|
PI = 0.2xmale sex-0.5xpathological W/H I+1.5xabnormal respiratory functional tests-0.5xDM-1.1xOSAS+0.5xhypercholesterolemia+0.6*MS+2.6xtime surgical >2hours-1.8xTIVA+0.1xBMI ? 40 Kg/m2 |
Once the score value was obtained for each patient, another ROC curve was constructed and the AUC calculated to see its discriminatory capacity.
Finally, the empirical distribution of the index values was divided in the validation sample. These three zones would be delimited by the empirical 33.3 and 66.6 percentiles that divide the possible range of values into three equal zones. In this way, a first zone would be delimited between the lowest value (-1.40) and the 33.3 percentile that would be a low risk area for complications, an intermediate zone between the 33.3 percentile (-1.40) and 66.6 (0.484) that would be of medium risk that could be called doubtful, “gray zone” or intermediate and above the 66.6 percentile (> 0.484) would be the area with the highest risk of complications. By way of (conceptual) validation of these divisions, the percentage of complications for each zone was calculated and it was evaluated whether there were differences between these percentages by means of the Bartholomew chi (c2) square test. It would be expected to find the highest frequency of complications in the high risk zone and the lowest frequency in the low risk zone.
Results
Of the total of patients studied, 71.3% presented a BMI greater than or equal to 40 Kg/m2 that is, classified as morbidly obese.
The two groups were similar in relation to age and gender distribution. The average age was 38.3 ± 8.6, with a majority between 20 and 49 years. There was a predominance of female sex in 63.9% of patients. The overall average BMI of the total of patients was 45.4 ± 9.0, the waist circumference had a mean in the total sample of 132.7 ± 15.7. In all cases, values above those accepted as normal were observed, a matter to be expected since all the patients studied are obese. The majority of patients (68.7%) presented a waist/hip index considered as pathological.
Most of the patients were classified as ASA II physical status (79.2%), and the most frequent associated diseases were obstructive sleep apnea syndrome (32.6%), arterial hypertension (29.6%), diabetes mellitus (20.8%), arthropathy (18.9%) and hypercholesterolemia (15.1%), to a lesser extent the metabolic syndrome (8.6%) was identified, asthma bronchial (7.4%) and ischemic heart disease (4.4%). The results of respiratory functional tests showed a predominance of patients with normal functional tests in 82%. In the estimation group the predominant pattern was 53.5% restrictive, followed by the obstructive pattern in 41.9% and in the validation group, with the same pattern predominance, it was 47.6% and 40, 5%, respectively.
In the total sample there were 40 complicated patients (8.4%), predominantly in the intraoperative period followed by those who presented postoperative complications and only 3 of them had complications in both periods. There were no significant differences between the two groups (estimation and validation), in the latter there were 3 patients with complications in both periods (Table 1).
40 patients with complications presented a total of 63 complications, 32 during the intraoperative period and 31 in the immediate postoperative period. There were no differences between the two moments evaluated, however, during the intraoperative period, most of them were of cardiorespiratory origin, while in the postoperative period there were others such as nausea and vomiting that turned out to be the majority.
Table 1: Distribution of patients according to complications and study groups. HUGCG, 2005-2016
Source: Clinical history.
Table 2 represents the results of the logistic regression in the search for prognostic factors for complications. The variables that independently influenced the likelihood of complications were three. The patients with abnormal respiratory function have four times more chance of having complications than those who have a function reserved or normal respiratory (OR 4.343). The patients with a surgical time greater than two hours have approximately 14 times more chance of having complications (OR 13.652), and the patients with total intravenous anesthesia (TIVA) are less likely to have complications than those who had balanced (reference category), since the OR is less than one, behaves as a protective factor. The OR for patients with balanced anesthesia is 6.211 (1/0.161), that is, in those who were indicated a balanced anesthesia, complications were six times greater. The 95% CI for the OR of the RFT and the surgical time was wide due to the small sample size.
