European Journal of Cardiovascular Medicine

Anesthesia and surgical procedures often require patients to be positioned in ways that optimize surgical access and visibility. One such position is the prone position, which is frequently employed in various surgical procedures, including spinal surgeries, posterior fossa neurosurgeries, and certain thoracic interventions [1]. While the prone position offers several advantages from a surgical perspective, it presents unique challenges for anesthesiologists due to the significant physiological and hemodynamic changes it induces. Understanding these changes is crucial for maintaining patient safety and optimizing perioperative outcomes.

The transition from supine to prone position under general anesthesia is a critical moment that demands close monitoring and careful management. This positional change can lead to alterations in cardiovascular function, respiratory mechanics, and intracranial pressure, all of which can have profound implications for patient well-being [2]. The hemodynamic changes observed during this transition are of particular interest, as they can significantly impact tissue perfusion, organ function, and overall patient stability.

Hemodynamics, the study of blood flow through the cardiovascular system, encompasses various parameters including blood pressure, cardiac output, stroke volume, and systemic vascular resistance. These parameters are intricately interconnected and respond dynamically to positional changes, especially under the influence of general anesthesia [3]. The prone position, characterized by the patient lying face down with their chest and abdomen supported, introduces unique physiological challenges that can affect these hemodynamic parameters in complex ways.

One of the primary concerns during the supine to prone transition is the potential for cardiovascular instability. The prone position can lead to decreased venous return due to increased intrathoracic pressure and compression of the inferior vena cava [4]. This reduction in preload can result in a decrease in cardiac output and, consequently, blood pressure. Furthermore, the gravitational effects on blood distribution in the prone position can alter regional perfusion patterns, potentially affecting organ function and tissue oxygenation [5].

The magnitude and clinical significance of these hemodynamic changes can vary depending on several factors, including the patient's pre-existing cardiovascular status, the specific prone positioning technique employed, and the duration of surgery. Patients with compromised cardiovascular function or those undergoing lengthy procedures may be particularly vulnerable to adverse hemodynamic effects [6]. Therefore, a thorough understanding of these changes is essential for developing effective strategies to mitigate risks and maintain hemodynamic stability throughout the perioperative period.

Anesthesiologists play a crucial role in managing these hemodynamic challenges. Their responsibilities include anticipating potential complications, implementing appropriate monitoring techniques, and intervening promptly when necessary. One key aspect of this management is the judicious use of vasopressors, which may be required to counteract the hypotensive effects often associated with the prone position [7]. The decision to administer vasopressors, as well as the choice of specific agents, depends on a careful assessment of the patient's hemodynamic status and overall clinical picture.

Recent advances in monitoring technologies have enhanced our ability to detect and respond to hemodynamic changes in real-time. Continuous arterial pressure monitoring, minimally invasive cardiac output measurement techniques, and dynamic indices of fluid responsiveness have become valuable tools in the anesthesiologist's arsenal [8]. These technologies allow for more precise titration of fluids and vasoactive medications, potentially improving patient outcomes and reducing the incidence of complications related to hemodynamic instability.

Despite the growing body of knowledge surrounding hemodynamic changes in the prone position, several areas warrant further investigation. The optimal timing and method of prone positioning, strategies for predicting and preventing significant hemodynamic perturbations, and the long-term clinical implications of these changes are all topics of ongoing research [9]. Additionally, the interaction between prone positioning and specific anesthetic techniques or agents remains an area of interest, as different anesthetic approaches may influence the magnitude and nature of hemodynamic responses.

The study of hemodynamic changes from supine to prone position under general anesthesia is not merely an academic exercise but has direct clinical implications. Improved understanding of these physiological alterations can inform better patient selection, more effective preoperative optimization strategies, and refined intraoperative management protocols. This knowledge is particularly relevant in an era of enhanced recovery after surgery (ERAS) protocols, where minimizing physiological stress and optimizing organ function are key priorities [10].

