Continuous positive pressure ventilation during epidural blockade--effects on cardiac output distribution

Background: It has been shown that when cardiac output (CO) decreases during continuous positive pressure ventilation (CPPV), its regional distribution adapts with a favouring of vital organs. Does epidural blockade modify this adaptation? Methods: Regional blood flows were assessed by the microsphere technique (15 μm) in 17 anaesthetised pigs during spontaneous breathing and CPPV with 8 cm H₂O end‐expiratory pressure (CPPV8) before and after epidural blockade. The block was induced at either the Th_6–7 (Thep) or the L₆–S₁ (Lep) level with 1 ml of lidocaine 40 mg · ml^?1. Results: When Lep was combined with CPPV8, mean arterial pressure and CO decreased significantly, and they decreased even more when combined with Thep. In contrast, the relative perfusion of the central nervous system, heart and kidneys remained stable during the four conditions studied. The adrenal perfusion during CPPV8 was obviated by epidural blockade. The absolute and relative perfusion of the skeletal muscle decreased during epidural blockade. The administered doses of epidural lidocaine did not affect blood flow in the spinal cord. Conclusions: The locally mediated nutritive vasoregulation of vital organs outweighed the sympathetic blockade induced by epidural blockade. During Thep blockade the animals were less capable of responding to the haemodynamic changes induced by CPPV8, probably due to the blockade of the cardiac part of the sympathetic nervous system.     

Intermittent and continuous positive-pressure ventilation in the prophylaxis of endotoxin-induced lung insufficiency. A study in pigs

The effects of intermittent and continuous positive-pressure ventilation (IPPV and CPPV) instituted prophylactically were evaluated in a porcine model of endotoxin-induced pulmonary and cardiovascular failure. Pigs under ketamine anaesthesia were infused i.v. with E. coli endotoxin over 6 h. Twenty animals, breathing air spontaneously, received endotoxin without treatment. Fifteen animals were treated prophylactically with IPPV (normoventilation with air). Nine animals received prophylactic treatment with CPPV (positive end-expiratory pressure 0.8 kPa (8 cmH2O). Endotoxin infusion in spontaneously breathing animals caused profound deterioration of pulmonary gas exchange, a marked rise in pulmonary vascular resistance (PVR) and a moderate increase in extravascular lung water (EVLW). Cardiac output (Qt) and O2 delivery decreased considerably. Metabolic acidosis indicated oxygen deficit. Eleven of 20 animals died during the observation period. IPPV improved arterial oxygenation during endotoxin infusion, and the increase in EVLW tended to be lower. The alterations in pulmonary haemodynamics, Qt and O2 delivery, were of the same magnitude as in spontaneously breathing animals. Survival was improved. CPPV fully prevented the deterioration in pulmonary gas exchange and the development of pulmonary oedema. There was an accentuated increase in PVR. Qt and O2 delivery decreased markedly and a severe metabolic acidosis developed. All animals treated with CPPV died during the observation period. These results indicate that prophylactic IPPV and CPPV may counteract the development of sepsis-induced lung insufficiency in man. However, it must be emphasized that adequate cardiovascular support is essential in optimizing the treatment.     

Renal perfusion,oxygenation, and sympathetic nerve activity during volatile or intravenous general anaesthesia in sheep

Background

Global and intra-renal perfusion and oxygenation may be affected by the choice of anaesthetic. We compared the effects of isoflurane with those of propofol and fentanyl on renal blood flow (RBF) and intra-renal perfusion and oxygenation, and assessed how these were associated with renal sympathetic nerve activity (RSNA).

Effects of continuous haemofiltration vs intermittent haemodialysis on systemic haemodynamics and splanchnic regional perfusion in septic shock patients: a prospective, randomized clinical trial.

