The effect of four different surgical prone positions on cardiovascular parameters in healthy volunteers

Predictors of fluid responsiveness in the operating room: a narrative review

Prediction of fluid responsiveness has been considered an essential tool for modern fluid management. However, most studies in this field have focused on patients in intensive care unit despite numerous research throughout several decades. Therefore, the present narrative review aims to show the representative method's feasibility, advantages, and limitations in predicting fluid responsiveness, focusing on the operating room environments. Firstly, we described the predictors of fluid responsiveness based on heart-lung interaction, including pulse pressure and stroke volume variations, the measurement of respiratory variations of inferior vena cava diameter, and the end-expiratory occlusion test and addressed their limitations. Subsequently, the passive leg raising test and mini-fluid challenge tests were also mentioned, which assess fluid responsiveness by mimicking a classic fluid challenge. In the last part of this review, we pointed out the pitfalls of fluid management based on fluid responsiveness prediction, which emphasized the importance of individualized decision-making. Understanding the available representative methods to predict fluid responsiveness and their associated benefits and drawbacks through this review will aid anesthesiologists in choosing the most reliable methods for optimal fluid administration in each patient during anesthesia in the operating room.

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.

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.

Functional hemodynamic tests: a systematic review and a metanalysis on the reliability of the end-expiratory occlusion test and of the mini-fluid challenge in predicting fluid responsiveness

Background

Bedside functional hemodynamic assessment has gained in popularity in the last years to overcome the limitations of static or dynamic indexes in predicting fluid responsiveness. The aim of this systematic review and metanalysis of studies is to investigate the reliability of the functional hemodynamic tests (FHTs) used to assess fluid responsiveness in adult patients in the intensive care unit (ICU) and operating room (OR).

Methods

MEDLINE, EMBASE, and Cochrane databases were screened for relevant articles using a FHT, with the exception of the passive leg raising. The QUADAS-2 scale was used to assess the risk of bias of the included studies. In-between study heterogeneity was assessed through the I² indicator. Bias assessment graphs were plotted, and Egger’s regression analysis was used to evaluate the publication bias. The metanalysis determined the pooled area under the receiving operating characteristic (ROC) curve, sensitivity, specificity, and threshold for two FHTs: the end-expiratory occlusion test (EEOT) and the mini-fluid challenge (FC).

Results

After text selection, 21 studies met the inclusion criteria, 7 performed in the OR, and 14 in the ICU between 2005 and 2018. The search included 805 patients and 870 FCs with a median (IQR) of 39 (25–50) patients and 41 (30–52) FCs per study. The median fluid responsiveness was 54% (45–59). Ten studies (47.6%) adopted a gray zone analysis of the ROC curve, and a median (IQR) of 20% (15–51) of the enrolled patients was included in the gray zone. The pooled area under the ROC curve for the end-expiratory occlusion test (EEOT) was 0.96 (95%CI 0.92–1.00). The pooled sensitivity and specificity were 0.86 (95%CI 0.74–0.94) and 0.91 (95%CI 0.85–0.95), respectively, with a best threshold of 5% (4.0–8.0%). The pooled area under the ROC curve for the mini-FC was 0.91 (95%CI 0.85–0.97). The pooled sensitivity and specificity were 0.82 (95%CI 0.76–0.88) and 0.83 (95%CI 0.77–0.89), respectively, with a best threshold of 5% (3.0–7.0%).

Conclusions

The EEOT and the mini-FC reliably predict fluid responsiveness in the ICU and OR. Other FHTs have been tested insofar in heterogeneous clinical settings and, despite promising results, warrant further investigations.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2545-z) contains supplementary material, which is available to authorized users.

Severe Hypotension and Hepatic Dysfunction in a Patient Undergoing Scoliosis Surgery in the Prone Position

Many patients with neuromuscular disorders develop progressive scoliosis and require corrective surgery. We present a patient with hereditary motor and sensory neuropathies who developed severe hypotension during corrective surgery for thoracolumbar scoliosis. The haemodynamic disturbance was probably secondary to thoracic hyperlordosis and the knee-chest position and was aggravated by surgical manipulation. This may be prevented by tailored preoperative evaluation of different patient prone position supports and frames in order to select that which causes least cardiovascular and respiratory disturbance. This patient also developed severely deranged liver function postoperatively and the possible aetiology is discussed.

