Postural tachycardia syndrome is defined by a heart rate increment of 40 beats/minute (bpm) (or a heart rate that exceeds 125 bpm) within 10 minutes of change from the supine position to an upright position in the absence of obvious orthostatic hypotension. There are multiple pathophysiological mechanisms that underlie postural tachycardia syndrome, including peripheral denervation, β-receptor supersensitivity, hypovolaemia, and impaired muscle pump. Some children afflicted with postural orthostatic tachycardia syndrome and hypovolaemic dysregulation have been found to have perturbed renin–angiotensin–aldosterone profile, disturbed vascular endothelial function, and abnormal vasodilation. The hyperadrenergic state in some postural tachycardia syndrome patients is likely a driver for orthostatic tachycardia. Other mechanisms include the presence of treatable autonomic neuropathies. An understanding of these pathophysiological mechanisms might be helpful for the effective treatment of postural tachycardia syndrome.

A high-Na diet may lead to the development of hypertension in both humans and rats; however, the causes of Na intake in amounts greater than physiologically needed as well as the mechanisms whereby high-Na food elevates blood pressure are not clear. Therefore, we decided to test the hypothesis that a high-Na diet introduced after suckling affects Na intake, food preference, resting blood pressure and blood volume in adult rats. Male Wistar-Kyoto (WKY) rats, 4 weeks old, were divided into three groups and placed on either a high-Na (3·28%), a medium-Na (0·82%) or a regular diet (0·22%) with the same energy content for 8 weeks. Subsequently, food preference, resting arterial blood pressure, blood volume, plasma osmolality and Na blood level were evaluated. When offered a choice of diets, all the groups preferred the regular chow, and there was no significant difference in total Na intake between the groups. When the rats experienced the change from their initial chow to a new one with different Na content, they continued to eat the same amount of food. Body weight, resting arterial blood pressure, blood volume, plasma osmolality and Na blood level were comparable between the groups. In conclusion, the results show that a high-Na diet introduced immediately after suckling does not affect Na preference and Na intake in adult WKY rats. Furthermore, the findings provide evidence that both blood volume and arterial blood pressure are highly protected in normotensive rats on a high-Na diet.

Summary

Background and objective: Measurement of central blood volumes (CBV), such as global end-diastolic volume (GEDV) and right ventricular end-diastolic volume (RVEDV) are considered appropriate estimates of intravascular volume status. However, to apply those parameters for preload assessment in mechanically ventilated patients, the influence of tidal volume (TV) and positive endexpiratory airway pressure (PEEP) on those parameters must be known. Methods: In 13 mechanically ventilated piglets, the effect of low (10 mL kg−1) and high (20 mL kg−1) TVs on CBV was investigated in absence and presence of PEEP (0 and 15 cmH2O). GEDV, RVEDV, right heart (RHEDV) and left heart end-diastolic volume (LHEDV) were measured by thermodilution. Blood flow on the descending thoracic aorta measured with an ultrasonic flow-probe served to determine stroke volume (SV). Measurements were performed during baseline conditions, after volume loading with previously extracted haemodilution blood (20 mL kg−1) and following haemorrhage (30 mL kg−1). Results: Application of PEEP decreased GEDV and SV significantly (P < 0.05). Augmenting TV did not reduce GEDV systematically, but significantly reduced SV (P < 0.05). Changes in ventilator settings only influenced RVEDV following volume loading (P < 0.05). RHEDV and LHEDV decreased following application of PEEP, but only RHEDV decreased after augmenting TV at baseline and following volume loading. Correlation of SV with parameters of CBV was r = 0.487 (P < 0.01) for GEDV, r = 0.553 (P < 0.01) for RVEDV, r = 0.596 (P < 0.01) for RHEDV and r = 0.303 (P < 0.01) for LHEDV. Conclusion: Application of PEEP decreases CBV and SV. Augmenting TV reduces SV but not CBV. There is a moderate correlation between parameters of CBV and cardiac performance.

Background and objective: Induction of general anaesthesia in combination with positive-pressure ventilation is often associated with a significant decrease of arterial pressure. A decreased preload may contribute to this phenomenon. The aim was to investigate whether a change in cardiac filling occurs following the induction of general anaesthesia with sufentanil under typical clinical conditions.

Methods: Fifteen patients scheduled for elective coronary bypass grafting were studied immediately before surgery. In addition to standard monitors, a transpulmonary double-indicator dilution technique measured in vivo intrathoracic blood volume, global end-diastolic volume and total circulating blood volume. For induction of anaesthesia 2 μg kg−1 sufentanil was given. Measurements were performed awake and after the induction of anaesthesia, intubation and mechanical ventilation of the lungs.

Results: To maintain arterial pressure during the induction period within −20% of baseline pressure, on average 22 ± 6 mL kg−1 crystalloids and 8 ± 6 mL kg−1 colloids were given. Despite these amounts of fluid, cardiac filling was decreased, whereas circulating blood volume increased significantly. Both central venous pressure and pulmonary capillary wedge pressure increased.

Conclusions: Induction of general anaesthesia with positive-pressure ventilation is regularly associated with a blood volume shift from intra- to extrathoracic compartments. Even in low-dose opioid monoanaesthesia with sufentanil – often regarded as relatively inert in haemodynamic terms – the phenomenon could be demonstrated as the primary cause of the often-observed decrease of arterial pressure. It seems, therefore, rationally justified to restore cardiac filling by generous administration of intravenous fluids, at least in patients with unaffected cardiac pump function. During induction of anaesthesia, central venous pressure and pulmonary capillary wedge pressure do not reliably indicate cardiac filling.