BACKGROUND: Parameters of splanchnic regional perfusion, like intramucosal pH (pHi) and pCO(2) (pCO(2)i), may predict outcome in septic shock patients. Continuous venovenous haemofiltration (CVVH) has been considered beneficial in haemodynamically unstable septic shock patients. In a prospective, randomized, clinical study, we investigated whether CVVH, in comparison to intermittent haemodialysis (IHD), is able to improve splanchnic regional perfusion in critically ill patients. METHODS: Thirty septic shock patients with acute renal failure were randomized to either CVVH (n=20) or IHD (n=10) groups for renal replacement therapy. Patient characteristics at baseline were not different in terms of severity of illness (APACHE II scores), haemodynamics, and pHi/pCO(2)i values. Systemic haemodynamics, oxygen transport variables, and splanchnic regional perfusion parameters were measured at 0.5, 2, 4 and 24 h after initiation of renal replacement therapy. There were no major changes in vasopressor support throughout the 24-h study period. RESULTS: In contrast to IHD, CVVH caused a decrease in heart rate (-3+/-11 vs +9+/-8/min, P<0.01) and an increase in systolic blood pressure (+12+/-1 vs -5+/-17 mmHg, P<0.05) after 2 h. After 24 h, increased systemic vascular resistance was found in the CVVH group in comparison with the IHD group (+312+/-755 vs -29+/-89 dyne/cm(5), P<0.05) and was accompanied by a decrease in cardiac output (-1.54+/-1.4 vs -0.25+/-0.9 l/min, P<0.01). However pHi values remained constant throughout the 24-h study period in both groups and were not different between the groups (CVVH 7.19+/-0.1 vs IHD 7.19+/-0.1, n.s.) as did the pCO(2)i values (CVVH +7+/-17 vs IHD 0+/-15 mmHg, n.s.) and pCO(2) gap values (CVVH +6+/-15 vs IHD +5+/-12 mmHg, n.s.). CONCLUSIONS: Despite different changes of systemic haemodynamics between CVVH and IHD, CVVH did not improve parameters of splanchnic regional perfusion like pHi, pCO(2)i or pCO(2) gap in septic shock patients.     

Co-administration of ephedrine prevents reductions in cardiac output and systemic oxygen delivery secondary to lung compression maneuvers during one-lung ventilation, without reducing arterial oxygenation

Purpose  

We previously showed that compression of the nondependent lung during one-lung ventilation (OLV) in patients undergoing esophagectomy improves arterial oxygenation but impairs cardiac output (CO) and systemic oxygen delivery (DO₂). The objective of this study was to test the hypothesis that the combination of nondependent lung compression and ephedrine improves arterial oxygenation without compromising DO₂.     

Evaluation of splanchnic perfusion and oxygenation during positive end-expiratory pressure ventilation in relation to subcutaneous tissue gases and pH. An experimental study in pigs with oleic acid-induced lung injury

Evaluation of splanchnic perfusion and oxygenation was performed by measurements of serosal tissue oxygen tension (PserO2) and intramucosal pH (pHi) in relation to subcutaneous oxygen tension (PscO2), subcutaneous carbon dioxide tension (PscCO2) and subcutaneous pH (pHsc) in pigs subjected to oleic acid-induced lung injury during ventilation with increasing levels of positive end-expiratory pressure (PEEP). Lung injury resulted in a general hypoxia and redistribution of perfusion away from the subcutaneous and splanchnic tissues, illustrated by a decrease in PaO2 from 93 to 37 mm Hg (p < 0.01), PscO2 from 45 to 17 mm Hg (p < 0.01), PserO2 from 80 to 30 mm Hg (p < 0.01) and pHi from 6.84 to 6.74 (p < 0.05) and a decrease of porta flow from 0.77 to 0.57 l/min. Application of PEEP up to 10-15 cm H2O resulted in an increase of portal vein oxygen tension (PportaO2) from 21 to 34 mm Hg (p < 0.01), PscO2 from 17 to 26 mm Hg (p < 0.05) and PserO2 from 30 to 55 mm Hg (p < 0.05). At PEEP 20 cm H2O PserO2 decreased to 47 mm Hg (p < 0.05). Porta flow decreased continuously with increasing levels of PEEP. PserO2 correlated with PportaO2 (r = 0.7, p < 0.001). pHi correlated poorly with PportaO2 (r = 0.2) and porta flow (r = 0.4). PscO2 and PserO2 correlated well (r = 0.8, p < 0.001). In summary, splanchnic perfusion and oxygenation was better reflected by serosal oxygen tension than pHi in the colon. Changes in serosal oxygenation of the colon paralleled changes in subcutaneous tissue oxygenation.     

