European Journal of Cardiovascular Medicine

Postoperative pulmonary complications (PPCs) are the most prevalent cause of postoperative noncardiac surgery morbidity, which is more likely to occur in relation to abdominal operations where pain, diaphragmatic dysfunction, atelectasis come together to limit ventilation and gaseous exchange. PPCs occur between temporary hypoxemia and respiratory distress in the post-anesthesia care unit (PACU) to pneumonia and respiratory failure with the need to reintubate and intensify care. Recent reviews underline the fact that the so-called minor early respiratory events have a clinical significance since they are often indicators of changing pulmonary compromise and are correlated with slower recovery and the use of more resources [1].

Massive observational cohort and risk validated models indicate that the risk of PPC occurs due to both patient related issues (age, comorbidity, baseline functional status) and perioperative factors (surgical location, time, anesthetic methodology). The value of the ARISCAT score and its indices demonstrates that even in a healthy adult, abdominal surgery and associated pulmonary risk comprise intermediate-to-high risk, which makes the adoption of effective intra- and immediate post-extubation measures to decrease the early respiratory degradation an imperative issue.

The emergence and extubation period is a critically delicate change of state. The protective actions of monitored ventilation and airway openness are lost during anesthesia- shallower depth, airway reflexes recover inconsistently, and the leftover depressant activity. During, major airway complications have been recurrently documented in the course of emergence, and hypoxemia was one of the most frequent physiological consequences of early airway or ventilatory collapse [4] Correspondingly, pulmonary aspiration, though comparatively uncommon, is marked by a skewed clinical outcome where it occurs and especially in patients with abnormal airway reflexes or slow gastric emptying. [5].

Notably, the postoperative hypoxemia is not an uncommon and temporary phenomenon. Nevertheless, sustained oximetry monitoring indicates that desaturation events are common and persistent after the operating room and in patients with no previous diagnosis of lung disease, indicating that early hypoxemia represents a conglomeration of atelectasis, ventilation-perfusion mismatch, opioid-induced hypoventilation, and residual anesthetics. [6]. Similar observational data collected in PACU also indicate the occurrence of adverse respiratory events in a significant minority of patients, which are closely linked with variable perioperative variables such as residual neuromuscular blockage and airway support requirement. [7].

Patient positioning is a cheap, non-intervention intervention that is plausibly physiologically beneficial during emergence. A semi-Fowler (head-up) position, as opposed to a supine position, can possibly enhance functional residual volume, enhance diaphragmatic motion, decrease cephalad displacement of abdominal contents, and ventilation perfusion matching, which might minimise hypoxemia and respiratory distress during and immediately after extubation. Abdominal surgery This clinical trial was suggested by a randomized controlled trial that arguing that extubation when in the semi-Fowler position can lead to improvement in comfort-related outcomes and coughing reduction, although clinical importance outcomes have been inconsistent and heterogeneous and evidence skewed on clinically significant early respiratory complications.

Consequently, the current randomized controlled trial had one main goal: to compare the results of extubation in supine and semi-Fowler position among adults who undergo elective abdominal surgeries during general anesthesia in terms of early post-extubation respiratory compromise (respiratory distress, hypoxemia, aspiration).

