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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.56 no.4 Campinas Set./Aug. 2006
Transportation of patients to the post-anesthetic recovery room without supplemental oxygen: repercutions on oxygen saturation and risk factors associated with hypoxemia*
Transporte de pacientes sin oxigenoterapia para la sala de recuperación postanestésica: repercusiones en la saturación de oxígeno y factores de riesgo asociados a la hipoxemia
Giancarlo MarcondesI; Fábio Scalet Soeiro, TSAII; Eduardo de Abreu FerreiraIII; Artur Udelsmann, TSAIV
IIAnestesiologista; Co-responsável pelo CET da Faculdade de Medicina de Sorocaba (PUC-SP)
IIIME3 do CET/SBA da FCM-UNICAMP
IVProfessor Doutor do Departamento de Anestesiologia da FCM-UNICAMP
OBJECTIVES: The transportation of patients from the operating room to the
post-anesthetic recovery room without supplemental oxygen is a common practice,
since oxygen supplementation is used only in patients at high risk of developing
hypoxemia. The objective of this study was to evaluate the incidence of changes
in oxygen saturation during this transportation and to identify the risk factors
associated to the development of hypoxemia.
METHODS: A cohort of 882 patients of both genders, physical status ASA I, II, and III, who underwent elective surgeries of several subspecialties using four different anesthetic techniques, was evaluated. Oxygen saturation was measured and recorded just before the patients left the operating room and as soon as they arrived in the recovery room.
RESULTS: There was a greater incidence of moderate to severe hypoxia during the transport of female patients (14.47%), patients with physical status ASA II and III (14.74% and 16.46%, respectively), and those who underwent cardiothoracic (28.21%), gastroproctologic (14.18%), and head and neck (18.18%) surgeries. Among the anesthetic techniques used, general anesthesia was a risk factor associated with the development of hypoxia.
CONCLUSIONS: There are factors associated with the development of hypoxia during the transportation of patients from the operating room to the post-anesthetic recovery room. The selective use of supplemental oxygen should be guided by the presence of those risk factors or by the use of a pulse oxymeter, in order to reduce the morbidity, mortality, and the incidence of hypoxemia early in the post-operatory period.
Key Words: COMPLICATIONS: hipoxemia; MONITORIZATION: pulse oximetry; POST-ANESTHETIC RECOVERY: monitorization.
Y OBJETIVOS: El transporte de pacientes de la sala de cirugía para
la sala de recuperación postanestésica sin el uso de oxigenoterapia
suplementaria es una práctica común, siendo utilizada apenas en
pacientes de alto riesgo con desarrollo de hipoxemia. El objetivo de este estudio
fue el de evaluar la incidencia de las alteraciones en la saturación
de oxígeno durante ese transporte e identificar los factores de riesgos
asociados al desarrollo de la hipoxemia.
MÉTODO: Se evaluó una muestra de 882 pacientes de ambos sexos, estado físico ASA I, II y III, sometidos a intervenciones quirúrgicas electivas de varias especialidades y bajo cuatro técnicas anestésicas. La variable de saturación de oxígeno se midió y registró inmediatamente antes de la salida de la sala de cirugía y nuevamente, a la admisión de la sala de recuperación postanestésica.
RESULTADOS: Se registró una mayor incidencia de hipoxemia moderada/intensa durante el transporte de pacientes del sexo femenino (14,47%), en los pacientes estado físico ASA II y III (14,74 y 16,46%, respectivamente) y en aquellos sometidos a cirugías cardiotorácicas (28,21%), gastro-proctológicas (14,18%) y de cabeza y cuello (18,18%). La anestesia general, entre las técnicas anestésicas empleadas fue un factor de riesgo asociado al desarrollo de la hipoxemia.
CONCLUSIONES: Existen factores asociados al aparecimiento de hipoxemia durante el transporte de la sala de cirugía hasta la sala de recuperación postanestésica. La utilización selectiva de oxigenoterapia debe ser orientada por la presencia de esos factores de riesgo, o por el uso del oxímetro de pulso, con la intención de disminuir la morbimortalidad y la incidencia de hipoxemia en el postoperatorio inmediato.
The impact of surgical anesthesia on the patient's lung function is responsible for the development of hypoxemia early in the post-operatory period1,2. This complication is more prevalent in some conditions, and the transportation to the recovery room is a critical step3. To implement preventive measures to decrease the morbidity and mortality associated with this transportation and, consequently, with the anesthesia, it is important to be aware of the risk factors associated with the increased incidence of this complication.
