Role of vasopressin in the haemodynamic response to laparoscopic cholecystectomy

We studied 10 patients undergoing laparoscopic cholecystectomy (group 1) and five control patients (group 2). We measured heart rate, arterial pressure, right atrial pressure (RAP), cardiac index (CI), systemic vascular resistance index (SVRI), intrathoracic pressure (ITP), plasma osmolality, adrenaline, noradrenaline and arginine vasopressin (aVP) concentrations, and serum renin activity (SRA), and calculated the atrial transmural pressure gradient (ATPG). We recorded significant decreases in mean arterial pressure (MAP), SVRI and CI in both groups (P < 0.05) after induction of anaesthesia. MAP and SVRI increased (P < 0.01) while CI decreased further in group 1 patients during the pneumoperitoneum. In group 1 plasma aVP concentration increased after insufflation of the pneumoperitoneum to a level sufficient to cause the recorded haemodynamic changes. ATPG decreased in group 1 patients during the pneumoperitoneum and this is a recognized trigger for aVP release.      

Plasma renin, catecholamines, vasopressin and aldosterone during hypotension induced by labetalol with isoflurane

Deliberate hypotension may induce secretion of stress hormones. In the present study, the effects of hypotension induced by labetalol with isoflurane or plasma renin activity, plasma concentrations of adrenaline, noradrenaline, vasopressin, and aldosterone were investigated in eight adult patients undergoing middle-ear surgery. The mean arterial pressure was 50 mmHg (6.7 kPa) during hypotension. Plasma renin activity rose significantly during anaesthesia before hypotension, being similar during hypotension and before hypotension, and in returned postoperatively to the initial level. Plasma adrenaline fell significantly during hypotension and rose after anaesthesia to the preanaesthetic level. Plasma noradrenaline rose slightly during hypotension and after anaesthesia, but not significantly. Plasma vasopressin rose significantly after anaesthesia. Plasma aldosterone increased slightly throughout the study, but not significantly during any phase. In conclusion, labetalol with isoflurane-induced hypotension seems to attenuate the stress response in these operations. During hypotension, plasma renin activity is not an essential compensatory mechanism, which antagonises the decrease of blood pressure. Plasma vasopressin has no role in regulating blood pressure during labetalol-induced hypotension.     

Plasma catecholamines and haemodynamic changes during pneumoperitoneum

Background: Insufflation of CO₂ into the abdomen is used during all kinds of laparoscopic operations. The procedure elicits haemodynamic and hormonal responses. The reports on sympathetic responses to laparoscopic surgery have been conflicting. However, few studies have assessed sympathetic and haemodynamic responses to CO₂ insufflation per se, eliminating possible effects of intubation, skin incision, surgical manipulation and positioning of the body. No studies have measured both venous and arterial plasma catecholamines, the latter being a more sensitive indicator of sympathetic activity. In the present study, we hypothesised an increased sympathetic activity during pneumoperitoneum and an association between haemodynamic and sympathetic responses. Methods: Plasma adrenaline and noradrenaline from the radial artery and superior vena cava were measured immediately before and 10 min after abdominal insufflation of CO₂ in 11 subjects. Haemodynamics were monitored invasively. Results: During pneumoperitoneum arterial plasma noradrenaline increased from 155 (106, 209) pg/ml (median, lowest and highest quartile) to 283 (188, 378) pg/ml (P=0.003), while there were no changes in arterial plasma adrenaline. The calculated arterial-superior vena cava difference in plasma noradrenaline did not change, indicating no increased sympathetic activity in the drainage area of the superior vena cava. Heart rate and cardiac index were unchanged, while total peripheral resistance and mean arterial blood pressure increased (P=0.002). The changes in arterial plasma noradrenaline were closely related to the changes in total peripheral resistance (r=0.69, P=0.01). Conclusions: Plasma noradrenaline increases during pneumoperitoneum and is associated with changes in total peripheral resistance. Plasma adrenaline is unchanged and there is no evidence of increased sympathetic outflow to the drainage area of the superior vena cava. Thus, the increase in plasma noradrenaline may be due to more local activation of the sympathetic nervous system, probably somewhere from the drainage area of the inferior vena cava.     