Haemodynamic changes during prone positioning in anaesthetised chronic cervical myelopathy patients

Background and Aims:

Anaesthetised patients, when positioned prone, experience hypotension and reduction in cardiac output. Associated autonomic dysfunction in cervical myelopathy patients predisposes them to haemodynamic changes. The combined effect of prone positioning and autonomic dysfunction in anaesthetised patients remains unknown.

Methods:

Thirty adult chronic cervical myelopathy patients, aged 18-65 years with Nurick grade ≥2 were recruited in this prospective observational study. Heart rate, mean blood pressure, cardiac output, stroke volume, total peripheral resistance and stroke volume variation were measured using NICOM^® monitor. Data were collected in supine before anaesthetic induction (baseline), 2 minutes after induction, 2 minutes after intubation, before and after prone positioning and every 5 minutes thereafter until skin incision. Repeated measures analysis of variance (ANOVA) was used to analyse the haemodynamic parameters across the time points. Bivariate Spearman's correlation was used to find factors associated with blood pressure changes. A P value <0.05 was kept significant.

Results:

Cardiac output during the entire study period remained stable (P = 0.186). Sixty percent of the patients experienced hypotension. At 15 and 20 minutes after prone positioning, mean blood pressure decreased (P = 0.001), stroke volume increased (P = 0.001), and heart rate and total peripheral resistance decreased (P < 0.001, P = 0.001, respectively). These changes were significant when compared to pre-prone position values. Number of levels of spinal cord compression positively correlated with the incidence of hypotension.

Conclusion:

Cervical myelopathy patients experienced hypotension with preserved cardiac output in prone position due to a reduction in total peripheral resistance. Hypotension correlated with the number of levels of spinal cord compression.

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.

Changes in cardiac output and cerebral oxygenation during prone and supine sleep positioning in healthy term infants

OBJECTIVE

To investigate the changes in systemic and cerebral haemodynamics between supine and prone sleep in healthy term infants during the early postnatal period.

DESIGN/METHODS

Healthy term infants without congenital anomalies, patent ductus arteriosus and/or small for gestational age status were enrolled. Infants were placed in supine (SP₁), prone (PP) and back in supine (SP₂) position for 15 min each while asleep. Cardiac output (CO) and stroke volume (SV) were assessed by electrical velocimetry (EV) and echocardiography (echo), and cerebral regional oxygen saturation (CrSO₂) in the frontal lobes was monitored by near-infrared spectroscopy. Heart rate (HR) and SpO₂ were continuously monitored by conventional monitoring.

RESULTS

In 34 healthy term infants (mean age 3.7±1.2 days; 16 females), 66 sets of serial CO measurements (34 EV and 32 echo) in three sleep positions were obtained. Mean CO_EV and CO_echo were 182±57 (SP₁), 170±50 (PP) and 177±54 (SP₂), and 193±48 (SP₁), 174±40 (PP) and 192±50 (SP₂) mL/kg/min, respectively. Mean SV_EV and SV_echo were 1.46±0.47 (SP₁), 1.36±0.38 (PP) and 1.37±0.39 (SP₂), and 1.54±40 (SP₁), 1.38±0.38 (PP) and 1.51±0.41 (SP₂) mL/kg, respectively. Repeated measures analysis of variance revealed a decrease in CO and SV during prone positions by both EV and echo, while HR, SpO₂ and CrSO₂ did not change. Thirty-eight per cent of the CO measurements decreased≥10% during prone positioning.

CONCLUSIONS

In healthy term infants, CO decreases in prone position due to a decrease in SV and not HR. CO recovers when placed back in supine. However, frontal lobe CrSO₂ does not change in the different positions.

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.

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.

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.

Modified prone position to dissect the popliteal fossa

Introduction

Traditionally, the prone position is used for dissecting the popliteal fossa, which requires endotracheal intubation. Access to the airway in this position is limited, hence the complications. It is not surprising that the prone position is not favoured by the anaesthetists, especially in patients with a high body mass index. We describe a safe and novel alternative to the prone position.

Methods

The modified prone position (MPP) is described as an alternative position that facilitates access to the airway.

Results

Between October 2007 and May 2010, 12 patients underwent popliteal fossa dissection using the MPP. All patients had general anaesthesia using a laryngeal mask airway with the exception of one, who had an epidural anaesthesia. There were no airway or haemodynamic complications. The surgical access to the popliteal fossa was as good as with the traditional prone position.

Conclusions

The MPP was satisfactory for both the surgeon and the anaesthetists. The authors now use this position routinely for dissecting the popliteal fossa.