Table 2: Results of the logistic regression for the search of prognostic factors for complications. HUGCG, 2005-2016
When calculating the probability using the logistic regression model in the validation sample, an AUC of 0.694 (95% CI: 0.588-0.800; p = 0.003) was obtained, which evidences a good discrimination of the model between patients with and without complication (Fig. 1).
Figure 1: ROC curve for the value of the probability of having complication in the validation sample.
When the proposed score was computed in the validation sample and the ROC curve was plotted, the ABC was 0.711 (95% CI 0.607-0.815; p = 0.001) (Fig. 2).
Figure 2: ROC curve of the prognostic index score for the presence of complications in the validation sample.
Table 3 shows different cut-off points for the prognostic index score in terms of sensitivity and specificity. For example, a value greater than or equal to 0.05 has a sensitivity of 0.773 and a specificity of 0.600, that is, a value of the prognostic index greater than or equal to 0.05, could predict 77.3% of patients who will actually have complications and 60.0% of those who will not have them. The cut-off value of 0.25 has a sensitivity of 0.682 and specificity of 0.651, so before a value greater than or equal to 0.25 of the proposed indicator, 68.2% of patients who will actually have complications can be detected and 65.1% of those who will not present them.
Table 3: Sensitivity and Specificity for different cut-off points of the prognostic index with the validation sample. HUGCG, 2005-2016
Table 4 summarizes the discrimination and calibration properties of the internal (EG) and external (VG) validation sample for the constructed index. The Hosmer-Lemeshow statistician in the two samples has an associated probability value greater than 0.05, therefore there is a good calibration of this indicator and the two AUC were high, which affirms good discrimination.
Table 4: Summary of the results of calibration and discrimination of the model for the prognostic index. HUGCG, 2005-2016
Table 5 shows the estimated coefficients of the logistic regression function to estimate the probability of having complications in bariatric surgery and weightings granted to each item on the scale.
The weighting values for each of the variables are the constants that are included in the formula for calculating the prognostic index. In the case of qualitative variables, they were categorized according to presence or not, in the first case with a value of 1 and in the second case with a value of 0. In this way the complication prognosis can be calculated.
Table 5: Estimated coefficients of the Logistic Regression Function to estimate the probability of having complications in bariatric surgery and weightings granted to each item of the scale. HUGCG, 2005-2016
a coefficient of each variable in the logistic regression function, b statistical significance, c balanced anesthesia reference category.
With these values, patients can be classified as Low Risk (IP < -1.400), Medium Risk (IP -1.400 – 0.484) and High Risk (IP > 0.484)
Fig. 3 shows the distribution of patients according to risk category and the presence of complications in the validated sample. As the risk increases, the percentage of said event increases. Complicated patients were distributed in the low risk, 13.6%, in the medium risk 27.3% and for the high risk 59.1%, which was significant (p = 0.014).
Figure 3: Distribution of patients (VG) according to risk and presence of complications. Bartholomew chi-square test (c2): p = 0.014
Discussion
This is one of the studies conducted in Cuba on anesthesia for bariatric surgery with more inclusion of patients, who underwent laparoscopic vertical gastroplication, taking into account the works published in the national literature.
The complications that occurred during the entire perioperative period were few and are mainly focused on those of the cardiovascular and respiratory type. In the literature reviewed there were no incidences of intraoperative or postoperative cardiovascular and/or respiratory complications developed during this type of surgical technique with which it could be compared.
Among the clinical factors that most relate to obesity with cardiovascular disorders are the patient's age, the time of evolution and the time of its appearance, the family pathological history of this condition, the severity of obesity and regional distribution of fat The latter constitutes a risk factor for cardiovascular disease and death, independent of total body fat, since patients with abdominal obesity (visceral or central) are more prone to suffer from cardiometabolic disorders, in relation to those where fat accumulates fundamentally gluteal-femoral level (León et al., 2014; López and Cortés, 2011; Cunha et al., 2014).
