CLINICAL REPORT

Marked hypercapnia during cardiopulmonary bypass for myocardial revascularization. Case report^*

Hipercapnia acentuada durante circulación extracorpórea en cirugía para revascularización del miocárdio. Relato de caso

Maurício Serrano Nascimento, TSA, M.D.^I; Cassiano Franco Bernardes, M.D.^II; Roberta Louro de Medeiros, M.D.^III

^IInstrutor do CET/SBA do Hospital Santa Rita, Anestesiologista do Hospital Santa Rita de Cássia
^IICo-responsável pelo CET/SBA do Hospital Santa Rita de Cássia,  Anestesiologista da Santa Casa de Misericórdia de Vitória e do Hospital e Maternidade Santa Paula
^IIIME₁ do CET/SBA do Hospital Santa Rita de Cássia

Correspondence

SUMMARY

BACKGROUND AND OBJECTIVES: Bypassing heart blood and returning it oxygenated to systemic circulation is achieved at the expenses of major cardiopulmonary physiologic changes. The aim of this report was to present an anesthetic complication during CPB and to warn for the need of interaction of the whole anesthetic-surgical team to prevent adverse perioperative events.
CASE REPORT: A brown female patient, 56 years old, 95 kg, height 1.65 m, physical status ASA IV, with chronic renal failure under hemodialysis was admitted for myocardial revascularization. Monitoring consisted of ECG, invasive blood pressure, pulse oximetry, capnography, esophageal temperature, central venous pressure and anesthetic gases analysis. Patient was premedicated with intravenous midazolam (0.05 mg.kg^-1). Anesthesia was induced with fentanyl (16 µg.kg^-1), etomidate (0.3 mg.kg^-1) and pancuronium (0.1 mg.kg^-1), and was maintained with O₂, isoflurane (0.5 - 1 MAC) and fentanyl continuous infusion. Blood gas analysis after induction has shown: pH: 7.41; PaO₂: 288 mmHg; PaCO₂: 38 mmHg; HCO₃: 24 mmol.L^-1; BE: 0 mmol.L^-1; SatO₂ 100%. A second blood gases analysis, sampled soon after CPB, returned in 30 minutes, showing: pH 7.15; PaO₂: 86 mmHg; PaCO₂ 224 mmHg; HCO₃: 29 mmol.L^-1; BE: -3 mmol.L^-1; SatO₂ 99%. Thorough and urgent checking of anesthetic and perfusion equipment was performed and revealed that the gas blender was connected to the O₂ line and to a CO₂ cylinder, when it should be connected to the compressed air cylinder.
CONCLUSIONS: Bypass circuit mechanical problems may occur in the intraoperative period, and demand prompt repairs. Technological advances in anesthesia equipment, monitoring and safety standards will lessen the possibility of cases such as this to be repeated, but will never replace anesthesiologists surveillance.

Key words: COMPLICATIONS: hypercapnia; SURGERY, Cardiac: myocardial revascularization

