Hemodynamic effect of the prone position during anesthesia

Prediction of hematocrit decline and the impact of peri-operative fluid use in lumbar spinal fusion surgery

PURPOSE

Peri-operative blood loss unaccounted for and post-operative hematocrit decline could have a significant impact on the outcome of elective spinal surgery patients. The study assesses the accuracy of predictive models of hematocrit decline and blood loss in spinal surgery and determines the impact of peri-operative fluid administration on hematocrit levels of patients undergoing first-time single level lumbar fusion surgery for degenerative spine disease and the trend thereof in the first 24 h post-operatively.

METHODS

Clinical and biochemical parameters were prospectively collected in patients undergoing single level lumbar spinal surgery. Predictive models were applied to assess their accuracy in intra-operative blood loss and post-operative hematocrit decline.

RESULTS

High correlation (0.98 Pearson correlation coefficient) occurred between calculated (predicted) and recorded hematocrit from hours 2 to 6 post-operatively. Predictive accuracy declined thereafter yet remained moderate. Patients received an average intra-operative fluid volume of 545.45 ml per hour (47% of estimated total blood volume). A significant hematocrit decline occurred post-induction (43.47-39.78%, p < 0.001) with total fluid volume received being the significant contributing variable (p < 0.001). Hypertensive patients were the only subgroup to drop below the safe hematocrit threshold of 30%.

CONCLUSION

Iatrogenic hemodilution can accurately be predicted for the first six hours post-operatively, with high risk patients identifiable. Fluid therapy should be goal directed rather than generic, and good communication between the surgeon and anesthesiologist remains the cornerstone to manage physiological changes secondary to blood loss. Although helpful, predictive formulas are not universally applicable to all phenotypes.

Impact of perioperative α1-antagonists on postoperative urinary retention in orthopaedic surgery: meta-analysis

BACKGROUND

Postoperative urinary retention (POUR) is a common complication following orthopaedic surgery. Previous studies attempted to establish the preventative role of α1-antagonist in POUR in the general surgical population; however, there is still no consensus regarding its use in orthopaedic surgery due to limited evidence.

METHODS

Electronic databases of Cochrane Library, Embase, MEDLINE, and ClinicalTrials.gov were searched by two independent investigators from inception to 1 March 2022 to identify relevant randomized clinical trials. Two reviewers independently completed a critical appraisal of included trials by using the Cochrane Risk of Bias tool version 2.0 and extracted data from included articles. Risk of POUR was summarized as risk ratio (RR) with 95 per cent confidence intervals (c.i.). Mean difference (MD) was used for meta-analysis of continuous outcomes.

RESULTS

Five randomized clinical trials involving 878 patients (α1-antagonist, 434; placebo, 444) undergoing hip/knee arthroplasty and spine surgeries were included. One study was assessed as high risk of bias from the randomization process and was excluded from the final meta-analysis. There was no difference in the risk of POUR between patients taking α1-antagonist and the placebo in arthroplasty (RR, 0.64; 95 per cent c.i., 0.36 to 1.14) and in spine surgeries (RR, 1.03; 95 per cent c.i., 0.69 to 1.55). There was no difference in length of stay (MD, -0.14 days; 95 per cent c.i., -0.33 to 0.05). Use of α1-antagonist was associated with a higher risk of adverse events (RR, 1.97; 95 per cent c.i., 1.27 to 3.06), with a composite of dizziness, light-headedness, fatigue, altered mental status, and syncope being the most commonly reported symptoms.

CONCLUSION

In patients undergoing spinal surgery and joint arthroplasty, routine administration of perioperative α1-antagonist does not decrease risk of POUR but does increase perioperative dizziness, light-headedness, and syncope.

Technologies in Anaesthesia for the Paediatric Patient

Spine surgery is an increasingly frequent surgery and includes a wide range of procedures, from minor surgeries (removal of herniated discs, simple laminectomies) to major surgeries (arthrodesis, removal of spinal meningiomas, etc.).These surgeries commonly involve complex patients (elderly population, ASA II-III) and are sometimes performed in emergency settings (polytrauma, cauda syndrome, pathological fractures), which require specific positions (pronation or lateral decubitus), whereby there can be difficulty in airway management, especially in surgeries that concern the cervical tract.One of the main peculiarities of spine surgery involves the prone position.Patient positioning on the operating bed is an action that must be carried out under medical supervision, in particular by the anaesthetist who is supposed to supervise the regular positioning of the patient at the very moment in which it is performed. The correct positioning of the patient is one of the most important moments of the patient care process in the operating room, given that an error in this field may cause serious damage to the patient by giving rise to permanent and significant nerve damage.The prone position is associated with a variety of complications (Kwee et al., Int Surg 100(2): 292-303, 2015). The points of greatest compression during pronation are eyes, nose, breasts, genitals and neck veins.Therefore, the main risks that can derive from an incorrect position are visual disturbances from inappropriate orbital compression, brachial plexus stretching, ulnar nerve compression and lateral femur-cutaneous nerve stretching. In addition, an inappropriate compression of the abdominal organs in this position, may cause ischemia and consequent organ failure resulting in hospitalization prolongation, permanent disability and sometimes even death (Edgcombe et al., Br J Anaesth 100: 165-183, 2008).In addition to the mechanical effects on anatomical structures, there are also the physiological effects of the prone position, which can be divided into circulatory and respiratory effects.These effects are even more pronounced in elderly patients, cardiopaths or patients with respiratory diseases.

The Impact of Individualized Hemodynamic Management on Intraoperative Fluid Balance and Hemodynamic Interventions during Spine Surgery in the Prone Position: A Prospective Randomized Trial

Background and Objectives: The effect of individualized hemodynamic management on the intraoperative use of fluids and other hemodynamic interventions in patients undergoing spinal surgery in the prone position is controversial. This study aimed to evaluate how the use of individualized hemodynamic management based on extended continuous non-invasive hemodynamic monitoring modifies intraoperative hemodynamic interventions compared to conventional hemodynamic monitoring with intermittent non-invasive blood pressure measurements. Methods: Fifty adult patients (American Society of Anesthesiologists physical status I−III) who underwent spinal procedures in the prone position and were then managed with a restrictive fluid strategy were prospectively randomized into intervention and control groups. In the intervention group, individualized hemodynamic management followed a goal-directed protocol based on continuously non-invasively measured blood pressure, heart rate, cardiac output, systemic vascular resistance, and stroke volume variation. In the control group, patients were monitored using intermittent non-invasive blood pressure monitoring, and the choice of hemodynamic intervention was left to the discretion of the attending anesthesiologist. Results: In the intervention group, more hypotensive episodes (3 (2−4) vs. 1 (0−2), p = 0.0001), higher intraoperative dose of ephedrine (0 (0−10) vs. 0 (0−0) mg, p = 0.0008), and more positive fluid balance (680 (510−937) vs. 270 (196−377) ml, p < 0.0001) were recorded. Intraoperative norepinephrine dose and postoperative outcomes did not differ between the groups. Conclusions: Individualized hemodynamic management based on data from extended non-invasive hemodynamic monitoring significantly modified intraoperative hemodynamic management and was associated with a higher number of hemodynamic interventions and a more positive fluid balance.