Increases in pulmonary artery pressure and cardiac output due to the inhibition of nitric oxide synthesis during operative stress

Pulmonary artery pressure (PAP), cardiac output (CO), and urinary nitrate, a stable endproduct of nitric oxide (NO), were measured pre- and postoperatively in eight patients who underwent esophagectomy for squamous cell carcinoma of the thoracic esophagus. A significant elevation of PAP and CO on the day of operation (POD 0) was accompanied by a low concentration of urinary nitrate. A reduction in PAP and CO, and an increase in nitrate to the preoperative levels, were found on PODs 2 and 3, respectively, but urinary nitrate decreased again after POD 3. Consequently, the changes in PAP and CO were closely correlated with the nitrate concentration. These results suggest that operative stress inhibited NO synthesis with a transitory induction of endogenous NO synthesis postoperatively.     

Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration during isoflurane anaesthesia in Shetland ponies

BACKGROUND: The arterial pharmacokinetics of ketamine and norketamine enantiomersafter racemic ketamine or S-ketamine i.v. administration wereevaluated in seven gelding ponies in a crossover study (2-monthinterval). METHODS: Anaesthesia was induced with isoflurane in oxygen via a face-maskand then maintained at each pony's individual MAC. Racemic ketamine(2.2 mg kg^–1) or S-ketamine (1.1 mg kg^–1)was injected in the right jugular vein. Blood samples were collectedfrom the right carotid artery before and at 1, 2, 4, 8, 16,32, 64, and 128 min after ketamine administration. Ketamineand norketamine enantiomer plasma concentrations were determinedby capillary electrophoresis. Individual R-ketamine and S-ketamineconcentration vs time curves were analysed by non-linear leastsquare regression two-compartment model analysis using PCNonlin.Plasma disposition curves for R-norketamine and S-norketaminewere described by estimating AUC, C_max, and T_max. Pulse rate(PR), respiratory rate (R_f), tidal volume (V_T), minute volumeventilation (V_E), end-tidal partial pressure of carbon dioxide(PE'_CO2), and mean arterial blood pressure (MAP) were also evaluated. RESULTS: The pharmacokinetic parameters of S- and R-ketamine administeredin the racemic mixture or S-ketamine administered separatelydid not differ significantly. Statistically significant higherAUC and C_max were found for S-norketamine compared with R-norketaminein the racemic group. Overall, R_f, V_E, PE'_CO2, and MAP weresignificantly higher in the racemic group, whereas PR was higherin the S-ketamine group. CONCLUSIONS: Norketamine enantiomers showed different pharmacokinetic profilesafter single i.v. administration of racemic ketamine in poniesanaesthetised with isoflurane in oxygen (1 MAC). Cardiopulmonaryvariables require further investigation.     

Regional and temporal changes in cardiovascular responses to norepinephrine and vasopressin during continuous infusion of lipopolysaccharide in conscious rats

Background. Reduced pressor responsiveness to norepinephrine(NE) in sepsis is well documented but the associated regionalhaemodynamic changes are less well characterized, and thereare varying reports of changes in haemodynamic responses toarginine vasopressin (AVP). We compared changes in regionalhaemodynamic responsiveness to AVP and NE during a 24 h continuousinfusion of lipopolysaccharide (LPS) in conscious rats. Methods. Conscious, male Sprague–Dawley rats were infusedwith saline (0.4 ml h^–1) or LPS (150 µg kg^–1h^–1). Renal, mesenteric, and hindquarter haemodynamicresponses to 3 min infusions of AVP (0.25, 0.625, and 1.25 ngkg^–1 min^–1) or NE (75, 250, and 750 ng kg^–1min^–1) were assessed 2, 6, and 24 h after the onset ofLPS or saline. Results. Two and six hours after the onset of LPS, all haemodynamiceffects of NE were markedly reduced, but by 24 h, there wassome recovery in the vasoconstrictor actions of NE althoughthe pressor and bradycardic effects were still depressed. Twohours after the onset of LPS, the cardiovascular effects ofAVP were depressed but there was some recovery in vascular responsivenessat 6 h. By 24 h, only the mesenteric vasoconstrictor effectof AVP was consistently reduced. Conclusions. During low dose LPS infusion, there are differentialchanges in haemodynamic responsiveness to AVP and NE, whichshow different temporal and regional profiles of recovery withtime. Furthermore, reduced pressor responsiveness to NE is notnecessarily accompanied by a reduced capacity of vessels forvasoconstriction.     

