Transportation of patients to the post-anesthetic recovery room without supplemental oxygen: repercutions on oxygen saturation and risk factors associated with hypoxemia

Abstracts

JUSTIFICATIVA E OBJETIVOS: O transporte de pacientes da sala de cirurgia para a sala de recuperação pós-anestésica sem o uso de oxigenoterapia suplementar é prática comum, sendo utilizada apenas em pacientes de alto risco para o desenvolvimento de hipoxemia. O objetivo deste estudo foi avaliar a incidência das alterações na saturação de oxigênio durante esse transporte e identificar os fatores de riscos associados ao desenvolvimento de hipoxemia. MÉTODO: Avaliou-se uma amostra de 882 pacientes de ambos os sexos, estado físico ASA I, II e III, submetidos a intervenções cirúrgicas eletivas de várias especialidades e sob quatro técnicas anestésicas. A variável de saturação de oxigênio foi medida e registrada imediatamente antes da saída da sala de cirurgia e, de novo, na admissão na sala de recuperação pós-anestésica. RESULTADOS: Houve maior incidência de hipoxemia moderada/intensa durante o transporte de pacientes do sexo feminino (14,47%), nos pacientes estado físico ASA II e III (14,74% e 16,46%, respectivamente) e naqueles submetidos a cirurgias cardiotorácicas (28,21%), gastroproctológicas (14,18%) e de cabeça-pescoço (18,18%). A anestesia geral, entre as técnicas anestésicas empregadas, foi fator de risco associado ao desenvolvimento de hipoxemia. CONCLUSÕES: Existem fatores associados à ocorrência de hipoxemia durante o transporte da sala de cirurgia até a sala de recuperação pós-anestésica. A utilização seletiva de oxigenoterapia deve ser orientada pela presença desses fatores de risco, ou pelo uso do oxímetro de pulso, com o intuito de diminuir a morbimortalidade e a incidência de hipoxemia no pós-operatório imediato.

COMPLICAÇÕES; MONITORIZAÇÃO; RECUPERAÇÃO PÓS-ANESTÉSICA

SCIENTIFIC ARTICLE

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 Marcondes^I; Fábio Scalet Soeiro, TSA^II; Eduardo de Abreu Ferreira^III; Artur Udelsmann, TSA^IV

^IAnestesiologista do HC-UNICAMP

^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

^{Correspondence to}

SUMMARY

BACKGROUND AND 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.

RESUMEN

JUSTIFICATIVA 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.

INTRODUCTION

The impact of surgical anesthesia on the patient's lung function is responsible for the development of hypoxemia early in the post-operatory period^1,2. 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 modality^4,5. 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.

METHODS

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.

RESULTS

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).

DISCUSSION

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 literature^8-11, 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 worse^1,4,8.

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 mortality^2,7,11,12.

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 factor^1,2,4.

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.

REFERENCES

Submitted for publication 21 de setembro de 2005

Accepted for publication 24 de abril de 2006

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• 09. Xue FS, Li BW, Zhang GS et al The influence of surgical sites on early postoperative hypoxemia in adults undergoing elective surgery. Anesth Analg, 1999;88:213-219.
• 10. Xue FS, Huang YG, Tong SY et al A comparative study of early postoperative hypoxemia in infants, children and adults undergoing elective plastic surgery. Anesth Analg, 1996;83:709-715.
• 11. Braz JRC Monitorização da oxigenação e da ventilação. Rev Bras Anestesiol, 1996;46:223-240.
• 12. Pedersen T, Dyrlund Pedersen B, Moller AM Pulse oximetry for perioperative monitoring. Cochrane Database Syst Rev, 2003; CD002013.
• 13. Grass JA The role of epidural anesthesia and analgesia in postoperative outcome. Anesthesiol Clin North Am, 2000;18:407-428.
• 14. Arozullah AM, Daley J, Henderson WG et al Multifatorial risk index for predicting postoperative respiratory failure in men after major noncardiac surgery. The National Veterans Administration Surgical Quality Improvement Program. Ann Surg, 2000;232:242-253.

*

Received from Departamento de Anestesiologia da Faculdade de Ciências Médicas da Universidade Estadual de Campinas (FCM-UNICAMP), Campinas, SP.

Publication Dates

• Publication in this collection
  24 July 2006
• Date of issue
  Aug 2006

History

• Accepted
  24 Apr 2006
• Received
  21 Sept 2005