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Lundgren Cavalcanti, Ruben; da Silva Serpa, Priscila Beatriz; Corrêa Natalini, Cláudio Hemodynamic and Respiratory Effects of Positive End-expiratory Pressure during a Pulmonary Distress Model in Isoflurane Anesthetized Swine Acta Scientiae Veterinariae, vol. 42, núm. 1, enero, 2014, pp. 1-7 Universidade Federal do Rio Grande do Sul Porto Alegre, Brasil

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Acta Scientiae Veterinariae, ISSN (Printed Version): 1678-0345 [email protected] Universidade Federal do Rio Grande do Sul Brasil

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RESEARCH ARTICLE ISSN 1679-9216 Pub. 1214

Hemodynamic and Respiratory Effects of Positive End-expiratory Pressure during a Pulmonary Distress Model in Isoflurane Anesthetized Swine

Ruben Lundgren Cavalcanti1,2, Priscila Beatriz da Silva Serpa1 & Cláudio Corrêa Natalini1,2,3

ABSTRACT Background: Several pulmonary and hemodynamic complications may occur during of the lungs. The use of a positive end-expiratory pressure (PEEP) can improve oxygenation and prevent atelectasis, although this method can cause important hemodynamic side effects. Mostly, these hemodynamic effects are due to increased airway pressure that is transferred to the intrapleural space, increasing the intrathoracic pressure, which decreases venous return to the heart. Cardiac output is significantly reduced with high PEEP levels which in turn precludes the improvement effects on blood oxygenation. The aim of this study was to evaluate hemodynamic and respiratory effects of different levels of carbon dioxide insufflations associated with different levels of PEEP under conventional two-lung ventilation in isoflurane anesthetized pigs. Materials, Methods & Results: Twelve juvenile pigs were anesthetized with ketamine and midazolam, and end tidal iso- flurane 2.0 V% for maintenance. Animals were submitted to tension through an acute intrathoracic insuf- flation with carbon dioxide at 0, 5, and 10 mmHg. Mechanical lung ventilation with 100% oxygen was started with zero

PEEP then increased to 5 and 10 cmH2O. Ventilatory, respiratory and hemodynamic parameters were measured, as well as blood gases. Tension pneumothorax of 10 mmHg, with both PEEP levels, induced a significant decrease in cardiac index, stroke volume, right ventricular stroke work index, dynamic compliance, arterial pH, arteriovenous oxygen difference, arterial blood pressure, in addition to significance increase in heart rate. Moreover, tension pneumothorax of 5 or 10 mmHg combined with 5 or 10 cmH2O PEEP produced a significant increase in alveolar-arterial oxygen difference, a significant decrease in arterial oxygen content, and arterial partial pressure of O2. Central venous pressure, mean pulmonary arterial pressure, physiologic , and arterial partial pressure of CO2 significantly increased with tension pneumothorax of

5 or 10 cmH2O when 5 or 10 mmHg PEEP was used. Arterial oxygenation improved significantly when 10 cmH2O PEEP was applied to 5 or 10 mmHg tension pneumothorax. Discussion: In this study, a thoracoscopic trocar was used to produce the acute respiratory function impairment. All animals showed the hemodynamic effects of an increased intrapleural pressure (IPP), such as hypotension and decreased SpO2. The major change observed was the increased shunt fraction, due to increased physiologic dead space. The hemodynamic changes observed were mainly due to compression of the large thoracic vessels as well as lung compression. When PEEP was applied without increased IPP, the hemodynamic depressive effects were less important. Levels of ETCO2 in our study did not present a significant increase, demonstrating that recruitment maneuvers are not always effective when there is a concomitant increased IPP. Dead space and V/Q mismatch significantly increased, demonstrating an important respira- tory depressant effect. We have demonstrated in this study that while arterial oxygenation and tissue oxygen extraction is improved when high PEEP strategy is used in a swine tension pneumothorax model, the mechanical ventilation of the lungs with low PEEP or high PEEP strategy produced significant depression of the hemodynamic function during tension pneumothorax.

