Objectives: Patients with chronic renal failure are prone to pulmonary complications. Renal transplant recipients should undergo complete preoperative evaluation to determine risk of postoperative pulmonary complications. The American Society of Anesthesiologists classification and the Assess Respiratory Risk in Surgical Patients in Catalonia risk index correlate well with incidence of postoperative pulmonary complications. Here, we compared their accuracy in predicting pulmonary complications following renal transplant.

Materials and Methods: We retrospectively reviewed medical records of renal transplant recipients between years 2004 and 2015. We collected patient data on Assess Respiratory Risk in Surgical Patients in Catalonia risk index, including demographics, smoking history, comorbidities, preoperative pulmonary risk score, laboratory results, surgery information, history of lower respiratory tract infection 1 month pret­ransplant, urgency of surgery, American Society of Anesthesiologists classification, and pulmonary complications within 1 month post­transplant.

Results: Of 172 patients (123 males; mean age 38.82 y), 22 (12.8%) developed pulmonary complication during the first month posttransplant, including effusion (9 patients), pneumonia (10 patients), respiratory inefficiency (2 patients), and pulmonary embolism (1 patient). Atelectasis was observed in 95.4% of patients with complications. A positive correlation was observed between age and development of com­plications (r = 0.171; P = .025). Regarding risk score, 75% of patients at high risk and 19.5% at intermediate risk developed pulmonary complications. Patients with low-risk scores had significantly lower complications than intermediate- and high-risk groups (P < .001). A positive correlation was observed between preope­rative risk score and complications (r = 0.34; P < .001). There was no association between the American Society of Anesthe­siologists scores and postoperative complications (P = .7).

Conclusions: The American Society of Anesthesiologists classification was found to be a weaker modality to predict pulmonary complications after renal trans­plant; as it relates to the general health status, than the Assess Respiratory Risk in Surgical Patients in Catalonia risk index.

Key words : Preoperative evaluation, Preoperative risk scores, Solid-organ transplantation

Introduction

Pulmonary complications are an important cause of morbidity and mortality in the postoperative period.¹ These complications are related to various risk factors such as type of surgery and the anesthesia, as well as comorbidities.

The American Society of Anesthesiologists (ASA) scale is commonly used to subjectively estimate preoperative health status. Although originally created for statistical data collection and reporting in anesthesia,² it is now used for allocating resources³ and predicting perioperative risk.^4-6 With this scale, patients are divided according to how their underlying medical problems produce functional impediments to their everyday activities (Table 1). Risks inherent to a specific procedure are not incorporated into the ASA classification. The Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) risk index is another tool to stratify risks while advising patients before surgery and, in some cases, to identify patients most likely to benefit from risk reduction interventions (Table 2).

Patients with chronic renal failure are prone to significant comorbidities due to various mechanisms. Patients who are selected for renal transplant must have a thorough preoperative evaluation to assess pulmonary status and to determine risk of post­operative pulmonary complications (POPC). Pulmonary complications are encountered in 2% to 19% of chronic renal failure patients undergoing nonthoracic surgery.^7,8 These complications mainly include pulmonary edema and pleural effusions.⁷ Other less frequent complications include pulmonary hypertension and pulmonary calcifications. These patients are needed to be followed and treated more aggressively to reduce POPC.

The preoperative pulmonary evaluation is in­creasingly driven by evidence-based medicine, rather than expert opinion. Patients undergoing renal transplant should routinely undergo general health assessment before surgery. Certain modifiable risk factors should be assessed and addressed to ensure minimal postoperative complications. In our recently published study, we have shown that the ARISCAT risk index is a useful tool to assess the POPC in the recipients of renal transplant.⁹ According to our literature search, however; there is lack of information on the need for the ASA scale in this patient population. We aimed to compare the ASA scale and ARISCAT risk index to predict POPC among patients undergoing renal transplant.

Materials and Methods

Patient population
Medical records of patients who underwent renal transplant at our institution between years 2004 and 2015 were retrospectively reviewed. Patient demographics, smoking history, comorbidities, preoperative pulmonary risk score (age, oxygen saturation, hemoglobin level, type of incision, length of surgery, history of lower respiratory tract infection 1 month before the surgery, urgency of surgery), ASA classification, and type of pulmonary complication within 1 month posttransplant were recorded. The study was approved by the Institutional Review Board and the Ethics Committee of the university. The protocols conformed to the ethical guidelines of the 1975 Declaration of Helsinki.