A versatile extracorporeal circuit for use during repair of descending and thoracoabdominal aortic aneurysms in high-risk patients with cardiac and/or pulmonary dysfunction: a novel approach to a significant perfusion management dilemma

The incidence of ischemic complications associated with repair of descending and thoracoabdominal aortic aneurysms has been significantly reduced by the use of distal aortic perfusion with moderate hypothermia, cerebral spinal fluid drainage, and segmental sequential clamping techniques. However, because the maintenance of proximal perfusion, the adequacy of left heart bypass (LHB), and the ability to ventilate patients on only one lung are all dependent on ventricular and pulmonary function, high-risk patients with descending and/or thoracoabdominal aortic aneurysms in the presence of cardiopulmonary insufficiency or instability present a difficult challenge for the surgical team. Traditional closed LHB circuits become nonfunctional in the event of cardiac arrest or refractory arrhythmias that create hemodynamic instability and are unable to provide necessary pulmonary support if the patient fails to ventilate adequately on one lung during thoracotomy. Furthermore, converting a patient from closed LHB to traditional venoarterial cardiopulmonary bypass (CPB) is frequently difficult, especially when the perfusionist works without the benefit of extra personnel to assist during such crises. Consequently, a modified extracorporeal circuit was designed to provide closed LHB with desired therapeutic adjuncts while also satisfying the additional need for a rapid infusion device, a source of supplemental ventilation/oxygenation, and, if necessary, the ability to convert the patient to venoarterial CPB conveniently in the event of cardiac and/or pulmonary failure during surgery to repair descending and/or thoracoabdominal aortic aneurysms.     

The effects of 10 degrees reverse trendelenburg position on ICP and CPP in prone positioned patients subjected to craniotomy for occipital or cerebellar tumours

Summary. Summary.   Background: Control of ICP-hypertension is of utmost importance during craniotomy. The effects of reverse Trendelenburg position (RTP) upon ICP and CPP have recently been studied in supine positioned patients.   Method: In this study we investigated changes in intracranial pressure (ICP), mean arterial blood pressure (MABP), CPP and jugular bulb pressure (JBP) before and one minute after 10^° RTP in 26 prone positioned patients with either occipital (n=12) or cerebellar tumours (n=14). ICP was measured by a subdural approach after removal of the bone flap. Tension of the dura was estimated by the surgeons by digital palpation before and after change in position.   Findings: In patients with occipital tumours ICP decreased from 21.0 to 15.6 mm Hg (p<0.05). MABP decreased from 87.9 to 83.3 mm Hg (p<0.05), JBP decreased from 14.3 to 7.7 mm Hg (P<0.05), while CPP was unchanged. In patients with cerebellar tumours ICP decreased from 18.3 to 14.2 mm Hg (p<0.05). MABP decreased from 93,8 to 90.5 mm Hg (p<0.05), JBP decreased from 12.1 to 5.0 mm Hg (P<0.05), while CPP was unchanged. There were no significant differences between the two groups with regard to changes in ICP, MABP, CPP and JBP. The change in ICP was accompanied by a significant decrease in dural tension (p<0.05).   Interpretation: In prone positioned patients 10^° RTP significantly reduces ICP, JPB and MABP within one minute, while CPP is unchanged. Published online July 18, 2002