consequence of augmented Rdiff-L, but this finding could be prevented by the use of PEEP. Est-rs and Est-L increased in the three groups after surgery. Groups D and E were comprised of four animals each. Both underwent median sternotomy and in group E, PEEP was applied. Histopathologic examination of the lungs demonstrated a higher degree of lung collapse in group D.

Effect of internal mammary harvest on postoperative pain and pulmonary function

Forty-three patients undergoing median sternotomy were evaluated for postoperative pain and pulmonary function. Group 1 (n = 26) had harvest of the internal mammary artery (IMA) and group 2 (n = 17) did not. Postoperative pain and pulmonary function were evaluated on the fifth postoperative day. Both groups showed a decrease in forced expiratory volume in 1 second (group 1, 44%; group 2, 39%), but there was no significant difference in the loss between the two groups (p = 0.32). Using a numeric rating scale, there was significant increase in postoperative pain in group 1 (group 1, 6.35; group 2, 3.82; p = 0.0002). There is a suggestion that internal mammary artery harvesting itself worsens postoperative pulmonary function tests, and this may be related to a significant increase in postoperative pain.

Postoperative pulmonary function abnormalities after coronary artery bypass surgery

In 18 patients, postoperative effects of coronary bypass surgery were evaluated. Pulmonary function studies were conducted preoperatively, and 1 and 6 weeks postoperatively, by means of spirometry, respiratory pressures, body plethysmography and impedance measurement of the respiratory system using the forced oscillation technique. One week postoperatively, total lung capacity (P less than 0.0001), inspiratory vital capacity (P less than 0.0001) forced expiratory volume (P less than 0.0001) and functional residual capacity (P less than 0.01) decreased significantly, while residual volume remained unchanged. This restrictive respiratory impairment was accompanied by significant decreases in inspiratory (P less than 0.0001) and expiratory (P less than 0.01) mouth pressures and significant decreases in respiratory resistance values (P less than 0.01). Six weeks postoperatively, significant differences in total lung capacity (P less than 0.0001), inspiratory vital capacity (P less than 0.0001) and forced expiratory volume (P less than 0.0001) persisted, while respiratory pressures returned to the preoperative values. It is concluded that respiratory muscle weakness contributes to the immediate postoperative restrictive lung function loss. Furthermore, structural alterations of chest wall mechanics have to be supposed for the persisting late restrictive pulmonary impairment.

Functional results of muscle flap closure for sternal infection

The morbidity and mortality of infection after median sternotomy have been substantially reduced with the advent of treatment by wide sternal resection and muscle flap closure. A study was performed comparing the cardiorespiratory function of 13 such patients before and after operation as well as with a control group of 15 patients who underwent similar procedures without complication. The groups were comparable in preoperative pulmonary function, though more patients in the study group had evidence of chronic lung disease. Patients were studied 2 to 39 months after the original procedure. Late postoperative pulmonary function test results, exercise tolerance, and oxygen uptake were not significantly different between the groups, and pulmonary function test results were unchanged in those patients who were tested preoperatively. We conclude that muscle flap reconstruction for sternal infection can be expected to give good long-term functional results. Exercise tolerance and pulmonary function may not differ from a control group of cardiac surgical patients, despite the altered composition of the chest wall. Patients with chronic lung disease may be more prone to have this complication.

Pulmonary function after heart-lung transplantation using larger donor organs

Restrictive pulmonary function after heart-lung transplantation (HLT) has been attributed to the use of smaller donor lungs and/or an inability to generate normal negative pleural pressures. Pleural pressure generation depends on both the size of the recipient thoracic cage and its neuromuscular integrity. To determine whether lung volumes after heart-lung transplantation are more dependent on donor lung size or on recipient chest wall characteristics, seven HLT recipients were evaluated before and after transplantation. Postoperative values initially (average, 2 months), 6, and 12 months after transplantation were compared with predicted lung volumes for the recipient and donor organs. TLC dropped from a mean of 5.2 +/- 0.5 L preoperatively to 3.7 +/- 0.3 L (p less than 0.05) 2 months after HLT, but it improved with time and ultimately was not different from preoperative values. The predicted TLC of the HLT donor organs were significantly larger than those of the recipient's predicted TLC, with a mean of 6.9 +/- 0.4 versus 5.3 +/- 0.3 L (p less than 0.05). DLCO, arterial PO2, and PCO2 did not change after surgery. Within limits, larger donor lungs appear to adapt to the constraints of the recipient chest and may be used with clinical success, without apparent adverse effects.

Respiratory mechanics in anesthetized young patients with kyphoscoliosis. Immediate and delayed effects of corrective spinal surgery

To our knowledge, the effects of corrective spinal surgery on total respiratory mechanics and its components in anesthetized patients with kyphoscoliosis have not been previously reported in detail. We studied 13 patients with kyposcoliosis; their mean (+/- SD) age was 24.7 +/- 2.1 years; eight underwent anterior and posterior spinal fusions (AF and PF, respectively) two weeks apart (group A), four underwent PF alone (group B), and one had a three-stage procedure. Mean total respiratory elastance (Ers), static and dynamic lung elastance (Est,L and Edyn,L, respectively), chest wall elastance (Ew), and lung resistance (RL) were derived according to previously described methodology. In group A, Ers and Ew increased by 39 percent and 58 percent, respectively, following AF and by 20 percent and 129 percent following PF, while Est,L and Edyn,L did not change or declined following PF. Lung resistance increased 19 percent and 41 percent by the end of AF and PF, respectively, in group A. In group B, Ew more than doubled, resulting in a 39 percent increase in Ers. Increases in Ers, Ew, and respiratory flow resistance observed at the time of spinal corrective surgery for kyphoscoliosis may result from rib cage trauma and changes in airway caliber related to microatelectasis and uneven distribution of mechanical properties within the lungs. Spinal correction results in immediate and short-term deterioration of respiratory mechanics measured under anesthesia.

Total respiratory compliance in infants and young children with congenital heart disease

The multiple occlusion technique was used to measure total respiratory system compliance (Crs) in 62 infants and young children with congenital heart disease (age range, 2 days to 2 years). Measurements were found to be reproducible in nine infants in whom repeat measurements were possible (maximum deviation between measurements less than 10%). The incidence of failure to obtain accurate results was no greater than when studying infants without cardiopulmonary disease. However, in the presence of severe growth retardation or alinearity of volume-pressure data, results may be difficult to interpret in individuals. Results of Crs were related to non-invasive assessments of cardiac disease severity using chest radiography and echocardiography. After the effects of growth had been taken into account, a significant negative relationship was found between Crs and the right pulmonary artery to aortic ratio, which reflects pulmonary vascular engorgement (P = 0.003, R2 = -0.40). However, no significant relationship was found between Crs and chest X-ray score (P = 0.27).