Sub-Saharan African Journal of Medicine

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 5  |  Issue : 3  |  Page : 65--68

Can preoperative haemoglobin concentration and patients’ age predict American Society of Anesthesiologists’ scores?


Saidu Y Yakubu1, Sani Awwalu2, Livingstone G Dogara3, Aliyu D Waziri2, Lawal I Ibrahim1, Kasim M Pindiga2, Aisha I Mamman2,  
1 Department of Anaesthesia, Ahmadu Bello University, Zaria, Kaduna State, Nigeria
2 Department of Haematology & Blood Transfusion, Ahmadu Bello University, Zaria, Kaduna State, Nigeria
3 Department of Haematology, Kaduna State University, Kaduna, Kaduna State, Nigeria

Correspondence Address:
Dr. Saidu Y Yakubu
Department of Anaesthesia, Ahmadu Bello University, Zaria, Kaduna State
Nigeria

Abstract

Introduction The latest version of the American Society of Anesthesiologists (ASA) score approved by the ASA House of Delegates in 2014 is used preoperatively to assess patients’ physical status (PS) before administration of anaesthesia and surgery. The ASA score does not take into consideration the patients’ age, gender or results of laboratory investigations. This study was to determine any relationship between preoperative haemoglobin (Hb) concentration, age and ASA scores. Materials and Methods Clinical records of 205 patients who had elective surgeries in a tertiary hospital for more than a period of six months were analysed for patients’ ages, gender, Hb concentrations and ASA scores, retrospectively. Data were analysed using SPSS version 20.0 with level of significance set at P ≤ 0.05. Results There were 205 patients who had surgeries during the period under review with females making up 110 (53.7%). The mean Hb and ages were 12.0 ± 1.7 g/dl and 32.2 ± 19.0 years, respectively. The median (interquartile range [IQR]) ASA-PS score was 2 (0). Most of the patients were anaemic (N = 105, 51.2%), whereas 12 (5.9%) were ≥65 years. The distribution of ASA-PS scores varied significantly across age categories (KWH statistic = 25.313, df = 4, P = <0.001). Post hoc analyses revealed that ≥65-year-olds had comparable ASA-PS scores to the ≤1 year category but higher scores compared to the 2–12-, 13–18- and 19–64-years categories. Anaemic patients had higher mean rank ASA-PS scores compared to those without anaemia (111.50 vs. 94.07, MWU statistic = 4357.000, P = 0.013). Spearman correlation analyses for ASA/Hb and ASA/age were ρ = –0.161, P = 0.021 and ρ = 0.257, P = <0.001, respectively. Multiple ordinal regression analyses to predict ASA-PS scores from Hb and age were negative with Hb (estimate = –0.261, P = 0.004) but positive with age (estimate = 0.036, P = <0.001). Conclusion Higher preoperative Hb is associated with lower ASA-PS score; older patients are more likely to have higher ASA-PS scores.



How to cite this article:
Yakubu SY, Awwalu S, Dogara LG, Waziri AD, Ibrahim LI, Pindiga KM, Mamman AI. Can preoperative haemoglobin concentration and patients’ age predict American Society of Anesthesiologists’ scores?.Sub-Saharan Afr J Med 2018;5:65-68


How to cite this URL:
Yakubu SY, Awwalu S, Dogara LG, Waziri AD, Ibrahim LI, Pindiga KM, Mamman AI. Can preoperative haemoglobin concentration and patients’ age predict American Society of Anesthesiologists’ scores?. Sub-Saharan Afr J Med [serial online] 2018 [cited 2020 Sep 24 ];5:65-68
Available from: http://www.ssajm.org/text.asp?2018/5/3/65/263564