Cabrera, et al. (2013) in a study carried out in Havana, used the waist-to-hip index of the Cuban tables in order to identify which of the abdominal measurements (W/H I and WC) is the most appropriate for the diagnosis of metabolic syndrome, using different pediatric definitions, in first-degree relatives of people with type 1 diabetes. They concluded that according to their data, the waist-hip index should be used and not the waist circumference suggested by the Latin American Diabetes Association, for the diagnosis of metabolic syndrome.
In a 2014 Spanish study (Fernández et al., 2014), it was shown that the W/H index or waist circumference constitute a specific marker of central obesity that together with the association with other diseases such as diabetes mellitus and arterial hypertension are part of the metabolic syndrome with a high degree of complications and cardiovascular mortality.
Thus, it seems increasingly clear that measuring total body fat and using central fat markers such as waist circumference or indexes that involve it would be better than using only BMI. However, in the present investigation it did not turn out to be an independent risk factor.
In obese people, a restrictive respiratory deterioration is characteristic with a decrease in thoracic compliance and pulmonary elasticity. These alterations predispose them to the appearance of respiratory complications during any anesthetic-surgical act (Hatem et al., 2019). If one takes into account that there is a restrictive component due to obesity itself to which an obstructive disease such as bronchial asthma or chronic obstructive pulmonary disease can be added, then it is logical to think that perioperative complications related to these alterations may occur, which can explain what was found in the present investigation.
In the literature reviewed no research was found that seeks to determine the role of alterations in the functional respiratory tests of the obese patient as a risk factor in the occurrence of perioperative complications.
Two studies that evaluate the usefulness of spirometry in predicting postoperative events show weak predictive power and have serious methodological biases (Burgos et al., 2008; Celli et al., 2004). A review with the creation of an evidence-based clinical guide proposed by the American College of Chest Physicians (ACCP) (Brunelli et al., 2013) indicates that the prognostic value as a clinical factor of perioperative risk of forced expiratory volume in the first second (FEV1) preoperative is controversial. They recommend other predictive variables such as the diffusion capacity of carbon monoxide, the assessment of exercise capacity with the measurement of maximum oxygen consumption, the walking test for six minutes and the climbing stairs test.
However, other authors (Vargas et al., 2011) indicate that a FEV1 or forced vital capacity (FVC) less than 70% of the expected value, or a FEV1/FVC ratio less than 65% are predictors of complications. The predictive value of spirometry varies in different studies with a relative risk for pathological spirometry ranging from 0.9-3.8 and 95% confidence intervals ranging from 0.5-12.4 (Wang et al., 2017; Al Ghobain, 2012).
Nguyen, et al. (2001) in a study conducted in 70 obese patients operated with gastric bypass via conventional and laparoscopic route, assessed functional respiratory tests on the 1st, 2nd, 3rd and 7th postoperative days, finding that during the first three days with laparoscopic surgery the patients they had significantly less deterioration of lung function in relation to conventional surgery. On the 7th day he finds that the ventilatory parameters had returned to their preoperative level, in those operated by laparoscopic route, not in patients operated by conventional route.
Surgical time is considered an important factor in the association of perioperative complications, since the patient is for a longer time at risk of mechanical ventilation, administration of drugs with varying degrees of cardiovascular depression, infusion of fluids with changes in the internal environment, disorders of temperature, risk of bleeding with use of blood components, among others (Weingarten et al., 2015; Morgan and Ho, 2016).
The prolonged duration of the procedure as a risk factor is supported by most studies. Surgical procedures lasting more than three hours are associated with a high risk of suffering from perioperative complications, especially those of the respiratory type (Moonesinghe et al., 2014). Due to this, it is recommended that the time and surgical procedure be adjusted as much as possible in high-risk patients, such as the morbidly obese.