Study design, setting, and duration A single-center, prospective, parallel-group randomized controlled study was conducted over 6 months in the operating rooms and PACU of R.L. Jalappa Hospital and Research Centre, Tamaka, Kolar, India. Participants Adult patients aged 18–65 years with ASA physical status I–II scheduled for elective abdominal surgery under general anesthesia were screened. Inclusion criteria: 1. Age 18–65 years; 2) ASA I–II; 3) elective abdominal surgery requiring endotracheal intubation. Exclusion criteria: 1. Pre-existing respiratory disease (e.g., COPD, uncontrolled asthma, restrictive lung disease); 2) contraindication to head-of-bed elevation (e.g., hemodynamic instability, spinal precautions); 3) anticipated difficult airway requiring nonstandard extubation strategy; 4) emergency surgery. Ethics. Institutional ethics committee approval was obtained before initiation, and written informed consent was obtained during pre-anesthetic evaluation. The study was reported in accordance with CONSORT principles. Randomization and allocation concealment Block randomization (variable block sizes of 4 and 6) generated a 1:1 allocation sequence by an investigator not involved in outcome assessment. Sequentially numbered, opaque, sealed envelopes were opened immediately before planned emergence. Perioperative management Even the patients were provided with standardized care (ECG, non-invasive blood pressure, pulse oximetry). Intravenous opioid and hypnotic agent induced general anesthesia according to departmental protocol and was maintained by inhalational anesthesia administration encompassing neuromuscular blockage habitually. The anticholinesterase/anticholinergic agents were used to reverse neuromuscular blockade at the end of surgery as soon as the clinical criteria were achieved. The case of extubation was conducted according to the standard criteria (sufficient spontaneous ventilation, purposeful response, presence of airway reflexes, hemodynamic stability). Interventions • Supine group: extubation performed at 0° head elevation; patient remained supine for the first 30 minutes in PACU. • Semi-Fowler’s group: extubation performed at 30° head-of-bed elevation (verified using bed angle scale); position maintained for the first 30 minutes in PACU. All patients received supplemental oxygen immediately after extubation (face mask per PACU protocol) with escalation permitted if clinically indicated. Outcomes Primaryoutcome: Respiratory distress within 30 minutes post-extubation, defined as any of the following: 1. airway obstruction requiring jaw thrust and/or airway adjunct; 2. assisted ventilation (bag-mask) for hypoventilation/obstruction; 3. tachypnea with accessory muscle use requiring clinician intervention; 4. escalation of oxygen therapy beyond routine PACU flow to maintain SpO₂ ≥94%. Secondary observations: • Hypoxemia (SpO₂ <92% for >30 seconds), • Suspected aspiration (new cough/wheeze with regurgitation or particulate matter; or new oxygen requirement with witnessed regurgitation). Respiratory rate, SpO₂, heart rate, and blood pressure were recorded at extubation (T0) and at 5, 10, 20, and 30 minutes in PACU. Sample size To compare two proportions based on a two-sided 10.5 alpha and 80% power, sample size was determined. Adverse respiratory event rates Baseline reported adverse respiratory event are nearly 20 percent in observational cohorts. A clinically important change of 5 per cent with semi-Fowler positioning was assumed and therefore 75 participants in each group (n=150 overall) were needed (Charan and Biswas methodology). Statistical analysis The intention-to-treat principle was used in analysis. The summary of categorical variables was obtained as counts and percentages, the summary of continuous variables was obtained as mean (SD) or median (IQR) as necessary. The main outcome (incidence of respiratory distress) was analyzed with the help of the chi-square test, and the effect sizes were reported as RR, absolute risk difference, and 95% intervals. The statistically significant case was only achieved at two-sided p<0.05.

Main findings

One hundred and sixty-eight patients were evaluated as eligible; 150 of them were randomized (75 in each group). Every participant, who was assigned at random, did the 30 minutes PACU observation and was incorporated in the main analysis (Figure 1). Demographic and surgical baseline factors were well matched across groups (Table 1), as the age, sex, and ASA class were equally distributed, as well as procedures.

Early post-extubation respiratory distress was reduced in the group of semi-Fowler. The incidence of respiratory distress among supine patients (18.7% versus semi-Fowlers 6.7 percent) had a relative risk ratio of about 64% less (Table 3). The supine group had the most frequent clinical phenotype of the distress phenotype with upper airway blockage that necessitated jaw thrust/airway adjunct and intermittent ventilatory support.

Table 4 supported the secondary observations with fewer hypoxemia and fewer events with aspiration in the semi-Fowler group. Mean SpO₂ patterns during the initial 30 minutes were slightly greater in the semi-Fowler arm, and the rise in oxygen therapy was not as common (Table 2; Figure 2), which were not pre-specified to test the hypothesis.

