Special Circumstances

, Amy Gospel2, Andrew Griffiths3 and Jeremy Henning4



(1)
Intensive Care Unit, James Cook University Hospital, Middlesbrough, UK

(2)
Tyne and Wear, UK

(3)
The York Hospital, Middlesbrough, UK

(4)
James Cook University Hospital, Middlesbrough, UK

 



By the end of this chapter you should understand the specific management issues associated with:



  • Hypothermia


  • Paediatrics


  • Obstetrics


  • Head injury


  • Transferring patients by air


8.1 Hypothermia


This is defined as a core temperature less than 35 °C. It is associated with a number of undesirable effects:



  • Cardiovascular arrhythmias occur at 30 °C, ventricular fibrillation (VF) at 28 °C


  • Vasoconstriction makes intravenous access difficult and increases myocardial work


  • Increased blood viscosity reduces tissue perfusion


  • Thrombocytopenia – platelets are sequestered in the liver and spleen


  • Shift of oxygen haemoglobin dissociation curve to the left – worsens oxygen delivery to tissues


  • Reduced level of consciousness (unconscious at 30 °C)

There are two main issues to be dealt with in the hypothermic casualty: dealing with the hypothermia, but also appreciating and managing the reason for the hypothermia. The casualty who has simply become overwhelmed by the cold needs careful handling and possibly intubating (depending on Glasgow Coma Score (GCS)), prior to transportation to a hospital where they can be re-warmed. In severe cases the use of cardiac bypass may allow more rapid warming and transfer to a unit capable of doing this should be considered. Some of these cases may be due to alcohol excess causing reduced consciousness and loss of awareness of cold. It is important to consider that unconsciousness may have preceded hypothermia, e.g. head injury, vascular intracerebral event, hypoglycaemia, severe hypovolaemia etc. Depending on the diagnosis, these patients may be better transferred to a neurosurgical or trauma unit with emphasis on managing the underlying injury rather than rapid warming.

Patients with multiple trauma and no head injury have been shown to have a markedly worse outcome if they are hypothermic. In this patient group a core temperature of <32 °C is invariably fatal (Jurkovich et al. 1987). One reason may be because coagulation depends on enzymes which function best at 37 °C. Hypothermia therefore impairs blood clotting and will potentially result in increased blood loss. Hypothermia may also partly be a marker of the severity of haemorrhagic shock, and the resultant depression of metabolism and heat generation by the body.

It is not usually possible to increase core temperature in the pre-hospital environment. Management should be aimed at minimising further heat loss. This is done by removing wet clothing, sheltering from wind/rain, covering with heat reflective blankets, using heat-generating packs (care must be taken to avoid skin burns) and increasing the ambient temperature of the transport vehicle. The hypothermic patient who has suffered cardiac arrest should be treated as per national guidelines (usually with double the interval between drug dosages and fewer attempts at defibrillation until normothermia is achieved).

It can also be difficult to diagnose death in the hypothermic patient. Unless there are obvious external signs of death (e.g. de-capitation), or a good history of death preceding hypothermia, it is probably best to use the mantra ‘they are not dead, until they are warm and dead’. This means keeping resuscitation attempts going until the casualty is in the hospital at the very least.

A meta-analysis of eight randomised controlled trials (RCTs) of therapeutic hypothermia after traumatic brain injury led the Brain Trauma Foundation to issue a Level III recommendation for the optional and cautious use of hypothermia following traumatic brain injury (TBI) in adult patients (Peterson et al. 2008). Good quality evidence is, however, lacking. In 2009 a Cochrane meta-analysis (Sydenham et al. 2009) on 23 trials with a total of 1614 patients found no convincing evidence that hypothermia was beneficial in TBI patients. They selected RCTs of hypothermia to a maximum of 35 °C for at least 12 consecutive hours in patients with closed TBI, and investigated effects on death, Glasgow Outcome Scale and pneumonia. Out of these trials, only nine were of good quality and concealment. Although results showed an overall trend towards benefit for hypothermia to reduce deaths (OR 0.85, 95 % CI 0.68–1.06), significance was only found in the low quality trials. No improvement in mortality was found with the high quality trials (OR 1.11, 95 % CI 0.82–1.51). There are trials ongoing that may help to address this (EUROTHERM 3235 Trial, NABIS: H IIR)