[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.

Prospective assessment of patient morbidity from prone sacral positioning

OBJECT

Sacrectomy positioning must balance surgical exposure, localization, associated operative procedures, and patient safety. Poor positioning may increase hemorrhage, risk of blindness, and skin breakdown.

METHODS

The authors prospectively identified positioning-related morbidity in 17 patients undergoing 19 prone sacral procedures from September 2008 to August 2009 following institution of a standardized positioning protocol. Key elements include skull traction/head suspension, an open radiolucent frame, and wide draping for associated closure and reconstructive procedures.

RESULTS

Tumors included 5 chordomas, 4 high-grade sarcomas, 1 chondrosarcoma, 2 presacral extradural myxopapillary ependymomas, and 5 others. Mean patient age was 49.9 years (range 17-74 years); mean body mass index was 27.6 kg/m(2) (range 19.3-43.9 kg/m(2)). Mean preoperative Braden skin integrity score was 21.1 (range 17-23). Average operative time was 501 minutes (range 158-1136 minutes). Prone surgery was a part of staged anterior/posterior resections in 8 patients. Localization was conducted using fluoroscopy in 13 patients and intraoperative CT in 4 patients. All imaging studies were successful. One patient developed a transient ulnar nerve palsy attributed to positioning. Three patients (two of whom were morbidly obese) developed Stage I pressure injuries to the chest and another developed Stage II pressure injury following a 1136-minute procedure. Morbidity was only observed in patients with morbid obesity or with procedures lasting in excess of 10 hours.

CONCLUSIONS

A positioning protocol using head suspension on an open radiolucent frame facilitates oncological sacral surgery with reasonable patient morbidity. Morbid obesity and procedure times in excess of 10 hours are risk factors for positioning-related complications. To the authors' knowledge, this is the first report of surgical positioning morbidity in this patient population.

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.

Awake endotracheal intubation and prone patient self-positioning: anesthetic and positioning considerations during percutaneous nephrolithotomy in obese patients

BACKGROUND AND PURPOSE

Obesity is associated with adverse outcomes with certain urologic procedures and may make patient positioning more difficult. We describe our technique of awake intubation and prone patient self-positioning before percutaneous nephrolithotomy (PCNL), and review the literature regarding prone positioning in obese patients and the impact of obesity on PCNL.

METHODS

Patient preparation begins with detailed preoperative counseling regarding the procedure. Premedication with a sedative and antisialagogue is followed by airway topicalization to suppress gag reflex and pain. Fiberoptic bronchoscope intubation is then carried out. The patient then positions himself/herself comfortably before induction of general anesthesia.

RESULTS

We have successfully performed awake intubation and patient prone self-positioning followed by PCNL, most recently in a 58-year-old (body mass index 51.3 kg/m(2)) man with a history of gastric bypass, diabetes mellitus, and hypertension, without added morbidity. Adverse effect on patient cardiopulmonary dynamics can be minimized in the prone position.

CONCLUSIONS

The technique of awake intubation with prone patient self-positioning can be helpful for positioning morbidly obese patients before PCNL and has been safe and effective in properly selected patients. Efficacy of PCNL should not be impacted by obesity or prone positioning and morbidity minimized provided that surgical and anesthesia teams understand and safeguard against potential complications.

Correlation between centrally versus peripherally transduced venous pressure in prone patients undergoing posterior spine surgery

STUDY DESIGN

Prospective clinical observational study.

OBJECTIVE

To evaluate the correlation and agreement between peripherally and centrally transduced venous pressures in prone spine surgery patients.

SUMMARY OF BACKGROUND DATA

In view of a variety of potential complications associated with the placement of central venous lines for the purpose of central venous pressure (CVP) monitoring, a number of authors have suggested that the use of peripherally transduced pressures (PVP) instead may yield similar results. Data confirming the validity of this technique for the purpose of intravascular fluid volume monitoring in prone patients undergoing spine surgery remain scarce.

METHODS

After protocol approval by the internal review board, we enrolled 40 patients who underwent spine surgery in the prone position. CVP and PVP were recorded simultaneously. The data pairs were analyzed for correlation. Bland and Altman plots were created to evaluate the degree of agreement between the 2 modes of venous pressure monitoring.