Assessment of postoperative pulmonary risk
Documented surgical information, including an ASA scale assigned by the anesthesiologist in the operating room, was reviewed for all patients. The ARISCAT risk index was used to predict the overall incidence of POPCs (of any severity), by assigning a weighted point score to 7 independent risk factors. These risk factors are advanced age, low oxygen saturation at rest, preoperative low hemoglobin level, type of incision, length of surgery, history of lower respiratory tract infection 1 month before surgery, and need for emergency surgery.¹

Definitions of postoperative pulmonary com­plications
Types of pulmonary complications within 1 month after transplant were also recorded. Lower res­piratory tract infection was defined as presence of cough with purulent sputum production, tem­perature higher than 39°C, and leukocytosis with response to appropriate antimicrobial therapy. Pneumonia was defined as presence of the above symptoms along with new lung infiltrates on chest radiographs. Although micro­biologic studies were ordered, a positive result was not mandatory to confirm the diagnosis.

Pulmonary embolism was suspected based on patient clinical presentation and laboratory data (D-dimer, chest radiograph, arterial blood gases) and objectively confirmed using computed tomography pulmonary angiography. Deep venous thrombosis was diagnosed using bilateral deep venous compression and Doppler ultrasonography.

Statistical analyses
Data were analyzed using commercially available software (Statistical Product and Services Solutions, version 20.0, SPSS Inc., Chicago, IL, USA). Kolmogorov-Smirnov and Shapiro-Wilks tests and histograms were used as tests of normality. Continuous data are presented as means ± standard deviation. Chi-squared test was used to compare the qualitative variables. For investigation of associations between nonnormally distributed or ordinal variables, correlation coefficients and their significance were calculated with the Spearman test. All P values are 2-tailed, and P values < .05 were considered statistically significant.

Results

Our study included 172 patients (123 males; mean age 38.82 ± 12.57). Demographic characteristics of the patients are shown in Table 3. Our results showed that 22 patients (12.8%) developed pulmonary complications during the first month after transplant: pleural effusion (9 patients), pneumonia (10 patients), respiratory inefficiency (2 patients), and pulmonary embolism (1 patient). Atelectasis was observed in 95.4% of the patients who developed pulmonary complications (Table 4). There were no deaths directly attributed to pulmonary complications. The number of complications according to ASA scale is depicted in Table 5.

A positive correlation was observed between age and the development of POPC (r = 0.171; P = .025) (Figure 1). In 4 patients with high preoperative pulmonary risk score, 3 developed pulmonary complications. Sixteen of 82 patients with intermediate preoperative pulmonary risk score developed pulmonary complications. Patients with low-risk scores had lower rates of pulmonary complications than those in the intermediate- and high-risk groups, with differences statistically significant (P < .001) (Table 6 and Figure 2). A positive correlation was observed between the preoperative pulmonary risk score and the POPC (r = 0.34; P < .001).

There was no significant association between the ASA scores and POPC (P = .7). There was little con­cordance between ASA scores and the ARISCAT risk index.

Discussion

To our knowledge, the relation between ASA scale and pulmonary complications has not yet been studied. In addition, the value of the ASA scale has not been compared against the ARISCAT risk index to estimate the POPC. In the present study, the ASA scale was found to be a weaker modality to predict the pulmonary complications after renal transplant, whereas the ARISCAT risk index was found to be more reliable.

The ASA scale is commonly used to subjectively estimate preoperative health status. Most reliability studies of the ASA found only fair interrater agreement about predicting the perioperative risk, thus raising concerns about the scale’s reliability.^10,11 However, Sankar and associates showed that ASA scale has moderate interrater reliability in clinical practice.¹²

Age has been previously noted as a source of disagreement in ASA ratings.¹³ Of note, there are no guidelines on how a patient’s age should be considered when assigning ASA scores. On the other hand, a systematic review prepared by the American College of Physicians estimated the effect of age on POPC among studies that used multivariable analyses to adjust for age-related comorbidities.¹⁴ This review made a novel observation that age > 50 years was an important independent predictor of risk after renal transplant. The ARISCAT risk index has a similar classification of age as an independent risk factor. In our study, we scored the patients ac­cordingly and observed a positive correlation between age and the development of POPC.