Sudden arrhythmia in the prone position during spinal surgery: A case report

RATIONALE

The prone position is the most commonly required position during spinal surgery. Decreasing lumbar lordosis is necessary to facilitate the accessibility of the surgical field. And this can affect the hemodynamic circulation of the patients. The Jackson spine table is one of the most preferred methods, known to have minimal effects on cardiac function.

PATIENT CONCERNS

We report a case of sudden arrhythmia that developed during the prone position using a Jackson spine table. It occurred 30 minutes after the positional change.

DIAGNOSES

Arrhythmia showed bizarre P and QRS waves. Ectopic P, bundle branch block, or both was suspected.

INTERVENTIONS

Because it was difficult to define the exact type or cause of this sudden arrhythmia and considering that other vital signs remained stable, we decided to keep close observation during the operation rather than applying uncertain antiarrhythmic medication.

OUTCOMES

Arrhythmia spontaneously developed and subsided repeatedly. And it recovered to normal sinus rhythm immediately after the positional change to the supine position. Therefore, increased intrathoracic pressure caused by the prone position was highly suspected to be the cause of this event.

LESSONS

Although the Jackson spine table is known to have the least effect on cardiac function, the patient experienced arrhythmia in our case. Hence, to achieve better clinical outcomes, an understanding of physiological alterations and possible complications caused by the prone position is necessary for earlier diagnosis and management.

Risk factors for postoperative urinary retention following elective spine surgery: a meta-analysis

BACKGROUND CONTEXT

Limited studies have investigated risk factors for postoperative urinary retention (POUR) following elective spine surgery. Furthermore, some discrepancies have been found in the results of existing observational studies.

PURPOSE

This study aimed to review the available literature on risk factors associated with POUR following elective spine surgery.

STUDY DESIGN

A systematic review with meta-analysis was performed.

PATIENT SAMPLE

A total of 31,251 patients (POUR=2,858, no POUR=28,393) were included in the meta-analysis.

OUTCOME MEASURES

Demographics, type of elective spine surgery, country, definition of POUR, and potential risk factors for POUR were evaluated.

METHODS

The Cochrane Library, Embase, and Medline electronic databases were searched to identify relevant studies. Binary outcomes were reported as odds ratio (OR). Weighted mean differences (WMD) or standardized mean differences (SMD), with 95% confidence intervals (CI), were used for meta-analysis of continuous outcomes.

RESULTS

Eleven studies (2 prospective and 9 retrospective) were included in the analysis. Patients with POUR were older than those without POUR (WMD, 7.13; 95% CI, 4.50-9.76). Male patients were found to have an increased risk of POUR (OR, 1.31; 95% CI, 1.04-1.64). The following variables were also identified as significant risk factors for POUR: benign prostatic hyperplasia (BPH; OR, 3.79; 95% CI, 1.89-7.62), diabetes mellitus (DM; OR, 1.50; 95% CI, 1.17-1.93), and previous urinary tract infection (UTI; OR, 1.70; 95% CI, 1.28-2.24). Moreover, longer operative time (WMD, 19.88; 95% CI, 5.01-34.75) and increased intraoperative fluid support (SMD, 0.37; 95% CI, 0.23-0.52) were observed in patients with POUR. In contrast, spine surgical procedures involving fewer levels (OR, 0.75; 95% CI, 0.65-0.86), and ambulation on the same day as surgery (OR, 0.65; 95% CI, 0.52-0.81) were associated with a decreased risk of POUR.

CONCLUSIONS

Based on our meta-analysis, older age, male gender, BPH, DM, and a history of UTI are risk factors for POUR following elective spine surgery. We also found that longer operative time and increased intravenous fluid support would increase the risk of POUR. Additionally, multi-level spine surgery may have a negative effect on postoperative voiding.

Equal Ratio Ventilation Reduces Blood Loss During Posterior Lumbar Interbody Fusion Surgery

STUDY DESIGN

A prospective randomized double-blinded study.

OBJECTIVE

The aim of this study was to compare the effect of two different ventilator modes (inspiratory to expiratory ratio [I:E ratio] of 1:1 and 1:2) on intraoperative surgical bleeding in patients undergoing posterior lumbar interbody fusion (PLIF) surgery.

SUMMARY OF BACKGROUND DATA

During PLIF surgery, a considerable amount of blood loss is anticipated. In the prone position, engorgement of the vertebral vein increases surgical bleeding. We hypothesized that equal ratio ventilation (ERV) with I:E ratio of 1:1 would lower peak inspiratory pressure (PIP) in the prone position and consequentially decrease surgical bleeding.

METHODS

Twenty-eight patients were randomly assigned to receive either ERV (ERV group, n = 14) or conventional ventilation with I:E ratio of 1:2 (control group, n = 14). Hemodynamic and respiratory parameters were measured at 5 minutes after anesthesia induction, at 5 minutes after the prone position, at the time of skin closure, and at 5 minutes after turning to the supine position.

RESULTS

The amount of intraoperative surgical bleeding in the ERV group was significantly less than that in the control group (975.7 ± 349.9 mL vs. 1757.1 ± 1172.7 mL, P = 0.030). Among other hemodynamic and respiratory parameters, PIP and plateau inspiratory pressure (Pplat) were significantly lower and dynamic lung compliance (Cdyn) was significantly higher in the ERV group than those of the control group throughout the study period, respectively (all P < 0.05).

CONCLUSION

Compared to conventional ratio ventilation, ERV provided lower PIP and reduced intraoperative surgical blood loss in patients undergoing PLIF surgery.Level of Evidence: 2.