RESULTS

A total of 1275 data pairs were collected. The mean PVP was 17.55 mm Hg +/- 4.93 mm Hg and the mean CVP 15.52 mm Hg +/- 4.77 mm Hg (P < 0.001), thus yielding a mean difference of 2.04 mm Hg +/- 1.39 mm Hg. PVP and CVP correlated well over a wide range of pressures (r = 0.949, r = 0.920 [P < 0.001]). A high level of agreement was found between both methods of venous pressure measurement.

CONCLUSION

CVP and PVP correlate well under conditions associated with prone spine surgery. With a high level of agreement found in this study, PVP may represent an attractive alternative to CVP monitoring to assess fluid volume trends intraoperatively.

Prone positioning for head and neck reconstructive surgery

Certain head and neck surgical cases require the patient to be positioned prone. Such positioning carries with it an attendant subset of risks and complications not otherwise encountered in more traditional supine positioning. Gaining awareness of these risks and complications, and developing proactive positioning strategies, will enable the surgical team to position the patient optimally for the procedure and provide for every consideration of patient safety. This article consists of a specific literature review of those issues directly related to the anatomical and physiological concerns arising from prone positioning. Particular attention is paid to the cardiopulmonary, renal, ophthalmologic, and neurological vulnerabilities unique to this position. Proper planning by the surgical team and utilization of the correct equipment are a necessity. A tailored approach to the needs of the individual patient and an intimate awareness of the potential pitfalls will contribute to better outcomes when using the prone position.

Anaesthesia in the prone position

Prone positioning of patients during anaesthesia is required to provide operative access for a wide variety of surgical procedures. It is associated with predictable changes in physiology but also with a number of complications, and safe use of the prone position requires an understanding of both issues. We have reviewed the development of the prone position and its variants and the physiological changes which occur on prone positioning. The complications associated with this position and the published techniques for various practical procedures in this position will be discussed. The aim of this review is to identify the risks associated with prone positioning and how these risks may be anticipated and minimized.

Risks and benefits of patient positioning during neurosurgical care

Positioning of the surgical patient is an important part of anesthesia care and attention to the physical and physiologic consequences of positioning can help prevent serious adverse events and complications. The general principles of patient positioning of the anesthetized and awake neurosurgical patient are discussed in this article.

Anesthetic considerations in the treatment of cervical myelopathy

BACKGROUND CONTEXT

The safe surgical treatment of patients with severe cervical spondylotic myelopathy involves a team approach incorporating special anesthetic considerations. This patient population is more vulnerable to perioperative complications. Advanced age, prolonged periods of immobility, multiple medical co-morbidities, and the risk of worsening neurologic injury mandate that the anesthesiologist pay special attention in the preoperative, induction, surgical, and recovery phases.

PURPOSE

To review the literature regarding the anesthetic management of patients undergoing surgery for cervical spondylotic myelopathy.

CONCLUSION

A basic understanding of the pathophysiology of cervical myelopathy as well as the nuances of the surgical treatment plan can help to ensure safe and effective patient management.

Effect of prone positioning systems on hemodynamic and cardiac function during lumbar spine surgery: an echocardiographic study

STUDY DESIGN

Prospective randomized study of patients undergoing spine surgery.

OBJECTIVE

To compare changes in hemodynamic and cardiac function after prone positioning using different prone positioners.

SUMMARY OF BACKGROUND DATA

Prone positioning decreases blood pressure and cardiac function. Several studies have evaluated changes in cardiac function after prone positioning, and linked them to reduced venous return and ventricular compliance. This study compares different prone positioners using transesophageal echocardiography, and determines their effect on cardiac function and hemodynamics.

METHODS

After correction of fluid deficits with the patient under stable anesthesia, hemodynamic and cardiac performance was measured using transesophageal echocardiography. After prone positioning, repeat measurements were performed, and comparisons were made between prone and supine positions.

RESULTS

No intergroup differences in demographics, fluid deficit, baseline hemodynamics, or differences from supine to prone position were noted. Cardiac output decreased with the Wilson (Union City, CA) and Siemens AG (Munich, Germany) frames, while cardiac index and stroke volume decreased with the Andrews (Hollywood, CA), Wilson, and Siemens systems. Cardiac preload decreased using the Andrews frame. The Jackson spine table (Hollywood, CA) and bolsters had the least effect on cardiac performance.

CONCLUSION

Adequate fluid replacement reduced hypotension and hemodynamic instability after prone positioning. The Jackson spine table and longitudinal bolsters had minimal effects on cardiac function, and should be considered in patients with limited cardiac reserve.

