The Intensive Care Unit
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.
STAFFING AN INTENSIVE CARE UNIT
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
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
Assessment of Patients
Limbs/Skin and Wounds
Surgical wounds and trauma sites should be inspected for adequate healing or infection.
MONITORING IN ICU
Invasive Monitoring
Pulmonary Artery Catheter
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.
INSTITUTION OF INTENSIVE CARE
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
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
Can patient talk in sentences?
Are they awake and orientated?
What is the pulse, BP and respiratory rate?
Is the patient using accessory muscles of respiration?
Can they cough effectively to clear secretions?
Do they appear exhausted? Exhaustion and impending respiratory failure that is likely to require ventilatory support is an end-of-bed diagnosis.
Management of Respiratory Failure
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:
TABLE 45.5
Indications for Ventilatory Support
Indications for ventilatory support in respiratory failure
Continuous Positive Airway Pressure (CPAP): CPAP is provided via a tightly fitting mask or hood. A high gas flow (greater than the patient’s peak inspiratory flow rate) is required to keep the positive pressure set by the expiratory valve (+ 5–10 cmH2O) almost constant throughout the respiratory cycle. CPAP increases functional residual capacity (FRC), reduces alveolar collapse and improves oxygenation but it requires a co-operative patient, with no facial injuries. It does not generally help the patient with type 2 respiratory failure. There is a small risk of aspiration as a result of stomach distension.
Non-Invasive Positive Pressure Ventilation (NIPPV or NIV): Non-invasive techniques have been successfully used to treat acute exacerbations in patients with COPD, in the management of pulmonary oedema and as a weaning aid. Biphasic or bi-level positive airway pressure (BiPAP or BPAP) is a common form where a set inspiratory pressure enhances the patient’s own respiratory effort to increase achievable tidal volume and the set expiratory pressure is analogous to CPAP.
Mechanical Ventilation
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.
After neuromuscular blockade has been produced, the tube should be inserted by the route which is associated with the least delay.
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.
Cricoid pressure should be applied to minimize the risk of aspirating gastric contents.
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.
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.
to maintain the airway, e.g. reduced level of consciousness, upper-airway obstruction
to protect the airway, e.g. bulbar palsy, brain injury
for bronchial toilet, e.g. excessive secretions/inadequate cough
for weaning from IPPV, e.g. patient comfort, reduction of sedation.
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 |