Table 1. Baseline characteristics and operative profile (n=150)

The two randomized groups were similar at baseline. Age, sex distribution, BMI, and ASA physical status were structured well, which restricted the confounding of preoperative risk. There was also similarity in the operative exposure, as that very early indications of respiratory variations showed an open/laparoscopic approach and the mean duration of operation and this assertion is in accord with the presumption of early recovery respiratory variations, but not case-mix imbalance.

Table 2. Early PACU respiratory physiology and interventions (first 30 minutes)

The use of semi-Fowler was linked to slightly greater average values of SpO₂ and reduced early rise of recovery enhancement in oxygen support. It had a coherent clinical pattern: there were decreased airway adjuncts requirements and reduced oxygen escalations that are all indicative of enhanced airway openness and functional residual volume of the airways in a head-up posture at emergence. Although these supporting interventions were not aimed as primary outcomes, they are parallel to the results of the respiratory distress events observed.

Table 3. Primary outcome—Respiratory distress within 30 minutes

 The semi-Fowler approach achieved a statistically significant, clinical meaningful, decrease in the early respiratory distress. The risk reduction of 12 percent would suggest that the placement of some nine or so patients head-up on the occasion of extubation would avoid one instance of the occurrence of clinically significant distress necessitating intervention. The RR confidence interval indicates that the benefit is probably not a trivial one and that the intervention is recommended as a low-cost, workflow compatible intervention to achieve safety in abdominal surgery recovery.

Table 4. Secondary observations

Whereas not powered to test a hypothesis, the pattern of secondary events was more consistent with the positioning of semi-Fowler who had a frequency ratio about half as high of hypoxemia episodes that were observed and no events which were consistent with aspiration found in the head-up arm. The minimal aspiration rates are anticipated in elective cohorts of ASA I and ASA II and are to be heeded with care. The direction of the effect, however, is biologically possible in view of the established effect of reflux/aspiration risk and the gas exchange based on body position.

Figure

FIGURE 1.EARLY RESPIRATORY EVENTS

Recruiting and retention were robust, and all of the randomized participants finished the initial PACU observation, and participated in the initial analysis. Lack of post randomization exclusions minimizes the impact of attrition bias, and enhances internal validity. The flow also promotes the pragmatic feasibility: the head-of-bed elevation at the time of extubation needed no special equipments and did not mixed up the protocol compliance within the normal operating room and PACU routine operations.

FIGURE 2. PRIMARY OUTCOME VISUALIZATION—RESPIRATORY DISTRESS INCIDENCE BY GROUP

The effect size between groups is both large and visually significant and in line with the clinically important effect size. There is a significant decrease in the number of distress events associated with the semi-Fowler arm, which can be attributed to the number of airway maneuvers and the number of rescue respiratory support. The most significant approach to curtailing the frequency of these initial destabilizing instances in recovery regions where the quantity of staffing and monitoring is variable is the implementation of reducing the frequency of the events, which may yield smoother PACU throughput and less downstream escalation, which is consistent with the broader findings that positioning can meaningfully impact post-extubation oxygenation. 

This randomized controlled study of adults undergoing elective surgery of the abdomen under general anesthesia compared extubation at the semi-Fowler position with the supine position and found that extubation at the semi-Fowler position had a lower incidence of early postoperative respiratory compromise than did extubation at the supine position. The clinically significant variation observed was motivation mainly by presence of less post-extubation hypoxemia and respiratory distress episodes in the immediate setting and occurrence of fewer aspiration in both groups was rare. These results facilitate the idea that a low hepatic head position on emergence can have a significant effect on initial respiratory stability at the PACU.

Directionally, our findings are consistent with existing randomized evidence indicating the possible benefit of semi-recumbent positioning, which is operative at or around the time of emergence. In a randomized trial of patients in abdominal surgery, semi-Fowler extubation was related to higher emergence-related tolerance (less coughing and more comfort), but no indicator of higher injury. [8]. Even though the outcome of that trial stressed the outcomes in comfort and airway irritation, such a physiological direction is congruous: decreased airway stimulation and improved mechanics in a head-up posture can result in fewer clinically appreciable respiratory events. A more recently-reported large randomized clinical trial on laparoscopic upper abdominal surgery showed that semirecumbent positioning of 30 degrees during anesthetic recovery lowered the incidence of hypoxemia during the postoperative period than a supine position, the quality of supportive evidence was so high that adequate evidence was provided to support the criterion that a head-up position can affect the prevention of desaturation in the PACU environment. [9].