In an era in which cost reduction is important, as well as decision making based on solid evidence, the use of supplemental oxygen must be done rationally; however, one should not underestimate the risk of potentially severe complications caused by not using this treatment modality4,5. A study with patients who underwent coloproctologic surgeries6 showed that the prevention of hypoxemia by the administration of supplemental oxygen early in the post-operatory period is not the only goal, since it can also improve the outcome by reducing the risk of infection of the surgical wound and the incidence of nausea and vomiting. In spite of what is known, it is common practice to transport the patient to the recovery room without adequate monitoring or the administration of supplemental oxygen.
The objective of this study was to evaluate the incidence of the changes in the peripheral saturation of oxygen (SpO2) and relate it to several variables in order to identify the risk factors associated with the development of hypoxemia during the transportation of patients to the recovery room without supplemental oxygen.
Eight hundred and eighty two patients who underwent elective surgeries (except toco-gynecologic) using four different anesthetic techniques in a tertiary university hospital (HC-UNICAMP) were evaluated. This study included patients of both genders, whose ages varied from 0 to 88, and physical status I, II, or III according to the criteria of the American Society of Anesthesiologists (ASA).
Patients who needed and increase in the fraction of inspired oxygen during the transport, who remained intubated in the immediate postoperative period, who were transferred to the ICU, or who underwent emergency surgeries were excluded. All patients participating in the study were transported under the supervision of the anesthesiologist who performed the anesthesia and without supplemental oxygen.
The peripheral oxygen saturation was measured using a pulse oxymeter just before leaving the surgical room. The hemoglobin saturation was classified as normal (> 95%), mild hypoxemia (between 91% and 95%), moderate (between 86% and 90%), and severe (< 85%). Since even moderate levels are not acceptable, the patients who presented moderate to severe hypoxemia were considered as one group. The SpO2 was verified again when the patient arrived at the recovery room.
The Chi-square test was used to determine the relationship between hypoxemia and the categorical variables, while the Kruskal-Wallis test was used to determine the relationship between hypoxemia and the continual variables. The significant level adopted was 5% or p < 0.05.
Table I shows the demographics data of the patient population.
The SpO2 levels were considered normal in 531 patients (60.2%) upon arrival in the recovery room. Two hundred and forty five patients (27.8%) developed mild hypoxemia, and 106 patients (12%) presented levels considered moderate/severe (Table II).
There was a greater incidence of moderate/severe hypoxemia in 56 female patients and mild hypoxemia in 152 male patients (Table III).
There was no statistically significant correlation among the different age groups and the development of hypoxemia (Table IV).
The incidence of moderate/severe hypoxemia was greater in the patients classified as ASA II and III when compared to the patients ASA I (Table V).
The anesthetic techniques used for the surgical procedures were divided in four groups: general anesthesia, general anesthesia with epidural anesthesia; regional blockade with sedation, and regional blockade alone. Seven hundred and thirty seven patients (83.5%) received general anesthesia with or without regional blockade. Of those, 98 developed moderate/severe hypoxemia, which was statistically significant when compared to the patients who received regional blockade alone or associated with sedation that did not require tracheal intubation (Table VI).
The duration of anesthesia did not have a statistically significant correlation with the development of hypoxemia during the transportation to the recovery room (Table VII).
Forty-five patients distributed among the surgical subspecialties of head and neck, cardiothoracic, and gastro-proctologic had a greater incidence of severe hypoxemia in the immediate post-operatory period, which was statistically significant (Table VIII).
The hemoglobin dissociation curve is the clinical standard used to predict the partial pressure of oxygen from the determination of the peripheral saturation of hemoglobin. Hypoxemia is defined as a reduction of the arterial oxygen content, being diagnosed by the presence of low levels of PaO2 in the arterial blood (below 60 mmHg) or by a reduction in the SpO2 (below 95% or a reduction greater than 5% of the initial value). Severe hypoxemia is defined by a SpO2 value below 85%7.
The factors implicated in the reduction of the arterial content of oxygen include all those that change the amount of hemoglobin, the inspired fraction of oxygen, and the fractionated saturation of oxyhemoglobin. The genesis of the changes occurring during the immediate postoperative period is multifactorial, including the synergy of the patient's disease, the effects of anesthesia, and the changes caused by the surgery itself. According to the literature8-11, the fundamental components involved in that process are the age of the patient, his/her preoperative lung function, the residual action of the anesthetics used, the site of the surgery, the duration of the anesthesia, and the type of postoperative analgesia used.
Patients who underwent surgeries of the upper abdomen and the thorax have marked reduction of the residual functional lung capacity in the postoperative, as well as of the vital capacity, affecting considerably the ventilation/perfusion relationship. The diaphragmatic dysfunction that occurs in the postoperative period is caused, mainly, by the residual effects of neuromuscular blockers, and by the inadequate postoperative analgesia, which are responsible for the reflex inhibition of the physiologic diaphragmatic pacemaker4.
