Table of Contents    
ORIGINAL ARTICLE
Year : 2019  |  Volume : 10  |  Issue : 3  |  Page : 7-10  

Effect of oxygen content on postoperative cognitive dysfunction in patients undergoing open-heart surgery


Department of Anesthesiology and Intensive Care, Cipto Mangunkusumo General Hospital, Universitas Indonesia, Jakarta, Indonesia

Date of Web Publication14-Jan-2020

Correspondence Address:
Ratna Farida Soenarto
Cipto Mangunkusumo General Hospital, Diponegoro Street 71, Jakarta 10430
Indonesia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jnsbm.JNSBM_28_19

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   Abstract 


Introduction: Brain's decreased oxygen delivery is proposed as a risk factor for postoperative cognitive dysfunction (POCD). This study's objective was to investigate the effect of arterial oxygen content (CaO2) on POCD in patients undergoing open-heart surgery. Subjects and Methods: Adult patients listed for elective open-heart surgery at Cipto Mangunkusumo General Hospital were enrolled. The patients' cognitive function was tested using the Rey Auditory Verbal Learning Test, trail-making test, and digit span test (forward–backward) before and 5 days after surgery. The hemoglobin level, arterial saturation (SaO2), and arterial oxygen partial pressure (PaO2) were measured at the following five time points: before induction, 10 min after the commencement of cardiopulmonary bypass (CPB), 10 min after the cessation of CPB, 6 h postoperatively, and 1 day postoperatively. The CaO2 was calculated as follows: CaO2= 1.36 × hemoglobin × SaO2 + 0.003 × PaO2. Data were compared using Student's t-test or the Mann–Whitney test with SPSS software version 20.0 (IBM Corp., Armonk, NY, USA). Results: POCD was found in nine patients (47.4%). The CaO was significantly lower in patients with POCD than those without POCD at 10 min after the cessation of CPB (12.1 ± 2.6 vs. 14.5 ± 1.7, respectively; P = 0.03). The hemoglobin level appeared to be the cause of the decreased CaO2 in the POCD group (8.5 ± 2.3 vs. 10.2 ± 1.2, P = 0.06). Decreased oxygen content after CPB cessation may impair brain tissue oxygenation that causes POCD. Conclusion: Hemoglobin level may play an important role in POCD development after open-heart surgery.

Keywords: Hemoglobin, oxygen delivery, PaO2, postoperative cognitive dysfunction, SaO2


How to cite this article:
Soenarto RF, Arbi A. Effect of oxygen content on postoperative cognitive dysfunction in patients undergoing open-heart surgery. J Nat Sc Biol Med 2019;10, Suppl S1:7-10

How to cite this URL:
Soenarto RF, Arbi A. Effect of oxygen content on postoperative cognitive dysfunction in patients undergoing open-heart surgery. J Nat Sc Biol Med [serial online] 2019 [cited 2020 Jan 27];10, Suppl S1:7-10. Available from: http://www.jnsbm.org/text.asp?2019/10/3/7/275580




   Introduction Top


Postoperative cognitive dysfunction (POCD) is defined as a decrease in cognitive function after surgery. It is a reversible condition but may become permanent in patients aged ≥65 years. The clinical interest in POCD is increasing because it has been recognized to disturb patients' social life. According to the International Study of POCD,[1] the incidence of POCD in patients of advanced age undergoing noncardiac surgery is 25.8% in the 1st week postoperatively and 9.9% at 3 months postoperatively. The incidence is higher (40%) for patients undergoing cardiac surgery.[1],[2],[3],[4],[5]

Although several studies have been performed to investigate factors that contribute to POCD, many questions about POCD remain unanswered. Tissue hypoxia is suspected to be the cause of POCD. Several factors can affect oxygen delivery during cardiac surgery with cardiopulmonary bypass (CPB). Assuming that good cardiac output is maintained during CPB, the outcomes with respect to cognitive function vary. The present study was performed to investigate the effect of oxygen content on POCD in patients undergoing open-heart surgery.[1],[3],[6]


