Patients with severe illnesses often require a variety of interventions that include emergency stabilisation, diagnostic imaging, emergency anaesthesia/surgery and intensive care postoperatively. Although much attention is devoted to each of these areas as distinct phases of management, perhaps overlooked critical periods include the transitions from one phase to another. A particularly delicate period is the transition from emergency anaesthesia/surgery to the intensive care unit (ICU) and this will be the focus of this discussion. An important point to remain cognisant of, regarding these patients, is that proper communication between the anaesthetist, surgeon and critical care clinician is paramount and far more important than any other technique or monitoring device.

Key pieces of information that are required for optimal management in the intensive care unit include the working diagnosis for the particular patient, the current list of pertinent medical problems, a list of current treatments, agents used during anaesthesia, how the patient dealt with anaesthesia and surgery, and the anticipated immediate postoperative needs. Effective communication amongst the anaesthetist, surgeon and critical care team is required to ensure that all of the patient's needs are met, including defining each person's role in respect of the patient. From maintaining communication with the client to writing the postoperative treatment orders, the plan for each patient should be discussed and agreed upon. The immediate postoperative concerns relate to institution or continuation of supportive measures including administration of analgesics as well as what monitoring will be required for the management of the patient. It is imperative that such communications include the nursing staff, who form an essential element of the critical care team.

Monitoring of critically ill patients is essential in the evaluation of improving or deteriorating patient status and allows interventions to be performed early if necessary when change in status is seen. A variety of parameters may be monitored using non-invasive and invasive techniques to evaluate proper recovery from anaesthetics and how the patient is coping with the added stress of the surgical procedure. Important aspects of anaesthetic recovery include whether the patient had a smooth or complicated recovery, the degree of pain or discomfort, heart rate, respiratory effort, body temperature and time to extubation. In most animals, warming body temperature aids in anaesthetic recovery and therefore this may be one of the first priorities in critically ill patients. This may aid in normalising blood pressure, which may have been low during anaesthesia. During this period other monitoring devices including electrocardiogram (ECG) pads, blood pressure cuffs, urinary catheters may also be placed. Ideally, the most appropriate time to instrument these patients is when they are brought from the surgery theatre to the ICU. By having determined which monitoring devices and supportive measures will be required, setting up the patient in ICU can be expedited.

Monitoring the Cardiovascular System

Monitoring parameters of cardiovascular function provides a great amount of information regarding overall cardiac function, vascular tone and volume, as well as reflecting changes in other systems such as red blood cell concentration, respiratory function and blood electrolyte concentrations. Cardiovascular function can be assessed by monitoring heart rate, pulse quality, mucous membrane colour and by the use of ECG and blood pressure monitors.

ECG Monitoring

ECG monitoring in critically ill patients provides a means to monitor heart rate and rhythm, and a continuous ECG monitor greatly improves the early detection of arrhythmias and heart rate changes. ECG analysis may demonstrate tachyarrhythmias due to hypovolaemia, anaemia, hypercapnia or hypoxaemia; bradyarrhythmias may be indicative of electrolyte abnormalities such as hyperkalaemia, or increased vagal tone (e.g., due to elevation in intracranial disease, brachycephalic conformation, respiratory or intra-abdominal disease). Although ECG analysis is valuable for following heart rate and rhythm changes, it is important to remember that this is not a good indicator of overall cardiac function. ECG monitoring should therefore always be performed in conjunction with other means of assessing systemic perfusion. This is most easily accomplished by assessing peripheral pulse quality, urine output, mucous membrane colour and capillary refill time.

Arterial Blood Pressure Monitoring

Arterial blood pressure is a major force driving tissue perfusion, and therefore is an important parameter to measure in critical patients. During excessive hypotension (mean arterial pressure lower than 60 mmHg) or hypertension (mean arterial pressure greater than 150 mmHg) decreases in perfusion to major organs may occur. Blood pressure may be monitored by non-invasive techniques, such as automated oscillometric blood pressure measuring devices or by the use of a sphygmomanometer, and Doppler ultrasonography.

Automated non-invasive blood pressure monitoring techniques produce values for systolic, diastolic and mean arterial pressures, can be programmed to perform measurements at regular intervals and reduce the human error associated with rapid cuff deflation rate. However, they remain dependent on peripheral blood flow, often failing during severe vasoconstriction or hypotension, and produce inaccurate readings when an incorrect cuff size is used. Oscillometric blood pressure measurements are also often not possible to obtain in small patients (e.g., less than 7-8 kg).