Keywords: PEEP, ventilation, pigs, intrapleural pressure, pneumothorax.

Received: 15 May 2014 Accepted: 4 October 2014 Published: 24 October 2014 1Programa de Pós-graduação em Medicina Animal: Equinos (PPGMAE), Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, Brazil. 2Programa de Pós-graduação em Ciências Biológicas: Fisiologia (PPGFisio), UFRGS, Porto Alegre. 3School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy, SA, Australia. CORRESPONDENCE: C.C. Natalini [[email protected] - Tel.: +(61) 08 8313 1921]. The University of Adelaide, School of Animal and Veterinary Sciences, Roseworthy Campus, Roseworthy SA 5371, Australia.

1 R.L. Cavalcanti, P.B.S. Serpa & C.C. Natalini. 2014. Hemodynamic and Respiratory Effects of Positive End-expiratory Pressure during a Pulmonary Distress Model in Isoflurane Anesthetized Swine. Acta Scientiae Veterinariae. 42: 1214.

INTRODUCTION were then obtained with zero PEEP (ZEEP) and no Mechanical ventilation is a therapeutic support tension pneumothorax with zero intrapleural pressure (ZIPP). Positive end-expiratory pressure at 5 cmH O for the patient which is aimed to produce ventilation of 2 the lungs without micro structural pulmonary lesions was initiated and after a stabilization period of 10 min [12]. The mode of ventilation is selected according measurements were obtained (T1). For T2, PEEP of 10 cmH O was established and data collected after 10 to patient necessities in order to prevent trauma to 2 min of stabilization. the lungs. While low ventilation is be- In order to produce the experimental lung lieved to improve arterial oxygenation, conventional mechanics impairment and respiratory dysfunction the tidal volumes combined with other strategies such as region of the eighth right intercostal space was blocked positive end-expiratory pressure (PEEP) is still not with 2% lidocaine and punctured with a 12 mm thora- completely studied. coscope trocar. After the trocar insertion, 5 mmHg ten- When PEEP is used in variable expiratory sion pneumothorax was produced, and after 10 min of pressure, different degrees of hemodynamic impair- stabilization measurements were taken with PEEP set to ment occur. High PEEP strategy, when used in tension 5 cmH2O (T3). These events were repeated sequentially pneumothorax such as in thoracoscopy procedures, until all treatments were applied: PEEP 10 cmH O + IPP may produce deleterious effects on blood oxygenation 2 5 mmHg (T4), PEEP 5 cmH O + IPP 10 mmHg (T5), [1,11,22]. High PEEP may also reduce mortality in 2 and PEEP 10 cmH O + IPP 10 mmHg (T6). comparison to low PEEP in acute respiratory distress 2 syndrome (ARDS) [9,16], but it is not associated with Instrumentation improved outcome in acute lung injury (ALI) [8]. Animals were kept in supine position throughout Concerning pulmonary injuries and respira- the study. After orotracheal intubation, with a 7.0 ID tory impairment studies, several animal models are tracheal tube, podal artery, and external jugular vein available. Pulmonary injury model is different from were surgically exposed and a 5 Fr sheath was inserted respiratory impairment model, being the former more in the artery and a 7.5 Fr sheath in the vein. A pediatric 5 related to primary ARDS, which involves increment in Fr Swan-Ganz pulmonary artery catheter was advanced permeability of the alveolar-capillary membrane, and through the central access and positioned in the pulmo- the latter more related to chest trauma [22]. nary artery. Correct positioning of the catheter tip was In order to produce a model similar to chest confirmed by typical waveforms of the pressure tracings. trauma to investigate the effects of thoracic insuffla- Ventilatory parameters and airway pressures and flows tions and the benefits of positive end-expiratory pres- were measured with a monitor. Respiratory sure, we did compare the effects of two PEEP levels gases and respiratory parameters were monitored with with zero PEEP in a tension pneumothorax swine an anesthesia gas monitor1. Blood gas analysis was done model. We hypothesized that high PEEP would im- with a digital monitor2 and calculated parameters were prove blood oxygenation as compared to low PEEP or obtained automatically with the same equipment. Mean zero PEEP when a tension pneumothorax is produced. arterial and pulmonary arterial blood pressures (MAP, MPAP) and heart rate (HR) were measured continu- MATERIALS AND METHODS ously using the hemodynamic monitor system of the anesthesia monitor1. Cardiac output (CO) measurements Experimental protocol were performed by conventional thermodilution method. Twelve juvenile (mean body weight 19.83 ± 1.13 kg) domestic pigs (Sus scrofa domestica) were Statistical analysis anesthetized with ketamine (10 mg/kg) and midazolam Functional variables are presented as mean (± (2 mg/kg) intramuscularly, and end tidal isoflurane SD). Two-way repeated-measures analysis of variance 2.0 V% for maintenance. Mechanical lung ventila- was used for comparison between treatment and time tion was used and animals were instrumented after x treatment effects. All tests were performed using anesthesia was stabilized for 20 min. Depth of anes- SPSS3. Corrections for multiple measurements were thesia was monitored continuously by arterial blood performed by Bonferroni post-tests. Statistical signifi- pressure and heart rate. Baseline measurements (T0) cance was accepted if P < 0.05.

