The Intensive Care Unit

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The Intensive Care Unit

Historically, critical care medicine can be traced as far back as the Crimean war and Florence Nightingale’s pioneering work in monitoring the critically ill patient. The poliomyelitis outbreak in Denmark in the 1950s saw the onset of positive pressure ventilation in specific designated areas, and continued evolution has led to what we recognize as intensive care medicine today. This chapter aims to provide an overview of the provision of general adult intensive care.

The key components of intensive care are resuscitation and stabilization, physiological optimization to prevent organ failure, support of the failing organ systems and recognition of futility of treatment. The Department of Health NHS Executive defines intensive care as ‘a service for patients with potentially recoverable conditions who can benefit from more detailed observation and treatment than can safely be provided in general wards or high dependency areas’. Levels of care within the hospital can be described from level 0 (ward-based care) to level 3 (patients requiring advanced respiratory support alone or a minimum of 2 organs being supported) (Table 45.1). There is now a move towards a comprehensive critical care system, where the needs of all patients who are critically ill, rather than just those who are admitted to designated intensive care or high dependency beds, are met with consistency.

TABLE 45.1

Levels of ICU Care

image

In the UK, intensive care beds generally account for 1–2% of the total number of acute beds. The design of ICUs varies from hospital to hospital but they are characterized by being designated areas in which traditionally there is a minimum nurse:patient ratio of 1:1 in addition to a nurse in charge at all times, 24 h cover by resident medical staff (without commitments elsewhere) and the facilities to support organ system failures. High-dependency units (HDUs) are designated areas with a nurse:patient ratio of 1:2 in addition to a nurse in charge at all times, continuous availability of medical staff either from the admitting specialty, or from the ICU, and an appropriate level of monitoring and other equipment. While ICU and HDU may be situated separately in the hospital, all critical care beds should ideally be in adjacent locations.

The physical floor space for each bed in an ICU should be greater than 20 m2, more than on an ordinary ward because several nurses may need to treat a patient simultaneously and bulky items of equipment often need to be accommodated. Increased bed spacing and the presence of isolated side rooms may help to reduce the risk of nosocomial infection. Each bed area is supplied with piped oxygen, suction, and medical compressed air. The plethora of electronic monitors requires at least 12 electric power sockets (with emergency backup electrical supply) at each bed. Sufficient bedside storage space, at least 5 m2, is needed for drugs and disposable equipment. Each bed area should be equipped with a self-inflating resuscitation bag to enable staff to maintain artificial ventilation if the mechanical ventilator, gas or electricity supply fails.

STAFFING AN INTENSIVE CARE UNIT

Care of the individual patient in an ICU is increasingly complex and involves contributions from a variety of medical staff, as well as high standards of care from nurses, physiotherapists, dieticians, pharmacists and other health professionals. Each member of the multidisciplinary team has a broad spectrum of experience and skills and it is worth remembering the value of good teamwork to ensure that high standards of quality patient care are provided. Often the consultant in the specialty under which the patient was admitted may still be nominally in charge, but confusion is minimized if day to day decisions are made through the ICU team, in close liaison with the parent specialty. Good communication is paramount, both within the ICU environment and with the various other teams.

The ICU Consultant

There must be twenty-four hour cover of the ICU by a named consultant who has appropriate experience and competencies. Difficult therapeutic and ethical policy decisions may be required at any time in the ICU and it is essential that they are taken by an individual whose previous experience allows a reasonable assessment of the likely outcome, and whose therapeutic expertise is likely to give the patient the optimal chance of recovery. The ICU consultant, if not physically present in the unit, must always be available by telephone and should not be involved in any activity which precludes his or her attendance there within 30 min. Because of the critical nature of ICU patients’ illnesses, the ICU consultant expects to be informed immediately of any significant change in their condition. Similarly they should be informed of any potential admissions and all new patients should be seen within 12 hours. The consultant’s base specialty is less important than appropriate training and experience.

