Principles of artificial ventilation

The application of intermittent positive pressure ventilation (IPPV) during the 1952 Copenhagen polio epidemic led to the development of the world’s first intensive care unit. The requirement for ventilatory support is the most common indication for intensive therapy unit (ITU) admission and is a defining feature of the specialty. Ventilator technology continues to develop and there are many ways to deliver IPPV. The variety of modes of ventilation is increasingly complex and expanding, without evidence that any one mode is associated with improved outcome. Ventilatory support is part of the treatment for a range of conditions including acute respiratory failure, raised intracranial pressure (ICP) and circulatory shock. Ventilator-associated lung injury is reduced by using low tidal volumes and limiting plateau airway pressure to less than 30 cmH₂O. Prolonged artificial ventilation has an associated morbidity and mortality and thus should be reviewed by an expert clinician on a daily basis. Weaning aims to identify those patients who will be able to breathe spontaneously. Protocols exist to facilitate timely extubation without the need for re-intubation.     

Principles of artificial ventilation

The application of intermittent positive pressure ventilation (IPPV) during the 1952 Copenhagen polio epidemic led to the development of the world's first intensive care unit. The requirement for ventilatory support is the most common indication for intensive therapy unit (ITU) admission and is a defining feature of the specialty. Ventilator technology continues to develop and there are many ways to deliver IPPV. The variety of modes of ventilation is increasingly complex and expanding, without evidence that any one mode is associated with improved outcome. Ventilatory support is part of the treatment for a range of conditions including acute respiratory failure, raised intracranial pressure (ICP) and circulatory shock. Ventilator-associated lung injury is reduced by using low tidal volumes and limiting plateau airway pressure to less than 30 cmH₂O. Prolonged artificial ventilation has an associated morbidity and mortality and thus should be reviewed by an expert clinician on a daily basis. Weaning aims to identify those patients who will be able to breathe spontaneously. Protocols exist to facilitate timely extubation without the need for re-intubation.     

Ventilatory support in the intensive care unit

Mechanical ventilation is a crucial supportive intervention that allows time to facilitate investigations and provide definitive treatment in critically unwell patients. This article focuses on the various modes of respiratory support available, and the mechanical ventilation strategies used in specific disease processes. It also highlights the possible complications associated with mechanical ventilation and the adjuncts that can be used to aid oxygenation.     

Management of the airway in intensive care

Airway management in the intensive care unit (ICU) is largely uneventful; there is a higher incidence of airway difficulties, however, than those encountered in the operating suite. Management of the airway in the ICU presents challenges unique to this environment that must be coped with by a multidisciplinary team that may be less experienced in airway management than clinicians in the operating theatre. The risks associated with this situation, I believe, may be ameliorated by planning and forethought. This article outlines some of the specific difficulties faced by clinicians in ICU and attempts to provide some guidance as to how these may be overcome, or at least abated. Drug choices are discussed, as are equipment choices. A suggestion for a difficult airway algorithm for use in the ICU is put forward. The timing of tracheostomy is discussed. Finally, the importance of the team and the human factors that are at play are touched upon.     

Management of the airway in intensive care

Airway management in intensive care is often routine; however there is a higher incidence of problems with a difficult airway that is under-reported. Management of these patients is by a multidisciplinary team who may have less familiarity and experience to manage the difficult airway than that which is commonly found in the operating theatre environment. In this article we explain the predictable and unpredictable aspects of airway management in this important group of patients. Particular emphasis is placed on the specific problems associated with extubation in the ICU and there is detailed discussion of the aspects of multiple organ failure that are commonly experienced in the critically ill patient and the impact they have on airway management. Problems with oxygen delivery and ventilation/perfusion mismatch are touched upon. The important role of early tracheostomy in the management of the complex airway in ICU is addressed in some detail. We also address the importance of non-technical skills, rehearsal and planning to increase the safe and effective management of airway problems in the critically ill. We provide generic suggestions for the drugs and equipment immediately required to optimise the safe management of these patients.     