Effects of pneumoperitoneum and body position on the morphology of the caudal cava vein analyzed by MRI and plastinated sections

Background

Pneumoperitoneum and patient positioning are essential factors during laparoscopic surgical procedures. They cause hemodynamic and anatomical changes in several abdominal organs among which the caudal cava vein (CCV) is involved. Hemodynamic changes in this vein (decreased venous return) have been described in the porcine model, but how the vein morphology and size is affected at different abdominal levels is unknown. We sought to assess the morphological and morphometrical changes in the CCV of the pig caused by pneumoperitoneum and the reverse Trendelenburg position by in vivo magnetic resonance imaging (MRI).

Methods

Six pigs were scanned via MRI under four situations: S1, control (no pneumoperitoneum); S2, control in the reverse Trendelenburg position; S3, pneumoperitoneum (14 mmHg); and S4, pneumoperitoneum in the reverse Trendelenburg position. MRI and plastinated body sections were used to evaluate the topography, morphology and cross-sectional area of the CCV.

Results

Two portions of the CCV were differentiated: a prehepatic portion (located between the vertebral levels L1–T15) with flat and irregular morphology, and a hepatic portion (between T14–T11) that was almost rounded. The reverse Trendelenburg position caused an increase in the lumen affecting mainly the prehepatic portion, while pneumoperitoneum caused a decrease in the total vascular lumen, exerting a greater effect on the hepatic portion. The combination of both situations resulted in a further decrease in the vascular area and global morphological changes.

Conclusions

The pneumoperitoneum and reverse Trendelenburg position caused morphological and morphometrical changes in the prehepatic and hepatic portions of the CCV, which should assist in gaining a better understanding of the hemodynamic changes described in the literature.     

TRANSOESOPHAGEAL ECHOCARDIOGRAPHIC ASSESSMENT OF HAEMODYNAMIC FUNCTION DURING LAPAROSCOPIC CHOLECYSTECTOMY

We have measured cardiovascular changes associated with insufflationof carbon dioxide and the reverse Trendelenburg position duringlaparoscopic cholecystectomy, using trans-oesophageal echocardiographyin 13 healthy patients. End-tidal carbon dioxide values increasedafter insufflation of carbon dioxide, with values significantly(? < 0.05) increased after lateral tilt positioning. Creationof a pneumoperitoneum was associated with increases (? <0.05) in left ventricular end-systolic wall stress, concomitantwith increases (P < 0.01) in peak airway pressure and systemicarterial pressure. In addition, left ventricular end-diasto/icarea decreased (? < 0.05) after reverse Trendelenburg positioning.Left ventricular ejection fraction was maintained throughoutthe study. (Br. J. Anaesth. 1993; 70: 621–625)      

Acute and chronic effects of captopril on bicyclo-PGEm, the stable bicyclic end product of prostaglandin E2 in essential hypertension

Hemodynamic and hormonal actions of acute (50 mg) and chronic (150 mg/day) captopril were tested in 10 patients with essential hypertension. Under short-term conditions blood pressure was reduced, heart rate and plasma adrenaline did not change, plasma angiotensin II and plasma aldosterone decreased. Plasma renin activity, basal plasma noradrenaline and bicyclo-PGEm, a novel stable metabolite of prostaglandin E2, increased after captopril. With chronic captopril treatment blood pressure was reduced after 4 weeks before readministration of captopril, heart rate did not change, plasma renin activity and bicyclo-PGEm remained elevated for 12 h after the last captopril dose. Angiotensin II remained suppressed, aldosterone and plasma catecholamines did not change between doses. Readministration of captopril led to a further reduction in blood pressure. Angiotensin II and aldosterone were further suppressed, bicyclo-PGEm levels increased from a higher baseline. Heart rate and plasma catecholamines did not change. Taken together, the results suggest that prostaglandin E2 is involved in the acute and chronic hypotensive response of captopril in patients with essential hypertension.     