As surgical techniques continue to evolve and more complex procedures are performed in the prone position, the importance of understanding and managing associated hemodynamic changes becomes increasingly apparent. This field of study represents a critical intersection of anesthesiology, physiology, and surgical science, highlighting the need for a multidisciplinary approach to patient care.

The transition from supine to prone position under general anesthesia presents unique hemodynamic challenges that require careful consideration and management. By studying these changes in detail, we can develop more effective strategies for maintaining cardiovascular stability, optimizing tissue perfusion, and ultimately improving patient outcomes.

Aims and Objectives

The primary aim of this study was to investigate the changes in hemodynamic parameters that occur when patients are transitioned from the supine to prone position following the induction of general anesthesia. This objective focused on quantifying and analyzing alterations in key cardiovascular indicators such as heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, oxygen saturation, end-tidal carbon dioxide, and peak airway pressure. By examining these parameters at specific time intervals during the positional change, the study sought to provide a comprehensive understanding of the acute hemodynamic responses to prone positioning in anesthetized patients.

A secondary objective of the study was to evaluate the requirement for vasopressors following the shift from supine to prone position. This aim addressed the clinical implications of the observed hemodynamic changes, particularly focusing on instances where blood pressure decreased significantly enough to necessitate pharmacological intervention. By assessing the frequency and timing of vasopressor administration, the study aimed to provide valuable insights into the management strategies required to maintain cardiovascular stability during this critical phase of anesthesia and patient positioning.

This observational study was conducted at Yenepoya Medical College Hospital in Mangalore, India, from December 2019 to October 2021. The study population comprised patients admitted for elective spine surgery under general anesthesia. A sample size of 54 healthy consenting adult patients was determined based on a previous study by Eun-A-Jang, which reported a standard deviation of 18 mmHg for the difference between paired measurements of mean arterial pressure. The sample size calculation was performed using a 5% level of significance and a standard normal variate of 1.96. Participants were selected using a closed envelope method to ensure randomization.

The study included adult patients of both genders who were scheduled for elective surgeries requiring prone positioning. Exclusion criteria were strictly applied to minimize confounding factors. Patients with clinically significant cardiovascular, respiratory, hepatic, renal, psychiatric, or metabolic diseases were excluded from the study. Additionally, individuals with diabetic neuropathy were not included to avoid potential autonomic dysfunction that could influence hemodynamic responses.

Prior to the procedure, all patients underwent a thorough pre-anesthetic evaluation, including routine investigations. Informed written consent was obtained from each participant after explaining the anesthesia and surgical procedures. Premedication consisted of oral ranitidine 150 mg administered the night before surgery and on the morning of the procedure, along with oral alprazolam 0.5 mg the night before surgery.

Upon arrival in the operating room, standard monitoring was established, including continuous electrocardiography, non-invasive blood pressure measurement, pulse oximetry, and capnography. A wide-bore peripheral intravenous cannula was secured, and an infusion of Ringer's lactate solution was initiated. Patients received intravenous premedication with midazolam 0.02 mg/kg, glycopyrrolate 0.005 mg/kg, and fentanyl 1.0 mcg/kg, administered 1-2 minutes before induction.

Anesthesia was induced following pre-oxygenation with 100% oxygen for 3 minutes. Intravenous propofol 2 mg/kg was used for induction, and neuromuscular blockade was achieved with intravenous vecuronium 0.15 mg/kg to facilitate endotracheal intubation. An appropriately sized armored endotracheal tube was inserted under direct laryngoscopy, and correct placement was confirmed by chest movement, capnography, and adequate tidal volume.

Mechanical ventilation was initiated with a tidal volume of 8 ml/kg and a respiratory rate of 12 breaths per minute. Anesthesia was maintained using a mixture of oxygen and nitrous oxide (50:50), isoflurane (1.5 MAC), and intermittent doses of vecuronium. Baseline hemodynamic parameters, including heart rate, systolic blood pressure, diastolic blood pressure, mean arterial pressure, oxygen saturation, end-tidal carbon dioxide, and peak airway pressure, were recorded with the patient in the supine position using a BPL multiparameter monitor and the Drager Fabius plus XL ventilator.