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: La función primordial de desviar el sangre del corazón y retornarlo oxigenado a la circulación sistémica es conseguida a expensas de importantes alteraciones en la fisiología cardiopulmonar. El objetivo de este relato es presentar una complicación anestésica que ocurrió durante la CEC y alertar para la necesidad de la interacción de todo el equipo anestésico-quirúrgico en la prevención de eventos adversos per-operatorios.
RELATO DE CASO: Paciente femenina, parda, 56 años, 95 kg, altura 1,65 m, estado físico ASA IV, portadora de insuficiencia renal crónica en hemodiálisis, fue admitida para realización de revascularización del miocardio. La monitorización constó de eletrocardiograma (ECG), medida invasiva de la presión arterial, oximetria de pulso, capnografia, temperatura esofágica, presión venosa central y análisis de los gases anestésicos. La paciente recibió como medicación pré-anestésica, midazolam (0,05 mg.kg^-1), por vía venosa. Se inició inducción venosa con fentanil (16 µg.kg^-1), etomidato (0,3 mg.kg^-1) y pancuronio (0,1 mg.kg^-1). La manutención fue hecha con oxígeno, isoflurano (0,5 - 1 CAM) e infusión continua de fentanil. La gasometria arterial cogida después de la inducción demostró: pH: 7,41; PaO₂: 288 mmHg; PaCO₂: 38 mmHg; HCO₃: 24 mmol.L^-1; BE: 0 mmol.L^-1; SatO₂: 100%. La segunda gasometria arterial, cogida luego después del inicio de la CEC, llegó en 30 minutos y presentó: pH 7,15; PaO₂: 86 mmHg; PaCO₂ 224 mmHg; HCO₃: 29 mmol.L^-1; BE: -3 mmol.L^-1; SatO₂: 99%. Fue hecha una verificación completa y urgente de los equipamientos anestésicos y de perfusión. Fue constatada conexión del mezclador de gases de perfusión (blender) a la red de O₂ y a un cilindro de dióxido de carbono (CO₂), cuando debería estar conectado al cilindro de aire comprimido.
CONCLUSIONES: Fallas mecánicas de los componentes del circuito de extracorpórea pueden ocurrir en el per-operatorio y exigen correcciones rápidas. Los avanzos tecnológicos en los equipamientos de anestesia, monitorización y normatizaciones de seguridad atenuaron la posibilidad de que casos como ese se repitan, más jamás substituirán la presencia vigilante del anestesiólogo.

INTRODUCTION

Cardiopulmonary bypass (CPB) was introduced during the 50’s and represented the acme of studies started in the 19^th century. In 1953, Gibbon performed the first successful surgical procedure to correct an atrial septum defect. The development of techniques and equipment, as well as the knowledge brought about by the use of CPB have allowed major advances in cardiac surgeries ¹. Bypassing heart blood and returning it oxygenated to systemic circulation is achieved at the expenses of major cardiopulmonary physiologic changes. Several CPB-related complications have been described. So, cardiac surgery anesthesiologists must understand CPB mechanisms, principles and possible intercurrences ^1,2.

The aim of this was to present an anesthetic complication during CPB and to warn for the need of interaction of the whole anesthetic-surgical team to prevent adverse perioperative events.

CASE REPORT

A brown female patient, 56 years of age, 95 kg, 1.65 m, with chronic renal failure under hemodialysis, admitted for myocardial revascularization. By the time, she presented with acute coronary failure (rest angina), having been submitted to hemodialysis the day before. Physical status was defined as ASA IV, with the following preoperative results: urea: 35 mg.dl^-1, creatinine: 7.6 mg.dl^-1, hematocrit: 31.8%, hemoglobin: 10.4 mg.dl^-1; sinus rhythm in ECG and 53% ejection fraction with left ventricular hypertrophy.

Monitoring consisted of ECG, invasive blood pressure, pulse oximetry, capnography, esophageal temperature, central venous pressure and anesthetic gases analysis. Patient was premedicated with intravenous midazolam (0.05 mg.kg^-1). Anesthesia was induced with fentanyl (16 µg.kg^-1), etomidate (0.3 mg.kg^-1) and pancuronium (0.1 mg.kg^-1), and was maintained with O₂, isoflurane (0.5 - 1 MAC) and fentanyl continuous infusion. Blood gas analysis after induction has shown: pH: 7.41; PaO₂: 288 mmHg; PaCO₂: 38 mmHg; HCO₃: 24 mmol.L^-1; BE: 0 mmol.L^-1; SatO₂ 100%. A second blood gases analysis, sampled soon after CPB, returned in 30 minutes, showing: pH 7.15; PaO₂: 86 mmHg; PaCO₂ 224 mmHg; HCO₃: 29  mmol.L^-1; BE: -3  mmol.L^-1; SatO₂ 99%. Circulatory parameters were kept stable until CPB. At this point, the possibility of lab mistake was considered. The lab was contacted and confirmed blood gases analysis. Marked hypercapnia led perfusionists and anesthesiologists to perform a thorough and urgent checking of anesthesia and perfusion equipment, which revealed that the gas blender was connected to the O₂ line and to a CO₂ cylinder, when it should be connected to a compressed air cylinder. CO₂ cylinders were immediately replaced by compressed air and two new blood gas analyses were performed and indicated a gradual return to pre-CPB values (Table I). Cardiopulmonary bypass lasted for 205 minutes and weaning was achieved with vasoactive drugs in normal doses. After the surgical procedure, which lasted for 345 minutes, patient was taken to the ICU and 12 hours later she was extubated. Postoperative evolution was satisfactory, with no neurological sequelae.

