BJA Advance Access originally published online on June 18, 2007
British Journal of Anaesthesia 2007 99(2):184-190; doi:10.1093/bja/aem126
Severe pulmonary hypertension complicates postoperative outcome of non-cardiac surgery
1 Department of Anaesthesiology
2 Cardiovascular Centre, Taichung Veterans General Hospital, Taichung, Taiwan
3 School of Medicine
4 Cardiovascular Research Centre, National Yang-Ming University, Taipei, Taiwan
5 Chung-Gang University College of Medicine
6 Chung-Gang Memorial Hospital, Taipei, Taiwan
7 Chung-Shang Medical University, Taichung, Taiwan
* Corresponding author: Cardiovascular Center, Taichung Veterans General Hospital, Taichung, 407, Taiwan. E-mail: trliu{at}vghtc.gov.tw
Accepted for publication April 5, 2007.
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Abstract |
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Background: Whether and how pulmonary hypertension (PH) impacts perioperative outcome in non-cardiac surgery is incompletely understood.
Methods: From November 1999, all patients undergoing non-cardiac, non-local anaesthetic surgery and ever examined by echocardiography within 30 days before surgery were screened. Those having echocardiographic pulmonary artery systolic pressure >70 mm Hg were enrolled provided they were not already intubated. Case-matched peers with normal pulmonary pressures served as controls. Perioperative outcomes were compared between the two groups, and predictors of adverse perioperative outcomes were investigated by multivariate logistic regression analysis.
Results: From November 1999 to August 2004, a total of 62 patients (male 38, mean age 67 yr) with PH were found. Compared with the case-matched controls, patients with PH experienced equivalently smooth operative courses, but significantly more frequent postoperative heart failure (9.7 vs 0%, P = 0.028), delayed tracheal extubation (21 vs 3%, P = 0.004), and in-hospital deaths (9.7 vs 0%, P = 0.028). Multivariate regression analysis identified emergency surgery [odds ratio (OR), 44.738; P = 0.028], coronary artery disease (CAD; OR, 9.933; P = 0.042), and systolic pulmonary artery pressure (OR, 1.101; P = 0.026) as independent predictors of postoperative mortality and surgery-specific cardiac risk level (OR, 6.791; P = 0.033) and CAD (OR 6.546, P = 0.017) as predictors of morbidity.
Conclusion: PH is an important predictor of adverse cardiopulmonary outcome in non-cardiac surgery as reflected by markedly increased postoperative complications, especially in patients with coexistent high-risk clinical and surgical characteristics.
Keywords: complication, pulmonary hypertension; monitoring, echocardiography; surgery
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Introduction |
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Pulmonary hypertension (PH) may develop from diverse aetiologies.1 2 The resultant elevated right heart afterload, decreased venous return, reduced cardiac output, and deficient oxygen saturation renders patients extremely vulnerable to physical stresses. Perioperative management remains a challenge to anaesthesiologists and surgeons.3 In fact, a variety of cardiac and obstetric operations have been considered high-risk procedures or even being contraindicated in patients with PH because of the anticipated fluctuations of hemodynamics and ensuing aggravation of cardiopulmonary function.4–10 Nevertheless, to date, only a few studies have ever described the general characteristics of PH in non-cardiac surgery, most of them either enrolling only a small series of patients4–8 or lacking controls for comparison.9 10 Whether and how PH affects perioperative outcome in non-cardiac surgery remains incompletely understood. Aiming at clarifying the influence of PH in non-cardiac surgery, this study was therefore designed to evaluate the perioperative outcome of patients with and without PH and to identify factors predictive of adverse outcome.
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Methods |
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Patients
The present research is part of a project aiming at investigating novel cardiopulmonary outcome predictors in non-cardiac surgery. From November 1999, all patients undergoing non-cardiac, non-local anaesthetic surgery and ever evaluated by two-dimensional Doppler echocardiography within the preceding 30 days of the index surgery were screened. Patients were excluded from the study if they were already intubated for respiratory failure. Patients were enrolled into the PH group if they were documented to have an echocardiographic right ventricular systolic pressure (RVSP) value of >70 mm Hg. When more than one non-cardiac operation was performed in a single patient, only the first was selected for outcome analysis. Controls were peers case-matched to the PH patients in age (<5 yr in difference), sex, anaesthetic technique, echocardiographic left ventricular ejection fraction (LVEF, <5% in difference), surgery-specific cardiac risk level,11 and urgency of the surgery, but with an RVSP of <35 mm Hg. The study protocol had been approved by the institutional review committee on human research.
