Institution-based, prospective observational study design was conducted at Jimma Medical Center (JMC), a tertiary teaching medical center located in Jimma town, Southwest of Ethiopia. The study was conducted from March 01 to May 30, 2021. All consecutive patients who were undergoing emergency operation under GA with ETT during the study period were included in the study. Patients who underwent emergency surgery under GA and not admitted to PACU, on oxygen therapy before surgery, or sustained injury around the chest that could lead to hypoxemia (e.g., patients with pneumothorax) and patients who cannot communicate were excluded from the study after being verified by checking from their medical records and observations.
Independent factors included in the body of structured questionnaire were reached by reviewing the patient’s charts and interviewing the patients. Anesthesia and surgery-related data (e.g., type of volatile anesthetics, time of the day anesthesia administered, intravenous (IV) anesthetics, intraoperative analgesia, duration and type of surgery, and surgeon experience) was obtained from the anesthetic record sheet, patient’s chart, and operation registration books. Patients were interviewed by the data collectors to self-report socio-demographic factors and patient-related factors of EPH. During the interview of the patients, the questionnaire prepared in English was translated into Afan Oromo and Amharic, which are spoken by local community. Like other independent factors, the time of the day anesthesia ended was collected from the anesthesia chart too.
A manual pulse oximetry was used to record SpO2 during transferring the patient from the operation room (OR) to PACU and in-built pulse oximetry machine monitor was used to measure the dependent variable at PACU. Peripheral arterial oxygen saturation, heart rate (HR), blood pressure, and body temperature were also recorded with the advent of the patient monitor (except body temperature, which was recorded manually using a thermometer) at PACU at admission and at 5-min intervals for 20 min.
At the same time, patient’s sedation score (0 = agitated, 1 = calm, alert, 2 = sleepy and awaking after verbal command, 3 = sleepy and awaking after tactile stimulation, and 4 = comatose), ventilation score (0 = apnea, 1 = limited breathing, respiratory obstruction, bronchospasm or HR below 8 breath per minute, and 2 = free breathing), muscular strength score (1 = keeps grip for > 15 s or 0 = does not keep grip or keeps it for less than 15 s), and verbal pain score (0 = no pain or no answer, 1 = mild pain, 2 = moderate pain and 3 = severe pain) were recorded (Filho et al. 2001).
Covid-19 infection prevention was implemented by all bodies (principal investigator, supervisor, data collectors, and participants) involved in this study. This was achieved by using face mask and sanitizer after touching the patient’s charts and other materials and practicing recommended physical distance. For data collectors, COVID-19 infection prevention was part of the training, as well as they were enforced to wear face mask during contact with participants to collect data. Appropriate hand hygiene before touching a patient and after touching a patient and patient’s surrounding was implemented by data collectors using water and soap.
Two BSc anesthetists and two Diploma nurse Anesthesia assistants were recruited, and 1-day training was given on how to complete data collection, and they were supervised by the investigators and supervisors during data collection.
To measure the incidence of EPH, the pulse oximetry (a small device that clips to a patient finger or to a patient toes, in case the patient has no finger) was used. Pulse oximetry has become an essential technology to detect, treat, and reduce the degree of hypoxemia in the developed world. Pulse oximetry has been endorsed by the Canadian Anesthesiologists’ Society, American Society of Anesthesiologists (ASA), World Federation of Societies of Anesthesiologists, and the WHO as a minimal monitoring standard during surgery (Nesthesia and Anesthe 2010). Reliably, it monitors the peripheral oxygen saturation of the patient noninvasively. The data collectors had been alerting the PACU nurses once the patient become hypoxemic to put on oxygen.
Thus, in this study, pulse oximetry was used to measure the presence of EPH among adult patients who have undergone different emergency surgery under general anesthesia at JMC. Consequently, clinically important EPH was defined as a pulse oximetry reading less than or equal to 92% at any time throughout the study time (starting from the time patient transferring to the stretcher up to 20 min in the PACU). A pulse oximetry reading with normal wave stay for more than 30 s was taken throughout the 20 min, every 5 min. As most hypoxemic events occur during the 15 min following patients’ admission to PACU (Quintero-cifuentes and Pérez-lópez 2018a), we enforced to observe for 20 min at PACU. Another factor that limits us to the first 20 min is we had been working under budget and time constraints.