2 R.L. Cavalcanti, P.B.S. Serpa & C.C. Natalini. 2014. Hemodynamic and Respiratory Effects of Positive End-expiratory Pressure during a Pulmonary Distress Model in Isoflurane Anesthetized Swine. Acta Scientiae Veterinariae. 42: 1214.

Table 1. Mean + standard deviation for hemodynamic parameters in swine submitted to zero end-expiratory pressure (ZEEP), positive end-expiratory pressure (PEEP) from 5 to 10 cmH2O, and intrapulmonary pressure (IPP) from 0 (ZIPP) to 10 mmHg in the seven times studied (T0 to T6). Systolic blood pressure (SAP), diastolic blood pressure (DAP), mean blood pressure (MAP), central venous pressure (CVP), heart rate (HR), cardiac index (CI), Stroke volume index (SVI), Mean pulmonary arterial pressure (MPAP). T0 T1 T2 T3 T4 T5 T6 Parameter ZEEP PEEP 5 PEEP 10 PEEP 5 PEEP 10 PEEP 5 PEEP 10 ZIPP ZIPP ZIPP IPP 5 IPP 5 IPP 10 IPP 10 SAP (mmHg) 90±5 85±10 72± 12 80± 15 82± 14 64± 6 68± 5 DAP (mmHg) 46±5 44± 5 46± 9 45± 9 47± 9 43± 7 46± 6 MAP (mmHg) 60± 5 57± 9 55± 8 57± 12 60± 12 51± 6 53± 5 A ABC AB AB BC CD D CVP (cmH2O) 8±1 10± 3 10± 1 11± 2 12± 1 16± 2 17± 1 HR (bpm) 105± 8A 102± 7A 106± 14A 115± 29A 130± 24AB 179± 42BC 193± 35C CI (L/min/m2) 5 ± 0.5A 5 ± 0.3A 4.6 ± 0.4AB 4.5 ± 0.6AB 5 ± 0.5A 3.0 ± 0.6BC 2 ± 0.3C SVI (mL/beat/m2) 51± 6A 52 ± 5A 44 ± 3.5A 42 ± 9A 41± 8A 19 ± 6B 12± 3B MPAP (mmHg) 18 ±4 A 24 ±8AB 23 ±5AB 26 ±6B 26 ±6B 29 ±3B 28±5B Different capital letters in the same line indicates statistically significant differences (P < 0.05).