DISCUSSION

Cooper et al. ³ have reviewed 1089 critical surgical events which led to 70 severe anesthetic complications. The authors concluded that 82% of the accidents were associated to human errors and only 4% of them were related to technical problems and anesthetic equipment failures, thus confirming the idea that human errors are critical factors for anesthetic incidents. Most common errors reported were respiratory circuit disconnections, wrong syringes and inadequate gas flow control. Critically ill patients are mostly affected by such errors. The authors suggest preventive measures, such as better professional training, surveillance, organization and adequate monitoring. Williamson et al. ⁴ have evaluated the role of human errors in 2000 anesthetic incident reports and concluded that they were present in 83% of times, being 25% of them related to equipment checking errors. Caplan et al. ⁵ have analyzed 1541 incident reports and observed that respiratory events accounted for 34% of complaints and were responsible for 85% of deaths or neurological sequelae. Adequate monitoring could have prevented 72% of those episodes. Caplan et al. ⁶ have warned that inadequate anesthesia equipment handling is three times more frequent than mechanical failures per se. Cardiopulmonary bypass components may present intraoperative mechanical failures. These problems demand prompt anesthetic-surgical team responses to prevent severe damage to the patients. Specific protocols to detect and resolve critical problems help saving precious time and decreasing morbidity ². Gas supply interruption may be caused by decreased line pressure, connection leakages, disconnections and unintentional wrong gas supplying. Until recently, the only way to measure blood gases was through serial blood gas analyses. Currently, monitors coupled to the CPB circuit allow continuous blood gas measurements and early disturbances diagnosis ². Intraoperative hypercapnia causes acid-base balance changes, such as respiratory acidosis, and arrhythmias, also increasing chances for brain edema due to arterial vasodilation.

Compressed air cylinder was replaced by the CO₂ cylinder because the connection plugs were the same, what should not occur. With the increase in laparoscopic surgeries, in the use of pneumatic saws and drills, the number of cylinders in surgical centers has increased. So, one should be alert to the possibility of wrong connections because, even with the standards prepared by the Associação Brasileira de Normas Técnicas (ABNT), we still face risk situations caused by lack of Brazilian standards for all connections. In our case, if the diagnosis was delayed, we probably would have had bypass weaning problems or even a lethal outcome. Technological advances in anesthesia equipment, monitoring and safety standards will lessen the possibility of cases such as this to be repeated, but will never replace anesthesiologists surveillance.

REFERENCES

01. Braz JRC, Auler Jr JOC, Amaral JLG et al - O Sistema Cardiovascular e a Anestesia. São Paulo, Editora UNESP, 1996; 147-162.        [ Links ]

02. Hensley FA, Martin DE - A Practical Approach to Cardiac Anesthesia. 2^nd Ed, Boston, Little Brown, 1995;465-481.        [ Links ]

03. Cooper JB, Newbower RS, Kitz RJ - An analysis of major errors and equipment failures in anesthesia management: considerations for prevention and detection. Anesthesiology, 1984;60: 34-42.        [ Links ]

04. Williamson JA, Webb RK, Sellen A et al - The Australian incident monitoring study. Human failure: an analysis of 2000 incident reports. Anaesth Intensive Care, 1993;21:678-683.        [ Links ]

05. Caplan RA, Posner KL, Ward RJ et al - Adverse respiratory events in anesthesia: a closed claims analysis. Anesthesiology, 1990;72:828-833.        [ Links ]

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Correspondence to
Dr. Cassiano Franco Bernardes
Rua Pedro Daniel 50/704 - Barro Vermelho
29055-500 Vitória, ES
E-mail: cassbern.vix@zaz.com.br

Submitted for publication August 13, 2001
Accepted for publication October 16, 2001

^* Received from Hospital Santa Rita de Cássia, Vitória, ES