The ICU Resident

The junior medical staff in ICU have a pivotal role in the co-ordination of all aspects of patient care, particularly to maintain good lines of communication between the different teams involved. Because of their continuous presence in the unit, the ICU resident is best informed about the patient’s recent diagnostic results, physiological status and therapeutic responses and should attempt to use current knowledge to guide treatment along rational lines. Daily work comprises at least one main ward round, usually in the presence of the multidisciplinary team, whereby clinical decisions are made. Following patient assessment, findings should be documented, the results of relevant investigations reviewed and appropriate actions taken. Because of the potential to change, the patients’ clinical state should be frequently reassessed. Other duties may include discussion with relatives, but as with all aspects of intensive care, both clinical and non-clinical duties should fall within the expertise and remit as set by both the junior and consultant. There is a broad range of training opportunities to be had with time spent on the unit, and training in intensive care should be focused on a competency-based programme.

Nursing Staff

It should be appreciated that the nursing staff provide most of the care that patients receive in ICU. ICU nurses have greatly extended roles, experience and responsibility. They have undergone specific training to enable them to perform titration of fluid replacement, analgesia, vasoactive drug therapy and weaning from mechanical ventilation. The route by which complex instructions and information are transmitted between medical and nursing staff is of vital importance. A system in which a relatively junior clinician serves as a ‘final common pathway’ for all instructions works well in practice, provided that the doctor involved is present within the unit at all times so that the nurses may obtain clarification of instructions, report changes in status and receive immediate help in emergencies. It is essential that a nurse is present and takes part when discussions take place with the patient, or their relatives or friends. The content of such discussions must be recorded accurately in the patient’s notes. The resident should remember that the majority of ICU nurses (especially the senior nurses) have an enormous amount of ‘bedside’ experience with critically ill patients and considerable reliance should be placed on their observations.

The Microbiologist

Critically ill patients are immunocompromised as a result of the underlying pathological process, the impact of treatments (such as steroids) and the presence of surgical/traumatic wounds, multiple vascular catheters and other invasive tubing. This predisposes them to hospital-acquired infections. Prolonged use of broad-spectrum antibiotics encourages the development of resistant pathogens and overgrowth of other organisms. In order to effectively treat sepsis and prevent resistance, there is usually a nominated microbiologist, who is familiar with the flora and resistance patterns of the unit, and who visits the ICU daily to advise on microbiology results and antibiotic therapy. It is also essential to adhere to local policies aimed at reducing cross infection and minimizing the number of hospital-acquired infections. The National Patient Safety Agency (NPSA) also has a number of helpful guidelines for personnel working on ICU (www.npsa.nhs.uk).

OUTREACH/FOLLOW-UP

The critical care outreach team collaborates between the ICU and other areas of the hospital. The aims of the outreach team are to identify the deteriorating patient early with the aim of averting ICU admission, to facilitate timely admission to ICU if required, and to assist in the timely and appropriate discharge from ICU. It is important to identify those patients who are unlikely to benefit from further resuscitation or critical care support due to the nature of their acute illness or underlying diseases, to prevent futile interventions and ensure equitable use of scarce ICU resources. By following up patients discharged from ICU/HDU, a level of continuity of care can be provided and in addition critical care skills may be shared between the team and ward-based staff. The team may comprise of senior members of medical, nursing and physiotherapy staff.

A number of scoring systems based on abnormal physiological variables, such as the modified early warning score (MEWS) (Table 45.2), can be recorded by ward staff; the outreach team can be contacted accordingly once a trigger score has been reached. Care needs to be taken with younger fitter patients, who have good physiological reserve and who may not deteriorate in terms of MEWS score until a peri-arrest situation develops (e.g. in presence of bleeding or severe sepsis). Children, obstetric, neurological, renal and other sub-specialty groups have adapted scores to allow for altered background physiological status.