Total intravenous anesthesia successfully suppresses the stress response, decreases the risk of adverse cardiovascular events, thromboembolism, immune depression, bacterial translocation, infections, tumor spread, among others. On the contrary, inhalation agents do not suppress the stress response, thus depriving the patient of all these advantages (Orozco, 2014).
Several studies (Boveri, 2014; Caballero, 2014) demonstrate the advantages of total intravenous anesthesia (TIVA) over techniques with halogenated agents, since with TIVA less intra and postoperative stress was observed, with significant attenuation of the sympathetic-adrenergic reaction, which makes it advantageous for patients with problems cardiovascular and metabolic, as well as lower cortisol levels and lower cytokine release, especially interleukin 6, which is a very sensitive marker of tissue damage.
Although in the last 30 years perioperative mortality decreases due to advances in anesthetic care, surgical techniques and intensive care, determining the predictive factors of complications and mortality of the surgical patient is the tool for the anesthesiologist to adjust and improve the perioperative behavior (Hines, 1992; Bainbridge et al., 2012).
Yurcisin BS, et al. (2009) developed a mortality risk scale in bariatric surgery in which a point value is assigned for each risk factor presented by the patient. In that classification, from 0 to 1 the risk of mortality is 0.2%, from 2 to 3 is 1.1% and from 4 to 5 is 2.4%.
Khan MA, et al. (2013) evaluated factors capable of predicting perioperative mortality up to 30 days after surgery based on preoperative characteristics of a population of obese patients who required laparoscopic bariatric surgery. They used the database of the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) to collect all bariatric procedures performed between 2007 and 2009. They identified 44 408 patients, 79% female and 21% male, with age average 45 ± 11 years. Independent predictors associated with significantly increased mortality included age over 45 years, male sex, BMI of 50 Kg/m2 or more, open bariatric procedures, diabetes, functional status of total dependence before surgery, prior coronary intervention, preoperative dyspnea, and blood disorders. Risk stratification based on the number of risk factors showed an exponential increase in mortality as set out below: 0-1 factor (0.03%), 2-3 factors (0.16%), and 4 or more factors (7.4%).
The index constructed in this research on the estimated sample is useful to predict the risk of complications in obese patients treated with laparoscopic bariatric surgery and thus take preventive actions that lead to improvement in their perioperative care. It was possible to validate in an independent sample to that estimated by means of a logistic regression model, with which an ROC curve was constructed that evidenced a good discrimination of the model between patients with and without complications. In this way, an index that classifies patients as high, medium and low risk could be proposed.
Despite the high theoretical anesthetic-surgical risk of the morbidly obese, the results of a multicenter study (National Bariatric Surgery Registry) on 5 178 bariatric surgery interventions show a low complication rate (10.3%) and a low mortality rate (0.1%), similar results to the present investigation. The majority of complications were of respiratory origin and the risk of complications was higher in men and was directly related to age and preoperative BMI, but not to the type of intervention (Mason et al., 1992).
Improving the results requires determining the causes and redesigning the treatment strategies of the risk patients. The motivation of the patient against the surgical process, the intraoperative optimization, the adoption of preventive measures of complications, with the aim of reducing the number of organs in post-operative failure are useful (Renshaw et al., 2008).
The problems derived from anesthesia are multifactorial and are basically related to the patient's clinical condition, but also to the selection and conduct of anesthesia (Merry and Mitchell, 2018).
Conclusions
Three variables were determined that constituted an independent risk factor for the appearance of complications. With the combination of 11 of the explanatory variables considered as potential risk factors for the occurrence of complications, a predictive index was constructed that allowed patients to be classified as low, medium and high risk. The constructed index was validated in a sample different from the estimated one, with a good discrimination power.
Ethical Aspects
Due to the deliberate non-intervention for experimental purposes for the execution of the project and for the retrospective collection of the data, it was not considered necessary or appropriate to obtain the informed consent of the patients to enter the study, but the anonymity of the data collected, complying at all times with what is established in international and national regulations to safeguard the confidentiality and identity of each patient and only provide results for all of them.
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