Scott Segal, MD
Associate Professor of Anaesthesia, Harvard Medical School
Brigham and Women's Hospital
The ASA Physical Status classification (ASA PS) has a tortuous and colorful history spanning over 60 years. Originally designed to provide a common language for anesthesiologists to describe the preanesthetic status of patients (1), it has also been used to predict surgical morbidity and mortality (2), adjust for case mix in clinical studies (3), and less successfully, to estimate anesthetic risk (4). Although investigators have used it in ways far exceeding its original intent, the essential features of the scale have not changed since its earliest iterations. When one returns to these original and still valid roots, I contend that nearly all obstetric patients should be coded with an "E" modifier.
Keats has meticulously reviewed the strange journey of the ASA PS (5). Saklad, Rovenstein, and Taylor first described a "grading of patients for surgical procedures" in 1941 (1). The scale they proposed addressed the patient's preoperative state only, not the surgical procedure or other factors that could influence surgical outcome. They hoped anesthesiologists from all parts of the country would adopt their "common terminology," making statistical comparisons of morbidity and mortality possible by comparing outcome to "the operative procedure and the patient's preoperative condition. It is this preoperative condition that we term the `Physical State'" (1).
They described a six-point scale, ranging from a healthy patient to one with an extreme systemic disorder that is an imminent threat to life. The first four points of their scale roughly correspond to today's ASA classes 1-4, which were first published in 1963 (6). The original authors included two classes that encompassed emergencies which otherwise would have been coded in either the first two classes (class 5) or the second two (class 6). Importantly, unlike later iterations of the ASA PS, this original statement clearly defined emergency: "An emergency operation is arbitrarily defined as a surgical procedure which, in the surgeon's opinion, should be performed without delay" (1). By the time of the 1963 publication of the present classification, two modifications were made. First, a class was added for moribund patients not expected to survive 24 hours, with or without surgery. Second, separate classes for emergencies were eliminated in lieu of the "E" modifier of the other classes (6).
With the exception of planned elective cesarean sections and cerclage placements, surely we can agree that obstetric procedures are performed "without delay." We do not ask laboring women to be NPO for 8 hours before receiving labor analgesia (or delivering their babies!) (7). For women in labor, and even in induced labors, anesthesia services are given without delay upon maternal request for analgesia, or obstetrical request for anesthesia for operative or surgical delivery. Indeed, ASA and the American College of Obstetricians and Gynecologists (ACOG) agree that "maternal request is a sufficient indication for pain relief in labor" (8). The unpredictable timing of provision of obstetric anesthesia services has been explicitly recognized by ASA as a reason that usual preoperative preparation guidelines are often not practical (7).
Some may argue that labor analgesia is qualitatively different than other anesthetics for true surgical procedures. I do not find this argument compelling. First, the anesthetic takes on the same importance to the patient in most cases (9). Second, any laboring patient can become a surgical patient at any time (and some 15-25% do). And third, the developers of the original Physical Status specifically stated that it was to be assigned without reference to the planned procedure (1, 5, 6). A second counterargument, that the "E" designation may be abused to increase reimbursement for anesthesia services, is cynical and untrue in most situations. In most regions of the country, the E modifier does not add to reimbursement, and indeed HCFA does not allow it under any circumstances (10). A third counterargument is that the E designation implies increased risk to the patient, but data does not support such an increase in risk. This is simply a misinterpretation of the E designation, and indeed the entire ASA PS system, which explicitly was not intended to be a direct estimation of either surgical or anesthetic risk (1, 5).
Therefore, obstetric anesthetic procedures are performed urgently and generally without delay to relieve labor pain or provide anesthesia for instrumental vaginal or cesarean delivery. Considering the framers' original intent when drafting the ASA physical status, it is appropriate to use the E modifier of the ASA Physical Status for nearly all parturients.
1. Saklad M. Grading of patients for surgical procedures. Anesthesiology 1941; 2:281-4.
2. Prause G, Ratzenhofer-Comenda B, Pierer G, Smolle-Juttner F, Glanzer H, Smolle J. Can ASA grade or Goldman's cardiac risk index predict peri-operative mortality? A study of 16,227 patients. Anaesthesia 1997 Mar; 52(3):203-6
3. Cullen DJ, Apolone G, Greenfield S, Guadagnoli E, Cleary P. ASA Physical Status and age predict morbidity after three surgical procedures. Ann Surg 1994 Jul;220(1):3-9.
4. Marx GR, Mateo CV, Orkin LR. Computer analysis of post anesthetic death. Anesthesiology 1973; 39:54-58.
5. Keats AS. The ASA classification of physical status—a recapitulation. Anesthesiology 1978; 49:233-236.
6. New classification of physical status. Anesthesiology 1963; 24:111.
7. Practice guidelines for obstetrical anesthesia: a report by the American Society of Anesthesiologists Task Force on Obstetrical Anesthesia. Anesthesiology. 1999 Feb; 90(2):600-11.
8. American College of Obstetricians, American Society of Anesthesiologists. Pain relief during labor. Number 231, February 2000.
9. Geary M, Fanagan M, Boylan P. Maternal satisfaction with management in labour and preference for mode of delivery. J Perinat Med. 1997;25(5):433-9.
10. Anesthesia Answer Book. UCG: Rockville MD, 2002 Quarterly Edition, p. 16101.