Prone restraint cardiac arrest: A comprehensive review of the scientific literature and an explanation of the physiology

Deaths occurring among agitated or violent individuals subjected to physical restraint have been attributed to positional asphyxia. Restraint in the prone position has been shown to alter respiratory and cardiac physiology, although this is thought not to be to the degree that would cause asphyxia in a healthy, adult individual. This comprehensive review identifies and summarizes the current scientific literature on prone position and restraint, including experiments that assess physiology on individuals restrained in a prone position. Some of these experimental approaches have attempted to replicate situations in which prone restraint would be used. Overall, most findings revealed that individuals subjected to physical prone restraint experienced a decrease in ventilation and/or cardiac output (CO) in prone restraint. Metabolic acidosis is noted with increased physical activity, in restraint-associated cardiac arrest and simulated encounters. A decrease in ventilation and CO can significantly worsen acidosis and hemodynamics. Given these findings, deaths associated with prone physical restraint are not the direct result of asphyxia but are due to cardiac arrest secondary to metabolic acidosis compounded by inadequate ventilation and reduced CO. As such, the cause of death in these circumstances would be more aptly referred to as "prone restraint cardiac arrest" as opposed to "restraint asphyxia" or "positional asphyxia."

Goal-Directed Fluid Therapy Based on Pulse-Pressure Variation Compared with Standard Fluid Therapy in Patients Undergoing Complex Spine Surgery: A Randomized Controlled Trial

Study Design

Prospective, randomized, controlled study.

Purpose

To determine whether the use of goal-directed fluid therapy (GDT) guided by pulse-pressure variation (PPV) and fluid management protocol can reduce intraoperative hypotension, blood transfusion requirements, and postoperative complications in adults undergoing complex spine surgery.

Overview of Literature

Complex spine surgeries involve a significant risk of blood loss and intraoperative hypotension. Previous studies showed that GDT reduces intraoperative hypotension and postoperative complications in these surgery types; however, limited information exists about GDT guided by PPV.

Methods

Sixty adults (18–70 years) patients undergoing complex spine surgeries at Siriraj Hospital, Mahidol University, Thailand were enrolled. Patients were allocated to two groups (30 patients in each) using computer-generated randomization. Intraoperative fluid and vasopressor were administrated via either GDT or standard care. The GDT algorithm used PPV and fluid protocol as the primary tool to guide hemodynamic management. The incidences and episodes of perioperative hypotension were measured as the outcomes.

Results

Fifty-seven patients were analyzed (three patients in the GDT group were excluded). The baseline characteristics and surgical procedures of the two groups did not differ significantly. The prevalence of intraoperative hypotension was 80.0% for the control group and 66.7% for the GDT group (p=0.25). Two episodes (1–3) of intraoperative hypotension occurred in the control group, and one episode (0–3) occurred in the GDT group; the difference was not significantly different (p=0.57). The intraoperative blood transfusion requirements and postoperative complications were similar in both the groups. In the subgroup analysis, patients with intraoperative hypotension exhibited a higher incidence of postoperative bowel dysfunction.

Conclusions

PPV-guided GDT and fluid protocol, as compared with standard practice, did not show significant advantages with respect to intraoperative hypotension, blood transfusion, or postoperative complications in patients undergoing complex spine surgery in the prone position.

Transient left bundle branch block after posture change to the prone position during general anesthesia: A case report

RATIONALE

The prone position is commonly used in spinal surgery. There have been many studies on hemodynamic changes in the prone position during general anesthesia. We report a rare case of transient left bundle branch block (LBBB) in a prone position.

PATIENT CONCERN

Electrocardiogram (ECG) of a 64-year-old man scheduled for spinal surgery showed normal sinus rhythm change to LBBB after posture change to the prone position.

DIAGNOSIS

Twelve lead ECG revealed LBBB. His coronary angio-computed tomography results showed right coronary artery with 30% to 40% stenosis and left circumflex artery with 40% to 50% stenosis. The patient was diagnosed with stable angina and second-degree atrioventricular block of Mobitz type II.

INTERVENTION

Nitroglycerin was administered intravenously during surgery. Adequate oxygen was supplied to the patient. After surgery, the patient was prescribed clopidogrel, statins, angiotensin II receptor blocker, and a permanent pacemaker was inserted.

OUTCOME

Surgery was completed without complications. After surgery, the transient LBBB changed to a normal sinus rhythm. The patient did not complain of chest pain or dyspnea.

LESSON

The prone position causes significant hemodynamic changes. A high risk of cardiovascular disease may cause ischemic heart disease and ECG changes. Therefore, careful management is necessary.

Effects of controlled hypotension with restrictive transfusion on intraoperative blood loss and systemic oxygen metabolism in elderly patients who underwent lumbar fusion

BACKGROUND

The effects of restrictive fluid therapy combined with controlled hypotension in the elderly on systemic oxygen metabolism and renal function are clinical concerns. The aim of this study was to evaluate blood loss, oxygen metabolism, and renal function in different levels of controlled hypotension induced by intravenous nitroglycerin, in combination with limited infusion, in elderly patients undergoing posterior lumbar fusion.

METHODS

A total of 40 patients, aged 60-75 with ASA grade II or III, who were planned for posterior lumbar fusion were randomly allocated into two groups: experimental group [target mean arterial pressure 65 mmHg (MAP 65) or control group (MAP 75)]. Indicators for blood loss, hemodynamic, systemic oxygen metabolism, and renal function evaluation index were recorded before operation (T0), 1 h after induced hypotension (T1), 2 h after hypotension (T2), and in recovery (T3). We compared changes in these parameters between groups to evaluate the combined effects of controlled hypotension with restrictive infusion.

RESULTS

CI, DO₂I, and VO₂I were lower in both groups at T1-T3 compared with T0 (p < 0.05). DO₂I and VO₂I in the MAP 65 group were lower than the MAP 75 group after operation. In both groups, SCysC increased at T1, T2, and T3 (p < 0.05) compared with T0.

CONCLUSIONS

Restrictive transfusion and control MAP at 65 mmHg can slightly change in renal function and reduce the risk of insufficient oxygen supply and importantly have no significant effect on blood loss and postoperative complications.

TRIAL REGISTRATION

ChiCTR-INR-16008153 . Registered on 25 March 2016.

Investigating Association between Intraoperative Hypotension and Postoperative Neurocognitive Disorders in Non-Cardiac Surgery: A Comprehensive Review

Postoperative delirium (POD) and postoperative cognitive decline (deficit) (POCD) are related to a higher risk of postoperative complications and long-term disability. Pathophysiology of POD and POCD is complex, elusive and multifactorial. Intraoperative hypotension (IOH) constitutes a frequent and vital health hazard in the perioperative period. Unfortunately, there are no international recommendations in terms of diagnostics and treatment of neurocognitive complications which may arise from hypotension-related hypoperfusion. Therefore, we performed a comprehensive review of the literature evaluating the association between IOH and POD/POCD in the non-cardiac setting. We have concluded that available data are quite inconsistent and there is a paucity of high-quality evidence convincing that IOH is a risk factor for POD/POCD development. Considerable heterogeneity between studies is the major limitation to set up reliable recommendations regarding intraoperative blood pressure management to protect the brain against hypotension-related hypoperfusion. Further well-designed and effectively-performed research is needed to elucidate true impact of intraoperative blood pressure variations on postoperative cognitive functioning.