Effect of the degree of reverse Trendelenburg position on intraocular pressure during prone spine surgery: a randomized controlled trial

Background contextPostoperative vision loss complicates an estimated 1 in 1,100 prone spine surgical cases. This complication has been attributed to ischemic optic neuropathy, with one proposed reason being perioperative elevations in intraocular pressure (IOP). Previous research has studied the effects of table inclination on IOP in awake volunteers; however, the effects in spine surgery patients have not been investigated for reverse Trendelenburg positioning using a prospective, randomized controlled study design.PurposeTo assess the effect of table inclination on IOP in patients undergoing prone spine surgery.Study designSingle-center, prospective randomized controlled study.Patient sampleNineteen patients with no history of eye pathology, undergoing prone spine surgery at Dwight D. Eisenhower Army Medical Center, were randomly assigned to a table position: neutral, 5°, or 10° of reverse Trendelenburg.Outcome measuresIntraocular pressure, mean arterial pressure (MAP), estimated blood loss, fluid resuscitation, and ophthalmologic complication were assessed before and after induction and at incremental times during surgery, beginning at 30 minutes, 60 minutes, and 60-minute increments thereafter.MethodsMultivariate analyses evaluated surgical time, IOP, MAP, estimated blood loss, and fluid resuscitation as a function of table inclination to determine the effect of patient positioning on identified risk factors for postoperative vision loss.ResultsSurgical times ranged from 33 to 325 minutes. A rapid increase in IOP was noted after prone positioning, with continued increases as time elapsed. The neutral group exhibited statistically higher IOP compared with the 5° reverse Trendelenburg group after 60 minutes and the 10° group through 60 minutes of surgery. The trend continued through 120 minutes; however, because of a lack of power, we were unable to determine the statistical significance. There were no statistically significant differences between the 5° and 10° reverse Trendelenburg groups.ConclusionsReverse Trendelenburg positioning elicits decreased IOP compared with prone positioning for surgery times less than 120 minutes. Ten degrees of reverse Trendelenburg attenuate the rise in IOP during prone spine surgery superiorly in comparison with 5°. No significant complications were associated with reverse Trendelenburg positioning.     

Effects of Posture and Prolonged Pneumoperitoneum on Hemodynamic Parameters during Laparoscopy

BACKGROUND: The present prospective study was designed to evaluate hemodynamic changes associated with head-down positioning and prolonged pneumoperitoneum during totally endoscopic robot-assisted radical prostatectomy. METHODS: Ten American Society of Anesthesiologists (ASA) physical status I-III patients undergoing totally endoscopic robot-assisted radical prostatectomy were enrolled in the study. Invasive hemodynamic parameters were measured by transpulmonary arterial thermodilution using the PiCCO system with a femoral artery catheter. Cardiac index (CI), heart rate (HR), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), intrathoracic blood volume (ITBV), and central venous pressure (CVP) were recorded with the patient in the supine position, after head-down tilt, intraoperatively after 30 min, 1 h, 2 h, 3 h, and 4 h of pneumoperitoneum at an insufflation pressure of 12 mmHg, after deflation still with head-down positioning, and finally, with the patient in the supine position. RESULTS: Placing the patient in the Trendelenburg (head-down) position caused a significant increase in CVP (from 9.9 +/- 3.4 to 15.1 +/- 2.3 mmHg), whereas all other hemodynamic parameters remained nearly unaffected. The induction of pneumoperitoneum resulted in a significant increase in MAP (from 74.9 +/- 12.9 to 95.4 +/- 11.9 mmHg). No other parameter was affected. Even at 4 h of pneumoperitoneum only mild hemodynamic changes were observed. After release of the pneumoperitoneum with the patient still in the head-down position, HR (49.0 +/- 4 versus 63.9 +/- 12.4 min(-1)) and after placing the patient in the supine position, CI (2.4 +/- 0.2 versus 3.3 +/- 0.7 l min(-1 )m(-2)) increased significantly, whereas CVP returned to baseline values. CONCLUSIONS: Patients undergoing totally endoscopic radical prostatectomy with 4 h of pneumoperitoneum in the Trendelenburg position experienced no significant hemodynamic depression during posture and pneumoperitoneum.     