Ten minutes after induction, patients were carefully turned from the supine to prone position for surgery. Hemodynamic parameters were again recorded immediately before prone positioning, immediately after turning prone, and at 5 and 10 minutes following the position change. The study protocol specified that if blood pressure fell by 20% or more from preoperative values, interventions including bolus doses of intravenous fluids and vasopressors (mephentermine or ephedrine) would be administered.

At the conclusion of surgery, residual neuromuscular blockade was reversed with intravenous neostigmine 0.05 mg/kg and glycopyrrolate 0.01 mg/kg. Patients were extubated once satisfactory recovery was achieved and subsequently transferred to the post-anesthesia care unit for continued monitoring.

Data analysis was performed using SPSS (Statistical Package for Social Sciences) version 20. Descriptive statistics were calculated for all variables, including means and standard deviations for quantitative data and frequencies and proportions for qualitative data. The paired t-test was employed to assess mean differences in hemodynamic variables between supine and prone positions. Repeated measures ANOVA was utilized to evaluate the statistical significance of changes in hemodynamic parameters at different time intervals in the prone position. The level of statistical significance was set at 5% for all analyses.

The study examined hemodynamic changes in 54 patients undergoing elective spine surgery under general anesthesia, transitioning from supine to prone position. The patient cohort consisted of 40 males (74.1%) and 14 females (25.9%). The age distribution was as follows: ≤20 years (7.4%), 21-30 years (20.4%), 31-40 years (22.2%), 41-50 years (22.2%), 51-60 years (18.5%), and 61-70 years (9.3%).

Hemodynamic parameters were measured in supine position and at three time points after prone positioning: immediately, 5 minutes, and 10 minutes. Statistical analysis was performed using paired t-tests and repeated measures ANOVA.

Heart rate showed a slight decrease from supine (78.46 ± 11.048 beats/min) to prone position. Immediately after positioning, it decreased to 77.50 ± 10.586 beats/min (p=0.204, mean difference 0.963). At 5 minutes, it further decreased to 76.30 ± 9.595 beats/min (p=0.022, mean difference 2.167), and at 10 minutes, it was 76.72 ± 9.616 beats/min (p=0.094, mean difference 1.741). The changes were only statistically significant at the 5-minute mark.

Systolic blood pressure demonstrated significant changes throughout. It decreased from 127.74 ± 14.275 mmHg in supine to 114.81 ± 10.436 mmHg immediately after prone positioning (p<0.001, mean difference 12.926). At 5 minutes, it rose to 118.56 ± 10.164 mmHg (p<0.001, mean difference 9.185), and further increased to 122.52 ± 9.853 mmHg at 10 minutes (p<0.001, mean difference 5.222), all remaining significantly lower than supine values.

Diastolic blood pressure also showed significant reductions from supine (74.22 ± 7.000 mmHg) to immediate prone (70.44 ± 6.392 mmHg, p<0.001, mean difference 3.778), 5 minutes prone (71.04 ± 5.667 mmHg, p<0.001, mean difference 3.185), and 10 minutes prone (71.85 ± 5.668 mmHg, p=0.005, mean difference 2.370).

Mean arterial pressure (MAP) followed a similar pattern, decreasing significantly from 92.19 ± 8.405 mmHg in supine to 85.61 ± 7.061 mmHg immediately after prone positioning (p<0.001, mean difference 6.574). MAP showed a gradual increase to 86.89 ± 6.468 mmHg at 5 minutes (p<0.001, mean difference 5.296) and 88.67 ± 6.463 mmHg at 10 minutes (p<0.001, mean difference 3.519), but remained significantly lower than supine values.

Peak airway pressure (PAP) increased significantly from supine (13.91 ± 1.521 cmH2O) to all prone measurements: immediate (15.54 ± 1.563 cmH2O, p<0.001, mean difference -1.630), 5 minutes (15.89 ± 1.313 cmH2O, p<0.001, mean difference -1.981), and 10 minutes (15.81 ± 1.230 cmH2O, p<0.001, mean difference -1.907).