Haynes and associates found that anesthesiologists assigned patients undergoing minor surgical procedures to lower ASA classes than would be otherwise expected, even when the patients had serious medical diseases.¹⁵ Saklad stated that the ASA grade had no relation to the operative procedure, the ability of the surgeon or the anesthesiologist, or to the type of anesthesia that the patient received.² Nonetheless, many anesthesiologists still consider the ASA scale as an anesthesia risk predictor.¹¹ Although renal transplant is a major surgery, we had only 1 patient who had ASA scale of 4 and developed no pulmonary complications.

As mentioned earlier, no data exist in the literature regarding the relation between ASA scale and POPC. Nevertheless, the scale does have a moderate ability to predict postoperative mortality and cardiac complications.¹² The present study also demonstrated no relation between ASA and POPC; however, larger cohorts are required to confirm the findings.

The ARISCAT risk index is useful to stratify risk when advising patients before surgery and, in some cases, to identify patients most likely to benefit from risk-reduction interventions. In the present study, patients with low-risk scores had fewer pulmonary complications than those in the intermediate- and high-risk groups. A positive correlation was also observed between the preoperative pulmonary risk score and POPC.

Preoperative oxygen saturation levels gain an importance to estimate POPC and stay as a risk factor in the ARISCAT risk index. In uremia, pulmonary edema, pleural effusions, and respiratory muscle myopathy¹⁶ lead to diminished pulmonary function and may alter respiration. Thus, a reduction in vital capacity, decreased expiratory flows, decreased respiratory muscle strength, and hypoxemia may occur.¹⁷

Data regarding the risk of POPC among adults with recent upper respiratory infections are limited. It has been shown that children with active upper respiratory infection have more minor postoperative respiratory events such as oxygen desaturation, but no apparent increase in morbidity or long-term sequelae.¹⁸ Whether the same applies to surgical outcomes in adults is still unknown. However, it would seem wise to defer elective surgery in this setting. In the present study, only 1 patient reported recent upper respiratory infection.

Several large-scale retrospective studies have reported that preoperative anemia is associated with an increased risk of 30-day postoperative mortality.^19-21 Moreover, anemia with chronic kidney disease, if severe and left untreated, can result in increased risk of morbidity and mortality. Pre­operative assessment and correction of hemoglobin concentrations to normal values might reduce mortality and reduce the intensive care resource use in renal transplant recipients. In the present study, 78 patients (45.3%) had hemoglobin levels of less than 10 g/dL.

Surgical site is the single most important factor in predicting the overall risk of POPC; the incidence of complications is inversely related to the distance of the surgical incision from the diaphragm. Renal transplant surgeries are done with flank incision at our center; thus, the surgical incision site would never be considered as a risk factor for POPC according to the ARISCAT index. Surgical procedures lasting more than 3 to 4 hours are associated with a higher risk of pulmonary complications.^22,23 Renal transplant surgery is a lengthy procedure, adding a high score for POPC before the procedure starts.

There are several limitations to this study worthy of discussion. First, it is a retrospective study with a low population number from a single institution. Second, the number of patients scaled as ASA 3 and 4 was low, as these patients would not be selected for renal transplant. The reason for this is that renal transplant usually is not an emergent surgery. Thus, we would not know the complication rate in high ASA scores.

In conclusion, health care professionals caring for renal transplant recipients should be aware of possible risk factors that can be addressed before surgery. Renal transplant centers should evaluate patients according to the risk assessment indexes to estimate postoperative complications. Although ASA scale is commonly used to subjectively estimate preoperative health status, ARISCAT risk index is a stronger tool to predict POPC in the renal transplant population. It also has the advantage of being simple to calculate manually at the bedside with readily available clinical information.

References:

1. Canet J, Gallart L, Gomar C, et al. Prediction of postoperative pulmonary complications in a population-based surgical cohort. Anesthesiology. 2010;113(6):1338-1350.
   CrossRef - PubMed
   
2. Saklad M. Grading of patients for surgical procedures. Anesthesiology. 1941;2:281-284.
   CrossRef
   
3. Vogt AW, Henson LC. Unindicated preoperative testing: ASA physical status and financial implications. J Clin Anesth. 1997;9(6):437-441.
   CrossRef - PubMed
   
4. Dalton JE, Kurz A, Turan A, Mascha EJ, Sessler DI, Saager L. Development and validation of a risk quantification index for 30-day postoperative mortality and morbidity in noncardiac surgical patients. Anesthesiology. 2011;114(6):1336-1344.
   CrossRef - PubMed
   