Intraoperative Fluid Management in Patients Undergoing Spine Surgery: A Narrative Review

Fluid management has been widely recognized as an important component of the perioperative care in patients undergoing major procedures including spine surgeries. Patient- and surgery-related factors such as age, length of the surgery, massive intraoperative blood loss, and prone positioning, may impact the intraoperative administration of fluids. In addition, the type of fluid administered may also affect post-operative outcomes. Published literature describing intraoperative fluid management in patients undergoing major spine surgeries is limited and remains controversial. Therefore, we reviewed current literature on intraoperative fluid management and its association with post-operative complications in spine surgery.

Venous Thromboembolism Complicated with COVID-19: What Do We Know So Far?

Coronavirus disease (COVID-19) is caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and is responsible for the ongoing 2019-2020 pandemic. Venous thromboembolism (VTE), a frequent cardiovascular and/or respiratory complication among hospitalized patients, is one of the known sequelae of the illness. Hospitalized COVID-19 patients are often elderly, immobile, and show signs of coagulopathy. Therefore, it is reasonable to assume a high incidence of VTE among these patients. Presently, the incidence of VTE is estimated at around 25% of patients hospitalized in the intensive care unit for COVID-19 even under anticoagulant treatment at prophylactic doses. In this review, we discuss present knowledge of the topic, the unique challenges of diagnosis and treatment of VTE, as well as some of the potential mechanisms of increased risk for VTE during the illness. Understanding the true impact of VTE on patients with COVID-19 will potentially improve our ability to reach a timely diagnosis and initiate proper treatment, mitigating the risk for this susceptible population during a complicated disease.

[Cardiorespiratory effects of perioperative positioning techniques]

The supine position is still the most frequently used type of positioning during surgical procedures. Positions other than the supine position lead to physiological alterations that have a relevant influence on the course of anesthesia and surgery. As a matter of principle, hemodynamic stability is at risk because venous blood is pooled in the lower positioned body parts. In addition, head down positions (Trendelenburg position) may lead to an impairment of respiratory function by reducing lung volumes as well as lung compliance. Upright positions (beach chair position) are characterized by a relative hypovolemia accompanied by a reduction of mean arterial pressure, cardiac output and stroke volume, whereas pulmonary functions remain unchanged. Some severe adverse events have been described in the literature (e.g. intraoperative apoplexy, postoperative blindness). The pathophysiological principles and effects of hemodynamic alterations as well as potential strategies to avoid complications are presented and discussed in this lead article. Head down positions, especially the Trendelenburg position, cause a relative (intrathoracic) hypervolemia and an increase in cardiac preload that is usually well-tolerated in patients without heart problems; however, the Trendelenburg position, especially if combined with a capnoperitoneum, significantly impairs pulmonary function, can have a negative effect on intracerebral pressure and may reduce blood flow of intra-abdominal organs. The pathophysiological intraoperative changes caused by Trendelenburg positioning are described and approaches suitable for risk reduction are discussed. The prone position and lateral decubitus position have little influence on the intraoperative homeostasis. Nevertheless, there is an ongoing discussion concerning the efficacy of a 15° left lateral position during caesarean section, which is also discussed in a separate section of this review.

Surgical Treatment for Severe Scoliosis in Patients with Reduced Cardiorespiratory Function after Surgery for Congenital Heart Disease: A Report of Two Cases

Purpose

Congenital heart disease (CHD) is associated with an increased risk of scoliosis. The prognosis of scoliosis patients with CHD has improved because of advances in cardiac care. As a result, the frequency of surgery for scoliosis in this population has increased, although the risk of perioperative complications remains high. We treated two patients with CHD who underwent surgery for severe scoliosis. To avoid perioperative complications, we evaluated the preoperative cardiac status and anesthetic risks before posterior correction and fixation in both patients.

Methods

An expert anesthesiologist evaluated the anesthetic risk in each case, and an adequate reservoir of autologous blood was collected preoperatively. The patient in case 1 was at risk of significant blood loss and required extremely careful operative technique. The patient in case 2 had low cardiac output preoperatively. We therefore performed a thorough preoperative cardiac evaluation. Both patients were admitted to the intensive care unit postoperatively.

Results

Neither patient suffered serious complications, and both achieved favorable outcomes.

Conclusions

Appropriate surgical technique and teamwork among experts are the keys to success in patients with severe scoliosis and CHD.

An Observational Study of Cerebral Blood Flow Velocity Evaluation in the Prone Position During Posterior Lumbar Surgery

BACKGROUND

Prone positioning (PP) is necessary for surgical access during posterior spine procedure. However, physiological changes occur in the PP. Typical findings are a decrease in arterial blood pressure and in cardiac output that could potentially lead to an alteration in cerebral perfusion. Therefore, we decided to study cerebral blood flow velocity (CBFV) with transcranial Doppler ultrasonography to evaluate the effect of the PP on cerebral hemodynamics.

METHODS

Twenty-two patients undergoing spine surgery in the PP were studied. General anesthesia was induced using 250 μg of fentanyl, 2 mg/kg of propofol, and 0.1 mg/kg of vecuronium, and was maintained with 0.25%-0.5% isoflurane, 50% nitrous oxide in oxygen, continuous infusion of 100 μg/kg/min of propofol, 1.5 μg/kg/h of fentanyl, and 0.15 mg/kg/h of ketamine. Continuous invasive arterial blood pressure, heart rate, electrocardiogram, and end-tidal carbon dioxide were monitored. CBFV with transcranial Doppler in the middle cerebral artery was first measured with the patients under general anesthesia in the supine position. Patients were then placed in the PP and remained in this position throughout surgery. CBFV, end-tidal carbon dioxide, heart rate, and blood pressure were measured continuously for 75 minutes after initiation of PP. This coincided with surgical exposure and minimal blood loss. Data were analyzed every 15 minutes for statistical significant change over time.

RESULTS

Mean arterial blood pressure decreased 15 minutes after the installation of the PP and onward, but this decrease was not statistically significant. CBFVsyst (the maximal CBFV during the systolic phase of a cardiac cycle) and CBFVmean (the time averaged value of the maximal velocity envelope over 1 cardiac cycle) did not vary at any time points. CBFVdiast (the CBFV just before the acceleration phase [systole] of the next waveform) was lower at T3 (30 minutes after PP) compared to T1 (value derived averaging the first measure in the PP with the ones at 5 and 10 minutes) (P = .01), and the pulsatility index was higher at T5 (60 minutes after PP) compared to T0 (baseline, patient supine under general anesthesia) (P = .04). Data were analyzed at specific time points (T0 and T1). This value was derived by computing an average of the CBFV values collected at the first measure in the PP and at 5 and 10 minutes thereafter: T2, 15 minutes after PP; T3, 30 minutes after PP; T4, 45 minutes after PP; T5, 60 minutes after PP; and T6, 75 minutes after PP.