Haemodynamic effects of the prone position: a comparison of propofol total intravenous and inhalation anaesthesia

The haemodynamic changes of the prone position were investigated in 40 ASA I-II patients undergoing lumbar spine surgery. Patients were randomly assigned, following propofol intravenous induction, to receive maintenance of anaesthesia using either isoflurane 1-1.2% in air or target controlled propofol 3 microg.ml(-1) infusion. Measurements of non-invasive blood pressure, heart rate and cardiac output were made in the supine position. The patient was then turned prone onto a Montreal pattern mattress and measurements repeated. Cardiac output measurements were made using a non-invasive cardiac output monitor. We found a significant reduction in cardiac index in both groups and a significantly greater change with propofol compared to isoflurane on turning supine to prone (CI change 0.4 vs 0.7 l.min(-1).m(-2) p = 0.001 and SVRI change 89 vs 177 dyne.s(-1).cm(-5), p = 0.041). We conclude that turning healthy patients prone produces a clinically significant reduction in cardiac output, the change being greater during maintenance of anaesthesia using propofol compared to isoflurane.

A prospective randomized study comparing perioperative outcome variables after epidural or general anesthesia for lumbar disc surgery

General and regional anesthesia (spinal and epidural) can be performed successfully for lumbar disc surgery. The aim of this study was to assess the superiority of general anesthesia or epidural anesthesia techniques in lumbar laminectomy and discectomy. Sixty patients undergoing lumbar partial hemilaminectomy and discectomy were randomly divided into two groups receiving standardized general anesthesia (GA) or epidural anesthesia (EA). Demographically, both groups were similar. Surgical onset time (36.72 +/- 5.47 vs. 25.40 +/- 7.83 minutes) was longer in the EA group, but total anesthesia time (154.32 +/- 35.73 vs. 162.40 +/- 26.79 minutes) did not differ between the two groups. Surgical time (118.80 +/- 35.42 vs. 139.60 +/- 26.80 minutes) was longer in the GA group. The heart rate and mean arterial pressure values of the EA group measured 15, 20, and 25 minutes after local anesthetic administration to the epidural catheter were found to be lower than in the GA group measured after induction of general anesthesia. The frequency of bradycardia (EA vs. GA, 3 vs. 2), tachycardia (3 vs. 7), and hypotension (6 vs. 4) during anesthesia did not differ between the groups, but the occurrence of hypertension (1 vs. 7) was higher in the GA group. Blood loss was less in the EA group than in the GA group (180.40 +/- 70.38 vs. 288.60 +/- 112.51 mL). Postanesthesia care unit (PACU) heart rate and mean arterial pressure were higher in the GA group. Peak pain scores in PACU and postoperative 24 hours were higher in the GA group when compared with the EA group. Nausea was more common in the GA group both in PACU and 24 hours after surgery. There was no difference between the hospitalization duration of the groups. In conclusion, this study suggests that EA is an important alternative to GA during lumbar disc surgery.

Induction of anesthesia and insertion of a laryngeal mask airway in the prone position for minor surgery

The use of the prone position for surgery presents potential obstacles to rapid tracking of patients during ambulatory anesthesia. We describe a prospective audit of 73 patients who placed themselves in the prone position; anesthesia was induced in this position and a laryngeal mask airway (LMA) was used to maintain the airway. Additional increments of propofol were given to one patient who had laryngospasm and to nine who required deepening of anesthesia before the LMA could be inserted. Of four cases with LMA malpositioning, the LMA was adjusted easily in three, but in one patient who was edentulous, it was necessary to hold the LMA for the duration of the procedure. Manual ventilation of the lungs via the LMA was required because of arterial oxygen desaturation and hypoventilation in four patients. Blood was noted outside the nostrils in two patients, presumably caused by soft tissue trauma after insertion of the LMA, and bradycardia occurred in five patients. In the postoperative period, hoarseness and sore throat were observed in one and six patients, respectively. With experience and appropriate patient selection, it is possible to induce and maintain anesthesia using a LMA in patients in the prone position for ambulatory surgery.

IMPLICATIONS

With experience and appropriate patient selection, it is possible to induce and maintain anesthesia using a laryngeal mask airway in patients in the prone position for ambulatory surgery.

