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Effects of sternotomy on heart lung interaction in patients undergoing cardiac surgery receiving pressure controlled mechanical ventilation
No full textEffects of sternotomy on heart-lung interaction in patients undergoing cardiac surgery receiving pressure-controlled mechanical ventilation.
De Blasi RA, Palmisani S, Cigognetti L, Iasenzaniro M, Arcioni R, Mercieri M, Pinto G.
Source
Department of Anesthesia and Intensive Care Medicine, University La Sapienza, 2nd Faculty of Medicine, Sant'Andrea Hospital, Rome, Italy. [email protected]
Abstract
BACKGROUND:
The key concept underlying the dynamic indexes of preload dependence is the physiological heart-lung interaction. During sternotomy this interaction undergoes various changes, some of which remain unclear. Our primary aim was to investigate how the interaction changes during sternotomy by evaluating pulse pressure variations (PPV) with the chest closed and after sternotomy in patients ventilated using the pressure-controlled mode.
METHODS:
We prospectively studied 25 patients undergoing coronary artery bypass grafting (CABG) receiving pressure-controlled ventilation. Standard hemodynamic data, PPV and tidal volume delivered were recorded before and after sternotomy, and, with the chest open, before and after positive end-expiratory pressure (PEEP) was applied and inspiratory pressure was increased.
RESULTS:
Sternotomy left all variables statistically unchanged from values before thoracotomy although in the subgroup of patients with a PPV > 8% (56%) sternotomy significantly reduced PPV (from 14.4 +/- 5.2% to 8.9 +/- 4.5%). With the chest open, when PEEP was applied at 5 cm H(2)O, tidal volume decreased (from 643 +/- 83 to 587 +/- 104 ml) and stroke volume decreased (from 77 +/- 17 to 72 +/- 15 ml) but PPV remained unchanged. When PEEP was discontinued and inspiratory pressure was increased by 5 cm H(2)O, tidal volume increased (from 643 +/- 83 to 814 +/- 89 ml) and PPV increased (from 8.2 +/- 3.9% to 12.3 +/- 6.8%) but stroke volume remained unchanged.
CONCLUSIONS:
In patients ventilated in the pressure-controlled mode, except those with a pre-sternotomy PPV > 8% (fluid responders), sternotomy leaves standard hemodynamic data and PPV unchanged. When the chest wall is open, cyclic changes (tidal volume) but not continuous changes (PEEP) in intrathoracic pressure directly influence PPV.
PMID: 17378782 [PubMed - indexed for MEDLINE]
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Lateral or posterior popliteal approach for sciatic nerve block: Difference is related to the anatomy
No full textTo the Editor:
March and colleagues (1) comparing single- and double-injection techniques for blockade of the sciatic nerve block via a posterior popliteal approach, concluded that double-nerve stimulation resulted in similar onset time and overall success rate when compared with that after single-nerve stimulation. In the double-injection group, they located both common peroneal and tibial nerve, whereas in the single-injection group they preferentially elicited foot inversion, interpreting this motor response to reflect needle proximity to both sciatic nerve trunks (2).
Our group has extensive experience providing regional anesthesia for outpatients undergoing foot surgery (3). We recently showed that, when using a lateral popliteal sciatic nerve block, a single injection targeting the tibial nerve is more effective than a single injection targeting the peroneal nerve and is also as effective as a double injection of both branches of the sciatic nerve (4).
We believe that results from March's work lend further support for our results, even when the different drugs and dosages used are taken into account. When a double-injection procedure is employed, the success rates after the lateral or posterior approaches are similar (respectively, 94% vs 87%) whereas a single-injection technique yields similar or even better results only if it is performed via a lateral approach and it is targeted at the tibial branch of the sciatic nerve (success rate: lateral 94% vs posterior 77%).
Considering the anatomy of the sciatic nerve at the popliteal level (5), targeting the tibial nerve via a lateral popliteal approach will likely result in injecting local anesthetic within the adventitia that envelops both branches of the sciatic nerve (4). On the other hand, the same single injection technique performed via a posterior approach will not assure that local anesthetic is injected within the tibial and peroneal common perineural space.
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only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
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Microvascular dysfunction and skeletal muscle oxygenation assessed by phase-modulation near-infrared spectroscopy in patients with septic shock
No full textEffects of remifentanil-based general anaesthesia with propofol or sevoflurane on muscle microcirculation as assessed by near-infrared spectroscopy.
No full textAbstract BACKGROUND: Although anaesthetics are known to alter microcirculation no study has, to our knowledge, documented changes in human skeletal microcirculatory function during general anaesthesia. METHODS: Forty-four patients undergoing maxillofacial surgery at a university hospital were prospectively randomized to receive general anaesthesia with remifentanil combined with propofol or sevoflurane. Muscle microcirculation was investigated with near-infrared spectroscopy (NIRS) before general anaesthesia was induced and 30 min later. An NIRS device (NIMO, Nirox) was used to quantify calf deoxyhaemoglobin [HHb], oxyhaemoglobin [HbO2], and total haemoglobin [HbT] concentrations, coupled to a series of venous and arterial occlusions to measure calf blood flow, muscle oxygen consumption, calf vascular resistance, microvascular compliance, and haemoglobin resaturation rate (RR). RESULTS: In both the groups, general anaesthesia induced marked changes in muscle microcirculation: the tissue blood volume increased (+33% in remifentanil-sevoflurane and +45% with remifentanil-propofol groups), microvascular resistance decreased (-31% and -38%, respectively), and the post-ischaemic haemoglobin RR decreased (-48% and -36%, respectively). In the remifentanil-propofol group, the muscle blood flow increased (P0.001), whereas in the remifentanil-sevoflurane group microvascular compliance and muscle oxygen consumption decreased (P0.01). CONCLUSIONS: Remifentanil-based general anaesthesia with propofol or sevoflurane altered the muscle microcirculation in different ways. Quantitative NIRS, a technique that takes into account the optical tissue properties of the individual subject, can effectively measure these changes non-invasively
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