Ventilatory support in the intensive care unit

This article focuses on the functional features of positive-pressure ventilators, the modes of invasive and non-invasive mechanical ventilation, and the main ventilator settings. It also highlights the potential complications of mechanical ventilation, the basic principles of weaning, and the pathophysiological basis of patient-ventilator dyssynchrony.     

多普勒组织显像评估严重心力衰竭而QRS间期正常患者的左室收缩不同步

目的:应用多普勒组织显像(DTI)评估严重心衰而QRS间期正常的患者左室收缩不同步的发生率。方法:应用DTI分析20例QRS间期正常的严重心衰患者和20例正常人的左室侧壁、后间隔、前壁、下壁、前间隔及后壁的基底段和中段共12个节段的脉冲组织多普勒频谱,测量每例的QRS波起始至各个左室壁节段多普勒频谱收缩峰起始的时间(以Ts表示)。计算每例最大Ts与最小Ts的差值(Ts-MD)、Ts的标准差(Ts-SD)和Ts的变异系数(Ts-CV),用以评估两组对象左室收缩不同步的差异。结果:HF组的Ts-MD、Ts-SD和Ts-CV均较正常对照组明显增大(P<0.001),表明QRS间期正常的心衰患者存在左室壁收缩不同步。以TS-MD53.08 ms、Ts-SD18.08 ms和Ts-CV0.91(正常值单侧95%可信区间,x 1.65s)作为切断值,HF组左室收缩不同步的发生率分别为55.0%(11/20)、55.0%(11/20)和55.0%(11/20),显著高于对照组(P均<0.001);且QRS间期正常的心衰患者最大收缩延迟部位亦不完全相同。结论:DTI显示左室收缩不同步在严重心衰而QRS间期正常的患者中常见。这个结果支持心衰患者即使QRS间期正常也可能从CRT中受益。     

Determinants of mortality in patients undergoing cardiac resynchronization therapy: baseline clinical, echocardiographic, and angioscintigraphic evaluation prior to resynchronization

BACKGROUND: In dilated cardiomyopathy (DCM) patients (pts) with cardiac resynchronization therapy (CRT) for ventricular dyssynchrony, long-term predictors of mortality and morbidity remain poorly investigated. METHOD AND RESULTS: We reviewed data of 102 pts, 68 +/- 10 years, NYHA Class II-IV (14 Class II, 67 Class III, 21 Class IV), who benefited from CRT (69 CRT, 33 CRT-ICD). Fifty-two patients had an ischemic DCM, 36 a previously implanted conventional PM/ICD, 29 a permanent atrial fibrillation, and 19 needed dobutamine in the month preceding implant. QRS duration was 187 +/- 35 ms, left ventricular end-diastolic diameter 72 +/- 10 mm, mitral regurgitation severity 1.9 +/- 0.8, echographic aorto-pulmonary electromechanical delay 61.5 +/- 25 ms and septo-lateral left intraventricular delay 86 +/- 56 ms, pulmonary artery pressure (PAP) 43 +/- 11 mmHg, angioscintigraphic left ventricular ejection fraction (EF) 20 +/- 9%, and right ventricular EF 30.5 +/- 14%. Over a mean follow-up of 23 +/- 20 months, 26 pts died (18 heart failures (HFs), 1 arrhythmic storm, 7 noncardiac deaths). Positive univariate predictors of death from any cause were NYHA Class IV (P < 0.001), and need for dobutamine the month preceding CRT (P < 0.008), while use of beta-blocking agents (P < 0.08) and left ventricular EF (P < 0.09) were negative ones. NYHA Class IV was the only independent predictor at multivariate analysis (P < 0.01). Survival at 24 months was 85% in Class II, 80% in Class III, and 37% in Class IV (II vs III, P = ns; III vs IV, P < 0.001). When using a composite endpoint of death from any cause and unplanned rehospitalization for a major cardiovascular event, there were 48 events (14 HF deaths, 3 noncardiac deaths, 26 HF rehospitalizations, 2 paroxysmal atrial fibrillation, 2 sustained ventricular tachycardia, 1 nonfatal pulmonary embolism). Predictors of death from any cause/unplanned rehospitalization for a major cardiovascular event in the follow-up were NYHA Class IV (P < 0.001), need for dobutamine during the month preceding CRT (P < 0.002), and PAP (<0.02). NYHA Class IV was the only independent predictor at multivariate analysis (P < 0.05). Event-free proportion at 24 months was 70% in Class II, 64% in Class III, and 37% in Class IV (II vs III, P = ns; III vs IV, P < 0.01). When considering determinants of mortality only in NYHA Class IV patients, no variable was significantly correlated to mortality. Need for dobutamine during the last month preceding CRT did not add an adjunctive mortality risk. CONCLUSION: Baseline NYHA Class IV at implantation appears as the most important determinant of a poor clinical outcome in terms of both mortality and morbidity. No predictive criteria seem available for NYHA Class IV patients, in order to discriminate who will die after CRT and who will not. NYHA Class IV strongly influences the clinical outcome, suggesting that, in future studies planned on mortality and rehospitalization as major endpoints, baseline NYHA Class IV should be separately taken into account.     

Successful biventricular cardiac resynchronization therapy in a failing Fontan patient: Implications of ventriculo‐ventricular interdependency in single ventricle physiology

We describe a Fontan patient with severe heart failure who was successfully treated with biventricular cardiac resynchronization therapy (CRT). Our case shows that strain imaging might play a crucial role in guiding placement of pacing leads and in characterizing the electromechanical substrate associated with a favorable CRT response. Furthermore, we demonstrate for the first time that ventriculo‐ventricular interdependency seems an important mechanical concept, which can be utilized to augment cardiac performance in failing Fontan patients with a functional hypoplastic ventricle.