Management of the airway in intensive care

Airway management in the intensive care unit (ICU) is largely uneventful; there is a higher incidence of airway difficulties, however, than those encountered in the operating suite. Management of the airway in the ICU presents challenges unique to this environment that must be coped with by a multidisciplinary team that may be less experienced in airway management than clinicians in the operating theatre. The risks associated with this situation, we believe, may be ameliorated by planning and forethought. This article outlines some of the specific difficulties faced by clinicians in ICU and attempts to provide some guidance as to how these may be overcome, or at least abated. Drug and equipment choices are discussed. A suggestion for a difficult airway algorithm for use in the ICU is put forward. The timing of tracheostomy is discussed. Finally, the importance of the team and the human factors that are at play are touched upon.     

Management of and indications for tracheostomy in care of the critically ill patient

Tracheostomy is a procedure that has evolved over many hundreds of years. In the 21st century, the majority of tracheostomies are now inserted by intensivists in the intensive care unit (ICU). Commonly performed to assist in weaning patients from mechanical ventilation, the procedure is performed using a percutaneous dilatational technique. Percutaneous tracheostomy can generally be performed safely in the ICU, although a number of contra-indications and complications do exist. Recent publications have highlighted weaknesses in the quality of care both in the immediate and longer term. Consequently, a number of organizations, based in the UK and internationally, have turned the focus in recent years to improving the quality of care delivered to these patients. Clinicians caring for patients with tracheostomies should not only be familiar with the indications, anatomy and insertion techniques, but also current guidance on routine care and the emergency management of complications.     

Traumatic Brain Injury and Subarachnoid Hemorrhage: In Vivo Occult Pathology Demonstrated by Magnetic Resonance Spectroscopy may not be “Ischaemic”. A Primary Study and Review of the Literature

Summary.  Objectives: To look for evidence of early ischaemic neurochemical changes in patients suffering severe traumatic brain injury (TBI) and severe subarachnoid haemorrhage (SAH). Proton metabolite concentrations were measured in normal and abnormal areas of brain on T2 MR imaging, in regions considered particularly vulnerable to ischaemic injury.  Methods: Intensive care patients underwent T2 weighted imaging in a 1.5 Tesla MR scanner and proton magnetic resonance spectroscopy (single voxel or chemical shift imaging). Metabolite values in areas that appeared `normal' and `abnormal' on T2 MR imaging were compared with those obtained from normal controls.  Results: 18 TBI and 6 SAH patients were imaged at 1 to 26 days. N-acetyl aspartate (NAA) was lower in TBI and SAH patients compared to controls in both T2 normal and T2 abnormal areas (p<0.0005). SAH, but not TBI patients also had increased choline and creatine compared to controls in the T2 normal (p<0.02, p<0.02 respectively) and T2 abnormal (p=0.0003, p=0.003) areas. No lactate was found in TBI or SAH patients.  Conclusions: Significant loss of normal functioning neurones was present in TBI and SAH, but no evidence of anaerobic metabolism using lactate as a surrogate marker, questioning the role of `ischemia' as a major mechanism of damage. Increased choline and creatine were found in SAH patients suggestive of increased cell-wall turnover. Current theories of brain injury after TBI or SAH do not explain these observed neurochemical changes and further research is required. Published online September 2, 2002 Acknowledgments  We thank Mr J. Cannon, radiographers, nursing staff and porters for their help, Mr M. Connell for computing support and Mrs P. Jones for assistance with demographic data. The CSI data has been presented in part to the Neuroanaesthesia Societies of Great Britain, Ireland, Scandinavia and Finland, Helsinki 1998 and a technical paper published by Wild J. et al.: Magnetic Resonance Materials in Physics, Biology, & Medicine 8(2): 109–115, 1999. Correspondence: Dr. Carol Macmillan, University Department of Anaesthetics, Ninewells Hospital, Dundee DD1 9SY, UK.     