The decrease in respiratory distress and hypoxemia have a number of converging pathways that are mechanistically plausible explanations. To begin with, supine position correlates with a lower functional residual capacity and elevated dependent airway closure, especially following abdominal surgery, when diaphragmatic splinting and cephalad pressure caused by abdominal contents are severe. These effects can be partly compensated by reproducing diaphragmatic excursion and ventilation-perfusion equivalents granting Semi-Fowler a mitigating position against shunt physiology and desaturation. It has clinical implications as post-operative hypoxemia was demonstrated as frequent and sustained, even in general surgical patients, and that a modest increase in gas exchange during the emergence period can deter the escalation cascade (airway maneuvers, rescue ventilation, extended PACU stay). [6,9]

Second, the emergence is a phase where residual drug effects play a significant role in negative respiratory occurrences. PACU observational data have shown adverse respiratory events to be concentrated around airway blockage, hypoventilation and hypoxemia, and linked to changeable causes such as residual neuromuscular blockade. [7]. Suboptimal monitoring strategies and reversal practices are also associated with intermediate-acting neuromuscular blockers, contributing to postoperative respiratory complications in incomplete recovery of neuromuscular function as neuromuscular blockade during anaesthetic care is a research gap and is strongly linked to critical respiratory events in the PACU, probably through impaired upper airway dilator tone, weakened hypoxic ventilatory response and poor inspiratory muscle performance.

Third, there is aspiration risk which though minimal, is clinically significant. Traditional descriptions of the series of perioperative pulmonary aspiration are unusual but could be very severe, resolution depends on the volume, the burden of the particulate and the host factors. [5]. A head-up posture can decrease the risk of passive regurgitation and contacts fewer cephalad secretions during coughing or retching, as well as neutralize cephalad migration of secretions. Although our intervention was not power-maximized to find differences in rare aspiration events, the magnitude of effect (no positive effect in relation to semi-Fowler positioning) is more encouraging and in line with the safety profile of some earlier randomized trials on head-up positional intervention. [8,9].

The implementation perspective of the semi-Fowler extubation is that the tool is easy, cost-effective, and extubation is not a procedure that necessitates extra equipment. Since PPCs are common following abdominal surgery and can become a significant part of morbidity, even minor decreases in the early hypoxemia and respiratory distress may result in the less-commonly used rescue interventions and balanced PACU throughout. [13,7].

Limitations are to be taken into consideration. It was a one-centre trial with pragmatic constraints which restricts blinding in the process of positional interventions. The only outcomes were early PACU respiratory compromise; no further pulmonary complications later (ex: pneumonia) were determined. The sample, ASA I-II elective abdominal surgery patients, might not be applicable to the general population where the potential population is at a greater risk, or where the head-up positioning hemodynamic tolerance might be more tightly regulated. And monitoring is done only in till PACU stay. Followup needed for further evaluation.

Future studies will need to test the semi-Fowler extubation in a cohort in various centers, higher-risk group, and downstream ramifications (necessity of noninvasive ventilation, reintubation, pneumonia, length of stay). Additional quantitative lung volume measures and objective neuromuscular monitoring included in mechanistic substudies might help to establish who the greatest beneficiary is.

In adults who had an elective abdominal surgery, the use of extubation and early PACU recovery in a 30o semi-Fowler position substantially decreased early postoperative respiratory distress as compared with traditional supine position. The clinical significance of the effect was significant and obtained with a low cost intervention that involved no extra equipment or pharmacologic modification. Even the descriptive trends indicated less incidence of hypoxemia and absence of events corroborated by aspiration in the head up group albeit such observations require bigger confirmatory samples. Adopting the positioning described by semi-Fowler at the moment of emergence can be a feasible, scalable improvement on PACU respiratory safety protocols in patients undergoing regular abdominal surgery.

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