End-tidal CO2 (etCO2) showed a slight increase from supine (34.48 ± 2.944 mmHg) to immediate prone position (35.19 ± 2.768 mmHg, p=0.070, mean difference -0.704). The values at 5 minutes (34.76 ± 2.464 mmHg, p=0.454, mean difference -0.278) and 10 minutes (34.67 ± 2.442 mmHg, p=0.625, mean difference -0.185) were not significantly different from supine.

Oxygen saturation (SpO2) showed minimal changes. It increased slightly from supine (98.80 ± 0.998%) to immediate prone (99.07 ± 0.866%, p=0.004, mean difference -0.278), with changes at 5 minutes (98.98 ± 0.835%, p=0.077, mean difference -0.185) and 10 minutes (99.07 ± 0.773%, p=0.008, mean difference -0.278) showing mixed statistical significance.

Repeated measures ANOVA revealed significant changes over time in prone position for systolic blood pressure (p=0.001), MAP (p=0.001), PAP (p=0.003), and etCO2 (p=0.027). Heart rate (p=0.16), diastolic blood pressure (p=0.067), and SpO2 (p=0.442) did not show significant changes over time in prone position.

Pairwise comparisons of prone measurements showed that systolic blood pressure continued to increase significantly at each time point (p<0.001 for all comparisons). The mean differences were: immediate to 5 minutes (-3.741 mmHg), immediate to 10 minutes (-7.704 mmHg), and 5 to 10 minutes (-3.963 mmHg).

MAP showed significant increases between immediate and 10-minute measurements (-3.056 mmHg, p<0.001) and between 5 and 10-minute measurements (-1.778 mmHg, p=0.006). The difference between immediate and 5-minute measurements (-1.278 mmHg) was not significant (p=0.107).

PAP showed significant differences between immediate and both 5-minute (-0.352 cmH2O, p=0.009) and 10-minute (-0.278 cmH2O, p=0.037) measurements, but not between 5 and 10 minutes (0.074 cmH2O, p=0.627).

EtCO2 comparisons between prone measurements were not statistically significant: immediate to 5 minutes (0.426 mmHg, p=0.115), immediate to 10 minutes (0.519 mmHg, p=0.079), and 5 to 10 minutes (0.093 mmHg, p=1.000).

These comprehensive results indicate that prone positioning in anesthetized patients undergoing spine surgery leads to significant hemodynamic changes, particularly in blood pressure and airway pressure. Most changes occur immediately after positioning, with some parameters showing gradual recovery over time. The study provides detailed insights into the time course and magnitude of these changes, which is crucial for optimal patient management during such procedures.

Table 1: Age Distribution

Table 2: Gender Distribution

Table 3: Comparison of Haemodynamic Parameters Between Supine and Immediate Prone Position

(p value calculated using paired t-Test)

Table 4: Comparison of Haemodynamic Parameters Between the Supine and After 5 Mins of Prone Position

Table 5: Comparison of Haemodynamic Parameters Between the Supine and After 10 Mins of Prone Position

Table 6: Comparison of Haemodynamic Variables in Prone Position at Different Time Intervals

Table 7: Comparison of Statistically Significant Variables in Prone Position

This study investigated the hemodynamic changes that occur when patients are transitioned from supine to prone position under general anesthesia for spine surgery. The findings reveal significant alterations in several key parameters, particularly blood pressure and airway pressure.

One of the most notable findings was the significant decrease in systolic blood pressure (SBP) immediately after prone positioning, with a mean reduction of 12.926 mmHg (p<0.001). This is consistent with previous studies, such as the work by Edgcombe et al. [11], who reported a mean decrease in SBP of 14 mmHg (p<0.05) in prone-positioned patients. Our study further demonstrated a gradual recovery of SBP over time, though it remained significantly lower than baseline even after 10 minutes. This time course of SBP changes has not been extensively reported in previous literature and provides valuable insight for anesthesiologists managing these cases.