CONCLUSIONS

Our data on CBFV during PP for spine surgery demonstrate preservation of cerebral perfusion during stable systemic hemodynamic conditions. The present results do not allow us to determine whether the PP would be similarly tolerated with increasing length of surgery, variations in systemic hemodynamics, and in different patient populations.

Non-invasive evaluation of cardiac index by impedance cardiography in patients undergoing percutaneous nephrolithotomy

INTRODUCTION

Percutaneous nephrolithotomy (PNL) is an endoscopic treatment of renal lithiasis. It is usually two-staged: it begins in the lithotomy position for ureteral catheter placement and retrograde pyelography, and subsequently an optimal renal access is obtained in the prone position. Some patients under epidural anesthesia do not tolerate the prone position and the PNL cannot be continued. This may be related to changes occurring within the circulatory system. The aim of this prospective randomized double-blind study was to evaluate the changes of the cardiac index (CI) during PNL.

MATERIAL AND METHODS

In a group of 50 patients, with ASA physical status grade 1-2, epidural anesthesia with either 0.2% ropivacaine or 0.25% bupivacaine was performed and then the CI was evaluated by impedance cardiography.

RESULTS

Forty-five patients were included in the analysis; all tolerated the PNL well. After turning prone, a decrease in the CI was always recorded, a maximum after 10-15 min - 22.58 ±11.47%. There was significant variability of recorded values. The average CI dropped from 2.96 ±0.42 l/min/m² to 2.28 ±0.39 l/min/m². In 7 patients the decrease in the CI was greater than 35%. No correlation was observed with the arterial blood pressure or the heart rate. The decrease in the CI occurred irrespective of the type of local anesthetic used (p = 0.91).

CONCLUSIONS

A decrease in the CI was observed in every case, and it should be taken into consideration during qualification for PNL in the prone position.

Cerebral Oxygenation Under General Anesthesia Can Be Safely Preserved in Patients in Prone Position: A Prospective Observational Study

BACKGROUND

The effects of prone position (PP) on cerebral tissue metabolism are not well known. The aim of this investigation was to evaluate regional cerebral oxygen desaturation in patients undergoing lumbar spine surgery in PP during routine anesthesia management.

MATERIALS AND METHODS

Between July 2013 and October 2013, 50 consecutive patients undergoing lumbar spine surgery under general anesthesia in PP were enrolled. The anesthetic technique was standardized. Using near-infrared spectroscopy, bilateral regional cerebrovascular oxygen saturation was recorded during the surgery.

RESULTS

After 30 and 60 minutes of prone repositioning, significant decreases in bilateral regional cerebral oxygen saturation were observed compared with the values in the supine position (from 76.24% to 73.18% at 30 min and 72.76% at 60 min on the right side and from 77.06% to 73.76% at 30 min and 72.92% at 60 min on the left side; P<0.05). These changes were not clinically important and returned to supine values after 90 minutes of prone positioning. Decreases in cerebral oxygen saturation were accompanied by reductions in heart rate and mean arterial pressure (P<0.05). Older age and higher perioperative risk had a significant effect on the reduction of cerebral oxygen values (P<0.05).

CONCLUSIONS

The results of our study show that margin of safety against impaired cerebral oxygenation can be maintained in PP. Preventing bradycardia and arterial hypotension is crucial. Older patients and those at higher perioperative risk need more meticulous attention.

Effects of positive end-expiratory pressure on intraoperative core temperature in patients undergoing posterior spine surgery: prospective randomised trial

Objective Positive end-expiratory pressure (PEEP) causes carotid baroreceptor unloading, which leads to thermoregulatory peripheral vasoconstriction. However, the effects of PEEP on intraoperative thermoregulation in the prone position remain unknown. Methods Thirty-seven patients undergoing spine surgery in the prone position were assigned at random to receive either 10 cmH₂O PEEP (Group P) or no PEEP (Group Z). The primary endpoint was core temperature 180 minutes after intubation. Secondary endpoints were delta core temperature (difference in core temperature between 180 minutes and immediately after tracheal intubation), incidence of intraoperative hypothermia (core temperature of <36°C), and peripheral vasoconstriction-related data. Results The median [interquartile range] core temperature 180 minutes after intubation was 36.1°C [35.9°C-36.2°C] and 36.0°C [35.9°C-36.4°C] in Groups Z and P, respectively. The delta core temperature and incidences of intraoperative hypothermia and peripheral vasoconstriction were not significantly different between the two groups. The peripheral vasoconstriction threshold (36.2°C±0.5°C vs. 36.7°C±0.6°C) was lower and the onset of peripheral vasoconstriction (66 [60-129] vs. 38 [28-70] minutes) was slower in Group Z than in Group P. Conclusions Intraoperative PEEP did not reduce the core temperature decrease in the prone position, although it resulted in an earlier onset and higher threshold of peripheral vasoconstriction.

Hemodynamic Responses at Intubation, Change of Position, and Skin Incision: A Comparison of Multimodal Analgesia with Conventional Analgesic Regime

Background:

Lumbar spine surgery is associated with hemodynamic variations at intubation, change of position, and skin incision. A balanced anesthesia with multimodal analgesia (MMA) is necessary to attenuate these changes.

Aim:

To assess the relative effectiveness of preemptive MMA compared with the conventional analgesic regime in suppressing the hemodynamic response to endotracheal intubation, prone positioning, and skin incision.

Settings and Design:

A randomized, prospective study involving 42 patients belonging to the American Society of Anesthesiologists Physical Status 1 and II scheduled to undergo elective lumbar spine surgery were allocated into two groups of 21 each.

Materials and Methods:

Forty-two patients were randomly allocated into Groups A and B. Group A (study group) received diclofenac, paracetamol, clonidine, and bupivacaine with adrenaline skin infiltration and Group B (control group) injection paracetamol and saline with adrenaline skin infiltration.

Statistical Analysis Used:

Hemodynamic parameters (heart rate [HR], systolic blood pressure [SBP], diastolic blood pressure [DBP], and mean arterial pressure [MAP]) between the groups following intubation, prone position, and skin incision were noted and compared using repeated measure analysis of variance. One sample t-test was used to compare the standard mean concentration with the means of the study and control groups. P < 5% being considered statistically significant.

Results:

In the study group, HR, SBP, DBP, and MAP were lower at intubation and change of position as compared to the control group and were statistically significant.