Water immersion-induced endocrine alterations in women with EPH gestosis

In 12 healthy pregnant women, 14 women with mild or moderate late pregnancy gestosis (EPH) and in 12 non-pregnant women, the influence of head out water immersion (WI) on mean blood pressure (MAP), the renin-aldosterone system, vasopressin (AVP) and atrial natriuretic hormone (ANF) was examined. WI induced a prompt fall in MAP in all examined groups. This decrease of MAP was maximal after 1 h WI, showing a tendency to rise later on in pregnant women. Simultaneously a decrease of plasma renin activity (PRA), plasma aldosterone, AVP and an increase of ANF was noted. The WI induced endocrine reaction pattern was qualitatively similar, but quantitatively different in the examined groups. In contrast to the response of non-pregnant women, healthy pregnant women and women with EPH gestosis showed a significantly smaller increase in ANF secretion induced by WI. No correlation was found between PRA, plasma AVP, aldosterone and ANF respectively. In addition changes in PRA, aldosterone, AVP and ANF did not correlate with WI-induced changes in MAP. From data obtained in this paper it seems, that WI-induced MAP changes are not related significantly to changes of the above mentioned hormonal factors.     

Hormonal changes related to reduced renal blood flow and low urine output under prolonged increased intra-abdominal pressure in pigs.

OBJECTIVE: To investigate effects of prolonged increased intra-abdominal pressure (IAP) on diuresis, renal blood flow, and hormones that influence renal function, in particular endothelin. DESIGN: Experimental study. SETTING: Haukeland University Hospital, Norway. ANIMALS: 21 domestic pigs. METHODS: The TAP was maintained at normal (n = 7) or at 20 mmHg (n = 7) or 30 mmHg (n = 7) for three hours. MAIN OUTCOME MEASURES: Urine output, renal venous pressure, renal artery blood flow (transit-time flowmetry), renal cortex blood flow (microspheres), and renin, aldosterone, atrial natriuretic factor (ANF), adrenaline, noradrenaline, cortisol, and endothelin-1 (ET-1) in renal venous blood. RESULTS: An IAP of 20 mmHg was followed by no significant changes in the variables studied. An IAP of 30mmHg was associated with anuria, considerably reduced renal blood flow and increased renal vascular resistance. The renin activity and the blood concentrations of ET-1, aldosterone, noradrenaline, adrenaline, and cortisol increased during the three hours that IAP was at 30 mmHg. CONCLUSION: An IAP of 20 mmHg did not influence renal haemodynamics or diuresis. The low renal blood flow observed at an IAP of 30 mmHg probably results from reduced arteriovenous pressure difference and vasoconstriction. Increased concentrations of endothelin, angiotensin II, and noradrenaline may account for the vasoconstriction. The anuria can be explained by low renal blood flow and increased reabsorption of sodium in renal tubules caused by aldosterone.     

Changes in plasma potassium concentration during carbon dioxide pneumoperitoneum

Hyperkalaemia with ECG changes had been noted during prolonged carbon dioxide pneumoperitoneum in pigs. We have compared plasma potassium concentrations during surgery in 11 patients allocated randomly to undergo either laparoscopic or open appendectomy and in another 17 patients allocated randomly to either carbon dioxide pneumoperitoneum or abdominal wall lifting for laparoscopic colectomy. Despite an increasing metabolic acidosis, prolonged carbon dioxide pneumoperitoneum resulted in only a slight increase in plasma potassium concentrations, which was both statistically and clinically insignificant. Thus hyperkalaemia is unlikely to develop in patients with normal renal function undergoing carbon dioxide pneumoperitoneum for laparoscopic surgery.      