Echocardiography
Standard M-mode, two-dimensional Doppler transthoracic echocardiography was performed and interpreted by cardiology specialists according to American College of Cardiology/American Heart Association (ACC/AHA) guidelines,12 using HP 2.0-/2.5-MHz transducer on HP Sono 1000, 2000, 2500, or 5500 series (Hewlett-Packard, Andover, MA, USA). If repeated echocardiographic examinations were carried out, the closest one to the index surgery was selected for data collection. Levels of RVSP were routinely estimated by adding the right ventricular–right atrial pressure gradient (measured from Doppler peak systolic pressure gradient of tricuspid regurgitation) to the right atrial pressure (assumed to be 10 mm Hg).13 The pulmonary artery systolic pressure was in turn acquired from the RVSP, which was theoretically equal to pulmonary arterial systolic pressure in the absence of right ventricular outflow tract obstruction. Values of pulmonary arterial systolic pressure derived from this method have been shown to correlate well with those obtained from invasive cardiac catheterization study.14 The LVEF was always measured by Simpson's rule from at least two apical planes.
Clinical parameters and perioperative outcome
All clinical data were obtained by reviewing the outpatient records and the medical records taken during the entire hospitalization, including hospital admission notes, progress notes, post-anaesthetic care unit records, and discharge summary notes. Pre- and intra-operative factors recorded for the analysis included baseline characteristics of patients, co-morbid illnesses, potential aetiology of PH defined in the Evian classification,1 surgery-specific cardiac risk levels of the surgical procedures classified in ACC/AHA guidelines,11 anaesthetic technique, and utilization of invasive monitoring during surgery. The surgery-specific cardiac risk level is related to the type of the surgery and the degree of haemodynamic stress it imposes.11 Briefly, high-risk surgery includes major aortic/peripheral vascular surgery and prolonged procedures associated with large fluid shifts, blood loss or both. Intermediate risk procedures include intraperitoneal and intrathoracic surgery, carotid endartectectomy, head and neck surgery, orthopaedic surgery, and prostate surgery. Low-risk procedures include endoscopic and superficial procedures, cataract surgery, and breast surgery.11 Perioperative outcomes were dichotomized into intra-operative and postoperative components delimited by the termination time-point of anaesthesia and up to hospital discharge. Intra-operative adverse events monitored included hypotension (systolic pressure <90 mm Hg or a 30% decrease from baseline), haemodynamically significant bradycardia (heart rate <55 beats min–1), pulmonary oedema (pink foamy sputum with elevated central venous pressure), myocardial ischaemia/infarction (evident from traditional electrocardiographic or biochemical markers), cardiac dysrhythmias requiring cardioversion, and mortality. Postoperative complications comprised heart failure (new pulmonary oedema or pump failure), respiratory failure (delayed tracheal extubation >24 h or reintubation for refractory respiratory failure/hypoxemia), myocardial ischaemia/infarction,15 16 cerebral stroke documented by computed tomography, cardiac dysrhythmias requiring cardioversion, and in-hospital death.
Statistical analysis
Continuous variables were expressed as mean (SD). Normally distributed continuous data were compared using unpaired Student’s t-test, whereas non-parametric continuous data were compared using Mann–Whitney U-test. Categorical variables were compared using 
2 analysis with Yate’s correction. Univariate followed by multivariate logistic regression analysis was used to identify independent correlates of perioperative mortality and morbidity in patients with PH. Rationale variables enrolled for regression analysis included patient characteristics, co-morbid illnesses, echocardiographic indicators, and operative/anaesthetic parameters. Variables were included and tested in a backward conditioned multivariate logistic regression model if their univariate P-values were <0.20. Statistical significance was defined as multivariate P < 0.05. The odds ratios (ORs) and their 95% confidence intervals from the multivariate logistic regression analysis were used as estimates of relative risk. All analyses were performed using SPSS software, version 10.1. With these statistical and regression analyses, this study was dedicated to testing the impact of PH on the perioperative outcome and to identifying independent variables that were predictive of perioperative mortality and morbidity in patients with PH undergoing non-cardiac surgery.