Conclusion:

Preemptive MMA with balanced anesthesia is effective in attenuating the hemodynamic responses to multiple noxious stimuli during lumbar spine surgery.

Effect of Mechanical Ventilation Mode Type on Intra- and Postoperative Blood Loss in Patients Undergoing Posterior Lumbar Interbody Fusion Surgery

Background

The aim of study was to evaluate the effect of mechanical ventilation mode type, pressure-controlled ventilation (PCV), or volume-controlled ventilation (VCV) on intra- and postoperative surgical bleeding in patients undergoing posterior lumbar interbody fusion (PLIF) surgery.

Methods

This was a prospective, randomized, single-blinded, and parallel study that included 56 patients undergoing PLIF and who were mechanically ventilated using PCV or VCV. A permuted block randomization was used with a computer-generated list. The hemodynamic and respiratory parameters were measured after anesthesia induction in supine position, 5 min after patients were changed from supine to prone position, at the time of skin closure, and 5 min after the patients were changed from prone to supine position. The amount of intraoperative surgical bleeding, fluid administration, urine output, and transfusion requirement were measured at the end of surgery. The amount of postoperative bleeding and transfusion requirement were recorded every 24 h for 72 h.

Results

The primary outcome was the amount of intraoperative surgical bleeding, and 56 patients were analyzed. The amount of intraoperative surgical bleeding was significantly less in the PCV group than that in the VCV group (median, 253.0 [interquartile range, 179.0 to 316.5] ml in PCV group vs. 382.5 [328.0 to 489.5] ml in VCV group; P &lt; 0.001). Comparing other parameters between groups, only peak inspiratory pressure at each measurement point in PCV group was significantly lower than that in VCV group. No harmful events were recorded.

Conclusion

Intraoperative PCV decreased intraoperative surgical bleeding in patients undergoing PLIF, which may be related to lower intraoperative peak inspiratory pressure.

The effect of prone positioning with surgical bolsters on liver blood flow in healthy volunteers

This study sought to identify changes in hepatic flood flow and cardiac output during prone positioning on surgical bolsters in awake volunteers, and was prompted by a local incident of significant hepatic dysfunction following surgery in the prone position. Cardiac output was determined using the non-invasive Peñáz technique, and plasma disappearance rate of indocyanine green (ICG-PDR) was measured as a surrogate maker for hepatic blood flow along with serum hepatic enzyme assays. Measurements were made after one hour in supine, prone and returned supine positions. Ten volunteers completed the study. There were significant changes in the disappearance rate of indocyanine green, which decreased this from mean (SD) 31.1 (9.70) supine to 19.6 (4.37)%.min prone, respectively (p = 0.02), increasing on return to the supine position to 24.6 (5.54)%.min (p = 0.019). Cardiac output was also significantly reduced when changing from the supine to the prone position, from mean (SD) 4.7 (1.0 to 3.5 (1.1) (l.min(-1) ), respectively (p = 0.002). We demonstrated an acute and reversible change in both hepatocellular function and cardiac output associated with the prone position.

A case of pituitary apoplexy following posterior lumbar fusion surgery

Pituitary adenoma is a common primary brain neoplasm. Pituitary apoplexy (PA) is a rare complication of pituitary adenoma and occurs as the result of sudden tumor growth and following different comorbidities. The authors describe the first case of PA following posterior lumbar fusion surgery performed while the patient was prone. In patients with a preexisting pituitary adenoma, thorough clinical and laboratory investigations should be conducted using an interdisciplinary approach before any planned surgery. In unknown cases of pituitary adenoma, PA should be kept in mind for the differential diagnosis in a case with headache, nausea, vomiting, ophthalmoplegia, visual loss, and electrolyte imbalance concurrent with an ongoing disease state.

Comparison of Retrograde Intrarenal Surgery and Percutaneous Nephrolithotomy: From the View of an Anesthesiologist

PURPOSE

To determine the differences among the hemodynamics, neuroendocrine stress response (NESR), and postoperative visual analogue scale (VAS) scores of pain between the procedures of retrograde intrarenal surgery (RIRS) and percutaneous nephrolithotomy (PNL) for lower pole kidney stones.

PATIENTS AND METHODS

Fifty-six patients undergoing RIRS and PNL with lower puncture approach, under general anesthesia, were prospectively enrolled in our study. Perioperative blood pressure (systolic, diastolic, and mean), heart rate, and peripheral oxygen saturation (SpO2) values were recorded at intervals. Arterial blood gas (ABG) and blood glucose, serum insulin, and cortisol levels as stress response markers were analyzed in the perioperative period. Postoperative VAS scores were recorded at 30 minutes and 2, 4, 6, and 12 hours after extubation. Duration of surgery, stone sizes, and stone-free rates (SFRs) were noted.

RESULTS

SFRs were 93.3% in the PNL group (28/30 patients) and 88.5% in the RIRS group (23/26 patients) (p = 0.52). There was no statistical difference between the hemodynamics of both groups. Perioperative ABGs and NESRs were similar between groups (p > 0.05). Postoperative VAS scores and analgesic consumptions were also similar between groups (p > 0.05). Duration of surgery was significantly shorter in the RIRS group (p = 0.001). Stone size was significantly higher in the PNL group (p = 0.013).

CONCLUSION

Although the PNL is assumed to be more invasive than the RIRS procedure among urologists and anesthesiologists, both techniques may have similar perioperative outcomes in terms of hemodynamics, ABG, NESR, and pain scores in the management of lower pole stones with lower pole approach.

Lithotomy versus jack-knife position on haemodynamic parameters assessed by impedance cardiography during anorectal surgery under low dose spinal anaesthesia: a randomized controlled trial

BACKGROUND

Although the prone position providing better exposure for anorectal surgery is required it can cause a reduction of cardiac output and cardiac index. The goal was to compare haemodynamic changes assessed by impedance cardiography during anorectal surgery under low-dose spinal anaesthesia in lithotomy and jack-knife position.

METHODS

The prospective randomized controlled study included 104, ASA I-II adult patients admitted for elective minor anorectal surgery, assigned to be performed in lithotomy (groupL, n = 52) or jack-knife position (groupJ, n = 52). After arrival to operating room the standard monitoring, impedance cardiography device was connected to the patient, and the following variables were recorded: cardiac output, cardiac index, systemic vascular resistance, stroke index at times of arrival to operating room, placement for, start and end of surgery and placement to bed. Spinal block was made in the sitting position with 4 mg of 0.5% hyperbaric bupivacaine and 10 μg of Fentanyl injected over 2 min. Comparison was based on haemodynamic changes between and inside groups over time. Student's t, chi square tests were used for statistical analysis with p < 0.05 regarded as statistically significant.