   Subjects and Methods Top


This was a prospective cohort study. The study population comprised adult patients who were listed for elective open-heart surgery in Cipto Mangunkusumo General Hospital [Table 1]. All the enrolled patients were mentally healthy as assessed by the Mini–Mental State Examination.[7] Patients with neuropsychiatric dysfunction, consumption of psychotropic drugs, or an inability to speak and write in Bahasa Indonesia were excluded from the study. CPB was used in all surgeries. Patients who did not fulfill the clinical pathway (i.e., were ready to be discharged from the hospital on postoperative day 5) were excluded from the study.
Table 1: Preoperative and intraoperative characteristics

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One day before the surgery, the patients underwent testing with several neurocognitive instruments: the Rey Auditory Verbal Learning Test (immediate and delayed), trail-making test (A and B), and digit span test (forward–backward).[7],[8],[9] These tests, validated by the Department of Psychiatry at Cipto Mangunkusumo General Hospital, were used to assess the patients' cognitive function, especially attention, memory, and executive function. All the tests were conducted in Bahasa Indonesia. The patients were tested alone, unaccompanied by any relative. These cognitive tests were repeated on postoperative day 5. Cognitive dysfunction was defined as a ≥20% decrease in the cognitive score for at least two tests.

On the day of surgery, approximately 1–2 cc blood samples were taken at the following five time points: before induction, 10 min after the commencement of CPB, 10 min after the cessation of CPB, 6 h after surgery, and 1 day after surgery. Data derived from the blood samples were the hemoglobin level, arterial oxygen saturation (SaO2), and partial pressure of oxygen (PaO2). The oxygen content (CaO2) was calculated by the following formula: CaO2= 1.36 × hemoglobin × SaO2 + 0.003 × PaO2.

Data were analyzed using SPSS software version 20.0 (IBM Corp., Armonk, NY, USA). Statistical analysis was performed by Student's t-test or the Mann–Whitney nonparametric test. P < 0.05 was considered statistically significant. Ethical clearance for this study was obtained from the Ethical Committee of the Faculty of Medicine, Universitas Indonesia (0364/UN2.F1/ETIK/2018).


   Results Top


This study involved 19 patients, of which nine (47.4%) developed POCD. The CaO2 was statistically significantly lower in patients with POCD than those without POCD at 10 min after the cessation of CPB (12.1 ± 2.6 vs. 14.5 ± 1.7, respectively; P = 0.03 [Figure 1]) [Table 2]. All patients had good and stable PaO2 and SaO2 levels during the surgery. The hemoglobin level was lower in the POCD group compared to non-POCD group, but not statistically significantly (8.5 ± 2.3 vs. 10.2 ± 1.2, respectively; P = 0.06) as described in [Table 2].
Figure 1: CaO2 between POCD and non-POCD groups. The CaO2 was similar at all time points except post-CPB, at which time it was lower in the POCD group. CaO2: oxygen content, POCD: Postoperative cognitive dysfunction, CPB: Cardiopulmonary bypass

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Table 2: Analysis of oxygen content variables between postoperative cognitive dysfunction and non- postoperative cognitive dysfunction groups

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With respect to the type of surgery, most patients with POCD had undergone coronary artery bypass graft alone (n = 7). No patients who underwent isolated valve surgery developed POCD in this study. We found that the duration of CPB was slightly longer in patients with POCD than those without POCD (136.9 ± 28.2 vs. 128.5 ± 31.0 min, respectively) [Table 2].

The statistical analysis showed that the only variable that was statistically significantly different between the POCD and non-POCD groups was the CaO2 at 10 min after CPB (12.1 ± 2.6 vs. 14.5 ± 1.7, respectively; P = 0.03). At the same measurement time point, the hemoglobin level showed that there was no statistical significance between the two groups (P = 0.06). The hemoglobin level was also not statistically significantly different between the two groups at 6 h after surgery (P = 0.08). The PaO2 and SaO2 were not significantly different between the two groups at any time point. The CaO2 was statistically significantly lower in patients with POCD than those without POCD at 10 min after the cessation of CPB (12.1 ± 2.6 vs. 14.5 ± 1.7, respectively; P = 0.03). Based on these findings, the hemoglobin level was apparently found to be the cause of the lower CaO2 in the POCD group when compared to non-POCD group (8.5 ± 2.3 vs. 10.2 ± 1.2, respectively; P = 0.06). However, lack of statistical significance was probably due to the small sample size.