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Results |
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Study population
From November 1999 to August 2004, of the 63 964 patients undergoing 87 740 non-cardiac, non-local anaesthetic surgical procedures in this tertiary referral institution, there were 9593 subjects ever evaluated by a prior echocardiographic examination within 30 days of the index surgery. Among them, a total of 67 patients were documented to have an echocardiographic RVSP of >70 mm Hg, including 5 subjects who were intubated before surgery. These five patients were excluded, and the remaining 62 patients [male, 38; mean age 67 (15) yr; RVSP range, 70–122 mm Hg, mean 78.8 (9.4) mm Hg] fulfilling the inclusion criteria comprised the PH group. Another 62 case-matched patients with an echocardiographic RVSP of <35 mm Hg served as controls. These patient characteristics data in both groups are detailed in Table 1. The potential aetiologies of PH for the study group patients are listed in Table 2. In either of these two groups, there were 40 patients classified as having intermediate surgery-specific cardiac risk,11 and 22 subjects as low risk. These surgical procedures and their corresponding cardiac risk classifications are described in Table 3. However, no patient in this study was classified as having high surgery-specific cardiac risk.
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50% in any of the coronary arteries on previous coronary angiograms. CAD, coronary artery disease; LVEF, left ventricular ejection fraction; PASP, pulmonary arterial systolic pressure; NS, not significant
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PH found incidentally without apparent underlying illness identified
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Perioperative outcomes
The intra- and postoperative outcomes of both groups are detailed in Tables 4 and 5. During the intra-operative period, patients with PH encountered comparable frequency of intra-operative adverse events to the controls (19 vs 21%, P = NS), and all of these events were limited to episodes of reversible hypotension and bradycardia. In contrast, throughout the postoperative period, these PH patients had experienced significantly worse outcome than the controls in terms of heart failure, delayed tracheal extubation, and in-hospital deaths (Table 5).
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Predictors of mortality and morbidity
Univariate and multivariate logistic regression analysis revealed that urgency of surgery, CAD, and pulmonary artery pressure level predicted in-hospital deaths for the PH patients (Table 6), whereas the level of surgical risk and CAD as independent predictors of postoperative morbidity (Table 7).
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Discussion |
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The overall prevalence of PH has been reported to be as high as 28% in elderly subjects.17 However, its impact on the perioperative outcome had often been overlooked during preoperative risk stratification, because it was never classified as one of the cardiac risk factors.11
This study scrutinizing a large number of patients undergoing non-cardiac surgery reveals that advanced PH of various aetiologies is rare (67/9593, or 0.70%) and associated with a high postoperative morbidity and mortality. The patient population in this study was not uniform with respect to the underlying aetiologies of PH and may therefore provide firm evidence for PH to be a significant predictor of adverse outcome in non-cardiac surgery.
Although pulmonary vasodilator therapy has been recommended to patients with PH,3 18 none of our study patients had received this special treatment perioperatively. Even so, these patients still experienced an equivalently smooth operative course as control patients. These results may be largely attributable to the high fraction of oxygen (usually 50–100%) given during anaesthesia, which could maintain oxygen saturations at nearly 100% as monitored by intra-operative pulse oximetry, prevent the occurrence of hypoxemia-induced pulmonary vasoconstriction, and thereby avoided aggravation of PH in face of surgical stresses.3 19 20 Another possible reason might be the common peripheral vasodilatory effects of anaesthetics, which would well decrease the right ventricular preload and thereafter ameliorate the severity of PH and right ventricular ischaemia.3
Among 62 patients in this study with PH undergoing non-cardiac surgery, the i.v., intrathecal, epidural, and volatile anaesthetics used for maintenance of anaesthesia included propofol and midazolam (5 patients), bupivacaine (21 patients), isoflurane (10 patients), desflurane (12 patients), and sevoflurane (14 patients). Almost all of these agents have peripheral vasodilatory effects, but their pulmonary-specific vasoactive effects are incompletely known. Propofol was shown to potentiate pulmonary vasodilation in one study,21 whereas to attenuate pulmonary vasodilatation and induce vasoconstriction in other investigations.22–24 Some researches have demonstrated isoflurane25–27 to be a pulmonary vasodilator, but others reported the opposite results.28 29 Desflurane was once described to be neutral to the pulmonary circulation,30 yet it was later reported be a promoter of pulmonary vasoconstriction,31 in contrast to the pulmonary vasodilatory effect of sevoflurane.31 As no significant difference of intra-operative outcome was found between patients anaesthetized with various anaesthetics, no obvious clinical benefit of one anaesthetic over others was visible.