Full Text



 Introduction



The latest version of the American Society of Anesthesiologists (ASA) physical status (PS) score approved by the ASA House of Delegates in 2014 is used preoperatively to assess a patients’ PS before administration of anaesthesia and surgery. It was initially developed for patient data collection and reporting in anaesthesia.[1] Presently, it is used for the reimbursement of anaesthesia services[2] and prediction of perioperative risk,[3],[4] among others. Its utility in perioperative risk stratification has led to a need for continuous updates with six categories of PS classifications presently in use.[5]

The ASA-PS gives a score of 1 for normal healthy patients, 2 for mild systemic disease, 3 for severe systemic disease and 4 for severe systemic disease that is a constant threat to life. In addition, scores of 5 and 6 are used for patients who are moribund (and not expected to survive without the operation) and brain dead, respectively. Although a suffix ‘E’ denotes emergency procedures,[6] lower ASA scores predict lower risks.

The function of the ASA-PS score among others is to quantify the amount of physiological reserve that a patient possesses at the time of assessment for a surgical procedure and as a method of adjusting healthcare billing in the USA.[7] However, the current version of the ASA-PS score does not provide specific defining examples of ‘un-wellness’ for each class. The subjectivity of this is evident as a cohort of anaesthetists may ascribe different ASA-PS score to the same patient.[7] The ASA-PS score was therefore originally designed to focus only on the preoperative comorbid state of the patient and not the surgical procedure or any other factors that could influence the outcome of surgery.[8]

Hence, there is a need to assess how simple, unambiguous and readily accessible parameters relate to ASA-PS scores in patients undergoing elective surgical procedures. We selected two parameters that are readily available, which are age and haemoglobin concentration (Hb). Both of these may be postulated to approximate to physiological reserves.[9],[10]

Haemoglobin concentration, the relative proportion of red blood cells in whole blood, is a veritable tool in assessing anaemia. Preoperative anaemia has been demonstrated to be related to the severity of underlying diseases, as well as being associated with morbidity and mortality in the first one month after the surgery.[11] It has been demonstrated that low Hb leads to relatively compromised tissue oxygenation and cardiac performance—factors that have negative consequences intra and postoperatively.[12] This is because red blood cells are important in oxygen delivery to tissues at room air or with oxygen therapy.[13] Similarly, adequate oxygenation prevents wound infection and enhances healing.[14] Halm et al.[15] demonstrated that patients with higher preoperative haemoglobin have shorter length of stay and lower odds of death and readmission 60 days after discharge.

A second factor we propose but not explicitly specified by ASA-PS score is age—a physiologic factor with several consequences on the anatomical and physiological make-up of individuals. There is a variable but progressive decline in function of the respiratory, cardiovascular and renal systems, among others, with advancing age.[16],[17],[18] These occur regardless of the presence or absence of morbidity. Hence, age is an important consideration because of these unique features.

Although some studies have attempted to assess anaemia and its impact on surgery, we were unable to get locally relevant studies. The impact of this is that population-specific characteristics may be missed. We therefore sought to assess any relationship between preoperative Hb concentration, age and ASA-PS score among patients undergoing elective surgery in Ahmadu Bello University Teaching Hospital in Zaria, Nigeria.

 Materials and Methods



Clinical records of 205 patients who had elective surgeries in a tertiary hospital in Zaria between 1 November 2016 and 30 April 2017 were analysed for patients’ ages, gender, Hb concentration and ASA-PS scores, retrospectively. Age was categorized into ≤1, 2–12, 13–18, 19–64 and ≥65 years. The first three age categories are suggested by the Pediatric General Surgery Referral Guidelines of the American Academy of Pediatrics.[19] The ≥65-years category is based on cut-off for elderly surgical patients.[20] Anaemia was defined as Hb < 11.0 g/dl (for <5 years), 11.5 (for 5–11-year-olds), 12.0 (for 12–14 years and non-pregnant women of ≥15 years), 11.0 (pregnant women) and 13.0 (men ≥15 years).[21] Data were analysed using SPSS version 20.0. Continuous variables were summarized as means ± standard deviations or medians and IQRs (IQR = 75th percentile value − 25th percentile value). Ordinal variables were reported using medians IQRs.

