Intracranial pressure monitoring in a resource-constrained environment: A technical note
Most published literature supports the use of ICP monitoring as a standard of care, though the benefit has never been conclusively proved by a prospective, randomized trial. Unfortunately, ICP monitoring is routinely performed in very few centers in India on a systematic basis. This is probably due to the common perception that it requires very sophisticated facilities and is prohibitively expensive for most patients. The author’s institution was also faced with a comparable situation, and we have therefore developed a simple and economical system that is presented in practical detail. No custom-made equipment is necessary, and all disposables should be available in any hospital pharmacy. It is our hope that this will enable any center with an ICU for the management of neurosurgical patients to begin monitoring ICP. The system has been in consistent use for 3 years in our institution, and over 100 patients have been monitored successfully.
Though there is no Class I evidence that intracranial pressure (ICP) monitoring improves outcome in head injury, the bulk of published data supports this view.,,, Therefore ICP monitoring should form an integral part of the management of severe head injuries, as well as of other neurosurgical and neurological conditions where indicated. Unfortunately, although there are centers in India that monitor ICP, the practice is routinely performed in very few institutions. This is probably due to the assumption that ICP monitoring is technologically very demanding, and also because commercially available systems are extremely expensive in the Indian setting.
The ideal ICP monitoring device should be accurate, reliable, cost-effective and should cause minimal morbidity. There are several techniques available for monitoring ICP, with differing accuracy and reliability, and with substantial differences in costs. An economical, accurate and safe system that also offers the advantage of therapeutic CSF drainage is described for use in the Indian context, with the total cost of disposables being less than Rs 500.
All the equipment necessary for ICP monitoring by this technique should be readily available in any hospital with an ICU and monitors for the care of head injury patients. These include (a) a monitor capable of invasive pressure recording (such as arterial pressure) with ordinary transducer; (b) size 8 Fr infant feeding tube (preferably gas sterilized again for absolute sterility); (c) disposable plastic items (a pressure line extension, 3 three-way stopcocks, two IV sets, one glass bottle of 100 ml saline, arterial pressure dome and a sterile CSF collection bag or bottle; (d) a drill capable of making a 3mm craniostomy (we use a manual twist drill).
Placement of ventricular catheter
With a slight modification of the conventional methods used for ventricular drainage, even the small ventricles of a trauma patient can be cannulated in over 90% of cases. The site of the craniostomy is on the medial canthal parasagittal line (usually on the right) immediately in front of the coronal suture. The ventricular cannula is angled perpendicularly on the sagittal plane and minimally medially in the coronal plane. This trajectory causes the catheter to follow the obliquity of the frontal horn and helps in ensuring that the hole-bearing segment is within the ventricle. Changes may have to be made in case of midline shift - however, our experience has been that an attempt on the side to which the shift has taken place is invariably successful. Care must be taken to ensure that more than 7 cm of the catheter is not introduced into the skull. The catheter may be tunneled before entering the skull, and the entire site dressed appropriately.
The connections of the system are as shown in the schematic diagram [Figure - 1]. However, the sequence of connections is important in ensuring that accurate readings are obtained.
The ventricle is cannulated and the feeding tube stoppered. This may also be done after all the following connections are made. The pressure monitoring line, the three-ways stopcocks and the pressure dome are connected as in the figure. After thorough cleaning of the top of the saline bottle, IV set 1 is connected to the saline and three-way 1 and the entire system is filled with saline without bubbles. The bottle is drained, without the IV set being touched at any time by anyone except the operator. Care must be taken to ensure that the third stem of three-way 2 has no fluid in it. The saline bottle is then removed (keeping the top sterile) and the CSF collection device is connected to IV set 1. IV set 2 is connected to the third stem of three-way 2 and the other end to the empty bottle, making sure that the residual saline does not enter the IV set. The airway of the IV set is now opened and closed once to equate the pressure of the air in the bottle with the atmosphere. The end of the pressure line extension is now firmly connected to the ventricular catheter; this junction is dressed with antiseptic-soaked sterile gauze and reinforced with adhesive. The pressure dome is appropriately mounted on the transducer.
Measurement of ICP and CSF drainage
Once the system is set up it is utilized as follows:
Zeroing of the transducer is carried out by opening it to the air in the bottle, which is henceforth assumed to be equal to atmospheric pressure. This is done by turning three-way 2 to cut off the patient side of the circuit. It has been calculated that the pressure in the bottle varies by less than 1 mm Hg for every 10C change in temperature. This closed system of zeroing is recommended as it prevents the system being periodically exposed to the exterior with the attendant risk of infection.