Effect of low-dose dopamine on kidney function and vasoactive hormones in pediatric patients with advanced renal failure

Dopamine (DA) was infused in a dose of 2 micrograms/kg/min in 12 children and adolescents with chronic renal failure to test the vasodilatory reserve capacity of the kidney. Mean basal GFR and ERPF were 17.8 and 93.1 ml/min/1.73 m2, respectively. DA infusion had no significant influence on GFR but effective renal plasma flow (ERPF) increased by 14% (p less than 0.05). After DA, GFR did not correlate with ERPF. There was a significant increase in urinary sodium excretion (+22%). Sodium excretion correlated with osmotic clearance and urine flow rate with free water clearance. Plasma prolactin concentration was decreased (p less than 0.01), whereas noradrenaline, adrenaline and free dopamine increased significantly after DA. Plasma renin activity, aldosterone, arginine vasopressin and atrial natriuretic peptide levels remained unchanged. The data indicate that in pediatric patients with advanced renal failure DA fails to increase filtration capacity, whereas effective renal plasma flow and sodium excretion are stimulated. It is speculated that in this situation preglomerular and tubular renal functions regulated by dopamine receptors are better conserved than those affecting glomerular microcirculation.     

Effect of sympathetic and plasma renin activity on hemodialysis hypertension

BACKGROUND: The reasons for poor control of blood pressure in hemodialysis (HD) patients are not clear, while patients have achieved their desirable dry weight and excess weight are not different between the hypertensive and normotensive patients. A link between sympathetic activity and HD hypertension could be an alternative explanation. PATIENTS AND METHODS: We studied the effect of sympathetic and plasma renin-aldosterone activity of 10 hypertensive patients, 5 men and 5 women, aged from 30 to 60 years. The results were compared to those of another 10 normotensive hemodialysis patients. Blood samples were taken before HD and at the end of a 4-hour HD session for plasma aldosterone (ALDO), renin activity (PRA), adrenaline and noradrenaline determination. One month dialysis records, which includes 13 dialysis sessions and 26 blood pressure readings for each patient were used, for pre-dialysis and post dialysis mean arterial blood pressure (MAP) measurement. RESULTS: Pre-dialysis plasma adrenaline was 124.12 +/- 12.93 pg/ml vs. 121.12 +/- 14.71 pg/ml and plasma noradrenaline was 260.88 +/- 140.86 pg/ml vs. 138.11 +/- 122 +/- 32 pg/ml for hypertensive and normotensive patients, respectively. Post-dialysis plasma adrenaline and noradrenaline levels were 119.37 +/- 8.81 pg/ml vs. 120.62 +/- 15.35 pg/ml and 210.44 +/- 126.71 pg/ml vs. 94.88 +/- 64.05 pg/ml for hypertensive and normotensive patients, respectively. Pre-dialysis PRA was 8.70 +/- 6.37 ng/ml/h vs. 2.77 +/- 1.8 ng/ml/h and plasma ALDO was 457.07 +/- 245.54 pg/ml vs. 197.74 +/- 87.46 pg/ml for hypertensive and normotensive patients, respectively. Pre-MAP was 109.76 +/- 5.21 mmHg vs. 99.28 +/- 7.13 mmHg and post-MAP was 107.22 +/- 6.74 mmHg, vs. 91.61 +/- 7.27 mmHg for hypertensive and normotensive patients, respectively. Plasma ALDO and fluid volume removed by ultrafiltration were found to be significantly correlated (p < 0.05). PRA and plasma adrenaline-noradrenaline levels were not correlated with MAP or body weight alterations. CONCLUSIONS: It is suggested that sympathetic activity, as it was expressed by plasma catecholamine alterations, is not associated with hemodialysis hypertension.     

Effects of pneumoperitoneum and reverse Trendelenburg position on cardiopulmonary function in morbidly obese patients receiving laparoscopic gastric banding