Management of and indications for tracheostomy in care of the critically ill patient

Tracheostomy is a procedure which has evolved over many hundreds of years. In the 21st century, the majority of tracheostomies are now inserted by intensivists in the intensive care unit (ICU). Commonly performed to assist in weaning patients from mechanical ventilation, the procedure is performed using a percutaneous dilatational technique (PDT). Percutaneous tracheostomy can generally be performed safely in ICU, although a number of contraindications and complications do exist. Recent publications have highlighted weaknesses in the quality of care both in the immediate and longer term. Consequently, a number of organizations, based in the UK and internationally, have turned the focus in recent years to improving the quality of care delivered to these patients. Clinicians caring for patients with tracheostomies should not only be familiar with the indications, anatomy and insertion techniques, but also current guidance on routine care and the emergency management of complications.     

Hypotension in anaesthetized patients during aneurysm clipping: not as bad as expected?

Background: Patients with aneurysmal subarachnoid haemorrhage (SAH) often have disturbed autoregulation of cerebral blood flow. A reduction in systemic blood pressure during surgery may therefore lead to delayed cerebral ischaemia (DCI). To assess the incidence and severity of intra-operative hypotension, we performed a retrospective cohort study in 164 patients with recent SAH and surgical clipping of the aneurysm.
Methods: Intra-operative hypotension was defined in three levels of severity, as a decrease in mean arterial pressure (ΔMAP) of more than 30%, 40% or 50% compared with the pre-operative pressure. For each patient the total amount of time with intra-operative hypotension was retrieved. Logistic regression analysis was performed to study the relation between intra-operative hypotension and the occurrence of DCI and poor outcome.
Results: A period with ΔMAP>30% occurred in 128 patients (78%) with a median duration of this period of 105 min (25–75‰ 50–171 min). ΔMAP>40% occurred in 88 patients (54%) and ΔMAP>50% occurred in 22 patients (13%). In univariate analysis, ΔMAP>50% was associated with poor outcome. After adjusting for age and World Federation of Neurological Surgeons grade, the association with poor outcome was no longer statistically significant [odds ratio (OR) 1.018; 95% CI 0.996–1.041].
Conclusion: Hypotension during surgical clipping of intracranial aneurysms occurred frequently. In our study population of patients mostly in good clinical condition, hypotension was not confirmed as an independent risk factor for DCI or poor outcome. Anaesthesia may have had a cerebral protective effect.     

Therapeutic hypothermia and acute brain injury

The neuroprotective effects of therapeutic hypothermia (TH) have been recognized for decades, but these have generally failed to translate these into improved outcome in clinical studies. Here, we provide an overview of the putative mechanisms of hypothermia-induced neuroprotection, the technical considerations for the clinician wishing to use TH, and review the evidence for the clinical application of TH after acute brain injury (ABI).Although TH is increasingly used as a tool in the management of intracranial hypertension, its role in different ABI types is not yet fully established. Many questions remain regarding the logistics of cooling (including length of treatment), and how best to manage complications of therapy, particularly shivering. The only level I evidence for its benefit lies in adult cardiac arrest and neonatal hypoxic-ischaemic encephalopathy. Further high-quality studies are needed to assess the role of TH in other ABI types.     

Dysphagia and Respiratory Care in Individuals with Tetraplegia: Incidence,Associated Factors,and Preventable Complications

Dysphagia occurs in a significant number of individuals with spinal cord injury (SCI) presenting to acute care and inpatient rehabilitation. This prospective study has found dysphagia in nearly 40% of individuals with tetraplegia. Tracheostomy, mechanical ventilation, nasogastric tube, and age are significant risk factors. The detrimental complications of dysphagia in SCI can cause significant morbidity and delays in rehabilitation. Thus, early and accurate diagnosis of dysphagia is imperative to reduce the risk of developing life-threatening complications. Incidence and risk factors of dysphagia and the use of the bedside swallow evaluation (BSE) and videofluoroscopy swallow study (VFSS) to diagnose dysphagia are presented. The often underappreciated role of respiratory therapists, including assist cough, high tidal volume ventilation, and the use of Passy-Muir valve, in the care of individuals with SCI who have dysphagia is discussed. Improved secretion management and respiratory stabilization enable the individuals with dysphagia to be evaluated sooner and safely by a speech pathologist. Early evaluation and intervention could improve upon morbidity and delayed rehabilitation, thus improving overall clinical outcomes.     