A history of snore and apnea during sleep suggests strongly the presence of obstructive sleep apnea, an important risk factor for postoperative apnea leading to hypoxemia. This disease is responsible for instances of episodic nocturnal and persistent hypoxemia, which is worsened by the physiopathologic respiratory disturbances occurring in the postoperative period. Obstructive sleep apnea is more common in obese, elderly men, is associated with hypertension, cardiac arrhythmias, congestive heart disease, coronary artery disease, and myocardial infarction. Episodic nocturnal hypoxemia is also associated with ischemic cardiac events, and may contribute to the increased frequency of postoperative deaths occurring at night1.
Respiratory sleep problems occur in the postoperative period even in patients without a prior history of obstructive sleep apnea. Sedatives and analgesics diminish the tonus of the hypopharynx, the ventilatory response, and awakening stimulated by hypoxia, increased CO2 level, and obstruction. The supine position, frequently used while transporting patients and in the recovery room, is another factor that makes this situation worse1,4,8.
The immediate postoperative period starts when the patient is taken to the recovery room. The oxygen monitors to be used in the perioperative period must operate continuously for the early detection of adverse events and, ideally, reduce the anesthetic-surgical morbidity7. Currently, the reduction of the SpO2 measured by the pulse oxymeter is the earliest and main sign of hypoxemia. A metanalysis published recently12 showed that several studies confirmed the need to use pulse oxymetry to detect hypoxemia and its consequences in the immediate postoperative period. Besides being a non-invasive and cost effective tool, it contributes to the early detection of cardiac events secondary to hypoxic events, reducing myocardial ischemia and bradycardia. It also identifies the occasional need for supplemental oxygen therapy after the discharge from the recovery room, thus reducing the rate of complications and the postoperative mortality2,7,11,12.
The results of this study reproduce the risk factors for the development of postoperative hypoxia. The severity of the hypoxemia during the immediate postoperative period is strongly associated with the site of the surgery9. Surgeries in the superior abdomen, here referred to as gastroproctologic surgeries, had moderate/severe hypoxemia in 14.18% of the patients, and the cardiothoracic surgeries in 28.21% of the cases. In our institution, the service of head and neck surgery is also responsible for oncologic surgeries; the results found (18.18% of the cases presented moderate/severe hypoxemia) may represent the physical and nutritional fragility of those patients (high incidence of patients with advanced age, smoking, and alcoholism) and the association with general anesthesia, which is the only one used in this specialty10.
As for the anesthetic technique used, our study reproduced the data found in the literature, which includes the residual effects of the anesthetics, the ventilatory changes imposed by mechanical ventilation, or the type of analgesia used to control the postoperative pain; 98 patients who underwent general anesthesia presented severe/moderate hypoxemia during the transportation to the recovery room without supplemental oxygen. Epidural blockades seem to be associate with a smaller incidence of severe postoperative hypoxemia, even though the difference was not statistically significant13.
The physical compromise of the patients (ASA II and III) involving the presence of systemic comorbidities was also associated with a higher frequency of hypoxemia during the transportation, and can be considered a risk factor1,2,4.
Recent efforts have been made to establish a pulmonary risk index for the development of respiratory deficiency in patients who undergo non-cardiac surgeries14. The greater difficulty in elaborating this type of preventive measure is the non-uniformity of the patient cohort being studied, making it impossible to control the biases.
Due to the similarity among the groups, the higher incidence of moderate or severe hypoxemia in female patients was a random result; further studies on this population are necessary to evaluate this event.
The results of our study showed that the risk of hypoxemia during the transportation of the patient to the recovery room is real, frequent, and can be prevented. It demonstrated that pulse oxymetry is an effective and reliable tool for the early diagnosis of hypoxemia. Currently, the reduction of the oxygen saturation measured by the pulse oxymeter is the earliest and main sign of hypoxemia in the postoperative period. It allows for fast intervention and, along with the risk factors present, selects which population actually needs an increased fraction of inspired oxygen, therefore reducing the postoperative morbidity and mortality. This study concluded that female patients, patients with ASA II and/or III, the presence of general anesthesia and gastroproctologic, cardiothoracic, and head and neck surgeries are important risk factors for hypoxemia during the transportation to the recovery room. The selection of the patient that can be transported without supplemental oxygen should be based on those results. It is necessary to monitor the population of patients with increased risk for hypoxemia, who should be transported with supplemental oxygen.
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Dr. Artur Udelsmann
Av. Professor Atílio Martini, 213
13083-830 Campinas, SP
Submitted for publication
21 de setembro de 2005
Accepted for publication 24 de abril de 2006
* Received from Departamento de Anestesiologia da Faculdade de Ciências Médicas da Universidade Estadual de Campinas (FCM-UNICAMP), Campinas, SP.