Despite the smooth surgical course mentioned above, patients with PH had encountered significantly more major adverse events (24%) and in-hospital deaths (9.7%) than the control group. The risk of postoperative morbidity found in this study was comparable with the previous data (ranging from 22 to 38%), but mortality rate (9.7%) was somewhat higher than the reported data (only 3.4–7%).9 32 The difference in mortality may be because of the relatively higher severity of PH in our study population (mean pulmonary arterial systolic pressure up to 79 mm Hg) than that in others (no more than 68 mm Hg).9 32 The findings that most of the postoperative deaths were preceded by refractory hypoxemia and ensuing cardiopulmonary failure, as similarly reported,9 suggest that the haemodynamic impact of PH could be aggravated by the surgical stress lasting to the convalescence stage, such as would pain, fluid shift, nutritional insufficiency, sympathetic activation, and potential infection, which in turn increased pulmonary vascular tone,3 compromising pulmonary oxygenation and cardiac output. These data indicate that the postoperative period is a critical time-point at which major cardiopulmonary adverse events might possibly occur, and implicate the decisive importance of meticulous fluid balancing and proper cardiopulmonary backup during the postoperative stage of non-cardiac surgery for this population of patients whenever necessary.
Coronary artery disease is known to increase substantially the perioperative risk of major non-cardiac surgery in the general population.33 34 This study further illustrates its independent predictive role of poor postoperative outcome in patients with PH undergoing low to immediate risk levels of surgery. Urgency and high-risk surgery have also been well accepted to predict the operative risk in the general population.9 35 The poor outcome associated with these two factors merits a strategy of downgrading the complexity of surgery to lower risk classes such as splitting a major operation into several lower risk operations or switching from an open operation to an endoscopic or percutaneous procedures to limit surgical stress, wound size, fluid loss, and duration of anaesthesia. Also transforming the operations from urgent to elective in order to medically stabilize patient’s vital signs instead of performing immediate surgical intervention may be an option in certain situations. Importantly, the increased risks of postoperative complications imposed by emergency surgery (OR, 44.738), CAD (OR, 6.546–9.933), and higher-risk surgery (OR, 6.791) in our patients with PH were significantly higher than the previously reported for the general population (ORs, 1.24–4.4 for emergency surgery,36–39 2.4–3.8 for CAD,33 and 2.6–2.8 for high-risk type of surgery33), implying that the unfavourable impact of these risk factors on postoperative outcome of non-cardiac surgery was further exaggerated in patients with PH.
Pulmonary artery systolic pressure reflects the degree of pulmonary vascular pathology. The correlation of pulmonary arterial systolic pressure with postoperative in-hospital death, found in this study, is consistent with the previous reports on the inverse relationship between survival and pulmonary arterial systolic pressure in patients with PH undergoing liver or lung transplantation.35 40 Aggressive measures to monitor and decrease pulmonary arterial systolic pressure, such as pulmonary artery catheterization, oxygen administration, and pulmonary vasodilator therapy with inhaled (e.g. nitric oxide and iloprostat), oral (e.g. sildenafil, L-arginine, and bosentan), s.c. (e.g. treprostinil), and i.v. (e.g. epoprostenol and prostaglandin I2) agents in the postoperative period may thus be indicated.
As the presence of CAD was determined by previous medical records alone rather than routine preoperative coronary angiography, the prevalence of CAD in patients with PH might be underestimated, and the corresponding impact on the postoperative outcome might need to be re-addressed in future studies.
In conclusion, patients with advanced PH could experience a relatively smooth intra-operative course in non-cardiac surgery when managed with current operative and anaesthetic strategies. Nonetheless, during the postoperative periods, these patients are expected to encounter a significantly higher incidence of major adverse events in terms of heart failure, prolonged tracheal intubation, and in-hospital death, especially for those with concurrent CAD, undergoing emergency operations, and with higher pulmonary arterial systolic pressure. PH may thus be viewed as a novel predictor of adverse postoperative outcome, and justifies an aggressive management of these patients after operation.
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Acknowledgement |
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This study was supported in part by the Yen-Tjing-Ling Medical Foundation CI-96.
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References |
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