ADMISSION TO THE INTENSIVE CARE UNIT

The decision to admit a patient to the intensive care unit may be straightforward, but is often difficult and confounded by increasing expectations in an ever increasing elderly population with multiple co-morbidities. ICU resources are finite and costs high, so in the face of limited prospects for benefit or survival of an individual patient, a number of complex ethical issues can arise surrounding admission, provision and discontinuation of intensive care therapy. It is therefore necessary that all individual cases are discussed with the ICU consultant, as the decision regarding whether to admit the patient often comes down to multidisciplinary team discussion and clinical expertise. Blanket admission policies may be unhelpful, and decisions should consider the individual patient, taking into account their wishes and values. Senior staff should discuss with the patient (where possible) and/or their relatives potential treatment options and possible outcomes and alternatives. However, acutely ill patients can rarely discuss details of their care, and relatives may find it difficult to make an objective judgement. If a patient has made an Advance Directive (‘Living Will’) then its contents must be respected.

In essence, the aim of intensive care is to support patients while they recover. It is not to prolong life when there is no hope of recovery. In many cases, unless the outlook is obviously futile, patients will be admitted for a trial of treatment to see whether they will stabilize and improve over time. Patients with little or no prospect of survival may occasionally be admitted to intensive care. This can facilitate more appropriate terminal care, or to allow the relatives time to visit and the bereavement process to be better managed. In the very short term this is a justifiable and appropriate use of a critical care facility.

Assessment of Patients

When dealing with a newly admitted patient with acute disease, assessment and resuscitation often take place simultaneously and follow the standard pattern of recognizing and dealing with problems in the order of airway, breathing and circulation. The resident should heed all the patient’s problems and the responses to the treatments instigated and to do this, it is essential to approach the assessment of the patient in a systematic manner.

Formulating a Plan

Finally an action plan needs to be formulated, with special regard to both active and ongoing problems. A plan for each organ system requiring support should be put into place as well as a ventilation and/or weaning proposal. A review of nutrition, 24 h fluid balance and changes to drug therapy should also be undertaken and any planned procedures/interventions should be discussed with the consultant. Communicate back any change in plans to the relevant nursing staff and bear in mind that relatives appreciate honest, up to date progress reports. It is important to note that patient confidentiality should never be compromised via discussion or documentation. Full assessment and examination should be repeated at least daily even in stable patients, because the physiological state of critically ill patients can change rapidly.

MONITORING IN ICU

There is a plethora of monitoring equipment in ICU, which may at first be daunting. It is important to know that all equipment is working, and accurate and calibrated correctly. Always question whether additional monitoring is necessary and whether it would safely provide further information.

Invasive Monitoring

Pulmonary Artery Catheter

Pulmonary artery (PA) catheterization was for a number of years considered the ‘gold standard’ for cardiovascular monitoring in ICU. This technique enabled the measurement of pulmonary artery pressure, pulmonary artery occlusion pressure (wedge pressure, PAOP) and CO, and also allowed many other haemodynamic variables to be derived. The value of pulmonary artery catheters has been questioned and its use has fallen significantly with the introduction of alternative forms of monitoring. Given the controversy regarding its potential advantages, its use should be based on the risk/benefit ratio for each individual patient.

Pulse Contour Analysis: The peripheral arterial pulse waveform is a function of the cardiac output, the peripheral vascular resistance, peripheral vascular compliance and the arterial pressure. If the cardiac output is measured for a given peripheral arterial waveform, then after calibration, changes in the peripheral pulse waveform can be used to calculate changes in the cardiac output. To calibrate the system an indicator is injected into a venous catheter and is detected by an arterial line producing a standard dilutional CO measurement. Systems such as PiCCO and LiDCO use thermodilution and lithium respectively as the indicators. Aside from cardiac output, stroke volume and systemic vascular resistance, other variables available with PiCCO include global end diastolic volume (cardiac preload) and intrathoracic blood volume. Dynamic measures, using heart–lung interactions to predict fluid responsiveness, can also be widely determined using beat to beat cardiac output monitoring.

Other Technologies

ICP/Jugular Venous Saturation/Compressed Spectral Array/BIS

Indications for ICP monitoring vary between units, but may include any cause of coma, commonly head injury and intracranial head injury. Types of monitoring may include extradural fibreoptic probes, a subarachnoid screw, ventricular drain or intracerebral transducer. ICP monitoring allows calculation of cerebral perfusion pressure; both variables can then be used to guide management.