The waveform on the monitor must be pulsatile or it is not reliable. The response to raised ICP in the author's ICU is to check for technical error, zero the transducer, look for non-neurosurgical causes like restlessness, fighting ventilator, non-ideal head or neck position, etc., check adequacy of ventilation and only then assume that the cause is intracranial - in over 90% of raised ICP alarms the cause is systemic.
Once the systemic causes are ruled out CSF is drained under direct vision. This cannot be overemphasized because if the ventricle is allowed to collapse onto the catheter it will get blocked - the commonest reason for failure of the system. Drainage is carried out by turning three-way 1 to divert CSF into the collection device. The IV set should be held in one's hand to ensure continuous flow, and the three-way should be turned off the moment the flow stops. It is recommended that the drainage be carried out in aliquots of 1-2 ml.
If ICP is not controlled with drainage, other measures including mannitol, hyperventilation and repeat CT scan may be taken as preferred.
The site of craniostomy is much closer to the midline than usual - care must be taken to ensure that it does not slip onto the midline. When there is marked midline shift, care must be taken to ensure that the angle of the cannula does not lead to breach of the pia-arachnoid on the medial surface of the hemisphere. Any accidental breach of the system after set-up is an indication for the immediate removal of the entire system to avoid the risk of ventriculitis. If collection of CSF is essential, the procedure should be performed with at least glove and mask precautions.
There are several techniques available for monitoring, which have been ranked by the Brain Trauma Foundation based on their accuracy, stability and ability to drain CSF as follows:
· Intraventricular devices - fluid-coupled catheter with an external strain gauge or catheter tip pressure transducer
· Parenchymal catheter tip pressure transducer devices
· Subdural devices - catheter tip pressure transducer or fluid-coupled catheter with an external strain gauge
· Subarachnoid fluid-coupled device with an external strain gauge
· Epidural devices
The reference standard for ICP monitoring is still the intraventricular device, and it is necessary for all the other systems to be compared against it for accuracy. Of the few centers in India which routinely monitor ICP, the majority use subarachnoid bolts that are comparatively less accurate and do not offer the therapeutic option of CSF drainage. The ability to drain CSF is an important additional treatment alternative in the control of raised ICP that is available only with ventricular catheters. It permits direct lowering of ICP without the systemic effects of all the other measures such as sedation, osmotic agents, hyperventilation and chemical paralysis.
Selection of patients
Though there is a broad consensus on the indications for monitoring in head injury,, there are no guidelines for ICP monitoring in non-trauma patients. The decision regarding these patients will depend on the experience of the institution and the estimation of risk versus benefit for a particular patient.
The Brain Trauma Foundation analysis of the costs of various systems of ICP monitoring makes the statement that “generally, fluid-coupled ICP systems were less than half the cost of other systems”. The cost of all the disposables is less than Rs.400, and even after allowing Rs 100 for the cost of the pressure dome (reused an average of 4 times with ethylene oxide sterilization), the total expense to the patient is less than Rs 500. The only other device with comparable accuracy is the parenchymal catheter tip transducer. This requires the purchase of a dedicated monitor, and the disposables (not by any means universally available) cost more than Rs 4,000. In addition, if used as a parenchymal monitor CSF drainage is not possible. Other devices available are not as accurate as these two alternatives.
The reported complication rate for ventricular catheters varies widely. Infection rates range from 0% to 10.3%., The incidence of infection increases with the duration of the monitoring, and also with breach of the closed system. It is for this reason that the closed system of zeroing was developed, and monitoring is discontinued if there is any breach in the system. Published reports of hemorrhage rates also vary, with an average incidence of 1.1%.,,
The infection rate with the system described here was 2% in our series. Though routine scans are not carried out in our institution, a strict protocol ensures that patients with ICP requiring paralysis or those who deteriorate clinically have repeat CT scans. The incidence of hemorrhage detected with this protocol is 2%. One of these was an extradural hematoma caused by operator inexperience (attempting to penetrate the dura with a blunt cannula) and the other a parenchymal hematoma.
This is a simple, economical and accurate system that can be used in any ICU managing neurosurgical patients. The only limitations of the system are the number of connections and the absolute dependence on a patent fluid column - once the catheter gets blocked the system is useless. There is a learning curve for both doctors (cannulation of small ventricles) and all ICU staff (preventing catheter block and appropriate response to raised ICP), but once this period is passed monitoring becomes a matter of routine. It is hoped that this system will come into general use in centers where ICP monitoring has so far not been carried out due to economic reasons.
This technique of ICP monitoring was presented by the author at the National Neurotrauma Conference 2002, Agra.