Background and objective: Assessment of the effects of normovolaemic haemodilution on middle cerebral artery blood flow velocity with transcranial Doppler ultrasonography, intracranial pressure, cerebral perfusion pressure, arterial oxygen content and cerebral oxygen delivery.

Methods: Normovolaemic haemodilution was induced in rabbits under general anaesthesia, and the haematocrit was allowed to decrease to 30% in Group 1 (n = 6) and to 20% in Group 2 (n = 6). Peak systolic and diastolic velocities, mean blood flow velocity, and pulsatility and resistance indices of the middle cerebral artery were measured by transcranial Doppler ultrasonography. Changes in intracranial pressure, cerebral perfusion pressure, arterial oxygen content and cerebral oxygen delivery were also assessed.

Results: In Group 2, middle cerebral artery blood flow velocity increased from 0.4 ± 0.01 to 0.51 ± 0.02 m s−1 after the induction of normovolaemic haemodilution (P = 0.04), while arterial oxygen content decreased from 16.2 ± 0.1 to 8.5 ± 0.1 mL dL−1 (P = 0.002). The decrease in cerebral oxygen delivery from 6.5 ± 0.2 to 4.3 ± 0.2 was also significant (P = 0.02). However, no associated changes in intracranial pressure and cerebral perfusion pressure could be demonstrated.

Conclusions: Normovolaemic haemodilution resulted in an increase in the mean blood flow velocity of the middle cerebral artery. However, this increase did not compensate for the consequences of the altered oxygen delivery to the brain when the haematocrit was reduced to 20%

Background and objective: The feasibility of monitoring measured intravascular volumes and the cardiac filling pressures were compared to reflect the optimal volume status of postoperative patients.

Methods: In a prospective clinical study, 14 hypovolaemic adult patients were included after cardiac surgery. All patients received 1000 mL hydroxyethyl starch after meeting the authors’ criteria for hypovolaemia. Pressures were measured by use of a pulmonary artery catheter and volumes were determined by double-indicator dilution technique.

Results: Stroke volume index (SVI), central venous pressure (CVP), pulmonary artery occlusion pressure (PAOP), intrathoracic blood volume index (ITBVI) and total circulating blood volume (TBVIcirc) increased significantly after volume loading (30.7 ± 9.8 to 41.7 ± 9.6 mL m−2, 4.9 ± 1.7 to 9.1 ± 2.3 mmHg, 6.6 ± 1.3 to 10.6 ± 1.9 mmHg, 858 ± 255 to 965 ± 163 mL m−2, and 1806 ± 502 to 2110 ± 537 mL m−2, respectively). During the subsequent 1 h steady-state period, CVP and PAOP decreased significantly (9.1 ± 2.2 to 7.4 ± 2.2 mmHg and 10.6 ± 1.9 to 9.2 ± 2.0 mmHg, respectively), whereas SVI and intravascular volumes remained unchanged. The changes of CVP and PAOP did not correlate with changes in stroke volume during volume loading (r2 = 0.06 and 0.03, respectively) and during steady-state (r2 = 0.17 and 0.00 respectively). On the other hand, a significant correlation was found between changes of the intrathoracic blood volume and changes in stroke volume during the volume loading (r2 = 0.67) and also during the steady-state phase (r2 = 0.83).

Conclusions: Intrathoracic blood volume reflects more accurately the preload dependency of cardiac output in postoperative patients than left/right-sided cardiac filling pressures.

Background and objective Patients undergoing coronary artery bypass grafting often require volume loading after operation. In this situation hypertonic saline may be beneficial in restoring the haemodynamic balance and removing excess extravascular fluid.

Methods Forty coronary artery bypass grafting patients were randomly assigned to receive either hypertonic saline 7.5% (20 patients) or 0.9% saline (20 patients) as a single dose of 4 mL kg−1 over 30 min in the postoperative rewarming phase in the intensive care unit.

Results Mean arterial pressure increased in the hypertonic saline group from 82 ± 10 (SD) to 104 ± 17 mmHg (P = 0.002 vs. the normal saline group), and the cardiac index rose from 2.3 ± 0.5 to 3.4 ± 0.8 L min−1 m2 (P = 0.002 vs. the normal group). The haemodynamic effect of hypertonic saline lasted only about 1 h. Diuresis was greater in the hypertonic saline group both at 1 h (hypertonic saline: 490 ± 274 vs. normal saline: 204 ± 130mL; P = 0.001) and 10 h (hypertonic saline: 1952 ± 554vs. normal saline: 1421 ± 514mL; P = 0.003).

Conclusions No adverse effects were seen. The hypertonic saline had a strong diuretic effect and may be beneficial in coronary artery bypass graft patients after operations. This is because of its value as a short-term plasma expander and the diuresis eliminates excessive fluid from the body. A larger study is needed to determine whether the benefits outweigh the possible side-effects in these patients.

Ringer's solution expands blood volume by between 20% and 25% in awake volunteers, but little is known about its volume effect during general anaesthesia. In 35 men with a mean age of 70 years, the power of various intra-operative factors to change blood volume as estimated by the haemoglobin dilution method were analysed by multiple linear regression every 10 min during transurethral resection of the prostate performed under enflurane anaesthesia. The results show that blood volume increased by 60% of the infused Ringer's solution and by 35% of the irrigating fluid absorbed directly into the blood, while it decreased by slightly more than 100% of the bled volume. There was no correlation between systolic pressure and blood volume changes. This suggests that the volume effect of Ringer's solution in the blood is greater than generally believed during general anaesthesia.