Spearman correlations were conducted, whereas Mann–Whitney U (MWU) and Kruskal–Wallis H (KWH) tests were conducted to assess the distribution of ASA-PS scores across the categories of Hb (anaemic vs. non-anaemic) and age categories. The level of significance was set at P ≤ 0.05 for all analyses. However, in the case of significant KWH test, further pairwise comparisons were conducted using series of MWU tests after adjusting level of significance using the Bonferroni approach. Additional multiple ordinal regression analyses were performed with age and Hb as predictor variables and ASA scores as the outcome variable.

 Results



There were 205 patients who had elective surgeries during the study period with females making up 110 (53.7%). The mean Hb and ages were 12.0 ± 1.7 g/dl and 32.2 ± 19.0 years, respectively. The median (IQR) ASA-PS score was 2 (0). Most of the patients were anaemic (N = 105, 51.2%), whereas 12 (5.9%) were ≥65 years [[Figure 1]].{Figure 1}

The distribution of ASA-PS scores varied significantly across age categories (KWH statistic = 25.313, df = 4, P = <0.001). Post hoc analyses revealed ≥65-year-olds had high mean rank ASA scores that were statistically comparable to those of the ≤1 year category but higher than those of the 2–12, 13–18 and 19–64-years categories [[Figure 2]]. Anaemic patients had higher mean rank ASA-PS scores compared to those without anaemia (111.50 vs. 94.07, MWU statistic = 4357.000, P = 0.013). Spearman correlation analyses for ASA/Hb and ASA/age were ρ = –0.161, P = 0.021 and ρ = 0.257, P = <0.001, respectively. Multiple ordinal regression analyses to predict ASA levels from Hb and age were negative with Hb (estimate = –0.261, P = 0.004) but positive with age (estimate = 0.036, P = <0.001).{Figure 2}

 Discussion



The ASA-PS score is a very important tool in assessing intraoperative risks; however, it does not consider some very important objective indices that may affect risk stratification.

The presence of higher ASA-PS scores among patients with anaemia in this study is an expected finding.[22] This is because patients with severe systemic illnesses have higher ASA scores, and anaemia is an indicator of severe or advanced illnesses. The implication of this finding is that anaemia exposes these patients to poor oxygen delivery to tissues. This is supported by the reports of Beattie et al.[23] who demonstrated that, when co-morbidities are controlled among surgical cases excluding cardiac cases, preoperative anaemia is an independent risk factor for hospital mortality. Conversely, Alan et al.[22] did not find any relationship between preoperative anaemia and adverse outcomes among neurologic surgery cases, although they were able to demonstrate greater length of hospital stay among anaemic patients.These data suggest that elderly patients have higher ASA-PS scores compared to younger age groups. This may be attributed to the presence of more co-morbidity with increasing age. Furthermore, it has been shown that the occurrence of perioperative complications increases with increasing age.[24] Interestingly, data from this study indicate that elderly patients have similar ASA-PS scores with the ≤1 year category. This finding corroborates the opinion of Doyle and Garmon who, in their classification of ASA class, stated that ‘the ASA PS classification system implicitly assumes that age is unrelated to physiological fitness, an assumption which is simply not true since neonates and the very elderly, even in the absence of disease, are far more “fragile” in their tolerance of anesthetics compared to young adults’.[25]

It is noteworthy that, although our findings indicate that parameters of age and Hb demonstrate significant differences in the distribution of ASA-PS scores, exploring these factors on a continuous scale reveals that these effects are small and weak. However, we recommend clinical trials assessing operative risks by comparing ASA-PS score on one hand with ASA-PS score enhanced with parameters such as age and preoperative Hb concentration.

 Conclusion



This study shows that higher preoperative Hb is associated with lower ASA-PS score; older patients are more likely to have higher ASA-PS scores possibly because of the presence of co-morbidities with increasing age.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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