5. Hightower CE, Riedel BJ, Feig BW, et al. A pilot study evaluating predictors of postoperative outcomes after major abdominal surgery: physiological capacity compared with the ASA physical status classification system. Br J Anaesth. 2010;104(4):465-471.
   CrossRef - PubMed
   
6. Saraçoğlu A, Yavru A, Küçükgöncü S, et al. Predictive factors involved in development of postoperative pulmonary complications. Turk J Anaesthesiol Reanim. 2014;42(6):313-319.
   CrossRef - PubMed
   
7. Fairshter RD, Vaziri ND, Mirahmadi MK. Lung pathology in chronic hemodialysis patients. Int J Artif Organs. 1982;5(2):97-100.
   PubMed
   
8. Fisher BW, Majumdar SR, McAlister FA. Predicting pulmonary complications after nonthoracic surgery: A systematic review of blinded studies. Am J Med. 2002;112(3):219-225.
   CrossRef - PubMed
   
9. Küpeli E, Dedekarginoğlu BE, Ulubay G, Haberal M. Association between preoperative pulmonary risk scores and postoperative complications in renal transplant recipients. Exp Clin Transplant. 2016;14(Suppl 3):82-86.
   CrossRef - PubMed
   
10. Mak PH, Campbell RC, Irwin MG; American Society of Anesthesiologists. The ASA physical status classification: inter-observer consistency. Anaesth Intensive Care. 2002;30(5):633-640.
    PubMed
    
11. Aronson WL, McAuliffe MS, Miller K. Variability in the American Society of Anesthesiologists Physical Status classification scale. AANA J. 2003;71(4):265-274.
    PubMed
    
12. Sankar A, Johnson SR, Beattie WS, Tait G, Wijeysundera DN. Reliability of the American Society of Anesthesiologists physical status scale in clinical practice. Br J Anaesth. 2014;113(3):424-432.
    CrossRef - PubMed
    
13. Owens WD, Felts JA, Spitznagel EL Jr. ASA physical status classifications: a study of consistency of ratings. Anesthesiology. 1978;49(4):239-243
    CrossRef - PubMed
    
14. Smetana GW, Lawrence VA, Cornell JE; American College of Physicians. Preoperative pulmonary risk stratification for noncardiothoracic surgery: systematic review for the American College of Physicians. Ann Intern Med. 2006;144(8):581-595.
    CrossRef - PubMed
    
15. Haynes SR, Lawler PG. An assessment of the consistency of ASA physical status classification allocation. Anaesthesia. 1995;50(3):195-199.
    CrossRef - PubMed
    
16. Prezant DJ. Effect of uremia and its treatment on pulmonary function. Lung. 1990;168(1):1-14.
    CrossRef - PubMed
    
17. Sidhu J, Ahuja G, Aulakh B, Narang A, Whig J, Sidhu U. Changes in pulmonary function in patients with chronic renal failure after successful renal transplantation. Scand J Urol Nephrol. 2007;41(2):155-160.
    CrossRef - PubMed
    
18. Tait AR, Malviya S. Anesthesia for the child with an upper respiratory tract infection: still a dilemma? Anesth Analg. 2005;100(1):59-65.
    CrossRef - PubMed
    
19. Wu WC, Schifftner TL, Henderson WG, et al. Preoperative hematocrit levels and postoperative outcomes in older patients undergoing noncardiac surgery. JAMA. 2007;297(22):2481-2488.
    CrossRef - PubMed
    
20. Saager L, Turan A, Reynolds LF, Dalton JE, Mascha EJ, Kurz A. The association between preoperative anemia and 30-day mortality and morbidity in noncardiac surgical patients. Anesth Analg. 2013;117(4):909-915.
    CrossRef - PubMed
    
21. Musallam KM, Tamim HM, Richards T, et al. Preoperative anaemia and postoperative outcomes in non-cardiac surgery: a retrospective cohort study. Lancet. 2011;378(9800):1396-1407.
    CrossRef - PubMed
    
22. Brooks-Brunn JA. Predictors of postoperative pulmonary complications following abdominal surgery. Chest. 1997;111(3):564-571.
    CrossRef - PubMed
    
23. McAlister FA, Khan NA, Straus SE, et al. Accuracy of the preoperative assessment in predicting pulmonary risk after nonthoracic surgery. Am J Respir Crit Care Med. 2003;167(5):741-744.
    CrossRef - PubMed