We prospectively evaluated the effects of pneumoperitoneum and reverse Trendelenburg position on cardiopulmonary function in 20 ASA physical status II-III morbidly obese patients (body mass index > 35 kg m(-2)) undergoing laparoscopic gastric banding. After general anaesthesia was induced, patients' lungs were ventilated using intermittent positive pressure ventilation (at measurement times, the following parameters were used: tidal volume 12 mL kg(-1) ideal body weight, respiratory rate of 12 bpm, an inspiratory to expiratory time ratio of 1:2). Haemodynamic variables, blood gas parameters, and lung/chest compliance were recorded: in the supine position, after induction of general anaesthesia (T0, baseline) and induction of pneumoperitoneum (T1); after placing the patient in a 25 degree reverse Trendelenburg position (T2); during the surgical time (T3); before deflating the abdomen (T4); after pneumoperitoneum resolution (T5), and before the end of anaesthesia, with the patient supine (T6). The PaO2, PaO2/FiO2 ratio, and lung/chest compliance decreased during the study. After the pneumoperitoneum had been resolved, lung/chest compliance but not oxygenation parameters returned to baseline values. The arterial to end-tidal CO2 tension difference progressively increased from 0.38+/-0.3 kPa (2.85+/-2.25 mmHg) (T0) to 0.63+/-0.3 kPa (4.73+/-2.25 mmHg) (T6). In morbidly obese patients, undergoing laparoscopic gastric banding, a CO2 pneumoperitoneum markedly affected gas exchange and lung/chest compliance, while positioning the patient in a 25 degree reverse Trendelenburg position had no beneficial effects.     

Control of aldosterone responsiveness in terminal renal failure.

Control of aldosterone responsiveness in terminal renal failure. Plasma aldosterone concentration in 30 hemodialysis patients correlated closely with renin concentration, renin activity or renin and potassium concentrations combined (r is greater than or equal to 0.62; P is less than 0.01), and increased consistently in response to upright posture or corticotropin administration. Aldosterone response to hemodialysis was variable. Significant correlations (r is greater than or equal to 0.65; P is less than 0.01) were demonstrated between postural plasma aldosterone and renin responses, between aldosterone responses to corticotropin and basal plasma aldosterone or renin and potassium values, between hemodialysis-induced changes in plasma aldosterone and those in potassium or renin; but not between various indexes of heparin treatment and aldosterone activity. Bilateral nephrectomy reduced basal plasma renin and aldosterone concentrations and aldosterone responsiveness in five preoperatively normoreninemic or hyperreninemic patients, but not in a hyporeninemic patient. These results demonstrate the complementary roles of circulating renin and potassium in the control of aldosterone release under basal and stimulatory conditions in patients with terminal renal failure. Administration of heparin in dosages used during long-term hemodialysis does not appear to significantly interfere with aldosterone control.     

Influence of Epidural Analgesia on the Catecholamine and Cyclic AMP Responses to Surgery

The effects of neurogenic block on plasma concentrations of adrenaline, noradrenaline and cyclic AMP were studied. Eighteen patients were subjected to surgery of moderate or minor extent under enflurane anesthesia with or without epidural analgesia. The results show that adrenaline secretion during surgical stress is a response to neurogenic stimuli, since the increase found in patients subjected to hysterectomy under general anesthesia is blocked by the addition of epidural analgesia. Furthermore, plasma adrenaline after neurogenic block is comparable with adrenaline levels during minor surgical stress.
The plasma noradrenaline concentration does not correlate with the extent of trauma. In contrast to adrenaline levels, noradrenaline concentrations varied insignificantly during and after surgery. However, the addition of epidural block induced a postoperative increase in noradrenaline apparently unrelated to changes in heart rate or blood pressure. Simultaneous measurements of the catecholamines and cyclic AMP indicate that adrenaline is of minor importance for plasma cyclic AMP in resting patients, whereas the increase in cyclic AMP elicited by surgery reflects adrenaline-stimulated beta-adrenergic activity.     

PLASMA CATECHOLAMINE RESPONSES TO TRACHEAL INTUBATION

Plasma adrenaline and noradrenaline concentrations were measuredin 24 patients during the induction of anaesthesia and the subsequenttracheal intubation. The patients received either suxamethonium1 mg kg^–1 or pancuronium 0.1 mg kg^–1 to facilitatetracheal intubation. Mean arterial pressure (MAP) increasedin both groups following laryngoscopy and tracheal intubationand there were concomitant increases in the plasma catecholamineconcentrations, the changes being more marked in the suxamethoniumgroup. There was a significant correlation between MAP and plasmacatecholamine concentrations in the suxamethonium group. Measurementof plasma catecholamine concentrations in samples obtained simultaneouslyfrom central venous, peripheral venous and arterial sites werein broad agreement; the greatest changes occurred in centralvenous samples. ^*Present address: Department of Anaesthesia, Northampton GeneralHospital, Northampton.     