Table 2. Mean + standard deviation for respiratory parameters in swine submitted to zero end-expiratory pressure (ZEEP), positive end-expiratory pres- sure (PEEP) from 5 to 10 cmH2O, and intrapulmonary pressure (IPP) from 0 (ZIPP) to 10 mmHg in the seven times studied (T0 to T6). Arterial partial pressure of oxygen (PaO2), arterial (SaO2), arterial oxygen content (CaO2), arterio-venous difference in oxygen content (a-vDO2), oxygen delivery (DO2), alveolar-arterial oxygen difference (A-aDO2), dynamic compliance (Cdyn), dead space, (V̇E), tidal volume (VT), (RR), pH, bicarbonate (HCO3-), end tidal carbon dioxide (ETCO2), and arterial partial pressure of carbon dioxide (PaCO2). T0 T1 T2 T3 T4 T5 T6 Parameter ZEEP PEEP 5 PEEP 10 PEEP 5 PEEP 10 PEEP 5 PEEP 10 NIPP NIPP NIPP IPP 5 IPP 5 IPP 10 IPP 10 PaO 2 233±74AB 264±37A 320±96A 103±30BCD 137±17ABD 72±15C 96±32CD (mmHg)

A A A AB AB AB B SaO2 (%) 100± 0.3 100 ± 0.2 100 ± 0.2 97 ± 1.8 99 ± 1 92 ± 7 96 ± 3 CaO 18.76 ± 19.04 ± 2 20 ± 0.3A 20.27 ± 0.41AB 20.54 ± 0.42A 19.35 ± 0.54BCD 20.01 ± 0.55ABD (mL/dL) 0.64C 0.79CD a-vDO 2 3.3± 0.8A 2.8 ± 0.5A 3± 0.3A 2 ± 1A 4.0± 0.5A 6 ± 3B 5± 2B (mL/dL) DO 2 700 ± 81A 690 ± 5A 620 ± 7A 564 ± 6AB 645 ± 6A 368 ± 7B 275 ± 2B (mL/min) A-aDO 2 321 ± 185AD 370± 124AB 280 ± 130A 515 ± 80BC 469± 135ABC 543 ± 49C 505 ± 82BCD (mmHg) C (mL/ dyn 56 ± 15A 50 ± 9A 49 ± 5AB 40 ± 7AB 43 ± 10AB 28 ± 6B 30 ± 6B cmH2O) Dead 12 ± 4A 15 ± 4A 14± 5A 22 ± 5AB 24 ± 4AB 33 ± 2B 31 ± 8B space (%) V̇ E 4,2 ± 1,4A 3,6 ± 1,2A 4,0 ± 0,4A 3,6 ± 0,6A 3,7 ±1,0A 3,4 ± 0,6A 3,0 ± 0,5A (L/min) V T 220± 69A 156 ± 5.6A 145 ± 28AB 152 ± 30AB 123 ±38ABC 111 ± 13BC 96 ± 21C (mL/kg) RR (bpm) 22 ± 4A 26 ± 7AB 32± 2B 27 ± 3A 37 ± 9B 33 ± 4B 36± 4B pH 7.45 ± 0.04A 7.42 ± 0.03AB 7.42 ± 0.02AB 7.37 ± 0.04BC 7.36 ± 0.06BC 7.31 ± 0.04C 7.29 ± 0.05C HCO - 3 31 ± 1 31 ± 1 32 ± 1 30.± 1 30 ± 1 31 ± 0.5 29 ± 1 (mEq/L) ETCO 2 39±2 42±4 43±1 42±5 42±4 42±3 44±2 (mmHg) PaCO 2 45 ±4A 50± 4A 50 ± 3A 54 ± 5B 55 ± 7AB 62 ± 7B 63± 11B (mmHg) Different capital letters in the same line indicates statistically significant differences (P < 0.05). 3 R.L. Cavalcanti, P.B.S. Serpa & C.C. Natalini. 2014. Hemodynamic and Respiratory Effects of Positive End-expiratory Pressure during a Pulmonary Distress Model in Isoflurane Anesthetized Swine. Acta Scientiae Veterinariae. 42: 1214.