Jugular venous bulb oxygen saturation is an indirect indicator of cerebral oxygen utilization and provides a measure of global cerebral oxygenation. It involves a catheter being placed retrogradely up the internal jugular vein.

Compressed spectral array and bispectral index (BIS) are computerized assessments of EEG signals, which allow depth of anaesthesia and sedation to be assessed. The former will allow seizure activity to be seen and the presence of burst suppression can be used to indicate a greater depth of anaesthesia consistent with a reduced cerebral oxygen demand.

INSTITUTION OF INTENSIVE CARE

It is impossible to provide a comprehensive review of all the conditions requiring ICU care and their full treatment regimens in one chapter. The following sections are an overview of the management of some common problems presenting to ICU.

The Respiratory System

Respiratory failure is one of the commonest reasons for admission to the ICU (Table 45.3). It may be the primary reason for admission or a feature of a non-respiratory pathological process, e.g. adult respiratory distress syndrome (ARDS) in sepsis. Respiratory failure may encompass hypoxaemia with a normal/low PaCO2 (type 1) or a combination of hypoxaemia and high PaCO2 (type 2).

TABLE 45.3

Causes of Respiratory Failure

Reduced central drive Brainstem injury/CVA
Drug effects, e.g. opioids
Metabolic encephalopathy
Airway obstruction Tumour
Infection
Sleep apnoea
Foreign body
Lung pathology Asthma
COPD
Pneumonia
Fibrosis
ALI/ARDS
Lung contusion
Neuromuscular defects Spinal cord lesion
Phrenic nerve disruption
Myasthenia gravis
Guillain–Barré syndrome
Critical illness polyneuropathy
Musculoskeletal Trauma
Severe scoliosis

Assessment of the Patient with Respiratory Failure

Clinical assessment is often the most rapid way to evaluate the patient with respiratory failure (Table 45.4):

TABLE 45.4

Signs of Impending Respiratory Arrest

Marked tachypnoea, or hypoventilation, patient exhausted

Use of accessory muscles

Cyanosis and desaturation, especially if on supplemental oxygen

Tachycardia or bradycardia if peri-arrest

Sweaty, peripherally cool/clammy

Mental changes, confusion and leading to coma in extreme conditions

A full history including previous functional status, and physical examination are mandatory. Serial arterial blood gases are required to determine the extent of the respiratory failure and response to any therapy. The chest X-ray and other available investigations such as peak flow will aid evaluation of the patient’s condition.

Management of Respiratory Failure

Management is directed at correcting hypoxia/ hypercarbia and reversing the underlying condition if possible. Simple manoeuvres such as supplying supplemental oxygen should be instituted initially. Give oxygen via facemask, preferably humidified. Higher concentrations of oxygen can be achieved with a reservoir system and a fixed performance device (e.g. Venturi) may be preferable in titrating oxygen concentrations in those COPD patients who rely on hypoxia to drive their ventilation. The effect of oxygen therapy should be assessed by pulse oximetry and arterial blood gas analysis after around 30 min.

Other therapies may be useful such as bronchodilators, steroids, diuretics and physiotherapy in the first instance depending on the mechanism of respiratory failure. Many patients may be dehydrated due to poor fluid intake and increased losses and will require IV fluids. If there is no improvement over time, additional respiratory support may be necessary (Table 45.5). Options include:

Mechanical Ventilation

The usual indication for mechanical ventilation is in patients with potentially reversible pathology who are unable to maintain adequate oxygenation or who develop hypercapnia. In some cases, blood gases may be normal but are predicted to deteriorate because the patient is becoming exhausted.

Tracheal Intubation: To enable mechanical ventilation to be carried out effectively, a cuffed tube must be placed in the trachea either via the mouth or nose, or directly through a tracheostomy stoma. In the emergency situation, an orotracheal tube is usually inserted. If the patient is conscious, anaesthesia should be induced carefully with an appropriate dose of an i.v. anaesthetic induction agent and neuromuscular blocker. The full range of adjuncts for difficult intubation should be available.

