Letter for the article Effects of Low-Concentration Nitrous Oxide Anes

Mr Editor

We read with interest the article titled “Effects of Low-Concentration Nitrous Oxide Anesthesia on Patient Anxiety during Cataract Surgery: A Retrospective Cohort Study” published by Sasajima et al in the reputable journal “CLINICAL OPTHALMOLOGY”. We applaud this study and congratulate the authors for successful publication.

This retrospective hospital study analyzed the medical and ocular history of patients undergoing cataract surgery between October 12, 2021 and December 23, 2021. The study includes 63 patients divided into two cohorts; one had 39 patients undergoing cataract surgery with local anesthesia and N2O and the other had 24 patients undergoing surgery with only local anesthesia. The study concluded that the application of low N2O anesthesia significantly reduced patients’ anxiety and pain as well as intraoperative systolic blood pressure and diastolic blood pressure during cataract surgery.1 Although this study is very thorough, we believe that it has certain shortcomings and we would like to remedy them.

First, while Sasajima et al carefully monitored blood pressure and vital signs before administering anesthesia, they did not mention whether there were any patients with heart failure, kidney dysfunction, and liver dysfunction and whether precautions were taken when administering local anesthesia to these patients.1 Patients with stage A and stage B heart failure must receive anesthesia that does not interact with their long-term treatment, while patients with stage C and D heart failure present perioperative management challenges fluids and medical as well as the aforementioned challenges.2 Similarly, during anesthesia, hepatic blood flow decreases by 35% to 42% in the first half hour of anesthesia, but in patients with liver dysfunction, there is no compensation for the decrease blood flow which can lead to liver dysfunction and postoperative loss of consciousness. .3 On the other hand, in patients with renal insufficiency, compromised renal function can prolong the effects of anesthetic drugs by decreasing the elimination of these drugs, resulting in a prolonged anesthetic effect.4

Second, the amount of anesthesia required to maintain a clinically acceptable level of sedation differs from patient to patient, and generally patients who present with a high level of preoperative anxiety require a higher dose. Sasajima et al gave the same dosage of anesthesia (4% xylocaine eye drops) and did not take this important parameter into account, so we believe this study is subject to bias.1 A study by Maranets et al concluded that patients with higher preoperative anxiety while undergoing bilateral laparoscopic tubal ligation require a higher dose of anesthesia.5

Third, nitrous oxide anesthesia has its drawbacks such as respiratory depression, diffusion hypoxia, and postoperative nausea, so we believe that the cohort receiving N2O anesthesia should have been informed of these consequences before proceeding. be administered anesthesia.6

Although no patients in this study reported side effects from the use of nitrous oxide, we believe that a large trial with more patients should be conducted in several centers before approving the use of nitrous oxide to reduce pain and anxiety during cataract surgery.


The authors report no conflict of interest in this communication.


1. Sasajima H, Zako M, Ueta Y, Murotani K. Effects of low-concentration nitrous oxide anesthesia on patient anxiety during cataract surgery: a retrospective cohort study. Clin Ophthalmology. 2022;16:2803–2812. doi:10.2147/OPTH.S382476

2. Kotzé A, Howell SJ. Heart failure: pathophysiology, risk assessment, community management and anesthesia. Continuous Edu Anaesth Crit Care Pain Med. 2008;8(5):161–166. doi:10.1093/BJACEACCP/MKN028

3. Rahimzadeh P, Safari S, Reza Faiz SH, Alavian SM. Anesthesia for patients with liver disease. Hepat Mon. 2014;14(7):19881. doi:10.5812/HEPATMON.19881

4. Domi R, Huti G, Sula H, Baftiu N, Kaci M, Bodeci A. From pre-existing renal failure to perioperative renal protection: the anesthetist’s dilemmas. Anesth Pain Med. 2016;6(3):32386. doi:10.5812/AAPM.32386

5. Maranets I, Kain ZN. Preoperative anxiety and intraoperative anesthetic needs. anesthesia and analgesia. Anesthesia Analg. 1999;89(6):1346.

6. Knuf K, Maani CV. Nitrous oxide. In: StatPearls. StatPearls Edition; 2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532922/. Accessed September 52022.

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