RESULTS

The reduction of cardiac output was statistically significant after placement of the patient into the prone position: from baseline 7.4+/-1.6 to 4.9+/-1.2 after placement for and 4.7+/-1.2 at the start and end of surgery (mean +/-SD l/min). The difference of cardiac output between groups was 2.0 l/min after positioning for and the start of surgery and 1.5 l/min at the end of surgery (p < 0.05). Mean cardiac index reduced from baseline 3.9+/-0.8 to 2.6+/-0.7 and 2.4+/-0.6 (mean+/-SD l/min/m(2)) in groupJ and between groups: by 1.0 l/min/m(2) after placement for, 1.1 at the start and 0.8 at the end of surgery (p < 0.05). Systemic vascular resistance increased from baseline 1080+/-338 to 1483+/-479 after placement for, 1523+/-481 at the start and 1525+/-545 at the end of surgery in groupJ (mean+/-SD dynes/sec/cm(-5), p < 0.05).

CONCLUSIONS

According to impedance cardiography, jack-knife position after low-dose spinal anaesthesia produces transitory, but statistically significant reduction of cardiac output and cardiac index with increase of systemic vascular resistance, compared to insignificant changes in lithotomy position.

TRIAL REGISTRATION

Clinical Trials NCT02115178.

Cardiac function changes with switching from the supine to prone position: analysis by quantitative semiconductor gated single-photon emission computed tomography

BACKGROUND

Prone positioning is required in certain operations such as spinal surgery. Changes in cardiac function in the prone position have been studied with various methodologies. Few studies have investigated changes in left ventricular diastolic function and rhythm in subjects turned prone.

METHODS AND RESULTS

Cardiac function was evaluated in the supine and prone positions in 90 patients without atrial fibrillation who underwent (99m)Tc-tetrofosmin quantitative gated single-photon emission computed tomography. Three groups of 30 patients each were classified as "no history of myocardial ischemia or cardiomyopathy" (Group A), "history of myocardial infarction" (Group B), and "ischemic heart disease without myocardial infarction history" (Group C). Upon assuming the prone position, the cardiac index and any dyssynchrony worsened in all groups. Ejection fraction changes occurred only in Group B, and diastolic function changes occurred in Groups B and C, but not in Group A. The changes caused by prone positioning were more severe in the patients with poor cardiac function.

CONCLUSIONS

Prone positioning induces significant changes in systolic and diastolic function, as well as dyssynchrony. The negative effects of prone positioning are more severe in patients with poor baseline cardiac function.

Stroke volume-directed administration of hydroxyethyl starch (HES 130/0.4) and Ringer’s acetate in prone position during neurosurgery: a randomized controlled trial

PURPOSE

General anesthesia in the prone position is associated with hypotension. We studied stroke volume (SV)-directed administration of hydroxyethyl starch (HES 130 kDa/0.4) and Ringer’s acetate (RAC) in neurosurgical patients operated on in a prone position to determine the volumes required for stable hemodynamics and possible coagulatory effects.

METHODS

Thirty elective neurosurgical patients received either HES (n = 15) or RAC (n = 15). Before positioning, SV measured by arterial pressure waveform analysis was maximized by fluid boluses until SV did not increase more than 10 %. SV was maintained by repeated administration of fluid. RAC 3 ml/kg/h was infused in both groups. Thromboelastometry assessed coagulation. Mann–Whitney U test, Wilcoxon signed-rank test, ANOVA on ranks, and a linear mixed model were applied.

RESULTS

Comparable hemodynamics were achieved with the mean cumulative (SD) boluses of HES or RAC 240 (51) or 267 (62) ml (P = 0.207) before positioning, 340 (124) or 453 (160) ml (P = 0.039) 30 min after positioning, and 440 (229) or 653 (368) ml at the end of surgery (P = 0.067). The mean dose of basal RAC infusion was 813 (235) and 868 (354) ml (P = 0.620) in the HES and RAC group, respectively. Formation and maximum strength of the fibrin clot were decreased in the HES group. Intraoperative blood loss was comparable between groups (P = 0.861).

CONCLUSION

The amount of RAC needed in the prone position was 25 % greater. The cumulative dose of 440 ml HES induced a slight disturbance in fibrin formation and clot strength. We suggest cautious administration of HES during neurosurgery.

Optimal perioperative management of arterial blood pressure

Perioperative blood pressure management is a key factor of patient care for anesthetists, as perioperative hemodynamic instability is associated with cardiovascular complications. Hypertension is an independent predictive factor of cardiac adverse events in noncardiac surgery. Intraoperative hypotension is one of the most encountered factors associated with death related to anesthesia. In the preoperative setting, the majority of antihypertensive medications should be continued until surgery. Only renin-angiotensin system antagonists may be stopped. Hypertension, especially in the case of mild to moderate hypertension, is not a cause for delaying surgery. During the intraoperative period, anesthesia leads to hypotension. Hypotension episodes should be promptly treated by intravenous vasopressors, and according to their etiology. In the postoperative setting, hypertension predominates. Continuation of antihypertensive medications and postoperative care may be insufficient. In these cases, intravenous antihypertensive treatments are used to control blood pressure elevation.

Cerebral oxygenation in preterm infants

BACKGROUND AND OBJECTIVE

Prone sleeping is a major risk factor for sudden infant death syndrome (SIDS) and preterm infants are at significantly increased risk. In term infants, prone sleeping is associated with reduced mean arterial pressure (MAP) and cerebral tissue oxygenation index (TOI). However, little is known about the effects of sleeping position on TOI and MAP in preterm infants. We aimed to examine TOI and MAP in preterm infants after term-equivalent age, during the period of greatest SIDS risk.

METHODS

Thirty-five preterm and 17 term infants underwent daytime polysomnography, including measurement of TOI (NIRO-200 spectrophotometer, Hamamatsu Photonics KK, Japan) and MAP (Finapress Medical Systems, Amsterdam, Netherlands) at 2 to 4 weeks, 2 to 3 months, and 5 to 6 months postterm age. Infants slept prone and supine in active and quiet sleep. The effects of sleep state and position were determined by using 2-way repeated measures analysis of variance and of preterm birth by using 2-way analysis of variance.

RESULTS

In preterm infants, TOI was significantly lower when prone compared with supine in both sleep states at all ages (P < .05). Notably, TOI was significantly lower in preterm compared with term infants at 2 to 4 weeks, in both positions (P < .05), and at 2 to 3 months when prone (P < .001), in both sleep states. MAP was also lower in preterm infants in the prone position at 2 to 3 months (P < .01).