To ensure data quality, training and adequate orientation were given to all data collectors. Then, the prepared format and questionnaire were given to data collectors. For validation of the questionnaire, a pre-test was conducted on 5% of study participants at Shenen Gibe Hospital, Jimma Zone, 2 weeks before the actual data collection time, and few modifications were made. During data collection, regular supervision and follow-up were provided by the principal investigator and the data was cross checked for completeness and consistency on daily basis. After the data collected checked for completeness, consistency, and accuracy, it was entered into Epi-data software version 4.6.0.4 using data entry template.
Operational definitions
EPH
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Patients had been sorted as hypoxemic, if at any time during the observation period they were presented with SpO2 below or equal to 92% on room air for more than 30 s, and normoxaemic, if no SpO2 below 92% without oxygen therapy during the study period
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Anesthesia ended time:
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Time at which anesthesia ended was used to define it as nighttime and daytime
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Nighttime
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Anesthesia ended between 8:00 pm and 7:59 am
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Daytime
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Anesthesia ended between 8: am and 7:59 pm
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Evening
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6–9 pm
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Late evening
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9–midnight
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Late at night
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Midnight–6 am
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Toward morning
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3–6 am
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Morning
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6am–noon
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Early-morning
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6–9 am
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Mid-morning
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8–10 am
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Late morning
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9 am–noon
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Afternoon
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noon–6 pm
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Early afternoon
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noon–3 pm
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Mid-afternoon
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2–4 pm
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Late-afternoon
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3–6 pm
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General Anesthesia
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A combination of amnesia, analgesia, muscle relaxation, and ETT
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Transferring time
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Is a time of moving the patient from OR table up to PACU arrival
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Muscular strength score 1
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When patients keep a hand grip for > 15 s, while observing after letting them do so
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Muscular strength 0
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When the patient does not keep a hand grip or keep it for less than 15 s, while observing after letting them do so
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The minimum sample size required was calculated using a single population proportion formula as follows:
$$n=\frac{N(\mathrm{Z\alpha }/2 ){2}P(1-P)}{d{2} \left(N-1\right)+(\mathrm{Z\alpha }/2 ){2}P(1-P)}$$
where.
n = minimum sample size required for the study.
N = number of the study population, the annual number of patients undergone emergency surgery during the study period, which is 2650.
Zα/2 = confidence Interval (CI) at 95% which is 1.96.
d = margin of error tolerated which is (5%).
P = 50%, assumed incidence of EPH at JMC.
By substituting to the above formula, the minimum sample size required for the study was 336.
Adding 5% of non-response rate, finally, a total of 352 study participants were enrolled in the study.
Consecutive sampling technique was used, i.e., all consecutive adult patients who have undergone emergency surgery under GA with ETT, who fulfilled inclusion criteria during the study period, were included and recruited prospectively until the sample size would meet. The data was collected during the day and nighttime, as emergency surgery takes place at any time of the day.
Statistical data analysis was done using SPSS software version 22. Descriptive statistics were done and presented using tables and figures. Pearson chi-square test was used to test the level of significance. A p-value of less than 0.05 with a 95%CI was considered to constitute a statistically significant difference. Bivariable and multivariable binary logistic regressions were conducted to see the existence of the association between dependent and independent variables. All variables that were found to be statistically significant (p value less than or equal to 0.2) on bivariable analysis were entered into a multivariable logistic regression analysis to determine the significant independent predictors of EPH in those particular groups of patients.
The analyzed, compiled, and organized data was compared and discussed. Consequently, the result was presented in tables and graphs, and finally, conclusions and recommendations were generated according to the result obtained.
Ethical clearance and approval were obtained from the institutional review board of Jimma University and were brought to the office of JMC, OR head. Then, a formal letter of permission to conduct the study was taken. Oral informed consent was also obtained from each study participant after a clear orientation of the study objective, benefit, and procedures. Confidentiality of participant’s information was kept using unique codes and medical record numbers rather than personal identification. Moreover, the data collected from each study participant were used solely for the intended purpose.