   Discussion Top


POCD refers to temporarily impaired cognitive function associated with surgery. This dysfunction can occur in patients of any age, but most cases occur in patients of advanced age.[10] However, this problem is less common than postoperative cardiopulmonary complications, pain, and nausea and vomiting.[1],[2],[11] This study revealed that the incidence of POCD after open-heart surgery was 47.4%. Hypoxia was assumed to be the cause of POCD after open-heart surgery. Hypoxia may be caused by cerebral hypoperfusion, low brain oxygen saturation, bleeding, or hemodilution that lowers the hematocrit to <30%. Low oxygenation due to poor oxygen delivery was not considered to be the cause of POCD in this study. During the entire period of surgery, oxygen saturation was closely monitored which remained adequate, as shown by the PaO2, SaO2, and peripheral capillary oxygen saturation. The PaO2 and SaO2 remained adequate in both groups.[1],[6] No massive bleeding that could have led to decreased oxygen delivery to the brain occurred in this study.

The CaO2 was slightly lower in the POCD group when compared to non-POCD group at all the five time points, but the only measurement that was statistically significantly different between the two groups was the CaO210 min after CPB (P = 0.03). CaO2 is determined by the PaO2, SaO2, and hemoglobin level. SaO2 and PaO2 should remain high throughout CPB regardless of the patient's preoperative condition because these parameters are totally controlled by the perfusionist. In the present study, because the PaO2 and SaO2 were adequate in all patients, hemoglobin may have played a significant role in determining the difference between the two study groups. The hemoglobin level fluctuates during CPB. After commencing CPB, the hemoglobin level usually drops as hemodilution begins. Although the amount of priming solution was the same for all patients in this study, the hemoglobin level was lower in the POCD group when compared to non-POCD group. The amount of intravenous fluid given by the anesthesiologist was not recorded, which is considered a limitation of this study.

The early period after completion of CPB seems to be the most critical time for oxygen delivery. During this period, the circulatory system is in transition from extracorporeal circulation to physiologic circulation. Hemoglobin and hematocrit are usually low due to hemodilution during CPB. Efforts to correct the hemoglobin level are often postponed until objective findings are available. This study showed that care must be taken in the critical time after CPB. The hemoglobin level should be determined before CPB completion so that any correction needed can be initiated early. Another important time point is 6 h postoperatively. Early postoperative care for patients who have undergone cardiac surgery is often focused on their hemodynamic state, especially in patients with potentially life-threatening conditions. Correction of electrolyte and hemoglobin imbalances is often delayed because they are not displayed on the bedside monitor. This study indicates that the 6-h postoperative hemoglobin level could contribute to POCD. Another modality used to measure the hemoglobin level immediately after surgery should be available so that a low hemoglobin level can be corrected as soon as possible. This study has three main limitations. First, we did not test the correlation between the hemoglobin level and the incidence of POCD. Second, we did not analyze the flow rate during CPB. Alston et al.[12] found that CaO2 may be associated with the flow rate during CPB. Finally, the sample size was relatively small. A larger sample size is needed for further study of the relationship between CaO2 and POCD. To conclude, CaO2 may play an important role in the development of POCD after open-heart surgery. As PaO2 and SaO2 were both adequately maintained in this study, we can infer that the factor which influence the development of POCD in our study was hemoglobin level.


   Conclusion Top


Hemoglobin level may play an important role in POCD development after open-heart surgery. Clinicians should provide efforts to maintain hemoglobin level during open-heart surgery.

Financial support and sponsorship

The 3rd ICE on IMERI (International Conference and Exhibition on Indonesia Medical Education and Research Institute) committee supported the peer review and manuscript preparation of this article. This study has been supported in part by grant PITTA UI (Publikasi Internasional Terindeks untuk Tugas Akhir Mahasiswa Universitas Indonesia [2043/UN2.R3.1/HKP.05.00/2018]).

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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Chen CW, Lin CC, Chen KB, Kuo YC, Li CY, Chung CJ. Increased risk of dementia in people with previous exposure to general anesthesia: A nationwide population-based case-control study. Alzheimers Dement 2014;10:196-204.  Back to cited text no. 10
    
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Alston RP, Singh M, McLaren AD. Systemic oxygen uptake during hypothermic cardiopulmonary bypass. Effects of flow rate, flow character, and arterial pH. J Thorac Cardiovasc Surg 1989;98:757-68.  Back to cited text no. 12
    


    Figures

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    Tables

  [Table 1], [Table 2]



 

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