Harley S. L Moseley

Capnometry and anaesthesia

In the last decade, capnography has developed from a research instrument into a monitoring device considered to be essential during anaesthesia to ensure patient safety. Hence, a comprehensive understanding of capnography has become mandatory for the anaesthetist in charge of patients in the operating room and in the intensive care unit. This review of capnography includes the methods available to determine carbon dioxide in expired air, and an analysis of the physiology of capnograms, which are followed by a description of the applications of capnography in clinical practice. The theoretical backgrounds of the effect of barometric pressure, water vapour, nitrous oxide and other factors introducing errors in the accuracy of CO2 determination by the infra-red technique, currently the most popular method in use, are detailed. Physiological factors leading to changes in end-tidal carbon dioxide are discussed together with the clinical uses of this measurement to assess pulmonary blood flow indirectly, carbon dioxide production and adequacy of alveolar ventilation. The importance of understanding the shape of the capnogram as well as end-tidal carbon dioxide measurements is emphasized and its use in the early diagnosis of adverse events such as circuit disconnections, oesophageal intubation, defective breathing systems and hypoventilation is highlighted. Finally, the precautions required in the use and interpretation of capnography are presented with the caveat that although no instrument will replace the continuous presence of the attentive physician, end-tidal carbon dioxide monitoring can be effective in the early detection of anaesthesia-related intraoperative accidents.RésuméLa capnographie est maintenant un élément essentiel du monitorage des patients pendant l’anesthésie générate et tout anesthésiste doit comprendre les principes de fonctionnement de cette technique. La présente révision décrit les méthodes disponibles de mesure de gaz carbonique (CO2) expiré, ainsi qu ’une analyse de la physiologie associée aux différents capnogrammes. Une description des applications cliniques de la capnographie fait suite à ces énoncés théoriques. Les effets de la pression barométrique, de la vapeur d’eau, du protoxide d’azote et de plusieurs autres facteurs affectant la mesure du CO2 a l’aide d’infra-rouge sont décrits. La capnographie permet une mesure indirecte de la circulation pulmonaire, de la production de CO2 et de la ventilation alveolaire. Ces mesures sont influencees par de nombreux facteurs physiologiques qu ’il importe de bien connaître afin de déterminer les limites de ce monitorage. Une bonne interprétation de la forme des cburbes de capnographie est nécessaire afin de permettre la détection précoce d’incidents dangereux tels un défaut ou débranchement du circuit anesthésique, une intubation oesophagienne ou une hypoventilation. Le présent travail permet à l’anesthésiste de revoir toutes ces notions et rappelle que même si la capnographie ne remplace pas la vigilance du clinicien, elle peut permettre la détection rapide d’événements qui pourraient mener à des complications anesthésiques.

Arterial to end tidal carbon dioxide tension difference during Caesarean section anaesthesia

The relationship between arterial carbon dioxide tension and end tidal carbon dioxide tension was studied in 19 patients during general anaesthesia for Caesarean section. Thirteen patients scheduled for elective abdominal hysterectomy formed a nonpregnant group. There was significant correlation between arterial and end tidal CO2 tensions in both groups. During Caesarean section, this difference was significantly less than in the nonpregnant group.

A new tool for measurement of process‐based performance of multispecialty tertiary care hospitals

There is an increasing need of a model for the process-based performance measurement of multispecialty tertiary care hospitals for quality improvement. Analytic hierarchy process (AHP) is utilized in this study to evolve such a model. Each step in the model was derived by group-discussions and brainstorming sessions among experienced clinicians and managers. This tool was applied to two tertiary care teaching hospitals in Barbados and India. The model enabled identification of specific areas where neither hospital performed very well, and helped to suggest recommendations to improve those areas. AHP is recommended as a valuable tool to measure the process-based performance of multispecialty tertiary care hospitals.

Terminology and the current limitations of time capnography: A brief review

The carbon dioxide (CO2) trace versus time (time capnography) is convenient and adequate for clinical use. This is the method most commonly utilized in capnography. However, the current terminology in time capnography has not yet been standardized and is, therefore, a potential source of confusion. Standard terminology that is based on convention and logic to represent the various phases of a time capnogram is essential. The time capnogram should be considered as two segments: an inspiratory segment and an expiratory segment. The inspiratory segment is termed as phase 0; the expiratory segment is divided into phases I, II, III, and, occasionally, IV, Phase I represents the CO2-free gas from the airways (anatomical dead space); phase II consists of a rapid S-shaped upswing on the tracing due to mixing of dead space gas with alveolar gas; and phase III, the alveolar plateau, represents CO2-rich gas from the alveoli. The physiologic basis of phase IV, the terminal upswing at the end of phase III, which is observed in capnograms recorded under certain circumstances (such as in pregnant subjects and obese subjects) is discussed in detail. The clinical implications of the alpha angle, which is the angle between phases II and III, and the beta angle, which is the angle between phases III and the descending limb of phase 0, are outlined. The subtle but important limitations of time capnography are reviewed; its current status as well as its future potential are explored.