The observed decrease in mean arterial pressure (MAP) aligns with findings from Dharmavaram et al. [12], who reported a mean MAP reduction of 7.5 mmHg (p<0.01) in prone-positioned patients. Our study found a similar initial decrease (mean difference 6.574 mmHg, p<0.001), with partial recovery over the 10-minute observation period. This persistent reduction in MAP highlights the need for continued vigilance and potentially proactive management strategies during prolonged procedures in the prone position.

The increase in peak airway pressure (PAP) observed in our study (mean increase 1.630 cmH2O, p<0.001) is a well-documented phenomenon in prone positioning. Pelosi et al. [13] reported a similar magnitude of change, with a mean increase of 1.8 cmH2O (p<0.05) in their cohort. This consistent finding across studies underscores the importance of careful ventilator management and monitoring in prone-positioned patients.

Interestingly, our study found no significant changes in heart rate over the observation period, contrasting with some previous reports. For instance, Sudheer et al. [14] observed a mean increase in heart rate of 5 beats/min (p<0.05) after prone positioning. This discrepancy could be due to differences in study populations, anesthetic techniques, or the specific prone positioning method used.

The lack of significant changes in end-tidal CO2 and oxygen saturation in our study is reassuring and suggests that, despite the alterations in blood pressure and airway pressure, gas exchange was not significantly compromised in the immediate post-positioning period. However, Chui et al. [15] reported a small but significant increase in PaCO2 (mean increase 2.3 mmHg, p<0.05) in prone-positioned patients, indicating that longer-term monitoring of these parameters may be warranted.

Our findings regarding the time course of hemodynamic changes provide valuable information for clinical practice. The observation that most parameters showed some degree of recovery by the 10-minute mark suggests that a period of stabilization may occur after the initial positional change. However, the persistence of significant differences from baseline values even at 10 minutes emphasizes the need for ongoing monitoring and management throughout the procedure.

The study has several limitations. The sample size, while adequate for detecting major changes, may have limited the power to identify more subtle alterations. Additionally, the 10-minute observation period, while clinically relevant for the immediate post-positioning phase, does not provide information on longer-term hemodynamic changes during prolonged procedures. Future studies with extended monitoring periods could provide valuable insights into the stability of these parameters over time.

In conclusion, this study confirms and extends previous findings regarding hemodynamic changes associated with prone positioning under general anesthesia. The observed alterations in blood pressure and airway pressure, along with their time course, provide important considerations for anesthetic management in spine surgery and other procedures requiring prone positioning.

This study provides comprehensive insights into the hemodynamic changes that occur when patients are transitioned from supine to prone position under general anesthesia for spine surgery. The findings demonstrate significant alterations in blood pressure and airway pressure, with most changes occurring immediately after positioning and some parameters showing gradual recovery over time.

The observed decreases in systolic, diastolic, and mean arterial pressures, along with increases in peak airway pressure, underscore the need for vigilant monitoring and proactive management strategies during prone positioning. The time course of these changes, with some recovery noted by the 10-minute mark but persistent differences from baseline, highlights the dynamic nature of these physiological responses.

While heart rate, end-tidal CO2, and oxygen saturation showed minimal changes, the significant alterations in other parameters emphasize the complex physiological adaptations that occur with positional changes under anesthesia. These findings have important implications for anesthetic management, potentially influencing decisions regarding fluid administration, vasopressor use, and ventilator settings.

The study's results align with much of the existing literature while also providing new insights, particularly regarding the time course of hemodynamic changes. However, limitations such as the relatively short observation period and moderate sample size suggest avenues for future research, including longer-term monitoring and larger cohort studies.

In conclusion, this study enhances our understanding of the hemodynamic consequences of prone positioning in anesthetized patients. The findings can inform clinical practice, contributing to improved patient safety and outcomes in procedures requiring prone positioning.

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