Influence of the patient positioning on respiratory mechanics during pneumoperitoneum

The aim of this study was to evaluate the effect of patient positioning during laparoscopic cholecystectomy on respiratory mechanics and arterial blood gases. Thirty patients of ASA I were included. Ventilation was controlled mechanically. Tidal volume and ventilator frequency were kept unchanged throughout the operation. Intra-abdominal pressure was kept constant at 12 mmHg. Ventrak respiratory system was used for measuring respiratory mechanics. The airway resistance (Raw), the dynamic compliance (Cdyn), and the peak inspiratory pressure (PIP) were monitored. Measurements were made in five intervals: "a" after induction of general anesthesia, "b" after insufflation, "c" in the Trendelenburg position of 40 degree, "d" in the Fowler position of 40 degree, and "e" after desufflation. Samples of arterial blood gases were collected while the respiratory mechanics were being recorded. The mean arterial pressure (MAP) and heart rate (HR) were also monitored. In our study, during intervals "c" and "d", PCO2, was increased and pH decreased. With the initiation of insufflation, Cdyn, PIP, and Rawx, were altered (P < 0.05). The patient positioning had a significant effect on respiratory mechanics. After desufflation only Cdyn changed (P < 0.05). Although HR remained in normal limits, MAP increased during pneumoperitoneum (P < 0.05). We conclude that blood gas changes and respiratory mechanics were affected by the duration of pneumoperitoneum and patient positioning. The Fowler position had the least influence on respiratory mechanics.     

Time course of cerebrovascular autoregulation during extreme Trendelenburg position for robotic‐assisted prostatic surgery

Trendelenburg positioning in combination with pneumoperitoneum during robotic‐assisted prostatic surgery possibly impairs cerebrovascular autoregulation. If cerebrovascular autoregulation is disturbed, arterial hypertension might induce cerebral hyperaemia and brain oedema, while low arterial blood pressure can induce cerebral ischaemia. The time course of cerebrovascular autoregulation was investigated during use of the Trendelenburg position and a pneumoperitoneum for robotic‐assisted prostatic surgery using transcranial Doppler ultrasound. Cerebral blood flow velocity was correlated with arterial blood pressure and the autoregulation index (Mx) was calculated. In 23 male patients, Mx was assessed at baseline, after induction of general anaesthesia, during the Trendelenburg position (40–45°), and after repositioning. During the Trendelenburg position, Mx increased over time, indicating an impairment of cerebrovascular autoregulation. After repositioning, Mx recovered to baseline levels. It can be concluded that with longer durations of Trendelenburg position and pneumoperitoneum, cerebrovascular autoregulation deteriorates, and, therefore, blood pressure management should be adapted to avoid cerebral oedema and the duration of Trendelenburg position should be as short as possible.     

Effect on aging on plasma renin and aldosterone in normal man.

The influence of aging on the renin-angiotensin-aldosterone system was evaluated by comparing young (20 to 30 yr) with elderly (62 to 70 yr) healthy subjects. Despite comparable body sodium-fluid balance in the two age groups, serum renin concentration, plasma renin activity and aldosterone concentrations were lower in the elderly. The age-related decreases in circulating renin and aldosterone concentrations were slight while subjects were supine and receiving normal sodium intake; when upright and during sodium depletion, they were more pronounced. Inverse renin-blood pressure interrelations were noted during two of four study conditions involving normal sodium intake or mild sodium depletion (r = --0.44 and --0.47, respectively), but not during progressive sodium depletion. Plasma renin levels were decreased in the elderly regardless of the presence or absence of an inverse relationship with blood pressure. Aldosterone and cortisol responses to corticotropin infusion were unaltered in the elderly. It is concluded that aging may cause a decrease in circulating renin, with parallel lowering of plasma aldosterone concentrations.