The Effect of Preemptive Analgesia in Postoperative Pain Relief—A Prospective Double-Blind Randomized Study

OBJECTIVE To analyze the effect of infiltration of local anesthetics on postoperative pain relief. DESIGN Prospective randomized double-blind trial. Setting. University Teaching Hospital in Barbados, West Indies. PATIENTS Patients undergoing total abdominal hysterectomy. Interventions. Patients were randomly allocated into one of four groups according to the wound infiltration: 1) preoperative and postoperative 0.9% saline; 2) preoperative saline and postoperative local anesthetic mixture (10 mL 2% lidocaine added to 10 mL 0.5% bupivacaine); 3) preoperative local anesthetic mixture and postoperative saline; and 4) preoperative and postoperative local anesthetic mixture. Both patients and investigators were blinded to the group allocation. All patients received pre-incision tenoxicam and morphine, standardized anesthesia, and postoperative morphine by patient-controlled analgesia. Outcome measures. The amount of morphine used and the intensity of pain as measured by visual analog pain scale were recorded at 1, 2, 3, 4, 8, 12, 24, and 48 hours postoperatively. RESULTS Eighty patients were studied with 20 in each group. Total dose of morphine used by patients who received preoperative and postoperative local anesthetic infiltration was lesser compared to other groups, although there was no statistically significant difference. Similarly, there was no difference in the intensity of pain between any groups. CONCLUSIONS Local anesthetic infiltration before and/or after abdominal hysterectomy does not reduce the intensity of postoperative pain and analgesic requirements.

Arterial to end-tidal carbon dioxide tension difference during anaesthesia for tubal ligation.

Twenty‐nine patients scheduled for postnatal tubal ligation by minilaparotomy under general anaesthesia were studied. Arterial and end‐tidal carbon dioxide tensions were determined during anaesthesia. The mean arterial to end‐tidal carbon dioxide tension difference was 0.08 kPa (SEM 0.05). Thirty‐one percent of the patients had negative values. These results were similar to those observed during Caesarean section. The physiological changes responsible for reduced arterial to end‐tidal carbon dioxide values, persist into the postnatal period. It is predicted from the regression analysis of the time between delivery and anaesthesia for tubal ligation and arterial to end‐tidal CO2 difference, that the values might return to normal nonpregnant levels by 8 days following delivery.

Futility-of-care decisions in the treatment of moribund intensive care patients in a developing country

PurposeTo analyze the characteristics of moribund patients in a surgical intensive care unit (ICU) and highlight the dilemmas inherent in treating such patients.MethodsData on all patients admitted to the surgical ICU during the period of three years from July 1999 to June 2002 were collected prospectively. Data were collected on very ill patients who died, in whom it appeared obvious that treatment could not have improved their condition and whose death could have been anticipated. The case notes were subjected to further analysis to determine the difficulties encountered in managing patients whose therapy was considered to be futile.ResultsOf 662 admissions, 100 (15.1%) died and 30 (4.5%) patients were treated aggressively, even after a prognosis which reflected futile treatment. The overall mean length of stay for survivors was 7.5 ± 9.0 [standard deviation (SD)] days and that for the non-survivors was 12.8 ± 18.1 (SD;P < 0.001). The cost incurred for the treatment of non-survivors was significantly higher than that for the surviving patients. The factors relating to the decisions to continue futile therapy were age of the patient, legal considerations, family wishes and differing opinions between treating physicians.ConclusionConsideration of futility during end-of-life care did not receive adequate attention in this unit which incurred additional human and material resources.RésuméObjectifAnalyser les caractéristiques des patients moribonds d’une unité de soins intensifs chirurgicaux (USI) et souligner les dilemmes inhérents au traitement de ces patients.MéthodeNous avons rassemblé prospectivement les données concernant tous les patients admis à l’USI chirurgicaux de juillet 1999 à juin 2002. Nous avons gardé les données sur des patients gravement malades qui sont décédés, pour qui il est apparu évident que le traitement n’avait pas amélioré la condition et dont la mort pouvait être prévue Les informations ont été ensuite soumises à une analyse supplémentaire afin de préciser les difficultés de prise en charge de ces patients dont le traitement était considéré inutile.RésultatsDes 662 patients admis, 100 (15,1 %) sont décédés et 30 (4,5 %) ont reçu un traitement énergique, même après un pronostic qui révélait l’inutilité du traitement. La moyenne globale de la longueur du séjour hospitalier des survivants a été de 7,5 ± 9,0 jours [écart type] et celle des non survivants a été de 12,8 ± 18,1 jours (écart type; P < 0,001). Le coût du traitement des non survivants a été significativement plus élevé que celui des survivants. Les facteurs qui ont amené à poursuivre un traitement inutile étaient l’âge du patient, des préoccupations légales, des demandes de la famille et des divergences d’opinions entre les médecins traitants.ConclusionOn ne se préoccupe pas suffisamment de l’inutilité des soins aux personnes en fin de vie à l’USI chirurgicaux, ce qui entraîne l’utilisation de ressources humaines et matérielles supplémentaires.