RESULTS In our study, a thoracoscopic trocar was used Tension pneumothorax of 10 mmHg, with both to produce the acute respiratory function impair- PEEP levels, induced a significant decrease in cardiac ment. Tension pneumothorax model in pigs has been described before, produced through insertion of an index, stroke volume, dynamic compliance, arterial intrathoracic balloon occlusion catheter, surgically pH, arterial blood pressure, in addition to significan- placed into the right pleural space [7]. The major ce increase in heart rate (Table 1). Moreover, tension change observed was the increased shunt fraction, due pneumothorax of 5 or 10 mmHg combined with 5 or 10 to increased physiologic dead space. In our study the cmH O PEEP produced a significant increase in alveo- 2 effects of increased shunt fraction was demonstrated lar-arterial oxygen difference, a significant decrease in as the PaO decreased significantly after an increased arterial oxygen content, and arterial partial pressure of 2 intrathoracic pressure of 10 mmHg. Studies in sheep O2 (Table 2). Central venous pressure, arterio-venous and swine have demonstrated progressive as difference in oxygen content, mean pulmonary arterial the earliest sign of increased intrapleural pressure [7]. pressure, physiologic dead space, and arterial partial Hemodynamic studies showing the effects of pressure of CO2 significantly increased with tension raised IPP in ventilated animal models demonstra- pneumothorax of 5 or 10 cmH O when 5 or 10 mmHg 2 ted an early rise in central venous pressure [7]. We PEEP was used. Arterial oxygenation improved signi- have demonstrated in this study that when IPP is not ficantly when 10 cmH O PEEP was applied to 5 or 10 2 increased, PEEP will not impact the CVP. However, mmHg tension pneumothorax (Tables 1 and 2). an increased IPP from 0 to 10 mmHg will produce a DISCUSSION significant increase in CVP. When PEEP from 0 to 10

cmH2O is applied to ZIPP, no significant change in Mechanical ventilation is a strategic approach CVP was observed in our study. Similar effects were when patient needs respiratory support in acute or chro- described before [17,20,21,25]. nic pulmonary disease. Since mechanical ventilation Central venous pressure, mean pulmonary arte- involves several mechanisms in which the patient may rial pressure, physiologic dead space, and arterial partial have a better outcome when the proper modality is pressure of CO significantly increased with tension chosen, several ventilation modes have been described 2 pneumothorax of 5 or 10 mmHg when 5 or 10 cmH2O [12]. The techniques involved are well established and PEEP was used. Tension pneumothorax of 10 mmHg, the complication as well as the benefits is known to with both PEEP levels, induced a significant decrease increase the survival rate during ALI/ARDS in man in cardiac index, stroke volume, dynamic compliance, [2,10]. Positive end-expiratory pressure (PEEP) is a arterial pH, in addition to significance increase in heart technique used when hypoxemia in acute lung injury/ rate. These hemodynamic changes are well described acute respiratory stress syndrome occurs. This pheno- and explained by compression of the large thoracic menon occurs when a high shunt fraction is formed due vessels as well as lung compression. Decreased thoracic to non-aerated areas in the lungs [1,11,23]. transmural pressures, resulting in decreased end dias- In order to investigate the effects of PEEP in a tolic volumes are the main causes of hypotension and tension pneumothorax model it would be important to decreased cardiac output when the intrathoracic pressure investigate the different modes of ventilation. In this is increased with increased IPP [3,6,13,26,27]. When study, a pressure controlled mode of ventilation was the PEEP is applied without increased IPP, the hemodyna- only model investigated combined or not with PEEP. mic depressive effects were less important in our study All animals showed the hemodynamic effects of an in- similarly to what has been described before in swine in creased intrapleural pressure (IPP) such as hypotension cardiovascular studies [13]. and decreased SpO2. Hemodynamic function would Recruitment maneuvers and PEEP besides tidal deteriorate in patients under mechanical ventilation ventilation titration have been recommended to improve which produces an increased alveolar pressure, and arterial oxygenation during acute respiratory distress when tension pneumothorax develops, the increased syndrome [4,5,13]. The animals in our study showed alveolar pressure above pulmonary venous or arterial an improvement in arterial oxygenation when higher pressure decreases cardiac output [7,14,18,19,28]. than 5 cmH2O PEEP was applied during increased IPP.