Direct blood pressure monitoring involves the placement of an arterial catheter (often into the dorsal pedal artery), which is connected by a fluid-filled extension line to a pressure transducer and then to the output monitor. The output monitor then displays an arterial pressure wave tracing in addition to measured values for systolic, mean and diastolic blood pressures. This method produces the most accurate blood pressure readings; the presence of an arterial catheter also permits blood sampling for arterial blood gas analysis. Inaccurate blood pressure readings may occur if the arterial catheter has become partially occluded by a blood clot; however, this generally results in dampening of the waveform on the monitor, and therefore can be easily recognised and corrected by flushing the catheter with heparinised saline. Frequent catheter flushing is necessary as arterial catheters are more prone to occlusion than venous catheters. Continuous blood pressure readings require the availability of monitors designed to measure direct arterial blood pressure. The arterial catheter should be clearly labelled to prevent accidental intra-arterial injection of intravenous medications.

Central Venous Pressure Monitoring

Monitoring central venous pressure (CVP) provides an indication of intravascular fluid volume, specifically venous blood volume and cardiac preload. Because CVP is also dependent on cardiac output, a high CVP in conjunction with a low cardiac output indicates heart failure. Increasing CVP measurements suggest that the patient is at risk of fluid overload or right-sided heart failure. Conversely a low CVP reading indicates the patient is hypovolaemic. CVP measurements are therefore extremely useful in patients that are at risk for both hypovolaemia and heart failure (for example a patient with hypovolaemia secondary to sepsis that also has a history of heart disease). They are also useful in patients whose fluid volume status is confusing, such as a patient that is polyuric or one that is effusing a large volume of fluid into its abdomen, such as in pancreatitis or following certain abdominal surgeries. In patients such as these, with large ongoing fluid losses, greater intravenous fluid rates than expected are often required to prevent hypovolaemia, and therefore utilisation of CVP monitoring can help guide fluid therapy.

Normal values for central venous pressure are 0-5 cmH₂O (0-3.7 mmHg). Patients that are hypovolaemic therefore have a CVP less than 0, patients with values greater than 10 cmH₂O (7.5 mmHg) are likely to be volume-overloaded (or have right-sided heart failure). Following the CVP trends is often more useful than a single measurement; if a patient has progressive increases or decreases in CVP, or has a sudden change when previous measurements have been constant, this may reflect a change in fluid volume status that requires intervention, even if the CVP value remains within the normal range.

Respiratory Function

A great deal of information regarding patient respiratory function can be obtained from the physical examination and auscultation, with increased respiratory rate and effort being commonly associated with abnormal respiratory function. However, additional information regarding respiratory function and the possible sites of pathology (lung parenchyma, upper airways, respiratory musculature, central nervous system (CNS) respiratory control centers) can be obtained using monitoring devices detecting arterial oxygen and carbon dioxide levels. This information is most accurately determined by obtaining an arterial blood gas analysis, which requires an on-site blood gas analyser.

Urinary Output

Adequate urinary output is generally defined as >0.5 ml/kg/hr. However, this should be viewed as an absolute minimum and not an 'appropriate' amount. In fact, it is preferable that the urinary output matches fluid administration. This is usually referred to as 'matching ins and outs', which basically means that fluid administration is matching the requirements of the patient. Poor urinary output (or overt mismatching) can be indicative of inadequate fluid administration, excessive fluid retention, occluded catheter or failing kidney function. Excessive fluid retention can quickly lead to life-threatening fluid overload and pulmonary oedema.

Summary

The transition from anaesthesia to critical care is an extremely important period in which effective communication amongst all members of the team is crucial to ensure optimal patient management. Setting up patients in the ICU requires accurate assessment of the patient's current condition and anticipation of the patient's needs.

References

1.  Chan DL. Monitoring critical care patients. In: Rozanski, EA; Rush, JE. eds. A color handbook of small animal emergency and critical care medicine. London: Manson Publishing Ltd, 2007; 213-219.

2.  Raffe MR. Complications of anesthesia. In: Lipowitz, AJ; Caywood, DD; et al. eds. Complications in small animal surgery: diagnosis, management, prevention. Philadelphia: Williams & Wilkins, 1996; 73-97.