The effect of the prone position on pulmonary mechanics is frame-dependent

By compressing the abdomen and restricting chest wall movement, the prone position compromises pulmonary compliance. For spine surgery, placing the anesthetized patient into the prone position increases the risk of improper ventilation. In this study, we tested the hypothesis that the compromise in pulmonary compliance is related to the patient's body habitus and the surgical frame used to support the patient while in the prone position. Seventy-seven adult patients were divided into three groups according to body mass index: normal (n = 36) < or = 27 kg/m2, heavy (n = 21) 28-31 kg/m2, and obese (n = 20) > or = 32 kg/m2. Patients were placed in the prone position supported by chest rolls, a Wilson frame, or the Jackson spinal surgery table (Jackson table) according to the surgeon's preferences. Peak airway pressure (at the proximal endotracheal tube), pleural pressure (esophageal balloon), and mean arterial pressure were recorded in the supine position and prone position within 15 min of the turn. Dynamic mean (+/- SD) pulmonary compliance (mL/cm H2O) decreased when turning from the supine to the prone position in all three body mass groups when using chest rolls (normal 37+/-5 to 29+/-6; heavy 43+/-2 to 34+/-4; obese 42+/-8 to 32+/-6) or the Wilson frame (normal 39+/-6 to 32+/-7; heavy 43+/-16 to 34+/-10; obese 36+/-11 to 28+/-9). The dynamic pulmonary compliance was not altered in patients positioned on the Jackson table. Regardless of body habitus, using the Jackson table for prone positioning was not associated with a significant alteration in pulmonary or hemodynamic variables. We conclude that moving patients from the supine to the prone position during anesthesia results in a decrease in pulmonary compliance that is frame-dependent but that is not affected by body habitus.

IMPLICATIONS

We hypothesized that compromise in pulmonary compliance in the prone position is related to the patient's body mass index and the surgical frame used. In this study, we demonstrated that prone positioning during anesthesia results in a decrease in pulmonary compliance that is frame-dependent but that is not affected by body mass index.

Transoesophageal echocardiography during scoliosis repair: comparison with CVP monitoring

PURPOSE

Accurate haemodynamic assessment during surgical repair of scoliosis is crucial to the care of the patient. The purpose of this study was to compare transoesophageal echocardiography (TEE) with central venous pressure monitoring in patients with spinal deformities requiring surgery in the prone position.

METHODS

Twelve paediatric patients undergoing corrective spinal surgery for scoliosis/kyphosis in the prone position were studied. Monitoring included TEE, intra-arterial and central venous pressure monitoring (CVP). Haemodynamic assessment was performed prior to and immediately after positioning the patient prone on the Relton-Hall table. Data consisted of mean arterial blood pressure (mBP), heart rate (HR), CVP, left ventricular end-systolic and end-diastolic diameters (LVESD and LVEDD respectively) and fractional shortening (FS). Right ventricular (RV) function and tricuspid regurgitation (TR) were assessed qualitatively. Analysis was performed using descriptive statistics, Student's t test, sign rank, and correlation analysis.

RESULTS

There was an increase in CVP (8.7 mmHg to 17.7 mmHg; P < .01), and decreases in LVEDD (37.1 mm to 33.2 mm; P < .05), and mean blood pressure (75.0 mmHg to 65.7 mmHg; P < .05) when patients were placed in the prone position. Fractional shortening, LVESD, and HR did not change from the supine to the prone position. Right ventricular systolic function and tricuspid regurgitation were unchanged.

CONCLUSION

These data indicate that the CVP is a misleading monitor of cardiac volume in patients with kyphosis/scoliosis in the prone position. This is consistent with previous studies. In this clinical situation, TEE may be a more useful monitoring tool to assess on-line ventricular size and function.

[Surgery of the supratentorial and ventral spine: view-point of the surgeon]

The prone position for posterior fossa and cranio-spinal surgery is becoming the standard posture for neurosurgical teams. We analyze the reasons of such a change and specify indications of this posture. Thereafter, the procedure for optimal positioning is considered and the benefits of the prone position for the neurosurgeon and the anaesthetist are discussed. The selected references originate from Medline search (1991-1997), the Year Book of Neurology and Neurosurgery and the major neurosurgical review articles published between 1980 and 1996.

[Cerebral risks in surgical position: position of the body, position of the brain]

The posture of the neurosurgical patient depends first on the approach and working position of the surgeon, and the spatial orientation during surgery. Venous outflow is probably the major factor for optimal brain retraction and for preventing venous haemorrhage. No one of the postures presently in use is fully free from the risk of air embolism. Respiratory and cardiac diseases are often limiting factors for the choice of a posture. Thoracic and abdominal compression must be cautiously avoided.