Hypothermia maintained after out of hospital VF cardiac arrest has been accepted therapy in order to improve neurological outcome (European Resuscitation Council 2005). A Cochrane review in 2012 also found benefit in neurological outcome by using induced hypothermia after cardiopulmonary resuscitation (Arrich et al 2012). A more recent trial has, however, cast doubt on the benefits of hypothermia (Nielsen et al 2013). This was a large (939 patients), well-designed RCT, and the results were unequivocally negative. Following this, some editorials have called for therapeutic hypothermia to be abandoned, rather aiming for a temperature of 36 °C and ensuring that hyperthermia does not occur, as this is undoubtedly associated with worse outcomes. Others have highlighted potential issues with the trial and believe therapeutic hypothermia should still be used (Stub 2014). The current advice for pre-hospital staff is therefore not to actively rewarm patients who survive cardiac arrest, and that any fever should be cooled if possible.

There is some interest in profound hypothermia (suspended animation) in those trauma patients who arrest when practitioners are present. This, at the moment, can only be described as experimental, and so should be left for controlled research groups.


8.2 Paediatrics


Trauma accounts for up to 40 % of childhood deaths. In a 12 years period London HEMS attended 1933 children (Nevin et al. 2014). There were 315 (16.3 %) pre-hospital intubations; 81 % received a rapid sequence intubation (RSI) and 19 % were intubated without anaesthesia in the setting of near or actual cardiac arrest. The most common injury mechanisms in this population were road traffic incidents and falls from height. Intubation success was 99.7 % with only a single failed intubation during the study period. Eich et al. (2009) reported similar success rates (98.3 %) for pre-hospital paediatric intubation.

There is as yet no evidence to support the assumption that intubation is superior to assisted face mask ventilation for the treatment of children less than 12 years or weighing less than 40 kg in terms of survival or neurological outcome after injury. The only randomised controlled trial is poor quality, looks at non-drug assisted intubation and is inconclusive (Gausche et al. 2000). Many pre-hospital doctors will have limited, if any experience, of anaesthetising children, and as children desaturate much more quickly than adults when they stop breathing, the threshold for pre-hospital anaesthesia (PHA) may be higher than for adults.

If the age of the child is known at dispatch then drug doses can be calculated en-route to the scene. Drug dose calculators and Broselow tapes can help in doing this effectively. Whenever drug doses are calculated for children it is sensible to check the dose with another trained crew-member.

A child is not simply a miniature adult and a more considered approach should therefore be taken when preparing for intubation. The paediatric airway differs significantly from the adult airway (Table 8.1). This may require an alteration in intubation technique.


Table 8.1
Comparing infant and adult airways







































 
Infant

Adult

Tongue

Relatively larger

Relatively smaller

Larynx

Opposite second and third cervical vertebrae

Opposite fourth, fifth, and sixth cervical vertebrae

Epiglottis

“U” shaped, large, floppy

Flat, flexible, erect

Hyoid/thyroid separation

Very close

Further apart

Smallest diameter

Cricoid ring

Vocal cord aperture

Consistency of cartilage

Soft

Firm

Shape of head

Pronounced occiput

Flatter occiput

The airway is smaller and as a result requires increased dexterity for manipulation and specialised equipment. The tissues of the airway are softer and more pliable. This means airway obstruction is more likely at extremes of head position and with relatively little external pressure, especially under the chin when supporting a face mask.

Children have a disproportionately large head relative to their chest until around the age of 8 years old. This forces the cervical spine into relative kyphosis (head flexion) when lying on a firm surface. Young children (<3 years) should have a 1–2 cm pad under their chest and nothing under their head to provide an optimal intubating position (see Fig. 8.1). To ensure transport with the neck in a neutral position (particularly when there is concern regarding cervical spine injury), children under 9 years old should be transported with a pad/blanket under their chest (Herzenberg et al 1989). The correct thickness of support is best judged by aligning the external auditory meatus with the centre of the shoulder.
Sep 22, 2016 | Posted by in ANESTHESIA | Comments Off on Special Circumstances
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