Letters to Editor hemoglobin after surgery and on postoperative day one B-9, NFH, Sree Chitra Residential Complex, Poonthi Road, Kumarpuram, Trivandrum - 695 011, Kerala, India. was 13.1 and 12.2 gm/dl respectively. We generally E-mail: [email protected] transfuse patients with coronary artery disease if their hemoglobin falls below 12 gm/dl. We are aware that REFERENCES SNP administration may impair myocardial circulation; 1. Gupta A, Mehta Y. Phlebotomy for the purpose of optimizing myocardial however, we administered it for a few minutes only for stress in coronary artery disease: A questionable modality. Ann Cardic lowering the systolic arterial blood pressure to ~100 Anaesth 2010;13:74-6. mmHg so as to facilitate safe application of the aortic 2. Neema PK, Vijayakumar A, Manikandan S, Rathod RC. Infrarenal abdominal aortic aneurysm repair in presence of coronary artery cross clamp; it should be noted that the monitored disease: Optimization of myocardial stress by controlled phlebotomy. ECG remained unchanged during its administration. Ann Cardic Anaesth 2009;12:133-5. In our present practice, we deepen the level of 3. Poldermans D, Boresma E, Bax JJ, Thomson IR, van de Ven LL, Blankensteijn JD, et al. The effect of bisoprolol on perioperative anesthesia a few minutes before application of aortic mortality and myocardial infarction in high-risk patients undergoing cross clamp by increasing inspired concentration of vascular surgery. N Eng J Med 1999;341:1789-94. 4. Lindenauer PK, Pekow P, Wang K, Mamidi DK, Gutierrez B, Benjamin EM. isoflurane (2-3%); and now we do not administer SNP Perioperative beta blocker therapy and mortality after major noncardiac for reducing the systolic arterial pressure. One can surgery. N Eng J Med 2005;353:349-61. administer nitroglycerine also; however, its arterial pressure lowering effect is very weak as compared to SNP. Additionally, we monitor these patients for An anesthetic in use with regional wall motion abnormality by transesophageal bronchodilator inhaler: A echocardiography (TEE). fact less known The issue of sympathetic stimulation accompanying surgical stimulation is highly complex and does DOI: 10.4103/0971-9784.58847 not necessarily indicate inadequate analgesia; one can attenuate sympathetic responses by opioids, by The Editor, β- blockade, by neuraxial blockade, or by inhalation anesthetics, etc. The attenuation of sympathetic Agent gas monitoring (AGM) is becoming an integral part responses by epidural blockade or by high dose opioids of intraoperative monitoring. The use of hydrofluoalkane (HFA) pressurized metered dose inhaler (PMDI) during can effectively prevent the increases in preload that general anesthesia indicates an error in anesthetic gas accompany the cross-clamping of aorta but potentially agent measurement. The analyzer incorrectly identifies results in paralyzed vascular system. As we have the gas as enflurane or halothane or as a mixture of high stated, major vascular surgery is often associated concentrations [Figure 1]. Literature review to study the with significant blood loss; in such events, intact effects of inhaler contents on infrared analyzers used sympathetic vasoconstriction is the mechanism that in AGM revealed interesting facts. instantly restores the perfusion pressure. Conceivably, preservation of responsive vascular tree that can ensure myocardial perfusion and normalization of myocardial stress are the logical goals for patients undergoing vascular surgery.

Lastly, it should be appreciated that the case reports are not recommendations and there are several ways of managing a patient; what is most important is to know the intricacies of the method one is practicing and ensure safety of the patient.

Praveen Kumar Neema, Arun Vijayakumar, Manikandan S, Ramesh Chandra Rathod Department of Anaesthesiology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India Figure 1: Sharp spike in concentration of anesthetic with agent mixture and Address for correspondence: Dr. Praveen Kumar Neema, halothane on screen

Annals of Cardiac Anaesthesia  Vol. 13:1  Jan-Apr-2010 77 Letters to Editor

Infrared (IR) analyzers which are in common use are as early as 1967.[3] It was found to have moderate based on the principle that gases with two or more potency, requiring approximately 50 vol% to induce dissimilar atoms in the molecule (nitrous oxide, CO2, anesthesia, but was never developed for usein humans. and the halogenated agents) have specific and unique Levin et al. opine that similarities in absorption spectra IR light absorption spectra. Multiple wavelengths are between HFA 134a and anesthetic gases can, in part, required to distinguish between different anesthetic be predicted from the similarity in their molecular gases. The 8–12µm range represents the area of IR structure. The propellant has been shown to be safe spectrum where anesthetic gases show maximum and nonanesthetic in doses associated with inhaler use. absorbance.[1] One of the most crucial components of [4] However, norflurane is an anesthetic. This should PMDI is its propellant. The propellant provides the force caution physicians of anesthetic effect with repeated to generate the aerosol cloud and is also the medium administration or long term use. in which the active component must be suspended or dissolved. It makes up more than 99 % of the delivered Prashant Kummar, Grace Korula, Sarah Ninan, dose. Salbutamol/other drugs as such do not cause Chandrasekaran Karthikeyan interference in IR spectra because its quantity is less Department of Anesthesia, Christian Medical College and Hospital, than that of the propellant and it is in particulate form, Vellore, India not as gas. Address for correspondence: Dr. Prashant Kummar, Department of Anesthesia, Christian Medical College and Hospital, Vellore, India. After December 2008, in compliance with the UN E-mail: [email protected] Environment Program protocol on substances that deplete the ozone layer,[2] use of inhalers containing REFERENCES chlorofluorocarbons (CFCs) as a form of propellant has 1. Levin P D, Levin D, Avidan A. Medical aerosol propellant interference been discontinued for hydrofluoroalkane-pressurized with infrared anaesthetic gas monitors. Br J Anaesth 2004;92:865-9. metered dose inhalers (HFA PMDI's). The 134a HFA, 2. www.epa.gov/ozone/science/sc_fact.html. [last accessed on 2009 Dec 30] propellant in inhalers, is: 1,1,1,2-tetrafluoroethane, also 3. Shulman M, Sadove MS. 1112- Tetrafluoroethane: an inhalation known as Norflurane. From a historical point of view it anesthetic agent of intermediate potency. Anesth Analg 1967;46:629-35. 4. Huchon G, Hofbauer P, Cannizzaro G, Iacono P, Wald F. Comparison of is interesting to note that 1,1,1,2-tetrafluoroethane was the safety of drug delivery via HFA- and CFC-metered dose inhalers in developed and tested as an anesthetic agent in animals CAO. Eur Respir J 2000;15:663-9.

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