Knowledge, attitudes and practice of medical students at the Cave Hill Campus in relation to ethics and law in healthcare

OBJECTIVES The purpose of this study is to assess the knowledge, attitudes and practices among medical students in relation to medical ethics and law. The results of the study will be a useful guide to tutors of medical students and curricula designers. METHODS A thirty-item self-administered questionnaire about knowledge of law and ethics, and the role of an ethics committee in the healthcare system was devised, tested and distributed to all levels of students and staff at the Queen Elizabeth Hospital in Barbados (a tertiary care teaching hospital) in 2003. The data from the completed questionnaires were entered into an SPSS database and analyzed using frequency and multiple cross-tabulation tables. RESULTS Completed responses were obtained from 55 (96%) of the medical students. Medical students generally attested to the importance of ethical knowledge but felt that they knew little of the law. Students varied widely as regards the frequency with which they saw ethical or legal problems, with a quarter seeing them infrequently, but another quarter seeing them every day. They received their knowledge from multiple sources and particularly from lectures/seminars, and found case conferences the most helpful. Only a few students felt that text books had been helpful. Students were generally knowledgeable about most ethical issues, but many had uncertainties on how to deal with religious differences in treating patients, on the information to be given to relatives, and how violent patients should be treated. CONCLUSIONS The results of the study highlight that medical students felt an inadequacy of knowledge of law as it pertains to their chosen career Since most of their knowledge of law was obtained from lectures, these should be reviewed and other avenues of tuition explored. The study also highlights the need to identify the minority of students who have problems with their ethical knowledge and to devise means whereby any deficiencies can be discussed and modified.

Inspiratory valve malfunction in a circle system: pitfalls in capnography

Capnography is a useful technique in monitoring the integrity of anaesthetic equipment such as the malfunctioning of unidirectional valves in circle system. However, the lack of a precise mechanism in existing capnographs to identify the start of inspiration and the beginning of expiration in the capnograms, makes the analysis of the carbon dioxide waveforms during inspiration difficult and thus results in inaccurate assessment of rebreathing. We report a case where, during the malfunction of the inspiratory unidirectional valve in the circle system, the capnograph failed to detect the presence of substantial rebreathing. Critical analysis of the capnogram recorded during the malfunction revealed that there was substantial rebreathing which was underestimated by the capnograph as it reports only the lowest CO2 concentration rebreathed during inspiration in such abnormal situations.RésuméLa capnographie peut être utile pour évaluer le fonctionnement de l’appareil d’anesthésie et en particulier des valves du circuit unidrectionnel. Cependent, pour les capnographes en usage présentement, l’absence d’un mécanisme approprié permettant d’identifier le debut de l’inspiration et de l’expiration, rend difficile l’analyse de la courbe du gaz carbonique et peut faire rater l’apparition du rebreathing. Nous rapportons ici un incident au cours duquel, le capnographe a été dans l’impossibilité de détecter un rebreathing important causé par le mauvais fonctionnement d’une valve unidirectionnelle du circuit anesthésique. Une analyse rétrospective du capnogramme enregistré pendant l’incident a montré un rebreathing considerable, sous-estimé par le capnographe, car cet appareil ne peut qu ’qfficher la plus basse concentration de CO2 réinspirée pendant l’inhalation, même dans une situation anormale telle que décrite.

Arterial to end-tidal carbon dioxide tension difference during anaesthesia in early pregnancy

Sixteen patients requiring general anaesthesia for termination of pregnancy by dilatation and evacuation of the uterus were studied. Arterial and end-tidal carbon dioxide tensions were determined during anaesthesia. The mean arterial to end-tidal carbon dioxide tension difference was 0.07 kPa (-0.02-0.16, 5-95 per cent confidence limits). These results were similar to those observed during Caesarean section and those during anaesthesia for post-delivery tubal ligations. The physiological changes such as increased cardiac output, haemodilution, and increased blood volume which manifest by 12 weeks of gestation probably result in a reduced (a-E’)PCO2 value.RésuméSeize patientes requérant une anesthésie générale pour avortement par dilatation et évacuation de ľutérus ont été étudiées. Lors de ľanesthésie, la différence entre la PCO2 artérielle et la PCO2 enfin ďexpiration fut déterminée. La différence moyenne de la PCO2 artérielle et de la PCO2 enfin ďexpiration était de 0.07 kPa (-0.02-0.16, 5-95 pour cent de limite de confiance). Ces résultats sont similaires à ceux observés lors ďune césarienne et lors ďune anesthésie après accouchement pour ligature tubaire. Les altérations physiologiques comme ľaugmentation du débit cardiaque, ľhémodilution et ľaugmentation du volume sanguin qui se manifestent 12 semaines après la gestation, amènent probablement une réduction des valeurs de (a-E’) PCO2.