4 R.L. Cavalcanti, P.B.S. Serpa & C.C. Natalini. 2014. Hemodynamic and Respiratory Effects of Positive End-expiratory Pressure during a Pulmonary Distress Model in Isoflurane Anesthetized Swine. Acta Scientiae Veterinariae. 42: 1214.

In order for the recruitment maneuvers to be effective, showed but used to calculate a-vDO2) presented. a sudden increase in ETCO2 should indicate a signal of According to Karzai & Schwarzkopf [15], oxygena- recruitment [4]. Levels of ETCO2 in our study did not tion during video thoracoscopic surgeries depends present a significant increase, demonstrating that recruit- not only on the magnitude of the shunt fraction, but ment maneuvers are not always effective when there is also the oxygenation of the shunted blood because a concomitant increased IPP. The resulting significant there is a dependence of SaO2 by SvO2 at different decreased dynamic complacency, probably explains the levels of shunt . Thus, factors that lead to reduced lack of efficacy of our recruitment maneuvers [7,14]. oxygenation of the shunted venous blood, e.g. ca- In our study, tension pneumothorax of 5 or 10 ses of increased oxygen extraction by tissues, as observed in our study, or low levels, mmHg combined with 5 or 10 cmH2O PEEP in venti- lated pigs, produced a significant increase in alveolar- can directly affect arterial oxygenation (PaO2) [15]. -arterial oxygen difference, a significant decrease in CONCLUSION arterial oxygen content, and arterial partial pressure of Positive end-expiratory pressure of 5 or 10 O2. Arterial oxygenation improved significantly when 10 cmH2O PEEP was applied to 5 or 10 mmHg ten- cmH2O improve arterial oxygenation during mecha- sion pneumothorax, although important hemodynamic nical ventilation. When tension pneumothorax 5 or 10 depressive effects do occur. Following those changes, mmHg is used the effects of recruitment maneuvers are not efficient enough to prevent an increase in tissue the PaCO2 levels, before IPP increase were lower than during and after IPP increase. Therefore, dead space oxygen extraction. Hemodynamic depressive effects and V/Q mismatch significantly increased, demonstra- of PEEP during IPP are extremely deleterious. ting an important respiratory depressant effect. SOURCES AND MANUFACTURERS Improving tissue oxygenation is the main 1Datex Ohmeda S/5, Datex-Ohmeda Division, Instrumentarium Corp., goal when PEEP strategies are used. The results of Helsinki, Finland. 2RapidLab 865-2, Bayer, Fernwald, Germany. our study demonstrated that when SaO2 decreased, 3SPSS version 17.0, Chicago, IL, USA. CaO2 also decreased which is physiologically expec- ted [28]. Interestingly, the a-vDO was significantly 2 Acknowledgements. The authors thank Hospital de Clínicas higher when PEEP of 5 or 10 cmH2O was combi- de Porto Alegre and its Animal Experimental Unit for financial ned with IPP of 10 mmHg (T5 and T6), showing (Research Foundation of the Hospital de Clínicas de Porto an increased tissue oxygen extraction. A possible Alegre -FIPE - Universidade Federal do Rio Grande do Sul) and infrastructure support. explanation is the significant increase in heart rate, with a significant decrease in cardiac index and Ethical Approval. The complete study proposal was approved systolic index, which leads to decreased blood flow by the Institutional Animal Care Committee (N° 07.288) and Brazilian Federal regulation for care and use of laboratory to peripheral tissues. Thus, even significant increase animals of the Hospital de Clínicas de Porto Alegre (HCPA- in cardiac workload did not produce an increase in UFRGS), Porto Alegre, RS, Brazil. blood flow. The significant reduction in CO observed in this study, in addition to the increased a-vDO , Declaration of Interest. None of the authors of this paper 2 has a financial or personal relationship with other people or probably was also the cause of the reduction in organizations that could inappropriately influence or bias the systemic venous oxygen saturation (SvO2, data not content of the paper.

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