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.     

Pre- and post-operative changes in serum immunoglobulin level in neurosurgical patients

Summary 46 patients treated by operative neurosurgery for spontaneous subarachnoid haemorrhage, intracranial tumour and spinal diseases were studied. Levels of circulating immunoglobulin and complement were measured pre-operatively and serially in the first 10 post-operative days.Prior to operation immunoglobulin levels in all categories of patients were distributed normally. However, immediately post-operatively IgG and IgM fell sharply. Conversely IgA rose in a marked manner and C₃ levels showed a gradual increase. Later, antibody levels tended to return to normal.     

重症患者两种撤机方式的比较

目的 比较SmartCare/PS(SC)和压力支持通气(PSV)模式在重症患者中的撤机效果.方法 将41例行机械通气的重症患者,在满足临床撤机条件后,随机分为SC组(n=21)和PSV组(n=20),分别采用SC和PSV模式撤机.记录撤机时间、总通气时间(TVT)、人工操作次数,以及再插管率、气管切开率、气胸发生率和呼吸机相关肺炎(VAP)发生率.结果 SC组撤机时间、TVT较PSV组明显缩短(P<0.05);SC组人工操作次数较PSV组明显减少(P<0.05);两组再插管率、气管切开率、气胸发生率和VAP发生率差异无统计学意义.结论 SC模式可缩短重症患者的撤机时间、TVT和减轻医务人员工作量.     

Concomitant cranio-cerebral and vertebro-medullary injuries. Analysis of 121 cases

Summary The management of the ruptured intracranial aneurysm is studied in two consecutive series: an earlier series, including 328 patients admitted from 1972 through 1984, for which the general attitude was delayed surgery, and a later series, including 140 patients admitted from 1985 through 1989, in which selected patients were submitted to early surgery and other patients were postponed for delayed surgery, according to two main parameters: the clinical status and the patient's age. When we compare both series, the overall management results demonstrate an improvement of 10% of satisfactory results and a decrease of 10% in the death rate in favour of the later series; for the surgical results, the figures are respectively 6% and 5% in favour of the later series. The relationship between age and outcome shows a considerable improvement: over 50 years of age, we observed plus 25% of satisfactory results and minus 22% in death in favour of the later series. Similarly the relationship between state of consciousness and outcome, demonstrated a great improvement; for drowsy and stuporous patients the figures are respectively plus 22% and minus 21% in favour of the later series. When we consider the later series alone, the patients were admitted at 4 intervals of time from SAH (D0-3, D4-6, D7-15, D16 and over). The most favourable outcome was observed for those patients admitted late (after D7) and already stabilized. Patients admitted early (D0-3) were operated on at four intervals of time (D0-3, D4-6, D7-15, D16 and over). The most favourable outcome was observed for those patients operated on early (D0-3) or very late (D16 and over). For patients admitted early and being under 50 years of age, the results were: satisfactory 92%, poor 2.5%, death 5%. The relationship between age and outcome shows a very small difference between patients under or over 50 years of age. The relationship between level of consciousness and outcome still demonstrates an appreciable difference: plus 22% (satisfactory) and minus 7% (death) in favour of alert patients.Rebleeding was the cause of disability or death in 2.8% of the overall later series and 2.7% of patients admitted early; as for vasospasm the figures are respectively 4.2% and 5.4%. These results are presented with reference to those of the Co-operative Study.After this experience, the author's general attitude for the timing of surgery is neither systematic early surgery, nor systematic delayed surgery, but modulated surgery, based upon the evaluation of the operative risk: minor risk, major risk, intermediate risk. Schematically the authors propose: early surgery in alert patients and under 50 years of age (minor risk), late surgery in patients with disturbances of consciousness and over 50 years of age (major risk); preferably early surgery in younger patients even with disturbances of consciousness (intermediate risk); preferably late surgery in older patients, even being alert (intermediate risk).