CONCLUSIONS

Cerebral oxygenation is reduced in the prone position in preterm infants and is lower compared with age-matched term infants, predominantly in the prone position when MAP is also reduced. This may contribute to their increased SIDS risk.

Deep vein thrombosis after spine operation in prone position with subclavian venous catheterization: a case report

We experienced a case of deep vein thrombosis after spine surgery in the prone position with a central venous catheter (CVC). Posterior lumbar interbody fusion was performed on a 73-year-old female patient who was diagnosed with spinal stenosis. Accordingly, in the operation room under general anesthesia, two-lumen CVC were inserted into the left subclavian vein. The surgery was performed in the prone position with a Wilson frame. On the next day, there was a sudden occurrence of severe edema in the patient's left arm. By ultrasonography and computed tomography scanning, extensive deep vein thrombosis was observed in the left subclavian vein. The existence of a factor affecting blood flow such as the prone position may increase the risk of thrombus formation. Therefore, careful perioperative evaluation should be implemented.

Perioperative concerns in pediatric patients u10/1/2013ndergoing different types of scoliosis correction surgery: A retrospective observational study

Background:

Advances in scoliosis surgery have now made it possible for younger patients to be taken up for scoliosis correction.

Objectives:

To ascertain the patient profile, perioperative complications and need for intensive care management in children undergoing posterior fusion and instrumentation (PF), anterior release (AR), and growth rod (GR) insertion surgery.

Patients and Methods:

After taking parental consent, data were collected retrospectively for 33 patients who underwent 37 procedures (four patients had both anterior and posterior procedures) on 2 days of the week mainly from August 2008 to February 2010 at a tertiary care institution.

Results:

Children undergoing GR surgery were younger (8.1 ± 2.1 years) than patients undergoing AR (12.9 ± 1.7 years) or posterior fusion (14.2 ± 2.2 years). AR children had a significantly higher Cobb's angle and more rigid curves. (P = 0.057) Associated congenital abnormalities especially neurological were commoner in the GR children. Surgical duration and blood loss was significantly more for PF (2207.5 ± 1224.13 ml) than GR (456 ± 337.5 ml), or AR (642.85 ± 304.72 ml), (P = 0.0002). PF patients needed Intensive care unit (ICU) care mainly due to the blood loss and prolonged surgery (35%). AR performed via thoracotomy was associated with the need for mechanical ventilation in 28.6%. The GR patients had major intraoperative hemodynamic events and 20% needed ICU care.

Conclusions:

Post-operative ventilation may be required in 20-35% patients undergoing procedures for scoliosis correction. Despite GR insertion involving lesser blood loss; younger age, congenital abnormalities, positioning, and surgical manipulation resulted in life threatening events in these patients.

Changes in cardiac index and blood pressure on positioning children prone for scoliosis surgery

In this prospective observational study we investigated the changes in cardiac index and mean arterial pressure in children when positioned prone for scoliosis correction surgery. Thirty children (ASA 1-2, aged 13-18 years) undergoing primary, idiopathic scoliosis repair were recruited. The cardiac index and mean arterial blood pressure (median (IQR [range])) were 2.7 (2.3-3.1 [1.4-3.7]) l.min(-1).m(-2) and 73 (66-80 [54-91]) mmHg, respectively, at baseline; 2.9 (2.5-3.2 [1.7-4.4]) l.min(-1).m(-2) and 73 (63-81 [51-96]) mmHg following a 5-ml.kg(-1) fluid bolus; and 2.5 (2.2-2.7 [1.4-4.8]) l.min(-1).m(-2) and 69 (62-73 [46-85]) mmHg immediately after turning prone. Turning prone resulted in a median reduction in cardiac index of 0.5 l.min(-1).m(-2) (95% CI 0.3-0.7 l.min(-1).m(-2), p=0.001), or 18.5%, with a large degree of inter-subject variability (+10.3% to -40.9%). The changes in mean arterial blood pressure were not significant. Strategies to predict, prevent and treat decreases in cardiac index need to be developed.

[Controversies in neuroanaesthesia: positioning in neurosurgery]

Positioning of the neurosurgical patient has several features such as the existence of specific positions (i.e: sitting, prone hyperlordotic, crouching ou kneeling positions) or the range of facilities for the same surgical indications. The last point, a source of controversy, is the subject of this review. Current indications for the sitting position, positioning for lumbar spine surgery and prevention of eye injuries are successively addressed.

Cardiac Output and Propofol Concentrations in Prone Surgical Patients

The aim of this study was to compare cardiac output and plasma propofol concentrations in the supine and prone positions in healthy adult patients presenting for lumbar spine surgery. Patients received propofol and remifentanil via effect-site steered target-controlled infusions. Cardiac output and plasma propofol concentration were compared during 20 minutes in the supine position and 20 minutes after positioning on a Wilson frame. Cardiac output did not change significantly over 20 minutes in either position (P=0.37) and was similar at 20 minutes in the supine (6.1 [1.6] l/minute) and prone positions (6.1 [1.9] l/minute) (P=0.87). Propofol concentrations were similar in the supine and prone positions at 20 minutes (2.55 [0.89] and 2.53 [0.90] μg/ml; P=0.93). We conclude that prone positioning on the Wilson frame does not affect cardiac output or plasma propofol concentration.

The effect on respiratory mechanics when using a Jackson surgical table in the prone position during spinal surgery

Background

Respiratory dynamics may be monitored and evaluated indirectly by measuring the peak inspiratory pressure and plateau pressure. In this study, the respiratory dynamics of patients undergoing spinal surgery using a Jackson surgical table were observed with a device after converting their position from supine to prone. The effects of the dynamic compliance and airway resistance were observed from the changes in peak inspiratory pressure and plateau.

Methods

Twenty five patients were selected as subjects scheduled to undergo lumbar spine surgery. After intubation, the patients were ventilated mechanically with a tidal volume of 10 ml/kg and a respiration rate of 10/min. Anesthesia was maintained with sevoflurane 1.5%, nitrous oxide 2 L/min and oxygen 2 L/min. The peak inspiratory pressure, plateau pressure, resistance, compliance, arterial oxygen tension, carbon dioxide tension, heart rate and arterial blood pressure were measured at 10 minutes after the induction of anesthesia. These parameters were measured again 10 minutes after placing the patient in the prone position.

Results

The prone position did not significantly affect the arterial oxygen tension, carbon dioxide tension, blood pressure and heart rate, but significantly increased the peak inspiratory pressure and resistance and decreased the dynamic compliance.

Conclusions

The peak inspiratory pressure was increased using a Jackson surgical table to minimize the abdominal pressure when converting from the supine to prone position. This might be due to a decrease in lung and chest compliance as well as an increase in airway resistance.