The critically ill patient is often exquisitely sensitive to i.v. anaesthetic drugs, and cardiovascular collapse may occur; consequently, full resuscitation equipment must be immediately available. I.v. fluid resuscitation and vasoactive drug infusions are often required.

If the patient is unconscious, a neuromuscular blocker alone may be necessary (but not obligatory) to facilitate the passage of the tube; however, an i.v. anaesthetic induction agent and neuromuscular blocker should always be used in patients with severe head injury to prevent an increase in intracranial pressure (ICP) during laryngoscopy and tracheal intubation.

Many patients are hypoxaemic, and it is essential that 100% oxygen is administered before tracheal intubation.

image After neuromuscular blockade has been produced, the tube should be inserted by the route which is associated with the least delay.

image If the patient is unconscious and the victim of blunt trauma, when cervical spine injury is a possibility, the cervical spine should be immobilized during intubation using manual in-line immobilization.

image Cricoid pressure should be applied to minimize the risk of aspirating gastric contents.

image A sterile, disposable plastic tube with a low-pressure cuff should be used. The tube should be inserted such that the top of the cuff lies not more than 3 cm below the vocal cords.

image The head should be placed in a neutral or slightly flexed position (on one pillow) after tracheal intubation and a chest X-ray taken to ensure that the tip of the tube lies at least 5 cm above the carina.

Bronchial intubation is a common complication during mechanical ventilation as the tracheal tube may migrate down the trachea when the patient is moved during normal nursing procedures. Intubation of the right main bronchus cannot be detected reliably by observation of chest movements or by auscultation of the chest because of the exaggerated transmission of breath sounds during IPPV, although absent or asynchronous chest movement may occur when pulmonary collapse has taken place. Bronchial intubation is one of the causes of a sudden decrease in compliance, and restlessness and coughing often occur if the end of the tube irritates the carina. If this is suspected, the tube should be withdrawn gradually by up to 5 cm while lung compliance and chest expansion are observed carefully. The position of the tube should always be confirmed by a chest radiograph.

When the upper airway or larynx is obstructed and conventional tracheal intubation is not possible (e.g. occasional cases of epiglottitis or laryngeal trauma), the emergency airway of choice is cricothyroidotomy.

Tracheostomy is increasingly performed percutaneously on the ICU and is most frequently an elective decision. Indications include:

The recently completed Tracman study confirmed no clear benefit from early compared with delayed performance of tracheostomy.

Sedation and Analgesia: Once tracheal intubation has been performed, some amount of sedative drugs will be required to tolerate the tube and facilitate effective mechanical ventilation. The balance between providing adequate sedation to permit patient co-operation with organ system support and oversedation, which leads to a number of detrimental effects (Table 45.6) is often difficult. The aims of sedation include patient comfort and analgesia, minimizing anxiety, and to allow a calm co-operative patient who is able to sleep when undisturbed and able to tolerate appropriate organ support. Patients must not be paralysed and awake but the efficiency of supportive care will be reduced in the patient who is agitated and distressed. Clearly the patient’s needs for sedation will alter with changes in clinical condition and requirements for care, so regular review and sedation scoring are helpful (Table 45.7).

TABLE 45.6

Problems and Potential Consequences of Excessive Sedation in ICU

Problem Potential consequence
Accumulation with prolonged infusion Delayed weaning from supportive care
Detrimental effect on cardiovascular system Increased requirement for vasoactive drugs
Detrimental effect on pulmonary function Increased VQ mismatch
Tolerance Withdrawal on stopping sedation
No REM sleep Sleep deprivation and ICU psychosis
Reduced intestinal motility Impairment of enteral feeding
Potential effects on immune/endocrine function Drugs such as opioids may have a role in immunomodulation and risk of infection
Adverse effects of specific drugs e.g. propofol infusion syndrome, with cardiovascular collapse

TABLE 45.7

Sedation Scoring Using the Ramsay Sedation Scale

Ramsay Sedation Scale

1. Patient anxious, agitated or restless

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